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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 (δ 13 C, δ 15 N, δ 34 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., (© 2017 by the Ecological Society of America.)

Because many marine invertebrates have a dispersive planktonic phase, the spatial scale of demographic, connectivity among local populations remains a key, but elusive, parameter driving population and metapopulation dynamics. However, temporal variation in the scale of connectivity remains largely undocumented, despite its recognized importance for predicting population responses to environmental changes. To assess the temporal stability of metapopulation connectivity, we conducted a large-scale survey of a blue mussel (Mytilus spp.) metapopulation for five years along a 100-km section of coastline of the Gaspé Peninsula, Québec, Canada. For each year, we estimated the scale of demographic coupling among 27-29 sites within our study region, using the spatial cross-covariance between adult abundance and recruit density across sites. Despite large interannual variability in overall recruit abundance, our analysis revealed stationary spatial distributions of adult and recruit abundance. More importantly, our analysis revealed a consistent demographic coupling among populations at a distance ranging from 12 to 24 km in all but one of the five years studied. The scale of connectivity in this system is thus temporally stable, but can occasionally show irregular fluctuations, and our results provide evidence in support of the integration of time-varying connectivity to marine metapopulation and reserve network theories.

Most sedentary marine animals disperse from their place of origin during their initial life stages as larvae. The delivery of planktonic larvae back to coastal adult habitats after weeks or months of offshore development is commonly thought to be stochastic, resulting in large recruitment fluctuations and making predictive understanding of population dynamics difficult. Time series of invertebrate settlement on intertidal shores have been used to infer how various oceanographic processes deliver planktonic larvae ashore. However, the possibility that successful settlement may involve a series of different transport mechanisms, which are sequentially utilized by late-stage larvae, has received little attention. To address this, we monitored both the delivery of mussel and barnacle larvae to inner-shelf moorings positioned 200-1400 m from the shore, and larval settlement in the intertidal adult habitat, at two contrasting sites: a headland forming an upwelling center and a downstream bay. Model selection was employed to determine the most likely scenario(s) of larval onshore transport from four a priori transport mechanisms individually and in combination: (1) upwelling or relaxation/downwelling, (2) tidal motions, (3) diurnal sea breezes, and (4) surface waves. Mussel larvae were delivered to the inner shelf during upwelling in the bay, but during downwelling at the headland, and were further transported to the shore by surface waves at both locales. In contrast, the delivery of barnacle larvae to the inner shelf occurred during relaxation/downwelling events at both sites, and intertidal settlement coincided with spring tides, suggesting a role for internal tides in their onshore transport. Thus, sequential mechanisms appear to be utilized by larvae to get to the shore, involving interactions of regional-scale upwelling/downwelling processes and local-scale tidal and surface-wave processes, which differ among taxa and among sites with different topography. A bottleneck for larval delivery across the surf zone may be a result of out-of-phase steps in sequential transport mechanisms leaving larvae lost "in transit."

Extreme heat events cause patchy mortality in many habitats. We examine biophysical mechanisms responsible for patchy mortality in beds of the competitively dominant ecosystem engineer, the marine mussel Mytilus californianus, on the west coast of the United States. We used a biophysical model to predict daily fluctuations in body temperature at sites from southern California to Washington and used results of laboratory experiments on thermal tolerance to determine mortality rates from body temperature. In our model, we varied the rate of thermal conduction within mussel beds and found that this factor can account for large differences in body temperature and consequent mortality during heat waves. Mussel beds provide structural habitat for other species and increase local biodiversity, but, as sessile organisms, they are particularly vulnerable to extreme weather conditions. Identifying critical biophysical mechanisms related to mortality and ecological performance will improve our ability to predict the effects of climate change on these vulnerable ecosystems.

As the main witnesses of the ecological and economic impacts of invasions on ecosystems around the world, ecologists seek to provide the relevant science that informs managers about the potential for invasion of specific organisms in their region(s) of interest. Yet, the assorted literature that could inform such forecasts is rarely integrated to do so, and further, the diverse nature of the data available complicates synthesis and quantitative prediction. Here we present a set of analytical tools for synthesizing different levels of distributional and/or demographic data to produce meaningful assessments of invasion potential that can guide management at multiple phases of ongoing invasions, from dispersal to colonization to proliferation. We illustrate the utility of data-synthesis and data-model assimilation approaches with case studies of three well-known invasive species--a vine, a marine mussel, and a freshwater crayfish--under current and projected future climatic conditions. Results from the integrated assessments reflect the complexity of the invasion process and show that the most relevant climatic variables can have contrasting effects or operate at different intensities across habitat types. As a consequence, for two of the study species climate trends will increase the likelihood of invasion in some habitats and decrease it in others. Our results identified and quantified both bottlenecks and windows of opportunity for invasion, mainly related to the role of human uses of the landscape or to disruption of the flow of resources. The approach we describe has a high potential to enhance model realism, explanatory insight, and predictive capability, generating information that can inform management decisions and optimize phase-specific prevention and control efforts for a wide range of biological invasions.

Recently researchers have gone to great lengths to measure marine metapopulation connectivity via tagging, genetic, and trace-elemental fingerprinting studies. These empirical estimates of larval dispersal are key to assessing the significance of metapopulation connectivity within a demographic context, but the life-history data required to do this are rarely available. To evaluate the demographic consequences of connectivity we constructed seasonal, size-structured metapopulation matrix models for two species of mytilid mussel in San Diego County, California, USA. The self-recruitment and larval exchange terms were produced from a time series of realized connectivities derived from trace-elemental fingerprinting of larval shells during spring and fall from 2003 to 2008. Both species exhibited a strong seasonal pattern of southward movement of recruits in spring and northward movement in fall. Growth and mortality terms were estimated using mark-recapture data from representative sites for each species and subpopulation, and literature estimates of juvenile mortality. Fecundity terms were estimated using county-wide settlement data from 2006-2008; these data reveal peak reproduction and recruitment in fall for Mytilus californianus, and spring for M. galloprovincialis. Elasticity and life-stage simulation analyses were employed to identify the season- and subpopulation-specific vital rates and connectivity terms to which the metapopulation growth rate (lambda) was most sensitive. For both species, metapopulation growth was most sensitive to proportional changes in adult fecundity, survival and growth of juvenile stages, and population connectivity, in order of importance, but relatively insensitive to adult growth or survival. The metapopulation concept was deemed appropriate for both Mytilus species as exchange between the subpopulations was necessary for subpopulation persistence. However, highest metapopulation growth occurred in years when a greater proportion of recruits was retained within the predominant source subpopulation. Despite differences in habitat and planktonic duration, both species exhibited similar overall metapopulation dynamics with respect to key life stages and processes. However, different peak reproductive periods in an environment of seasonal current reversals led to different regional (subpopulation) contributions to metapopulation maintenance; this result emphasizes the importance of connectivity analysis for spatial management of coastal resources.

Recent work demonstrates that nearshore oceanography can generate strong variation in the delivery of resources (nutrients and larvae) to benthic marine communities over spatial scales of tens to hundreds of kilometers. Moreover, variation in the strength of these bottom-up inputs is often spatially consistent, linked to regional centers of upwelling, coastal topography, and other stable features of the coastline. Whereas the ecological effects of these oceanographic links are increasingly clear, the possibility that these same bottom-up forces might impose spatially varying selection on consumers has not been addressed. Here, we test the hypothesis that a carnivorous snail (Nucella canaliculata) with direct development is locally adapted to persistent differences in prey recruitment within two adjacent oceanographic regions (northern California and Oregon, USA). Previous laboratory studies demonstrated that snails from Oregon rarely drilled the thick-shelled mussel Mytilus californianus, whereas snails from California readily drilled this prey. To test whether these differences reflect local adaptation, snails from two populations in each region were raised through two laboratory generations to minimize the potential influence of nongenetic effects. We then reciprocally outplanted these F2 generation snails to field enclosures at each of the four sites and monitored their growth for 11 months. Recruitment and availability of preferred prey (the acorn barnacle Balanus glandula and blue mussel Mytilus trossulus) at the experimental sites were 1-3 orders of magnitude lower in California than in Oregon. At the California sites, snails that originated from Oregon sources failed to drill larger M. californianus, encountered few alternative prey, and showed almost no growth. In contrast, snails from California drilled M. californianus and showed substantial growth. These results strongly suggest that the capacity of California snails to drill M. californianus allows these snails to succeed in an oceanographic region where the recruitment of alternative, preferred prey is low. More broadly, our results suggest that persistent spatial variation in recruitment and other oceanographically mediated processes may lead to adaptive differentiation among populations of consumers in adjacent coastal regions.

Theory predicts that species extinction or invasion can affect the temporal dynamics of ecological communities by altering feedback patterns and by damping or amplifying environmental variation via changes in the network of species interactions, but because of the logistical challenges of investigating temporal dynamics, evidence from natural ecosystems is lacking. In a long-term experimental manipulation of a rocky intertidal community on Tatoosh Island, Washington, U.S.A., chronic removal of the dominant species Mytilus californianus altered the dynamics of the system, causing reductions in the temporal variability of three subdominant species but no consistent change in the spectral characteristics or the order of density dependence across experimental replicates. This pattern of results suggests that Mytilus californianus impacted the temporal dynamics by amplifying environmental stochasticity, rather than by changing feedback pathways as is emphasized in most theoretical predictions and laboratory studies. Hence, further investigation of the mechanisms and implications of transmission of environmental stochasticity in natural ecosystems is merited.

The extent to which community processes can be generalized from local field studies to larger spatial scales remains a contentious issue. The search for broad generality can be hampered when species interactions vary geographically, a common phenomenon attributed to a wide range of underlying ecological factors. Less attention has been directed toward understanding the additional role that evolutionary processes may play in modifying the way that pairs of species interact over large spatial scales. Here we examine whether marked geographic variation in the interaction between a predatory snail (Nucella canaliculata) and an intertidal mussel (Mytilus californianus) arises from phenotypic plasticity or fixed genetic differences among snail populations. Over a three-year period, we reared snails from eight populations in California and Oregon, USA, through two laboratory generations and tested whether family lines differed in their ability to drill M. californianus. Remarkably, F2 generation snails from Oregon sources were generally unable to drill mid-sized Mytilus californianus (5-7 cm long), whereas snails from California readily drilled this prey. Because snails were raised through two generations on a common diet (Mytilus trossulus), these differences among populations likely have a genetic basis. Snails from California and Oregon readily interbred and produced viable offspring in the laboratory, suggesting that populations belong to a single biological species. Field surveys of mussel beds revealed striking geographic variation in predation that closely matched the observed differences in the drilling capacity of N. canaliculata. Drilled M. californianus were common at all sites in California and included many large mussels (> 10 cm long). In contrast, drilled M. californianus were rare on the central Oregon coast and consisted mostly of small mussels (< 3 cm). We hypothesize that persistent variation in prey recruitment along the coast has selected for interpopulation differences in the drilling capacity of this direct-developing snail, with potential consequences for the size structure of mussel beds. Combined with growing evidence of restricted gene flow and low connectivity among many marine populations, this study highlights the importance of considering the contribution of evolutionary processes to geographic variation in species interactions.

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.