Spatial and temporal characterization of soft bottom polychaetes in a shallow tropical bay (colombian Caribbean)

Abstract

The spatial and temporal variations of the polychaete assemblages were studied within and off a shallow (10-25 m) tropical bay (Bahía de Portete). The polychaete abundances at family level and their trophic mechanisms were used for this purpose. Sediment samples were collected at six stations in this bay during the wet and dry seasons. Multivariate analysis indicated that off- Bay polychaete assemblages were different from the bay ones; this spatial variation was related to sedimentary characteristics, depth and turbid-water conditions. On the other hand, these assemblages did not show significant differences between the dry and wet seasons. The differences between these two assemblages were given specially by the Syllidae, Gonidadidae, Nephtyidae, Dorvilleidae, Ampharetidae, Sabellidae, Glyceridae, Lumbrineridae, Opheliidae and Maldanidae families, being more abundant and frequent off the bay, while Magelonidae, Cirratulidae, Cossuridae and Eulephetidae were more abundant and frequent within the bay. The first ten families were related to a higher sand content, lower organic matter content and lower turbid-water conditions; while the last four were related to higher mud percentages, higher organic matter content and higher turbid-water conditions. Trophic guilds data showed similar assemblages as described above, which differ in their feeding mechanisms; the bay stations were dominated by surface and subsurface deposit feeders showing the importance of detritus; while off-bay stations the carnivores were the dominant organisms, reflecting the high predation. In these assemblages, the trophic and taxonomic structure is more affected by the spatial variation in the physical characteristics of the water column and sediment than by the seasonal variation.