This review provides an integrated synthesis with timelines and evaluations of ecological responses to eutrophication in Chesapeake Bay, the largest estuary in the USA. Analyses of dated sediment cores reveal initial evidence of organic enrichment in ~200 yr old strata, while signs of increased phytoplankton and decreased water clarity first appeared ~100 yr ago. Severe, recurring deep-water hypoxia and loss of diverse submersed vascular plants were first evident in the 1950s and 1960s, respectively. The degradation of these benthic habitats has contributed to declines in benthic macroinfauna in deep mesohaline regions of the Bay and blue crabs in shallow polyhaline areas. In contrast, copepods, which are heavily consumed in pelagic food chains, are relatively unaffected by nutrient-induced changes in phytoplankton. Intense mortality associated with fisheries and disease have caused a dramatic decline in eastern oyster stocks and associated Bay water filtration, which may have exacerbated eutrophication effects on phytoplankton and water clarity. Extensive tidal marshes, which have served as effective nutrient buffers along the Bay margins, are now being lost with rising sea level. Although the Bay's overall fisheries production has probably not been affected by eutrophication, decreases in the relative contribution of demersal fish and in the efficiency with which primary production is transferred to harvest suggest fundamental shifts in trophic and habitat structures. Bay ecosystem responses to changes in nutrient loading are complicated by non-linear feedback mechanisms, including particle trapping and binding by benthic plants that increase water clarity, and by oxygen effects on benthic nutrient recycling efficiency. Observations in Bay tributaries undergoing recent reductions in nutrient input indicate relatively rapid recovery of some ecosystem functions but lags in the response of others. KEY WORDS: Eutrophication · Nutrients · Chesapeake Bay Resale or republication not permitted without written consent of the publisherChesapeake Bay is a large estuary which has undergone many changes in its ecological properties and processes in response to nutrient enrichment over the last 2 centuries. Susceptibility of the Bay to eutrophication arises in part from the long dendritic shoreline that intimately connects it to its large watershed (covering an area 15 times that of the Bay) which contains expanding human population centers and extensive agricultural activities. (Satellite image from MODIS,

We examined the effects of anthropogenic and climatic perturbations on nutrient-phytoplankton interactions and eutrophication in the waters of the largest estuarine systems in the U.S.A., the Chesapeake Bay (CB), Maryland/ Virginia, and the Neuse River Estuary/Pamlico Sound (NRE/PS) system, North Carolina. Both systems have experienced large post-World War II increases in nitrogen (N) and phosphorus (P) loading, and nutrient reductions have been initiated to alleviate symptoms of eutrophication. However, ecosystem-level effects of these nutrient reductions are strongly affected by hydrologic variability, including severe droughts and a recent increase in Atlantic hurricane activity. Phytoplankton community responses to these hydrologic perturbations, including storm surges and floods, were examined and when possible, compared for these systems. In both systems, the resulting variability in water residence time strongly influenced seasonal and longer-term patterns of phytoplankton biomass and community composition. Fast-growing diatoms were favored during years of high discharge and short residence time in CB, whereas this effect was not observed during high discharge conditions in the longer residence time NRE/ PS. In the NRE/PS, all phytoplankton groups except summer cyanobacterial populations showed decreased abundance during elevated flow years when compared to low flow years. Although hurricanes affected the CB less frequently than the NRE/PS, they nonetheless influenced floral composition in both systems. Seasonally, hydrologic perturbations, including droughts, floods, and storm-related deep mixing events, overwhelmed nutrient controls on floral composition. This underscores the difficulty in predicting seasonal and longer-term phytoplankton production and compositional responses to nutrient input reductions aimed at controlling eutrophication of large estuarine ecosystems.

Environmental DNA (eDNA) technology potentially improves the monitoring of marine fish populations. Realizing this promise awaits better understanding of how eDNA relates to fish presence and abundance. Here, we evaluate performance by comparing bottom trawl catches to eDNA from concurrent water samples. In conjunction with New Jersey Ocean Trawl Survey, 1-l water samples were collected at surface and depth prior to tows at about one-fourth of Survey sites in January, June, August, and November 2019. eDNA fish diversity from 1 l was same as or higher than trawl fish diversity from 66 M litres swept by one tow. Most (70–87%) species detected by trawl in a given month were also detected by eDNA, and vice versa, including nearly all (92–100%) abundant species. Trawl and eDNA peak seasonal abundance agreed for ∼70% of fish species. In log-scale comparisons by month, eDNA species reads correlated with species biomass, and more strongly with an allometric index calculated from biomass. In this 1-year study, eDNA reporting largely concorded with monthly trawl estimates of marine fish species richness, composition, seasonality, and relative abundance. Piggybacking eDNA onto an existing survey provided a relatively low-cost approach to better understand eDNA for marine fish stock assessment.

Gyrodinium galatheanum is a photosynthetic, rnixotrophic dinoflagellate that is capable of ingesting other protists, including cryptophytes. Ingestion of cryptophycean prey involves formation of a protrusion near the flagellar pores in the sulcus region of the dinoflagellate, by which prey are captured and phagocytized. In phototrophically growing G. galatheanum, a total of 12 chlorophylls and carotenoids are detected using HPLC pigment analysis. In G. galatheanum that had been fed cryptophycean prey for 41 h, traces of pigments that were derived from prey were found. This suggests that ingested prey were not fully digested or that some chloroplasts from prey were retained by the dinoflagellate. G, galatheanum cultured in nutrient-replete medium had net positive growth under phototrophic conditions (i.e. without addition of prey). It could not survive inprolongeddarknesseven vnth sufficient food supply, and thus is incapable of strictly heterotrophic growth. Under mixotrophic conditions (i.e. in the light with addition of a saturating concentration of prey), growth rates of G. galatheanum were 2-to 3-fold higher than under strictly phototrophic conditions at the same irradiances. Mixotrophically grown G. galatheanum had higher cellular chl a, cell volume, and cellular carbon content than cultures grown without particulate food. Phagotrophy also leads to enhanced photosynthetic performance of G. galatheanum due to increased photosynthetic capacity (PmaXCe"), and/or by increased photosynthetic efficiency (ace"), particularly when the cells were grown under low light and/or nutrient-limited conditions. These results indicate that G. galatheanum is an obligately phototrophic species and that both photosynthesis and phagotrophy play significant roles in supporting the higher growth rates associated with mixotrophic than with strictly autotrophic growth.

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The shallow depth of field of conventional microscopy hampers analyses of 3D swimming behavior of fast dinoflagellates, whose motility influences macroassemblages of these cells into oftenobserved dense ''blooms.'' The present analysis of cinematic digital holographic microscopy data enables simultaneous tracking and characterization of swimming of thousands of cells within dense suspensions. We focus on Karlodinium veneficum and Pfiesteria piscicida, mixotrophic and heterotrophic dinoflagellates, respectively, and their preys. Nearest-neighbor distance analysis shows that predator and prey cells are randomly distributed relative to themselves, but, in mixed culture, each predator clusters around its respective prey. Both dinoflagellate species exhibit complex highly variable swimming behavior as characterized by radius and pitch of helical swimming trajectories and by translational and angular velocity. K. veneficum moves in both left-and right-hand helices, whereas P. piscicida swims only in right-hand helices. When presented with its prey (Storeatula major), the slower K. veneficum reduces its velocity, radius, and pitch but increases its angular velocity, changes that reduce its hydrodynamic signature while still scanning its environment as ''a spinning antenna.'' Conversely, the faster P. piscicida increases its speed, radius, and angular velocity but slightly reduces its pitch when exposed to prey (Rhodomonas sp.), suggesting the preferred predation tactics of an ''active hunter.'' T he swimming behavior of dinoflagellates, biflagellated planktonic protists that are sometimes associated with harmful algal blooms or ''red tides'' (1), is vital to their success in aquatic ecosystems (2). Predation, which involves complex microbial interactions, is an important facet of the behavior of heterotrophic and mixotrophic (combining phototrophic and heterotrophic nutrition) dinoflagellates (3). Dinoflagellates typically move in helical trajectories (4, 5), which may help them in detecting nutrient gradients (6), although little is known about how differences in species or environment (i.e., resource availability) affect their swimming characteristics. However, evidence suggests that certain dinoflagellates adapt swimming strategy that increases their encounter rate with prey as the quarry concentration decreases (7).Being limited by the shallow depth of field of conventional microscopy, most studies of dinoflagellates' swimming have been performed in thin containers, where ''wall effects'' are likely to affect behavior. Triggering of imaging systems as subjects cross in-focus planes or 3D traversing systems that follow organisms provide only limited solutions to this problem. The tendency of dinoflagellates to cluster together in dense suspensions further complicates measurements of behavior of individuals in their natural setting. In this study, we use high-speed cinematic digital holographic microscopy, as described in Materials and Methods, to overcome these challenges. Ensuing analysis provides simultaneous data...

Climate effects on hydrology impart high variability to water-quality properties, including nutrient loadings, concentrations, and phytoplankton biomass as chlorophyll-a (chl-a), in estuarine and coastal ecosystems. Resolving longterm trends of these properties requires that we distinguish climate effects from secular changes reflecting anthropogenic eutrophication. Here, we test the hypothesis that strong climatic contrasts leading to irregular dry and wet periods contribute significantly to interannual variability of mean annual values of water-quality properties using in situ data for Chesapeake Bay. Climate effects are quantified using annual freshwater discharge from the Susquehanna River together with a synoptic climatology for the Chesapeake Bay region based on predominant sea-level pressure patterns. Time series of waterquality properties are analyzed using historical and recent data for the bay adjusted for climate effects on hydrology. Contemporary monitoring by the Chesapeake Bay Program (CBP) provides data for a period since mid-1984 that is significantly impacted by anthropogenic eutrophication, while historical data back to 1945 serve as historical context for a period prior to severe impairments. The generalized additive model (GAM) and the generalized additive mixed model (GAMM) are developed for nutrient loadings and concentrations (total nitrogen-TN, nitrate +nitrate-NO 2 +NO 3 ) at the Susquehanna River and waterquality properties in the bay proper, including dissolved nutrients (NO 2 +NO 3 , orthophosphate-PO 4 ), chl-a, diffuse light attenuation coefficient (K D (PAR)), and chl-a/TN. Each statistical model consists of a sum of nonlinear functions to generate flow-adjusted time series and compute long-term trends accounting for climate effects on hydrology. We present results identifying successive periods of (1) eutrophication ca. 1945-1980 characterized by approximately doubled TN and NO 2 +NO 3 loadings, leading to increased chl-a and associated ecosystem impairments, and (2) modest decreases of TN and NO 2 +NO 3 loadings from 1981 to 2012, signaling a partial reversal of nutrient over-enrichment. Comparison of our findings with longterm trends of water-quality properties for a variety of estuarine and coastal ecosystems around the world reveals that trends for Chesapeake Bay are weaker than for other systems subject to strenuous management efforts, suggesting that more aggressive actions than those undertaken to date will be required to counter anthropogenic eutrophication of this valuable resource.