L. Meng et al., Using winter flounder growth rates to assess habitat quality across an anthropogenic gradient in Narragansett Bay, Rhode Island, ESTUARIES, 24(4), 2001, pp. 576-584
We used growth rates of juvenile winter flounder Pseudopleuronectes america
nus to assess anthropogenic influence on habitat quality at three sites in
Narragansett Bay, Rhode Island. The upper bay site, Gaspee Point, had the h
ighest population density and concentration of total nitrogen; human inputs
decreased down bay. Growth rates of individually marked fish were measured
in three 15-d experiments from June 8 to July 6, 1998 in 1-m(2) cages plac
ed at upper, middle, and lower bay sites. Water temperature, salinity, diss
olved oxygen (DO), and benthic food were also measured. Stable isotopes of
nitrogen and carbon were measured in experimental fish as possible indicato
rs of nutrient enrichment and to identify organic carbon sources. Growth ra
tes were 0.22-0.60 mm d (1), with the highest average at the mid-bay site.
Growth was initially fastest at Gaspee Point, but dropped off as DO concent
rations fell. Step-wise multiple regression indicated that location (upper,
middle, or lower bay) explained most of the variability in fish growth (40
%). Coefficients of other significant variables indicated that fish grew fa
ster at lower salinities, smaller sizes, and with decreased time that DO wa
s below 2.3 mg 1 (1). Benthic prey varied among sites and there was signifi
cantly less food and fewer species at Gaspee Point. Polydora cornuta was a
favored food at all sites and was found in over half the stomachs. Values o
f delta N-15 in fish and sediments did not reflect differences in total nit
rogen concentrations recorded near the sites. We suggest that anthropogenic
influences, such as nutrients and sewage, affected habitat quality by redu
cing DO, which lowered fish growth rates.