Guilds among epiphytal foraminifera on fibrous substrates, Nevis, West Indies

Abstract

The nearshore foraminifera of the oligotrophic Caribbean region are predominantly epiphytal, living on calcareous algae and seagrasses. However, their community ecology (interactions between and associations among species) is little understood. Cluster analysis is used here to identify guilds among the epiphytal foraminifera, a guild being a group of species that forms an arena of intense competition within which species' niches overlap considerably in habitat, time and food. Samples were collected monthly between September 1994 and August 1995 from (a) calcareous algae and (b) seagrass rhizomes and leaf bosses from two bays around Nevis, northern Lesser Antilles. One bay was impacted by organic enrichment from a leaking septic tank. Data from both bays were combined to form a metapopulation, analysis of which was conducted using common species (i.e., those that formed > 1% of the recovery from any substrate in either bay). Q-mode cluster analysis using populations on all substrates of common species clearly separated the two bays, despite sampling of the same substrate in both, indicating that the bays occupy different biofacies. However, Q-mode analysis did not separate the different substrates in the individual bays. R-mode cluster analysis of the two-bay metapopulation based on common species revealed three clusters that are interpreted as guilds: Guild I A higher-energy guild intolerant of nutrient enrichment. Guild II A guild of rapidly-reproducing opportunists on short-lived substrates. Guild III A lower-energy guild tolerant of nutrient enrichment. These guilds are not limited to any one bay, but vary in proportion between the two, Guild I being most prolific in the virtually pristine back-reef bay on the windward side of the island, and Guilds II and III forming a greater proportion of the epiphytal foraminiferal fauna in the bay impacted by lower-energy waves and a flux of organic matter. Guild II shows a preference for the bushy capitulae of the alga Penicillus capitatus. In cross-correlation of 12-month time-series for the three guilds, the virtually pristine bay showed that they bloomed sequentially, at intervals of 4 months. The recognition of guilds clears the way for improved understanding of the foraminiferal community ecology of nearshore areas. Nearshore sediments in the Caribbean yield primarily foraminifera washed from phytal substrates. The palaeoecology of these assemblages can now be interpreted with greater confidence.