Growth and production of three macrozoobenthic species in the Gulf of Riga, including comparisons with other areas

Abstract

Three soft-bottom stations in the southern part of the Gulf of Riga were studied during the period December 1993 to January 1995. The amphipods, Monoporeia affinis and Pontoporeia femorata, and the poychaete Marenzelleria viridis, were analysed for production, using the cohort growth method. Animals were also analysed for carbon and nitrogen content in a CHN-analyser. Based on size measurements, the quantitative data were divided into age-classes and the growth of each cohort was calculated first as wet weight and then converted into carbon and nitrogen content. Total annual production of each species was calculated as well as turnover ratios. The turnover ratio for Monoporeia affinis was estimated at 1.3–1.7, which is lower than earlier reported from the Baltic Proper. For Pontoporeia femorata the turnover ratio was estimated at 1.6 which is the same, or slightly more, than earlier reported from the Baltic Sea, but considerably lower than what has been reported from the NW Atlantic. For Marenzelleria viridis the turnover ratio at two stations with stable populations was between 0.4 and 0.5, while at a third station, with a growing population, a value of 1.0 was calculated. These figures are lower than those found for a German coastal lagoon, and substantially lower than the values found for the NW Atlantic.