Population structures among epiphytal foraminiferal communities, Nevis, West Indies

Brent Wilson

doi:10.1144/jm.27.1.63

Abstract

Abstract. The taxocene of live epiphytal foraminifera was for one year monitored monthly on six phytal substrates in shallow water (<1 m) in two bays around Nevis, NE Caribbean Sea. Mosquito Bay was subject to a nutrient flux from a leaking septic tank. Long Haul Bay was comparatively undeveloped. SHE Community Structure Investigations (SHECSIs) revealed that the populations on five plants had logarithmic series distributions of species abundances, the slopes of lnS vs. lnE for these five time-series being within −1±0.3. In three time-series, they were within −1±0.05.Cluster analysis of twenty-five sediment samples in shallow water (<3 m) indicates that Nevis is largely surrounded by a single thanatacoenosis, for which SHECSI indicates a logarithmic series population structure. However, it is not possible to reconstruct perfectly the epiphytal population from the sediment thanatacoenosis. The thanatacoenosis included 40% allochthonous Amphistegina gibbosa, Archaias angulatus and Asterigerina carinata, washed in from offshore reefs, and few planorbulinids, although the latter dominates the biocoenosis on seagrass leaves in the backreef.

Highlights

It is axiomatic in ecology that in any multi-species population some species will be common and others rare (Magurran, 1988; Buzas & Hayek, 2005)
The Caribbean region is ideal for investigating population structures among epiphytal foraminiferal communities
A population is accepted as having a logarithmic series distribution of species abundances if it shows three characteristics: 1. changes in the accumulative values of H are not significantly correlated with the rise in accumulated lnN at a 95% confidence level, but are instead shown by linear regression to fluctuate around an almost stationary value; 2. regression of lnS against lnE gives a constant approximating to the final value of accumulated H and a slope of approximately 1; and 3. the slopes of lnS and lnE vs. lnN are of opposite sign and approximately equal

Summary

Introduction

It is axiomatic in ecology that in any multi-species population some species will be common and others rare (Magurran, 1988; Buzas & Hayek, 2005). Most shallow-water foraminifera in the oligotrophic Caribbean Sea are epiphytal (Cushman, 1922a; Brasier, 1975; Wilson, 1998, 2000), living on (a) the calcareous algae Penicillus capitatus, Halimeda spp. and Dasycladus vermicularis, and (b) the seagrasses Thalassia testinudum and Syringodium filiforme (Waszczak & Steinker, 1978). On seagrasses they inhabit (a) leaves and (b) exposed rhizomes and leaf bosses, which can bear distinctly different communities (Langer, 1993; Ribes et al, 2000). This paper compares population structures of the foraminiferal biocoenses on phytal substrates with that of the thanatacoenosis in the associated sediment, and determines the extent to which knowledge of the population structure of the epiphytal assemblages helps in the interpretation of fossil sediment assemblages

Methods

Results

Discussion

Conclusion