Physiological and behavioral response of the Asian shore crab, Hemigrapsus sanguineus, to salinity: implications for estuarine distribution and invasion.

The invasive Asian shore crab, Hemigrapsus sanguineus, is ubiquitous in the rocky intertidal zone of the western North Atlantic. A likely contributor to this colonization is that H. sanguineus is able to handle a wide range of salinities, and is thus more likely to spread through a greater geographic area of estuaries. This study investigated the salinity effects on this animal by observing survival across a range of salinities, the maintenance of hemolymph osmolality under different salinities, and behavioral preference for and avoidance of salinities. H. sanguineus showed high survival across a broad range of salinities, had little change in hemolymph osmolality over a short-term salinity shock, and behaviorally distinguished between salinities when presented with a choice, under both acclimation salinities of 5 PSU or 35 PSU. Such results suggest H. sanguineus has a hardiness for the rapid changes in salinity that happen in the intertidal zone, yet is capable of physically moving to a more optimal salinity. This enhances their competitiveness as an invader, particularly surviving lower salinities that present challenges during high-precipitation events in rocky intertidal areas, and partially explains this species' dominance in this habitat type.

Community shelter use in response to two benthic decapod predators in the Long Island Sound.

To investigate community shelter effects of two invasive decapod species, Hemigrapsus sanguineus and Carcinus maenas, in the Long Island Sound (LIS), we deployed artificial shelters in the intertidal and immediate subtidal zones. These consisted of five groups during the summer: a control, a resident H. sanguineus male or female group, and a resident C. maenas male or female group. We quantified utilization of the shelters at 24 h by counting crabs and fish present. We found significant avoidance of H. sanguineus in the field by benthic hermit crabs (Pagurus spp.) and significant avoidance of C. maenas by the seaboard goby (Gobiosoma ginsburgi). The grubby (Myoxocephalus aenaeus) avoided neither treatment, probably since it tends to be a predator of invertebrates. H. sanguineus avoided C. maenas treatments, whereas C. maenas did not avoid any treatment. Seasonal deployments in the subtidal indicated cohabitation of a number of benthic species in the LIS, with peak shelter use corresponding with increased predation and likely reproductive activity in spring and summer for green crabs (C. maenas), hermit crabs (Pagurus spp.), seaboard gobies (G. ginsburgi), and grubbies (Myoxocephalus aenaeus).

Elucidating the mechanism of action of tributyltin (TBT) in zebrafish.

Tributyltin (TBT), an antifouling agent, has been implicated in the masculinization of fish species worldwide, but the masculinizing mechanism is not fully understood. We have examined the actions of TBT as an endocrine disruptor in zebrafish (Danio rerio). In HeLa cells transiently co-transfected with plasmid constructs containing the zebrafish estrogen receptors (zfERα, zfERß(1) and zfERß(2)) and the zebrafish estrogen response element (zfERE-tk-luc), ethinyl estradiol (EE2) induced luciferase activity 4 to 6-fold and was inhibited by TBT. In HeLa cells transiently co-transfected with the zebrafish androgen receptor (zfAR) and the murine androgen receptor response element (ARE-slp-luc), testosterone induced luciferase activity was not inhibited by TBT. In HeLa cells co-transfected with zfERα, zfERß(1) and zfERß(2) and a plasmid containing zebrafish aromatase (zfCyp19b-luc), TBT inhibited luciferase activity. In zebrafish exposed to 1mg/kg and 5mg/kg TBT in vivo, there was a increase in liver sulfotransferase and a decrease acyl-CoA testosterone acyltransferase activity. Real-time PCR analysis of sexual differentiation markers in fish exposed to TBT in vivo revealed a tissue-specific response. In brain there was increased production of Sox9, Dax1, and SF1 mRNA, an androgenizing effect, while in the liver there was increased production of Dax1, Cyp19a and zfERß(1) mRNA but decreased production of Sox9 mRNA, a feminizing effect. In the gonads there was increased production of zfERα and zfCyp19a mRNA, again a feminizing effect. TBT has an overall masculinizing effect but the masculinizing effect is tempered by a feminizing effect on gene transcription in certain tissues. These results are discussed in the context of TBT as an endocrine disruptor in zebrafish.

Cortisol alters carbonic anhydrase-mediated renal sulfate secretion.

Active transepithelial sulfate secretion rate by winter flounder renal proximal tubule epithelium in primary culture (fPTC) is dependent on intracellular carbonic anhydrase (CA) and enhanced by cortisol. To further evaluate this relationship, a partial cDNA clone (327 bp) of carbonic anhydrase II (CAII) with high sequence similarity to CAII from numerous species including fish, chicken, and human was obtained from fPTCs. The majority of CA activity and CAII protein was present in the cytosol of fPTCs; however, significant amounts of both (in addition to SDS-resistant CA activity, i.e., CAIV-like isoform) were present in concentrated plasma membranes. CAII from concentrated membranes migrated differently than purified CAII on nondenaturing PAGE gels, suggesting that CAII associates with another membrane component. Treatment of fPTCs with the cell-soluble CA inhibitor methazolamide (100 microM) caused a 58% reduction in active transepithelial SO4(2-) secretion. fPTCs that were previously cultured under high-cortisol concentrations, when subjected to 5 days of low physiological levels of cortisol, had decreased CA activity (28%), CAII protein abundance (65%), and net active SO4(2-) secretion (28%), with no effect on epithelial differentiation. Methazolamide and low-cortisol treatment in combination inhibited net active SO4(2-) secretion 56%, which was not different than the effect of methazolamide treatment alone. These data indicate that cortisol directly increases renal CA activity, CAII protein abundance, and CA-dependent SO4(2-) secretion in the marine teleost renal proximal tubule.