NITROGEN RELEASE FROM DECOMPOSING SEAWEEDS - SPECIES AND TEMPERATURE EFFECTS

This study determined the rate at which nitrogen accumulated in seawee ds is released during decomposition and the effect of temperature on t heir rates of decomposition and nitrogen release. Gracilaria verrucosa and Ulva lactuca decomposed rapidly in outdoor mesocosms. Ulva, but n ot Gracilaria, became nitrogen-enriched during decomposition. Maximal weekly rates of nitrogen release were 5.91 +/- 2.23 and 6.37 +/- 2.59 g N m-2 d-1, respectively for Gracilaria and Ulva. Temperature had a s ignificant effect on the decomposition rate of Gracilaria in a laborat ory experiment: decomposition was greater at 30-degrees-C than at 25-d egrees-C. No net decomposition was observed at 16-degrees-C. Gracilari a became nitrogen enriched at 30-degrees-C, but not at 16-degrees or 2 5-degrees. The release of stored nutrients from decaying seaweeds shou ld be included in nutrient budgets and models when seaweed standing st ocks are significant. Seaweed source-sink relationships are important ecologically and can be applied to attempts at using seaweeds as envir onmental monitors of anthropogenic eutrophication and to efforts of cu ltivating seaweeds for the improvement of water quality.