One Fish, Two Fish, Red Fish, Blue Fish: How Reef Fish See Color and Why Fish Coloration is Ecologically Relevant

Posted on March 22, 2017 by sft4

In my last blog post, I promised that I would discuss the importance of coral reef fishes’ colors and patterns. So, this post will be entirely about reef fish! First, I’ll share some research that examines how coral reef fish see color. Then, I’ll talk about why colors on coral reef fish are ecologically relevant, in terms of mating, camouflage, signaling and more. Finally, I’ll talk about how colorful coral reef fish can be affected by coral bleaching. As a refresher, coral bleaching occurs when corals get stressed and expel their symbiotic algae, which contain photosynthetic pigment.

Just like other classes of life boast incredible diversity, reef fish are diverse too! As one example, reef fish can be diverse in how they are able to see color. Some fish species have a single photoreceptive cone (monochromatic) and others have up to four different types of cone cell, which each have different absorption spectra (tetrachromatic)1. Reef fish usually have two or three types of cone cell for color vision. For all fish, but especially predatory fish, what colors are, and are not, visible can determine how successfully they hunt for food.

A study by Cheney and Marshall explored the perceptual ability of predatory fish to distinguish between a fish (called a model) and another fish that looks like the model (called a mimic). Fish with more distinct cone photoreceptors were shown to outperform fish with fewer cone photoreceptors when distinguishing between a fish and a mimic2.

Another study published in The Journal of Experimental Biology assessed the visual capabilities of the Picasso triggerfish, Rhinecanthus aculeatus1. The researchers tested how triggerfish would respond to a choice between edible stimuli, either colored or gray. They made sure to control for differences in luminance, which characterizes brightness, that the fish might use to distinguish stimuli instead of the intended color cues.

Some of their experimental results are shown below. The researchers found that fish were significantly more likely to choose a colored stimulus over gray distractors (Figure 1). This finding held for all colors tested, including blue, orange, green, yellow, and red. These researchers also found that fish showed a preference for red stimuli. Preference was approximated by the first colored stimuli pecked by a fish21. This study, and others, not only show that coral reef fish can see color, but that the ability to distinguish between colors is beneficial for predatory fish.

Figure 1. This figure shows the number of times, as a percentage, that fish in the study chose the colored stimulus over two gray distractors. The dashed line represents the 33% threshold value if fish were randomly choosing stimuli. For all colors, the fish chose the colored stimulus more than the gray distractors.  

The ecological relevance of reef fish coloration and color vision has been of interest to the scientific community. Coloration may play a role in mate recognition, visual warning for predators, displays for reproductive potential, or as camouflage3. Mimicry is also achieved through coloration, as shown in the Cheney and Marshall experiment above. Moland et al. also researched mimics, and contend that mimicry is “a widespread and common phenomenon in coral reef fishes”4.

The contrast, or lack of contrast, in color bands or patches on fish can be important. Bright, contrasting coloration can warn predators that a fish is poisonous. Large spots on the tails of prey can serve as “fake eyes” which mislead and misdirect predators23.

Camouflage on coral reefs has been a prominent focus of scientific study. Some species of fish, like the moon wrasse (shown below), appear super colorful up close, but the patterns and colors blur when they are seen through water or from far away3. Also, the ideal colors for visual camouflage vary with depth and environment. In deep water, all colors other than blue appear blue or black because long wavelengths of light are preferentially absorbed. Thus, being bright red or orange is an effective form of camouflage in deeper water3.

Norfolk Island, Australia. Female.

Figure 2. A moon wrasse (Thalassoma lunare) shown above, has a blue lower body and multi-colored patterns on the head, clearly visible to the human eye. Underwater and through the eyes of a predatory fish, the patterns blend well into the reef scape.     Source: https://seafishes.wordpress.com/page/2/

Logically, it makes sense that coloration that camouflages into the surrounding environment can help prey confuse or escape their predators. When the reef environment changes, fish that depend on camouflage for survival become more vulnerable. Coker et al. published a paper in Behavioral Ecology showing that coral-dwelling damselfishes are more susceptible to predation when they are associated with dead and bleached corals. Predation rates on coral-dwelling damselfish were found to be 17% higher on bleached or dead coral colonies5. In the figures below, you can see that carnivorous fish, Pseudochromis fuscus, visited healthy and algae-covered reefs most often (Figure 1 below) but made the most predatory strikes on dead coral (Figure 2 below). Damselfish on dead and bleached coral were thus most vulnerable to predation.

Figure 3. Within a 20 minute period, researchers monitored the number of visits and predatory strikes by Pseudochromis fuscus on damselfish. The dead coral and bleached coral were the habitats with the most predatory strikes, despite being the habitats visited the least by the predatory fish.

This paper highlights yet another reason why we need to protect our reefs as best we can against bleaching. Coral bleaching can have cascading effects on all parts of the coral reef ecosystem, in this case, damselfish are negatively affected.

Reef fish aren’t colorful just because it looks cool! There are many ecological explanations for reef fish colorations and there are often advantages accrued by colorful fish. Reef fish are an exciting and important part of the coral reef ecosystem. Tune in soon for the last installment of my colorful coral reef blog!

References:

1 Cheney, Karen et al. “Colour vision and response bias in coral reef fish.” The Journal of Experimental Biology. 10 July 2013. Web. 19 March 2017.

2 Karen L. Cheney, N. Justin Marshall. “Mimicry in coral reef fish: how accurate is this deception in terms of color and luminance?”Behavioral Ecology.   Wed. 21 March 2017. doi: 10.1093/beheco/arp017

3 Sheppard, Charles R.C. et al. “The Biology of Coral Reefs.” Oxford University Press. 2012. Print.

4 Moland, Even et al. “Ecology and Evolution of Mimicry in Coral Reef Fishes.” Oceanography and Marine Biology: An Annual Review. June 2005. Web. 21 March 2017.

5 Coker, Darren J. et al. “Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes.” Behavioral Ecology.19 August 2009. Web. 19 Feb 2017.

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Unexplained Coral Deaths Plague Pristine Flower Garden Banks

Posted on March 22, 2017 by ak56

Now that I’ve introduced the Flower Garden Banks in a broad sense, I can get into the specifics of the conservation status of this National Marine Sanctuary. It’s pretty much common knowledge at this point that globally, coral reefs are not doing very well. A variety of factors, many of which can be traced back to human influence, are altering the very fragile balance of abiotic and biotic conditions that coral reefs depend on for survival and growth. Last week, I established that the Flower Garden banks were special in that they remained pristine compared to other reefs around the world: seemingly unaffected by the bleaching events that plague many of these other reefs. In this post, I will discuss a recent and bizarre turn of events which contradicts the claim I made in my first post. The East Flower Garden Banks, which together with the West and Stetson Banks comprise this National Marine Sanctuary, has been undergoing a bleaching event since last summer which has caused considerable damage to the reef.

Recreational divers first noticed something was wrong in July 2016, when they discovered uncharacteristically murky, greenish waters surrounding the East Banks.1 The divers also noted large white patches splayed out on the large reef-building coral heads, and dead animals lying on the seafloor. Scientists were immediately informed about the coral die-offs, and they sent boats to extensively sample both affected and unaffected corals, along with the water in the area, and anything else that might turn up clues about the cause of the coral deaths. The extent of the damage was also surveyed, and fortunately the event did not extend to either of the other two Banks in the reef system. While only about 6% of corals at the site were affected by this event, mortality rates upwards of 70% were observed in these discrete areas.1 This doesn’t seem very high, but since this reef has historically been one of the healthiest in the region, the die-offs are quite worrisome. Many of the afflicted corals followed the same pattern of death in which the bottom section of the coral started dying and then spread up towards the top, as seen below. The same disease signs found at the East Flower Garden Banks affected some sponges on a nearby oil platform, which raised concerns that the event may have been more widespread than researchers had initially believed.1

These images, courtesy of FGBNMS/G.P.Schmahl, depict the different patterns of coral death that afflicted the East Banks last summer. Note the bottom-up pattern of death which could shed light on the nature of the die-offs.

Despite extensive sampling and effort, no definitive answer could be given for the cause of the die-offs. Temperature conditions had not been out of the ordinary. The same can be said of salinity and nutrient upwelling events.1 Shipping activity records were reviewed and ruled out the possibility that a ship could have somehow polluted the water in the area. While direct causes of bleaching events can usually be traced by looking for changes that abiotic conditions such as temperature, salinity, nutrients, and light out of tolerable ranges, no such changes were present at the East Flower Garden Banks.

Instead of these traditional causes, it could be worthwhile to examine other aspects of the reef that could have been thrown off balance. The two main coral species that form this reef are Orbicella franksi and Pseudodiploria strigosa2. We know that there are differences in the way that these corals fertilize and release their larvae into the water column: Orbicella franksi fertilizes slowly and disperses larvae across vast expanses of sea, while Pseudodiploria is more effective at settling into local areas.2 Together these corals are effective at proliferating themselves and building up the reefs that form the Flower Garden Banks. A disruption of these processes, perhaps of unknown origin, could be the cause of last summer’s die-offs. Increasing numbers of invasive lionfish at the East Banks have been documented in recent years.3 It’s possible that these lionfish, like the one pictured below, could be playing a role in disrupting the processes I just described, or otherwise have a hand in the bleaching event some other way, like bringing a disease from their native habitat that the corals are unequipped to deal with.

“Lionfish, Navarre Beach, Florida” by Dave C. This is only one of countless invasive lionfishes that are populating and spreading through the Gulf of Mexico, including the Flower Garden Banks. It’s possible invasive species like this one could be responsible for the coral deaths. (from Flickr Creative Commons)

By the time the damage had been noticed and extensive analysis had begun, it seemed as though the event had ended. Bleaching had already ceased to spread, and no additional organisms around the reef were dying at rates that were out of the ordinary.1 Last summer’s bleaching event destroyed coral colonies that have been growing for hundreds and thousands of years in a matter of days and weeks. Though scientists have still been unable to pinpoint how this event came to be, it is crucial that we understand as much as we can about the causes of this event so that we can appropriately act to end it, and prevent future events of the same nature both in the Flower Garden Banks and in vulnerable reefs around the world.

 

Sources:

  1. “Scientists Investigate Mysterious Coral Mortality Event at East Flower Garden Bank.” Scientists Investigate Mysterious Coral Mortality Event at East Flower Garden Bank. National Ocean Service, 9 Aug. 2016. Web. 21 Mar. 2017.
  2. Davies, Sarah, Marie E. Strader, Johnathan T. Kool, Carly D. Kenkel, and Mikhail V. Matz. “Coral Life History Differences Determine the Refugium Potential of a Remote Caribbean Reef.” BioRxiv (2016): n. pag. Web. 21 Mar. 2017.
  3. Johnston, Michelle, Marissa Nuttall, Ryan Eckert, John Embesi, Travis Sterne, Emma Hickerson, and George Schmahl. “Rapid Invasion of Indo-Pacific Lionfishes Pterois Volitans (Linnaeus, 1758) and P. Miles (Bennett, 1828) in Flower Garden Banks National Marine Sanctuary, Gulf of Mexico, Documented in Multiple Data Sets.” BioInvasions Records 5.2 (2016): 115-22. Web. 21 Mar. 2017.
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The Hidden Devastation behind Beautiful Aquariums

Posted on February 25, 2017 by jjf5

Do you remember those mesmerizing aquariums that decorated the walls of the dentist’s office? The multitude of vibrantly hued fish and coral are nothing less than captivating. But where did those fish and coral come from? Behind aquariums’ exotic exterior is a distressing tale of coral reef damage. While the aquarium trade has bolstered the economy of many countries, mainly in coastal communities, its detrimental effects on coral reef health is nonetheless concerning.

First, I should explain what exactly the aquarium trade is and how it relates to coral reefs. The global aquarium trade harvests and transports marine ornamentals such as reef fish, invertebrates, and coral. A rapidly expanding enterprise, it was estimated to garner a global import value of around US $200-330 million in 20055. A possible reason for its increasing popularity over the past few decades could be due to influence from media like Pixar’s 2003 movie Finding Nemo3. Many children yearned for a Dory or Nemo of their own after watching that adventure! Coral reef organisms are sold to consumers mainly in the U.S, followed by Japan and Europe1. The most recent estimates peg the trade as dealing with over 150 species of stony corals, hundreds of species of non-coral invertebrates, and at least 1,472 reef fish species from 50 families3. However, it is also important to note that there are large discrepancies between governmental statistics of imported species and what many scientists believe are the actual statistics2.

Although the aquarium trade is not as pressing as global warming on coral reef decline, it is especially concerning in countries in the Coral Triangle (like the Philippines, Solomon Islands and Indonesia), where collection is heavily concentrated1. A few places outside of the Coral Triangle are also being pressured by the demands of the industry. For example, largely all fish species collected in Hawaii are now classified as endemic and suffering from significant population declines as shown by the graphic below.

Fig.1. Showcases the large scale fish species population decline in Hawaii.
Source: http://uhbiology.kahikai.org/?p=672

Several critical effects of the aquarium trade include:

  1. Disruption of reproductive cycle by taking out colorful males during reproductive season2.
  2. Interruption of coral reef food chain2.
  3. Habitat alterations2.
  4. Transportation of different species across borders lead to issues with invasive species1.
  5. Decimation of species populations beyond recovery due to specifically targeting popular species in commercial trade2.

Fish are selectively removed based on their color and size, with species that range from 2-9 centimeters being the most popular2. For instance, the Yellow Tang, which has made up a large majority of the fish caught in the industry, has suffered a sharp decrease in numbers5. This removal of species then sets up a domino effect where biodiversity on the reef as a whole is reduced as some species cannot survive without another.

The Yellow  Tang, a popular and heavily collected reef fish species.
Source: http://animalia-life.club/fishes/yellow-tang.html

In order to see how the removal of one species may affect another, let’s examine a study on aquarium fishing’s effect on anemone and anemone fish (popular reef organisms for collectors) in Cebu, Philippines. In this study, researchers found that removal of anemones strongly correlated with a declining population of anemone fish, as the vast majority of anemone fish are symbiotic with host anemone species. Low density of anemones accounted for over 80% of the reduced density of anemone fish in exploited areas4.

Researchers began their study by classifying sites into “protected” and “unprotected,” with unprotected sites being where there are extensive fishing activities. The researchers used fishery logbooks and free swim census techniques to quantify the number of anemone and anemone fish in all the sites. The results were startling. As seen below in Figures 2 and 3, the densities of anemone fish species and host anemones strongly correlated with each other and were significantly higher in protected sites when compared to unprotected sites4. The study concludes that aquarium fishing activities drastically influenced the decline of anemone and anemone fish.

Fig 2&3. Graph on top depicts two anemonefish species’ (A. clarkii and D. trimaculatus, n=448) densities in protected and exploited sites. Gray is exploited and white is protected. Graph on bottom depicts host anemone species’ (H. crispa and others n=98, protected n=2, exploited n=3) densities in protected and exploited sites. Notice the strong correlation between anemonefish and host anemone densities.                                                 Source: Shuman, C.S., Hodgson, G. & Ambrose, R.F. Coral Reefs (2005) 24: 564. ProQuest, doi:10.1007/s00338-005-0027-z

This shows how taking out one reef species can influence the decline of another. Therefore, aquarium trade collecting have the potential to not only deplete the species they are collecting, but also other species that may depend on the one being removed.

Now more than ever, the magnificent beauty, resources, and biodiversity of coral reefs are in danger of disappearing forever. Because of their immense resources and scientific importance, as well as their role in the global economy, it is of utmost importance that we do all we can to preserve them. With the U.S being a major player in the global aquarium trade, it is crucial for us to understand the environmental cost of our aesthetic desires. Since aquarium exports are an integral part of the economy, especially for tropical countries like the Philippines and Indonesia2, it would be ill-advised to stop it entirely. However, the techniques we use in collecting reef organisms and implementing trade regulations can help lessen the negative impacts of the aquarium trade. These ideas will be discussed in further detail in future posts. Stay tuned for more information on the aquarium trade and coral reefs and what YOU can do to make a difference!

 

References:

1Rhyne, A. L., Tlusty, M. T., Schofield, P. J., Morris, J. A., Jr., & Bruckner, A. W. (2012). Revealing the Appetite of the Marine Aquarium Fish Trade: The Volume and Biodiversity of Fish Imported into the United States. PLOS ONE, 7(5). doi:10.1371/journal.pone.0035808

2Aquarium Trade Impacts. (n.d.). Retrieved February 21, 2017, from http://www.forthefishes.org/Aquarium_Trade_Impacts.html

3Prosek, J. (2010) Beautiful Friendship. Nat Geo Mag 217: 120–124.

4Shuman, C.S., Hodgson, G. & Ambrose, R.F. Coral Reefs (2005) 24: 564. ProQuest, doi:10.1007/s00338-005-0027-z

5Kai, Kahi. “UH Biology.” UH Biology RSS. UH Biology, 14 Mar. 2012. Web. 21 Feb. 2017.

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Heating Up the Reefs

Posted on February 22, 2017 by lem5

Because they are among the most diverse ecosystems, coral reefs are essential to thousands of oceanic species, and people also rely on them for food, protection and even income1.  It seems to be common knowledge that climate change is having devastating effects on oceanic wildlife, and those effects extend to killing coral reefs. While most people might understand  that climate change, specifically higher  water temperatures, can cause destruction of coral reefs, the term “bleaching” of the coral is probably a new concept. While some environmentalists are familiar with that term, most people are not really aware of what is happening during bleaching.

Corals are hosts to symbiotic algae, called Symbiodinium, which provide most of the food for the coral through photosynthesis2. In a symbiotic relationship, two beings (in this case the coral and the algae) mutually benefit from living together in close proximity.  The plantlike algae gains an appropriate living space and the coral benefits from having its dinner close by.  Under different stressful conditions, including high temperatures, coral expel their symbiotic algae and turn white, which is called coral bleaching as shown in figures 1 and 22. Without the algae, the coral no longer has its major source of food and is susceptible to disease and death.

Figure 1: This coral has been bleached at the tips. The tips are white and no longer contains its Symbiodinium while the bottom is brown and still has its Symbiodinium. Photo by Oregon State University.  Licensed by CC BY-SA 2.0.

Figure 2: This coral colony is completely bleached. Photo by Matt Kieffer. Licenced by CC BY-SA 2.0.

A recent study by Derek Manzello suggests that the warming of coral reefs has been under-estimated3. In his research, he analyzed temperature records of the Florida Keys to calculate average daily and monthly temperatures and the rate of seasonal warming3.  He found that the average number of days per year where the temperature reached over 31.5oC (88.7 oF) has increased over 2500% from the 1990’s to the present compared with the 1970’s to the 1990s3. These temperature analyses show that thermal stress is increasing annually and predict that the reefs will bleach annually, starting sometime between 2020 and 2034, which is earlier than previously predicted3.  In the past, the prevailing thought was that bleaching would begin to occur sometime around 20503.

Given that temperatures on reefs are rising quickly and temperature is an important stressor that leads to coral bleaching, do the corals have any means of defense against climate change? Many studies have looked at temperature sensitivity in corals and have found that different factors affect a coral’s sensitivity to temperature and subsequent bleaching, including temperature, nutrients and light. Variation in bleaching susceptibility has been found between different coral species, between conspecific (individuals of the same species) corals housing different species of symbiotic zooxanthellae (algae that use photosynthesis to produce nutrients), and even between conspecific and congenetic (individuals with the same genetics) colonies found at different locations4.

Hoping to understand differences in temperature sensitivity, Ulstrup, et. al.,5 compared the thermal tolerance of corals of different species, found at different geographic latitudes, and housing different symbiotic companions. In their experiment, samples of two corals, Pocillopora damicornis and Turbinaria reniformis, were taken from different sites on the Great Barrier Reef, and then were subjected to different temperatures for different time periods in the lab5. After subjecting them to these stressful conditions, the researchers recorded the coral’s mortality rate, symbiont density (the amount of  symbionts in the coral tissue), and photochemical efficiency (or how well the symbionts created food) with respect to the different temperature treatments5. They first found that T. reniformis was more resilient to higher temperatures, dying at a temperature 2oC (3.6o F) higher than P. damicornis. They also found that corals found at a higher latitude bleached faster, and at lower temperatures, than those found at lower latitudes5. They believe the reason for this difference is local adaptation – lower latitude corals are naturally exposed more to higher temperatures than higher latitude corals and therefore have adapted to be able to handle slightly higher temperatures5. Finally, this study showed that the symbiont Symbiodinium clade D is more heat resilient than Symbiodinium clade C and that corals that did not have clade D were more sensitive to higher temperatures5.  The term “clade” simply  refers to a group of zooxanthellae that has arisen from one common ancestor, so apparently the clade D-containing corals had adapted themselves and their symbiotic algae to be more heat resilient.

A previous study by Dr. Rob Rowan6 also showed that Symbiodinium clades C and D differ in their heat tolerance. He suggests that corals housing Symbiodinium clade D may be able to better adapt to rising temperatures.

While these differences in temperature sensitivity are small and may seem insignificant, they may actually be very important to saving the reef from warmer waters caused by climate change. Drs. Ruth Gates and Madelein van Oppen7, 8  are helping corals adapt to higher temperatures by exposing them to such temperatures in a lab before attempting to transplant them to reefs in Hawaii and Australia, a technique called “assisted evolution.” The success of these experiments is yet to be determined.

Coral reefs are a very important part of the ocean ecosystem and are important to many people whether for food, source of income, or just the beauty and biodiversity associated with reefs. Although these new methods may help the corals better adjust to higher sea water temperature, the issue of climate change still needs to be addressed if the coral reefs are to survive long term. The increased timeline proposed for coral bleaching should be a major red flag that climate change must be addressed sooner rather than later.

 

Footnotes:

  1. National Oceanic and Atmospheric Administration. http://www.noaa.gov/resource-collections/coral-ecosystems
  2. US Department of Commerce, N.O. and A.A. What is coral bleaching? http://oceanservice.noaa.gov/facts/coral_bleach.html.
  3. Manzello, D.P. (2015). Rapid Recent Warming of Coral Reefs in the Florida Keys. Scientific Reports 5, 16762.
  4. Fabricius, K.E., Mieog, J.C., Colin, P.L., Idip, D., and H. Van Oppen, M.J. (2004). Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories: CORAL-ZOOXANTHELLAE ASSOCIATIONS IN PALAU. Molecular Ecology 13, 2445–2458.
  5. Ulstrup, K.E., Berkelmans, R., Ralph, P.J., and Van Oppen, M.J. (2006). Variation in bleaching sensitivity of two coral species across a latitudinal gradient on the Great Barrier Reef: the role of zooxanthellae. Marine Ecology Progress Series 314, 135–148.
  6. Rowan, R. (2004). Coral bleaching: Thermal adaptation in reef coral symbionts. Nature 430, 742–742.
  7. Riley, A. The women with a controversial plan to save corals. http://www.bbc.co.uk/earth/story/20160322-the-women-with-a-controversial-plan-to-save-corals.
  8. Oppen, M.J.H. van, Oliver, J.K., Putnam, H.M., and Gates, R.D. (2015). Building coral reef resilience through assisted evolution. PNAS 112, 2307–2313.

 

 

 

 

 

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Undoing the Damage We’ve Done

Posted on February 21, 2017 by mnc1

Humans have an undeniable impact on the world around them, but it’s often hard to see the damage we’ve done when it’s out of sight under the sea. Often compared to the terrestrial biome of the tropical rainforest, coral reefs are bursting with biodiversity despite their relatively small size. And again similar to the tropical rainforest, coral reefs are dying at alarming rates due to human actions. However, recognizing the danger that coral reefs are in, conservationists, biologists, and activists are taking action across the world, raising awareness of the issues, researching management techniques, and advising the general public on how they can help protect these fragile ecosystems.

Coral reefs are important ecosystems provide habitat for thousands of different species, ranging from predatory fish to symbiotic single-celled organisms, and are especially critical for providing nursery habitat for young.

Reefs don’t just support marine life; humans vastly benefit from the presence of reefs and their biodiversity, and not because they provide us with food. Coral reefs can protect land from erosion by taking the brunt of wave energy heading for shorelines. This is relevant for humans as erosion can be detrimental for settlements and cities, especially with rising sea levels already posing serious threats to coasts. Additionally, tourists regularly flock to coral reefs because of their aesthetic qualities and the exposure to with marine life. These tourists bring in money to coastal economies, especially in developing areas such as the Caribbean and Pacific Islands 1.

Humans are negatively impacting coral reefs from all sides. The most global and widely reaching of these impact is climate change, as ocean acidification is breaking down calcium carbonate structures while increasing temperatures are killing off coral polyps as well as the inhabitants of these reefs. More locally, reefs suffer physical damage from anchoring, tourism, and marine debris. Additionally, eutrophication, or the sharp increase in nutrients, has been increasing due to human sewage inputs as well as agricultural practices, which provides an advantage to coral competitors like macroalgaes. Lastly, overexploitation is removing resources faster than they can be replaced, slowly emptying corals of any signs of life 2,3.

Despite, or perhaps because of, the dim future for coral reefs, there are dedicated humans out there that have made it their mission to protect coral reefs and the marine life that call reefs home. Without hope for the future, there is no point for conservation efforts, but luckily there are a number of things that should be giving us hope. One example is in this image, which features a sunken ship serving as an artificial reef at the Florida Keys National Marine Sanctuary, which is just one creative way humans can offset tourist pressure at coral reefs while providing safe habitat for marine life 4, 5.

One of four sunken ships featured at the Florida Keys National Marine Sanctuary. Each ship and site was critically evaluated before installation, and sites are regularly monitored and evaluated. Source: Florida Keys National Marine Sanctuary, NOAA

Topics in this blog series will focus on positive anthropogenic effects and effective conservation methods on coral reefs by highlighting ways scientists and activists are fighting back against the continuing damage we are dealing to these beautiful ecosystems. This blog will cover projects such as declaring reefs to be protected areas, the creation of artificial reefs, and activism focusing around reefs, culminating in ways you as an individual can do your part to reduce your impact on marine life. I hope you will join me on this exploration of how humans are attempting to remedy this dire situation under the sea.

  1. Correa, Adrienne S. “Course Overview, Why Reefs Matter.” Coral Reef Ecosystems, 12 January 2017, Rice University, Houston TX. Class Lecture.
  2. Mora, Camilo. “A Clear Human Footprint in the Coral Reefs of the Caribbean.” Proceedings of the Royal Society B: Biological Sciences 275, no. 1636 (April 7, 2008): 767. doi:10.1098/rspb.2007.1472.
  3. Halpern, Benjamin S., Shaun Walbridge, Kimberly A. Selkoe, Carrie V. Kappel, Fiorenza Micheli, Caterina D’Agrosa, John F. Bruno, et al. “A Global Map of Human Impact on Marine Ecosystems.” Science 319, no. 5865 (February 15, 2008): 948. doi:10.1126/science.1149345.
  4. Hackradt, Carlos Werner, Fabiana Cézar Félix-Hackradt, and José Antonio García-Charton. “Influence of Habitat Structure on Fish Assemblage of an Artificial Reef in Southern Brazil.” Marine Environmental Research 72, no. 5 (December 2011): 235–47. doi:10.1016/j.marenvres.2011.09.006.
  5. Feary, David A., John A. Burt, and Aaron Bartholomew. “Artificial Marine Habitats in the Arabian Gulf: Review of Current Use, Benefits and Management Implications.” Ocean & Coastal Management 54, no. 10 (October 2011): 742–49. doi:10.1016/j.ocecoaman.2011.07.008.
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Corals of the Caribbean: The Curse of the Black Band

Posted on February 21, 2017 by Liseth Perez

Close your eyes and picture a Caribbean coral reef.

You probably saw a beautiful landscape, with colorful patterns and exotic fish. But the sad truth, is that it is not all rainbows and butterflies. Lately, coral reefs have been attacked by infectious diseases and are currently facing deterioration. The Caribbean reefs have been referred to a “disease hot spot”1 and rightfully so. Over the past 30 years, they have lost 80% of their coral cover, leaving the coral vulnerable.2

Corals are living organisms that heavily rely on their environment and their surroundings to survive and thrive. Important factors  to keep in mind are water temperature, chemistry and light. Inherently, under prime  conditions an abundance of corals will flourish. However, this also allows for a prime environment where diseases are more likely to spread amongst the breadth of corals. It is easier for a disease to spread, within the same species (Figure 1). Therefore, if there is a primary coral in the coral reef that makes up the majority, they are more likely to be attacked.3

Figure 1. Right of coral being affected by Black Band Disease and the left has Christmas treeworms.                                               Copyright: “Causes of Coral Disease.” Reef Resilience. The Nature Conservancy, 30 Aug. 2016. Web.

Now, imagine lighting a corner of a paper and observing the flame spreading and consuming the rest of the paper…this is what happens when a coral is affected by the Black Band Disease (BBD), the process just occurs across a span of months. This disease is due to bacteria overtaking the coral and exposing it to hydrogen sulfide and leaving it with no access to oxygen.4   Where the bacteria is attacking the coral at the moment a black band is seen and coral it has already affected is a pale white, this is depicted in Figure 2. The first case of BBD was reported in the 1970s and it was assumed that the bacteria, Phormidium corallyticum, was the root of evil.5 However, when researchers took a further look into the composition of the bacteria that makes up the black band, there were several cyanobacteria present. These attack the coral tissue and leave the coral’s skeleton exposed.5 The abundance of certain bacteria fluctuates between the different geographic locations around the Caribbean Sea. This group of bacteria forms a band and digests the tissue as it progresses along the coral colony.

Figure 2. Experimental site where surface area of coral affected by BBD is being measured. Copyright: Voss, Joshua D., and Laurie L. Richardson. “Nutrient Enrichment Enhances Black Band Disease Progression in Corals.”Coral Reefs. (2006) 25: 569.

BBD has been seen to affect other species of corals that grow close to the coral originally affected. Once affected by BBD, it is difficult for the coral to survive. If affected for several months, the coral colony dies.4 There are cases however, where if the cyanobacteria invader goes away, there is a possibility that the coral recover5; but it will never be the same.

In general, the decline in water quality, allows for the perfect environment for bacteria and microbes that attack corals, and it is linked to human pollution and increased water temperatures.The origin of this cyanobacteria or how it begins to attack the coral, still remains unclear. But there has been a correlation between the presence of coallivorous fish and the presence of BBD.3 Through studies, there has been proof that nutrient high environments help speed up the rate at which BBD affects the coral, partially because of increased nitrate production.2 Furthermore, there is a correlation between warmer seawater temperatures and the abundance of BBD amongst coral colonies as seen in Figure 3.6

Figure 3. a) Seawater Temperature b) Amount of colonies affected by BBD.                              Copyright: Edmunds, Peter J. “Extent and Effect of Black Band Disease on a Caribbean Reef.” Coral Reefs (1991): 161-65.

Corals are sensitive animals that are part of a delicate ecosystem and they must be taken care of. In 1991, BBD was still not a major concern and affected very few coral reefs; it was even seen in the perspective of diseases serving as a natural regulator for marine environments. 6 Now the position is very different and as noted above BBD had become a prevalent issue. So moving forward, scientists are researching the specifics of the origin of the disease and looking for ways to control the environmental factors that exacerbate the spread of the BBD.

1. Weil, E., G. Smith, and Dl Gil-Agudelo. “Status and Progress in Coral Reef Disease Research.”Diseases of Aquatic Organisms 69 (2006): 1-7. Web.

2. Voss, Joshua D., and Laurie L. Richardson. “Nutrient Enrichment Enhances Black Band Disease Progression in Corals.”Coral Reefs. (2006) 25: 569.

3. “Causes of Coral Disease.” Reef Resilience. The Nature Conservancy, 30 Aug. 2016. Web. <http://www.reefresilience.org/coral-reefs/stressors/coral-disease/causes-of-coral-disease/>.

4. “Causes of Coral Disease.”Reef Resilience. The Nature Conservancy, 30 Aug. 2016. Web. 21 Feb. 2017. <http://www.reefresilience.org/coral-reefs/stressors/coral-disease/causes-of-coral-disease/>.

5. Frias-Lopez, Jorge, George T. Bonheyo, and Qusheng Jin And. “Cyanobacteria Associated with Coral Black Band Disease in Caribbean and Indo-Pacific Reefs.” Applied and Environmental Microbiology. 69.4 (2003) 2409-2413. Web.

6. Edmunds, Peter J. “Extent and Effect of Black Band Disease on a Caribbean Reef.” Coral Reefs3 (1991): 161-65. Web.

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More Than Just a Pretty Picture: The Economic Importance of Coral Reefs

Posted on February 21, 2017 by mhp2

Although many of us are aware that coral reefs around the world are threatened by various factors, the fact seems fairly unrelated to most of our daily lives. However, the truth of the matter is that globally, although in some regions more than others, coral reefs can be major contributors to the economy. This may not be such a surprise when we think about an image of a bright and healthy coral reef ecosystem, which tends to be very visually busy with all of its living and non-living members.

It makes sense then, that coral reefs are actually able to provide us with quite valuable and widely used resources. For example, there are many kinds of seafood which can be gleaned from coral reef environments, with reef-related fisheries making up about 9-12% of the total fisheries worldwide¹. Additionally, many pharmaceutical companies are taking advantage of the high biodiversity found in coral reef ecosystems which includes many organisms that possess beneficial medicinal properties¹.

Coral reefs also are responsible for providing us with services such as protection from erosion. In the Pacific Island countries and territories, for example, the reefs in the area not only protect the coast, but also is home to some of the largest tuna fisheries in the world². In the Southern Ocean region, coral reefs are important fisheries, as well as sources for the growing market of health supplements, and are major attractions for tourists².

The economic contributions of coral reefs is so vast in fact, that initiatives have been put in place to restore reefs in various places, including Florida and the Caribbean³ (Image 1). Several organizations have partnered together to ensure the longevity of coral in these areas in the future (Image 2). To put some numbers with it, the value of one hectare of coral reef has been calculated to provide an average of $130,000 worth of services with the highest calculated value resting around $1.2 million¹. In other words, coral reefs have so much more to offer than simply being aesthetically pleasing, and whether we are aware of it or not, they provide us with resources that help our economies flourish, and allow for us to live the lives we do.

 

Image 1
Marine biologists restore reefs near Grenada by planting young corals.
Credit: Tim Calver
http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/florida/newsroom/initiative-to-restore-one-million-corals-launches-in-florida-and-the-caribbe.xml

Image 2
Ken Nedimyer, a marine biologist, observes the state of staghorn coral near Key Largo, Florida.
Credit: Tim Calver
http://blog.nature.org/science/2013/06/06/future-coral-reef-restoration-science/

References

¹ Moberg, Fredrik, and Carl Folke. “Ecological goods and services of coral reef ecosystems.” Ecological economics 29.2 (1999): 215-233.

² Cavanagh, Rachel D., et al. “Valuing biodiversity and ecosystem services: a useful way to manage and conserve marine resources?.” Proc. R. Soc. B. Vol. 283. No. 1844. The Royal Society, 2016.

³ “The Nature Conservancy.” The Nature Conservancy. N.p., n.d. Web. 20 Feb. 2017. <http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/florida/newsroom/initiative-to-restore-one-million-corals-launches-in-florida-and-the-caribbe.xml>.

¹ Diversitas. “What Are Coral Reef Services Worth? $130,000 To $1.2 Million Per Hectare, Per Year.” ScienceDaily. ScienceDaily, 28 October 2009. <www.sciencedaily.com/releases/2009/10/091016093913.htm>.

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Mangroves: Their Importance on Both Reef Species’ and Human’s Environments

Posted on February 21, 2017 by skg5

When situated near coral reefs, mangroves affect the reef communities in many interesting ways. Mangroves are trees that can grow in environments with poor oxygen content. Mangroves can grow in fresh, brackish, and salt water. The term ‘mangrove’ does not actually refer to a specific taxonomic grouping; rather, it refers to the group of plants that can survive in such tough conditions. There are seven types of mangroves, but the three most common species of mangroves are the red, white, and black mangroves. Personally, the red mangrove (Rhizophoramangle) is what I picture when I think of a mangrove (see image). Red mangroves have easily identifiable large tangled root systems. Mangroves serve as shoreline protection, and, when situated near reefs, as nurseries for many species of reef fish.

Red mangroves. Note the complex root system which is integral to their efficacy as a nursery habitat. (credit http://www.reelfl.org/wp-content/uploads/2014/10/Red-mangrove.png)

Only thirty five percent of coral reefs have mangroves nearby. Therefore, mangroves clearly are not necessary for reef ecosystems’ success. It is estimated that there is only a 6-8% chance that a larval fish, when spawned on a random reef, will find a coral reef with a mangrove close by.(1) However, reefs that are situated near mangroves can have increased biomasses of over 162 fish species. These include herbivores, invertivores, and piscavores.(2)  For example, it was found that the Scarus iseri species of parrotfish had significantly higher biomass on reefs with mangroves nearby and that the Scarus guacamaia species of parrotfish’s juveniles depended on mangroves for survival.(3) Interestingly, some species’ biomasses decrease on reefs near mangroves. This is probably because their predators use the mangroves and thus are present in higher numbers.(4) An example of a species that would probably suffer as a result of nearby mangroves would be the macroalgae grazed on by the parrotfish species that benefit from the presence of mangroves.

View underwater of the mangroves root system (credit https://lh3.googleusercontent.com/1s3bSP0A14P4-dT7An8fwhbA4-wCP7ERffVfC1yC8JXmGwF5_BqnD7JHmZvmoc28g6kmrZbZhbX4LUlsRrEeVpwnbp3PLo-6WjVZqftjGr_zWBENxzhgxDAjUXuPUgc4bb5PBCM)

Most reef fish that use the mangrove habitat do so as juveniles. Fish oftentimes will use different habitats at different stages of their lives. Some reasons for this include changes in food requirements with age and changing risks of predation as the fish grow.Some use the mangroves as a nursery habitat, and others use it as an intermediate habitat between seagrasses, where they spend their juvenile stage, and the reef, where they will spend their adult stage.(5)  A nursery is defined as a “habitat for a particular species that contributes a greater than average number of individuals to the adult population on a per-unit-area basis in comparison to other habitats used by juveniles.”(6) Mangroves make a good nursery habitat because there is lots of food available. Also there is a decreased predation risk within the mangrove roots because, as seen in the above image, they live in shallow water and because the complex, maze-like structure provides many hiding places. Another cause for the decreased predation risk is high turbidity and poor visibility within the mangrove roots.(7)

Another majorly important function of mangroves near reefs is shoreline protection. Mangroves were found to be more effective than the coral reefs at decreasing wave energy. Mangroves are able to reduce non-storm waves by 70% of their near shore height!(8) They are also very effective at diminishing storm waves. Additionally, mangroves can slow erosion and soil loss from the shoreline due to the frictional drag that their roots apply to the water column.(9) In this way, they also can protect reefs from the shoreline, as sediment and nutrient run off can be very damaging to reefs. Obviously, people are more inclined to care about mangroves for their function in protecting our own environments rather than their role on reefs. Just last week, the Jamaican government dedicated additional funds to rehabilitate mangrove habitats in order to better protect their suffering shoreline (see image).(10)

The eroding Jamaican shoreline, which officials hope to improve through mangrove rehabilitation. (credit http://cdn4.antiguaobserver.com/wp-content/uploads/2017/02/Palisadoes-2.jpg?x54148)

For several reasons, mangroves should be important to us all.

Footnotes:
1: Brown et. al, “Uniting paradigms of connectivity in marine ecology.” Ecology.  97, 9, 2016, pp. 2447-2457.

2:Peter Mumby, “Connectivity of reef fish between mangroves and coral reefs: ALgorithms for the design of marine reserves at seascape scales.” Biological Conservation. 28, 2006, pp. 215-222.

3:Harborne et. al, “Direct and indirect effects of nursery habitats on coral-reef fish assemblages, grazing pressure and benthic dynamics.” Oikois. 125, 2016, pp. 957-967.

4: Brown et. al

5: Mumby

6:Lee et. al, “Ecological role and services of tropical mangrove ecosystems: a reassessment.” Global Ecology and Biogeography, 23, 2016, pp. 726-743.

7: Lee et. al

8:Guannel et. al, “The Power of THree: Coral Reefs, Seagrasses and Mangroves Protect Coastal Regions and Increase Their Resilience.” Plos One. 11, 7,2016.

9: Guannel et. al

10: http://antiguaobserver.com/government-allocates-funds-to-monitor-mangrove-rehabilitation/

 

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“EN-SO” the Bleaching Goes On

Posted on February 21, 2017 by cbm8

If you live in the United States, you may have noticed that 2015 was a hotter, rainier year than usual. If so, then you were certainly on to something; temperature and precipitation levels in 2015 were significantly above historical averages for much of the contiguous states (Figure 1). In fact, it was the second-hottest year ever for the US, and one of the highest globally since data started being collected in 18951. While human-induced climate change clearly has been a major cause of recent temperature increases around the world, there’s another culprit behind 2015’s particular extremity: El Niño.

Figure 1: 2015 Temperature (Top) and Precipitation (Below) Rankings for the Contiguous US – States are labelled with a number from 1-121, corresponding to their rank among past 121 years (1895-2015) at that location
Source: https://www.ncdc.noaa.gov/sotc/national/201513 (Reference 1)

El Niño is the warm phase of a sea surface temperature and climate pattern in the Pacific, called the El Niño-Southern Oscillation2 (ENSO), that takes place every 2-7 years; the cool phase that follows is called La Niña. In late 2014 and early 2015, warm water began to rise near the equator, and a wave of heavy rainfall hit the western coast of the Americas, characteristic of the beginning of the El Niño phase (Figure 2). The drastic elevation of sea surface temperatures across the Pacific Ocean that resulted quickly became cause for major global concern.

Figure 2: El Niño Global Climate Impacts, First Year – Colors represent different climate conditions; see legend above 
Source: https://www.climate.gov/news-features/featured-images/global-impacts-el-ni%C3%B1o-and-la-ni%C3%B1a (Reference 2)

Because Indonesia, Australia and numerous Pacific islands are home to some of the world’s largest and most diverse coral reefs, the severity of this El Niño event was a particularly troubling development for these areas. Many coastal fishing economies in this region rely on the presence and health of reefs, which are extremely diverse marine ecosystems that harbor large fish populations3.

When sea surface temperatures rise too high, reefs can become blanketed in white and experience widespread mortality through a process called coral bleaching. According to the National Oceanic and Atmospheric Administration (NOAA), coral bleaching occurs when the coral organism is “stressed by conditions such as temperature,” expelling the algae responsible for their coloration and inhibiting essential feeding processes4.

Historically, strong El Niños have resulted in some of the worst coral bleaching events on record. For instance, in 1998, statistically one of the strongest ENSO cycles ever, a staggering 16% of coral reefs worldwide perished5. Scientists with the NOAA declared this the first “global bleaching event,” on account of its widespread impact and reef mortality rates3. It mainly affected tracts of reef in Southeast Asia, and during the La Niña phase of 1999, the South Pacific.

The global bleaching event ran its course, and transitioned into 10-12 years of uninterrupted (by ENSO) coral recovery. By the time the less (but still) severe 2010 El Niño began, many bleached, more rapid-growing corals in the Pacific had had an opportunity to regrow3, which somewhat lessened the impact of this “second” global bleaching event. However, when a mere four years later, the 2014-15 El Niño came into effect with nearly unprecedented global air and sea surface temperature increases, the Pacific coral reefs were not even close to sufficiently recovered. Today, in 2017, this “third” event has not yet fully ended, making it one of the most impactful, and the single longest-lasting mass bleaching event in modern history3.

Figure 3: Side-by-Side of December 2014 (left) and February 2015 (right) shows devastating effects of the current (third) mass bleaching event on reefs near American Samoa in the Pacific
Source: http://science.sciencemag.org/content/352/6281/15.full (Reference 5)

A 2016 Science article by Dennis Normile details the severity of the current, third global bleaching event, and warns of the threat climate change and El Niño-driven ocean warming pose to the long-term survival of coral reefs. As early as February 2015, coral reef off the coast of American Samoa had already shown significant signs of bleaching (Figure 3), and by April, over half of corals in parts of Indian Ocean reefs were bleached to some extent5; spring 2016 surveys of Australia’s Great Barrier Reef similarly revealed extensive strands of bleaching and mortality. Normile asserts that “it is not clear what percentage of the bleached coral will die5,” but if the observations accumulated following the record-breaking heat of 2015 are any indication, the global prospects of coral reef survival percentages through the current ENSO (2014-17) are rather grim.

That being said, understanding the strength and frequency of ENSO events is essential for predicting when, and for how long global coral bleaching events will occur in the years to come. Especially as coral restoration efforts continue to progress, we need to know more about the duration of ENSO, in order to best structure the timeline of these processes and ensure the survival of coral reefs for future generations.

References:

1 “National Overview for Annual 2015.” NOAA National Centers for Environmental Information – State of the Climate, pub. online January 2016. Web. 20 Feb. 2017. http://www.ncdc.noaa.gov/sotc/national/201513

2 Lindsey, Rebecca. “Global impacts of El Niño and La Niña.” Climate.gov – NOAA, pub. online 9 Feb. 2016. Web. 20 Feb. 2017. https://www.climate.gov/news-features/featured-images/global-impacts-el-ni%C3%B1o-and-la-ni%C3%B1a

3 “El Niño prolongs longest global coral bleaching event.” News and Features – NOAA, pub. online 23 Feb. 2016. Web. 20 Feb 2017. http://www.noaa.gov/media-release/el-ni-o-prolongs-longest-global-coral-bleaching-event

4 “What is coral bleaching?” What is coral bleaching? – Ocean Facts. National Ocean Service – U.S. NOAA, n.d. Web. 20 Feb. 2017. http://oceanservice.noaa.gov/facts/coral_bleach.html

5 Normile, Dennis. “El Niño’s warmth devastating reefs worldwide.” Science, 01 Apr 2016. Vol. 352, Issue 6281, pp. 15-16. Accessed online, 19 Feb. 2017. http://science.sciencemag.org/content/352/6281/15.full

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Rainforests of the Sea: Mutualism on Coral Reefs

Posted on February 21, 2017 by bfm3

Coral reefs are home to some of the most diverse ecosystems on the planet. The intricate shapes and bright colors found on reefs can be reminiscent of the Dr. Seuss books that we all read as kids. They are also sometimes called the rainforests of the sea, mostly because coral reefs rival tropical rainforests in biodiversity, but also because of the obvious biological complexities that can be observed on any part of a reef. One of these complexities can be viewed in the form of symbiotic relationships, which occur between all kinds of reef-dwelling (or building!) organisms.

There are three main types of symbiotic relationships found in nature: mutualism, commensalism, and parasitism. In blog posts that I will update over the next few months, I will outline how each of these relationships are prevalent on coral reefs while providing examples of each, how human impact is affecting them, and how this will ultimately affect coral reef ecosystems on a global scale.

The first type of symbiotic relationship, and the main focus of this post, is mutualism. In these kinds of interspecific relationships, both (or all) organisms involved benefit from the interactions. There are numerous examples of mutualism on coral reefs. One is the relationship that cleaner shrimp (Lysmata anboinensis) have with many species of larger ‘client’ fish, who come to the shrimp to be cleaned of parasites and dead skin, which the shrimp then eat¹. If you’ve ever seen Finding Nemo, the character Jacques was actually a cleaner shrimp! This is a prime example of a mutualistic relationship; the shrimps benefit because they get food while the fish benefit because they get rid of possibly harmful parasites and dead skin. This relationship is pictured below.

Image 1: L. anboinensis ‘works’ on a yellow-edged moray eel (Gymnothorax flavimarginatus) to rid the fish of parasites and dead tissues. Credit: Jesse Cancelmo

 

Another example of mutualism on reefs is one that is vital to the health of the reef and all its inhabitants: the relationship that corals have with zooxanthellae. Corals are animals that consist of vast carbonate (limestone) skeletons produced by tiny individual polyps, which comprise the actual animal part of the coral. Zooxanthellae (dinoflagellates that live in symbiosis with many types of invertebrates) live within the polyp tissue and use carbon dioxide and H2O from the coral to carry out photosynthesis. They in turn provide the coral with sugars, lipids, and oxygen for growth and the continuation of the cycle of cellular respiration².

You might have heard of something called ‘coral bleaching’ – this is the phenomenon by which corals lose their symbiotic zooxanthellae due to drastically changing ocean conditions (including temperature, salinity, and acidity). Coral bleaching is characterized by white, thin-looking corals as opposed to brown or greenish corals that are fuller in composition (pictured below).

Image 2: Acropora coral experiences bleaching on the Great Barrier Reef. Credit: Prof. Ove Hoegh-Guldberg: Chair, CRTR Coral Bleaching Working Group; http://www.gefcoral.org/en-us/targetedresearch/bleaching.aspx

 

Because corals are completely dependent on zooxanthellae, losing this critical relationship is a blow to any reef that experiences bleaching. Bleached coral can recover, but only if zooxanthellae return to the corals in a relatively short amount of time (usually a few days). After this, the coral dies and becomes a part of the extensive skeletal structure of the reef. Although reef growth requires the accumulation of coral carbonate skeleton, infinitely more important is the presence of live coral, which provides many ecological benefits beyond the zooxanthellae.

Figure 1: Mean survivorship of 4 prey fish associated with different habitat treatments (n = 6 for each treatment): 1) healthy, 2) bleached, 3) dead, 4) algal covered, and 5) control (no predator) after being exposed to a predator for 75 h. Mean SE = 6.5%, 4.3%, 4.2%, and 3.7%.³

The very possible continued global bleaching of coral reefs not only threatens corals themselves, but also the many species of fish and other marine creatures that make reefs their home (this in and of itself is an example of mutualism). Reefs serve many roles, including the role of protector from predators for many species. Many predators use contrasting coloration to find prey, and for this reason many prey species have adapted to resemble certain parts of reefs. Since bleaching changes the color of corals, this can make coral-dwellers more susceptible to predation3. The structural degradation of reefs can also attribute to greater predation rates, since prey species won’t be able to hide in the same nooks and crannies that they have in the past. See Figure 1 for an idea as to how much prey species rely on corals.

Since close to a quarter of marine biodiversity depends on reefs in some way4, it is vital that their structural and functional integrity remain intact. Reefs provide some of the greatest examples of mutualism in nature, and their existence as a resource for biologists and other researchers remains something worth protecting.

Resources:

1 Lysmata amboinensis: WAZA: World Association of Zoos and Aquariums

2 NOAA’s National Ocean Service: Diagram of coral and zooxanthellae relationship

3 Darren J. Coker, Morgan S. Pratchett, Philip L. Munday; Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes. Behav Ecol 2009; 20 (6): 1204-1210. doi: 10.1093/beheco/arp113

4 Nancy Knowlton. Corals and Coral Reefs. Comp. The Ocean Portal Team. N.d.

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