Marine benthic invertebrates use multimodal cues for defense against reef fish

The use of bright coloration to warn predators of toxic prey, termed aposematism, is a defensive strategy well studied in terrestrial ecosystems. Some marine animals have contrasting color patterns and chemical defenses but few studies have tested the behavior of marine predators in response to aposematic coloration. In this study we tested fish feeding behavior in response to different types of cues including contrasting color patterns and sponge and nudibranch chemical extracts in the field at 2 reefs on Guam. Using agar-based food to keep food quality consistent, chemical extracts and 2 out of 5 contrasting color patterns reduced feeding by natural assemblages of reef fish at both reefs. Phyllidia varicosa (from Palau), P. elegans (Guam) and Phyllidiella pustulosa (Palau) crude extracts deterred feeding by fish, but P. pustulosa extracts from Guam did not. To determine if a chemical extract can act as an olfactory defense we videotaped fish behavior as they approached food containing nonpolar extracts of Acanthella cavernosa, the dietary sponge of Phyllidiella granulatus. Fish approached and then tasted the food with the chemical extract significantly less often than the control and the crude extract of another sponge Stylissa massa. In feeding assays with a contrasting color pattern combined with the chemical extract at natural concentrations, fish were deterred by the extract regardless of the color pattern. At half natural concentration only the chemical extract and the contrasting color pattern together significantly decreased fish feeding. Reef fish can use multimodal signals including visual, taste and olfactory cues to avoid marine benthic invertebrates.