Variation in heat shock protein expression during queen conch larval metamorphosis

Variation in heat shock protein expression during queen conch larval metamorphosis

Heat stress is known to induce larval metamorphosis in a variety of marine invertebrates, including the queen conch, Strombus gigas. Although many of the cellular responses triggered by this induction are not well understood, increases in the expression of a number of proteins are thought to be associated with this process. In the current study, the role of heat shock proteins (HSP’s) in the induction of queen conch metamorphosis was examined. HSP’s are a family of proteins named for their molecular sizes, which range from 20-100 kDa. They are intracellular molecular chaperones that facilitate protein folding and assembly. Known to be produced in response to environmental stress, HSP’s are also involved in the routine folding and transport of cellular proteins under natural conditions. Changes in the expression of HSP 90, HSP 70, and HSP 60 during queen conch metamorphosis were compared between heat-induced larvae and larvae treated with a natural inducer of metamorphosis, an extract of the red alga Laurencia poitei. After exposure to heat stress or the algal inducer, larvae were homogenized in sample buffer, proteins separated by SDS-polyacrylamide gel electrophoresis and analyzed by immunoblotting with antibodies specific to the three HSP’s. Induction of metamorphosis was coupled to increases in the expression of HSP’s. However, the patterns for heat-treated larvae were different from those for larvae exposed to the algal extract, as increases in expression occurred earlier in the induction process for the heat-stressed larvae. These results suggest distinct roles for HSP’s during normal conch metamorphosis and in response to stressful environmental conditions.

Lauralyn Dyer.* Department of Zoology, University of New Hampshire, Durham, NH 03824, USA; e-mail ldyer@cisunix.unh.edu.

Peter J. Edmunds.* Department of Biology, California State University, Northridge, CA 91330, USA.

David B. Eggleston,* L. E. Etherington, and E. G. Johnson. Department of Marine, Earth, and Atmospheric Science, North Carolina State University, Raleigh, NC 27695-8208, USA.

During 1999-2001 we identified a concurrent and precipitous decline in abundance, spawning stock, young-of-the-year, and postlarval stages of the blue crab (Callinectes sapidus) in Pamlico Sound, NC. Specifically, adult abundance declined by 74%, spawning stock by 75%, young-of-the-year (YOY) by 63%, and postlarvae by 71%. Fisheries-dependent and -independent data suggests that the decline was due to the interacting effects of three sequential hurricanes in fall, 1999 (Dennis, Floyd, Irene), which caused 50- to 500-year flooding in the Pamlico Sound watershed, and intense localized fishing pressure. Floodwaters displaced three-fourths of the volume of the Sound which led to a massive relocation of crabs from up-estuary tributaries to the central portion of the Sound where salinities were higher. Crabs that were concentrated in the Sound were subject to intense fishing where catch rates tripled compared to average catch. Concurrently, postlarval supply to the Sound was extremely high during fall 1999 as a consequence of hurricane wind-driven transport, yet there was apparent recruitment failure in 1999. Our data suggests that recruitment failure was due, in part, to disruption of secondary, pelagic dispersal of early juvenile crabs to the Sound by hurricane floodwaters. We suggest that the concurrent and precipitous decline in NC’s blue crab population beginning in 1999-2000 was due to overfishing localized, high concentrations of crabs displaced by hurricane floodwaters and recruitment failure of YOY. A strong stock-recruitment relationship for the blue crab in NC indicates an urgent need to conserve spawning stock for long-term population persistence.


Development of horseshoe crab embryos and larvae in a hypersaline environment

G. S. Ehlinger* and R. A. Tankersley. Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA.

The American horseshoe crab, Limulus polyphemus, typically inhabits estuarine systems with salinities ranging from 5–34 psu. During spawning, females lay their eggs beneath the sand in the high intertidal zone. Previous studies indicate that the optimal temperatures and salinities for embryonic and larval development are 25–30°C and 20–30 psu, respectively. While embryos are able to develop at salinities < 40 psu, tolerance of higher salinities has not been investigated. Studies of the L. polyphemus population in the Indian River Lagoon (IRL), Florida indicate the population may be declining and that larval development and survival may be impacted by elevated temperatures and salinities that occur during the spawning period. The objectives of this study were (1) to determine the effect of high temperatures and salinities on the survivorship, hatching rate and embryonic development of L. polyphemus and (2) to determine the effects of changes in external salinity on the osmotic concentration of the perivitelline fluid. Artificially fertilized eggs were raised at five salinity (30-60 psu) and temperature (25-40°C) combinations. Both embryos and larvae successfully developed, hatched and molted at salinities as high as 60 psu. However, embryonic development and hatching failed at temperature > 35°C. To determine if developing embryos are buffered from changes in external salinity by the regulation of the perivitelline fluid, we exposed eggs reared at 30 psu to salinities ranging from 5-90 psu and measured the osmotic concentration over a six hour period. Under all test conditions, the osmotic concentration of the perivitelline fluid conformed to the surrounding media. These results indicate that high temperature and salinity conditions influenced the rate of horseshoe crab development, yet, had a limited effect on survivorship and do not account for the low abundance of larvae in the IRL.


Predation by Great Black-backed Gulls (Larus marinus) on crabs in the New England rocky intertidal and shallow subtidal

Julie C. Ellis,¹* Walter Chen,² and Myra Shulman.^{2 1}Brown University, Department of Ecology and Evolutionary Biology, Providence, RI, USA; ²Cornell University, Department of Ecology and Evolutionary Biology, Ithaca, NY, USA.

The intertidal is primarily a marine community; nearly all its inhabitants are marine in origin, and many have distributions that extend into the subtidal. However, terrestrial consumers may exploit the intertidal during low tides; such opportunistic foragers include birds and mammals. These consumers have the potential to influence abundances and upper distributional limits of prey species. Two species of gulls (Great Black-backed Gulls and Herring Gulls) nest on Appledore Island, in the Gulf of Maine; both forage in the intertidal. In this study, we focused on the predatory effects of Great Black-backed Gulls (Larus marinus) on intertidal populations. We examined: 1) temporal and spatial patterns in gull foraging in the intertidal, 2) rates of predation on three species of crab: Cancer borealis, C. irroratus, and Carcinus maenas, and 3) effects of predation on crab distribution. C. borealis was preyed upon far more often than Carcinus and C. irroratus, both in absolute numbers and relative to their abundance within the foraging range of the gulls. Per capita predation rate of gulls on crabs during a single tidal cycle per km of shoreline was 72.7 and 83.1 at the two study sites; the daily predation rate on C. borealis represented 36% to 50% of the standing crop found in the top stratum of the rocky subtidal. An experiment examining gull predation rates at 3 different tidal heights showed that 100% of tethered crabs were attacked at 1.0 m (relative to MLLW) and 0.0 m and only 40% or fewer attacked at –1.0 m. Both behavioral and experimental data indicate that despite their low densities, foraging Great Black-backed Gulls have a major impact on intertidal abundance and distribution of an important invertebrate predator, and may generate cascading effects on organisms at lower trophic levels.


Mangrove trimming: aesthetics at the expense of an ecosystem?

William Ellis* and S. S. Bell. University of South Florida, Biology, Department, 4202 East Fowler Ave., Tampa, FL 33620, USA.

Mangrove-dominated estuaries are highly productive coastal systems. The production of mangrove litter (i.e. leaves, wood, reproductive structures) and its subsequent consumption by higher trophic levels is said to represent a major pathway of energy flow. Consequently, damage to the mangrove canopy, where these vegetative structures are

produced, may impact ecosystem function.

We examined the impacts of mangrove trimming, a common horticultural practice in Florida, on the canopy density and litter dynamics of mangrove stands in the Rookery Bay National Estuarine Research Reserve. Litterfall was quantified monthly over a twenty-seven month period in twelve study plots (18.0 x 14.0 m) distributed throughout the Reserve. Six of these plots were randomly selected to serve as trimming sites after the initial fifteen months of litter collection. Within these six plots, 50% of the foliage of each mangrove tree was excised and removed from the site. Canopy density loss and any subsequent recovery was quantified by an analysis of digitized canopy photographs taken at fixed points within each study plot several times over the course of this investigation. The monthly mass of ground litter and the mean rate of its decomposition within the plot types (i.e. trimmed mangroves vs. reference) were also measured.

Mangrove trimming reduced canopy densities by an average of 30% with little evidence of recovery nineteen months after trimming was performed. Leaf litter production, the most severely impacted litter component, declined to one-half of that found in reference

plots. The amount of standing ground litter was not similarly impacted, as tidally driven imports and exports of litter obscured any corresponding changes in litter accumulation on the forest floor. Ground litter decomposition rates were higher in the reference plots than in the trimmed plots. These results indicate that mangrove trimming may considerably alter energy flow, particularly in systems with limited mangrove coverage.