Summary by: Jessica Wenclawiak
While many parasites directly impact their host’s mortality, others cause indirect effects, including behavioral and physiological changes that make the host more susceptible to predation. Along the South Carolina and Georgia coasts, many white shrimp are currently affected by a parasitic ciliate that causes a condition known as black gill. When infected with this parasite, the shrimp’s immune system responds by producing black nodules on its gills. The nodules interfere with the shrimp’s respiratory and cardiovascular systems, which can make them more vulnerable to predation. As shrimp catches decline in Georgia, scientists have begun researching the role of black gill in white shrimp mortality.
To determine whether black gill indirectly increases predation rates, a team of scientists, including CEID member Jeb Byers, created a study that compared the consumption of healthy shrimp and shrimp with black gill. Three common predators of white shrimp were used in the experiment: red drum, spotted seatrout, and blue crab. Each species was placed in small groups in tanks that contained an equal mix of symptomatic and asymptomatic shrimp. Researchers counted the number of shrimp eaten in each tank and used statistical tests to create a general predation rate for each species. Due to changes in physiology, shrimp with black gill were predicted to be consumed more frequently than healthy shrimp.
All three species differed in their predation rates of symptomatic and asymptomatic shrimp. However, each predator consumed black gill shrimp more frequently than healthy shrimp. On average, shrimp with black gill were two times more likely to be consumed, supporting the idea that black gill can indirectly increase the predation of white shrimp. Therefore, the presence of black gill is a probable factor in the loss of shrimp catches off the coasts of South Carolina and Georgia. This loss drives predators to consume other prey in the community, causing black gill to indirectly affect not only its host, but other vulnerable species.
Gooding, E.L., et al. (2020). Black gill increases the susceptibility of white shrimp, Penaeus setiferus(Linnaeus, 1767), to common estuarine predators. Journal of Experimental Marine Biology and Ecology, 524. https://doi.org/10.1016/j.jembe.2019.151284.