Decomposition in situ of the sublittoral Antarctic macroalga Desmarestia anceps Montagne

Large amounts of detached Antarctic macroalgae accumulate in hollows of the seabed, where decomposition rates of the detached macroalgae are expected to be low, caused by lack of contact of the major part of the macroalgae with the sediment. To determine decomposition rates in Antarctic waters, untreated and pre-killed Desmarestia anceps fronds contained in nylon net bags were studied for 10 months under natural conditions in Factory Cove, Signy Island. Physical decomposition was shown to be more important than microbial decomposition. A weight loss of 40% occurred in untreated material within 313 days, while prekilled material almost all disappeared within 90 days. Despite the weight loss, changes in chlorophyll a content were negligible during the experiment. Changes in the C:N ratio and tissue N indicated low rates of microbial decomposition. Therefore, it was concluded that weight loss was mainly caused by fragmentation, and particles disappearing from the nets accounted for most of the loss of original tissue. It remains unknown as to how long nutrients stay in Antarctic macroalgal litter before they become available to the system. [KEYWORDS: Spartina-alterniflora; nitrogen; dynamics; carbon; litter; degradation; sediments; detritus; decay; field]