Effects of a mass mortality event on gorgonian reproduction

Abstract

The impact of a disturbance is normally measured in terms of its effects on adult mortality, whilst the less obvious impact on reproductive biology is generally ignored. Although previous studies have contributed to understanding the effects of a mass mortality of gorgonians in 1999 at NW Mediterranean Sea, none of them have considered its impact on reproduction. The goal of this study was to determine the impact of mass mortality events on the reproduction of the gorgonian Paramuricea clavata, and examine the effect of the damage 1 year (June 2000) and 2 years (June 2001) after the event. The reproductive parameters of female colonies were more affected than those of males. In female colonies that were moderately or severely damaged, the proportion of fertile polyps decreased by about 22–35%, whilst in the worst affected males there was only a 12% decrease. Female colonies showed a progressive decrease in gonadal biomass with increasing damage to a maximum reduction of 73–75% of oocyte production observed in colonies with >33% injury. In contrast, in males, the gonadal biomass decreased rapidly for colonies with 5% of injured surface, with a reduction in spermary production of 49–64%. The same pattern of decrease in gonadal output compared to the extent of the injury was observed in 2001, two years after the mass mortality event. This indicated that the observed pattern was a response to the extent of the injury rather than a direct effect of the event. These severe effects on the reproduction of the red gorgonian species have implications for the recovery of affected populations in the long-term. This study demonstrated that an evaluation of the impact over different demographic parameters is needed to understand all the consequences of these disturbances.