A study of the benthos of soft bottoms, sek harbour, new guinea, using numerical analysis

Samples collected from 62 sites within c. 1½ sq miles by means of a van Veengrab contained a small number of species (animal and plant), dominated by twospecies of ophiuroids. Without sophisticated analyses it is possible to delimit obvious”communities” based on dominants and subdominants, for example an Amphioplus-Amphiacantha community and a soft coral-sponge community. Similarly areas ofhigh species diversities can be identified, these conforming approximately with therecordings of species occurring in single sites.Further analyses were made numerically after transformation of the data usingthe Bray and Curtis (1957) measure of affinity and the Lance and Williams (1967b)system of flexible sorting. Nine site groups were derived and ordinated by the”principal co-ordinate analysis” of Gower (1966, 1967). These groups were reducedto eight by detailed consideration of site characteristics.A gritty area is characterized by epifauna (soft coral and sponge), a “clean”area by a tubicolous polychaete Mesochaetopterus, and six areas by the two ophiuroidsAmphioplus and Amphiacantha. Amongst these the following can be distinguishedfrom a western to eastern (seawards) direction: (a) low numbers and patchydistribution of both ophiuroids and virtually nothing else, (b) both ophiuroids witha bivalve mollusc Tellina and a stomatopod Clorida, (c) moderate numbers of bothophiuroids, (d) large numbers of Amphioplus with moderate numbers of Amphiacanthaand three associated species, and (e) two areas which are essentially ecotones of thelast.The “associations” are compared in detail with others involving comparablegenera. While it was expected that in these warm waters there would be a heterogeneousbiota with indefinite “community patterns”, as just indicated the situationwas relatively simple.Data were of such complexity to be ideally suited for a comparative study ofmethods of numerical analysis, and these are outlined in the Appendix. Threestandard models were used, two of which were discarded. After prior transformationof the data (including elimination of species with a single occurrence and fusion of sites in proximity) the final technique proved satisfactory