Global warming causes the poleward shift of the trailing edges of marine ectotherm species distributions. In the semi-enclosed Mediterranean Sea, continental masses and oceanographic barriers do not allow natural connectivity with thermophilic species pools: as trailing edges retreat, a net diversity loss occurs. We quantify this loss on the Israeli shelf, among the warmest areas in the Mediterranean, by comparing current native molluscan richness with the historical one obtained from surficial death assemblages. We recorded only 12% and 5% of historically present native species on shallow subtidal soft and hard substrates, respectively. This is the largest climate-driven regional-scale diversity loss in the oceans documented to date. By contrast, assemblages in the intertidal, more tolerant to climatic extremes, and in the cooler mesophotic zone show approximately 50% of the historical native richness. Importantly, approximately 60% of the recorded shallow subtidal native species do not reach reproductive size, making the shallow shelf a demographic sink. We predict that, as climate warms, this native biodiversity collapse will intensify and expand geographically, counteracted only by Indo-Pacific species entering from the Suez Canal. These assemblages, shaped by climate warming and biological invasions, give rise to a ‘novel ecosystem’ whose restoration to historical baselines is not achievable.

Stony Coral Tissue Loss Disease (SCTLD) has affected Caribbean coral reef colonies since it was first detected in Florida in 2014. Its rapid spread and virulent nature are a major concern to coastal nations in the Caribbean Sea. Belize and Honduras have approached their management and strategies in somewhat different ways, but with the same goal of evaluating and controlling the spread and reducing mortality rates of their coral colonies. They both used amoxicillin trihydrate powder with Coral Ointment Base2B which proved effective in halting the spread of the disease and lowered mortality rates in treated corals. In addition to treatment, both countries have continued to monitor the extent of the disease, entering the data into the collaborative disease tracker platform on AGRRA.org. Between October 2020 and November 2021, a total of 14,495 corals from 29 species were assessed at sites in Belize and Honduras that were affected by SCTLD. The overall prevalence (all coral species) of SCTLD at these sites was 14%. Three species (Meandrina meandrites, Dendrogyra clyindrus and Dichocoenia stokesi) were in the top affected species in both countries, with 42%, 38% and 32% SCTLD prevalence, respectively. The sharing of information allowed Belize and Honduras to be relatively prepared for the onset of SCTLD in their waters through a series of monitoring and intervention actions. Although the treatment has proved to be somewhat effective, it is time and labor intensive. Reducing other well-known anthropogenic including sewage and dredging, is key to supporting coral reef health and resiliency.

<p>We quantify a large-scale extirpation of native species from the Israeli Mediterranean shelf, a region strongly affected by rapidly changing environmental conditions and the introduction of non-indigenous species, based on an extensive sampling programme of mollusks on intertidal to subtidal soft and hard substrata. We reconstruct historical species richness from shelly death assemblages, quantify the time range they cover with radiocarbon dating, and compare their richness with today’s living assemblage diversity. The median native richness is 50% of the historical richness for the intertidal, but only 8% for the subtidal down to 40 m. Samples from the mesophotic zone show a much higher median of 42%, which is likely an underestimation due to sampling constraints. In contrast, non-indigenous species show assemblages matching the historical richness. Seasonality is very strong: autumn samples, after the summer heat peak, are highly impoverished in native species but enriched in non-indigenous ones. Additionally, a comparison between today’s and historical native species maximum size shows that shallow subtidal native populations are mostly non-reproductive. In contrast, non-indigenous species reach reproductive size. These results suggest that a recent large-scale change in environmental conditions is strongly favoring non-indigenous species and is the main cause behind the shallow subtidal native species decline. Such an environmental factor is likely seawater temperature that plays a greater role in the shallow subtidal than in the cooler mesophotic zone, and affects subtidal species more than intertidal ones, pre-adapted to a climatically extreme environment.</p>

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