MEPS 559:13-20 (2016)  -  DOI: https://doi.org/10.3354/meps11893

ABSTRACT: Predator influence on the structure of prey communities can be mediated by habitat heterogeneity, the effects of which may cascade to the base of the food webs, altering producer biomass and species composition. We carried out a mesocosm experiment manipulating the identity and richness of predators and habitat heterogeneity to test their influence on resource use effectiveness, competition among predators, and trophic cascades in a model estuarine system with 3 trophic levels (microalgae, mysids, and the predators blue crab Callinectes sapidus, sand shrimp Crangon septemspinosa, and grass shrimp Palaemonetes pugio). We hypothesized that increasing predator species richness would increase mysid suppression because of complementarity among predators, that complementarity would be better expressed in more heterogeneous habitats, and that higher mysid suppression would increase algae biomass through cascading effects. Assemblages with multiple predators were more effective at suppressing prey than the average single predator, but not in comparison to the most effective predator (i.e. no transgressive overyielding). Predator diversity effects increased with habitat heterogeneity, possibly because it allowed interspecific complementarity among predators to be expressed. Moreover, habitat heterogeneity dampened intraspecific predation and/or negative behavioral interactions between predators. A trophic cascade was not observed because of the low mysid grazing impact on microalgae, probably related to the omnivorous feeding of mysids. Our findings indicate that the loss of both biodiversity and habitat heterogeneity should alter the energy flux in marine food webs; therefore, both must be considered for the proper management of natural ecosystems.

KEY WORDS: Biodiversity · Ecosystem functioning · Habitat structure · Predator richness · Trophic cascade · Food webs · Complementarity · Omnivory