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.     

Mesoscale and Nutrient Conditions Associated with the Massive 2008 Cochlodinium polykrikoides Bloom in the Sea of Oman/Arabian Gulf

Cochlodinium polykrikoides formed large blooms in the coastal waters of Oman from October 2008 through mid-January 2009, and satellite images from Aqua-MODIS and region-wide reports suggest that this bloom was found throughout the Arabian Gulf and Sea of Oman for more than 10 months. The unusual occurrence of this species appears to have supplanted the more regularly occurring bloom species, Noctiluca scintillans, in 2008–2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6?×?10³ to 9?×?10⁶ cells L^?1 and very high levels of chlorophyll a (78.0 μg L^?1) were also recorded. The regional progression of the bloom likely began with stronger than normal upwelling along the Iranian and northern Omani coasts during the southwest monsoon in late summer, followed by discharge of unusually warm coastal plume water along the coast of Oman with the reversal of monsoonal winds in late October. The occurrence and persistence of high densities of C. polykrikoides in Oman coastal water were also significantly influenced by an elevated nutrient load and warmer than normal temperatures. Concentrations of nutrients, especially NH₄ ⁺, urea, PO₄ ^3?, and organic nitrogen and phosphorus, were manyfold higher than observed in the year prior or since. These findings suggest that mesoscale features were important in bloom dynamics more regionally, but locally the bloom was sustained by nutrient enrichment supplemented by its mixotrophic capabilities.     

Effects of a Persistent Red Tide (<Emphasis Type="Italic">Karenia brevis</Emphasis>) Bloom on Community Structure and Species-Specific Relative Abundance of Nekton in a Gulf of Mexico Estuary

An unusually persistent red tide event caused by the ichthyotoxic dinoflagellate Karenia brevis occurred along the southwest Florida coast in 2005. Extensive fish kills led to concerns regarding the effect of red tide on fish populations and their subsequent recruitment. Community structure differences were analyzed for all small- and large-bodied nekton species collected by fisheries-independent monitoring from 1996 through 2006. Indices of abundance of five economically important fish species were also calculated from this time period. A significant change in small- and large-bodied nekton community structure was apparent from summer 2005 through spring 2006. Declines in the annual recruitment of juvenile spotted seatrout (Cynoscion nebulosus), sand seatrout (Cynoscion arenarius), and red drum (Sciaenops ocellatus) were evident in 2005 and 2006. Species-specific subadult and adult abundances, however, were consistent with those of previous years. These community shifts and species-specific declines appear to be associated with the red tide event.     

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.     

Physiological responses of a bloom-forming green macroalga to short-term change in salinity,nutrients, and light help explain its ecological success

Enteromorpha intestinalis is a bloom-forming species of macroalgae associated with eutrophication. The objective of this study was to investigate how this alga performs osmoregulation and nutrient uptake in order to proliferate under environmental conditions that covary with eutrophication. We quantified the response ofE. intestinalis to salinity, light, and nutrients. We performed two short-term (48 h) laboratory experiments (salinity alone and salinity × nutrients × light) to examine the algal responses of tissue water, potassium (K⁺), and nutrient (NO ₃ ⁻ and total N) content. Tissue water content decreased with increasing salinity, and although K⁺ concentration decreased from the initial concentration, it decreased less with increased salinity treatment demonstrating two mechanisms to withstand short-term salinity fluctuation. The salinity × nutrient × light experiment showed that, in the short term, light had an interaction with tissue K⁺. Total tissue N content was positively related to N treatment level, and light did not affect total nutrient concentration. The effect of light was present whether the nutrients were present in the tissue as inorganic or organic forms. With reduced light, we hypothe size that the assimilation of inorganic to organic N was energy limited. The ability of this alga to take up available nutrients rapidly for growth and short-term osmoregulation, even under low light and salinity levels, helps to explain the bloom potential ofE. intestinalis.     

Stress response model for the tropical seagrass<Emphasis Type="Italic">Thalassia testudinum</Emphasis>: The interactions of light,temperature, sedimentation,and geochemistry

Our modeling objective was to better define the relationship between subtropical seagrass and potential water column and sediment stressors (light, organic and particle sedimentation, sediment nutrients, and the porewater sulfide system). The model was developed and optimized for sediments inThalassia testudinum seagrass beds of Lower Laguna Madre, Texas, U.S., and is composed of a plant submodel and a sediment diagenetic submodel. Simulations were developed for a natural stressor (harmful algal bloom,Aureoumbra lagunensis) and an anthropogenic, stressor (dredging event). The observed harmful algal bloom (HAB) was of limited duration and the simulations of that bloom showed no effect of the algal bloom on biomass trends but did suggest that sediment sulfides could inhibit growth if the bloom duration and intensity were greater. To examine this hypothesis we ran a simulation using data collected during a sustained 4-yr bloom in Upper Laguna Madre. Simulations suggested that light attenuation by the HAB could cause a small reduction inT. testudinum biomass, while input of organic matter from the bloom could promote development of a sediment geochemical environment toxic toT. testudinum leading to a major reduction in biomass. A 3-wk dredging event resulted in sedimentation of a layer of rich organic material and reduction of canopy light for a period of months. The simulations suggested that the seagrass could have recovered from the effects of temporary light reduction but residual effects of high sulfides in the sediments would make the region inhospitable for seagrasses for up to 2.5 yr. These modeling exercises illustrate that both natural and anthropogenic stressors can result in seagrass losses by radically altering the sedimentary geochemical environment.     

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass <Emphasis Type="Italic">Thalassia testudinum</Emphasis> in Jobos Bay,Puerto Rico

We examined the effect of nutrients and grazers on Thalassia testudinum in Jobos Bay, Puerto Rico by fertilizing sediment and manipulating grazer abundances. Bottom-up effects were variable: Added nutrients did not increase seagrass aboveground biomass, but decreased belowground biomass—perhaps as a result of less biomass being allocated to belowground structures in response to greater nutrient supply in porewater. Experimental fencing of 1.5 × 1.5 m plots provided shelter that attracted large aggregations of fish, including seagrass herbivores. Seagrass biomass and shoot density decreased with increasing abundance of herbivorous fish, indicating a significant top-down effect. There were interactions between nutrient supply, provision of shelter, and grazing pressure. Fertilization enhanced seagrass %N; however, %N also increased in unfertilized plots that were fenced, most likely due to uptake of N excreted from the large numbers of fish associated with the fences. Only plots where shelter was provided and fertilizer was applied to sediments exhibited evidence of heavy grazing, reducing both seagrass cover and aboveground biomass. In the unfertilized fenced plots, signs of grazing were fewer despite large abundances of fish and enhanced nutritional quality of seagrass leaves. This suggests the possibility that high nutrient availability in sediments lowered concentrations of chemical defense compounds in the seagrass and that cues other than %N may have been involved in stimulating grazing. This study highlights the complexity of bottom-up and top-down interactions in seagrass systems and the important role of refuge availability in shaping the relative strengths of these controls.     

Tidal hydrology and habitat utilization by resident nekton in<Emphasis Type="Italic">Pragmites</Emphasis> and Non-<Emphasis Type="Italic">Phragmites</Emphasis> Marshes

We compared nekton densities over a range of measured flooding conditions and locations withinPhragmites australis andSpartina alterniflora (salt marsh cordgrass) at the Charles Wheeler Salt Marsh, located on the lower Housatonic River estuary in southwestern Connecticut. Nekton were sampled on nine spring high tide events from May to October 2000 using bottomless lift nets positioned between 0–5 and 10–20 m from the creek edge. Flooding depth, duration, and frequency were measured from each vegetation type during each sampling month. Benthic macroinvertebrate density was also measured within each vegetation type in May, July, and September. Frequency of flooding was 52% lower and flooding depth and duration were also significantly reduced inP. australis relative toS. alterniflora. A total of 4,197 individuals representing 7 species, mostlyPalaemonetes pugio (dagger-blade grass shrimp) andFundulus heteroclitus (common mummichog), were captured.P. pugio densities were significantly greater inS. alterniflora as were benthic macroinvertebrate density and taxa richness during May, but not during June or October. Total fish density was not significantly different betweenP. australis andS. alterniflora and was independent of location on the marsh. Significantly more juvenileF. heteroclitus were collected withinS. alterniflora relative toP. australis in June and July, suggesting that recruitment of this species may be lower inP. australis habitat. Fish density generally did not vary predictably across the range of flooding depth and duration; there was a positive relationship between flooding depth and fish density inS. alterniflora. The measured reduction in flooding frequency (52%) withinP. australis at the Housatonic site would result in an average total monthly fish use, expressed as density, of 447 ind m⁻² forP. australis and 947 ind m⁻² forS. alterniflora. WhenP. australis expansion results in reduction of flooding frequency and duration, nekton community composition can change, access to the marsh surface is reduced twofold, and nursery habitat function may be impaired.     

The decline and recovery of a persistent Texas brown tide algal bloom in the Laguna Madre (Texas, USA)

The Laguna Madre has experienced a persistent bloom ofAureoumbra lagunensis for over eight years. The persistence of this bloom may be due in part to the often hypersaline conditions in Laguna Madre (40–60 psu) that favor the growth ofA. lagunensis. Above-normal rainfall in the fall of 1997 reduced the salinities in Baffin Bay from >40 to<20 psu.A. lagunensis cell densities dropped from>10⁶ cells ml⁻¹ in July 1997 to c. 200 cells ml⁻¹ in January 1998. During this time of low brown tide density, phytoplankton biomass generally remained high and the Laguna Madre experienced successive blooms of diatoms (Rhizosolenia spp.) and cyanobacteria. Hypersaline conditions returned in 1998 and brown tide densities increased to>0.5 × 10⁶ cells ml⁻¹ by summer. The extraordinary persistence of the brown tide and the unusual sequence of intense blooms may be related in part to the reduction of zooplankton populations. Microzooplankton populations declined following the above-normal rain in the fall of 1997; populations did not recover until fall 1998. Copepod populations also declined sharply and remained low in Laguna Madre, but recovered by summer 1998 in Baffin Bay. Dilution experiments indicated that microzooplankton grazing and phytoplankton growth were usually balanced when measured during our cruises. The rapid recovery of theA. lagunensis bloom suggests that this alga may be a more resilient component of the Laguna Madre flora than previously suspected.     

Multivariate Analysis of Water Quality and Plankton Assemblages in an Urban Estuary

Raritan Bay, located between the states of New York and New Jersey, has a long history of cultural eutrophication and associated harmful algal blooms (HABs). Despite striking chemical and biological alterations occurring in Raritan Bay, publications in the early 1960s were the last to report consecutive measurements of both water quality parameters and plankton species composition in this system. The objectives of this study were to characterize water quality trends and plankton composition in a eutrophic estuary, compare current environmental conditions to those documented in Raritan Bay 50 years ago (i.e., at the same six sampling sites), and to further clarify the relationship among nutrients, secondary consumers, and algal bloom generation in this system using ordination techniques. This study (monthly data collected from April 2010–October 2012) indicates that Raritan Bay continues to exhibit numerous symptoms of eutrophication, including high algal biomass, high turbidity, violations of the dissolved oxygen standard to protect fish health, and blooms of potentially harmful phytoplankton species. Altered spatial and temporal patterns for nitrate and soluble reactive phosphorus (SRP) over the past 50 years may suggest new, changing, or expanding sources of nutrients. A total of 14 HAB species have been identified, including Heterosigma akashiwo, which formed a bloom in the upper Raritan Bay during summer 2012 in association with hypoxic conditions. Multivariate analyses indicate that abundance of this species is positively associated with high temperature, salinity, nitrate, and SRP and negatively associated with spring river discharge rates and total zooplankton abundance in Raritan Bay.     

Coupling Between the Coastal Ocean and Yaquina Bay,Oregon: Importance of Oceanic Inputs Relative to Other Nitrogen Sources

Understanding of the role of oceanic input in nutrient loadings is important for understanding nutrient and phytoplankton dynamics in estuaries adjacent to coastal upwelling regions as well as determining the natural background conditions. We examined the nitrogen sources to Yaquina Estuary (Oregon, USA) as well as the relationships between physical forcing and gross oceanic input of nutrients and phytoplankton. The ocean is the dominant source of dissolved inorganic nitrogen (DIN) and phosphate to the lower portion of Yaquina Bay during the dry season (May through October). During this time interval, high levels of dissolved inorganic nitrogen (primarily in the form of nitrate) and phosphate entering the estuary lag upwelling favorable winds by 2 days. The nitrate and phosphate levels entering the bay associated with coastal upwelling are correlated with the wind stress integrated over times scales of 4–6 days. In addition, there is a significant import of chlorophyll a to the bay from the coastal ocean region, particularly during July and August. Variations in flood-tide chlorophyll a lag upwelling favorable winds by 6 days, suggesting that it takes this amount of time for phytoplankton to utilize the recently upwelled nitrogen and be transported across the shelf into the estuary. Variations in water properties determined by ocean conditions propagate approximately 11–13 km into the estuary. Comparison of nitrogen sources to Yaquina Bay shows that the ocean is the dominant source during the dry season (May to October) and the river is the dominant source during the wet season with watershed nitrogen inputs primarily associated with nitrogen fixation on forest lands.     

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.     

The marine killers: Dinoflagellates in estaurine and coastal waters

Records of massive fish kills and paralytic shellfish poisoning (PSP) in Europe and North America go back to the 17th century. But, it was not until the 1940s when the relationship between PSP, red tide and toxic dinoflagellateGonyaulax was established. Recent records show that PSP and related poisons caused by toxic dinoflagellates in coastal waters and estuaries, are a world-wide problem. Diarrhetic shellfish poisoning (DSP) and neurotoxic poisoning (NSP), believed earlier as bacterial or viral infections are now shown to be caused by other toxic dinoflagellates such asDinophysis. The shellfish most often involved in the poisoning are mussels and clams. Other dinoflagellates,Gyrodinium, occasionally cause massive fish kills in vast coastal areas, resulting in fishery and economic losses.Factors promoting toxic dinoflagellate bloom development and PSP/DSP outbreaks are not fully understood. In previous studies, temperature was considered as the principal factor influencing dinoflagellate blooming. Recent studies showed that other factors such as salinity, sunlight, freshwater runoff and water stability are also important. Pollution from land drainage and sewage discharge in inshore waters were also implicated.Current knowledge indicates that although chemical and biotic factors are important forin-situ growth of dinoflagellate cells, convergence by thermal and tidal fronts is essential for cell accumulation and bloom development. Advances in physical oceanographic research, modelling and remote sensing enabled the detection of fronts and bordering eddies with high precision. There is a potential for an increased use of these technological advances in predicting and monitoring the bloom development.The present paper overviews the history and distribution of toxic dinoflagellates, and the physical factors influencing bloom development and PSP/DSP outbreaks. Future research needs to improve the predictability and control of this world-wide hazard are also discussed.     

Late Holocene palaeoproductivity changes: a multi‐proxy study in the Norwegian Trench and the Skagerrak,North Sea

To detect climatic linkages between the Baltic Sea, the Skagerrak and the Nordic Seas, we present multi‐proxy reconstructions covering the last 4500 years from three sediment cores taken in the Skagerrak and along the SW Norwegian margin. Foraminiferal assemblages at all three sites show a distinct change at c. 1700 years BP, associated with a transition from absence and rare occurrence of Brizalina skagerrakensis during c. 4500–2300 years BP to its subsequent abundance increase, suggesting a stronger influence of nutrient‐rich water‐masses during the last c. 1700 years. Increased nutrient availability, which probably stimulated higher primary productivity, is further supported by an increase in diatoms, total organic carbon and benthic foraminiferal species indicative of high productivity and carbon fluxes during the last c. 1700 years as compared to c. 4500–2300 years BP. The amplitude of the B. skagerrakensis signal is largest in the central Skagerrak and gradually becomes smaller towards the Norwegian Sea suggesting that the dominant source of the nutrient‐rich water was the brackish outflow from the Baltic Sea. The generally lower abundances of planktonic foraminifera since c. 1700 years BP support the hypothesis of less saline surface water conditions in the Skagerrak. These results agree with other studies, which suggest a stronger Baltic outflow over the last 1700 years coinciding with a general cooling, increased wintertime westerlies bringing more winter precipitation to northern Europe, increased river runoff and higher frequency of floods. The increase in outflow also occurs during deposition of laminated sediments in the deep Baltic Sea. Leakage of dissolved inorganic phosphorus from anoxic sediments, as well as enhanced erosion due to deforestation in combination with higher runoff from Norway, coastal upwelling and more vigorous frontal dynamics may all have contributed to higher nutrient availability within the adjacent Skagerrak during the last 1700 years BP as compared to c. 4500–2300 years BP, when low productivity prevailed in the study area.     

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.     

Fifty-Five Years of Fish Kills in Coastal Texas

The designation of Texas as a “hotspot” for fish mortalities relative to the other 22 coastal US states is of serious concern for scientists, resource managers, and the public alike. We investigated the major sources and causes of fish kills in coastal Texas from 1951 to 2006. During this 55-year period, more than 383 million fish were killed, 72% of which were Gulf menhaden (Brevoortia spp.). We examined the relationships between climate and the physical features of Texas bays and estuaries as well as the consequences of high-density industrialization and urbanization along several coastal centers on fish kills, including the impact of eutrophication, algal blooms (toxic and nontoxic), and hypoxia. Galveston and Matagorda Bays had the highest number of fish kill events and total number of fish killed. The largest number of fish kill events and the highest number of fish killed occurred during the warmest months, particularly in August. The leading cause of fish kills was found to be low dissolved oxygen concentrations caused by both physical and biological factors. From 1958 to 1997, about two thirds of the mortalities from low oxygen concentrations were caused by human activities. With the population predicted to double in Texas by 2050, mostly along the coastal areas, natural resources will require additional protection. Further increases in nutrient loading are expected in areas unable to keep up with construction of sewage treatment facilities. Defining the sources and causes of fish kill events in Texas will allow better management and conservation efforts.     

Mapping Phytoplankton Community Physiology on a River Impacted Continental Shelf: Testing a Multifaceted Approach

Seasonal phosphorus limitation occurs on the Louisiana continental shelf as a result of high nitrogen loads in the spring and early summer. Prior studies have assessed such nutrient limitation by laborious and time-consuming nutrient analyses, enzyme assays, and nutrient addition bioassays. We undertook surface (0.5–1 m) mapping of fast repetition rate fluorescence (FRRF) parameters to assess nutrient limitation in real time on the Louisiana continental shelf and Mississippi River plume from 29 June to 08 July, 2002 in an effort to further understand phytoplankton productivity in this region, as well as to better inform effective nutrient management strategies. Surface nutrient concentrations (NO₃⁻, NO₂⁻, NH₄⁺, PO₄³⁻), chlorophyll a biomass, alkaline phosphatase (AP) activity, and four FRRF parameters: the maximum quantum yield of photochemistry (F _v /F _m ), the functional absorption cross section for PSII, the time constant for Q _A reoxidation, and the connectivity factor, were measured during continuous underway mapping. Results from traditional methods to assess phytoplankton nutrient stress indicated widespread phosphorus limitation from the Mississippi River plume to the Atchafalaya River, manifested as high inorganic N/P ratios and elevated AP activities associated with phytoplankton biomass. The FRRF data indicated complex patterns of phytoplankton physiology that were likely driven by the rapidly changing conditions in local surface waters and heterogeneous phytoplankton community structure. Correlations of nutrient data and enzyme assays with FRRF parameters were significant but low, potentially due to differences in the manner and time scale with which nutrient limitation affects the different techniques used, indicating that further work is needed to interpret FRRF parameters in large, heterogeneous environments such as estuaries and continental shelves.     

Assessing the use of saltmarsh flats by fish in a temperate Australian embayment

Little is known about the importance of salmarshes to juvenile and adult fishes in temperate Australia. We assessed diel and feeding patterns of fish inhabiting saltmarsh in a sheltered embayment along the coast of Victoria, Australia, between October 2002 and May 2003. The saltmarsh flat was generally only inundated during low-pressure weather systems (barometric pressure <1,013 hP). Fish were sampled over the saltmarsh flats using fyke and seine nets. A total of 2,047 individuals (10 species, including juveniles and adults) were caught.Atherinasoma microstoma was most abundant (fyke [F], μ=1.6 fish h⁻¹; seine [S], μ=28.2 fish shot⁻¹), followed byFavonigobius, lateralis (F: 0.5; S: 0.6),Galaxias maculatus (F: 0.1),Heteroclinus adelaide (F:<0.1),Kestratherina esox (F: <0.1; S: 1.6),Leptatherina presbyteroides (F: <0.1; S: 7.1) andTetractenos glaber (F: 1). Commercial species, includingAldrichetta forsteri (F: <0.1; S: 3.2),Sillaginodes punctata (F: <0.1; S: 0.9), andRhombosolea tapirina (F: 0.4), were commonly sampled. Variability in species richness or fish abundance was not explained by water temperature, salinity, depth, or barometric pressure. Significantly more species were sampled with the seine during nocturnal periods (p=0.002); fish abundance did not vary between diel periods, nor did fish abundance and species richness in fyke net samples. Diets of the most abundant species (A. microstoma, A. forsteri, andF. lateralis) were primarily composed of gammaridean amphipods and hemipteran insects. There was no correlation between fish diets and the composition of benthic invertebrates as sampled at 3 different regions of the saltmarsh flat. The saltmarsh flats in our study region are inhabited by several species normally associated with alternative habitat types such as seagrass, and the patterns of habitat use observed appear to be partially attributed to foraging behavior.     

Spatial and temporal characteristics of nutrient and phytoplankton dynamics in the York River Estuary, Virginia: Analyses of long-term data

Ten years (1985–1994) of data were analyzed to investigate general patterns of phytoplankton and nutrient dynamics, and to identify major factors controlling those dynamics in the York River Estuary, Virginia. Algal blooms were observed during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas peak phytoplankton biomass during the summer bloom occurred in the tidal fresh-mesohaline transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential N and P limitation. Phytoplankton biomass in tidal fresh water regions was limited by high flushing rates. Water residence time was less than cell doubling time during high flow seasons. Positive correlations between PAR at 1 m depth and chlorophylla suggested light limitation of phytoplankton in the tidal fresh-mesohaline transition zone. Relationships of salinity difference between surface and bottom water with chlorophylla distribution suggested the importance of tidal mixing for phytoplankton dynamics in the mesohaline zone. Accumulation of phytoplankton biomass in the mesohaline zone was generally controlled by N with the nutrient supply provided by benthic or bottom water remineralization.     

Carbon dynamics of estuarine ponds receiving treated sewage wastes

The carbon dynamics of six estuarine ponds at Morehead City, North Carolina, were measured from August 1969 through August 1970. Three waste ponds received secondary treated sewage effluent and three served as controls. Total organic levels were determined by combustion with a Beckman total carbon analyzer. Inorganic levels were calculated from temperature, pH, and carbonate alkalinity. Carbon dioxide diffusion across the air-water interface was measured with a floating plastic dome and an infrared gas analyzer. Carbon metabolism was determined from diurnal changes in total inorganic carbon. From October through April the wastereceiving ponds were characterized by an intense bloom of a small alga,Monodus guttula. During the bloom organic levels reached 75 mg C per 1. The warmer months were characterized by a more diverse flora and organic concentrations averaging 25 mg per 1. Organic levels in the control ponds seldom were greater than 10 mg per 1. CO₂ diffused constantly out of the control ponds due to input of high alkalinity water supersaturated with inorganic carbon. During the bloom in the waste ponds diffusion of CO₂ from the atmosphere was as high as 0.5 g C per m² per day. CO₂ diffused into the water constantly because the high uptake rate of inorganic carbon by the small algae reduced the levels in the water to less than 5 mg per 1. Gross production of the waste receiving ponds avearaged 2,86 g C per m² per day during the bloom and 2.44 during the non-bloom period. The average productivity of the control ponds was 1.7. Corrections for CO₂ diffusion were significant in the control ponds and in the waste ponds during theMonodus bloom. Availability of carbon from diffusion and respiratory regeneration seemed to limit phytoplankton productivity during the bloom. The annual budgets for the two sets of ponds were distinctly different. For the control ponds, the input of organic matter was nearly equal to losses indicating almost no net production of organic material. A high net loss of organic material and a net gain of inorganic carbon for the waste ponds reflected the net productive nature.