Aspects of the biology and ecology of some intertidal Holothurians (Echinodermata) along the Eastern Cape coast of South Africa

Four species of dendrochirote holothurians, Roweia stephensoni John, Pseudocnella sykion Lampert, Aslia spyridophora Clark, Roweia frauenfeldi frauenfeldi Ludwig, and one aspidochirote holothurian, Neostichopus grammatus Clark, are common inhabitants of the intertidal regions of the eastern Cape rocky shores of South Africa. All five species are sympatric for most of their geographical distribution. The intertidal distributions, densities and biomasses of R. stephensoni, P. sykion and N. grammatus were examined at six sites from Port Elizabeth to East London in the eastern Cape. At all sites the three species showed similar overlapping zonations with R. stephensoni and P. sykion reaching their highest maximum mean densities and biomasses (drained wet weight) in the lower mid-shore region (401m² and 684g/m², 181m² and 269g/m², respectively at Port Elizabeth), whilst N. grammatus in the low-shore region (61m² and 72g/m², at Port Elizabeth). The highest densities and biomasses of all three species were recorded on boulder shores that had minimal sand inundation. Seasonality of reproduction of R. stephensoni, P. sykion and N. grammatus was compared at Port Elizabeth, using gonad index values, gonadal tubule diameters, egg diameters and spermatozoon content in tubules from January 1992 until August 1993. All three species are dioecious and did not deviate from a 1: 1 sex ratio. Sizes at first sexual maturity were 2.5-2.9 cm³ for R. stephensoni and P. sykion, and 3.0-3.9cm³ for N. grammatus. The gonads of R. stephensoni and P. sykion consist of a bunch of unbranched tubules of equal diameter, with males having more tubules of a smaller diameter than females. By contrast, the gonad of N. grammatus consists of two tufts of multiple branched tubules. All three species followed annual reproductive cycles, and in R. stephensoni and P. sykion gametogenesis occurred from March 1992 until August/September 1992, and maturity was maintained until the main spawning event in January 1993. By contrast, in N. grammatus gametogenesis occurred from July 1992 until September 1992, and maturity was maintained until the main spawning event in December 1992/January 1993. Unlike R. stephensoni and P. sykion the reproductive cycle of N. grammatus was more pronounced, in that the gonad regressed after spawning. Aspects of the feeding biology of R. stephensoni, P. sykion, A. spyridophora, R.ffrauenfeldi and N. grammatus were compared, using the gross buccal tentacle morphology, type and size range of ingested food particles, and gut lengths. Scanning electron microscopy revealed that the buccal tentacles of R. stephensoni, P. sykion and A. spyridophora could be classified as dendritic, branching numerous times with the tips terminating in numerous nodes covered with discs of papillate projections. The buccal tentacle structure of R. f frauenfeldi deviated from the typical dendrochirote dendritic form. The tentacles are stout with few branches which terminate in large bulbous nodes lacking discs of papillate projections. Neostichopus grammatus possesses buccal tentacles that could be classified as peltate, terminating in large nodes which also lacked discs of papillate projections. Roweia stephensoni, P. sykion and A. spyridophora are suspension-feeders, ingesting food particles mostly <53pm in size. Roweia f frauenfeldi was classed as a "heavy" suspension-feeder, ingesting food particles mostly between 250pm-l.18mm, while N. grammatus is a deposit-feeder, ingesting benthic sediments mostly between 106-500pm. The gut lengths of the dendrochirote holothurians were found to be significantly longer than that of the aspidochirote, and may be attributed to the nature of the food ingested.