Biology subjects

Leynaert, A.

Publications and source records attributed to Leynaert, A..

2 recordsLinked to original sources

bioRxiv2022

Nudibranch predation boosts sponge silicon cycling

Sponges are singular players in the marine silicon cycle. They accumulate vast stocks of biogenic silica within their bodies and in the sediments beneath them over long periods. These silica stocks are recycled at slow rates, much slower than that of other silicon users such as diatoms. The observation of an abrupt change in sponge biomass in a temperate coastal ecosystem led us to study the effect of nudibranch (Doris verrucosa) predation on the silicon budget of a sponge (Hymeniacidon perlevis) population on an annual scale. Predation rates and the associated sponge silicon fluxes were determined. After 5 months of predation, the abundance of sponge individuals did not change but their biomass decreased by 95%, of which 48% can be 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 consumption of dissolved silicon, with the highest rates ever recorded unexpectedly occurring when the dissolved silicon concentration was minimal in seawater (< 1.5 M). These findings reveal that the annual sponge predation-recovery cycle triggers unprecedented intra-annual changes in sponge silicon stocks and boosts nutrient cycling. They also highlight the need for intra-annual data collection to understand the dynamics and resilience of sponge ecosystem functioning.

ecology↗

bioRxiv2021

Sponge contribution to the silicon cycle of a diatom-rich shallow bay

In coastal systems, planktonic and benthic silicifiers compete for the pool of dissolved silicon, a nutrient required to make their skeletons. The contribution of planktonic diatoms to the cycling of silicon in coastal systems is often well characterized, while that of benthic silicifiers such as sponges has rarely been quantified. Herein, silicon fluxes and stocks are quantified for the sponge fauna in the benthic communities of the Bay of Brest (France). A total of 45 siliceous sponge species living in the Bay account for a silicon standing stock of 1215 tons, while that of diatoms is only 27 tons. The silicon reservoir accumulated as sponge skeletons in the superficial sediments of the Bay rises to 1775 tons, while that of diatom skeletons is only 248 tons. These comparatively large stocks of sponge silicon were estimated to cycle two orders of magnitude slower than the diatom stocks. Sponge silicon stocks need years to decades to be renewed, while diatom turnover lasts only days. Although the sponge monitoring over the last 6 years indicates no major changes of the sponge stocks, our results do not allow to conclude if the silicon sponge budget of the Bay is at steady state, and potential scenarios are discussed. The findings buttress the idea that sponges and diatoms play contrasting roles in the marine silicon cycle. The budgets of these silicon major users need to be integrated and their connections revealed, if we aim to reach a full understanding of the silicon cycling in coastal ecosystems.

ecology↗