title: Physiological and Behavioral Responses to Changes in Salinity in the Invasive Bivalve Nuttallia obscurata Compared to the Native Bivalve Leukoma staminea
Creators: name: Talkington, Tori B.
Publisher: name: Western Washington University
Year: 2015

description: <p><em>Nuttallia obscurata </em>is a euryhaline invasive clam with populations that are rapidly spreading along the northeast Pacific coast. It inhabits areas of changing salinity such as the high intertidal and areas of freshwater seepages, areas uninhabited by local clam species. <em>N. obscurata</em>’s euryhalinity, salinity tolerance, and ability to survive in uniquely stressful areas likely facilitated its settlement and rapid spread into these distinctive microclimates. Previous research on <em>N. obscurata</em> is minimal, however favorable physiological and behavioral responses likely allow <em>N. obscurata</em> to live in these environments. The physiological response of osmolyte production and the behavioral responses of filtration rate have yet to be studied in <em>N. obscurata</em>, but likely play in important role in their tolerance and therefore invasiveness. <em> </em>I compared these responses to those of <em>Leukoma staminea, </em>a local stenohaline clam that inhabits the mid-intertidal. By comparing the physiology and behavior of <em>N. obscurata </em>and <em>L. staminea,</em> I may be able to determine if euryhalinity and inhabitation of open niche areas helps <em>N. obscurata</em> invade.</p>
<p>The important osmolytes previously noted in bivalves, betaine and sorbitol, were examined using High Performance Liquid Chromatography. Osmolyte concentration in clams under different salinities (1 ppt, 20 ppt, 30 ppt, 40 ppt and 60 ppt), under short-term (5 to 90 minutes) exposure, and under long-term (24 hr) exposure was examined. Betaine was a cellular component in both <em>N. obscurata</em> and<em> L. staminea</em>. Large stores were found in <em>N. obscurata</em> under 30 ppt salinity with concentrations decreasing under hypoosmotic salinities (1 ppt and 20ppt). This suggests that betaine is produced in large amounts in <em>N. obscurata</em> tissue and possibly utilized for osmotic compensation under decreased salinities. Betaine concentration in <em>N. obscurata</em> decreased under hyperosmotic conditions, likely because <em>N. obscurata</em> was utilizing energy stores to survive and not regenerating betaine. Other osmolytes, such as proline, glycine or taurine, may also be utilized in <em>N. obscurata</em> to cope with osmotic stress. There was evidence that taurine was a cellular component in some samples, but the concentration of taurine could not be determined. <em>L. staminea</em> produced betaine at a very low concentration under 30 ppt salinity and increased betaine under hypoosmotic and hyperosmotic conditions, helping the species cope with osmotic stress. Betaine increased significantly over time in <em>N. obscurata</em> gill tissue, showing that <em>N. obscurata</em> accumulates betaine quickly to compensate with fast environmental changes. Whether this accumulation is part of <em>N. obscurata’s </em>normal cell function or a response to stress is unknown. Sorbitol was not a major cellular component in <em>N. obscurata </em>or<em> L. staminea</em>.</p>
<p>Filtration rates of <em>N. obscurata </em>and <em>L. staminea</em> were tested using fluorometry over multiple salinity levels (1 ppt, 20 ppt, 30 ppt, 40 ppt and 60 ppt) for 340 minutes. <em>N. obscurata</em> filtered under a wider range of salinities than did<em> L. staminea</em>. Salinity significantly affected filtration rate and neither species filtered under extreme hypoosmotic or hyperosmotic conditions (1 ppt and 60 ppt), implying that although <em>N. obscurata </em>inhabits some hypoosmotic areas, it is unlikely to expand populations to freshwater. Both species filtered at higher rates compared to previously studied bivalves. This is of special concern for the already invasive and expanding populations of <em>N. obscurata,</em> which already outcompete some local clam species in disturbed areas.</p>
<p>While physiological and behavioral responses were examined separately in this experiment, they likely interact as part of a complex system. Filtration rate altered the exposure level of clam tissue to the external environment, thereby affecting osmotic response and osmolyte concentration. Future studies should continue to examine physiology and behavior in <em>N. obscurata</em>.</p>