Influence of palatability on the feeding preferences of the endemic Hawaiian tiger cowrie for indigenous and introduced sponges

Abstract

Kāne‘ohe Bay has been invaded by at least 10 non-indigenous sponge species, some of which have become dominant over native sponges and even competitors against reef-building corals. We discovered the Hawaiian tiger cowrie Cypraea tigris schilderiana to be a voracious sponge predator, particularly on some of these non-indigenous sponges. This study sought to examine whether feeding preference for sponges by cowries was influenced by palatability of sponge chemical extracts. We quantified the consumption rate of 18 species of common native and non-native sponges in comparison to 3 native corals from Kāne‘ohe Bay in flow-through aquaria. When offered a smorgasbord of prey species in 4 replicate week-long trials, cowries exclusively fed on sponges, which included several non-native species, in a selective gradient. Three Dysidea spp. were consumed entirely within 72 h, followed by Mycale parishii, Haliclona caerulea, Halichondria coerulea, and Cladocroce burapha within 96 h, and M. grandis and Gelliodes wilsoni in 144 h. Preferred sponges spanned the full range of sponge mineral composition, from those with densely packed spicules that measured >300 µm to those with a collagen fiber skeleton. Among avoided sponges, only Monanchora clathrata produced compounds that, when extracted, proved to be a deterrent to cowries and the whitespotted toby Canthigaster jactator in feeding trials. Our study highlights the previously unrecognized importance of cowrie predation on introduced sponges in Hawaiian reefs, and suggests that palatability alone does not influence feeding preference. We encourage conservation for this overharvested, native spongivore because of its potential use in biological control for future sponge introductions.