Settlement of Perna perna larvae in successful and unsuccessful rehabilitation sites in Coffee Bay

Abstract

Settlement is a major determinant of intertidal organisms. Arrival and attachment on suitable substrata are essential requirements for species survival. Populations of the brown mussel Perna perna in the former Transkei have been reported to be depleted through over exploitation by subsistence harvesters. This is a problem because recovery after disturbance is very slow. There is a Mussel Rehabilitation Project in Coffee Bay which attaches mussels onto the rocks for rehabilitation and rehabilitation is considered as successful in some sites and unsuccessful in some sites. The study examined the effect of settlement of Brown mussel Perna perna larvae in successful and unsuccessful sites for rehabilitation. Brown mussel larvae settlement was monitored at 6 sites in Coffee Bay situated between Hole in the Wall and Umtata River mouth in the Eastern Cape, S.A. Each site had 6 artificial larvae collectors about 30cm apart. Larvae collectors were replaced fortnightly from May to September during spring low tide. Larvae abundance showed varying picks among sites, with high picks observed in successful sites for rehabilitation. There was a positive correlation between larvae settlement and rehabilitation success of brown mussels in Coffee Bay. The amount of larvae settlement was higher in successful sites than in unsuccessful sites. According to the MRP staff Nqutheni was the best site for rehabilitation and that was based on the rehabilitation success. However, in this study Ocean was the site with higher number of larvae settling. These results indicate that delivery of larvae in these sites is different, with some sites receiving more larvae than others. In conclusion, the effect of aspect on settlement highlights the importance in successful site selection, suggesting that mussel larvae settlement has an effect on mussel rehabilitation in Coffee Bay. Keywords: Perna perna, Larvae, Settlement, Rehabilitation,