Using winter flounder growth rates to assess habitat quality in Rhode Island's coastal lagoons

We used growth rates of juvenile winter flounder Pseudopleuronectes america nus, to assess habitat quality in 3 of Rhode Island's coastal salt ponds th at had differing levels of nutrients and human development. In each pond, 1 m(2) cages were placed in vegetated and unvegetated habitats and growth ra tes of individually marked fish were measured in three 10 to 15 d experimen ts from 4 June to 7 July 1997. Water temperature, salinity, dissolved oxyge n, and benthic food were also measured. Stable isotopes of C and N were mea sured in experimental and wild fish. Growth rates were 0.06 to 0.76 mm d(-1 ) and decreased through the experiments. Growth rates of wild fish (0.19 mm d(-1) in Point Judith Pond and 0.21 in Ninigret Pond) were similar to the average of the 2nd and 3rd experiments (0.24 mm d(-1)). Growth rates were t he same in vegetated and unvegetated sites. They were also the same in Poin t Judith and Ninigret ponds but lower in Green Hill Pond. An ANCOVA suggest ed that Green Hill's lower rates were caused by its higher temperatures, pa rticularly during the 3rd experiment. Benthic food was similar in the diffe rent ponds, different habitat types, and in cores taken inside and outside cages. Categories of food consumed by fish were not affected by the presenc e of vegetation in a cage, although food consumed did differ from pond to p ond. Amphipods were the preferred food in all ponds; fish consumed proporti onately more amphipods and fewer polychaetes in Ninigret Pond than in the o ther ponds. Values of delta(15)N in the fish varied with the degree of deve lopment in the watershed but not with total nitrogen in the water column. T he results of this study indicate that growth rates of fish can be used as indicators of habitat quality.