The scope of emerging national and international ocean-related issues facing society demands that we develop broad perspectives on graduate education and training in the ocean sciences. A multifaceted ocean workforce and new kinds of intellectual partnerships are needed to address ocean science research priorities, strengthen our understanding of coupled human-natural ocean systems, engage and inform public policy and management decision making, and increase ocean literacy. Alumni from graduate programs in ocean sciences are following diverse career paths in academia, government, nongovernmental organizations, and industry, and thus can inform us about the diverse skills needed to succeed. The ocean science academic community should build on its current strengths (e.g., multidisciplinary and multi-institutional research and education, international partnerships), and capitalize on what some might view as limitations (e.g., remote, yet inviting, coastal campuses, diversity of ocean science programs), to become an incubator of innovation that will advance the field and strengthen graduate education and training. Partnerships within and among institutions with ocean-related programs, and with professional societies, employers, and others, can help us provide cutting-edge, relevant academic options, facilitate professional development, and proactively position graduates for career paths that reflect and address important societal needs.

The strong association of contaminants with fine-grained or organic-rich sediments is well established. Contaminants focused at the sediment-water interface may be resuspended, transported, transformed or buried, depending on the phasing and interactions among biological, physical and chemical processes. Our long term goal is to develop a better understanding of how materials are exchanged across the sedimentwater interface and how these process influence the transport and fate of contaminants in coastal ecosystems. A knowledge of these processes is essential for ecological risk assessments for sediment-associated contaminants and for designing effective remediation strategies for contaminated coastal harbors.

Community-level responses of soft sediment macrobenthos to two relatively large-scale disturbance events associated with dredged material (DM) disposal are examined for subtidal (>10 m) lower Chesapeake Bay. Disturbance severity (DM thickness on initial sampling date following disposal) and date of sampling were important factors explaining the patterns and rates of recovery for species richness, abundance, biomass, and community composition, but sediment disposal had minimal effects when DM thickness was ≤15 cm. It took 1.5 years or less following the cessation of disposal activities for richness, abundance, biomass and community composition at high disposal severity (DM > 15 cm) to attain levels measured at reference stations representing the ambient community of the region. Positive correlations of community structure metrics between the disposal area and reference stations provide evidence that non-local processes influenced patterns of recovery in this estuarine setting. Species interactions and food limitation may also have been important at local scales.

Abstract Benthic organisms and their communities are key components of estuarine systems. We provide an overview of the biology and key ecological features of benthic communities of York River Estuary (YRE), which is the site of the Chesapeake Bay National Estuarine Research Reserve in Virginia (CBNERRVA). Major subtidal benthic habitats in YRE include soft mud and sand bottoms, with only limited distribution of submerged aquatic vegetation and oyster shell. Major taxonomic groups of macrofauna dominating muds and sands of YRE include annelids, molluscs and crustaceans; similar to those found in other temperate estuaries of the US Mid-Atlantic. Meiofaunal assemblages of YRE soft bottoms are dominated by nematodes and copepods. Species distribution patterns in YRE are strongly correlated with salinity and bottom type, while other factors such as eutrophication and hypoxia may be growing in importance. Much of the YRE benthos fails to meet the restoration goals set by the Chesapeake Bay Program. The poor condition of the benthos is expressed as low biomass and abundance and may be associated with degraded water quality, hypoxia and sediment disturbance processes. No comprehensive inventory of the benthic biota of the CBNERRS sites is available, which will make it difficult to assess future changes due to human impacts such as climate change or the introduction of exotic species. Given this paucity of data, a systemic cataloging of the benthic resources of the reserve sites and any potential invasive species is a much needed avenue of future research for CBNERRVA.

Sediment erodibility was measured at three sites in the York River, a sub-estuary of the Chesapeake Bay, monthly to bimonthly from April 2006 through October 2007. Erodibility at the three sites was similar during the summer and fall. A site near the estuary mouth maintained this level of erodibility greater than 90% of the time while two sites in the more physically dominated mid-estuary region exhibited a consistent and pronounced increase in erodibility in the late winter and spring. Weak to non-existent correlations between bed erodibility, solids volume fraction, and surficial concentrations of organic matter, colloidal carbohydrate, and extracellular polymeric substances, were not sufficient to explain the observed seasonal pattern in bed erodibility. Digital X-radiographs revealed thick sequences (10–20+cm) of laminated sediments at the surface in the middle estuary coincident with the period of highest erodibility and more biologically reworked sediment during the rest of the year, suggesting that periodic rapid deposition introduced new sediment that was seasonally easy to erode. The finding that seasonal deposition influenced erodibility at the mid-estuary sites is consistent with previous results indicating the occasional presence of a secondary turbidity maximum. Comparison of the biologically reworked, but still “low” erodibility condition in the York to other published Chesapeake Bay erodibility data revealed a consistent critical shear stress range and profile, suggesting that this equilibrium critical stress profile may be representative of other similar estuarine environments in the absence of rapid deposition. At relatively low stresses and in the absence of rapid deposition, we speculate that burrowing and/or pelletization may play a role in maintaining high equilibrium bulk water content without reducing the strength of the surface of the seabed.

Benthic indices are typically developed independently by habitat, making their incorporation into large geographic scale assessments potentially problematic because of scaling inequities. A potential solution is to establish common scaling using expert best professional judgment (BPJ). To test if experts from different geographies agree on condition assessment, sixteen experts from four regions in USA and Europe were provided species-abundance data for twelve sites per region. They ranked samples from best to worst condition and classified samples into four condition (quality) categories. Site rankings were highly correlated among experts, regardless of whether they were assessing samples from their home region. There was also good agreement on condition category, though agreement was better for samples at extremes of the disturbance gradient. The absence of regional bias suggests that expert judgment is a viable means for establishing a uniform scale to calibrate indices consistently across geographic regions.

Climate impacts on coastal and estuarine systems take many forms and are dependent on the local conditions, including those set by humans. We use a biocomplexity framework to provide a perspective of the consequences of climate change for coastal wetland ecogeomorphology. We concentrate on three dimensions of climate change affects on ecogeomorphology: sea level rise, changes in storm frequency and intensity, and changes in freshwater, sediment, and nutrient inputs. While sea level rise, storms, sedimentation, and changing freshwater input can directly impact coastal and estuarine wetlands, biological processes can modify these physical impacts. Geomorphological changes to coastal and estuarine ecosystems can induce complex outcomes for the biota that are not themselves intuitively obvious because they are mediated by networks of biological interactions. Human impacts on wetlands occur at all scales. At the global scale, humans are altering climate at rapid rates compared to the historical and recent geological record. Climate change can disrupt ecological systems if it occurs at characteristic time scales shorter than ecological system response and causes alterations in ecological function that foster changes in structure or alter functional interactions. Many coastal wetlands can adjust to predicted climate change, but human impacts, in combination with climate change, will significantly affect coastal wetland ecosystems. Management for climate change must strike a balance between that which allows pulsing of materials and energy to the ecosystems and promotes ecosystem goods and services, while protecting human structures and activities. Science-based management depends on a multi-scale understanding of these biocomplex wetland systems. Causation is often associated with multiple factors, considerable variability, feedbacks, and interferences. The impacts of climate change can be detected through monitoring and assessment of historical or geological records. Attribution can be inferred through these in conjunction with experimentation and modeling. A significant challenge to allow wise management of coastal wetlands is to develop observing systems that act at appropriate scales to detect global climate change and its effects in the context of the various local and smaller scale effects.

Legislation in US and Europe has been adopted to determine the ecological integrity of estuarine and coastal waters, including, as one of the most relevant elements, the benthic macroinvertebrate communities. It has been recommended that greater emphasis should be placed on evaluating the suitability of existing indices prior to developing new ones. This study compares two widely used measures of ecological integrity, the Benthic Index of Biotic Integrity (B-IBI) developed in USA and the European AZTI's Marine Biotic Index (AMBI) and its multivariate extension, the M-AMBI. Specific objectives were to identify the frequency, magnitude, and nature of differences in assessment of Chesapeake Bay sites as ‘degraded’ or ‘undegraded’ by the indices. A dataset of 275 subtidal samples taken in 2003 from Chesapeake Bay were used in this comparison. Linear regression of B-IBI and AMBI, accounted for 24% of the variability; however, when evaluated by salinity regimes, the explained variability increased in polyhaline (38%), high mesohaline (38%), and low mesohaline (35%) habitats, remained similar in the tidal freshwater (25%), and decreased in oligohaline areas (17%). Using the M-AMBI, the explained variability increased to 43% for linear regression, and 54% for logarithmic regression. By salinity regime, the highest explained variability was found in high mesohaline and low polyhaline areas (53–63%), while the lowest explained variability was in the oligohaline and tidal freshwater areas (6–17%). The total disagreement between methods, in terms of degraded-undegraded classifications, was 28%, with high spatial levels of agreement. Our study suggests that different methodologies in assessing benthic quality can provide similar results even though these methods have been developed within different geographical areas.

Abstract : Human activities along our nation's coasts often lead to habitat modification, pollution, and overexploitation of living resources in coastal and estuarine waters (U.S. Commission on Ocean Policy 2004). Coastal areas are the most developed regions of the United States. In addition to recreational and leisure activities, these areas support commercial fishing, aquaculture, shipping, and defense activities. Numerous human activities can have detrimental effects on biodiversity and the provision of ecosystem services that support and sustain human populations. Given their proximity to the land and human population centers, nearshore estuarine ecosystems are especially vulnerable. Effective management can be improved with a better understanding of relationships between ecological integrity and human pressures in these ecosystems (National Estuary Program 2007). Ecologists, coastal managers, and policy-makers are working together to develop better ways to measure and manage human effects on estuarine and coastal ecosystems. Management strategies can be framed in the context of human actions (pressure or stressor), resulting effects on community structure and ecosystem functions (state or condition), and management responsed.

Introduction and Methods Cohesive sediments in marine and coastal environments are responsible for degrading water quality, influencing the cycling and availability of particle bound contaminants, and infilling navigable waterways. In spite of their significance to coastal environments, there are still major gaps in our understanding of many of the fundamental processes governing cohesive sediment transport and deposition. In particular, seabed erodibility, which facilitates sediment exchange between the bed and water column, is under-resolved in field studies and is often treated as a tuning parameter in numerical models. The goal of this work is to evaluate variation in seabed erodibility over several seasons in a cohesive estuarine environment and gain insight into the dominant physical and biological processes influencing these variations. This study was conducted on the York River estuary, a sub-estuary of the Chesapeake Bay, USA (Fig. 1). The York River is tidally energetic with tidal currents reaching magnitudes of ~ 1m s at the surface during spring tide. A persistent estuarine turbidity maximum (ETM) has been reported just upstream of West Point in the Pamunkey and Mattaponi Rivers, the York’s main tributaries. Additionally, an ephemeral secondary turbidity maximum (STM) has been reported in the middle estuary near Clay Bank, ~ 25 km from the York River mouth (Lin and Kuo, 2001). Schaffner et al. (2001) reported a strong estuarine gradient in ecological diversity from the ETM region of the York into the main stem of the Chesapeake Bay. Both the ETM and STM regions were characterized by high suspended sediment concentrations resulting in unfavorable conditions for benthic biota. In contrast, the main stem of the Chesapeake Bay had lower suspended sediment concentrations and a more diverse benthic community. In this study, sediment erodibility was measured at three sites on the York River estuary, monthly to bimonthly over a 19-month period. Two sites were established in the more physically dominated middle estuary near Clay Bank, and one site was established in the more biologically influenced lower estuary near Gloucester Point. Each time a site was visited, cores were collected for erodibility measurement, Xradiography, and analysis of grain size, water content, and organic components. Within a few hours of core collection, seabed erodibility over the range of 0.01 to 0.6 Pa was measured with a dual core Gust erosion microcosm. Results and Discussion The two sites located in the Clay Bank region of the estuary (CS and CC) exhibited a pronounced seasonal cycle in seabed erodibility (Fig. 2). Both CS and CC had consistent and relatively low erodibility in the summer and fall of 2006 and 2007 and elevated erodibility in the late winter and spring of 2007. CS and CC also exhibited what appeared to be transitional periods of moderate erodibility prior to and after periods of highest erodibility. In contrast, erodibility at the Gloucester Point (GP) site (Fig. 2) was generally low and did not exhibit the pronounced seasonal pattern found at the two Clay Bank sites. Interestingly, the range in eroded mass and mean eroded mass found at GP year-round (except for May 2007) was quite similar to that measured at the Clay Bank sites in the summer and fall of 2006 and 2007. Weak to nonexistent correlations between bed erodibility, solids volume fraction, and components of organic matter were not sufficient to explain the observed seasonal pattern in erodibility at Clay Bank. X-radiographs from the GP site (Fig. 3a-c) revealed little temporal variability in the structure of the seabed. Similar to the GP site, X-radiographs from the CS site often appear mixed with few laminations (Fig. 3d). However, a more uniform surface layer, occasionally containing thin laminations and ranging in thickness from 1 to 15 cm, was occasionally observed (Fig. 3e-f). This layer was most distinct in March to May of 2007. Digital X-radiographs from the CC site revealed the most dramatic seasonal variability in bed structure. From May to September of 2006 the bed appeared mottled (Fig. 3g). In November, a surface layer, 2 cm thick and containing many fine laminations appeared (Fig. 3h). Similar laminations were then observed down to 10 cm in January of 2007 (Fig. 3i) and down to 20+ cm in March and April. In May 2007 only traces of laminations remained, and by June cores from the CC site appeared mottled once again (Figure 3l). The presence at Clay Bank of (i) thick sequences of laminated sediments coincident with the period of highest erodibility and (ii) more biologically reworked sediment during the rest of the year suggests that periodic rapid deposition introduced new sediment that was seasonally easy to erode. The presence of laminated bedding in the X-radiographs likely highlighted times when physical processes dominated bioturbation due to rapid deposition overwhelming the ability of benthic biota to mix the seabed. In contrast, sediments appearing mottled were indicative of the times with more active bioturbation and lower rates of deposition. The finding that seasonal deposition influenced erodibility in the Clay Bank region is consistent with previous results indicating the occasional presence of a secondary turbidity maximum. Comparison of the biologically reworked, but still “low” erodibility condition found at all three York River sites to other published Chesapeake Bay erodibility data revealed a remarkably consistent eroded mass versus critical shear stress profile. In the absence of rapid recent deposition (i.e., outside of turbidity maxima zones), it appears that muddy areas of moderate depth exhibit a notably consistent level of bed erodibility in both space and time. These common erodibilities suggest an equilibrium critical stress profile may exist which may be broadly representative of other similar estuarine environments. At relatively low stresses and in the absence of rapid deposition, we further speculate that burrowing and/or sediment pelletization may play a role in maintaining high equilibrium bulk water content without reducing the strength of the surface of the seabed. Thus the presence of biologically-induced heterogeneity may confound the otherwise expected relationship between muddy seabed water content and erodibility. Fig. 4 presents a conceptual model of processes in the York River estuary influencing bed erodibility. Following periods of high river discharge, a secondary turbidity maximum (STM) forms near Clay Bank, resulting in high suspended sediment concentrations dominated by fines and flocs, rapid deposition of an ephemeral layer 10’s of centimeters thick, a physically dominated seabed, and high bed erodibility. The lower estuary, including the GP site, lies outside of the region typically occupied by the STM. The result at Gloucester Point is lower suspended sediment concentrations, highly pelletized surficial sediment, a more actively burrowed seabed, and low erodibility. After an extended period of low river flow, stratification throughout the estuary breaks down, and the STM either moves up-estuary or dissipates, resulting in a period of divergent sediment transport and/or sediment bypassing. During this period, the conditions near Clay Bank more closely resemble Gloucester Point, with lower suspended sediment concentrations, increasingly pelletized sediment, more intense bioturbation, and lower erodibility.

Estuarine benthic organisms are frequently subjected to disturbance events caused by hydrodynamic processes that disrupt and move the sediment in which the animals reside, however the mechanisms by which physical disturbance processes affect infaunal and epifaunal populations and communities remain poorly resolved. The responses of three infaunal and two epifaunal estuarine benthic species to sediment disturbance (burial) were compared in laboratory experiments. Overburden stress (kPa) was calculated to quantify the force exerted on organisms by sediment burial for 6 d. At the levels tested (0–16 kPa), increasing overburden stress did not significantly decrease survival or growth of juvenile burrowing bivalves, Macoma balthica (Linnaeus). Survival of juveniles and adults of the tubiculous polychaete Streblospio benedicti (Webster) and neonates of the burrow-forming amphipod Leptocheirus plumulosus (Shoemaker) declined exponentially with increasing overburden stress. The mean S. benedicti survival rate was 4% of the control at an overburden stress of ≈4 kPa, while an overburden stress of 12 kPa was necessary to comparably reduce survival of L. plumulosus. At the low levels of overburden stress used in the experiments with epifauna (≤0.2 kPa), juvenile oyster Crassostrea virginica (Gmelin) did not suffer significant mortality at an overburden stress of 0.1 kPa. In contrast, the epifaunal tunicate Molgula manhattensis (DeKay) exhibited significant mortality when partially (one or two siphons exposed) or completely buried under sediment with an overburden stress of 0.2 kPa. Species-specific response to burial varied as a function of motility, living position, and inferred physiological tolerance of anoxic conditions while buried. We conclude that some benthic species exhibit mechanical and possibly physiological adaptations that may allow them to survive deposition events of the magnitude commonly encountered in estuarine environments.

Low dissolved oxygen (hypoxia and/or anoxia) has become a major cause of change to the benthic component of ecosystems around the world. We present the response of a benthic community to hypoxia in organically enriched environments in Korean coastal waters. Disturbances due to low dissolved oxygen (DO), and organic enrichment altered community dynamics, result in defaunation during summer hypoxia with delayed recolonization occurring in winter. As DO decreased, the number of taxa, their abundance and biomass of macrofauna dropped significantly at inner bay stations in Chinhae Bay and Youngsan River estuarine bay affected by hypoxia. With the return of normoxic conditions in Chinhae Bay, recolonization was initiated by opportunistic species, with a 1–4months lag. The polychaetes, Sigambra tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia, were most persistent under hypoxia. The first recolonizers were the polychaetes Paraprionospio pinnata, S. tantaculata, Glycinde gurjanovae and Nectoneanthes multignatha and the bivalve Theora fragilis. The second group of colonizers included the polychaetes Capitella capitata, Mesochaetopterus sp. and L. longifolia, and the bivalve Raetellops pulchella. Hypoxic and near anoxic conditions resulted in mass mortality in Chinhae Bay and Youngsan River estuarine bay, but communities did partially recover after return to normoxic conditions despite delayed recolonization.

Eh measurements by electrodes are commonly used to characterize redox status of sediments in freshwater, marine and estuarine studies, due to the relative ease and rapidity of data collection. In our studies of fine-grained estuarine seabeds, we observed that Eh values measured in intact sediment cores were influenced by different electrode insertion techniques. Sediment Eh measurements generated via lateral insertion of platinum electrodes through silicone-filled ports in acrylic cores were systematically more positive (on the order of 10–100mV) than profiles generated via vertical insertion of platinum electrodes downward through the sediment–water interface of the same cores. A review of the literature indicated that while researchers routinely use both insertion techniques to measure Eh, no discrepancy in output has previously been reported. We discuss the results of three experiments conducted to determine if the discrepancy in output was caused by electrode poisoning by sulfides during the stepwise vertical insertion technique, or was caused by contact of the electrode with the silicone plug during the lateral insertion technique. We conclude that contact between the platinum surface of the electrode and the silicone plug biases the Eh measurements, resulting in erroneously positive Eh values. Insertion of electrodes into sediment through silicone plugs produced Eh values that were an average of 105.6mV (±10.4 SE) more positive than values generated upon electrode insertion directly into sediment. Thus, we recommend against using an insertion technique where the platinum electrode remains in contact with the silicone plug, as this method results in misclassification of sediment redox state and estimated depth of the redoxcline.

A process-oriented sedimentary facies model is developed for the York River estuary, a sub-estuary of the lower Chesapeake Bay. This facies model was based on 210Pb and grain-size profiles, as well as X-radiographs taken from kasten cores and box cores collected in a series of across-river transects. Throughout most of the energetic microtidal York River, the seabed is characterized by physical mixing to depths of 25–200 cm. A strong cross-estuary gradient in processes is observed with one side, including channel, flank and shoal, dominated by frequent deep erosion and redeposition (physical mixing), while physical mixing is reduced on the other side, resulting in a greater preservation of biological mixing signatures. Within the physically dominated side of the river, the mixed layer is characterized by ‘stair-stepped’ 210Pb profiles with one or more segments (∼25–200 cm thick) of nearly uniform excess activity. X-radiographs reveal that, although a record of limited biogenic sediment modification is preserved, sedimentary structures within the mixed layer are dominated by centimeter to decimeter scale units of finely to coarsely laminated strata bounded by hiatal surfaces. This demonstrates that mixing results primarily from erosion, resuspension and deposition. Reduced salinity limits the number of benthic species in the York River. Physical disturbance leads to an impoverishment of this community, which is composed primarily of small, opportunistic species with a paucity of larger macrofauna. As a result, mixing in the biologically dominated side of the river is generally on the order of a few centimeters, but may be as deep as 40 cm, and 210Pb geochronology yields low biodiffusion rates (0.43–3.35 cm2 yr−1). X-radiographs reveal the presence of some laminations which suggest that although the mixing is controlled by biological processes the mixing intensity is relatively low. Based on 210Pb geochronologies, residence time estimates for particles within the mixed layer are on the order of centuries. Residence time calculations based on the sediment mass in the physically mixed layer is equivalent to 70 yr of river sediment yield, consistent with century-scale residence times from core data. The frequency and intensity of seabed mixing appears to differ between the lower and upper river. The lower York River is wider and deeper, and is more susceptible to large storms and sea surges, which we suspect drives much of the recorded seabed mixing. Within the upper river, longer-term events (storms) may cause the deepest mixing, but much of this record is destroyed by shorter-term, high-frequency events which produce shallow to mid-depth (<50 cm) mixing, probably driven by spring/neap tides, co-phased tidal constituents, and river flooding.

In some estuaries, the recruitment of epifaunal benthic invertebrates coincides with a significant environmental stress, low water-column dissolved oxygen, termed hypoxia (≥2 mg O2 l–1). Recruitment of epifaunal species was measured in the lower York River, a subestuary of the Chesapeake Bay, USA, which experiences predictable, periodic hypoxia associated with neap/spring tidal cycling during summer. Recruitment substrata were exposed during 48-h deployments in two areas with differing levels of hypoxia, and epifauna were allowed to recruit during periods of low oxygen (neap tides) and high oxygen (spring tides) in 1996 and 1997. Recruitment was often high during neap tides, even when severe oxygen depletion (<0.5 mg O2 l–1, <0.71 ml O2 l–1) occurred during deployments; indeed, peak recruitment episodes of several dominant epifaunal taxa, and of total epifauna, coincided with hypoxic events during both summers. Increased recruitment during neap tides suggests that factors besides hypoxia influenced recruitment in the York River; these factors may have included changes in larval availability and lower current speeds. This study illustrates how the relationship between recruitment and large-scale stresses, such as hypoxia, may be difficult to predict, since large-scale stresses are often correlated with numerous other factors. Short-term hypoxia appears to have little effect on recruitment in the field for many epifaunal species in this ecosystem, which may explain, in part, why substrata exposed for longer durations (1 month) in this system showed few effects of hypoxia on community composition or diversity. High larval tolerance of hypoxic stress may allow communities to persist even though the summer hypoxia season coincides with the recruitment of many epifaunal species. Electronic Supplementary Material is available if you access this article at http://dx.doi.org/10.1007/s00227-002-0930-6. On that page (frame on the left side), a link takes you directly to the supplementary material.

The York River Estuary, a tributary of the Chesapeake Bay, USA, experiences periodic low oxygen stress (hypoxia), yet epifaunal species form dense communities there. We studied hypoxia tolerance of common epifaunal species in the York River by exposing sessile and mobile epifauna to high and low oxygen concentrations in laboratory aquaria. Mortality in hypoxia varied among species, ranging from 0% to 100%, with trends of decreased tolerance by mobile species relative to sessile species. While most species tested experienced some mortality after being exposed to hypoxia (at 1 mg O2/l or 0.5 mg O2/l) for 5 days, many species had a median lethal time (LT50) in hypoxia greater than 1 week (3 of 6 species at 1 mg O2/l and 6 of 14 species at 0.5 mg O2/l), the maximum duration of typical hypoxic episodes in the York River, suggesting that hypoxia may cause little mortality for some species in this system. However, hypoxia had sub-lethal effects on behavior in all species tested. Epifaunal animals responded to hypoxia with behaviors that moved them higher in the water column or by entering resting states until hypoxia passed. Feeding and predation by a variety of taxa (the hydroid Obelia bicuspidata, the mud crab Neopanope sayi, juvenile blue crabs Callinectes sapidus, the flatworm Stylochus ellipticus, and the nudibranch Doridella leucolena) decreased during hypoxia, despite varying mortality responses to low oxygen stress, suggesting that short hypoxic episodes may create predation refuges for prey species. At least one highly tolerant species (O. bicuspidata) showed substantially decreased growth in hypoxia. Although relatively high tolerance of hypoxia by many estuarine epifaunal species limits serious disturbance during brief hypoxic episodes, hypoxia's greatest impact on York River epifaunal communities might be through its indirect effects on behavior and predation.

Benthic suspension feeders are functionally important components of many shallow estuarine and coastal ecosystems. Their relative importance in material and energy cycling depends on physical and biological factors, of which population dynamics of individual species are a key feature. We studied the demographics and secondary production of a population of the tubicolous, suspension feeding polychaete, Chaetopterus cf. variopedatus, of southern Chesapeake Bay, Virginia, to better understand its functional role in an estuarine ecosystem. Average worm densities in the study region ranged from 30 to >1000 individuals m−2 and were greatest after the summer recruitment period. Recruitment success varied threefold between 1994 and 1995. A two‐cohort model (juveniles and adults) with seasonality best described the data. High secondary production (18 g C m−2 yr−1 in 1994, 34 g C m−2 yr−1 in 1995) was mainly due to rapid growth and maturation of new recruits during summer and tube production. An interannual difference in production was associated with the interannual difference in recruitment success. General temporal trends of primary production and worm production were similar, and the worm population required 35%–100% of the estimated annual net water column community production per m2 for this region of the estuary. Chaetopterus cf. variopedatus is an important component of the lower bay ecosystem and should be considered when modeling carbon, nutrient, and energy flow. Our results further demonstrate that temporal variations in population dynamics lead to significant temporal variability in the relative importance of benthic suspension feeder effects for ecosystem function.