Spatial variability in fecundity of the gorgonian Paramuricea clavata (Risso, 1826)

In Mediterranean marine habitats, gorgonian corals (Octocorallia), form three-dimensional living habitats, known as ‘Marine Animal Forest’(MAF), structurally and functionally similar to terrestrial forests dominated by slow-growing, long-lived populations. Gorgonians, as ecosystem engineering species, can increase habitat heterogeneity, complexity, and biodiversity. However, the slow dynamic population and low recruitment rates of gorgonians make them vulnerable to the anthropogenic pressures and to worsening of climatic trends, leading them to mass mortality events. The recovery mechanisms of these species and population are related to the reproductive capacity of adult individuals. To provide useful information on the reproductive effort of the Mediterranean gorgonian Paramuricea clavata (Risso, 1826) populations and consequently on their responsiveness to climate change, the spatial variability in fecundity rate, sex ratio and oocytes size, along the northwest coast of the Mediterranean Sea, between the Ligurian (Italy) and Provence (France) coasts, were investigated. Results showed a statistically significant effect of geographic location on fecundity at Bergeggi and Portofino sites; the sex ratio was not statistically different from the balance 1:1 ratio. Finally, these sites also showed a positive correlation between oocytes size and fecundity rate. Overall, it is likely that a combination of factors contributes to the observed higher fecundity rates in P. clavata populations, including age and colonies size, and environmental factors, such as currents and food availability. Conversely, the populations with the lowest fecundity rates could be affected by heat stress and macroalgal overgrowth, that could reduce the energy budget for gonad development. The quantitative information obtained in this study provides a data-baseline for future long-term monitoring of this precious species, particularly relevant in a context of climate change.