PATH ANALYSES OF THE INFLUENCE OF SUBSTRATE COMPOSITION ON NEMATODE NUMBERS AND ON DECOMPOSITION OF STRANDED SEAWEED AT AN ANTARCTIC COAST

Large amounts of seaweed are deposited along the coast of Admiralty Ba y, King George Island, Antarctica. The stranded seaweed partly decompo ses on the beach and supports populations of meiofauna species, mostly nematodes. The factors determining the number of nematodes found in t he seaweed packages were studied. Seaweed/sediment samples were collec ted from different locations, along the coast near Arctowski station, covering gradients of salinity, elevation and proximity of Penguin roo keries. On the same locations decomposition rate was determined by mea ns of permeable containers with seaweed material. Models, including th e relations between location, seaweed and sediment characteristics, nu mber of nematodes and decomposition rates, were postulated and verifie d using path analysis. The most plausible and significant models are p resented. The number of nematodes was directly correlated with the hei ght of the location, the carbon-to-nitrogen ratio, and the salinity of the sample. Nematode numbers were apparently indirectly dependent on sediment composition and water content. We hypothesize that the differ ent influences of melt water and tidal water, which affect both salini ty and water content of the deposits, are important phenomena underlyi ng these results. Analysis of the relation between decomposition rate and abiotic, location-related characteristics showed that decompositio n rate was dependent on the water content of the stranded seaweed and sediment composition. Decomposition rates were high on locations where water content of the deposits was high. There the running water from melt water run-off or from the surf probably increased weight losses o f seaweed.