Demographic responses to warming: reproductive maturity and sex influence vulnerability in an octocoral

Abstract

Ocean warming, caused by climate change, is critically impacting marine coastal ecosystems. Benthic organisms, such as anthozoans, are increasingly submitted to high temperatures that cause massive mortalities in tropical and temperate seas. To broaden our understanding of their response to thermal stress, we tested the putative role of reproductive maturity and sex in the susceptibility of the Mediterranean red gorgonian, Paramuricea clavata, to high temperatures. We experimentally compared the response to thermal stress of sexually immature (i.e., juveniles) versus mature individuals (i.e., adults), and of males versus females. Colonies' response was firstly assessed by measuring the percentage of tissue area exhibiting necrosis. Then, the reproductive output (i.e., fertility, size, and number of gonads) of both sexes was characterized. When compared to juveniles, adults showed a significantly higher percentage of necrosis, suggesting that during the reproductive period they are more vulnerable to high temperatures. Males and females showed a similar percentage of tissue damage and a significant decrease in their reproductive output. However, females' reproduction was more impacted, suggesting that females are more susceptible to thermal stress than males. A differential energy investment in reproduction may be the underlying cause of the observed responses. Adults invest a large proportion of their energy budget in reproduction; hence, they have fewer resources available to cope with stress, compared to juveniles. A similar situation seems to apply to females, with respect to males. Considering the current ocean-warming trend, our results imply that the long-term viability of shallow populations of long-lived anthozoans may be jeopardized in the future. This study reveals potential demographic consequences of warming that go beyond its associated increment of mortality rates. Given the important ecological role of many anthozoan species, these results can help better predict the future effects of climate change on coastal ecosystems.

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

“…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.…”

“…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).…”

Divergent responses to warming of two common co-occurring Mediterranean bryozoans

“…The first temperature treatment simulated a relatively large period of high temperatures subjecting the colonies to 25 °C for a period of 44 days. This temperature has been recorded in several mass mortality events and identified as a critical threshold for several Mediterranean invertebrate species 22 , 48 , 49 . In contrast, the second temperature treatment was subjected to a sequential increase of temperature from 25 °C to 30 °C, to investigate thermotolerance features of both species and detect the maximum critical temperature.…”

“…One fragment of 3–5 cm height from 90 healthy colonies of each species were sampled at the same depth (approximately 20 m) in Medes Islands during October 2016 and transported in aerated seawater to the Experimental Aquarium Facilities of the Institute of Marine Sciences in Barcelona (in less than 24 hours). All the colonies were set in aquaria tanks (approximately 48 l volume), continuously supplied with seawater (salinity 38 ppm) and a current of flow rate around 60 l h −1 generated by a submersible pump and were subjected to an acclimation period of 7 days at 18 °C 21 , 48 . The colonies were fed three times per week with 3 ml of a liquid mixture of particles between 10 to 450 μm in size (Benthos Nutrition Marine Active Supplement, Maim, Vic, Spain) in each aquarium.…”

Postglacial range expansion shaped the spatial genetic structure in a marine habitat‐forming species: Implications for conservation plans in the Eastern Adriatic Sea

“…The larval phase was estimated between 8 and 25 days in aquarium (Linares, Coma, Garrabou, Díaz, & Zabala, ) but field observations reported high settlement rates near the mother colony (Coma et al., ). P. clavata is impacted by several local and global stressors (Linares & Doak, ) including mass mortality events (Arizmendi‐Mejía, Ledoux, et al., ; Garrabou et al., ). The spatial genetic structure of shallow (0–60 m depth) red gorgonian populations has been characterized from local, regional to global scales.…”