MEPS 247:93-101 (2003)  -  doi:10.3354/meps247093

Utilization of algal and bacterial extracellular polymeric secretions (EPS) by the deposit-feeding brittlestar Amphipholis gracillima (Echinodermata)

D. L. Hoskins1,*, S. E. Stancyk2, A. W. Decho3

1Marine, Environmental Science, and Biotechnology Research Center, Savannah State University, Savannah, Georgia, USA
2Marine Science Program, University of South Carolina, Columbia, South Carolina, USA
3Department of Environmental Health Sciences, University of South Carolina, Columbia, South Carolina, USA

ABSTRACT: Like many deposit-feeding organisms, the burrowing brittlestar Amphipholis gracillima feeds on particulate organic matter in surface sediments. Microbial exopolymeric secretions (EPS) are carbohydrate-enriched polymers produced by microalgae and bacteria that bind aggregates and form dense biofilms near the sediment-water interface. EPS are assimilable by some benthic infauna and may be utilized as a significant carbon source. EPS are absorbed by some deposit-feeders, including a holothurian, and may be supplemental sources of nutrition. The burrowing brittlestar A. gracillima is a deposit-feeder that was used in a mass balance approach to model the incorporation of radiolabeled EPS by bottom feeders. Brittlestars were fed 14C-labeled, laboratory-cultured EPS from the marine bacterium Pseudoalteromonas atlantica and a benthic diatom (Nitzschia sp.) via sediment-bound and aqueous exposures. Comparison of absorption efficiencies (AE) showed that both polymer types are highly absorbed by A. gracillima (AE = 83 to 99%). Absorption of sediment-bound bacterial and algal EPS was similar (92.2 and 90.1%), but bacterial EPS absorption was significantly (p < 0.05) higher in sediment-bound (92.2%) than aqueous (83.3%) exposures. Algal EPS absorption was significantly higher in aqueous (99.9%) exposures. These findings suggest that EPS may represent a significant energy source for this deposit-feeding ophiuroid and other organisms with similar feeding habits. Additionally, A. gracillima appears to be especially adept at utilizing EPS resources from benthic diatom communities.

KEY WORDS: Echinoderm · Extracellular polymeric secretions · Brittlestar · Deposit-feeding · EPS

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