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Corals and Seaweed: The Fight for Dominance

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By Konnor Payne, SRC Intern

Coral reefs exist because the environment around them gives them the means to survive. These conditions are also the perfect environment for seaweeds, which compete with the corals for space. Worldwide, there have been recorded occurrences of transitions from coral to seaweed dominance. Researchers at the University of California Santa Barbara theorized that this was due to the overfishing of herbivores that would otherwise keep the seaweeds at bay, or nutrient enrichment, leading to an explosion of seaweed. To test this hypothesis, they traveled to the barrier reef of Moorea, French Polynesia. This reef had experienced an outbreak of coral-eating sea stars in the past few decades that reduced the coral cover to less than 5%. For unknown reasons, the fore reef (outer slope) has recovered but not the corals in the lagoon (back reef), which have been taken over by a seaweed called Turbinaria ornata. Investigating the difference in the corals’ resilience along the fore reef and lagoon could give insight into herbivory tipping points to maintain a coral-dominant environment. There was also a chance of “hysteresis,” or the idea that a slight change in one parameter produces an environment that requires a more significant change in the same parameter to return the environment to its original state. 

Figure 1. Adult Turbinaria ornata in Moorea, French Polynesia that compete with corals for space and resources (Schmitt, 2019).

The resilience test was conducted in the lagoon by mimicking storms’ varying intensities for 26 months on patch reefs and observing their recovery over 37 months. The researchers replicated a storm disturbance by removing all or parts of seaweed on the sample site. The researchers compared the abundance of coral at the beginning of the experiment to the end. The corals were highly resilient to a moderate disturbance, but not severe disturbance, from which they failed to recover and became dominated by turf algae. If the amount of herbivory is insufficient, the area will convert fully to seaweed dominance due to fishing pressure. 

Figure 2. The exclusion cage is placed on a patch reef to limit herbivorous fish’s body size that graze on it (Schmitt, 2019).

To test for hysteresis, a series of cages with various-sized holes were placed across patch reefs to limit the herbivorous fish body size, limiting their feeding capacity (Fig. 2). The researchers left these sites for as long as needed until the system naturally reached a stable state. The researchers found hysteresis at both sites by comparing the stable states of coral versus seaweed across the fore reef and lagoon. However, the standard conditions on the fore reef had herbivory action high enough to prevent seaweed dominance. In contrast, the lagoon is on the tipping point. The lagoon is at risk for completely transitioning to a seaweed-dominant environment, whereas the fore reef will likely remain coral-dominated. The researchers concluded that reversing an undesired shift on coral reefs would be difficult due to the hysteresis effect. The results suggest that proactive management strategies to prevent shifts in the first place will be more effective than management strategies targeted at restoration. 

 

Works Cited

Schmitt, R. J., Holbrook, S. J., Davis, S. L., Brooks, A. J., & Adam, T. C. (2019). Experimental support for alternative attractors on coral reefs. Proceedings of the National Academy of Sciences, 116(10), 4372-4381.

Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia

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By Victor Munoz, SRC MPS student

When hearing about the effects of climate change on coral reefs, most will likely think of damage from coral bleaching events (Goldberg & Wilkinson, 2004). Because bleaching has been associated with higher sea temperatures, coral reefs exposed to colder waters can sometimes be viewed as more resilient to rises in temperature (West & Salm, 2003). However, those reefs might be just as vulnerable to climate change, although in a different way to what we may think.

Figure 1. A coral colony (Photo by Daniel Hjalmarsson on Unsplash)

A recent study by researchers from the University of Queensland (Kim et al., 2019) has evaluated the performance of 8,000 coral colonies across 22 sites on the southeastern coast of Australia during the hot summer of 2016 (Figure 2). After taking several snapshots of the corals at each site, the scientists gave them a score depending on how bleached they were. They then compared the status of different coral species to environmental factors including the hottest months’ temperatures, the annual temperature fluctuation and the solar irradiance the corals were exposed to.

They found that overall, these environmental factors poorly explained the health of corals. Some species were very sensitive to changes in temperature, while others showed greater resistance to heat stress. Instead, it seems like those increased temperatures may significantly affect the diversity of corals in colder waters, with some hardy species becoming dominant over more “fragile” ones. This could have serious implications for the less resistant cold-water corals, as locations closer to the poles (where they could potentially grow) lack the environments to sustain them. The disappearance of those “fragile” corals could then lead to a reduction of the overall coral diversity, with potential repercussions on the complex functionality of the reef’s ecosystem as a hole.

Figure 2. The 22 sites included in the study, across Australia’s southeastern coast. (Source: Kim et al., 2019)

Popular discussions around climate-change tend to focus on the species that we may lose (Willis et al., 2008), but new appearances or dominance of other species in affected habitats has been just as much of a reality (Rahel & Olden, 2008). The different ways every ecosystems may be impacted by the effects of climate change still need to be studied in greater depth, but what should be understood is that no location is truly “safe” from its consequences and that changes in the environment will be witnessed from the equator all the way to the poles.

Work cited:

Goldberg, J., & Wilkinson, C. (2004). Global threats to coral reefs: coral bleaching, global climate change, disease, predator plagues and invasive species. Status of coral reefs of the world, 2004, 67-92.

Kim, S. W., Sampayo, E. M., Sommer, B., Sims, C. A., Gómez‐Cabrera, M. D. C., Dalton, S. J., … & Figueira, W. F. (2019). Refugia under threat: Mass bleaching of coral assemblages in high‐latitude eastern Australia. Global change biology. doi: 10.1111/gcb.14772

Rahel, F. J., & Olden, J. D. (2008). Assessing the effects of climate change on aquatic invasive species. Conservation biology, 22(3), 521-533.

West, J. M., & Salm, R. V. (2003). Resistance and resilience to coral bleaching: implications for coral reef conservation and management. Conservation Biology, 17(4), 956-967.

Willis, C. G., Ruhfel, B., Primack, R. B., Miller-Rushing, A. J., & Davis, C. C. (2008). Phylogenetic patterns of species loss in Thoreau’s woods are driven by climate change. Proceedings of the National Academy of Sciences, 105(44), 17029-17033.

Small Gastropods Have A Larger Impact on Corals Than Expected

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By Delaney Reynolds, SRC intern

Logically, one might think that as a population of predators increases, the population of its prey decreases. This has been found to hold true for all species, including corals and their predators (corallivores). Larger, more recognizable corallivores, such as the crown-of-thorn sea star and horn drupe snail, can very negatively impact the composition and tenacity of corals. However, little is known about the impact that smaller corallivores, such as the Coralliophila violacea (violet coral shell snail), can have on coral species and habitats.

Figure 1. The Fiji Islands & C. violacea Density: Three fished areas and MPAs on the south coast, Coral Coast, of Viti Levu, Fiji were surveyed for this analysis. The violin plots depict the density of the C. violacea snails in each MPA and fished area. (Image Source: Clements, Cody S., and Mark Hay. “Overlooked Coral Predators Suppress Foundation Species as Reefs Degrade.” Ecological Applications, 2018, doi:10.31230/osf.io/hcmzg.)

In a study done by the Georgia Institute of Technology, a combination of observational and manipulative experiments were performed to look at how C. violacea densities and size frequencies, measured as shell height, impacted their common host coral Porites cylindrica’s ability to grow and survive in three different fished areas and Marine Protected Areas (MPAs) of Fiji.

In each of the three MPAs and fished areas, C. violacea densities were found to be 35-fold higher in the fished areas, but snails in the MPAs were significantly larger in size. As densities increased, and thus feeding on P. cylindrica increased, P. cylindrica growth was found to be extremely inhibited, supporting the hypothesis that smaller species can have a large, negative impact on their environments.

The decrease in the effects of C. violacea in MPAs make a concrete argument that MPAs are successful ways of protecting marine wildlife and that more should be created all over the world. Current MPAs are, for the most part, small in scale and while they are effective, larger scale protected areas would increase the protection of all sorts of vulnerable organisms, including vital coral species.

Figure 2. Coralliophila violacea. (Image Source: https://fr.wikipedia.org/wiki/Coralliophila_violacea)

 

 

 

 

 

 

 

 

 

 

The way that C. violacea impacts corals so significantly is by its intrusive method of feeding. When preying upon corals, C. violacea will insert its proboscis, a tube-like structure that aids in feeding, into the coral’s polyps and feed on the nutrients that the coral is transporting. This method is detrimental to the coral as it decreases the amount of nutrients that the coral itself intakes and suppresses its growth.

Keeping an eye on how smaller corallivores are impacting coral ecosystems is crucial because as our planet continues to warm and oceans get more acidic, coral populations become increasingly susceptible to bleaching and extinction, facing threats not only from predators but human induced climate change as well. The combination of these factors could lead to an underwater ecosystem devoid of corals and, in turn, of marine life in general.

Works Cited

Clements, Cody S., and Mark Hay. “Overlooked Coral Predators Suppress Foundation Species as Reefs Degrade.” Ecological Applications, 2018, doi:10.31230/osf.io/hcmzg.

Gravity of human impacts mediates coral reef conservation gains

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By Brenna Bales, SRC intern

Communities around the world depend on coral reefs for their livelihood, for tourism, and for protection against coastal degradation. With an increasing human population comes increasing human impact on these coral reefs and a decrease in the ability of a reef to provide the benefits listed above. Direct human impacts include overfishing, polluting the reef with trash or chemicals, and dredging; however, there are indirect human impacts such as anthropogenic climate change. Greenhouse warming affects ocean temperature which can stress corals (Jokiel 2004), and ocean acidification from carbon uptake can decrease the ability of corals to build limestone foundations (Langdon et al, 2000).

In Cinner et al’s analysis, the magnitude of human impact on of 1,798 tropical reefs in 41 nations/states/territories was described and quantified. In order to quantify this impact, the authors used a social science metric termed “gravity”, which has been used from economics to geography. For the adaptation to an ecological analysis, the gravity of human impact was measured as a function of how large and how far away a population of humans was to a certain coral reef (Figure 1). In each location, the status of reef management ranged from openly fished (little to no management), to highly protected marine reserves where fishing is completely prohibited.

Figure 1. The authors’ interpretation of “gravity” as a function of the population of an area
divided by the time it takes to travel to the reefs squared. (Cinner et al, 2018)

Two expected “conservation gains” (differences in the progress of a coral reef ecosystem when protected versus unprotected) in all regions were analyzed as to how they are influenced by human activity. The first was targeted reef fish biomass (species usually caught in fisheries) and the second was the presence of top predators within the ecosystem. Conservation gains can be beneficial to both people and ecosystems; When the health of a protected coral reef improves, it might drive new recruits and help re-establish other nearby reefs that are fished more. The authors hypothesized that the target conservation gains would decline with increasing gravity in areas where fishing was allowed, but that marine reserves would be less susceptible to these gravity influences.

Analysis of visual fish count data collected from 2004-2013 showed that gravity strongly predicted the outcomes for fish biomass in a reef ecosystem. Biomass in marine reserves showed a less steep decline with increasing impact as compared to openly fished and restricted areas (Figure 2). This was due to an unforeseen relationship between gravity and the age of a marine reserve. In high-gravity areas, older reserves contributed more to fish biomass when compared to low-gravity areas. These older reserves have had more time to recover after periods of high fishing stress. Even in the highest-gravity reserves, fish biomass was about 5 times higher than in openly fished areas. Top predators were only encountered in 28% of the reef sites, and as gravity increased, the chance of encountering a top predator dropped to almost zero. Overall, highly regulated marine reserves in low-gravity situations showed the highest biomass levels, and the greatest chance of encountering a top predator.

Figure 2. Modeled relationships showing reef fish biomass declines with gravity increases by
regulation type. Openly fished (red), restricted (green), and high-compliance marine reserves
(blue). (Cinner et al, 2018)

Four explanations for the decrease of fish biomass and top predator encounters were (i) human impact in the surrounding area of a marine reserve affecting the interior, (ii) poaching effects, (iii) life history traits of top predators making them susceptible to even minimal fishing stress, and (iv) high-gravity reserves being too young or too small for drastic improvement. The fourth explanation was further analyzed, where large versus small reserves were compared. Not surprisingly, larger reserves had higher biomass levels and top predator encounter probabilities. Lastly, the ages of the reserves were examined. The average reserve age was 15.5 years compared to older reserves (29 +/- years), and older reserves had a 66% predicted increase in biomass levels. Analysis of the likelihood of encountering a top predator was less definitive, suggesting high-density areas, no matter the age, reduce this probability greatly.

Ecological trade-offs such as high-gravity reserves being beneficial for conservation gains like reef fish biomass, but not so much for top predators, are important to consider. Top predators can face more fishing stress even in remote areas due to their high price in international markets, such as sharks for their fins, explaining the observed difference in low-gravity fished areas versus low-gravity marine reserves. Overall, when aiming to create an effective marine reserve or even regulations that aid in conservation gains, it is imperative to consider the gravity of human impact in the surrounding areas. How the impacts of gravity can be reduced is critical as populations grow along coastlines and climate change stressors increase as well. Multiple forms of management will most likely provide the most benefit to stakeholders (Figure 3) and the ecosystem.

Figure 3. A fisherman in the town of Paje, Tanzania takes his boat out behind the reef barrier to
catch a meal. Stakeholders are an important part in considering reef management decisions, as
millions of people rely on the reefs for their meals just as this fisherman.
(https://commons.wikimedia.org/wiki/File:Fisherman_in_Paje.jpg)

Works Cited

Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., Goddard, J., Marubini, F., Aceves, H., Barnett, H. and Atkinson, M.J., 2000. Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef. Global Biogeochemical Cycles, 14(2), pp.639-654.

Jokiel, P.L., 2004. Temperature stress and coral bleaching. In Coral health and disease (pp. 401-425). Springer, Berlin, Heidelberg.

Coral Bleaching of the Great Barrier Reef

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By Delaney Reynolds, SRC intern

Coral reefs are some of planet earth’s most spectacular, diverse and important ecosystems. Our planet’s coral reefs provide important shelter, habitats, and a source of food for many different species of marine organisms. They also act as a critical food source to humans, as well a natural barrier to help protect our coastlines from hurricanes and associated storm surges. Sadly, coral reefs face growing risks including the possibility of extinction from a variety of stresses that leads to coral bleaching.

Figure 1: Coral from which the zooxanthellae has been expelled, causing it to turn white (Image Source: https://en.wikipedia.org/wiki/File:Keppelbleaching.jpg)

Coral bleaching is the process in which zooxanthellae, algae living symbiotically within the coral, are expelled from coral colonies due to a number of factors including an increase in temperature, decrease in pH, exposure to UV radiation, reduced salinity, and bacterial infections. Zooxanthellae provide the coral 30% of its nitrogen and 91% of its carbon needs to the coral host in exchange for a shelter, as well as waste produced by the coral from nitrogen, phosphorus, and carbon dioxide that is required for the algae’s growth (Baird, 2002).

When corals bleach, it effects entire marine communities due to their immense diversity. Fish populations that reside around coral reefs “are the most species dense vertebrate communities on earth, contributing critical ecosystem functions and providing crucial ecosystem services to human societies in tropical countries” (Graham, 2008). Researchers have found that when an ecosystem endures physical coral loss, fish species richness is extremely likely to decline due to their heavy reliance on the coral colony itself (Graham, 2008).

Perhaps the most famous current example of coral bleaching is Australia’s Great Barrier Reef. Scientists have determined that the main cause of Great Barrier Reef coral bleaching is induced thermal stress and that about 90% of the reef has been bleached since 1998 (Baird, 2002). As the corals bleach and temperatures increase, researchers have determined that shark and ray species that live in the area may be vulnerable to these climactic changes.

Figure 2: Exposure of Ecological Groups of GBR Sharks and Rays to Climate Change Factors. This figure displays the vulnerability different elasmobranch species face due to climate change, as well as the specific effects of climate change that they are vulnerable to, in the specific zones of the Great Barrier Reef. (Image Source: Chin et al. 2010)

Most of the Great Barrier Reef is located on the mid-shelf of the ocean floor, the approximate mid-point between the shallower coast of Australia and the continental shelf where the ocean bottom significantly drops in depth. Researchers found that the mid-shelf is the area where most of the shark species studied reside, while most rays dwell in coastal waters or closer to the continental shelf. It was also found that both areas are the susceptible to rising temperature, increased storm frequency and intensity, increasing acidity, current alterations, and freshwater runoff, all being caused by climate change (Chin, 2010). Based on these findings, researchers have concluded that the areas these elasmobranchs live in should be protected and preserved. Species in these highly vulnerable areas should also be monitored and considered for future conservation actions, as many of the shark species are already experiencing the effects of climate change from some of the aforementioned factors.

Typically, sharks are considered some of the strongest animals on earth, and while they have lived on earth for at least 420 million years, they are slow to adapt. This slowness has impeded their ability to survive in our rapidly changing climate. In the near future it will be common to see some species of marine organisms demonstrate plasticity, the ability to adapt to their changing environment, but other species, such as elasmobranchs, are expected to simply distribute to other habitats in search of cooler waters. Even though sharks are a highly vulnerable species to climate change, they sit at the top of the trophic level in many different niches and, thus, wherever they migrate to, it will be easier for them to find food than it would be for other species such as fish or rays. However, this is most likely only the case for adult sharks as embryos and juvenile sharks may be more vulnerable to increased temperatures. For instance, researchers found that the survival of bamboo shark embryos decreased from 100% at current temperatures to 80% under future ocean temperature scenarios and that the embryonic period was also shortened, not allowing the embryo enough time to develop fully (Rosa, 2014).

To decrease the effects of climate change on coral bleaching, corrective and mitigation measures can be taken. By utilizing green energy sources such as implementing solar power or wind power, walking or biking, and driving electric cars, we can reduce our use of fossil fuels and carbon footprint, thus decreasing the amount of carbon dioxide polluting and warming our atmosphere and oceans. While underwater and not always visible, coral reefs are truly a vital part of our ecosystem and need to be cherished and protected for generations to come.

References

Baird, A. H., & Marshall, P. A. (2002, July 18). Mortality, growth and reproduction in scleractinian corals following bleaching on the Great Barrier Reef. Retrieved from https://researchonline.jcu.edu.au/1521/1/Baird_and_Marshall_2002.pdf

Chin, A., Kyne, P. M., Walker, T. I. and McAuley, R. B. (2010), An integrated risk assessment for climate change: analyzing the vulnerability of sharks and rays on Australia’s Great Barrier Reef. Global Change Biology, 16: 1936–1953. doi:10.1111/j.1365-2486.2009.02128.x

Graham, N. A., McClanahan, T. R., MacNeil, M. A., Wilson, S. K., Polunin, N. V., Jennings, S., . . . Sheppard, C. R. (2008, August 27). Climate Warming, Marine Protected Areas and the Ocean-Scale Integrity of Coral Reef Ecosystems. Retrieved from http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0003039

Rosa, R., Baptista, M., Lopes, V. M., Pegado, M. R., Paula, J. R., Trubenbach, K., . . . Repolho, T. (2014, August 13). Early-life exposure to climate change impairs tropical shark survival. Retrieved November 2, 2017, from http://rspb.royalsocietypublishing.org/content/royprsb/281/1793/20141738.full.pdf

Threats facing South Florida’s coral reefs and possible solutions

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By Molly Rickles, SRC intern

Coral reefs are dynamic ecosystems that harbor a quarter of all marine species while only occupying 0.2% of the world’s oceans (Chen, 2015). Coral Reefs are critical to the ocean’s health because of their biodiversity and complex ecosystems. However, climate change and anthropogenic disturbances has had a profound effect on coral reefs worldwide, with many reefs losing over 50% of their coral cover in the last 40 years (Baker, 2014). This is due largely to coral bleaching, a stress response induced by higher temperatures and excess nutrients. Bleaching is episodic, and the most severe events are coupled ocean-atmosphere events (CITE). Increased sea surface temperature causes coral cover to decrease when the temperature is higher than 26.85 degrees Celsius (Chen, 2015). Coral bleaching causes an increase in coral diseases as well as loss of habitat for many marine species. This eventually leads to a decrease in coral cover, which can disrupt the marine ecosystem and negatively impact the environment.

This map shows the location of South Florida’s reef system, which travels all the way down into the Florida Keys. The second image shows Dry Tortugas National Park, TNER is Tortugas North Ecological Reserve, TSER is Tortugas South Ecological Reserve, TBO is Tortugas Bank Open and DRTO is Dry Tortugas National Park. (Ault, 2013)

This map shows the location of South Florida’s reef system, which travels all the way down into the Florida Keys. The second image shows Dry Tortugas National Park, TNER is Tortugas North Ecological Reserve, TSER is Tortugas South Ecological Reserve, TBO is Tortugas Bank Open and DRTO is Dry Tortugas National Park. (Ault, 2013)

In addition to coral reefs being ecologically important, they are also economically important. Reefs generate $29.8 billion in global net benefit per year (Chen, 2015). Climate change has caused a decrease in ecotourism, resulting in a decrease in profits from coral reefs. It is estimated that the lost value in terms of global coral reef value could range from $3.95-23.78 billion annually (Chen, 2015). In order for many coastal areas to retain this profit from the reefs, corals must be protected from the harmful effects of climate change.

Florida’s coral reefs are particularly vulnerable to the effects of climate change, due to the high population concentration around the coast and the large amount of pollution in coastal waters. Since 1960, Florida’s population has increased by 379% (Ault, 2013). In addition, Southeast Florida is the 8th most densely populated area in the US (Futch, 2011). Increased population leads to increased pollution and runoff, which can be harmful to reef systems. In addition, large infrastructure projects, pipe systems, and beach nourishment can contribute to stresses on corals, all which occur in Florida. The Florida reef system supports the tourism and fishing industries, making it commercially valuable. Without the reef system, Florida would lose two of its largest income generating industries. It is necessary to implant policies that will protect Florida’s reefs from future destruction in order to support the tourism industry as well as to protect the ecosystem.

Another threat facing South Florida’s reefs is from sewage and waste runoff. Due to an increased population, the increased amount of sewage produced is something that the septic systems are not always prepared for. This leads to excess runoff. Water, sponge and coral samples were collected off of the Southeast Florida reef tract and noroviruses were detected in 31% of samples (Futch, 2011). Runoff is particularly dangerous because of wildlife contamination, which has already been observed, but also because excess nutrients in the water cause lead to algal blooms, which can then cause coral bleaching events (Futch, 2011).

This image show various types of corals as they were placed on reefs in South Florida to test the ability of the reef to recruit new corals to add to its growth. (Woesik, 2014)

This image show various types of corals as they were placed on reefs in South Florida to test the ability of the reef to recruit new corals to add to its growth. (Woesik, 2014)

Through the use of monitoring systems all throughout South Florida and the Florida Keys, it has been determined that there has been a 44% decline in coral cover since 1996. This shows that there is a dire need to protect Florida’s reef systems. There are various strategies that have been tested to see what works to preserve coral reefs. Often times, management policies are most successful in dealing with marine ecosystems, since they are generally difficult to directly monitor. One such strategy is the use of a marine protected area (MPA). Marine protected areas are generally very successful, and reefs in MPA’s normally show an increase in size, adult abundance and occupancy rates among reef fish (Ault, 2013). This strategy is especially important in Florida because of the large fishing industry. Intensive fishing has diminished top trophic levels, which affects the entire ecosystem’s balance (Ault, 2013). With the main goal of protecting coral reefs, MPA’s also make the entire ecosystem healthier and prevent unsustainable fishing. Environmental policies that limit the number of fish taken from a reef or limit the boating activity in a certain area are very effective at limiting the human disturbances on coral reefs, and can help marine ecosystems recover from anthropogenic disturbances.

In addition, coral recruitment has been used to regrow portions of bleached reefs. This was done in the Florida Keys and Dry Tortugas National Park. However, the results were not promising. Because of already present stressors such as pollution and warm temperatures, most of the corals did not survive once they were deployed on the reef. These results indicate that coral reefs have slow recovery times after bleaching events or environmental stressors (Woesik, 2014).

Coral reefs are vital to the health of the oceans. Without them, many marine species would be critically threatened. It is necessary to protect the reefs that are alive now to ensure their survival in the future. By implementing management policies, it is possible to protect the reefs from further anthropogenic disturbances, and allow them to recover from already-present stressors. If the health of coral reefs in South Florida increase, then Florida will not only benefit economically, but ecologically with improved marine ecosystems.

Works Cited

Ault, J. S., Smith, S. G., Bohnsack, J. A., Luo, J., Zurcher, N., Mcclellan, D. B., . . . Causey, B. (2013). Assessing coral reef fish population and community changes in response to marine reserves in the Dry Tortugas, Florida, USA. Fisheries Research, 144, 28-37. doi:10.1016/j.fishres.2012.10.007

Futch, J. C., Griffin, D. W., Banks, K., & Lipp, E. K. (2011). Evaluation of sewage source and fate on southeast Florida coastal reefs. Marine Pollution Bulletin, 62(11), 2308-2316. doi:10.1016/j.marpolbul.2011.08.046

Woesik, R. V., Scott, W. J., & Aronson, R. B. (2014). Lost opportunities: Coral recruitment does not translate to reef recovery in the Florida Keys. Marine Pollution Bulletin, 88(1-2), 110-117. doi:10.1016/j.marpolbul.2014.09.017

Chen, P., Chen, C., Chu, L., & Mccarl, B. (2015). Evaluating the economic damage of climate change on global coral reefs. Global Environmental Change, 30, 12-20. doi:10.1016/j.gloenvcha.2014.10.011

Baker, A. C., Glynn, P. W., & Riegl, B. (2008). Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook. Estuarine, Coastal and Shelf Science, 80(4), 435-471. doi:10.1016/j.ecss.2008.09.003

 

Coral Recruitment Shifts due to Sensitivity to Community Succession

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By Patricia Albano, SRC intern

Environmental disturbances such as natural disasters, anthropogenic effects, and weather pattern changes have a significant impact on ecosystems. Following such disturbances, communities must adapt and rebuild through succession where they evolve to respond to changes. In this study, researchers Christopher Doropoulous, George Roff, Mart-Simone Visser, and Peter Mumby of the University of Queensland studied the positive and negative interactions that impact community succession in the wake of a disturbance and how these interactions differ along environmental gradients.

Figure 1. Soft Corals Found on Palau Reef Caption: These are examples of the soft corals (Nephtheidae) that inhabit reefs in Palau. These corals are important for the structure and function of the reefs. Source: Wikimedia Commons

Figure 1. Soft Corals Found on Palau Reef
These are examples of the soft corals (Nephtheidae) that inhabit reefs in Palau. These corals are important for the structure and function of the reefs.
Source: Wikimedia Commons

Succession in ecosystems usually follows 2 models: facilitation and inhibition (Connel and Slayter 1977). Facilitating organisms “set the stage” for environmental modifications, making the habitat more accommodating for the later-successional species. Inhibiting organisms are early arrivers that reserve space in the habitat for themselves and prevent the invasion of later-successional species (Connel and Slayter 1977). All species interaction includes two components: negative (competition, predation, inhibition) and positive (facilitation) (Paine1980). These two interaction types allowed the researchers to classify the changes they saw in the coral reef ecosystem study sites. This series of experiments investigates how early succession affects coral reef recovery after 2 subsequent typhoons in the island of Palau in the Western Pacific (Figure1) These 2 typhoons (occurring in December 2012 and November 2013) occurred after no typhoon disturbances for over 70 years. This study site was used to explore how the changes in species interactions after a disturbance affect succession in benthic communities with different environmental gradients and how these successional changes affect coral recruitment and recovery after a disturbance (Doropoulos et al. 2016).

The researchers analyzed the eastern barrier reef of the island that had significantly reduced abundances of juvenile corals. Six sites were chosen within to different wave environments: 3 at reefs with lower wave exposure and 3 at reefs with higher wave exposure (Figure 2). Variables accounted for include: grazing potential of herbivorous fish on available grazeable substrate and percent cover of algae groups in the ecosystems.

Figure 2: Six Reefs of the Study Site in Palau Caption: This map indicates where the 6 reefs used in the study are located along the Palau coastline. The pictures indicate differences in coral recruitment between caged (shielded from herbivorous fish) and uncaged (open to grazing) portions of the reef. Source: Doropoulous et al. 2016

Figure 2: Six Reefs of the Study Site in Palau
This map indicates where the 6 reefs used in the study are located along the Palau coastline. The pictures indicate differences in coral recruitment between caged (shielded from herbivorous fish) and uncaged (open to grazing) portions of the reef.
Source: Doropoulous et al. 2016

The researchers found that 3 patterns in environmental drivers influenced the ecosystem. First, a 70% reduction in fish grazing potential was found at the sites that had loss of the majority of live coral cover after the typhoons. Second, shifts in dominance from coral to microalgae occurred at 3 sites with medium wave exposure. Last, microalgae was more abundant in microhabitat crevice areas within both the medium and low wave exposure sites. Coral recruitment was also higher in these crevice areas within the reefs. The researchers came to the conclusion that when herbivorous fish are excluded from reef habitats, a gradual shit towards an algae dominated system occurred at both medium and low wave exposure locations. The results collectively showed that differences in interaction strengths along environmental gradients can lead to changes in the early succession of benthic life that can lead to the inhibition of system recovery after a disturbance such as a typhoon. This experiment revealed important information on how ecosystems recover after disturbances. With this knowledge, nations and conservation organizations can effectively manage their reef ecosystems following a disturbance such as a natural disaster or a weather change. This study also reveals how important it is for healthy reefs to exist in order for ecosystems to continue thriving and support a vast array of life.

Works cited:

Paine, R. T. 1980. Food webs: linkage, interaction strength and community infrastructure. The Journal of Animal Ecology 49: 667-685.

Connell, J. H., and R. O. Slatyer. 1977. Mechanisms of succession in natural communities and their role in community stability and organization. American naturalist:1119- 1144.

Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific

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By Shannon Moorhead, SRC Masters Student

In the past several decades, it has become clear to researchers that populations of reef-building corals have suffered significant declines worldwide. In the 1970s, coral covered on average,50% of benthic habitat (the sea floor) in the Caribbean; in the early 2000s, this was reduced to an average of 10%, with an estimated 80% decline in total cover throughout the Caribbean. Similar observations have been made in the Pacific, with an estimated decrease from 43% coral cover on average in the 1980s, to 22% cover on average in 2003. These declines are caused by a large variety of both global and local threats. Globally, increasing temperatures, ocean acidification, sea level rise, and disease outbreaks have caused mass coral mortality events and decreased rates of calcification – the rate at which coral grows its calcium carbonate skeleton. In addition to these worldwide stressors, corals face local threats such as overfishing of important grazers and predators, elevated nutrient levels, and increasing amounts of terrestrial sediment in coastal waters. These human impacts kill corals either directly or indirectly, by creating conditions that allow faster-growing algae species to thrive and overtake corals. In some cases, this algal growth can lead to a phase-shift: a change in ecosystem composition and function when macroalgae replaces corals as the dominant benthic cover. Because of this, the majority of studies done to assess reef health have focused only on percent cover of macroalgae and corals. However, recent research indicates that when coral cover declines it is rarely replaced solely by macroalgae and studies have shown that coral and macroalgae together only comprise 19-55% of the reef benthos, organisms that live on the sea floor.

Figure 1. (a) Theses images show hard coral and macroalgae, the two groups most often used to assess reef health. (b) These images show reef builders and fleshy algae, which can be used to assess reef-health with a more community-based approach.

Figure 1. (a) Theses images show hard coral and macroalgae, the two groups most often used to assess reef health. (b) These images show reef builders and fleshy algae, which can be used to assess reef-health with a more community-based approach.

Methods

In this study, Smith et al. also investigated percent cover of other members of the benthos: crustose coralline algae (CCA) and turf algae. Turf algae have a negative impact on coral cover, by growing over and smothering adult corals and preventing the settlement of larval corals. On the other hand, CCA, which produces calcium carbonate like corals, promotes reef resilience by stabilizing reef structure and creating a place for coral larvae to reside and grow, because there are many coral species whose larvae prefer to settle on some types of CCA. Smith et al. considered the cover of all four groups (coral, CCA, turf algae, and macroalgae) to compare central Pacific reef communities surrounding uninhabited islands with communities that surround populated islands and suffer from significant anthropogenic, or human-caused, stressors. Specifically, they examined whether cover of reef-builders (CCA and coral) and fleshy algae (turf and macroalgae) were inversely related, as well as whether the two groups were more common in the absence or presence of human populations.

Figure 2. (a) A map of the five island chains and 56 islands from which data were collected for this study; (b) 17 Hawaiian Islands, (c) 21 islands from the Line and Phoenix Islands, (d) six islands from American Samoa, and (e) 14 islands in the Mariana Archipelago. Stars represent inhabited islands while circles represent uninhabited islands.

Figure 2. (a) A map of the five island chains and 56 islands from which data were collected for this study; (b) 17 Hawaiian Islands, (c) 21 islands from the Line and Phoenix Islands, (d) six islands from American Samoa, and (e) 14 islands in the Mariana Archipelago. Stars represent inhabited islands while circles represent uninhabited islands.

Results

Smith et al. evaluated reef communities of 56 islands from five central Pacific island chains between 2002 and 2009 and acquired some surprising results. While coral cover was higher on uninhabited islands, there was not a significant difference between the two. Macroalgae cover varied by archipelago: while there was greater macroalgae cover on populated islands in the Line and Mariana Islands, the Hawaiian Islands and American Samoa had higher macroalgae cover on uninhabited islands. In addition, there was no significant relation seen between total coral and macroalgae cover, contradicting previous ideas that macroalgae directly replaced coral on degraded reefs. However, the average cover of reef-builders was significantly higher on uninhabited islands versus inhabited islands, while the average cover of fleshy algae was significantly higher on inhabited islands versus uninhabited. This result suggests that local anthropogenic stressors play a direct role in changes to the benthic community, and potentially reef health.

Outcomes

In this study, the authors suggest that a good indicator of reef health is net accretion, where the reef-building organisms are building calcium carbonate skeletons faster than they are being eroded. Because it appears that inhabited islands have a lower abundance of reef-building organisms, the reefs surrounding these islands are not as healthy as those near uninhabited islands and may have a harder time bouncing back from large-scale disturbances such as bleaching events and typhoons. Local management on inhabited islands should consider this when developing management strategies and work towards improving the resilience of their reef ecosystems. This research also demonstrates that percent coral and macroalgae cover are not always reliable indicators of reef health; instead management should take a more holistic approach and evaluate other members of the benthos when assessing reef health, in addition to measuring indicators of reef resilience such as coral growth and recruitment, which will help managers predict trends and changes in the structure of the benthic community of coral reefs.

References

Smith, J. E., Brainard, R., Carter, A., Grillo, S., Edwards, C., Harris, J., . . . Sandin, S. (2016). Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific. Proceedings of the Royal Society of London B.

Photo of the Week: Queen Angelfish

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A queen angelfish (Holacanthus ciliaris) swims along a coral reef near Miami, Florida.

A queen angelfish (Holacanthus ciliaris) swims along a coral reef near Miami, Florida.

Trawling on seamounts: effects on corals

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By Jennifer Dean,
Marine Conservation student

Have you ever wondered how your seafood is caught?  Many of the species commonly consumed by humans, such as cod, flounder, and shrimp, are caught by a method called bottom trawling (montereybayaquarium.org).  Bottom trawling is a large scale fishing method that has been used for many years, consisting of dragging a large net or nets along the seafloor to scoop up fish that live near the bottom.  Unfortunately, this method is not very ecosystem-friendly.  Most trawl nets include heavy wooden or metal frames to keep the nets open, and these frames drag along the bottom, creating troughs, re-suspending sediment, and damaging organisms.  Recently people have begun to realize just how devastating these impacts can be on seafloor habitats.  In fact, just this past September it was shown that bottom trawling severely alters the ocean floor through smoothing of the local topography (Puig et al. 2012).  One ocean habitat that has been heavily impacted by bottom trawling is that of seamounts.

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