Echinothrix spp. is present at several sites along the Kenyan coast, amongst which the Mombasa District: Mombasa Marine National Park and Reserve (MMNP&R). In the MMNP 90% of the genus consist of the large bodied of Echinothrix diadema. Although in the older established parks a very significant decrease in its abundance has taken place, only a small decrease has been observed for the Mombasa area, of which the park is considered as a “transition reef’ (fish stock has only partially recovered). Since the establishment of the park in 1991 Echinothrix diadema’s biomass has not decreased like that of other sea urchins inhabiting the reef lagoon. Although E. mathaei has always been pointed out as the most important and competitive strongest herbivore, more recently eyes become fixed on E. diadema as a very important herbivore. However, as well worldwide as in the Kenyan reefs only few studies have been conducted related to this genus in general, towards a better understanding of its role in the coral reef community and its distribution. Therefore, surveys were carried out to first locate the species in Mombasa Marine National Park’s and Reserve’s fringing reef system. Later, during one month more detailed surveys were carried out at the inner reef of MMNP&R towards a better understanding of this species’ substrate and habitat preference. In the Mombasa Marine National Park and Reserve, Echinothrix diadema is restricted to the inner reef lagoon. As generalists, echinoids’ distribution is mainly determined to areas that they are physically able to tolerate. Therefore it can be said that due to its rather fragile test, Echinothrix diadema is primarily situated in the sheltered back reef. Furthermore, from literature study and personal observations it can be stated that Echinothrix diadema is considered as a coral reef echinoid, that can be of great influence on the reef community. The recorded data indicated E. diadema showed a high affinity for the topographically more complex areas of the reef, whereas this was shown more prominently in the park than in the reserve. Therefore the most obvious reason for this phenomenon would be the hiding from predators (mainly fish), of which the abundance is higher in the park. However, the predator guild feeding on E. diadema is probably very small. Another reason could be this sea urchin’s sensitiveness towards the high insolation it is receiving in these areas. Still, this is in contrast with the observations on this animal, found in tidal rock pools on the reef platform. Therefore it might be that the predation on this animal has been underestimated. Also, it may be avoiding competition from herbivorous fish by occupying hollows and borrows. |
