Asteroidea of Mombasa Marine National Park and Reserve.

Abstract

Biodiversity, abundance, feeding preference and habitat data on an assemblage of shallow water, coral-reef starfish (Asteroidea) were gathered over four months at Mombasa National Marine Park and Reserve. M1VINP&R contain a fringing reef and are situated between Mombasa town and Mtwapa creek on the East African coast of the Western Indian Ocean. It has not been known to carry an outbreak of the corallivorous crown-of-thorns starfish (Acanthaster planci) and its coral cover is well developed. Specimens required primarily for identification were collected by means of circlesampling, time transects and random searches. In addition, a selection of large and small, dead coral slabs were overturned and cryptic specimens located beneath these slabs were collected. Data for the abundance investigation was collected by means of 30' time transects in the inner and outer-reef. In the shallow inner-reef the surveys were done using snorkelling equipment while investigation of the outer-reef was done with the use of SCUBA gear. Additional investigation was done to obtain information about the habitat preferences of the species. When doing the transects for habitat, abundance or species presence surveys, species were turned over to detect the food preference of the animals. The identifications of the species were done under supervision of Prof. Jangoux at the laboratory for Oceanology, ULB Brussels. The finding of Choriaster granulatus, Fromia monilis, Neoferdina kuhli are new records for East Africa while Halityle regularis, Pentaceraster horridus, Pentaceraster tuberculatus and Euretaster cribrosus represent new records for the coast of Kenya It was found that MMNP&R carries a rich and diverse asterooid fauna but the imperfectness of the time transect method especially in regard to cryptic species indicates that additional species are still to be located. Of the 18 starfish species found in M1VINP&R, 6 (Choreaster granulatus, Fromia monilis, Gomophia egyptica, Linclda multiflore, Nardoa variolata and Neoferdina kuhli) were located only in the outer-reef. An additional seven species (Halityle regularis, Pentaceraster horridus, P. mammillatus, P. tuberculatus, Leiaster coriaceus, Asterina burtoni and Euretaster cribrosus) were found only in the inner-reef. Some specimens were located in the inner as well as the outer-reef (Acanthaster planci, Culcila schmideliana, Protoreaster lincki, Linckia laevigata and L. guidingii), though a preference for one of the reefs was obvious for some of these species. None of the species were found in intertidal areas. While, Acanthastar planci, Fromia monilis, Gomophia egyptiaca, Linckia multiphora, Neoferdina kuhli and Nardoa variolata were sometimes found at the base of the reef slope, they were never observed on the sea floor away from the reef The preceding species can be regarded as coral-reef species and their distribution differs from that of species such as Choreaster granulatus and Culcita schmideliana that were also found in the deeper off-reef waters in the MNP&R region or Pentaceraster spp and Protoreaster lincki who were manly found in the inner-reefs sea grass beds. The observation that most species (all except one) of , starfish found on MMNP&R belong to the order of the Valvatida corresponds with the results of other investigations done in the tropical regions, and a general increase in relative significance of this order toward the tropics is noted. The asteroids found on MMNP&R showed some inter-specific variation with respect to die but most species appeared to feed on in the inner-reef there is a general increase of the total number of starfish from the park to the reserve. This is most likely an effect of the full protection status of the park in regard to fishery, which is reflected in a higher density of the main predator of the starfish (the triggerfish Balistapus undulatus) at the park. In the park's outer-reef a dominance of Linckias was noted;, these species are well known for their extraordinary regenerative capacities and their autonomous asexual reproduction capabilities. These qualities surely increase their surviving opportunities in an area with high predation pressure. The asteroid communities of MMNP&R were clearly adult-dominated, although the juveniles of these species might complete their early development under boulders and are for that reason difficult to detect with the used method. Still, many workers who have studied coral reef asteroid populations have noted the adult-dominated size structure of these populations.