Data from: Protection of large predators in a marine reserve alters size-dependent prey mortality
Selden, Rebecca L., Rutgers University
Gaines, Steven D., University of California, Santa Barbara
Hamilton, Scott L., Moss Landing Marine Laboratories
Warner, Robert R., University of California, Santa Barbara
Published Jan 04, 2017 on Dryad.
Cite this dataset
Selden, Rebecca L.; Gaines, Steven D.; Hamilton, Scott L.; Warner, Robert R. (2017). Data from: Protection of large predators in a marine reserve alters size-dependent prey mortality [Dataset]. Dryad. https://doi.org/10.5061/dryad.1t6d0
Where predator–prey interactions are size-dependent, reductions in predator size owing to fishing has the potential to disrupt the ecological role of top predators in marine ecosystems. In southern California kelp forests, we investigated the size-dependence of the interaction between herbivorous sea urchins and one of their predators, California sheephead (Semicossyphus pulcher). Empirical tests examined how differences in predator size structure between reserve and fished areas affected size-specific urchin mortality. Sites inside marine reserves had greater sheephead size and biomass, while empirical feeding trials indicated that larger sheephead were required to successfully consume urchins of increasing test diameter. Evaluations of the selectivity of sheephead for two urchin species indicated that shorter-spined purple urchins were attacked more frequently and successfully than longer-spined red urchins of the same size class, particularly at the largest test diameters. As a result of these size-specific interactions and the higher biomass of large sheephead inside reserves, urchin mortality rates were three times higher inside the reserve for both species. In addition, urchin mortality rates decreased with urchin size, and very few large urchins were successfully consumed in fished areas. The truncation of sheephead size structure that commonly occurs owing to fishing will probably result in reductions in urchin mortality, which may reduce the resilience of kelp beds to urchin barren formation. By contrast, the recovery of predator size structure in marine reserves may restore this resilience, but may be delayed until fish grow to sizes capable of consuming larger urchins.
Sheephead Predation Trial Results
Results of field predation trials in which 15 urchins of three size classes (S,M,L) and two species (R, P) were presented in prey choice arenas. The size of sheephead attacking and consuming urchins in the arenas were recorded inside and outside of reserves at Catalina Island in August 2010.
Sheephead Surveys at Catalina
Sheephead abundance and size distribution were quantified using SCUBA surveys in August 2010 and August 2011. Fish were surveyed on five 30 m × 2 m transects conducted in two reef zones (the inner [~10 m depth] and outer [~15 m depth] edges of the kelp bed at each site) in each year. Sizes were estimated visually to the nearest cm (total length [TL]) by divers experienced in estimating fish lengths.