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Three bottom habitats in Biscayne Bay were sampled by 120 trawl samples taken during both day and night from April to August 1963. Daylight samples contained 1,391 fishes representing 41 species. Night samples contained 1,440 fishes and 49 species. The number of species per sample followed a Poisson distribution, the number of individuals per sample followed a negative binomial distribution, and the number of individuals per species followed Fisherˈs logarithmic series. The following generalizations apply to both number of species and number of individuals. More fishes were taken in the Thalassia area than in the Thalassia‐sand area, which in turn had more than the mud‐sand area. More were taken at night than during the day. Tidal direction had no significant effect. Analysis of data on the sample variance for paired 2‐minute samples showed that seven to eight replicates are needed to detect a difference of five species and 10 samples are needed to detect a 10% change in the number of individuals with 95% confidence.

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Few studies have been reported of the effects of power-plant discharges on tropical and semi-tropical marine environments where plants and animals in non-stressed conditions live close to their upper lethal thermal limits. This paper describes a multidisciplinary three-years' study made in Card Sound, Florida, before, during, and after, thermal effluents were released from a power-plant. Biomass, growth, and production, of Thalassia and macroalgae, were estimated. Animals were collected by trawl, drop-net, suction dredge, in artifical habitats, and on mesh-panels. Except in an area of 2–3 ha adjacent to the canal mouth, little damage to the benthic community was observed. This was very different from the effect of the first canal emanating from the same power-plant at Turkey Point, where a large area had been affected by heated effluents.