How Sedimentation, Nutrient Enrichment, and Overfishing Impact a Coral Reef Ecosystem Immediately Following a Disturbance

by Natalie Ireland

Coral reefs are regularly disturbed by natural phenomena such as bleaching, storms, and outbreaks of predators, such as the corallivorous sea star Ancanthaster planci. Corrallivores are animals that eat coral polyps. Coral reef ecosystems are resilient, and are often able to recover from large-scale disturbances quickly. However, anthropogenic stressors such as overfishing, nutrient enrichment, and sedimentation can prevent coral reefs from recovering. Nutrient enrichment, caused by terrestrial runoff, creates the perfect environment for benthic algae to grow on disturbed and broken coral reefs. Overfishing, working in tandem with nutrient enrichment, causes an overgrowth of algae if there are not enough fish to graze it, and the successive degradation of the reef. Sedimentation is also another side effect of terrestrial runoff. Sedimentation buries corals, which blocks light from reaching them and potentially stops coral recovery. However, sedimentation, when not paired with any other stressor, can also stop the growth of algae by burying surfaces for algae to grow on. Gil et. al. (2016) set out to test the interactive effects that overfishing, sedimentation, and nutrient enrichment have on coral reefs in French Polynesia. They hypothesized that these anthropogenic disturbances, when working interactively, will negatively impact corals, while promoting algal cover. Continue reading

Do Marine Protected Areas Save Seychelles Sea Cucumbers?

by Neha Vaingankar

Marine protected areas are a major cause of dispute especially in coastal and island regions like Seychelles, off the western coast of Africa. In recent times, tropical regions all over the world have experienced a huge boom in fishing of holothurians (sea cucumbers). Almost all of the holothurian fisheries are considered fully exploited, in decline, or entirely collapsed. The reason for the high demand is for the holothurian’s medicinal purposes as well as its supposed aphrodisiac qualities. In many tropical coral reef regions, locals rely on these invertebrates for their livelihoods. However, due to the density-dependent reproduction patterns and late maturing of these organisms, holothurians are very vulnerable to over-exploitation. Many MPAs were established in Seychelles 20 years ago that pre-date the wave of heavy exploitation in current times. Cariglia et al. (2013) aims to understand the effectiveness of these MPAs and measure the economic value of these holothurians. Continue reading

Calculating Overfishing for Tuna and Billfish

 

by Hannah Tannenbaum

Threatened fish stocks have generally only been identified as being overfished and potentially reaching extinction once they have already been exploited and are in population decline. This makes remediation efforts for overfished stocks much more difficult, because much of the damage has already been done. Burgess et al .(2013) defined the “eventual threat index” (T), taking into consideration primary effects on overfishing potential. The variables they used to understand exploitation potential include: vulnerability, population size, average catch-per-unit effort, maximum per-capita growth rate, as well as profitability. In particular, this study examined multispecies fisheries, referring to fisheries in which there is a target species, but often the fishery affects many other species as well. Therefore they identified the “key” species as the most commercially valued, or most environmentally sensitive, and therefore the most likely to be exploited. The authors then applied the eventual threat index for historical information on four Pacific tuna and billfish populations, and were successfully able to Continue reading