Allan W. Stoner

Size-specific predation of juvenile queen conch Strombus gigas: implications for stock enhancement

Abstract Mariculture has long been considered a mechanism for restoring populations of queen conch, Strombus gigas Linne, which have been seriously over-fished throughout the Caribbean. The extremely high mortality of small juveniles and differences in survivorship between hatchery and wild stocks are severe obstacles that must be overcome. We conducted a tethering experiment to determine optimal release size and to examine differential predation among ten size classes of juvenile conch from 20 to 130 mm in shell length. Smaller animals (20–75 mm) were hatchery-reared, and larger animals (75–130 mm) were from the wild. Mean mortality of 75 mm hatchery conch was significantly higher than that of 75 mm wild conch. After 54 days all 20–40 mm conch and 10% or fewer of the 90–130 mm conch were killed. Based on our survivorship curve, we recommend a minimum release size of 75–90 mm. Actual release size, however, will inevitably represent a compromise between the high survivorship of large animals and the low cost of producing small ones.

Pelagic Sargassum: has its biomass changed in the last 50 years?

Abstract The quantity and distribution of Sargassum in the Sargasso Sea, as estimated by various investigators, is reviewed. There has apparently been no significant change in the biomass of Sargassum from 1933 to 1981, except for an area northeast of the Antilles (20 to 25°N, 62 to 68°W), where measurements made in November 1977 and November 1980 were about 0.1% of values measured in February and March 1933. Because of the lack of change in the Bermuda, Bahamas, or Gulf Stream regions, the effect does not appear to be due to pollution or to broad climatic changes; it is most likely due to a seasonal change in Sargassum abundance or to a long-term shift of currents defining the southwestern boundary of the Sargasso Sea.

Pelagic Sargassum: Evidence for a major decrease in biomass

A survey of pelagic Sargassum spp. in the North Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico between 1977 and 1981 showed that the biomass of the plants in the Sargasso Sea was <6% of the values in 1933 to 1935. There were also major decreases in the Gulf of Mexico, in the slope water mass of North America, and near Bahama Islands. The drastic reduction over the past half century may be related to an increase in anthropogenic materials in the ocean.

Comparison of macrobenthos collected with cores and suction sampler in vegetated and unvegetated marine habitats

A comparison of shallow water benthic macrofauna collected with hand-held cores and a suction sampler shoed that the core method provided the best estimate of macrofaunal density and composition. In a bare sand habitat, suction methods collected 72.8% fewer individuals per unit surface area of sediment. The difference was 32.6% in a seagrass (Halodule wrightii) habitat. At each site the number of species collected with the two devices was similar; however, population densities of numerically important species were underestimated with the suction device resulting in effects on community statistics. In addition to high sampling efficiency and statistical advantages associated with the use of the multiple cores, ease of operation and low construction cost make simple core tubes the preferred gear for sampling small macrobenthos in soft sediments, with or without vegetation.

Macroinvertebrate associations on the egg masses of the sea hare,Aplysia brasiliana rang (Gastropoda: Opisthobranchia)

We examined the assemblage of macroinvertebrates that inhabits the egg masses of the sea hareAplysia brasiliana Rang. A total of 3,721 individuals belonging to 31 invertebrate species was recovered from 107 egg masses collected in the Indian River Lagoon in east-central Florida. The egg mass associates appeared to be a subset of the surrounding faunal assemblage. Amphipods, polychaetes, and molluscs comprised the majority of the egg mass fauna. Of these, approximately 10 species were abundant, and were collected with high frequency in the egg masses examined. Association analysis of the distribution patterns of the more common species indicates that only positive first order effects and second order interactions were potentially important in this assemblage.