Nitrogen release from decomposing seaweeds: species and temperature effects

Abstract

This study determined the rate at which nitrogen accumulated in seaweeds is released during decomposition and the effect of temperature on their rates of decomposition and nitrogen release. Gracilaria verrucosa and Ulva lactuca decomposed rapidly in outdoor mesocosms. Ulva, but not 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 significant effect on the decomposition rate of Gracilaria in a laboratory experiment: decomposition was greater at 30 °C than at 25 °C. No net decomposition was observed at 16 °C. Gracilaria became nitrogen enriched at 30 °C, but not at 16° or 25°. The release of stored nutrients from decaying seaweeds should be included in nutrient budgets and models when seaweed standing stocks are significant. Seaweed source-sink relationships are important ecologically and can be applied to attempts at using seaweeds as environmental monitors of anthropogenic eutrophication and to efforts of cultivating seaweeds for the improvement of water quality.