Response diversity in Mediterranean coralligenous assemblages facing climate change: Insights from a multispecific thermotolerance experiment

Abstract

Climate change threatens coastal benthic communities on a global scale. However, the potential effects of ongoing warming on mesophotic temperate reefs at the community level remain poorly understood. Investigating how different members of these communities will respond to the future expected environmental conditions is, therefore, key to anticipating their future trajectories and developing specific management and conservation strategies. Here, we examined the responses of some of the main components of the highly diverse Mediterranean coralligenous assemblages to thermal stress. We performed thermotolerance experiments with different temperature treatments (from 26 to 29°C) with 10 species from different phyla (three anthozoans, six sponges and one ascidian) and different structural roles. Overall, we observed species‐specific contrasting responses to warming regardless of phyla or growth form. Moreover, the responses ranged from highly resistant species to sensitive species and were mostly in agreement with previous field observations from mass mortality events (MMEs) linked to Mediterranean marine heat waves. Our results unravel the diversity of responses to warming in coralligenous outcrops and suggest the presence of potential winners and losers in the face of climate change. Finally, this study highlights the importance of accounting for species‐specific vulnerabilities and response diversity when forecasting the future trajectories of temperate benthic communities in a warming ocean.

The constraint of ignoring the subtidal water climatology in evaluating the changes of coralligenous reefs due to heating events

“…Nevertheless, the approach used in this study can only lead formulating predictions on large categories of taxa. In general, the expectation about the coralligenous community change to heating events, based on the overall vulnerability to warming treatments 38,39,45,60 , concerns the reduction of sea fan and encrusting sponge species abundance and the consequent increase of algae such as turfs or fast growing weeds 61 . In this study, although with the limit of the taxonomic resolution, some unequivocal predictions of the effects of heating events on the coralligenous community could be made, as there was a consistence response across sites and depths of associations (descriptor-coralligenous): these include the high predictive power of the median temperature for the taxa richness, for the encrusting coralline algae and bryozoans.…”

“…www.nature.com/scientificreports/ output regards the context-dependence of several predictions, either on the community or the categories of taxa, as the type of associations (negative or positive) changed among sites or depths. However, the categories of taxa are composed of numbered species whose contribution in abundance changes depending on the sitexdepth context and, because vulnerability to the heating may be species specific 44,45 and often depends on local adaptation 73 , the interpretation of unconsistent patterns could only be very oddly and speculative, until the relevancy of each single species is assessed. www.nature.com/scientificreports/ The present study uses the approach of relating different coralligenous communities to their thermal environment in order to contribute drawing the trajectories of change of the coralligenous community due to future warming scenarios.…”

“…The other output regards the context-dependence of several predictions, either on the community or the categories of taxa, as the type of associations (negative or positive) changed among sites or depths. However, the categories of taxa are composed of numbered species whose contribution in abundance changes depending on the sitexdepth context and, because vulnerability to the heating may be species specific 44 , 45 and often depends on local adaptation 73 , the interpretation of unconsistent patterns could only be very oddly and speculative, until the relevancy of each single species is assessed.…”

“…Overall, thermal tolerance has been highlighted mainly for gorgonians, bryozoans and sponges species, and lethal and sublethal responses (e.g. necrosis or decreased polyps activity) to the exceeding of heating thresholds or to manipulated duration of heating events have been identified 43 – 45 . Overall, the survival horizon of specific taxa as well as of the whole coralligenous reef is considered strongly dependent on heat waves occurrence 46 .…”

Animal Forest Mortality: Following the Consequences of a Gorgonian Coral Loss on a Mediterranean Coralligenous Assemblage

“…Calcareous encrusting algae constitute a secondary substrate where stratified assemblages including erect algae, sponges, bryozoans, gorgonian corals, and other alcyonaceans develop [24]. The maintenance of coralligenous organisms is likely related to relatively steady environmental conditions, and therefore they are particularly sensitive to local and global stressors [25][26][27][28][29]. MMEs have been described for many coralligenous species [30][31][32][33], but gorgonian corals and Paramuricea clavata (Risso, 1826) in particular appear to be mostly affected [34][35][36][37].…”