Low abundance of the dinoflagellates,Pfiesteria piscicida, P. shumwayae, andCryptoperidiniopsis spp., in South Carolina tidal creeks and open estuaries

The toxicPfiesteria complex are a group of dinoflagellates that have received considerable attention in recent years as causative factors in fish kill or lesion events in North Carolina estuaries and in the Pocomoke River of Chesapeake Bay. In response to the potentialPfiesteria threat, the South Carolina Task Group on Harmful Algae was formed in late 1997 and implemented programs to monitor harmful algal blooms and respond to fish kills or lesion events with particular emphasis on the Bushy Park (Cooper River, Charleston) region, a site of annually recurrent menhaden lesion events.Pfiesteria piscicida, Pfiesteria shumwayae, andCryptoperidiniopsis spp. were documented in South Carolina estuaries. Routine monitoring and fish kill or lesion event sampling consistently indicated low abundances compared to estimates from similar programs in North Carolina and Maryland that sampled areas with a history ofPfiesteria toxic activity. The finding thatPfiesteria-like organism (PLO) abundances were always low in samples collected during menhaden lesion events in Bushy Park suggested other causes for lesion progression, althoughPfiesteria spp. could not be ruled out as a factor in lesion initiation. Based on the previously demonstrated positive relationship between PLO abundance, chlorophylla, and inorganic nutrient concentrations (in laboratory experiments and North Carolina field observations), we hypothesized that the relatively low abundance ofPfiesteria spp. and other PLO (e.g.,Cryptoperidiniopsis) in South Carolina estuaries is related to the relatively low supply of phytoplankton prey, as supported by interstate comparisons in chlorophylla concentrations. Nitrate concentrations were generally much lower in South Carolina estuaries. Estuarine eutrophication may be an important consideration in explaining interstate differences in susceptibility toPfiesteria-related toxic events.     

Viruses as potential regulators of regional brown tide blooms caused by the alga,Aureococcus anophagefferens

Blooms of the brown tide organismAureccoccus anophagefferens have recurred in the coastal bays in New Jersey since 1995 and in the coastal bays of Long Island since 1985. Intracellular viral-like particles (VLPs) were documented during 1999–2000 brown tide blooms in Little Egg Harbor, New Jersey, but it was not determined whether cells were infected during the termination of the bloom. The objective of this study was to determine if VLPs infected and lysed natural populations ofA. anophagefferens in coastal bays of New Jersey and New York in 2002 with the same frequency as in 1999–2000 and especially at the termination of the bloom. Our results confirmed that the highest percentage (37.5%) of VLP-infected cells occurred at the termination of the brown tide bloom in New Jersey in 2002. Intracellular VLPs were present throughout the bloom event. The percentage of visibly infected cells was higher at the beginning of the bloom than during the peak of the bloom. The intracellular VLPs in natural populations ofA. anophagefferens were consistent in size and shape (approximately 140 nm in diameter) and comparable to those in previous studies. Concentrated viral isolates, prepared from waters during brown tide blooms in New York and New Jersey in 2002, infected healthy laboratoryA. anophagefferens cultures in vitro. The viral isolates associated with the highest laboratory viral activity (lysis positive) were concentrated from water samples having the highest viral and bacteria concentrations. The intracellular viruses in these virally infected laboratory cultures ofA. anophagefferens were similar in size and shape to those found in natural populations. The successful isolation of a virus specific toA. anophagefferens from a brown tide bloom in the field, the similarity of ultrastructure of VLPs infecting both natural populations and laboratory infected cultures, and the pattern of VLP infection during bloom activity in combination with the observed high percentage of VLP-infected cells during bloom termination, supports, the hypothesis that viruses may be a major source of mortality for brown tide blooms in regional coastal bays of New Jersey and New York.     

A review of the causes, effects, and potential management of harmful brown tide blooms caused byAureococcus anophagefferens (Hargraves et sieburth)

Brown tides caused by the harmful algaAureococcus anophagefferens abruptly appeared in some coastal embayments of the northeastern United States (Rhode Island, New York) in 1985. Since then, brown tides have vanished from some bays, chronically reoccurred in others, and recently have exhibited an apparent southern expansion into new regions (e.g., New Jersey, Delaware, Maryland, and Virginia). Brown tides have also recently been detected across the Atlantic Ocean in South Africa. Although blooms ofA. anophagefferens have no known direct, negative effects on human health, they are considered harmful because of their detrimental effects on estuarine organisms, such as suspension feeders (scallops and hard clams) and submerged aquatic vegetation. The selective effect of blooms on pelagic grazers (zooplankton and shellfish) is likely to affect food webs and biodiversity within affected ecosystems. Recent findings indicate brown tides occur in shallow estuaries with long residence times and high salinities (> 25‰). These estuarine characteristics may foster the accumulation of algal biomass and a nutrient environment (high dissolved organic matter and low dissolved in organic nitrogen) as well as a low light regime that encourages rapid cellular growth ofA. anophagefferens. A lack of sufficient grazing control by benthic and pelagic suspension feeders during the initiation phase of blooms is also implicated in brown tide development.     

Environmental and Physical Controls on the Formation and Transport of Blooms of the Dinoflagellate <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis> Margalef in the Lower Chesapeake Bay and Its Tributaries

Massive blooms of the harmful alga Cochlodinium polykrikoides Margalef occurred in the lower Chesapeake Bay and its tributaries during the summers of 2007 and 2008. The Lafayette and Elizabeth Rivers appeared to act as initiation grounds for these blooms during both years. However, in 2008 there were also localized sites of initiation and growth of populations within the mesohaline portion of the James River. Bloom initiation appeared to be correlated with intense, highly localized rainfall events during neap tides. Subsequent spring tides increased tidal flushing and transport of C. polykrikoides from the Lafayette and Elizabeth Rivers into the lower James River where it was transported upriver by local estuarine circulation. Blooms dissipated in response to increased wind-driven mixing associated with frontal systems moving through the region. A combination of physical factors including, seasonal rainfall patterns, increased stratification, nutrient loading, spring-neap tidal modulation, and complex estuarine mixing and circulation allowed C. polykrikoides to spread and form massive blooms over large portions of the tidal James River and the lower Chesapeake Bay.     

Changes in dissolved organic matter characteristics in Chincoteague Bay during a bloom of the pelagophyte<Emphasis Type="Italic">Aureococcus anophagefferens</Emphasis>

Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States. This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance). High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon: nitrogen (C:N) ratio, isotopic signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis ofA. anophagefferens could not be determined.     

Interannual Variability Influences Brown Tide (<Emphasis Type="Italic">Aureococcus anophagefferens</Emphasis>) Blooms in CoastalEmbayments

Blooms of Aureococcus anophagefferens in Chincoteague Bay were observed during 5 of 6 years between 2002 and 2007. In order to understand factors controlling blooms, interannual differences in nitrogen and carbon uptake and concentrations of dissolved constituents were compared at two sites in Chincoteague Bay, MD and VA over the 6-year time period. Over that time, we observed that there was no single nitrogen compound that fueled blooms each year. Instead, A. anophagefferens took up a wide range of nitrogen compounds to meet its nutritional demands. Although photosynthetic carbon fixation was the dominant form of carbon acquisition during blooms, organic carbon uptake contributed up to 30 % of the total carbon uptake. In addition to interannual variability in nitrogen and carbon uptake, we observed that there was an increase in bloom intensity and duration over the 6-year study period during which dissolved organic carbon appeared to accumulate in the system.     

Blooms of Dinoflagellate Mixotrophs in a Lower Chesapeake Bay Tributary: Carbon and Nitrogen Uptake over Diurnal,Seasonal, and Interannual Timescales

A multi-year study was conducted in the eutrophic Lafayette River, a sub-tributary of the lower Chesapeake Bay during which uptake of inorganic and organic nitrogen (N) and C compounds was measured during multiple seasons and years when different dinoflagellate species were dominant. Seasonal dinoflagellate blooms included a variety of mixotrophic dinoflagellates including Heterocapsa triquetra in the late winter, Prorocentrum minimum in the spring, Akashiwo sanguinea in the early summer, and Scrippsiella trochoidea and Cochlodinium polykrikoides in late summer and fall. Results showed that no single N source fueled algal growth, rather rates of N and C uptake varied on seasonal and diurnal timescales, and within blooms as they initiated and developed. Rates of photosynthetic C uptake were low yielding low assimilation numbers during much of the study period and the ability to assimilate dissolved organic carbon augmented photosynthetic C uptake during bloom and non-bloom periods. The ability to use dissolved organic C during the day and night may allow mixotrophic bloom organisms a competitive advantage over co-occurring phytoplankton that are restricted to photoautotrophic growth, obtaining N and C during the day and in well-lit surface waters.     

The Role of Zooplankton Grazing and Nutrient Loading in the Occurrence of Harmful Cyanobacterial Blooms in Florida Bay,USA

Florida Bay is Florida’s (USA) largest estuary and has experienced harmful picocyanobacteria blooms for nearly two decades. While nutrient loading is the most commonly cited cause of algal blooms in Florida Bay, the role of zooplankton grazing pressure in bloom occurrence has not been considered. For this study, the spatial and temporal dynamics of cyanobacteria blooms, the microbial food web, microzooplankton and mesozooplankton grazing rates of picoplankton, and the effects of nutrients on plankton groups in Florida Bay were quantified. During the study, cyanobacteria blooms (>3 × 10⁵ cells mL⁻¹) persisted in the eastern and central regions of Florida Bay for more than a year. Locations with elevated abundance of cyanobacteria hosted microzooplankton grazing rates on cyanobacteria that were significantly lower (p < 0.001) and less frequently detectable compared to sites without blooms. Consistent with this observation, cyanobacteria abundances were significantly correlated with ciliates and heterotrophic nanoflagellates at low cyanobacteria densities (p < 0.001) but were not correlated during bloom events. The experimental enrichment of mesozooplankton abundance during blooms yielded a significant decrease in the net growth rate of picoplankton but had the opposite effect when blooms were absent, suggesting that the cascading effect of mesozooplankton grazing on the microbial food web was also altered during blooms. While inorganic nutrient enrichment significantly increased the net growth rates of eukaryotic phytoplankton and heterotrophic bacteria, such nutrient loading had no effect on the net growth rates of cyanobacteria. Hence, this study demonstrates that low rates of zooplankton grazing and low rates of inorganic nutrient loading contribute to the persistence of cyanobacteria blooms in Florida Bay.     

Oysters and the Chesapeake Bay ecosystem: A case for exotic species introduction to improve environmental quality?

Restoration of the Chesapeake Bay ecosystem has been a priority for residents and governments of the bay watershed for the past decade. One obstacle in the efforts to “save the bay” has been continuing nutrient enrichment from agricultural and sewer runoff. The attainability of a mandated 40% nutrient reduction goal has yet to be seen. Furthermore, disappearance of certain organisms may have had an adverse effect on the resilience of the ecosystem. The Eastern oyster (Crassostrea virginica), once abundant in Chesapeake Bay, was a vital part of the food web, processing excess phytoplankton and depositing materials on the bottom. Over harvesting and disease have decimated the native oyster population. The introduction of an exotic species, the Japanese oyster (Crassostrea gigas), may be a way to reestablish a robust oyster community in the bay. The literature on the role of bivalve molluscs in estuarine ecosystems shows that they are an essential part of healthy estuaries around the world. A comparison ofC. virginica andC. gigas in terms of temperature and salinity tolerance and resistance to disease shows thatC. virginica is ideally adapted to conditions in Chesapeake Bay, but it is unable to stave off the endemic diseases, whereasC. gigas is adapted to conditions in the lower bay only but is much less susceptible to the same diseases. We conclude that the potential introduction ofC. gigas to Chesapeake Bay would be limited by the Japanese species’ physiological requirements but that the revitalization of a bivalve population is imperative to the restoration of ecosystem function.     

Contrasting Growth Patterns of Suspension-Feeding Molluscs (Mercenaria mercenaria, Crassostrea virginica, Argopecten irradians, and Crepidula fornicata) Across a Eutrophication Gradient in the Peconic Estuary, NY, USA

While many coastal ecosystems previously supported dense meadows of seagrass and dense stocks of bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have contributed to the decline of these important resources. Anthropogenic nutrient loading and subsequent eutrophication has been identified by some researchers as a primary driver of these losses, but others have described potential positive effects of eutrophication on some estuarine resources. The Peconic Estuary, Long Island, NY, USA, offers a naturally occurring nutrient-loading gradient from eutrophic tidal creeks in its western reaches to mesotrophic bays in the eastern region. Over 2 years, we conducted an experiment across this gradient to examine the effects of eutrophication on the growth of estuarine species, including juvenile bivalves (northern quahogs (Mercenaria mercenaria), eastern oysters, (Crassostrea virginica), and bay scallops (Argopecten irradians)) and slipper limpet (Crepidula fornicata). Water quality and phytoplankton community biomass and composition were concurrently monitored at each site, and the effects of these variables on the growth of estuarine species were analyzed with multiple regression model. Eutrophication seemed to impact shellfish through changes in the quality of food and not the quantity since the growth rates of shellfish were more often correlated with densities of specific cell types or quality of seston rather than bulk measures of phytoplankton and organic seston. Northern quahogs and eastern oysters grew maximally within eutrophic locales, and their growth was positively correlated with high densities of autotrophic nanoflagellates and centric diatoms in these regions (p?<?0.001). The growth rates of northern quahogs were also positively correlated with relative water motion, suggesting an important role for tidal currents in delivering seston to suspension feeders. Bay scallops and slipper limpets were negatively impacted by eutrophication, growing at the slowest rate at the most eutrophic sites. Furthermore, bay scallop growth was negatively correlated with densities of dinoflagellates, which were more abundant at the most eutrophic site (p?<?0.001). These results suggest that nutrient loading can have significant but complex effects on suspension-feeding molluscs with select species (e.g., oysters and clams) benefiting from eutrophication and other species performing poorly (e.g., scallops and slipper limpets). Future management approaches that seek to restore bivalve populations will need to account for the differential effects of nutrient loading as managers target species and regions to be restored.     

Eggs and early larvae of the bay anchovy,Anchoa mitchilli,and the weakfish,Cynoscion regalis,in lower Chesapeake Bay with notes on associated ichthyoplankton

The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.     

Distribution ofVibrio parahaemolyticus in Chesapeake Bay during the summer season

The distribution ofVibrio parahaemolyticus in Chesapeake Bay during the warmer weather of the summer months was examined. This species was found throughout the Chesapeake Bay and its tributaries, even in areas of very low salinity. Counts of this species ranged from 0.04 per 100 ml to 46 per 100 ml in the water column and 2.03 to ≥2.4×10³ per 100 cc of sediment. A variety of physical, chemical and bacteriological properties associated with the incidence and distribution ofV. parahaemolyticus were examined and salinity was found to be the major influence among the factors examined. Correlation and regression analysis showed that the population size of this species increased with increasing salinity in the estuary.     

Comparison of Nutrient and Microbial Dynamics over a Seasonal Cycle in a Mid-Atlantic Coastal Lagoon Prone to <Emphasis Type="Italic">Aureococcus anophagefferens</Emphasis> (Brown Tide) Blooms

To determine the roles of dissolved organic matter in the onset, duration, and decline of blooms of the “brown tide” pelagophyte, Aureococcus anophagefferens, nutrient and microbial dynamics, heterotrophic and autotrophic carbon (C) and nitrogen (N) uptake, and peptide hydrolysis were compared in natural populations: (1) seasonally, among physically similar sites in a mid-Atlantic coastal lagoon, Chincoteague Bay, (2) at an individual site as a bloom initiated, developed, and declined, and (3) in whole versus size-fractionated water. Throughout the year, urea was the dominant form of N taken up at both bloom and nonbloom sites. C acquisition in the A. anophagefferens (1.2–5.0 μm) size fraction was dominated by bicarbonate uptake during bloom initiation but organic C compounds were taken up later during and after the bloom. Bacterial productivity was enhanced during and just after the bloom and bacterial abundance was four times higher at the bloom versus nonbloom site.     

Composition of particulate organic matter in the southern Chesapeake Bay: Sources and Reactivity

The distribution of two classes of lipid biomarker compounds (fatty acids and sterols) was used in conjunction with several bulk parameters (total suspended solids, chlorophyll a, and particulate carbon and nitrogen concentrations) to examine spatial and temporal variability in the sources of particulate organic matter (POM) important to southern Chesapeake Bay. Based on these geochemical parameters, we found that suspended and sedimentary organic matter in the southern Chesapeake Bay is derived from autochthonous sources including a mixture of fresh and detrital phytoplankton, zooplankton, and bacteria. The dominant factor contributing to temporal variability during our study was phytoplankton productivity. Enrichments in particulate organic carbon, chlorophyll a, total fatty acids, total sterols, and a number of biomarkers specific to phytoplankton sources were found in particles collected from surface (1 m) and deep (1 m above the bottom) portions of the water column at several sites during the spring bloom in March 1996 and during a localized bloom in July 1995. Comparison of sites at the mouths of two tributaries (York and Rappahannock rivers) to southern Chesapeake Bay with two sites located in the bay mainsterm indicates spatial variation in the composition of POM was not significant in this region of the bay. The energetic nature of this region of the Chesapeake Bay most likely contributes to the observed homogeneity. Comparison with biomarker studies conducted in other estuaries suggests the high levels of productivity characteristic of the Chesapeake Bay contribute to high background levels of POM.     

Viral-like particles (VLPS) in the alga,Aureococcus anophagefferens (pelagophyceae), during 1999–2000 brown tide blooms in Little Egg Harbor, New Jersey

We assessed the presence and quantified the intracellular virus-like particles (VLPs) in natural populations ofAureococcus anophagefferens during the 1999–2000 brown tide blooms that occurred in New Jersey coastal waters. From displayed a wide range of ultrastructural changes from apparently healthy cells to those showing late stages of production of VLPs. VLP-infected cells usually had an electron dense plasma membrane and lacked the typical exocellular polysaccharide layer (EPS). The VLPs were similar in size (c. 140 nm) and morphology to those initially reported in natural populations ofA. anophagefferens and to brown tide viruses (BtVs) which were previously isolated and inoculated into laboratory cultures ofA. anophagefferens. VLP-infectedA. anophagefferens were found consistently throughout the brown tide blooms in both years in Little Egg Harbor. Percentages of VLP-infected cells were 8.1% at the beginning of a bloom, which decreased to less than 2% at the height of the blooms during both years, and increased at the end of the 2000 bloom to 2.5%. While these percentages appear low, the estimated VLP infection rate ofA. anophagefferens cells, which ranged from 0.83%–50% of the standing population, is comparable to other studies.     

Seed bank patterns in Chesapeake Bay eelgrass (Zostera marina L.): A bay-wide perspective

The decline of eelgrass (Zostera marina) in Chesapeake Bay in the 1960s and 1970s has been studied in the context of changes in water quality and habitat suitability; little effort has focused on the importance of reproductive ecology in understanding current and potential recovery of these populations. The spatial variability of seed-bank characteristics ofZ. marina in Chesapeake Bay was explored by a reproductive shoot and seed-bank sampling effort. Seed banks were sampled from 105 beds of submerged aquatic vegetation among 12 zones throughout the lower and middle Chesapeake Bay. Number of viable seeds was highly variable among and within zones, with seeds found in all but one zone and also found in cores not containing anyZ. marina shoots. Number of reproductive shoots was also highly variable among and within zones, with differences probably driven by different local environmental conditions. Bay-wide, viable seeds were found in more monospecificZ. marina cores than in mixed species or monospecificRuppia maritima cores suggesting local biological and environmental control on sexual reproduction. Lower densities of viable seeds in the middle Chesapeake Bay region reflect the lower abundance ofZ. marina in these regions and provide context for discussion of historical changes inZ. marina in Chesapeake Bay. While this study focused on a snap shot of the seed bank immediately after establishment, we highlight critical questions for future study that may be important for their conservation and restoration.     

A revised species list and commentary on the macroalgae of the Chesapeake Bay in Maryland

Macroscopic marine algae were collected at a variety of intertidal sites and on cruises throughout the Maryland Chesapeake Bay in 1972–73, and numerous specimens from the University of Maryland herbarium were examined. The revised species list contains 62 taxa as follows: 26 Rhodophyceae, 1 Xanthophyceae, 6 Phaeophyceae, 29 Chlorophyceae. Grinnellia americana, Neoagardhiella baileyi, Porphyra sp.,Vaucheria sp.,Desmotrichum undulatum, Ectocarpus confervoides, Enteromorpha compressa var.lingulata, E. linza, Entocladia viridis andUrospora sp. are new records for the flora of the upper Bay. Records ofAscophyllum are believed to represent discarded bait-packing material rather than an endemic population in the upper Bay. Ceramium, Polysiphonia, Cladophora, Enteromorpha andUlva are the genera most likely to be encountered in the upper Bay. In winter, brown algae, mainlyEctocarpus species, become a more conspicuous component of the flora. Comments on distribution, seasonality, taxonomic problems, and invalid or questionable records are included. Literature pertinent to the Delmarva region is reviewed briefly.     

Habitat requirements for submerged aquatic vegetation in Chesapeake Bay: Water quality, light regime, and physical-chemical factors

We developed an algorithm for calculating habitat suitability for seagrasses and related submerged aquatic vegetation (SAV) at coastal sites where monitoring data are available for five water quality variables that govern light availability at the leaf surface. We developed independent estimates of the minimum light required for SAV survival both as a percentage of surface light passing though the water column to the depth of SAV growth (PLW _min) and as a percentage of light reaching reaching leaves through the epiphyte layer (PLL _min). Value were computed by applying, as inputs to this algorithm, statistically dervived values for water quality variables that correspond to thresholds for SAV presence in Chesapeake Bay. These estimates ofPLW _min andPLL _min compared well with the values established from a literature review. Calcultations account for tidal range, and total light attenuation is partitioned into water column and epiphyte contributions. Water column attenuation is further partitioned into effects of chlorophylla (chla), total suspended solids (TSS) and other substances. We used this algorithm to predict potential SAV presence throughout the Bay where calculated light available at plant leaves exceededPLL _min. Predictions closely matched results of aerial photographic monitoring surveys of SAV distribution. Correspondence between predictions and observations was particularly strong in the mesohaline and polythaline regions, which contain 75–80% of all potential SAV sites in this estuary. The method also allows for independent assessment of effects of physical and chemical factors other than light in limiting SAV growth and survival. Although this algorithm was developed with data from Chesapeake Bay, its general structure allows it to be calibrated and used as a quantitative tool for applying water quality data to define suitability of specific sites as habitats for SAV survival in diverse coastal environments worldwide.     

Harmful algal blooms and eutrophication: Nutrient sources,composition, and consequences

Although algal blooms, including those considered toxic or harmful, can be natural phenomena, the nature of the global problem of harmful algal blooms (HABs) has expanded both in extent and its public perception over the last several decades. Of concern, especially for resource managers, is the potential relationship between HABs and the accelerated eutrophication of coastal waters from human activities. We address current insights into the relationships between HABs and eutrophication, focusing on sources of nutrients, known effects of nutrient loading and reduction, new understanding of pathways of nutrient acquisition among HAB species, and relationships between nutrients and toxic algae. Through specific, regional, and global examples of these various relationships, we offer both an assessment of the state of understanding, and the uncertainties that require future research efforts. The sources of nutrients potentially stimulating algal blooms include sewage, atmospheric deposition, groundwater flow, as well as agricultural and aquaculture runoff and discharge. On a global basis, strong correlations have been demonstrated between total phosphorus inputs and phytoplankton production in freshwaters, and between total nitrogen input and phytoplankton production in estuarine and marine waters. There are also numerous examples in geographic regions ranging from the largest and second largest U.S. mainland estuaries (Chesapeake Bay and the Albemarle-Pamlico Estuarine System), to the Inland Sea of Japan, the Black Sea, and Chinese coastal waters, where increases in nutrient loading have been linked with the development of large biomass blooms, leading to anoxia and even toxic or harmful impacts on fisheries resources, ecosystems, and human health or recreation. Many of these regions have witnessed reductions in phytoplankton biomass (as chlorophylla) or HAB incidence when nutrient controls were put in place. Shifts in species composition have often been attributed to changes in nutrient supply ratios, primarily N∶P or N∶Si. Recently this concept has been extended to include organic forms of nutrients, and an elevation in the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC∶DON) has been observed during several recent blooms. The physiological strategies by which different groups of species acquire their nutrients have become better understood, and alternate modes of nutrition such as heterotrophy and mixotrophy are now recognized as common among HAB species. Despite our increased understanding of the pathways by which nutrients are delivered to ecosystems and the pathways by which they are assimilated differentially by different groups of species, the relationships between nutrient delivery and the development of blooms and their potential toxicity or harmfulness remain poorly understood. Many factors such as algal species presence/abundance, degree of flushing or water exchange, weather conditions, and presence and abundance of grazers contribute to the success of a given species at a given point in time. Similar nutrient loads do not have the same impact in different environments or in the same environment at different points in time. Eutrophication is one of several mechanisms by which harmful algae appear to be increasing in extent and duration in many locations. Although important, it is not the only explanation for blooms or toxic outbreaks. Nutrient enrichment has been strongly linked to stimulation of some harmful species, but for others it has not been an apparent contributing factor. The overall effect of nutrient over-enrichment on harmful algal species is clearly species specific.     

Age and growth,movements and distribution of the cownose ray,Rhinoptera bonasus,in Chesapeake Bay

Ages were estimated for 115 of 899 cownose rays,Rhinoptera bonasus, collected primarily from commercial fishing gear, in lower Chesapeake Bay and vicinity from May through October, 1976–78. Age determinations were made using sectioned vertebral centra and estimates of von Bertalanffy parameters were for males DW_∞=119.2, K=0.126, and t₀=?3.699, and for females DW_∞=125.0, K=0.119, and t₀=?3.764. Females attained a larger adult size and the oldest specimen aged was a female 13 years old and 107 cm disc width. Both sexes mature after reaching about 70% of their maximum size and ages at maturity were estimated at 5 to 6 years for males and 7 to 8 years for females. In spring migrating rays schooled by size; they arrived along the North Carolina coast by April and entered Chesapeake Bay by early May. Rays were abundant in the major Virginia tributaries of Chesapeake Bay throughout summer and occurred in salinities as low as 8‰ and at water temperatures between 15–29 °C. Size segregation continued during summer and adults schooled by sex. Most rays left Chesapeake Bay by early October.