Range contractions, fragmentation, species extirpations, and extinctions of commercially valuable molluscs in the Mediterranean Sea—a climate warming hotspot

Abstract

The Mediterranean Sea is a global hotspot of climate warming and biodiversity loss where molluscs have provided valuable ecosystem services, such as provisioning and cultural value, since pre-historic times. A high rate of warming and range shift limitations due to the semi-enclosed nature of the basin raise concerns about molluscan population persistence in future climate scenarios. We modelled the future distribution of 13 Mediterranean species of molluscs subject to industrial fisheries exploitation on both the Mediterranean and Atlantic European coasts. We tested the hypothesis that range contractions, fragmentation, and species extirpations will become increasingly severe in the Mediterranean by modelling mid-century and end-century species distributions for four IPCC climate change scenarios. Already under mild emissions scenarios, substantial range contractions and fragmentation are projected in the Mediterranean, suggesting global extinctions by end-century for most endemic species. Colder deep waters do not act as refugia, contrary to expectations. Species also occurring along the Atlantic European coasts may benefit from warming through range expansions to higher latitudes or deeper waters. Most of the modeled species are already over-exploited, but their eradication from the Mediterranean will imply substantial financial losses and a profound cultural change in coastal communities.

The climate crisis affects Mediterranean marine molluscs of conservation concern

“…protandry in Patella ferruginea), low adult mobility, narrow vertical depth range, nearshore distribution and endemism, characteristics that render marine species vulnerable to extirpation and extinction (Roberts & Hawkins, 1999). Additionally, in a study with the same methodology targeting molluscs of commercial interest in the Mediterranean, three out of 13 modelled species are predicted to lose more than 95% of their range in the basin by the end of the century under the worst emission scenario RCP 8.5 (Gallagher & Albano, 2023). Such range losses may well approximate global extinctions being all three strictly endemic species.…”

“…Second, species sensitive to warming have gotten locally rarer or totally eradicated in the warmer sectors leaving behind a taxonomic and functional void (Albano et al, 2021;Rilov, 2016;Steger et al, 2021). For these species, accelerating warming will first make the coldest northern parts of the Mediterranean Sea the last refugia, but then these sectors will become cul-de-sacs leading eventually to high extinction risk for Mediterranean endemic species (Ben Rais Lasram et al, 2010;Gallagher & Albano, 2023). Due to the indented outline of the northern Mediterranean, where peninsulas delimit major sub-basins, such cul-de-sacs will host heavily fragmented populations with limited or ultimately no connectivity (Ben Rais Lasram et al, 2010).…”

“…Under RCP8.5 2100, Charonia variegata shows an extreme westward shift (−27°), an outlier not illustrated here.Most species show a north-westward shift that intensifies by the end of the century. Episcomitra zonata, Patella ferruginea and Pinna nobilis were projected to become extinct under RCP8.5 in 2100 and are thus absent from the plot Lasram et al, 2010;Gallagher & Albano, 2023)…”