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The genus Tethya, one of the most iconic groups in the phylum Porifera. includes nearly 100 valid species. Tethya shows a nearly cosmopolitan distribution, and thus this clade could help elucidate global mechanisms of speciation in sponges. Contrasting with many other marine organisms, Tethya peaks in diversity in the temperate region, with only ∼30% of diversity occurring in the tropics. This pattern may however be related to a lack of studies in the tropics, masked by dubious taxonomic identifications. To address this question, we studied new collections from the Western Atlantic (Caribbean and Brazil) and the Northeastern Atlantic, as well as museum material from the Indian Ocean. Combining morphological investigation with molecular phylogenetics and the study of the sponge's microbial communities, we conclude that four constitute new species that we describe here: Tethya martini Riesgo, Giribet, & Santodomingo, sp. nov.; Tethya simoni Santodomingo, Zea, & Riesgo, sp. nov.; Tethya erici Díez-Vives, Santodomingo, Moles, & Riesgo, sp. nov.; Tethya orioni Kenny, Santodomingo & Riesgo, sp. nov. Some species thought to be widespread (e.g., T. aurantium and T. seychellensis), each represent multiple species with unique geographic distributions. A phylogenetic analysis of Tethya (based on COI and 28S rRNA sequence data) recovered five main clades, which were also characterized by distinct prokaryotic communities. This suggests that microbiomes could be used as a guide for taxonomic identification in Tethya. We finally explored the existence of a phylosymbiotic pattern in sponges at different levels of prokaryotic taxonomic resolution (i.e., at phylum, class, and genus-level analysis of prokaryotes). Remarkably, our analysis revealed high levels of coevolution of Tethya and their associated microbial communities, even when microbiomes were analysed at the genus level. Our findings support the use of an integrative approach to better understand the evolutionary history of sponges. [ABSTRACT FROM AUTHOR]

Carbonate skeletal remains are altered and disintegrate at yearly to decadal scales in present‐day shallow‐marine environments with intense bioerosion and dissolution. Present‐day brachiopod death assemblages are invariably characterized by poor preservation on continental shelves, and abundant articulated shells of brachiopods with complete brachidia are thus not expected to be preserved if not rapidly buried. However, such preservation is paradoxically observed in shallow‐water Palaeozoic and Mesozoic brachiopod assemblages. Here, we show that a bathyal death assemblage time‐averaged to several millennia (Adriatic Sea) consists of sediment‐filled articulated shells of Gryphus vitreus with complete brachidia. Post‐mortem age distributions indicate that disintegration half‐lives exceed several centuries (c. 500–1700 years). The high frequency of articulated but centuries‐old shells (>50%) and the fitting of taphonomic models to post‐mortem ages indicate that disarticulation half‐life is unusually long (c. 200 years). Rapid sediment filling of shells: (1) inhibited disarticulation, loop fragmentation and colonization by coelobites; and (2) induced precipitation of ferromanganese oxides at redox fronts within shells. Sediment‐filled articulated shells, however, still resided at the sediment–water interface as indicated by encrusters and sponges that infested them after death. Sediment‐filled shells disintegrated through bioerosion and physical wear when residence in the taphonomically active zone exceeded c. 2000 years. We suggest that the articulation paradox is driven by the Mesozoic Marine Revolution (MMR) that escalated predation, bioturbation and organic matter recycling, all intensifying shell disintegration. A scenario with slow disarticulation in bathyal environments may have lead to preservation of articulated shells in shallow‐water assemblages prior to the MMR. [ABSTRACT FROM AUTHOR]

Dissolved silicon (DSi) is biologically processed to produce siliceous skeletons by a variety of organisms including radiolarians, silicoflagellates, choanoflagellates, plants, diatoms and some animals. In the photic ocean, diatoms are dominant consumers over competing other silicifiers. In Antarctica, where DSi is not particularly limiting, diatoms and sponges coexist in high abundances. Interestingly, diatom ingestion by sponges is a regular feeding strategy there. Although it was known that the diatom organic nutrients are readily metabolized by the sponges, what happened to the inorganic diatom silica skeleton remained unexplored. Here, we have conducted a multi-analytical approach to investigate the processing of diatom silica and whether it is reconverted into sponge silica. We have documented widespread diatom consumption by several demosponges, identifying storage vesicles for the diatom-derived silica by electron microscopy and microanalysis. Diatom-consuming sponges showed upregulation of silicatein and silicase genes, which in addition to the δ 30Si values of their silica, supports that the sponges are converting the ingested diatom silica into sponge silica without much further Si fractionation. Our multidisciplinary approach suggests that the reutilization of diatom silica by sponges is a common feature among Antarctic sponges, which should be further investigated in other latitudes and in other silicifiers. [ABSTRACT FROM AUTHOR]

Atlantic reef-building corals and coral reefs continue to experience extensive decline due to increased stressors related to climate change, disease, pollution, and numerous anthropogenic threats. To understand the impact of ocean warming and reef loss on the estimated extinction risk of shallow water Atlantic reef-building scleractinians and milleporids, all 85 valid species were reassessed under the IUCN Red List Categories and Criteria, updating the previous Red List assessment of Atlantic corals published in 2008. For the present assessment, individual species declines were estimated based on the modeled coral cover loss (1989-2019) and projected onset of annual severe bleaching events (2020-2050) across the Atlantic. Species traits were used to scale species' relative vulnerability to the modeled cover declines and forecasted bleaching events. The updated assessments place 45.88%-54.12% of Atlantic shallow water corals at an elevated extinction risk compared to the previous assessments conducted in 2008 (15.19%-40.51%). However, coral cover loss estimates indicate an improvement in reef coverage compared to the historic time-series used for the 2008 assessments. Based on this, we infer that, although remaining dangerously high, the rate of Atlantic reef coral cover decline has surprisingly slowed in recent decades. However, based on modeled projections of sea-surface temperature that predict the onset of annual severe bleaching events within the next 30 years, we listed 26 (out of 85) species as Critically Endangered in the IUCN Red List. Each of these species had previously been listed under a lower threatened category and this result alone highlights the severe threat future bleaching events pose to coral survival and the reef ecosystems they support., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Gutierrez et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)