A Tale of Two Labs

Today's post is from a super-fantastic undergraduate student who elected to do a directed independent study project with this year's Coastal and Ocean Policy capstone class.  Her undergaduate research experience provided her the opportunity to look at the politics hidden in the weeds of the scientific process.

Lara Noren is an undergraduate student studying marine biology and public administration at the University of North Carolina Wilmington graduating in May of 2018. In the future she hopes to attend graduate school to study ocean policy. 


Source: World Resources Institute

Coral reefs have an extensive legacy in many cultures around the world. Today, coral reefs are regarded as one of the most economically and biologically valuable ecosystems on the planet. They provide habitat for commercially important fish, storm surge protection to island communities, billions of dollars in tourism each year, and are one of the most biodiverse ecosystems globally. 

Economic Benefits of Tropical Reefs
Graph showing the economic value of coral reefs in Belize in billions of dollars per year. The graph depicts tourism, coastal protection, fisheries, and biodiversity.

Although coral reefs are incredibly important, there is a knowledge gap within the scientific community on many ecological processes of reef ecosystems. One of the poorly understood ecological processes is the debate of top-down and bottom-up control of sponge populations. Or in layman’s terms: are sponge populations in Caribbean coral reef controlled by predation from fish and sea turtles or controlled by nutrient availability? I find this topic fascinating because of the large controversy surrounding a seemingly straightforward scientific question.

Currently, this controversy surrounds two major labs in the Caribbean coral reef ecology field. Dr. Jospeh Pawlik's lab, and Dr. Michael Lesser and Dr. Marc Slattery's lab. Dr. Pawlik and colleagues propose that top-down control, limited by predation, are most impactful to Caribbean sponge’s populations. While Dr. Lesser, Dr. Slattery and colleagues believe that sponge populations are bottom-up controlled, limited by nutrient availability. Both lines of thoughts are reputable and scientifically proven, yet there is still a dichotomy in this field. 

Schematic representation of 3 primary factors affecting sponge community structure on most Caribbean reefs as a function of depth. Predation has effects across all depths, competition has effects to 30m, and turbulence (which impacts nutrient availibility) has effects to 15m. This graph represents the top-down controls and bottom-up controls on sponge populations. 

I am sure that to many people sponge proliferation sounds arbitrary, but it illuminates a larger conversation about coral reef conservation. Most importantly, if scientists can discern the population dynamics of sponges, then they can better understand the best ways to restore these ecosystems. Coral reefs are degrading globally. With large-scale bleaching events of coral and biodiversity loss on reefs, it is difficult to maintain optimism for the longevity of these precious habitats. 

Sponges play a significant role on these reefs because they are key competitors to hard coral, and often choke out these corals when overabundant. Further, population dynamics of sponges impact a coral reef’s response to anthropogenic and natural stresses. If top-down control is most impactful to sponge populations, then fisheries management should hold a larger precedent in coral reef conservation, because increased fishing pressures causes an over-abundance of sponges. If bottom-up control is most impactful then pollution management should hold more significance in coral reef conservation because nutrient loading causes overabundance of sponges in reef environments. 

Giant barrel sponge (Xestospongia Muta) with
member of Dr. Pawlik’s lab in the Caribbean.
Dr. Pawlik, Dr, Lesser and Dr. Slattery all have a similar end goal, to conserve coral reefs and contribute to the overall knowledge-base in sponge ecology. Their contributions to the scientific conversation help to explain why sponge science is important in the first place, even if it is conflicting. These sponge scientists do make management decisions about Caribbean coral reefs, but because of their subject area, they contribute to the policy discussions. Science can help guide the policy makers to the most effective conservation tool for these valuable ecosystems. 

Ideally, ecological processes would be most influential in the management techniques of these areas, but in reality, multiple other factors must be considered. Economic feasibility and cultural feasibility also play a large role in managing coral reef ecosystems, and these often take precedent when determining best management practices. Although sponge population dynamics will help determine some of the driving factors in coral reef decline, this study area cannot be solely relied on to solve all management issues. If anything, this controversy in sponge science shows that more research in the coral reef ecology field is needed to determine the most impactful anthropogenic effects, and the best ways to mitigate these effects. 

Both anthropogenic effects, nutrient overexposure and overfishing, cause negative impacts on Caribbean coral reefs for a variety of reasons. All anthropogenic effects deserve more consideration in management techniques in the Caribbean than they are currently given. Although sponge population dynamics will aid in determining which anthropogenic effect is most detrimental, it does not change the fact that action needs to be taken against all effects quickly. 

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