Mussel Mytilus Californianus Research Articles

Body temperature during low tide alters the feeding performance of a top intertidal predator

Although the direct effects of climate change on species distribution and abundance have become increasingly apparent, considerably less is known about the potential for thermal variations to influence community structure indirectly through altered species interactions. We examined how the low tide body temperature of the rocky intertidal sea star Pisaster ochraceus affected the rate at which this keystone species fed on the mussel Mytilus californianus. Patterns of intertidal distribution and sea star body temperatures were recorded in the field at Bodega Bay, California, in 2006 and 2007. Under controlled laboratory conditions, we separately examined the roles of short‐term (acute) and long‐term (chronic) exposures to high aerial body temperatures in driving patterns of feeding and growth. Upper limits to thermal tolerance were also quantified in the laboratory. Integrating field data on the vertical distribution, microhabitat, and body temperature of sea stars indicated that individuals typically experienced relatively high body temperatures over a series of short periods of time (acute exposures of a few days) and that they escaped from situations where they would have experienced such temperatures for longer periods (chronic exposure). Although sea stars never approached their upper thermal limit (35°C), laboratory trials demonstrated that chronic exposure to realistic peak aerial body temperatures (≥23°C) negatively affected both feeding and growth rates, whereas acute exposure had positive consequences on feeding rates but no effects on growth. Variations in aerial body temperature, and more specifically the frequency of exposure to high body temperatures, can influence interaction strength in this important predator‐prey system.

Seasonal stability in Late Holocene shellfish harvesting on the central California coast

Oxygen isotope determinations from 92 California mussel ( Mytilus californianus) shells from ten archaeological sites in central coastal California show relatively stable seasonal harvesting patterns between 3600 CAL BP and historic contact (AD 1769). Coastal occupants harvested mussels nearly year-round and seem to have occupied individual residential bases throughout the seasonal cycle. Interior groups returned with mussels from the coast mostly in the spring and early summer, but almost never in the late summer/early fall when nut crops were harvested. These findings suggest two inter-dependent groups with distinct seasonal settlement strategies: inland people, reliant on acorns and other nut crops harvested in the fall, and coastal inhabitants who were less involved with acorns. This pattern is supported by accounts recorded by the first Spanish explorers in AD 1769. While some interior groups may have been seasonally migrating “collectors,” coastal populations were less mobile, inhabiting individual residential sites throughout the year, albeit not necessarily on a permanent basis. These findings highlight the strong influence of coastal environments and resources on hunter-gatherer mobility.

Gene expression in the intertidal mussel Mytilus californianus: physiological response to environmental factors on a biogeographic scale

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 356:1-14 (2008) - DOI: https://doi.org/10.3354/meps07354 Gene expression in the intertidal mussel Mytilus californianus: physiological response to environmental factors on a biogeographic scale Sean P. Place, Michael J. O’Donnell, Gretchen E. Hofmann* Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California 93106-9610, USA *Corresponding author. Email: hofmann@lifesci.ucsb.edu ABSTRACT: We used a cDNA microarray to profile gene expression in the intertidal mussel Mytilus californianus across major portions of its biogeographic range. Overall, the expression pattern for the majority of genes assessed in this study varied significantly as a function of collection site and provides support for the hypothesis that the physiological response to emersion is distinct across populations of M. californianus. Gill tissue was dissected from adult, field-acclimatized M. californianus collected from 4 sites across 17° of latitude along the west coast of North America. First-strand cDNA prepared from 5 biological replicates from each site were competitively hybridized to a 2496 feature cDNA microarray. Gene expression patterns in mussels from Strawberry Hill, Oregon, displayed a unique expression phenotype that was distinct from the other 3 mussel populations sampled. In contrast, mussels sampled from Bamfield, British Columbia, and Jalama Beach, California, showed similar expression patterns. These data suggest that the physiological response of M. californianus to abiotic factors, such as temperature, cannot be predicted by a simple latitudinal gradient. This study highlights the usefulness of genomics-based approaches in assessing physiological responses to environmental variation across large spatial scales. KEY WORDS: Environmental genomics · Mytilus californianus · DNA microarray · Biogeography · Gene expression · Species range · Intertidal invertebrates · Mussel Full text in pdf format NextCite this article as: Place SP, O’Donnell MJ, Hofmann GE (2008) Gene expression in the intertidal mussel Mytilus californianus: physiological response to environmental factors on a biogeographic scale. Mar Ecol Prog Ser 356:1-14. https://doi.org/10.3354/meps07354 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 356. Online publication date: March 18, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Holdfast heroics: comparing the molecular and mechanical properties ofMytilus californianusbyssal threads

The marine mussel Mytilus californianus Conrad inhabits the most wave-exposed regions of the rocky intertidal by dint of its extraordinary tenacity. Tenacity is mediated in large part by the byssus, a fibrous holdfast structure. M. californianus byssal threads, which are mechanically superior to the byssal threads of other mytilids, are composed almost entirely of a consortium of three modular proteins known as the preCols. In this study, the complete primary sequence of preCols from M. californianus was deduced and compared to that of two related species with mechanically inferior byssal threads, M. edulis Linnaeus and M. galloprovincialis Lamarck in order to explore structure-function relationships. The preCols from M. californianus are more divergent from the other two species than they are from one another. However, the degree of divergence is not uniform among the various domains of the preCols, allowing us to speculate on their mechanical role. For instance, the extra spider silk-like runs of alanine-rich sequence in the flanking domains of M. californianus may increase crystalline order, enhancing strength and stiffness. Histidine-rich domains at the termini, in contrast, are highly conserved between species, suggesting a mechanical role common to all three. Mechanical testing of pH-treated and chemically derivatized distal threads strongly suggests that histidine side chains are ligands in reversible, metal-mediated cross-links in situ. By combining the mechanical and sequence data, yield and self-healing in the distal region of threads have been modeled to emphasize the intricate interplay of enthalpic and entropic effects during tensile load and recovery.

Response of a rocky intertidal ecosystem engineer and community dominant to climate change

To evaluate how climate change might impact a competitively dominant ecological engineer, we analysed the growth response of the mussel Mytilus californianus to climate patterns [El Niño-Southern Oscillation, Pacific Decadal Oscillation (PDO)]. Mussels grew faster during warmer climatic events. Growth was initially faster on a more productive cape compared to a less productive cape. Growth rates at the two capes merged in 2002, coincidentally with a several year-long shift from warm to cool PDO conditions. To determine the mechanism underlying this response, we examined growth responses to intertidal sea and air temperatures, phytoplankton, sea level and tide height. Together, water temperature (32%) and food (12.5%) explained 44.5% of the variance in mussel growth; contributions of other factors were not significant. In turn, water temperature and food respond to climate-driven variation in upwelling and other, unknown factors. Understanding responses of ecosystem engineers to climate change will require knowing direct thermal effects and indirect effects of factors altered by temperature change.

INTERTIDAL INVERTEBRATES LOCALLY ENHANCE PRIMARY PRODUCTION

The contribution of autochthonous vs. allochthonous inputs to productivity is an important determinant of ecosystem function across multiple habitats. In coastal marine systems, nutrients are thought to come primarily from the upwelling of deep, nutrient-rich water. Using experimental manipulations of a dominant tide pool animal, the mussel Mytilus californianus, I show that the presence of mussels greatly increases the supply of inorganic nitrogen and phosphorus. Mussels further had a direct effect on productivity: benthic microalgal abundance increased by a factor of 4-8, while the growth of a red alga was four times greater in the presence of mussels. The increase in nitrite and nitrate associated with mussels further suggests nitrifying activity by microbes. These findings have broad implications for coastal marine systems, including that regenerated nutrients may contribute more to productivity than previously recognized and that the presence of animal-generated nutrients sets the stage for numerous positive interactions.

MOSAIC PATTERNS OF THERMAL STRESS IN THE ROCKY INTERTIDAL ZONE: IMPLICATIONS FOR CLIMATE CHANGE

We explicitly quantified spatial and temporal patterns in the body temperature of an ecologically important species of intertidal invertebrate, the mussel Mytilus californianus, along the majority of its latitudinal range from Washington to southern California, USA. Using long-term (five years), high-frequency temperature records recorded at multiple sites, we tested the hypothesis that local ''modifying factors'' such as the timing of low tide in summer can lead to large-scale geographic mosaics of body temperature. Our results show that patterns of body temperature during aerial exposure at low tide vary in physiologically meaningful and often counterintuitive ways over large sections of this species' geographic range. We evaluated the spatial correlations among sites to explore how body temperatures change along the latitudinal gradient, and these analyses show that ''hot spots'' and ''cold spots'' exist where temperatures are hotter or colder than expected based on latitude. We identified four major hot spots and four cold spots along the entire geographic gradient with at least one hot spot and one cold spot in each of the three regions examined (Washington- Oregon, Central California, and Southern California). Temporal autocorrelation analysis of year-to-year consistency and temporal predictability in the mussel body temperatures revealed that southern animals experience higher levels of predictability in thermal signals than northern animals. We also explored the role of wave splash at a subset of sites and found that, while average daily temperature extremes varied between sites with different levels of wave splash, yearly extreme temperatures were often similar, as were patterns of predictability. Our results suggest that regional patterns of tidal regime and local pattern of wave splash can overwhelm those of large-scale climate in driving patterns of body temperature, leading to complex thermal mosaics of temperature rather than simple latitudinal gradients. A narrow focus on population changes only at range margins may overlook climatically forced local extinctions and other population changes at sites well within a species range. Our results emphasize the importance of quantitatively examining biogeographic patterns in environ- mental variables at scales relevant to organisms, and in forecasting the impacts of changes in climate across species ranges.

Spatial patterns of growth in the mussel, Mytilus californianus, across a major oceanographic and biogeographic boundary at Point Conception, California, USA

The Point Conception, California, USA region (hereafter PC) is one of the most important biogeographic and oceanographic discontinuities on the US west coast. Here we address how mesoscale oceanographic variability in the region around PC affects the growth of the competitively dominant species in the rocky intertidal assemblage: the mussel Mytilus californianus. Strong upwelling and high wave exposure dominate the California coast north of PC, and weak, seasonal upwelling and warmer water temperatures are characteristic of the region south/east of PC. We hypothesized that the oceanographic gradients in temperature, upwelling, wave exposure and productivity around PC would exert strong bottom–up influences on growth rates of mussels, potentially underlying large-scale differences in community structure around the PC region. We evaluated these predictions by measuring mussel growth rates across the PC region both in the intertidal and offshore on moorings. Intertidal mussels grew at much higher rates at sites south relative to north of PC and growth rates decreased in a gradient from south to north. The gradient in intertidal mussel growth around PC was uncorrelated with inshore concentrations of chlorophyll-a, and was most strongly correlated with the alongshore gradient in wave exposure and intertidal temperature. Mussels on moorings offshore from the intertidal sites grew at much higher rates than those in the corresponding intertidal areas, and mussel growth rates did not differ significantly among moored locations around PC. The gradient of increasing temperature from north to south among mooring sites was correlated with a decreasing gradient in productivity in the same direction, potentially contributing to equal and opposite effects on mussel growth at offshore moorings. This study suggests that environmental factors such as cold temperatures and high wave exposure contribute to the spatial pattern of decreasing mussel growth rates from south to north around PC, underlying large-scale patterns of community structure in this region.

Distribution, abundance, size and recruitment of the mussel, Mytilus californianus, across a major oceanographic and biogeographic boundary at Point Conception, California, USA

The Point Conception, California, USA region (hereafter PC) is one of the most important biogeographic and oceanographic discontinuities on the US west coast. Here we address how mesoscale oceanographic and environmental variability in the region around PC, CA may influence the distribution, abundance and size of the mussel Mytilus californianus, a competitively dominant species in rocky intertidal assemblages along the northeast Pacific. Strong upwelling and high wave exposure dominate the California coast north of PC, and weak, seasonal upwelling and warmer water temperatures are characteristic of the region south/east of PC. We hypothesized that the gradient in temperature, upwelling, and wave exposure around PC would greatly influence patterns of recruitment and abundance of mussels, potentially underlying large-scale differences in community structure. We evaluated these predictions by surveying intertidal community structure, mussel distribution, size, abundance and recruitment at a range of intertidal sites around PC. We found that intertidal communities north of PC were dominated mainly by macrophytes, while mussels and barnacles were relatively scarce. Intertidal communities south of PC were dominated by mussels and barnacles, with a low abundance of macrophytes. Mussels were larger and mussel beds were more expansive and extended lower in elevation at sites ranging from north to south around PC. At northern sites, high abundances of sea star predators and elevated wave exposure effectively displaced the entire mussel zone upwards. We found no differences in the numbers of mussel recruits to sites around PC, suggesting that spatial patterns of mussel abundance were not driven by differential recruitment. These results suggest that unlike other well-studied systems, supply of benthic larvae does not underly the large-scale gradient in community structure around PC. We suggest that environmental conditions favorable to macroalgal growth north of PC, and conditions favorable to filter-feeder growth south of PC may underly mesoscale patterns of intertidal community structure in this region.

New Perspectives on Perfluorochemical Ecotoxicology: Inhibition and Induction of an Efflux Transporter in the Marine Mussel, Mytilus californianus

The toxicological effects of perfluoroalkyl acids on the p-glycoprotein (p-gp) cellular efflux transporter were investigated using the marine mussel Mytilus californianus as a model system. Four of the perfluoroalkyl acids studied exhibit chemosensitizing behavior, significantly inhibiting p-gp transporter activity. The inhibitory potency is maximal for the longer chain acids perfluorononanoate (PFNA) and perfluorodecanoate (PFDA), with average IC50 values of 4.8 and 7.1 microM, respectively. Results indicate that PFNA inhibits p-gp by an indirect mechanism, and this inhibition is reversible and accompanied by a rapid loss of PFNA from the tissue. In addition, PFNA induces expression of the p-gp transporter after a 2-h exposure, a stress response that may result in a metabolic cost to the organism. Given that most organisms, including humans, share efflux transporters as a first line of defense against toxicants, the results of this study may have broader implications for the ecotoxicology of perfluoroalkyl acids.

Complex patterns of expression of heat‐shock protein 70 across the southern biogeographical ranges of the intertidal mussel Mytilus californianus and snail Nucella ostrina

AbstractAim It is often assumed that species reach their highest densities in the centre of their ranges and decline in abundance toward the edges of the range. Implicit in this notion, which we call the abundant centre hypothesis, is the assumption that the edges of the range are more stressful to organisms and are more likely to show responses to climate change. However, an earlier review and empirical study of patterns of abundance across the range of intertidal invertebrates show little support for the abundant centre hypothesis and further demonstrated that few studies have examined patterns in either abundance or stress across species ranges. In part this gap is due to the logistical difficulties of sampling species across large geographical ranges. Here we use intertidal invertebrates, which have relatively simple linear latitudinal ranges, and heat‐shock proteins, which have been shown to be an integrative measure of organismal stress, to test the hypothesis that species are more stressed at the edges of their range. We use complementary data on population density to test the relationship between stress proteins and overall species density across the species’ range.Location Our sampling programme covered the southern half of the large geographical ranges of two intertidal invertebrates on the Pacific Coast of North America. Sites were spread between northern Baja California, Mexico and Vancouver Island, Canada, a range of c. 22 degrees of latitude.Method We sampled levels of heat‐shock protein 70 (Hsp70) in eight to 12 individuals from each of 20 sites for the intertidal mussel Mytilus californianus and 11 sites for the intertidal snail Nucella ostrina, spread throughout the southern half of their geographical ranges. The relationships between levels of Hsp70 in individuals from a site and (1) latitude of the site, (2) the site's position in the species’ range and (3) average population density were determined.Results No significant relationship was found in either species between levels of Hsp70 and latitude, position in the range or population density. Complex patterns that did emerge may be explained by nonlinear gradients in environmental conditions along the Pacific coast. Specifically, we observed peak values of Hsp70 for both species in northern Oregon, where intertidal zones are disproportionately exposed to daytime emersion (exposure to air) in the summer months of collections. A second peak for M. californianus was found south of Point Conception, California, which is marked by dramatic shifts toward warmer sea temperatures and decreased wave exposure.Main conclusions Patterns that emerged were not predicted by simple models based on the abundant centre hypothesis. However, they are consistent with more complex pictures of heat stress, organismal condition and abundance along a latitudinal gradient that have been demonstrated in recent studies. We suggest that latitudinal complexity, species‐specific differences and local effects must be considered before generalizing the relationship between environmental stress, abundance, range limits and responses of ranges to climate change.

Long-term change in mussel (Mytilus californianus Conrad) populations along the wave-exposed coast of southern California

Mussel (Mytilus californianus) populations were studied throughout California to determine changes over the past few decades, and, in particular, to determine if declines reported for southern California have occurred outside of the region. We compared mussel cover, biomass, and bed thickness reported in historic studies in the mid-1970s to 1980s with measurements made in 2002. Mussel cover and biomass in southern California declined markedly over the past few decades with a mean cover loss of 31.2% (40.2% loss) and biomass loss of 25.1 kg m−2 (51.3% loss). Changes in mussel bed thickness were not as strong as cover and biomass, but also appeared to decline over time. Declines were limited to the southern California region, since mussel cover, biomass, and bed thickness remained unchanged or increased at sites in central and northern California. Causes for mussel declines in southern California are unknown, but may include human visitation, increased sea surface temperatures, and pollution.

A 6,000 Year Old Red Abalone Midden from Otter Point, San Miguel Island, California

For decades, researchers have been interested in archaeological sites on California's Channel Islands that contain large concentrations of red abalone ( Haliotis rufescens) shells. Known as red abalone middens and dated to between about 7500 and 3500 years ago, these sites have been used to understand broad subsistence patterns, provide chrono-stratigraphic control, and investigate past environmental changes in the region. Most detailed studies have focused on red abalone middens from Santa Cruz Island, with comparatively limited data from other islands. Analysis of a red abalone midden sample excavated from a large dune site on San Miguel Island illustrates the diversity of the red abalone site type and associated human behaviors. Rapid changes in the primary midden constituents, from California mussels ( Mytilus californianus) and sea mammals to red abalones, demonstrate the complexities of differentiating between the effects of environmental change, human food choices, and ecological changes associated with human impacts on local environments.

Evaluation of methods for improved detection of Cryptosporidium spp. in mussels ( Mytilus californianus)

Bivalve molluscs concentrate Cryptosporidium oocysts from fecal-contaminated aquatic environments and are therefore useful in monitoring water quality. A real-time TaqMan polymerase chain reaction (PCR) system was developed to allow for large scale quantitative detection of Cryptosporidium spp. in mussels ( Mytilus californianus). The TaqMan sensitivity and specificity were compared to conventional PCR and direct immunofluorescent antibody (DFA) assays, with and without immunomagnetic separation (IMS), to identify the best method for parasite detection in mussel hemolymph, gill washings and digestive glands. TaqMan PCR and two conventional PCR systems all detected 1 or more oocysts spiked into 1 ml hemolymph samples. The minimum oocyst detection limit in spiked 5 ml gill wash and 1 g digestive gland samples tested by TaqMan PCR and DFA was 100 oocysts, with a 1 log 10 improvement when samples were first processed by IMS. For tank exposed mussels, TaqMan and conventional PCR methods detected C. parvum in < 5% of hemolymph samples. No gill washings from these same mussels tested positive by TaqMan PCR or DFA analysis even with IMS concentration. All methods detected the highest prevalence of C. parvum-positive samples in digestive gland tissues of exposed mussels. In conclusion, the most sensitive method for the detection of C. parvum in oocyst-exposed mussels was IMS concentration with DFA detection: 80% of individual and 100% of pooled digestive gland samples tested positive. TaqMan PCR was comparable to conventional PCR for detection of C. parvum oocysts in mussels and additionally allowed for automated testing, high throughput, and semi-quantitative results.

Polycyclic aromatic hydrocarbons in bivalves from the San Francisco estuary: Spatial distributions, temporal trends, and sources (1993–2001)

Bivalve tissue samples were examined over a range of spatial and temporal scales (1993-2001) to determine PAH distributions, trends, and possible sources. Mussels (Mytilus californianus), oysters (Crassostrea gigas), and clams (Corbicula fluminea) were deployed for three months in the estuary at stations remote from known point source discharges. The range of summation operatorPAH detected in bivalves was oysters 184-6899 microg/kg dry wt (mean 678 microg/kg dry wt), mussels 21-1093 microg/kg dry wt (mean 175 microg/kg dry wt), and clams 78-720 microg/kg dry wt (mean 323 microg/kg dry wt). Linear regression analysis showed no statistically significant (p>0.05) temporal trends in clam and mussel summation operatorPAH at any of the deployment stations or estuary segments. On the other hand, a statistically significant (p<0.05) decreasing trend was found in summation operatorPAH in oysters at the Petaluma River station, and in the North Estuary segment. PAH isomer pair ratios applied as diagnostic indicators suggested that the bioaccumulated PAH were derived primarily from petroleum combustion, with lesser amounts derived from biomass and coal combustion, and unburned petroleum.

Growth of filter-feeding benthic invertebrates from a region with variable upwelling intensity

Coastal upwelling is an ocean feature thought to have important impacts on benthic marine communities by enhancing planktonic productivity in the nearshore environment. In this study, growth rates of 3 species of filter-feeders were examined over a geographic region that includes sites where upwelling is typically weak (south of Point Conception, California, USA) and sites where upwelling is often strong and frequent (at and to the north of Point Conception). The growth of the mussel Mytilus californianus, the gooseneck barnacle Pollicipes polymerus and the acorn barnacle Balanus glandula, as well as the body condition of M. californianus, were all up to 3-6 times higher at sites furthest south of Point Conception, and decreased dramatically moving north around the point. Spatial variation in food availability (measured as chlorophyll a, particulate organic carbon and particulate organic nitrogen) and food quality (measured as C/N ratios) did not explain these patterns of growth. Tidal height of the organisms also failed to account for persistent spatial variation in growth rates. Water temperature varied in a pattern consistent with growth rates (i.e. mean temperatures were warmer in the south), and was the one factor most often selected in stepwise regressions for models contributing to patterns of filter-feeder growth. This study suggests that factors other than, or in conjunction with, productivity may drive large-scale differences in benthic filter-feeder growth rates.

Levels and Distribution of Polybrominated Diphenyl Ethers in Water, Surface Sediments, and Bivalves from the San Francisco Estuary

Polybrominated diphenyl ethers (PBDEs) were found in water, surface sediments, and bivalve samples that were collected from the San Francisco Estuary in 2002. sigmaPBDE concentrations in water samples ranged from 3 to 513 pg/ L, with the highest concentrations found in the Lower South Bay (range 103-513 pg/L) region, which receives approximately 26% of the Estuary's wastewater treatment plant effluents. The sigmaPBDEs in sediments ranged from below detection limits to 212 ng/g dry wt, with the highest concentration found at a South Bay station (212 ng/g dry wt), which was up to 3 orders of magnitude higher than other stations. The sigmaPBDE concentrations ranged from 9 to 64 ng/g dry wt in oysters (Crassostrea gigas), from 13 to 47 ng/g dry wt in mussels (Mytilus californianus), and from 85 to 106 ng/g dry wt in clams (Corbicula fluminea). Only three PBDE congeners were detected in bivalves, BDE-47, BDE-99, and BOE-100; these are the most bioaccumulative congeners from the commercial Penta-BDE mixture.

INVERTEBRATE‐MEDIATED NUTRIENT LOADING INCREASES GROWTH OF AN INTERTIDAL MACROALGA1

Even in nitrogen‐replete ecosystems, microhabitats exist where local‐scale nutrient limitation occurs. For example, coastal waters of the northeastern Pacific Ocean are characterized by high nitrate concentrations associated with upwelling. However, macroalgae living in high‐zone tide pools on adjacent rocky shores are isolated from this upwelled nitrate for extended periods of time, leading to nutrient limitation. When high‐intertidal pools are isolated during low tide, invertebrate‐excreted ammonium accumulates, providing a potential nitrogen source for macroalgae. I quantified the influence of mussels (Mytilus californianus Conrad) on ammonium accumulation rates in tide pools. I then evaluated the effects of ammonium loading by mussels on nitrogen assimilation and growth rates of Odonthalia floccosa (Esp.) Falkenb., a common red algal inhabitant of pools on northeastern Pacific rocky shores. Odonthalia was grown in artificial tide pool mesocosms in the presence and absence of mussels. Mesocosms were subjected to a simulated tidal cycle mimicking emersion and immersion patterns of high‐intertidal pools on the central Oregon coast. In the presence of mussels, ammonium accumulated more quickly in the mesocosms, resulting in increased rates of nitrogen assimilation into algal tissues. These increased nitrogen assimilation rates were primarily associated with higher growth rates. In mesocosms containing mussels, Odonthalia individuals added 41% more biomass than in mesocosms without mussels. This direct positive effect of mussels on macroalgal biomass represents an often overlooked interaction between macroalgae and invertebrates. In nutrient‐limited microhabitats, such as high‐intertidal pools, invertebrate‐excreted ammonium is likely an important local‐scale contributor to macroalgal productivity.

Nitromusk and Polycyclic Musk Compounds as Long-Term Inhibitors of Cellular Xenobiotic Defense Systems Mediated by Multidrug Transporters

Synthetic musk compounds, widely used as fragrances in consumer products, have been detected in human tissue and, surprisingly, in aquatic organisms such as fish and mollusks. Although their persistence and potential to bioaccumulate are of concern, the toxicity and environmental risks of these chemicals are generally regarded as low. Here, however, we show that nitromusks and polycyclic musks inhibit the activity of multidrug efflux transporters responsible for multixenobiotic resistance (MXR) in gills of the marine mussel Mytilus californianus. The IC10 (concentration that inhibits 10%) values for the different classes of musks were in the range of 0.09–0.39 μM, and IC50 values were 0.74–2.56 μM. The immediate consequence of inhibition of efflux transporters is that normally excluded xenobiotics will now be able to enter the cell. Remarkably, the inhibitory effects of a brief 2-hr exposure to musks were only partially reversed after a 24- to 48-hr recovery period in clean seawater. This unexpected consequence of synthetic musks—a long-term loss of efflux transport activity—will result in continued accumulation of normally excluded toxicants even after direct exposure to the musk has ended. These findings also point to the need to determine whether other environmental chemicals have similar long-term effects on these transporters. The results are relevant to human health because they raise the possibility that exposure to common xenobiotics and pharmaceuticals could cause similar long-term inhibition of these transporters and lead to increased exposure to normally excluded toxicants.

Role of food subsidies and habitat structure in influencing benthic communities of shell mounds at sites of existing and former offshore oil platforms

Mussels (Mytilus californianus, M. galloprovincialis) and other organisms sloughed from offshore oil platforms provide a food subsidy to benthic consumers and alter underlying soft bottom habitat by creating hard substrate. The removal of overlying platforms eliminates this food subsidy, but large shell mounds remain. The distribution, abundance, and population characteristics of mobile macroinvertebrates differed among shell mounds beneath existing offshore oil platforms, shell mounds at the former sites of offshore oil platforms, and soft bottom. Predatory and omnivorous echinoderm and mollusk species were more abundant and generally larger on shell mounds under platforms than on shell mounds without platforms. Omnivorous and deposit feeding echinoderms were the most abundant macroinvertebrate taxa sampled on mound-only sites. The brown rock crab (Cancer antennarius), known to have a strong preference for hard substrate, was significantly more abundant on shell mounds, with or without platforms, than adjacent soft bottom sites. Results suggest that the effects of platform removal differed among benthic species according to trophic level, degree of mobility, and substrate preference. Although the shell mound habitat persists after removal of platform structures, species abundance and the composition of the associated benthic community is altered by removal of the platform structure.