Domoic acid depuration by intertidal bivalves fed on toxin-producing Pseudo-nitzschia multiseries.

Domoic acid (DA), a neurotoxin produced by certain species within the diatom genus Pseudo-nitzschia, has caused numerous persistent harvest closures for razor clam Siliqua patula along the outer coast of Washington State (USA) over the last three decades. In comparison, bivalve harvest closures for DA have only occurred three times in Washington's largest inland estuary, Puget Sound, which has a variety of bivalve species excluding razor clam. While differing bloom dynamics in the two locations are responsible for much of the disparity in shellfish harvest closures, species-specific differences in DA depuration may affect the duration of harvest closures in the two regions. Toxin-producing Pseudo-nitzschia multiseries were fed to four species of bivalves, followed by measurement of tissue DA content over time to estimate depuration rate. Experimental species include razor clam and three species of intertidal Puget Sound bivalves: soft-shell clam Mya arenaria, purple varnish clam Nuttallia obscurata and Manila clam Ruditapes philippinarum. Using an exponential decay model, DA depuration rates were estimated as: 0.02·day-1 ±0.08 for razor clam, 0.10·day-1 ±0.07 for purple varnish clam, 0.37·day-1 ±0.03 for soft-shell clam, and 0.44·day-1 ±0.02 for Manila clam. Puget Sound species depurated DA between five and 22 times as fast as outer coast razor clam. Within Puget Sound species, slow DA depuration rates in purple varnish clam indicate that it may be a good sentinel organism for assessing beach-wide maximum DA concentrations in Puget Sound bivalves.

Detrital shadows: estuarine food web connectivity depends on fluvial influence and consumer feeding mode.

We measured the influence of landscape setting on estuarine food web connectivity in five macrotidal Pacific Northwest estuaries across a gradient of freshwater influence. We used stable isotopes (δ13 C, δ15 N, δ34 S) in combination with a Bayesian mixing model to trace primary producer contributions to suspension- and deposit-feeding bivalve consumers (Mytilus trossulus and Macoma nasuta) transplanted into three estuarine vegetation zones: emergent marsh, mudflat, and eelgrass. Eelgrass includes both Japanese eelgrass (Zostera japonica) and native eelgrass (Zostera marina). Fluvial discharge and consumer feeding mode strongly influenced the strength and spatial scale of observed food web linkages, while season played a secondary role. Mussels displayed strong cross-ecosystem connectivity in all estuaries, with decreasing marine influence in the more fluvial estuaries. Mussel diets indicated homogenization of detrital sources within the water column of each estuary. In contrast, the diets of benthic deposit-feeding clams indicated stronger compartmentalization in food web connectivity, especially in the largest river delta where clam diets were trophically disconnected from marsh sources of detritus. This suggests detritus deposition is patchy across space, and less homogenous than the suspended detritus pool. In addition to fluvial setting, other estuary-specific environmental drivers, such as marsh area or particle transport speed, influenced the degree of food web linkages across space and time, often accounting for unexpected patterns in food web connectivity. Transformations of the estuarine landscape that alter river hydrology or availability of detritus sources can thus potentially disrupt natural food web connectivity at the landscape scale, especially for sedentary organisms, which cannot track their food sources through space.

Estimating Common Growth Patterns in Juvenile Chinook Salmon (Oncorhynchus tshawytscha) from Diverse Genetic Stocks and a Large Spatial Extent.

Life history variation in Pacific salmon (Oncorhynchus spp.) supports species resilience to natural disturbances and fishery exploitation. Within salmon species, life-history variation often manifests during freshwater and estuarine rearing, as variation in growth. To date, however, characterizing variability in growth patterns within and among individuals has been difficult via conventional sampling methods because of the inability to obtain repeated size measurements. In this study we related otolith microstructures to growth rates of individual juvenile Chinook salmon (O. tshawytscha) from the Columbia River estuary over a two-year period (2010-2012). We used dynamic factor analysis to determine whether there were common patterns in growth rates within juveniles based on their natal region, capture location habitat type, and whether they were wild or of hatchery origin. We identified up to five large-scale trends in juvenile growth rates depending on month and year of capture. We also found that hatchery fish had a narrower range of trend loadings for some capture groups, suggesting that hatchery fish do not express the same breadth of growth variability as wild fish. However, we were unable to resolve a relationship between specific growth patterns and habitat transitions. Our study exemplifies how a relatively new statistical analysis can be applied to dating or aging techniques to summarize individual variation, and characterize aspects of life history diversity.

Practical proxies for tidal marsh ecosystem services: application to injury and restoration.

Tidal marshes are valued, protected and restored in recognition of their ecosystem services: (1) high productivity and habitat provision supporting the food web leading to fish and wildlife, (2) buffer against storm wave damage, (3) shoreline stabilization, (4) flood water storage, (5) water quality maintenance, (6) biodiversity preservation, (7) carbon storage and (8) socio-economic benefits. Under US law, federal and state governments have joint responsibility for facilitating restoration to compensate quantitatively for ecosystem services lost because of oil spills and other contaminant releases on tidal marshes. This responsibility is now met by choosing and employing metrics (proxies) for the suite of ecosystem services to quantify injury and scale restoration accordingly. Most injury assessments in tidal marshes are triggered by oil spills and are limited to: (1) documenting areas covered by heavy, moderate and light oiling; (2) estimating immediate above-ground production loss (based on stem density and height) of the dominant vascular plants within each oiling intensity category and (3) sampling sediments for chemical analyses and depth of contamination, followed by sediment toxicity assays if sediment contamination is high and likely to persist. The percentage of immediate loss of ecosystem services is then estimated along with the recovery trajectory. Here, we review potential metrics that might refine or replace present metrics for marsh injury assessment. Stratifying plant sampling by the more productive marsh edge versus the less accessible interior would improve resolution of injury and provide greater confidence that restoration is truly compensatory. Using microphytobenthos abundance, cotton-strip decomposition bioassays and other biogeochemical indicators, or sum of production across consumer trophic levels fails as a stand-alone substitute metric. Below-ground plant biomass holds promise as a potential proxy for resiliency but requires further testing. Under some conditions, like chronic contamination by organic pollutants that affect animals but not vascular plants, benthic infaunal density, toxicity testing, and tissue contamination, growth, reproduction and mortality of marsh vertebrates deserve inclusion in the assessment protocol. Additional metrics are sometimes justified to assay microphytobenthos, use by nekton, food and habitat for reptiles, birds and mammals, or support of plant diversity. Empirical research on recovery trajectories in previously injured marshes could reduce the largest source of uncertainty in quantifying cumulative service losses.

Restoration of the Mississippi Delta: lessons from Hurricanes Katrina and Rita.

Hurricanes Katrina and Rita showed the vulnerability of coastal communities and how human activities that caused deterioration of the Mississippi Deltaic Plain (MDP) exacerbated this vulnerability. The MDP formed by dynamic interactions between river and coast at various temporal and spatial scales, and human activity has reduced these interactions at all scales. Restoration efforts aim to re-establish this dynamic interaction, with emphasis on reconnecting the river to the deltaic plain. Science must guide MDP restoration, which will provide insights into delta restoration elsewhere and generally into coasts facing climate change in times of resource scarcity.

An evaluation of the influence of natural science in regional-scale restoration projects.

Regional-scale restoration is a tool of growing importance in environmental management, and the number, scope, and complexity of restoration programs is increasing. Although the importance of natural science to the success of such projects generally is recognized, the actual use of natural science in these programs rarely has been evaluated. We used techniques of program evaluation to examine the use of natural science in six American and three Western European regional-scale restoration programs. Our results suggest that ensuring the technical rigor and directed application of the science is important to program development and delivery. However, the influence of science may be constrained if strategies for its integration into the broader program are lacking. Consequently, the influence of natural science in restoration programs is greatest when formal mechanisms exist for incorporating science into programs, for example, via a framework for integration of science and policy. Our evaluation proposes a model that can be used to enhance the influence of natural science in regional-scale restoration programs in the United States and elsewhere.

Indirect food web interactions: sea otters and kelp forest fishes in the Aleutian archipelago.

Although trophic cascades-the effect of apex predators on progressively lower trophic level species through top-down forcing-have been demonstrated in diverse ecosystems, the broader potential influences of trophic cascades on other species and ecosystem processes are not well studied. We used the overexploitation, recovery and subsequent collapse of sea otter (Enhydra lutris) populations in the Aleutian archipelago to explore if and how the abundance and diet of kelp forest fishes are influenced by a trophic cascade linking sea otters with sea urchins and fleshy macroalgae. We measured the abundance of sea urchins (biomass density), kelp (numerical density) and fish (Catch per unit effort) at four islands in the mid-1980s (when otters were abundant at two of the islands and rare at the two others) and in 2000 (after otters had become rare at all four islands). Our fish studies focused on rock greenling (Hexagrammos lagocephalus), the numerically dominant species in this region. In the mid-1980s, the two islands with high-density otter populations supported dense kelp forests, relatively few urchins, and abundant rock greenling whereas the opposite pattern (abundant urchins, sparse kelp forests, and relatively few rock greenling) occurred at islands where otters were rare. In the 2000, the abundances of urchins, kelp and greenling were grossly unchanged at islands where otters were initially rare but had shifted to the characteristic pattern of otter-free systems at islands where otters were initially abundant. Significant changes in greenling diet occurred between the mid-1980s and the 2000 although the reasons for these changes were difficult to assess because of strong island-specific effects. Whereas urchin-dominated communities supported more diverse fish assemblages than kelp-dominated communities, this was not a simple effect of the otter-induced trophic cascade because all islands supported more diverse fish assemblages in 2000 than in the mid-1980s.