Abundances of benthic microfauna in relation to outwelling of mangrove detritus in a tropical coastal region

Publisher Website
Google Scholar
Abstract
Mangrove litter outwells from tidal forests and deposits onto the adjacent coastal seafloor within the central Great Barrier Reef lagoon in tropical northeastern Australia. Previous studies in this region indicate that this detrital loading greatly influences edaphic characteristics (e.g. C/N ratios and POC-soluble tannin concentrations) and supports highly abundant and productive, sedimentary bacterial communities. Mean ciliate and flagellate densities (> 20 .mu.m) within surface (0 to 1 cm) sediments in this region ranged from 23 to 511 cells cm-3 and from 40 to 806 cells cm-3, respectively. Densities of nanoprotozoans (5 to 20 .mu.m) ranged from below detection limits to 260.5 .times. 103 cells cm-3. Seasonal fluctuations of all microfaunal groups were relatively minor. Total faunal densities generally declined with sediment depth, but low densities of sarcodinids, amoeboflagellates, and yeasts and yeast-like cells were discovered below the sediment surface at all of the stations sampled. Experimental additions of aged mangrove litter to mixed laboratory populations of Euplotes spp., hymenostomid and hypostomatid ciliates, and zooflagellates resulted in either no or poor growth, suggesting that outwelled litter is not a nutritious food. Densities of microfauna in these sediments are low compared to densities in temperate coastal habitats, and appear to be influenced more by preferences in sediment type than by detrital outwelling or by proximity to the mangrove forests. Poor food quality may partially explain the low densities and lack of a discernible effect of outwelling on the microfauna. Several factors such as low dissolved nutrient levels, high C/N ratios and low microalgal abundances are also cited to account for the low densities, but low water content and poor nutritional quality of litter are considered to be the major factors regulating the benthic microfauna in this region.