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.

Shallow rocky reef fish assemblages were studied in sites of low versus high fishing pressure (FP) across the Aegean Sea, in order to assess community structure at a large scale and investigate spatial variability in relation to FP, depth, and geographic location. A total of 15 pairs of high and low FP sites were selected (18 sites in North Aegean, 12 in South Aegean). The level of FP was defined based on a fishing pressure index specifically developed for coastal small-scale fisheries in the region. In each site, fish communities were investigated at two depth zones (5 and 15 m). Number of species, fish size (Total Length; TL) and abundance were recorded along strip transects through underwater visual surveys. Abundance and TL were used to estimate biomass, and fish species were assigned to distinct trophic and commercial status groups. An 8fold range in fish density and a 14-fold range in fish biomass were detected, while community structure was affected by all variables considered (FP, depth, geographic location). The N Aegean sites scored higher in number of species and biomass of carnivorous fish, whereas the S Aegean had a higher biomass of several allochthonous and thermophilous species. Abundance and biomass estimates were higher in low FP sites, and primarily at the 15 m depth zone, where low FP sites had the double abundance and 2.8 times higher biomass. Biomass of carnivores was generally very low, except at deep sites of low FP. Given that sites of lower FP represent areas of lower conflicting interests for fisheries whilst providing enhanced biomass levels, they should be included in future marine conservation planning schemes, as they could contribute to the replenishment of fisheries and the boosting of conservation benefits provided by MPAs, once properly managed.

BackgroundUnderwater visual surveys (UVSs) for monitoring fish communities are preferred over fishing surveys in certain habitats, such as rocky or coral reefs and seagrass beds and are the standard monitoring tool in many cases, especially in protected areas. However, despite their wide application there are potential biases, mainly due to imperfect detectability and the behavioral responses of fish to the observers.MethodsThe performance of two methods of UVSs were compared to test whether they give similar results in terms of fish population density, occupancy, species richness, and community composition. Distance sampling (line transects) and plot sampling (strip transects) were conducted at 31 rocky reef sites in the Aegean Sea (Greece) using SCUBA diving.ResultsLine transects generated significantly higher values of occupancy, species richness, and total fish density compared to strip transects. For most species, density estimates differed significantly between the two sampling methods. For secretive species and species avoiding the observers, the line transect method yielded higher estimates, as it accounted for imperfect detectability and utilized a larger survey area compared to the strip transect method. On the other hand, large-scale spatial patterns of species composition were similar for both methods.DiscussionOverall, both methods presented a number of advantages and limitations, which should be considered in survey design. Line transects appear to be more suitable for surveying secretive species, while strip transects should be preferred at high fish densities and for species of high mobility.