Biology subjects

Leynaert, A.

Publications and source records attributed to Leynaert, A..

4 recordsLinked to original sources

bioRxiv2026

The peculiar photobiology of a giant motile diatom inhabiting the subtidal sediments of the bay of Brest.

Microphytobenthos (MPB) contributes significantly to the marine primary production in estuarine ecosystems. MPB is mainly composed of benthic motile diatoms inhabiting intertidal and shallow subtidal sediments. Unlike intertidal small-sized diatom models, subtidal ([≥] 10 m depth) MPB and large-sized (>100 {micro}m) species, have comparatively received much less attention, especially as regards to their photosynthetic productivity. Yet, the subtidal light environment shows unusual (very) low intensities and a green-blue light spectrum at high tide. The present study investigates the light-dependent green-blue responses of the subtidal giant diatom Pleurosigma strigosum, combining in situ monitoring with laboratory experiments. In both MPB and P. strigosum, we documented a strong photophysiological plasticity, and a striking alignment with the photophysiology of (very) low light-adapted polar diatoms. Altogether, our results highlight the nature of subtidal photoadaptation: a very low green-blue light sensitive response, which explains the early blooming of P. strigosum at the very beginning of spring and underpins the ecological success of MPB in colonizing coastal subtidal sediments. The general coherence between subtidal P. strigosum and MPB light-responses offers a unique model species and growth form to further decipher the specific light-driven metabolism of subtidal MPB under precisely controlled environmental conditions.

ecology↗

bioRxiv2025

Warming up to a new coat: moulting king penguins exhibit hyperthermia and increased peripheral heat loss

Penguins are among the most specialized thermoregulators on the planet, however, the same adaptations that maximize heat retention underwater likely hinder heat dissipation on land, possibly creating dangerous thermoregulatory challenges when encountering warming terrestrial habitats. Penguins are subject to strictly terrestrial phases, such as moulting, when metabolic heat production, insulation, and energetic constraints are heightened. We assessed thermoregulation in moulting captive king penguins (Aptenodytes patagonicus) using simultaneous measurements of core and surface temperatures to test two hypotheses. Under the thermal challenge hypothesis, an initial rise in heat dissipation effort (i.e., increased peripheral vasomotion) followed by a rise in core temperature would indicate failure to prevent hyperthermia. Under the warm-up hypothesis, an initial rise of core temperature concomitant or followed by an increase of peripheral vasomotion would indicate regulated hyperthermia, possibly to accelerate feather development. Core and surface temperatures increased drastically but concomitantly during moult, providing tentative support for the warm-up hypothesis. Moulting penguins did not pant, suggesting that peripheral heat dissipation was sufficient to regulate moulting-induced hyperthermia. Core and subcutaneous temperatures in wild individuals resembled patterns measured in captivity, despite lower heat load and additional options for behavioural thermoregulation. These results indicate that hyperthermia is prevalent in moulting king penguins, and documenting the timing of temperature changes provides novel insights for the moulting physiology of penguins. Because moulting-induced hyperthermia may contribute to heat load, we caution that moulting may increase the susceptibility of wild penguins to heat stress, especially as regions near the poles warm at a disproportionately rapid rate.

physiology↗

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↗