Regional and local environmental conditions do not shape the response to warming of a marine habitat-forming species

Abstract

The differential response of marine populations to climate change remains poorly understood. Here, we combine common garden thermotolerance experiments in aquaria and population genetics to disentangle the factors driving the population response to thermal stress in a temperate habitat-forming species: the octocoral Paramuricea clavata. Using eight populations separated from tens of meters to hundreds of kilometers, which were differentially impacted by recent mortality events, we identify 25 °C as a critical thermal threshold. After one week of exposure at this temperature, seven of the eight populations were affected by tissue necrosis and after 30 days of exposure at this temperature, the mean % of affected colonies increased gradually from 3 to 97%. We then demonstrate the weak relation between the observed differential phenotypic responses and the local temperature regimes experienced by each population. A significant correlation was observed between these responses and the extent of genetic drift impacting each population. Local adaptation may thus be hindered by genetic drift, which seems to be the main driver of the differential response. Accordingly, conservation measures should promote connectivity and control density erosion in order to limit the impact of genetic drift on marine populations facing climate change.

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

“…Regardless of the possible mechanisms behind these differences, which in the case of Parazoanthus axinellae could include the presence of highly bioactive secondary metabolites only in the “slender” morphotype as chemical defences induced for coping with environmental changes (Cachet et al, ; Reverter et al, ), our results represent a good example of the diversity of responses to warming found among structurally, functionally and taxonomically related organisms dwelling in coralligenous outcrops. Previous studies dealing with habitat‐forming emblematic species from these assemblages, such as the red gorgonian Paramuricea clavata (Risso, 1826), the white gorgonian Eunicella singularis (Esper, 1791), the red coral Corallium rubrum (Linnaeus, 1758) or the bryozoans Myriapora truncata (Pallas, 1766) and Pentapora fascialis (Pallas, 1766), have already pointed to such diversity (Crisci et al, ; Linares et al, ; Pagès‐Escolà et al, ; Torrents et al, ). However, the low number of studied species impeded the assessment of whether the response diversity was limited or widespread at the community level.…”

“…A clear example of this is the Mediterranean coral Cladocora caespitosa (Ehrenberg, 1834), which, despite suffering recurrent warming‐induced mass mortalities in the field, showed resistance in single factor (temperature) experiments performed in aquaria while being impacted when exposed to additional factors such as the presence of invasive species (Kersting et al, ). Other factors that have been highlighted include food availability, pathogens, genetic differences or different physiologic processes (Arizmendi‐Mejía et al, ; Cebrian et al, ; Crisci et al, ; Linares et al, ; Pivotto et al, ). Therefore, bearing in mind the complex network of interacting factors that may ultimately determine vulnerability to warming in the field, determining the absolute thermal limits before which mortality of a given species should not be expected remains challenging.…”

“…As the response variable, we measured the percentage of necrotic tissue in each specimen, which was visually monitored on a daily basis. This variable has been widely used for coralligenous assemblages both in field mortality assessments and laboratory experiments as a proxy of partial and/or total mortality following disturbance (Cebrian, Uriz, Garrabou, & Ballesteros, ; Cerrano et al, ; Crisci et al, ; Garrabou et al, ; Kersting, Bensoussan, & Linares, ; Pagès‐Escolà et al, ). Following these similar previous studies, we considered necrotic tissue to be all areas with evident signs of irreversible damage, which may include the following: the loss of tissue, denudation/exposure of the skeleton, the loss of coloration derived from the total or partial loss of living tissue and/or the colonization by saprophytic microorganisms (see Supporting information Figure ).…”

“…Regardless of the possible mechanisms behind these differences, which in the case of Parazoanthus axinellae could include the presence of highly bioactive secondary metabolites only in the "slender" morphotype as chemical defences induced for coping with environmental changes (Cachet et al, 2015;Reverter et al, 2016) (Crisci et al, 2017;Linares et al, 2013;Pagès-Escolà et al, 2018;Torrents et al, 2008). However, the low number of studied species impeded the assessment of whether the response diversity was limited or widespread at the community level.…”

“…A clear example of this is the Mediterranean coral Cladocora caespitosa (Ehrenberg, 1834), which, despite suffering recurrent warming-induced mass mortalities in the field, showed resistance in single factor (temperature) experiments performed in aquaria while being impacted when exposed to additional factors such as the presence of invasive species (Kersting et al, 2015). Other factors that have been highlighted include food availability, pathogens, genetic differences or different physiologic processes (Arizmendi-Mejía et al, 2015;Cebrian et al, 2011;Crisci et al, 2017;Linares et al, 2013;Pivotto et al, 2015).…”