Seawater acidification more than warming presents a challenge for two Antarctic macroalgal-associated amphipods

Elevated atmospheric pCO2 concentrations are triggering seawater pH reductions and seawater temperature increases along the western Antarctic Peninsula (WAP). These factors in combination have the potential to influence organisms in an antagonistic, additive, or synergistic manner. The amphipods Gondogeneia antarctica and Paradexamine fissicauda represent prominent members of macroalgal-associated mesograzer assemblages of the WAP. Our primary objective was to investigate amphipod behavioral and physiological responses to reduced seawater pH and elevated temperature to evaluate potential cascading ecological impacts. For 90 d, amphipods were exposed to combinations of seawater conditions based on present ambient (pH 8.0, 1.5°C) and predicted end-of-century conditions (pH 7.6, 3.5°C). We recorded survival, molt frequency, and macroalgal consumption rates as well as change in wet mass and proximate body composition (protein and lipid). Survival for both species declined significantly at reduced pH and co-varied with molt frequency. Consumption rates in G. antarctica were significantly higher at reduced pH and there was an additive pH-temperature effect on consumption rates in P. fissicauda. Body mass was reduced for G. antarctica at elevated temperature, but there was no significant effect of pH or temperature on body mass in P. fissicauda. Exposure to the pH or temperature levels tested did not induce significant changes in whole body biochemical composition of G. antarctica, but exposure to elevated temperature resulted in a significant increase in whole body protein content of P. fissicauda. Our study indicates that while elevated temperature causes sub-lethal impacts on both species of amphipods, reduced pH causes significant mortality

Food Resource Utilization in the Sea Urchin Lytechinus variegatus in Contrasting Shallow-Water Microhabits of Saint Joseph Bay, Florida

The feeding activity and relative percentages of different foods consumed by the regular sea urchin Lytechinus variegatus in three contrasting microhabitats were examined over a 2-yr period in Saint Joseph Bay, FL, at its northern limits of distribution. In 1993, feeding activity levels of individuals at a site dominated by the seagrass Thalassia testudinum were higher on average than at a site characterized mostly by sand substrates alone or a site dominated by the seagrass Syringodium filiforme. No other significant difference in feeding activity levels was detected between sites or years. Feeding activity was markedly reduced at all sites in winter months of both years. Lytechinus variegatus in Saint Joseph Bay displayed generalist feeding behaviors with diets that appeared to be governed by the availability and palatability of food items. Foods consumed by sea urchins varied seasonally at each site, apparently in response to changes in food availability. Some seasonally abundant algae (e.g., the fleshy red alga Laurencia porteaur) were not consumed, presumably due to chemical defenses. Seasonal depressions in resource utilization and changes in food types likely impact aspects of growth and reproduction of individuals comprising subpopulations of L. variegatus that fringe on the northern limits of their biogeographic distribution

The Population Dynamics of the Brittlestar Ophioderma brevispinum in Near- and Farshore Seagrass Habitats of Port Saint Joseph Bay, Florida

The population dynamics of the brittlestar Ophioderma brevispinum were followed monthly from Jan. 1995 to March 1996 in a near- and farshore seagrass bed in Saint Joseph Bay, FL. Abiotic (sea water temperature and salinity) and biotic (seagrass cover and sublethal predation) factors that could influence populations were also measured. Densities of individuals at both sites peaked in winter and spring, then declined dramatically in early summer months, and increased once again in the early fall at the offshore site and in the late fall at the nearshore site. Mean monthly disc diameters of individuals did not reveal any evidence of juvenile recruitment, suggesting seasonal migrations of adults into and out of near- and farshore seagrass beds. Seagrass cover at both sites varied substantially with season, with the highest cover in the summer months when brittlestar densities were lowest. Sublethal predation, as measured indirectly by counting the numbers of arm tips regenerating in individuals, did not differ significantly between sites except for the month of Feb. 1995, when levels of arm tip regeneration were higher among individuals at the nearshore site. The high overall incidence of individuals with regenerating arms at both sites suggests that predators exert persistent sublethal predatory pressure and may contribute to mortality. Individuals may migrate into deeper water during summer months to avoid thermal stress, hypoxia, or high levels of ultraviolet radiation and to avoid predation when predator densities are likely to be highest

An Analysis of Cheliped Asymmetry in Three Species of Fiddler Crabs

Left-right cheliped asymmetry occurs in a variety of decapod species, Such asymmetries can be present in early development or can arise during sexual differentiation. Male fiddler crabs have a dimorphic enlargement of one of the two chelipeds. This major cheliped has been associated with male reproductive success as a result of female selection or advantage in male-male combat. Because the major cheliped occurs on either the right or the left side, selection pressure could produce populations with right or left cheliped dominance. To ascertain whether populations of dominantly enlarged right- or left-clawed males are present, three fiddler crab species, Uca longisignalis, U. minax and U. pugnax, from four North American marshes, two on the coast of the Atlantic Ocean, one on the coast of the Chesapeake Bay, and one on the coast of the Gulf of Mexico, were sampled. There were no significant differences in the number of males with right- or left-enlarged chelipeds within all species or marshes sampled. Similarly, when male crabs were grouped arbitrarily into two size classes (major chelipeds \u3c20 mm and 2:20 mm), the number of crabs with right or left major cheliped was similar among the size groups. Mean major propodus size for males was also similar for individuals with either right or left major chelipeds within each of the three species and four marshes. Comparison of morphometric parameters in each population indicated a strong correlation between claw size, carapace width, and carapace length, which was not affected by cheliped laterality. It appears that among these three species of Uca, there is no selection for males with cheliped enlargement on either the right or the left side within the geographical range of the species sampled

Abstracts of the Fifth North American Echinoderm Conference, Melbourne, Florida, 20-25 July 2008

These abstracts represent research studies presented at the Fifth North American Echinoderm Conference (NAEC) sponsored by the Florida Institute of Technology and the University of Alabama at Birmingham, 20-25 July 2008. The meeting was held on the campus of the Florida Institute of Technology in Melbourne, FL. Those attending the conference were gathered in large part to recognize the outstanding past, present, and future career of John M. Lawrence (see abstract by J. S. Pearse), the quintessential echinoderm biologist. We wish to thank Carolyn Wood (Assistant Editor) and Monty Graham (Editor) for facilitating publication in Gulf of Mexico Science

Observation of acoustic turbulence in a system of nonlinear second sound waves in superfluid 4He.

We discuss the results of recent studies of acoustic turbulence in a system of nonlinear second sound waves in a high-quality resonator filled with superfluid 4He. It was found that, when the driving amplitude was sufficiently increased, a steady-state direct wave cascade is formed involving a flux of energy towards high frequencies. The wave amplitude distribution follows a power law over a wide range of frequencies. Development of a decay instability at high driving amplitudes results in the formation of subharmonics of the driving frequency, and to a backflow of energy towards the low-frequency spectral domain, in addition to the direct cascade