Variability in prey communities as a function of algal habitat: linking algal habitat to fish predation

Background/Question/Methods

Understanding changes in species diversity resulting from natural or anthropogenic environmental alterations are key to management strategies of species and ecosystem functioning. This study tested the hypothesis that spatial and temporal variability in algal habitat is associated with similar patterns of invertebrates prey items and if prey utilization of fish predators is consistent with patterns of variability in algal and prey communities. Benthic surveys of algal habitat were conducted within the Monterey Bay National Marine Sanctuary at 6 kelp forests along the Monterey Peninsula, from July 2011 to September 2012. Sites vary in exposure to wave disturbance creating differences in composition of benthic red algal species. Replicates of benthic red algal species were collected and associated invertebrates were removed and enumerated. Fish diet was estimated with gut-content analysis using the painted greenling (Oxylebius pictus). Movement of painted greenlings is low and diet is known to vary with changes in available algal habitat. Diet analysis was conducted on replicate fish from two distinct reefs.

Results/Conclusions

Patterns of algal and invertebrate prey communities are significantly related (ANOVA, p=0.001) but strength of associations varies as a factor of algal species and wave disturbance to reefs. Of particular interest are gammarid and caprellid amphipods, which were the predominant prey item found in O. pictus stomachs. Gammarid amphipod abundance decreased or stayed the same across sites of increasing wave disturbance. The strength of this association was dependent on algal identity. Caprellid amphipod abundance was strongly correlated with algal identity (ANOVA, p=0.001) across sites but not with increasing wave disturbance. Diet composition of O. pictus was variable by site. Results indicate that identity of algal habitat is a strong driver of invertebrate prey composition and abundance and that effect of wave disturbance is variable by algal species and prey item.