Ecological role of Phyllophora antarctica drift accumulations in coastal soft-sediment communities of McMurdo Sound, Antarctica

• Published in: Polar biology 2004-07, Vol.27 (8), p.482-494
• Main Authors: NORKKO, Alf, THRUSH, Simon F, CUMMINGS, Vonda J, FUNNELL, Greig A, SCHWARZ, Anne-Maree, ANDREW, Neil L, HAWES, Ian
• Format: Article
• Language: English
• Subjects: Algae; ALGAL MATS; Animal and plant ecology; Animal, plant and microbial ecology; Aquatic life; Benthic communities; Biological and medical sciences; DELTA-C-13 MEASUREMENTS; DELTA-N-15 ANALYSIS; DETRITUS; Ecology; Ekologi; Environmental protection; Fluorometry; Food supply; Fundamental and applied biological sciences. Psychology; KELP; LAMINARIA-HYPERBOREA; Macrofauna; Marine; MARINE FOOD-WEB; Metabolites; Ocean floor; Particular ecosystems; Phyllophora antarctica; ROSS SEA; Sea water ecosystems; SEA-URCHINS; Seasonal variations; Secondary metabolites; SECONDARY PRODUCTION; Stable isotopes; Synecology; Trophic levels; TROPHIC RELATIONSHIPS
• ISSN: 0722-4060; 1432-2056
• DOI: 10.1007/s00300-004-0610-8

At Cape Evans on Ross Island, Antarctica, the rhodophyte Phyllophora antarctica is the dominant primary producer in terms of biomass from 10 to >30 m depth. The vast majority of Phyllophora occurs as accumulations of unattached plants. Whilst decomposition and incorporation of macroalgal drift material into the food web is rapid in temperate ecosystems, we predicted these processes to be slow in Antarctica. We address the functional role of macroalgal detritus in fuelling the biodiversity of benthic communities at Cape Evans during the summers of 2001 and 2002. Specifically we (a) describe the distribution and biomass of attached and drift algae, (b) assess the photosynthetic capacity and degradation of drift accumulations using in situ fluorometry, (c) assess the effect of patches of drift Phyllophora on underlying macrofaunal communities, and, (d) use stable isotopes to investigate the possible uptake of Phyllophora by macrofauna. We found drift Phyllophora accumulations throughout the depth range investigated (3-31 m), with peak biomasses of 140 plus or minus 30 g dwt m super(-2) in the 15-25 m depth strata. At this depth stratum Phyllophora was a conspicuous habitat element with the % cover on the seafloor averaging 30%. While initially the drift algal accumulations appeared in good health we measured significant declines in photosynthetic capacity between years suggesting ongoing, albeit slow, degradation of the drift algal accumulations. Our results demonstrate that Phyllophora drift accumulations have a structuring role on soft-sediment communities, which increases in strength with the gradual degradation of the algae. The longevity of Phyllophora is enhanced by secondary metabolites, which serve as protection against grazers, and their extreme shade adaptation. However, our carbon and nitrogen stable isotope data of polychaetes and amphipods associated with Phyllophora suggest that macroalgal detritus enters the food web, and although this process is slow, Phyllophora accumulations might serve to dampen the seasonality in food supply providing higher trophic levels with a more constant food source.