Restoration of Kenyan seagrass beds: a functional study of the associated fauna and flora

Abstract

Seagrass communities are subject to frequent anthropogenic and natural disturbances that can lead to alterations in vegetation complexity and hence may affect associated fauna. Seagrass loss in Kenya has been mainly due to extensive grazing by the sea urchin Tripneustes gratilla which has affected almost the entire coastline. This has led to habitat fragmentation and sometimes vast areas of defoliated beds that were formerly covered with seagrass. The most affected species has been Thalassodendron ciliatum. Diani beach, south of Mombasa, is an area that has been typically affected by seagrass depletion. Natural recovery has been reported in certain areas and transplantation projects were started. The challenge is to see if the system can recover fully and will be able to function as before. To test this, the current study focused on the density, diversity and community structure of meiofauna, and more specifically of harpacticoid copepods as a measure of the ability of the system to recover. Artificial seagrass mimics were planted in natural, replanted and areas of bare sand and harvested in a series of 2, 4, 6, 10, 14 and 21 days in order to collect the associated meiofauna. Related environmental parameters were collected at the same time intervals except for the sediment samples for environmental analysis that were sampled once during the study period at the last day of collection of mimics. Significant differences of meiofauna densities between the sites and the colonization days were found but for harpacticoid copepods there was only a significant effect of the colonisation time. The densities of meiofauna reached those of natural seagrasses by day 4 but most of them were opportunistic species and not true phytal dwelling meiofauna. Both passive migration from neighbouring seagrass patches and active migration from sediments were observed, based on the harpacticoid copepod family composition. In the bare and replanted sites similar community structures of harpacticoid copepods were observed from day 6 onwards while for the healthy site it was from day 10. Colonization by epiphytic biofilm was collected from day 10 in the bare and replanted sites but not the healthy site. In the previous days it was too negligible to be collected. The results thus suggest possible recovery of harpacticoid copepods after disturbance thanks to their mobility and ability to colonize new areas quickly. However, this may depend largely on the time the epiphytic flora are able to recover as well as the recovery time of the seagrass plants which may take approximately 4 years.