Nudibranch predation boosts sponge silicon cycling

Abstract

Diatoms play a key role in the marine silica cycle, but recent studies have shown that sponges can also have an important effect on this dynamic. They accumulate large stocks of biogenic silica within their bodies over long periods, which are thought to vary little on an intra-annual scale. The observation of an abrupt decline in sponge biomass in parallel with large increases in abundance of a spongivorous nudibranch (Doris verrucosa) led us to conduct a year-long study on the effect of nudibranch predation on the silicon budget of a sponge (Hymeniacidon perlevis) population. After 5 months of predation, the abundance of sponge individuals did not change but their biomass decreased by 95%, of which 48% was explained by nudibranch predation. About 97% of sponge spicules ingested by nudibranchs while feeding was excreted, most of them unbroken, implying a high rate of sponge silica deposition in the surrounding sediments. After predation, sponges partially recovered their biomass stocks within 7 months. This involved a rapid growth rate and large assimilation of dissolved silicon. Surprisingly, the highest rates of silicon absorption occurred when dissolved silicon concentration in seawater was minimal (< 1.5 µM). These findings suggest that the annual sponge predation-recovery cycle triggers unprecedented intra-annual changes in sponge silicon stocks and boosts the cycling of this nutrient. They also highlight the need for intra-annual data collection to understand the dynamics and resilience of sponge ecosystem functioning.

Investigation of the Dietary Preferences of Two Dorid Nudibranchs by Feeding-Choice Experiments and Chemical Analysis

“…Dorid nudibranchs (Order: Nudibranchia, Family: Dorididae) are slow-moving, shell-less, marine gastropod mollusks that feed on sessile prey, among which some species exclusively feed on sponges (Cimino et al 1999 ; López-Acosta et al 2023 ). Some sponge species are chemically defended and represent an important source of biologically active secondary metabolites, containing unique structures and displaying great diversity (Hong et al 2022 ).…”

Relative contribution of top-down and bottom-up controls on the regulation of the sponge Hymeniacidon perlevis (Montagu, 1814) in Patagonia: an experimental and observational approach.

“…Records of sponge consumers in temperate systems are scarcer and more fragmentary than in tropical environments. In temperate environments consumers of sponges are mostly invertebrates like opisthobranchs, sea stars, urchins, chitons, limpets, crabs and endobiont polychaetes (Guida 1976;Wulff 2006;López-Acosta et al 2023). Some authors agree that sponge populations from tropical coral reefs are mainly bottom-up controlled (Lesser 2006;Lesser and Slattery 2013;Trussell et al 2006), whereas others point out that they are only driven by a top-down control (Pawlik et al 2013(Pawlik et al , 2015.…”