Saxidomus Giganteus Research Articles

A multiaxial growth analysis of stable isotopes in the modern shell of Saxidomus gigantea: Implications for sclerochronology studies

Stable‐isotope ratios of two modern Saxidomus gigantea specimens from Namu, British Columbia, are presented to show intraspecimen and interspecimen isotopic variation. Isotopic profiles (δ13Cshell, δ18Oshell) were generated along the axis of maximum growth. The profiles show that analogous seasonal variation is recorded in δ18Oshell; however, significant variability is recorded in δ13Cshell. We suggest this is caused by differences in metabolic activity between individuals. Intrashell variability along a growth horizon shows good reproducibility in δ13Cshell but significant variability in δ18Oshell, especially at the sinistral margin. A multiaxial growth analysis generated several profiles from a single valve. Similar seasonal variations are recorded in δ18Oshell along all axes. δ13Cshell show significantly less covariation, possibly related to internal metabolic activity. This study highlights that δ18Oshell profiles generated from any portion of the shell can be used to evaluate seasonal fluctuations and may be excellent to evaluate types and rates of shell growth.

DEVELOPMENT OF A SAXIDOMUS PURPURATUS (MOLLUSCA: BIVALVIA) EGG-SPECIFIC ANTIBODY FOR THE QUANTIFICATION OF EGGS USING AN ENZYME-LINKED IMMUNOSORBENT ASSAY

We developed a polyclonal antibody from egg proteins of the butter clam, Saxidomus purpuratus, to quantify eggs using an enzyme-linked immunosorbent assay (ELISA). SDS-PAGE showed that the egg protein was composed of several peptides with molecular weights of 247, 200, 99, 91, 54 and 47 kDa. An immunoblotting assay indicated that the egg-specific antibodies were developed from the 200 and 99 kDa peptides. The rabbit anticlam egg IgG was able to detect as little as 0.078 μg/mL of S. purpuratus egg protein by ELISA. A weight-normalized gonadosomatic index (GSI, mg dry egg/mg dry tissue) was determined to follow the monthly changes in egg production of the clams. Clam-egg protein could be detected by ELISA during the entire sampling period (December to July), and GSI ranged from 0.035 (December) to 0.156 (February). The fecundity of the clams was measured from two spawning peaks in February and May and was estimated to be 22.6 million eggs (GSI of 0.16) in February and 16 million eggs in May (GSI of 0.15). The indirect ELISA used in this study was rapid, affordable and sensitive enough to assess minute amounts of egg protein, which is difficult to measure using traditional methods such as induced spawning or histology.

Assessing the reproducibility and reliability of estuarine bivalve shells ( Saxidomus giganteus) for sea surface temperature reconstruction: Implications for paleoclimate studies

Studies using oxygen isotopes (δ 18O) of mollusk shells to determine paleotemperature need to assume water δ 18O values, which could severely influence calculated temperatures. We analyzed aragonitic shells of the Butter Clam, Saxidomus giganteus (DeShayes, 1839), to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature. Furthermore, carbon isotopes are also investigated as an environmental proxy. The abundance of well-preserved S. giganteus shells in archeological and geological deposits in northwestern North America makes them a particularly suitable species for paleoclimate studies. Seasonally resolved stable oxygen isotope profiles in three S. giganteus shells collected from the same site in Puget Sound (Washington, USA) were well correlated (0.77 < R 2 < 0.87). Although there were differences up to 0.58‰ in high resolution δ 18O profiles of the three shells, the difference between the average δ 18O of each shell was less than half of this (0.19‰) and half of what has been reported for between-colony coral variability. δ 13C profiles on the other hand were more complex, with shell δ 13C being about 2.5‰ lower than expected equilibrium values. However, this roughly conforms to the idea that about 10% of the shell carbon originates from metabolic CO 2. Both δ 18O and δ 13C indicate that S. giganteus do not grow during periods of reduced salinity. Despite the excellent reproducibility of δ 18O between shells, and the fact that salinity effects were duly considered, calculated temperature still differed from instrumental temperature. Applying different salinity–δ 18O water relationships to average shell δ 18O, and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1.7 to 6.4 °C warmer than measured. Although we could not determine if S. giganteus precipitate their shells in isotopic equilibrium, we believe that the difficulty in predicting temperature arose from not being able to accurately determine δ 18O of the water at the time of shell precipitation. These data highlight the difficulties inherent to using stable isotope profiles of estuarine biogenic carbonates as environmental proxies.

Strong biological controls on Sr/Ca ratios in aragonitic marine bivalve shells

It is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments. Sr/Ca ratios have been successfully used as a temperature proxy in corals and sclerosponges. Previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on Sr/Ca ratios. As many studies have used bivalve growth rates to determine temperature, we tested if Sr/Ca ratios could predict temperature through its relationship with growth rate. Shells from the two species of clams from the same family (veneroidea) studied here, Saxidomus giganteus and Mercenaria mercenaria, show vastly different seasonal Sr/Ca profiles. A strong relationship between average annual Sr/Ca ratios and annual growth rate was found in S. giganteus shells from both Washington (R2 = 0.87) and Alaska (R2 = 0.64), USA, but not in M. mercenaria shells from North Carolina, USA. Furthermore, the Sr/Ca–growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in S. giganteus (R2 = 0.73). Although there were significant positive correlations between Sr/Ca ratios and temperature in S. giganteus shells, the correlations were weak (0.09 &lt; R2 &lt; 0.27), and thus Sr/Ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves. It is clear from this study that Sr/Ca ratios are not under thermodynamic control in either clam species, since thermodynamics predict a negative correlation between Sr/Ca ratios and temperature in aragonite. This points toward dominance of biological processes in the regulation of Sr2+. This is also reflected by the largely differing Sr/Ca partition coefficients (DSr) in these shells (DSr ≈ 0.25), when compared to inorganic, coral, and sclerosponge studies (DSr ≈ 1), all of which show a negative dependence of Sr/Ca on temperature. We suggest that caution be taken when using Sr/Ca in any biogenic aragonite as a temperature proxy when the DSr greatly deviates from one, as this indicates the dominance of biological controls on Sr/Ca ratios.

Chemosensory responses and foraging behavior of the seastar Pycnopodia helianthoides

Chemical cues released by damaged or dead organisms can affect how and where benthic organisms feed. These cues may cause predators to act as opportunistic scavengers in lieu of their normal predatory role. A scavenger, as defined in this study, is an organism that consumes damaged and/or dead organisms. In-situ experiments were performed to determine how the seastar Pycnopodia helianthoides (Brandt) reacts in the presence of chemical cues from one of its prey species, the butter clam Saxidomus giganteus (Deshayes), using both intact and damaged individuals. The results of these experiments suggest that P. helianthoides use their chemosensory abilities to locate damaged/dead prey. The role of current in propagating chemical cues was paramount in this foraging activity. P. helianthoides chose damaged prey over live prey even when live prey was encountered en route to the damaged individual. This study suggests that chemical cues emitted from damaged or dead individuals may cause significant changes in foraging tactics of key predators, thus altering food-web dynamics.

Decoding nonlinear growth rates in biogenic environmental archives

The record of an environmental proxy along a growth axis in biogenic carbonates can reflect changing environmental conditions experienced during the lifetime of the organism. When a chronology of the growth axis is not available, a method based on anchor points is commonly used to introduce a time grid. Between these anchor points a constant growth rate is generally assumed, despite the fact that growth rates change during life in most organisms. Here, we present a method which refines the constant growth rate assumption, at least in situations where the environmental proxy has a periodic component in its signal. A nonlinear growth rate can then be estimated, enabling the construction of a more realistic time base. The anchor point method and the method proposed here are first compared on a synthetic record. It is shown that the choice of the anchor points, which is always a subjective one, is largely influenced by the stochastic noise on the data record. This results in biased growth rate profiles and biased time grids. Next we apply the method on the Mg record in the bivalve Isognomon ephippium, on three samples of the clam Saxidomus giganteus from Washington State and on the Vanuatu coral stable isotope record. The method developed is applicable to a wide range of proxy records, which are measured along an indirect time grid and are complicated by nonlinear accretion rates. Furthermore, this method which takes variable growth rates into account opens perspectives on quantitative modeling of the relationship between environmental proxies recorded by accretive archives and the instrumental record, like temperature or salinity.

Harmful algal bloom toxins protect bivalve populations from sea otter predation

We demonstrate how harmful algal bloom (HAB) toxins can mediate the strength of consumer-prey interactions, and thus ecosystem level patterns and processes, by altering the foraging behavior of a keystone marine predator (sea otter Enhydra lutris). Our approach was to com- pare sea otter foraging behavior, diet, prey abundance and paralytic shellfish poisoning toxins (PSPT) across a range of sites within the Inside Passage of southeast Alaska recently occupied by sea otters. Sea otters in southeast Alaska modified their foraging behaviors depending on concentrations of PSPT in bivalve prey, especially their preferred prey, butter clams Saxidomus giganteus. At sites of intermediate prey toxicity (200 to 500 µg saxitoxin (STX) eq · 100 g -1 ), otters continued to forage on butter clams while discarding the most toxic body parts. At highly toxic sites (prey toxicity > 500 µg STX eq · 100 g -1 ) otters avoided butter clams and other large and abundant but toxic bivalve prey, and consumed smaller and/or less abundant non-toxic species. Butter clams were larger and more abundant in highly toxic feeding areas, supporting the hypothesis that PSPT toxicity provides a refuge from sea otter predation.

Quantification of Reproductive Output of the Butter Clam, Saxidomus purpuratus(Sowerby, 1852) Using Enzyme-Linked Immunosorbent Assay (ELISA)

An immunological method was developed in this study to quantify reproductive output of the female butter clam, Saxidomus purpuratus. A clam egg-specific polyclonal antibody was developed using the purified butter clam egg as an antigen. An indirect Enzyme-Linked Immunosorbent Assay (ELISA) was used in quantitative measurement of the eggs. Size of the butter clam eggs ranged from <TEX>$70.81{\pm}7.52{\mu}m$</TEX> in histology or <TEX>$88.56{\pm}11.31{\mu}m$</TEX> in intact eggs. The predominant egg constituent was protein (37.44%), followed by lipids (11.40%) and carbohydrates (9.68%). The SDS-PAGE showed that the egg proteins are composed of several peptides of molecular weights consisting of 247, 200, 99, 91, 54 and 47 kDa. ELISA indicated that the clams collected from Geoje Island in May 2002 produced 8.2 to 26.8% of their body weight as eggs or 9,307,309 to 31,156,333 with a mean of 16,931,893 eggs per individual clam. The results of this study thus suggest that indirect ELISA using rabbit anti-clam egg IgG as a primary antibody is a rapid, affordable and sensitive method to assess reproductive output of 5. purpuratus and possibly other bivalves using a small amount of eggs.

Malacological insights into the marine ecology and changing climate of the late Pleistocene – early Holocene Queen Charlotte Islands archipelago, western Canada, and implications for early peoples

The first intertidal species to colonize the Queen Charlotte Islands archipelago along the northeastern Pacific margin of Canada after the last glacial maximum (LGM) was Macoma nasuta at 13 210 ± 80 14C years BP. Prior to this time, molluscs were likely excluded where grounded ice extended from the 2 km thick Cordilleran ice sheet on mainland British Columbia. Low water temperatures, high sedimentation rates, high turbidity, dilution, and low primary productivity limited invertebrate colonization subsequent to the LGM, a period of rapid sea-level and climate change. As an adult, M. nasuta is a facultative deposit-suspension feeder that tolerates high turbidity and lowered salinity, and its pediveligers and early juveniles must also have been able to survive these conditions. Subsequently, in addition to M. nasuta, Macoma irus (inquinata), Saxidomus giganteus, Protothaca staminea, Protothaca tenerrima, Hiatella pholadis, Clinocardium nuttallii, and Mytilus trossulus constituted a typical intertidal bivalve assemblage. These findings are explained in terms of the physiology, feeding mechanisms, development, and sediment preferences of living molluscs. The disappearance of most bivalve species between ~11 000 and 10 000 14C years BP indicates the onset of a short interval of low sea-surface temperatures coincident with the Younger Dryas cooling event. Some cold-hardy species persisted, including Clinocardium californiense, Mya truncata, and Serripes groenlandicus. Bivalve species not previously reported as Pleistocene fossils were collected in sediments dating older than 10 000 14C years BP. They include Macoma incongrua, Musculus taylori, Mytilimeria nuttallii, and Tellina nuculoides. Fossil assemblages of intertidal molluscs are used to map ancient shorelines and indicate which species were available as a subsistence resource for early peoples from at least 13 210 ± 80 14C years BP. Intertidal food biomass densities may have reached present commercially harvested levels on southern Moresby Island by 8800 ± 70 14C years BP and on northern Graham Island by 8990 ± 50 14C years BP. When early peoples might have been migrating along the littoral zone, the molluscan productivity of the outer coast was much higher than it is at present.

Direct Competitive Enzyme-Linked Immunosorbent Assay for Saxitoxin and Neosaxitoxin

Using specific ployclonal antibodies against saxitoxin (STX) or neosaxitoxin (neo-STX) in combination with either STX−horseradish peroxidase (HRP) or neo-STX−HRP, the efficacy of four different direct competitive enzyme-linked immunoassorbent assay (dc-ELISA) formats for the analysis of STX and neo-STX was evaluated. Concentrations causing 50% inhibition (ID50) of binding of toxin−HRP conjugate to the antibodies by free toxins in various ELISAs were found in the range of 0.1−9.0 ng/mL. A dc-ELISA, using either anti-STX/STX−HRP or anti-neo-STX/neo-STX−HRP pairs (ID50 values of 0.28 and 0.18 ng/mL for STX and neo-STX, respectively), was found to be most effective for the analysis of STX and neo-STX in naturally contaminated shellfish samples. The analytical recoveries of STX added to viscera extracts of butter clams, dungeness crab, tanner crab, and blue mussels in the range of 0.5−10 ng/mL-1 g-1 were found to be 88.1, 92.7, 92.2, and 93.5% with coefficients of variation of 3.9, 2.7, 9.7, and 2.8%, respecti...

DIET AND FORAGING BEHAVIOR OF SEA OTTERS IN SOUTHEAST ALASKA

Abstract: Direct observations of feeding sea otters (Enhydra lutris) at 11 sites in southeast Alaska showed infaunal clams to be the primary prey utilized by otters throughout the region. Foraging dive times associated with clam and sea urchin prey were significantly longer than those for more easily captured prey (crabs and mussels). Dive times and surface intervals were also generally correlated with water depth or apparent difficulty in obtaining buried prey. Male otters, which fed more extensively on clams than females, made significantly longer foraging dives than females. Foraging success remained high, even at sites where prey numbers were found to be very low during a related study. The very deeply burrowing geoduck clam (Panope abrupta), while common at several otter feeding sites, was rarely captured by otters. These results, combined with those of a companion study on prey numbers, indicate that butter clams (Saxidomus giganteus) account for the majority of the sea otter diet in southeast Alaska, and that sea urchins may represent relatively short‐term prey in comparison to infaunal bivalves in regions where both prey types co‐exist. Furthermore, the importance of butter clams in the sea otter diet and the tendency for this bivalve to retain chronically high levels of paralytic shellfish poisoning toxins in southeast Alaska increases the probability that toxic phytoplankton blooms influence sea otter distribution in this region.

Cross-reacting antigens in the butter clam ( Saxidoma giganteus) and their relationship to total paralytic shellfish poison toxicity

A specific protein with an apparent mol. wt of 23,000 was identified in foot homogenate derived from paralytic shellfish poisoning (PSP) contaminated butter clams and was found to cross-react with crab-saxitoxin-induced protein (SIP) antiserum. Antiserum, once cross-absorbed against non-toxic shellfish material, was incubated with tissue homogenate derived from 52 butter clams with varying total PSP toxicities in a prototype ELISA. A significant ( r = 0.83; P < 0.001) correlation existed between soluble clam antigen content in foot homogenate and total PSP toxicity; the latter measured by the mouse lethality bioassay. From the ELISA results, a soluble antigen threshold of 0.1% total protein was successfully used to distinguish between PSP toxic and non-toxic butter clams. It is proposed that this type of screening assay could be used in conjunction with the standard mouse bioassay to increase PSP monitoring and potentially reduce unnecessary animal testing.

Presence of paralytic shellfish poisoning toxins and soluble proteins in toxic butter clams (Saxidomus giganteus)

Butter clams obtained from a variety of locations along the northern British Columbia coast were assayed for the presence of individual paralytic shellfish poisoning toxins (PSPT) by HPLC and total PSPT toxicity using the mouse bioassay. Specific organs, namely the siphon, adductor muscle, foot and mantle were examined for soluble antigens that crossreacted with crab Saxitoxin-Induced Protein (SIP) using immunochemical (Western blotting) techniques. Butter clams containing high concentrations of PSPT also had several proteins that crossreacted with crab anti-SIP serum. In particular, soluble proteins with distinctly different molecular weights were found in the siphon and foot, respectively, in toxic shellfish. These proteins were absent in nontoxic butter clams. The concept of using PSPT-induced proteins in the butter clam as a screen for identifying toxic shellfish is introduced.

Influenoe of sea otters on soft-bottom prey communities in southeast Alaska

Sea otters Enhydra lutris, well documented as 'keystone' predators in rocky marine communities, were found to exert a strong influence on infaunal prey communities in soft-sediment habitats. The effect of sea otter predation in subtidal soft-bottom prey communities in southeast Alaska was evaluated via a natural experiment comparing prey populations in similar habitats with and without sea otters. Results indicate that otters forage primarily on bivalve prey, especially the butter clam Saxidomus giganteus and dramatically reduce infaunal bivalve and sea urchin (Strongylocentrotus spp.) prey populations. Bivalve prey abundance, biomass and size were negatively correlated with sea otter occupancy. Otter-cracked shells of the deep-burrowing clams Tresus capax and Panope abrupta were rarely found, even at otter foraging sites where these clams accounted for the majority of available prey biomass, suggesting that these species have a partial depth refuge from otter predation. The differential impacts of otter predation on prey populations suggest that infaunal bivalves provide a more sustainable food base than do sea urchins.

44] Overview of toxins and drugs as tools to study excitable membrane ion channels: II. Transmitter-activated channels

Publisher Summary This chapter discusses the mechanisms of action of toxins and drugs to study the excitable membrane channels. Many chemicals are known to act on voltage-activated sodium channels, and several of them are employed as useful tools in the laboratory because of their specific or unique actions on ion channels. Chemicals acting on sodium channels may be classified into two large groups—namely, blockers and modulators. Tetrodotoxin (TTX) is a potent neurotoxin contained in the ovary and fiver of puffer fish, while saxitoxin (STX) is contained in the toxic Alaska butter clam Saxidoma giganteus, but the toxin actually derives from the dinoflagellate Gonyaulax catanella. Both TTX and STX exert an identical effect on the nerve membrane. Procaine and cocaine are found to block both sodium and potassium channels of squid giant axons. The enzyme pronase is a blocker of sodium channel inactivation, and is extensively to analyze the kinetics of sodium channel activation.

43] Overview of toxins and drugs as tools to study excitable membrane ion channels: I. Voltage-activated channels

This chapter discusses the mechanisms of action of toxins and drugs to study the excitable membrane channels. Many chemicals are known to act on voltage-activated sodium channels, and several of them are employed as useful tools in the laboratory because of their specific or unique actions on ion channels. Chemicals acting on sodium channels may be classified into two large groups—namely, blockers and modulators. Tetrodotoxin (TTX) is a potent neurotoxin contained in the ovary and fiver of puffer fish, while saxitoxin (STX) is contained in the toxic Alaska butter clam Saxidoma giganteus, but the toxin actually derives from the dinoflagellate Gonyaulax catanella. Both TTX and STX exert an identical effect on the nerve membrane. Procaine and cocaine are found to block both sodium and potassium channels of squid giant axons. The enzyme pronase is a blocker of sodium channel inactivation, and is extensively to analyze the kinetics of sodium channel activation.

Paralytic shellfish toxins sequestered by bivalves as a defense against siphon-nipping fish

Saxidomus giganteus (butter clams), are known to sequester diet-derived paralytic shellfish toxins (PST), highly potent neurotoxins, in their siphons. Captive staghorn sculpins (Leptocotus armatus), a marine fish species known to crop bivalve siphons, developed a significant aversion to siphons from toxic but not non-toxicS. giganteus following a single conditioning feeding of toxic siphon tissues. Control fish showed no aversive response to siphons from non-toxicS. giganteus during 11 feeding sessions over 56 d. Aversive and non-aversive behavior varied with the toxicity of the siphons, but not with the geographic origin of the clams. Both experimental and control fish ate freely and showed no aversion to siphons from toxic littleneck clams (Protothaca staminea). Littleneck clams, unlikeS. giganteus, retain PST in their visceral mass but not in their siphons. Both toxic and non-toxicS. giganteus extended their siphons significantly more often and higher above the sediment surface during dark hours, but toxicS. giganteus extended their siphons higher than non-toxic individuals. These results support the hypothesis that siphon-nipping by fish may have selected for the retention of PST in butter clam siphons as a chemical defense.

Paralytic shellfish poisoning toxins mediate feeding behavior of sea otters

Captive sea otters (Enhydra lutris)fed live Saxidomus giganteus (butter clams) ad libitum either reduced their prey capture and consumption rates or discarded the highly toxic siphons and kidneys when switched from clams containing very low levels of saxitoxin [37±9 µg STX (100 g)−1] to highly toxic clams [226±96 µg STX (100 g)−1]. Feeding rates returned to pretreatment levels when the otters were again switched to low‐toxicity clams, but siphon discard frequency remained high. Paralytic shellfish poisoning symptoms were observed only in an otter calculated to have consumed the most STX (154 µg kg−1 d−1), a dosage within the range of oral LD50s reported for other nonprimate mammals. None of the other otters displayed symptoms, and all subjects were eventually released in good health. These findings suggest that otters are not immune to paralytic shellfish poisoning toxins (PSPT) and that they have the ability to detect and avoid consumption of lethal amounts of toxic prey. This behavioral response is highly adaptive given the importance of butter clams in sea otter diets, and the chronic toxicity of butter clams in areas where toxic dinoflagellate blooms occur. A comparison of the distributions of otters and toxicity levels of butter clams in southeast Alaska suggests that the sequestering of PSPT may protect some clam populations from otter predation and limit the distribution of otters to the exposed outer coast where toxic clams are rare.

Relative insensitivity of butter clam neurons to saxitoxin; a pre-adaptation for sequestering paralytic shellfish poisoning toxins as a chemical defense

Relative insensitivity of butter clam neurons to saxitoxin; a pre-adaptation for sequestering paralytic shellfish poisoning toxins as a chemical defense

Pumping Rates, Water Pressures, and Oxygen Use in Eight Species of Marine Bivalve Molluscs from British Columbia

Pumping characteristics and oxygen utilization for Solemya reidi, Yoldia thraciaeformis, Chlamys hastata, Mytilus edulis, Crassostrea gigas, Clinocardium nuttallii, Saxidomus giganteus, and Mya truncata were studied. Pressures were recorded using a Yale A79 spinal tap needle inserted in the pallial cavity or siphonal aperture. Pumping volumes were determined through particulate analysis using a Model B Coulter counter and oxygen consumption by standard Winkler titration modified for small samples. The species chosen were selected to represent progressive increases in gill complexity and siphon length. The minimum pressure differential across the gill (20 Pa) was observed for Y. thraciaeformis while the maximum pressure gradient (600 Pa) was recorded for M. truncata. Pumping rates varied from 1.41 L∙h−1∙g−1 (Y. thraciaeformis) to 4.71 L∙h−1∙g−1 (C. hastata) and species with siphons tended to pump at lower rates. The deeply burrowing M. truncata consumed 3.5 times as much oxygen (0.63 mL O2∙h−1∙g−1) as S. reidi (0.18 mL O2∙h−1∙g−1) which inhabits anoxic environments. For all species, the metabolic cost of pumping was less than 1% of the total oxygen uptake.