Suprabenthic amphipods from the littoral zone of Barlovento, Venezuela: spatial distribution and seasonal variation

Peracarid crustaceans are a very diverse benthic group and one of the dominant taxa within the suprabenthic community. The Barlovento beaches in Venezuela are characterised by large inputs of organic matter and an important assemblage of amphipods has been observed to thrive in this area. In this paper we describe the species composition of this amphipod assemblage along with their spatial and temporal variation and relationship with some environmental variables on four beaches (Agua Sal, Los Timones, Las Cabañas, Valle Seco). Results showed no significant differences in the amphipod community structure and total density of organisms regardless of the season (rainy and dry). From the 7569 amphipods collected, a total of 20 species were identified within 14 families and 17 genera. The species Apohyale media (Dana, 1953), Metatiron tropakis (J. L. Barnard, 1972) and Nototropis minikoi (A. O. Walker, 1905) were the most abundant species in terms of density, and the last two also in terms of frequency of occurrence. Differences in biomass were not significant at any level (season, beach and their interactions); however, the highest amphipod biomass throughout the year was observed at Valle Seco Beach with peaks in January, August and December coinciding with large accumulations of bryozoans and wood debris. Amphipod density and biomass had low correlation values with the environmental variables; the material caught in the suprabenthos net being the most common variable influencing the community.

Diel density variation of amphipods associated with Sargassum beds from two shores of Ubatuba, Southeastern, Brazil

Densities of mobile epifaunal assemblages associated with macrophytes are very variable during the day and the activity of visually-oriented predators is thought to have an important influence on this pattern. Here we compared densities of amphipods associated with a common brown alga, Sargassum stenophyllum (Phaeophyceae), at sites contrasting in water turbidity. We expected that diel variation of amphipods would occur in a shore with clear waters (Perequê), whereas no variation was expected in a shore with turbid waters (Lamberto). Amphipod density varied during the day at both shores, with no indication of a larger variation at Perequê. Most species showed two density peaks, one at night and the other in the afternoon. These peaks occurred close the times of high tide, suggesting that tidal rhythms could influence more amphipod densities than the activity of predators. Thus, more studies are necessary to understand factors that influence short-term variation of epifaunal assemblages.

Test of Biotic and Abiotic Environmental Determinants of Amphipod (Hyalella azteca) Preamplexus

Variation in reproductive behavior (preamplexus) of the amphipod Hyalella azteca among 10 Canadian Shield lakes in Ontario was positively correlated with water temperature, possibly through its influence on either activity patterns or diapausal endocrinology. Intensity of preamplexus was not correlated with other abiotic variables including lake pH, alkalinity, total phosphorus, or chlorophyll a concentration. Similarly, the complicated evolutionary "strategies" suggested by Strong involving alterations in optimal mating tactics in response to differences in intensity offish predation, amphipod density, or habitat heterogeneity did not occur in these lakes.