Development and application of a macroinvertebrate functional-group approach in the bioassessment of remnant river oxbows in southwest Florida

Abstract

Invertebrate richness, density, mass, and functional-group analyses were used as surrogates for ecosystem attributes to evaluate conditions of 10 remnant oxbows along the channelized lower Caloosahatchee River in southwest Florida. Replicate 30-sec dipnet samples were taken in Hydrocotyle and Nuphar plant beds that accounted for >80% of cover in the oxbows. Dissolved oxygen (DO) was <65% saturation at the bottom in most oxbows, and all beds, except for 1 Hydrocotyle bed, were rated as heterotrophic. Invertebrate analyses indicated that most oxbows had sufficient coarse particulate organic matter to support normal summer shredder populations and an abundant supply of fine particulate organic matter to support large populations of filtering collectors. High ratios of predators to other functional groups were coupled with many rapid-turnover (i.e., short-life-cycle) prey taxa. Availability of invertebrate food for drift- and benthic-feeding fish was evaluated as generally poor. Overall rankings of ecological condition of oxbows, accomplished using all invertebrate categories and DO levels, formed the basis for recommendations about oxbow restoration along the river.