Anthropogenic effects on reproductive effort and allocation of energy reserves in the Mediterranean octocoral Paramuricea clavata

In order to better understand the sources, patterns and consequences of anthropogenic effects on populations of the Mediterranean gorgonian Paramuricea clavata, we examined the proportion of injured colonies among populations exposed to a combination of anthropogenic disturbances (recreational cast fishing, commercial lobster pots, gill nets and SCUBA diving), as well as the physiological response of injured corals. Between 10 and 33% of the colonies in unprotected populations were partially colonized by epibionts, most likely following tissue injury, whereas only 4 to 10% of the populations in a marine protected area were affected. Populations that were simultaneously exposed to fishing as well as intensive SCUBA diving showed the highest proportion of colonization. Colonies with approximately 30 to 35% of epibiont coverage showed significantly lower numbers of gonads per polyp. Similarly, concentrations of lipids were lower in females with epibionts, thus indicating allocation of resources into recovery of injured tissue instead of reproduction. Furthermore, whereas unaffected colonies showed a uniform distribution of carbohydrates and proteins through apical branches to more central ones, colonies with epibionts had significantly lower protein concentrations in branches that are positioned 3 branching order levels closer to the stem. The results thus indicate a preference of apical growth in recovering colonies, via a different distribution of food within the colony. Reproductive success in surface-brooding corals growing on walls and overhangs might also be reduced by SCUBA bubbles from divers passing below, as bubbles efficiently remove eggs brooded on colony branches.