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Narragansett Bay is an estuarine system in the western North Atlantic Ocean that harbors a diverse marine flora, providing structure, habitat, and food for native biodiversity. This area has been the center of numerous environmental, biological, ecological, and oceanographic studies; however, marine macroalgae have not been extensively examined using modern molecular methods. Here, we document the biodiversity of the red algal order Ceramiales based on DNA sequence comparisons of the 3′ end of the RuBisCo large subunit (rbcL-3P) and the universal plastid amplicon (UPA). Thirty-seven distinct species of this order were identified and validated with molecular data, including five new species reports and at least one new report of an introduced species, Antithamnionella spirographidis, in the vicinity of Narraganset Bay. Novel sequence data were generated for numerous species, and it was discovered that the UPA marker, which has been less frequently used in red algal floristics, revealed an identical inventory of ceramialean algae as the rbcL-3P marker. Thus, the shorter length of the UPA marker holds promise for DNA metabarcoding studies that seek to elucidate biodiversity across algal phyla. [ABSTRACT FROM AUTHOR]

Long-term ecological time series provide a unique perspective on the emergent properties of ecosystems. In aquatic systems, phytoplankton form the base of the food web and their biomass, measured as the concentration of the photosynthetic pigment chlorophyll α (chl α), is an indicator of ecosystem quality. We analyzed temporal trends in chl α from the Long-Term Plankton Time Series in Narragansett Bay, Rhode Island, USA, a temperate estuary experiencing long-term warming and changing anthropogenic nutrient inputs. Dynamic linear models were used to impute and model environmental variables (1959 to 2019) and chl α concentrations (1968 to 2019). A long-term chl α decrease was observed with an average decline in the cumulative annual chl α concentration of 49% and a marked decline of 57% in winter-spring bloom magnitude. The long-term decline in chl α concentration was directly and indirectly associated with multiple environmental factors that are impacted by climate change (e.g., warming temperatures, water column stratification, reduced nutrient concentrations) indicating the importance of accounting for regional climate change effects in ecosystem-based management. Analysis of seasonal phenology revealed that the winter-spring bloom occurred earlier, at a rate of 4.9 ± 2.8 d decade-1. Finally, the high degree of temporal variation in phytoplankton biomass observed in Narragansett Bay appears common among estuaries, coasts, and open oceans. The commonality among these marine ecosystems highlights the need to maintain a robust set of phytoplankton time series in the coming decades to improve signal-to-noise ratios and identify trends in these highly variable environments. [ABSTRACT FROM AUTHOR]

Narragansett Bay is an estuarine system in the western North Atlantic Ocean that harbors a diverse marine flora, providing structure, habitat, and food for native biodiversity. This area has been the center of numerous environmental, biological, ecological, and oceanographic studies; however, marine macroalgae have not been extensively examined using modern molecular methods. Here, we document the biodiversity of the red algal order Ceramiales based on DNA sequence comparisons of the 3′ end of the RuBisCo large subunit (rbcL-3P) and the universal plastid amplicon (UPA). Thirty-seven distinct species of this order were identified and validated with molecular data, including five new species reports and at least one new report of an introduced species, Antithamnionella spirographidis, in the vicinity of Narraganset Bay. Novel sequence data were generated for numerous species, and it was discovered that the UPA marker, which has been less frequently used in red algal floristics, revealed an identical inventory of ceramialean algae as the rbcL-3P marker. Thus, the shorter length of the UPA marker holds promise for DNA metabarcoding studies that seek to elucidate biodiversity across algal phyla.

Anthropogenic sources of nutrients cause eutrophication in coastal waters. Narraganset Bay (USA), the largest estuary in New England, has large seasonal zones of hypoxia. In response, management strategies have been implemented to reduce nutrient loadings. In this study, a mechanistic, mass balance fate and transport modeling framework was developed and applied to Narragansett Bay to improve our understanding of the processes governing hypoxia. Discrete and continuous observations were used for model comparison and evaluation. Simulations captured the general trends and patterns in dissolved oxygen (DO) with depth and space. Simulations were unable to capture the wide diurnal range of observed continuous DO and phytoplankton concentrations, potentially suggesting the need for improved understanding of processes at this time scale. Mechanistic modelling scenarios were performed to investigate how different sources of nutrients affect DO. Results suggest tributary sources of nitrogen affected upper layers of DO, while sediment oxygen demand and nutrient fluxes affected deeper waters. This work highlights the importance of understanding and simulating the legacy effects of historic nutrient loading to estuary systems to understand the magnitude and timing of long-term recovery due to reductions in nutrient loadings. [ABSTRACT FROM AUTHOR]

In 2016-17, shellfish harvesting closed for the first time in Narragansett Bay, Rhode Island, USA, from domoic acid (DA), a neurotoxin produced by diatoms of the Pseudo-nitzschia genus. Pseudo-nitzschia have occurred frequently for over 60 years in Narragansett Bay’s Long-Term Plankton Time Series (NBPTS), therefore it is surprising that the first closure only recently occurred. Pseudo-nitzschia species are known to vary in their toxin production, thus species identification is critical for understanding the underlying ecological causes of these harmful algal blooms (HABs). DNA in plankton biomass can be preserved for many years, so molecular barcoding of archived samples is useful for delineation of taxa over time. This study used amplification of the Pseudo-nitzschia-specific 18S-5.8S rDNA internal transcribed spacer region 1 (ITS1) in plankton samples and high throughput sequencing to characterize Pseudo-nitzschia species composition over a decade in Narragansett Bay, including eight years before the 2016-17 closures and two years following. This metabarcoding method can discriminate nearly all known Pseudo-nitzschia species. Several species recur as year-round residents in Narragansett Bay (P. pungens var. pungens, P. americana, P. multiseries, and P. calliantha). Various other species increased in frequency after 2015, and some appeared for the first time during the closure period. Notably, P. australis, a species prevalent in US West Coast HABs and known for high DA production, was not observed in Narragansett Bay until the 2017 closure but has been present in several years after the closures. Annual differences in Pseudo-nitzschia composition were correlated with physical and chemical conditions, predominantly water temperature. The long-term composition trends of Pseudo-nitzschia in Narragansett Bay serve as a baseline for identifying the introduction of new species, understanding shifting assemblages that contributed to the 2016-17 closures, and monitoring species that may be cause for future concern.

Many urban estuaries worldwide suffer from excess phytoplankton and hypoxia (low oxygen) due to high nutrient loads. A common water quality management strategy is to require wastewater treatment facility upgrades. This case study examines Narragansett Bay, a warming temperate mid-latitude urban estuary with seasonal periodic hypoxia, during June through September from 2005 to 2019. Within this period, numerous facilities were upgraded to nitrogen removal over several years. The response of the bay is more consistent with “textbook” expectations for reduced chlorophyll and hypoxia than what was seen in many other systems—despite its complex coastline geometry, numerous river inputs, and widely-distributed treatment facilities. River flow drives inter-annual variability with increased load, density stratification, chlorophyll, and hypoxia in wet years. Mean 2013-2019 bay-wide total nitrogen load was 34% less than the 2005-2012 mean, a reduction of about 106 kg yr-1, comparable to the range of flow-driven inter-annual variations. Chlorophyll Index and Hypoxia Index event-based metrics applied to high-frequency time series observations at eight sites quantify exceedances of severe and moderate thresholds. Relatively steady 33% and 16% Chlorophyll Index declines, for severe and moderate thresholds, occurred from about 2007 to 2019. The Hypoxia Index declined markedly by 2009 and 2014 for severe and moderate thresholds, respectively, and remained at or near zero from 2014 to 2019. The load reduction explains chlorophyll and hypoxia declines better than physical processes including river flow, stratification, tidal variations, winds, sea level differences, and temperatures. River flow about 55% higher than the 2005-2019 mean would increase non-treatment facility loads by an amount comparable to the managed load decrease, so future wet summers could partially reverse the improvements. Long-term trends include warming of about 0.5°C decade-1, which reduces oxygen saturation by 0.1 mg l-1 decade-1. This rate is likely a lower bound for temperature-driven oxygen decreases, because warming can also accelerate phytoplankton growth and bacterial consumption. Without warming, the managed load decrease would have curtailed hypoxia more effectively. Climate trends should be at least as important to future eutrophication as the managed load decline because, in addition to warming influences, long-term increases in river flow would increase load and stratification.

This work utilizes remotely sensed thermal data to understand how the release of thermal pollution from the Brayton Point Power Station (BPPS) affected the temperature behavior of Narragansett Bay. Building upon previous work with Landsat 5, a multi-satellite analysis is conducted that incorporates 582 scenes from Landsat 5, Landsat 7, and Landsat 8 over 1984–2021 to explain seasonal variability in effluent impacts, contrast data after the effluent ceased in 2011, identify patterns in temperature before and after effluent ceased using unsupervised learning, and track how recent warming trends compare to the BPPS impact. Stopping the thermal effluent corresponds to an immediate cooling of 0.26 ± 0.1°C in the surface temperature of Mt. Hope Bay with respect to the rest of Narragansett Bay with greater cooling of 0.62 ± 0.2°C found near Brayton Point; though, cooling since the period of maximal impact (1993–2000) totals 0.53 ± 0.2°C in Mt. Hope Bay and 1.04 ± 0.2°C at Brayton Point. During seasons with lower solar radiation (winter) and lower mean river input (autumn and late summer), the BPPS effluent impact is more prominent. The seasonal differences between the high impact and low impact periods indicate that river input played an important role in the heat balance when emissions were lower, but surface fluxes dominated when emissions were higher. Putting the BPPS effluent in context, Landsat data indicates that Narragansett Bay warmed 0.5–1.2°C over the period of measurement at an average rate of 0.23 ± 0.1°C/decade and that net warming in Mt. Hope Bay is near zero. This trend implies that Narragansett Bay has experienced climatic warming over the past four decades on the scale of the temperature anomaly in Mt. Hope Bay caused by the BBPS effluent.

The abundance of dominant zooplankton, the copepods Acartia hudsonica and Acartia tonsa, was observed for 19 years (1972–1990) as part of a long-term weekly monitoring program in a north temperate estuary, lower Narragansett Bay, Rhode Island, USA. Acartia abundance data were analyzed via time series and phenology analyses to detect changes in abundance and timing (phenology) of the seasonal appearance, disappearance and duration of the cryophilic (A. hudsonica) and thermophilic (A. tonsa) Acartia congeners. No long-term changes in A. hudsonica abundance (long-term mean abundance of 9244 animals m−3) or phenology were detected during 1972–1990. However, de-seasonalized mean A. tonsa abundance increased 2-fold from near 2500 animals m−3 in the early 1970s to near 5000 animals m−3 in the late 1980s. Acartia tonsa also displayed changes in the timing of its annual appearance and departure as observed at the lower Narragansett Bay monitoring station. During 1972–1990, the time of A. tonsa first appearance in the spring advanced by ~3 weeks moving from Week 25 (mid-June) in the early 1970s to Week 22 (mid-May) in the late 1980s. Additionally, A. tonsa tended to depart from the plankton later in the year in the late 1980s (departure in late February) compared to the departure time observed in the 1970s (mid-January). Together, these changes resulted in an increased duration of A. tonsa presence in the water column, with A. tonsa duration increasing from 31 weeks in the early 1970s to 38 weeks in the late 1980s. These changes in thermophilic A. tonsa abundance and phenology appear to have been initial, stimulatory responses to warming that were subsequently modified by changes in the phenology and abundance of gelatinous zooplankton predators. [ABSTRACT FROM AUTHOR]

The tight coupling between nitrogen and carbon cycling has important implications for global climate. These two cycles are under growing anthropogenic pressures (e.g., warming temperatures, changes in nitrogen loading). In this article, we use Narragansett Bay as a model system to explore how large- and small-scale human forcings alter marine sediment nitrogen cycling. We measured net sediment N2 fluxes at two stations in Narragansett Bay over a nine-year period (2005–2013), resulting in observed mean net denitrification rates of 85 µmol m–2 h–1 and 40 µmol m–2 h–1 at the highly impacted and the less impacted sites, respectively. However, mean net N-fixation was essentially the same at each site (–89 and –88 µmol m–2 h–1). We found significant relationships between mean summer (June, July, August) water column chlorophyll and mean summer sediment N2 fluxes. Using these relationships and the long-term chlorophyll record in Narragansett Bay, we predicted summer net sediment N2 fluxes for the last 40 years. This approach suggests that the coastal ocean nitrogen cycle responds rapidly to changes in organic matter availability. If such trends hold true for the global ocean, the marine nitrogen cycle as a whole may also be undergoing significant changes.

Excessive input of nitrogen to estuaries and coastal waters leads to eutrophication; the resulting organic matter over-enrichment of sediments and seasonal hypoxia of bottom water have significant deleterious effects on benthic community biodiversity, abundance, and biomass. Our goal was to better understand how these losses carry through to impairment of key ecosystem functions of benthic communities. Recent management efforts to address eutrophication have reduced nitrogen loading to several estuaries of the Virginian Biogeographic Province (northeast United States). How the ecosystems will respond remains to be seen. Using Narragansett Bay as an example estuary within this Province, we compared measures of community structure and function from stations in seasonally hypoxic areas with stations in normoxic areas. We analyzed a benthic data set spanning 20 years (1990-2010) and 155 stations, along with ancillary data from other sources. Hypoxic areas had half the species richness, many fewer rare species, and lower biomass. Benthic communities in the hypoxic areas had a significantly different abundance structure, were at an earlier successional stage, and bioturbated the sediments to a depth about one-fifth that of the normoxic areas. On average, sediments in the hypoxic areas took up more oxygen—used for aerobic metabolism and oxidation of reduced compounds from anaerobic metabolism—than those in normoxic areas. Sediments released into the overlying water two to three times more ammonium and phosphate. Mean flux of dissolved oxygen into the sediments of hypoxic areas and mean net flux of nitrogen gas (from sediment denitrification) out were slightly higher. Eutrophication-driven over-enrichment of organic matter, along with seasonal hypoxia in the northern part of the Bay have led to degradation of benthic community structure and function, which have serious implications for sustainable provision of ecosystem services. We quantified fifteen stressor-response relationships that can help understand how, following a reduction in nitrogen inputs, a recovery of benthic ecosystem functions in hypoxic areas could proceed.

In 2004, the Atlantic Ecology Division of the US Environmental Protection Agency’s Office of Research and Development began an annual winter waterfowl survey of Rhode Island’s Narragansett Bay. Herein, we explore the survey data gathered from 2004 to 2011 in order to establish a benchmark understanding of our waterfowl communities and to establish a statistical framework for future environmental monitoring. The abundance and diversity of wintering waterfowl were relatively stable during the initial years of this survey, except in 2010 when there was a large spike in abundance and a reciprocal fall in diversity. There was no significant change in ranked abundance of most waterfowl species, with only Bufflehead ( Bucephala albeola) and Hooded Merganser ( Lophodytes cucllatus) showing a slight yet significant upward trend during the course of our survey period. Nonmetric multidimensional scaling (NMDS) was used to examine the community structure of wintering waterfowl. The results of the NMDS indicate that there is a spatial structure to the waterfowl communities of Narragansett Bay and this structure has remained relatively stable since the survey began. Our NMDS analysis helps to solidify what is known anecdotally about the bay’s waterfowl ecology, and provides a formalized benchmark for long-term monitoring of Narragansett Bay’s waterfowl communities. Birds, including waterfowl, are preferred bioindicators and we propose using our multivariate approach to monitor the future health of the bay. While this research focuses on a specific area of New England, these methods can be easily applied to novel areas of concern and provide a straightforward nonparametric approach to community-level monitoring. The methods provide a statistic test to examine potential drivers of community turnover and well-suited visualization tools.

In 2004, the Atlantic Ecology Division of the US Environmental Protection Agency’s Office of Research and Development began an annual winter waterfowl survey of Rhode Island’s Narragansett Bay. Herein, we explore the survey data gathered from 2004 to 2011 in order to establish a benchmark understanding of our waterfowl communities and to establish a statistical framework for future environmental monitoring. The abundance and diversity of wintering waterfowl were relatively stable during the initial years of this survey, except in 2010 when there was a large spike in abundance and a reciprocal fall in diversity. There was no significant change in ranked abundance of most waterfowl species, with only Bufflehead ( Bucephala albeola) and Hooded Merganser ( Lophodytes cucllatus) showing a slight yet significant upward trend during the course of our survey period. Nonmetric multidimensional scaling (NMDS) was used to examine the community structure of wintering waterfowl. The results of the NMDS indicate that there is a spatial structure to the waterfowl communities of Narragansett Bay and this structure has remained relatively stable since the survey began. Our NMDS analysis helps to solidify what is known anecdotally about the bay’s waterfowl ecology, and provides a formalized benchmark for long-term monitoring of Narragansett Bay’s waterfowl communities. Birds, including waterfowl, are preferred bioindicators and we propose using our multivariate approach to monitor the future health of the bay. While this research focuses on a specific area of New England, these methods can be easily applied to novel areas of concern and provide a straightforward nonparametric approach to community-level monitoring. The methods provide a statistic test to examine potential drivers of community turnover and well-suited visualization tools.

In 2004, the Atlantic Ecology Division of the US Environmental Protection Agency’s Office of Research and Development began an annual winter waterfowl survey of Rhode Island’s Narragansett Bay. Herein, we explore the survey data gathered from 2004 to 2011 in order to establish a benchmark understanding of the Narragansett Bay’s waterfowl communities and to establish a statistical framework for future environmental monitoring. Abundance and diversity of Narragansett Bay’s wintering waterfowl were relatively stable during the initial years of this survey, except in 2010 when there was a large spike in abundance and a reciprocal fall in diversity. There was no significant change in ranked abundance of most waterfowl species, with only Bufflehead ( Bucephala albeola) and Hooded Merganser ( Lophodytes cucllatus) showing a slight yet significant upward trend during the course of our survey period. Nonmetric multidimensional scaling was used to examine the community structure of wintering waterfowl in Narragansett Bay. The results of the Nonmetric multidimensional scaling indicate that there is a spatial structure to the waterfowl communities of Narragansett Bay and this structure has remained relatively stable since the survey began. Our Nonmetric multidimensional scaling analysis helps to solidify what is known anecdotally about Narragansett Bay’s waterfowl ecology, and provides a formalized benchmark for long-term monitoring of Narragansett Bay’s waterfowl communities. Birds, including waterfowl, are preferred bioindicators and we propose using our multivariate approach to monitor the future health of Narragansett Bay.

Niche theory, the oldest, most established community assembly model, predicts that in sympatry, the realized niche will contract due to negative interspecific interactions, but fails to recognize the effects of positive interactions on community assembly. The stress gradient hypothesis predicts that positive interactions expand realized niches in stressful habitats. We tested the predictions of the stress gradient hypothesis in a cobble beach model system across both physical and biological stress gradients. We transplanted seven common littoral species within, adjacent to, and below Spartina alterniflora cordgrass stands in control, cage control, predator exclusion cage, shade, and shaded predator exclusion cage treatments to test the hypothesis that cordgrass expands intertidal organism habitats. On cobble beaches, cordgrass ameliorates physical and predation stresses, expanding the distribution and realized niches of species to habitats in which they cannot live without facilitation, suggesting that niche theory and species distribution models should be amended to accommodate the role of positive interactions in community assembly. [ABSTRACT FROM AUTHOR]

Historically, southern New England has supported one of the most productive American lobster (Homarus americanus) fisheries of the northeast United States. Recently, the region has seen dramatic declines in lobster populations coincident with a trend of increasingly stressful summer warmth and shell disease. We report significant declines in the abundance, distribution, and size composition of juvenile lobsters that have accompanied the warming trend in Narragansett Bay, Rhode Island, since the first comprehensive survey of lobster nurseries conducted there in 1990. We used diver-based visual surveys and suction sampling in 1990, 2011, and 2012, supplemented by post-larval collectors in 2011 and 2012. In 1990, lobster nurseries extended from the outer coast into the mid-sections of the bay, but by 2011 and 2012 they were largely restricted to the outer coast and deeper water at the mouth of the bay. Among five new study sites selected by the lobster fishing industry for the 2011 and 2012 surveys, the deepest site on the outer coast (15–17 m depth) harboured some of the highest lobster densities in the survey. Separate fixed site hydrographic monitoring at 13 locations in the bay by the Rhode Island Division of Fish and Wildlife recorded an approximately 2.0°C increase in summer surface temperatures over the period, with 2012 being the warmest on record. Additional monitoring of bottom temperatures, dissolved oxygen and pH at our sampling sites in 2011 and 2012 indicated conditions falling below physiological optima for lobsters during summer. The invasion of the Asian shore crab, Hemigrapsus sanguineus, since the 1990s may also be contributing to declines of juvenile lobster shallow zones (<5 m) in this region. Because lobster populations appear increasingly restricted to deeper and outer coastal waters of southern New England, further monitoring of settlement and nursery habitat in deep water is warranted. [ABSTRACT FROM AUTHOR]

Over the past three decades, Narragansett Bay has undergone various ecological changes, including significant decreases in water column chlorophyll a concentrations, benthic oxygen uptake, and benthic nutrient regeneration rates. To add to this portrait of change, we measured the net flux of N across the sediment-water interface over an annual cycle using the N/Ar technique at seven sites in the bay for comparison with measurements made decades ago. Net denitrification rates ranged from about 10-90 μmol N-N m h over the year. Denitrification rates were not significantly different among sites and had no clear correlation with temperature. Net nitrogen fixation (−5 to −650 μmol N-N m h) was measured at three sites and only observed in summer (June-August). Neither denitrification nor nitrogen fixation exhibited a consistent relationship with sediment oxygen demand or with fluxes of nitrite, nitrate, ammonium, total dissolved inorganic nitrogen, or dissolved inorganic phosphate across all stations. In contrast to the mid-bay historical site where denitrification rates have declined, denitrification rates in the Providence River Estuary have not changed significantly over the past 30 years. [ABSTRACT FROM AUTHOR]

A photosynthetic quotient (PQ) for Narragansett Bay, RI, USA was calculated using concurrent 14C and oxygen light–dark bottle primary production estimations. The current PQ (1.42 ± 0.09) was elevated over the PQ (1.24) calculated in a 1980's mesocosm experiment, stimulating a sensitivity analysis of physiological drivers of the PQ. We speculate that the factor that altered the PQ between surveys was wastewater treatment facility upgrades increasing NO3− effluent proportion from 10 to 40%. [ABSTRACT FROM AUTHOR]

Ocean acidification is predicted to impact the nitrogen cycle in a variety of ways. Specifically, manipulations of water column pH have shown that nitrification, the microbial conversion of ammonium to nitrate, is inhibited at low pH. A decrease in nitrification may impact phytoplankton composition and production, denitrification, and the production of nitrous oxide. We compiled an existing unique data set of concurrent water column nitrification rates and water column pH values from a temperate New England estuary (Narragansett Bay, RI, USA). Contrary to the current hypothesis, we found that nitrification rates were highest at low pH and significantly ( P = 0.0031) lower at high water column pH. In this study, pH varied up to 0.85 units, 20% more than the maximum predicted ocean pH decrease of 0.7 units. These results highlight that nitrifying organisms in coastal systems tolerate a wide range of pH values. Moreover, the degree of negative correlation with pH may depend on site-specific environmental conditions. Combined, these findings indicate that the current hypothesis of the negative impacts of ocean acidification on nitrification, at least for the coastal ocean, might need reevaluation. [ABSTRACT FROM AUTHOR]

Increasing growth in the aquaculture industry demands ecosystem-based techniques for management if that growth is to be ecologically sustainable and promote equity among users of the ecosystems in which it occurs. Models of carrying capacity can be used to responsibly limit the growth of aquaculture in increasingly crowded coastal areas. Narragansett Bay, Rhode Island, USA is one such crowded coastal region experiencing a rapid increase in bivalve aquaculture. An ecosystem mass-balance model was used to calculate the ecological carrying capacity of bivalve aquaculture. Cultured oyster biomass is currently at 0.47tkm−2 and could be increased 625 times without exceeding the ecological carrying capacity of 297tkm−2. This translates to approximately 38,950t of harvested cultured oysters annually which is 4 times the total estimated annual harvest of finfish. This potential for growth is due to the high primary productivity and large energy throughput to detritus of this ecosystem. Shellfish aquaculture has potential for continued growth and is unlikely to become food limited due, in part, to the large detritus pool. [Copyright &y& Elsevier]

Strong benthic-pelagic coupling is an important characteristic of shallow coastal marine ecosystems. Building upon a rich history of benthic metabolism data, we measured oxygen uptake and nutrient fluxes across the sediment-water interface along a gradient of water column primary production in Narragansett Bay, RI (USA). Despite the strong gradients seen in water column production, sediment oxygen demand (SOD) and benthic nutrient fluxes did not exhibit a clear spatial pattern. Some of our sites had been studied in the 1970s and 1980s and thus allowed historical comparison. At these sites, we found that SOD and benthic fluxes have not changed uniformly throughout Narragansett Bay. In the uppermost portion of the bay, the Providence River Estuary, we observed a significant decrease in dissolved inorganic phosphorus fluxes which we attribute to management interventions. At another upper bay site, we observed significant declines in SOD and dissolved inorganic nitrogen fluxes which may be linked to climate-induced decreases in water column primary production and shifts in bloom phenology. In the 1970s, benthic nutrient regeneration supplied 50% to over 200% of the N and P needed to support primary production by phytoplankton. Summer nutrient regeneration in the Providence River Estuary and Upper bay now may only supply some 5-30% of the N and 3-20% of the P phytoplankton demand. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the δ13 values of filter-feeding hard clams Mercenaria mercenaria from 13 locations in Greenwich Bay, Rhode Island. The values of δ13 of the clams showed a linear gradient of two percent over the four kilometer (km) length of Greenwich Bay. Study authors conclude that their findings suggest that δ13 values may be sensitive to the changes in inorganic carbon in estuarine systems. They add that the δ13 values in Mercenaria mercenaria may depict ecosystem metabolism variation.

Abstract: The Benthic Habitat Quality (BHQ) index was used to assess habitat visible in sediment profile images (SPI) following hypoxia disturbance in a shallow (<10m) estuarine embayment in Rhode Island, USA. We tested for associations between the BHQ, SPI features and water quality over several assessment windows (1, 3, 7, 14, and 28 days prior to imaging) and at multiple dissolved oxygen (DO) thresholds (2.0mgl−1, 2.9mgl−1, and 4.8mgl−1). Using categorical data analysis, we established empirical relationships between hypoxia prevalence and presence/absence of biogenic features visible in SPI. Fecal pellets, tubes, feeding pits, voids, mounds, and BHQ score were good affirmative features, meaning that their presence (or score greater than 5) indicated a high probability of good water quality. However, low sensitivity to hypoxia precluded their usefulness as indicators, and was attributed to rarity in images and to factors acting on time intervals longer than those examined, e.g. long-term organic enrichment or hypoxia. Burrow structures and the apparent redox potential discontinuity (aRPD), or oxidized layer of surface sediment, were good discriminatory features, with high sensitivity and specificity for both hypoxia and normoxia. Both were strong surrogates for water quality over multiple assessment windows and DO thresholds, and had the highest overall predictive values. We conclude that SPI images can be used to widen the spatial extent of water quality monitoring efforts by utilizing the relationships between aRPD, burrows and hypoxia prevalence. [Copyright &y& Elsevier]

Low dissolved oxygen events were characterized in Narragansett Bay (NB), a moderate-size (370 km²) temperate estuary with a complex passage/embayment geometry, using time series from 2001 to 2006 at nine fixed-site monitoring stations. Metrics for event intensity and severity were the, event-mean deficit relative to a threshold (mg O2 1-1) and the deficit-duration (mg O2 1-1) day; product of deficit and duration [day]). Hypoxia (threshold 2.9 mg O2 1-1) typically occurred intermittently from late June through August at most stations, as multiple (two to five per season) events each 2 to 7 days long with deficit-duration 2 to 5 mg O2 1-1 day. Conditions were more severe to the north and west, a pattern attributed to a north-south nutrient/productivity gradient and east-west structure of residual circulation. Spatial patterns for suboxic and severely hypoxic events (thresholds 4.8 and 1.4 mg O2 l-1) were similar. The view that different processes govern event variability in different regions, each influenced by local hydrodynamics, is supported by both weak spatial synchronicity (quantified using overlap of event times at different sites) and multiple linear regressions of biological and physical parameters against event severity. Interannual changes were prominent and season-cumulative hypoxia severity correlated with June-mean river runorf and June-mean stratification. Benthic ecological implications for areas experiencing events include: NB hypoxia classifies as periodic/episodic on a near-annual basis; highest direct mortality risk is to sensitive and moderately sensitive sessile species in the northern West Passage and western Greenwich Bay, with some risk to Upper Bay; direct risk to mobile species may be ameliorated by weak spatial synchronicity; and indirect impacts, including reduced growth rates and shifts in predator-prey balances, are very likely throughout the sampled area due to observed suboxic and hypoxic conditions. [ABSTRACT FROM AUTHOR]

We developed an assessment model to quantify the wildlife habitat value of New England salt marshes based on marsh characteristics and the presence of habitat types that influence habitat use by terrestrial wildlife. Applying the model to 12 salt marshes located in Narragansett Bay, RI resulted in assessment scores that ranged over a factor of 1.5 from lowest to highest. Pre-classifying the results based on marsh size and morphology helped to compare assessment scores between marshes, and demonstrated that even the lower ranking marshes had substantial habitat value. Stepwise multiple regression analysis of assessment scores and model components demonstrated that salt marsh morphology, the degree of anthropogenic modification, and salt marsh vegetative heterogeneity were significant variables and accounted for 91.3% of the variability in component scores. Our results suggest that targeting these components for restoration may lead to improved assessment scores for our study marshes. We also examined the use of lower resolution remote sensing data in the assessment in order to minimize the time and effort required to complete the model. Scores obtained using smaller-scale, lower resolution data were significantly lower than those obtained using larger-scale, higher resolution data ( df = 11; t = 2.2; p < 0.001). The difference was significantly positively correlated with the portion of the assessment score that could be attributed to trees, pools, and pannes and marsh size ( r2 =0.50, F = 4.6, p = 0.04), and could indicate a bias against smaller, more heterogeneous marshes. We conclude that potential differences need to be weighed against the time benefit of using this type of data, bearing in mind the marsh size and the goals of the assessment. Overall, our assessment can provide information to aid in prioritizing marshes for protection and restoration, identify marshes that may harbor significant biodiversity, or help monitor changes in habitat value over time. [ABSTRACT FROM AUTHOR]

Environmental factors, including the supply of organic matter and inorganic nutrient concentrations, are thought to influence rates of two opposing processes in the nitrogen (N) cycle, denitrification and N fixation. Using sediment cores from a temperate estuary we examined the effects of nitrate, phosphate, and ammonium enrichment of the overlying water on the net N2 flux across the sediment–water interface. In addition, we used sediment cores and large marine mesocosms to determine the effect of organic matter amendment. The addition of nitrate (50 μM), ammonium (50 μM), and phosphate (10 μM) to the overlying water had no effect on the net N2 flux. However, high ammonium fluxes (145 μmol m−2 h−1) were observed in the nitrate-amended cores, which is suggestive of dissimilatory nitrate reduction to ammonium. Organic matter enrichment first increased rates of N fixation, but ultimately switched the sediments from being a net source (N fixation dominated) to a net sink (denitrification dominated) of N. We observed a threshold where N fixation took place when organic matter deposition fell below about 0.3 g C m−2 day−1. On the basis of these results and the findings of others, we developed a conceptual model that links net sediment N2 flux with the organic matter production of a system. [ABSTRACT FROM AUTHOR]

Natural stress gradients can reduce predation intensity and increase prey abundances. Whether the harsh conditions of anthropogenic habitat degradation can similarly reduce predation intensity and structure community dynamics remains largely unexplored. Oxygen depletion in coastal, waters (hypoxia) is a form of degradation that has recently emerged as one of the greatest threats to coastal ecosystems worldwide due to increased rates of eutrophication and climate change. I conducted field experiments and surveys to test whether relaxed predation could explain the paradoxically high abundance of clams that have' sustained a fishery in a degraded estuary with chronic hypoxic conditions. Hypoxia reduced predation on all experimental species but enhanced the long-term survivorship of only sufficiently hypoxia-tolerant prey due to periodic extreme conditions. As a consequence, only the harvested quahog clam (Mercenaria inercenaria) thrived in hypoxic areas that were otherwise rendered dead zones with depauperate diversity and low abundances of other species. This suggests that enhanced populations of some key species may be part of a predictable nonlinear community response that sustains ecosystem services and masks overall downward trends of habitat degradation. [ABSTRACT FROM AUTHOR]

During the last several decades, the waters of mid Narragansett Bay, Rhode Island have increased in temperature and decreased in chlorophyll concentration, and it is possible that these changes affected the growth and success of a common benthic filter feeder, the hard clam, Mercenaria mercenaria. We determined recent hard clam growth rates through a sclerochronological analysis and compared them to the rich historical record of Narragansett Bay growth rates in order to understand how these opposing changes influenced hard clam growth. We found no significant differences in short-term growth between 1985 and 2000. Long-term juvenile growth showed a significant decrease between the 1960s and 1990s, while long-term adult (mature) growth showed a significant increase over this same time period. While it is not clear why the changes in juvenile and adult growth rates differ, it appears as though the decrease in chlorophyll concentration, together with a change in phytoplankton community composition, increasing water temperature, and an increase in predator abundance, may all have influenced hard clam growth between the 1960s and the 1990s. [ABSTRACT FROM AUTHOR]

The genetic population structure of winter flounder larvae was examined in Narragansett Bay, RI. Winter flounder larvae collected from 20 stations within Narragansett Bay and one station outside of the Bay were analyzed for six micro-satellite loci. When analyzed by geographic collection sites, there were 16 distinct genetic populations of winter flounder larvae (RST values from 0.1 to 0.6). The presence of distinct genetic populations was supported by assignment of individual larvae to populations by Bayesian analysis. Bayesian analysis resulted in 14 distinct genetic populations that overlapped with the geographically distributed populations (RST values from 0.1 to 0.6). Young-of-the-year juveniles collected in the same year as the larvae were also analyzed at the same six microsatellite loci. Juveniles were assigned to larvae populations by both a Bayesian approach and a neural network approach. Juveniles collected from within Narragansett Bay were found to arise from geographically adjacent Narragansett Bay winter flounder larval populations (>99%), suggesting no widespread movement of juveniles away from spawning grounds. These results are discussed in the context of winter flounder population biology in Narragansett Bay, RI. [ABSTRACT FROM AUTHOR]

Auker, L. A., and Oviatt, C. A. 2008. Factors influencing the recruitment and abundance of Didemnum in Narragansett Bay, Rhode Island. – ICES Journal of Marine Science, 65: 765–769.The non-indigenous colonial tunicate Didemnum sp. A has been observed in Narragansett Bay, Rhode Island, since 2000. We compared weekly recruitment of the species and environmental parameters (i.e. temperature, salinity, chlorophyll a, dissolved oxygen, pH, and nutrient concentrations) over a 6-month period among three sites: (i) the University of Rhode Island Graduate School of Oceanography dock (GSO), (ii) the Department of Environmental Management pier at Fort Wetherill (FW), and (iii) the Prudence Island T-wharf. At the GSO and FW, divers surveyed the sites for percentage cover of Didemnum. To assess the spread of Didemnum in the bay and what factors may predict the tunicate’s presence, we also surveyed intertidal sites in October and November 2005, noting Didemnum presence, salinity, number of boats and moorings, and distances to major ports at each site. GSO had the highest percentage cover of adults and the highest recruitment of the tunicate (p < 0.01), reaching average peak values of 319 individuals per 100 cm2 in September 2005. Temperature and salinity demonstrated the best correlation with recruitment, and higher boat and mooring numbers may be a reliable predictor of tunicate presence. Further monitoring is needed to assess the potential spread of Didemnum throughout Narragansett Bay. [ABSTRACT FROM PUBLISHER]

Although primary productivity in salt marshes is thought to be controlled by physical forces, recent evidence suggests that human disturbances can drive a switch to consumer control in these ecologically valuable ecosystems. We tested the hypothesis that nitrogen enrichment can trigger consumer control in salt marshes in Narragansett Bay, Rhode Island, with (1) a field experiment in which we manipulated nutrient availability (with nutrient additions) and insect herbivory (with insecticide application), (2) a survey of 20 salt marshes that examined the relationship between marsh nutrient status and herbivore pressure, and (3) insect herbivore removal at high and low nutrient input sites to directly test the hypothesis that nutrient enrichment is increasing insect herbivory in these marshes. Experimental nitrogen eutrophication initially increased plant productivity but eventually led to reduced plant biomass due to insect herbivory, and our surveys revealed that marsh nitrogen supply was a good predictor of herbivore damage to plants. Insects had minimal impacts on primary productivity in pristine marshes, but suppressed primary productivity in eutrophic salt marshes by 50–75%. Thus, eutrophication is currently triggering consumer suppression of primary productivity in New England salt marshes and may ultimately jeopardize the ecological and societal services these systems provide. [ABSTRACT FROM AUTHOR]

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ15N) and carbon (δ13C) The δ13N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ15N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ15N values in macroalgae there reflected preferential uptake of 14N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ13C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ15N (13.2±0.54‰ SD) and δ13C (-16.76±0.61‰ SD) throughout the bay, and the δ15N values were 2-5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources. [ABSTRACT FROM AUTHOR]

Abstract: Food chain and food web have been, thus far, depicted by number of individuals, matter (biomass) and energy, but not by the concept concerning to the second law of thermodynamics. The present paper takes up three U.S. mid-Atlantic estuaries and delineates marine trophic structure in the term of the concept of this missing link: the second law of thermodynamics. Homeostatic structure and function of living systems is maintained by chemical, physical and organic activities in biotic systems. These activities are supported by chemical energy released by decomposition of macromolecules in organisms by oxygen incorporated from the outside (respiration). This chemical energy finally becomes heat energy and is discarded to the outside. This heat energy is dissipation function in thermodynamics, and dissipation function divided by absolute temperature of organism–water is entropy production. As example, mid-Atlantic estuaries on the eastern U.S. coast are analyzed, based on the study of (Monaco, M.E., Ulanowicz, R.E., 1997. Comparative ecosystem trophic structure of three U.S. mid-Atlantic estuaries. Mar. Ecol. Prog. Ser. 161, 239–254). They give 13–14 trophic compartments in each estuaries, and respiration and other characteristic quantities for each trophic compartments. Trophic position of compartment in each estuary is adopted and arranged in accord to the food web diagrams of (Monaco, M.E., Ulanowicz, R.E., 1997. Comparative ecosystem trophic structure of three U.S. mid-Atlantic estuaries. Mar. Ecol. Prog. Ser. 161, 239–254). Plots of trophic number versus respiration become of half-pyramid shape, which is also applied to dissipation function because respiration is equal to dissipation function in thermodynamics. Annual average temperature at average depth in Narragansett estuary is, for example, 10.0°C (=283.2K). The difference between maximum and minimum temperature at averaged depth is 14.2°C (=287.4K). This difference is small compared with the absolute temperature scale. Hence let us make an approximation that the temperature of the water body of this estuary is about constant and uniform over a year and 10.0°C=283.2K. Entropy production is obtained by dividing dissipation function by this value. Pattern of trophic position versus entropy production multiplied by the temperature is of similar shape to dissipation function: half-pyramid. Other two estuaries show similar results. [Copyright &y& Elsevier]

Polychlorinated biphenyls (PCBs) were evaluated in 41 surface sediments collected from Narragansett Bay, RI in 1997–1998. Highest concentrations of total PCBs (1760 ng/g) were in rivers at the head of the bay and the values decreased southward toward the mouth of the bay, with elevated concentrations in some of the coves. The PCB levels in ∼43% of the samples exceeded the effects range median (ERM) guideline [Environ. Manage. 19 (1995) 81] indicating possible adverse biological effects at these stations.Principal component analysis (PCA) of the surface sediment PCBs separated the Taunton River samples from the rest of the samples. This result suggests that this river has a different PCB composition and sources than the other areas investigated. It also showed that this river has a limited influence on other bay stations as the adjacent samples downstream did not have the same chemical signature. Congener ratios derived from the PCA were useful in distinguishing stations that had different sources of PCBs than the bulk of the bay sediments. Although Aroclor 1268 and 1270 accounted for <1% of all PCB production, their major components, CB206 and CB209, account for 3–6% of the CBs in most bay samples. This may reflect more local use of these Aroclor mixtures and/or be indicative of their relative stability, compared to less chlorinated mixtures.Using linear alkyl benzenes (LABs) as a marker for sewage derived PCBs suggested that up to 95% of the PCBs at the most contaminated sites in the Seekonk, Providence, and Taunton Rivers were sewage derived. This analysis also showed that there is a high background level (167 ng/g) of PCBs in the Seekonk and Providence River, while the Taunton River had a relatively low background level (23.7 ng/g). At the furthest stations south in the Providence River, the sewage derived PCBs only accounted for 23% of the total which suggests that PCB associated with sewage particles are rapidly deposited and are therefore not the most significant source of these compounds to the lower reaches of Narragansett Bay. [Copyright &y& Elsevier]

The article discusses Computer-Aided Tomography (CT) scanning technology was applied to intact sediment cores to study estuary benthic communities. It discusses use of attenuation of X-rays to differentiate between sediment and water contained in macrobenthic tubes and tunnels. It also mentions measurement of percentage of tube and tunnel area (PTTA) to assess and monitor the effects of organic carbon loading on benthic communities in Narragansett Bay, Rhode Island.

Weekly measurements of Chl a were carried out between 1973 and 1990 in Narragansett Bay, Rhode Island, a temperate estuary along the north-eastern US coast. There was only a threefold variation in mean annual chlorophyll values but a considerably greater variation in the period when the annual maximum was reached. The inter-annual variation in annual means was relatively modest compared with monthly means. For a given month, the inter-annual variability in monthly mean chlorophyll varied from 3- to 30-fold; it was least during the summer months and maximal during the winter–spring bloom period. The long-term variability patterns characterizing individual months differed in their trends, cycles, and irregular fluctu-ations. Major blooms occurred during most of the year, and were not restricted to the annual winter–spring bloom. However, the frequency and magnitude of blooms were higher during winter–spring months than during summer months. A significant finding is that the annual mean chlorophyll decreased by more than 1 mg m−2 year−1 over the 18 year time series. This decrease apparently was under multifactorial control, with zooplankton grazing, sea surface temperature and windspeed being the most important factors. [ABSTRACT FROM PUBLISHER]

Some features of the patterns of variability which characterize phytoplankton species occurrences, community organization, biomass levels, blooms, and associated physico-chemical growth regulators are considered. Phytoplankton variability occurs in various patterns: as cycles, trends, fluctuations, unusual events, irregular pulses; at various scales: hourly or less, daily, seasonally, annually, decadal, etc.; even chaotically, and at various frequencies. Variability in winter–spring bloom inception, duration and magnitude is discussed, and 11 types of species-specific patterns of variability are described, with some examples from Narragansett Bay highlighted. It is suggested that the variable response capabilities of planktonic communities act as restructuring mechanisms which allow the community and its foodweb linkages to modify their dynamics to accommodate the changed(-ing) environmental conditions. The distinction between point and threshold events embedded within patterns of plankton variability is discussed. The inadequacy of traditional monitoring approaches and the need to replace such sampling strategies with a combination of observational and process-oriented, in situ rate measurements to quantify the causes and effects of plankton variability are pointed out. [ABSTRACT FROM PUBLISHER]

Observations of Secchi-disk depth and related parameters were made weekly, from 1972 through 1996, in lower Narragansett Bay, Rhode Island. A significant increase in Secchi depth, at a linearized rate of 0.05 m yr−1, was detected during this 25-year time series. Most of the increase in water clarity occurred between 1984 and 1994, when loading of total suspended solids (TSS) to the Bay via waste-water treatment plants decreased ca. 75%, and Secchi depths increased ca. 25%. Decreased annual TSS loading explained 43% of the variance in mean annual Secchi depth between 1983 and 1995. In addition to a long-term increase, there was also a strong seasonal pattern in water clarity. The rate of increase in Secchi depth in Narragansett Bay between 1972 and 1996 was similar to rates observed in other coastal waters that have had recent reductions in anthropogenic TSS loading. [ABSTRACT FROM PUBLISHER]