A POSSIBLE EFFECT OF SALINITY FLUCTUATION ON ABUNDANCE OF BENTHIC VEGETATION AND ASSOCIATED FAUNA IN NORTHEASTERN FLORIDA BAY

In southern Florida, a vast network of canals and water control struct ures mediate freshwater discharge into the coastal zone. Management pr otocol for one such canal network (C-111) is being modified in part to try to improve habitat for estuarine fish and wading birds in northea stern Florida Bay, an estuarine part of Everglades National Park. Chan ges in canal management could alter the spatial and temporal salinity regime in the estuary. To better predict the effect of such changes on estuarine habitat, abundances of submersed vegetation and benthic ani mals were sampled repeatedly at 12 stations that differed in salinity. A variety of other parameters were also measured (nutrients, light, t emperature, oxygen, sediment characteristics, and others). Mean salini ty among stations ranged from 11.4 parts per thousand to 33.1 parts pe r thousand. Densities of benthic plants and animals differed among sta tions by several orders of magnitude. The standard deviation of salini ty was the best environmental correlate with mean plant biomass and be nthic animal density: less biota occurred at stations with greater flu ctuations in salinity. The two stations with the least plant biomass a lso had the highest mean water temperatures. In a stepwise multiple re gression analysis, standard deviation of salinity accounted for 59% of the variation in the logarithm of mean plant biomass among stations. For every 3 parts per thousand increase in the standard deviation, tot al benthic plant biomass decreased by an order of magnitude. Mean wate r temperature accounted for only 14% of the variation, and mean salini ty was not included for lack of significance. At stations with widely fluctuating salinities, not only was biomass low, but species dominanc e also frequently changed. Severe fluctuation in salinity may have pre vented abundant benthos by causing physiological stress that reduced g rowth and survival. Salinity may not have remained within the range of tolerance of any one plant species for long enough to allow the devel opment of a substantially vegetated benthic community. Hence, gaining control over salinity fluctuation may be the key to estuarine habitat improvement through canal management in southern Florida.