Meeting Abstract
Biodiversity is often maintained by apex predators that alleviate consumption on lower trophic levels by controlling the abundance of intermediate or mesopredators. When top predators are removed, intermediate trophic levels proliferate. Known as mesopredator release, this phenomenon can decimate lower trophic levels and reduce biodiversity. In estuaries, fishes promote biodiversity by direct predation on crabs (i.e. mesopredators) and by releasing exudates that suppress crab foraging. Recently, we found that mesopredator release occurred by a previously unrecognized scenario. In estuaries, elevated turbidity attenuated predation by fishes that hunt using visual cues, causing fish abundance to decline while increasing the abundance of crabs that fish prey upon. Crabs locate prey by chemoreception and were unaffected by changes in turbidity. Increased crab abundance increased overall predation levels and significantly lowered biodiversity. Crab exudates are known to affect growth of bivalves and other organisms, and they were copious in higher turbidity. We found that eastern oysters ( Crassostrea virginica) reacted to crab exudates by growing thicker shells at a cost of reduced growth and fecundity in turbid waters. Continued investigations regarding oyster responses to crab exudates has revealed that (a) oysters responded to cues emanating from crab predators and from injured conspecifics and heterospecifics, (b) while costly, oysters increased their survival by altering their shell morphology, (c) oyster responses were strongest to predator exudates, and (d) the duration of exposure to predator exudates had significant effects on oyster morphology. Thus, turbidity affected chemical signaling between trophic levels, altered the growth of an important ecosystem engineer, and significantly altered estuarine trophic interactions and biodiversity.
