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River systems worldwide have become substantially influenced by human activities, including land use changes, river diversion operations, and flood control measures. Some of the unambiguous and best studied examples of effects of enhanced eutrophication on biotic resources can be found in Louisiana estuaries at the terminus of the Mississippi-Atchafalaya River system. The Mississippi River delta has experienced large losses of coastal wetlands due to a combination of human impacts and sea-level rise. State and Federal agencies are moving ahead with plans for building large-scale river sediment diversions, which will capture maximum sediment during spring flood pulses and direct a sediment subsidy into the eroding coastal basins. These large-scale river sediment diversions will also substantially increase freshwater and nutrient inputs and are likely to affect algal bloom formation, including harmful cyanobacterial blooms. There are concerns that discharge of river water containing high concentrations of N, P and Si may trigger algal blooms in the coastal receiving basins. River sediment diversions, as any other flood pulsing, will likely be disruptive to the coastal ecology and so balancing the benefits of slowing coastal land loss against potential negative effects on water quality remains a formidable management challenge. We review here the physical, chemical and biological factors affecting primary production in shallow coastal systems and provide known data on ecosystem response to freshwater diversions, large and small. We also discuss potential management approaches to mitigate the negative impacts of the diversions on the health and stability of the coastal food webs.

Ocean acidification has the potential to impact the ocean's biogeochemical cycles and food web dynamics, with phytoplankton in the distinctive position to profoundly influence both, as individual phytoplankton species play unique roles in energy flow and element cycling. Previous studies have focused on short-term exposure of monocultures to low pH, but do not reflect the competitive dynamics within natural phytoplankton communities. This study explores the use of experimental microcosms to expose phytoplankton assemblages to elevated pCO2 for an extended period of time. Phytoplankton communities were collected from two biogeochemically distinct Louisiana estuaries, Caillou Lake (CL) and Barataria Bay (BB), and cultured in lab for 16 weeks while bubbling CO2 enriched air corresponding to current (400 ppm) and future (1000 ppm) pCO2 levels. Results suggest that elevated pCO2 does not implicitly catalyze an increase in phytoplankton biomass (chlorophyll a). While pigment data showcased a parabolic trend and microscopic observations revealed a loss in species diversity within each major taxonomic class. By the end of the 16-week incubation, 10 out of the 12 cultures had a community structure analogous to that of the startup phytoplankton assemblage collected from the field. Natural phytoplankton assemblages exposed to elevated pCO2 experienced multiple transitional states over the course of a 16-week incubation, indicating that there is no deterministic successional pathway dictated by coastal acidification but community adaptation was observed.

A somewhat disparate, yet temporally cohesive, set of phytoplankton abundance, microphytobenthos, including the diatom Pseudo-nitzschia, benthic infauna, and sediment toxin data were used to develop a theory for the transfer of domoic acid (DA) from the toxic diatom to the benthos in the highly productive waters of the northern Gulf of Mexico near the Mississippi River plume. Archived samples and new data were used to test the theory that DA is likely to be incorporated into benthic consumers. High spring abundances of potentially toxic Pseudo-nitzschia diatoms were simultaneously present in the surface waters, bottom waters and on the seafloor. Examination of the gut contents of a typical deposit-feeding and suspension-feeding polychaete, Paraprionospio pinnata, during similar periods of high Pseudo-nitzschia abundance in surface water indicated consumption of the diatoms. Demersal fishes, particularly Atlantic croaker, are known to consume these polychaetes, with a potential for transfer of DA to even higher trophic levels. These findings warrant a theory to be tested with further studies about the trophic linkage of a phytoplankton toxin into the benthic food web.

The Deepwater Horizon oil spill of 2010 brought the ecology and health of the Gulf of Mexico to the forefront of the public's and scientific community's attention. Not only did we need a better understanding of how this oil spill impacted the Gulf of Mexico ecosystem, but we also needed to apply this knowledge to help assess impacts from perturbations in the region and guide future response actions. Phytoplankton represent the base of the food web in oceanic systems. As such, alterations of the phytoplankton community propagate to upper trophic levels. This review brings together new insights into the influence of oil and dispersant on phytoplankton. We bring together laboratory, mesocosm and field experiments, including insights into novel observations of harmful algal bloom (HAB) forming species and zooplankton as well as bacteria-phytoplankton interactions. We finish by addressing knowledge gaps and highlighting key topics for research in novel areas.

The presence of domoic acid (DA) toxin from multiple species of Pseudo-nitzschia is a concern in the highly productive food webs of the northern Gulf of Mexico. We documented the Pseudo-nitzschia presence, abundance, blooms, and toxicity over three years along a transect ∼100 km west of the Mississippi River Delta on the continental shelf. Pseudo-nitzschia were present throughout the year and occurred in high abundances (>104 cells l−1) in the early spring months during high Mississippi River (MSR) flow (∼20,000 m3 s−1) but were most abundant (>106 cells l−1) when MSR discharge was relatively lower among the spring months. A high particulate toxin production (maximum reaching 13 μg DA l−1) was associated with the high cell abundances and exceeded, by an order of magnitude, prior reports of particulate DA concentrations in Louisiana coastal waters. Differences in Pseudo-nitzschia peak times and its toxicity were correlated mainly with the timing and magnitude of MSR discharge and changes in associated parameters such as nutrient stoichiometry and salinity. A negative relationship between high MSR discharge and Pseudo-nitzschia and particulate DA concentrations was documented. These riverine dynamics have the potential to influence DA contamination in pelagic and benthic food webs in the coastal waters of the northern Gulf of Mexico.

Changes in iron (Fe) bioavailability influence diatom physiology and community composition, and thus have a profound impact on primary productivity and ecosystem dynamics. Iron limitation of diatom growth rates has been demonstrated in both oceanic and coastal waters of the Northeast Pacific Ocean and is predicted to become more pervasive in future oceans. However, it is unclear how the strategies utilized by phytoplankton to cope with low Fe bioavailability and resupply differ across these ocean provinces. We investigated the response of diatom communities to variable Fe conditions through incubation experiments performed in the Fe mosaic of the California Upwelling Zone and along a natural Fe gradient in the Northeast Pacific Ocean. Through coupling gene expression of two dominant diatom taxa (Pseudo-nitzschia and Thalassiosira) with biological rate process measurements, we provide an in-depth examination of the physiological and molecular responses associated with varying Fe status. Following Fe enrichment, oceanic diatoms showed distinct differential expression of gene products involved in nitrogen assimilation, photosynthetic carbon fixation and vitamin production compared to diatoms from low-Fe coastal sites, possibly driven by the chronic nature of Fe stress at the oceanic site. Genes of interest involved in Fe and N metabolism additionally exhibited divergent expression patterns between the two diatom taxa investigated, demonstrating that diverse diatoms may invoke alternative strategies when dealing with the identical changes in their environment. We report here several mechanisms used distinctly by coastal or oceanic diatom communities as well as numerous taxa-specific strategies for coping with Fe stress and rearranging nutrient metabolism following Fe enrichment.

River water entering estuaries affects the physical and chemical environment at irregular intervals creating a highly dynamic aquatic habitat. Phytoplankton are important primary producers in estuaries that respond quickly to their changing environment. Over a 12-month period, the phytoplankton response was examined in terms of biomass, abundance, community composition, and potential phycotoxin production to seasonal changes in river input entering the Breton Sound Estuary in Louisiana. Chlorophyll a (chl a) measurements estimated phytoplankton biomass and light microscopy identified phytoplankton abundance and community composition. Phycotoxins were measured using ultra-sensitive enzyme-linked immunosorbent assay (ELISA). During the study period, chl a and cell abundances exhibited an inverse relationship with the seasons, which were determined by temperature and diversion input rates. The community was dominated by cyanobacteria for most of the year, mainly corresponding to the warm-low flow season. For the rest of the year, cyanobacteria decreased while chlorophytes and centric diatoms increased to approximately equal contributions. Overall, the phytoplankton community composition was most commonly moderated by temperature, salinity, and dissolved inorganic nitrogen (DIN) availability using BIO-ENV. Microcystins (MCs) were detected throughout the year ranging from below detection to 2.92 μg MCs l−1. MC levels were highest during the warm-low flow season and toward the lower estuary. The detection of MCs for the first time in the Breton Sound Estuary illustrates a potential risk to human health and economically important estuarine food webs.

Scientific Literacy in America is very low compared to other developed countries. The public has a poor understanding of basic scientific principles (28% are considered scientifically literate) and outreach efforts to address this problem are limited. When looking at specific issues such as harmful algal blooms in freshwater systems there is hardly any active outreach programs. The basis for this study was to help the public understand what harmful algal blooms are and what visual indicators exist to warn of their presence. Initial surveys were conducted to find out what fishermen knew about algae and harmful algal blooms. The participants (age 11–70) had heard of algae (100%), but very few had heard of a harmful algal bloom (40%) and when the participants were pressed on the subject, few could define algae. An educational brochure was created from the baseline of data collected from the public and was distributed to the same fishing areas. A follow-up interview of these areas showed that the brochures were being taken by people, but finding those actual people proved difficult. Once brochures were viewed, many people were able to indicate something new they learned about algae such as algae produces oxygen. Scientists need to take a more active role in conveying their research to the public in order to increase scientific knowledge.

Diffusive flux of bioavailable soluble reactive phosphorus (SRP) across the sediment–water interface is one mechanism by which sediments can be a source of phosphorus to the water column in aquatic systems and contribute to primary productivity. This process is dependent on sediment biogeochemistry and SRP concentration gradients at the sediment–water interface. In systems subjected to episodic external pulses of nutrient-rich water, SRP concentration gradients can have potential implications for diffusive flux. In this study, we sought to investigate two hypotheses: (1) diffusive flux of SRP from sediments is a significant source of SRP in the annual budget for the oligohaline Lake Pontchartrain estuary and (2) under SRP-depleted water column conditions following large episodic, external pulses of nitrogen-rich Mississippi River water to the estuary, internal SRP loading by diffusive flux can regenerate SRP in the water column to previously observed levels rapidly. Our specific objectives were to: (i) determine sediment, water column, and phytoplankton characteristics at multiple locations in the estuary, (ii) measure rates of SRP diffusive flux from sediments using intact cores under aerobic and anaerobic incubations, (iii) estimate the potential for water column SRP regeneration by diffusive flux under SRP-depleted conditions using a simple model, and (iv) estimate the annual load of SRP from the sediments by diffusive flux. Results indicate that diffusive flux of SRP from Lake Pontchartrain sediments likely contributes ~30–44% of the annual SRP load to the estuary. Further, internal SRP loading by diffusion has the potential to regenerate SRP in SRP-depleted waters to previously observed concentrations in

Blooms of the toxin-producing diatom Pseudo-nitzschia commonly occur in Monterey Bay, California, resulting in sea lion mortality events. The links between strandings of California sea lions suffering from domoic acid (DA) toxicity, toxic cell numbers, and their associated DA concentration in Monterey Bay and in sea lion feces were examined from 2004 to 2007. While Pseudo-nitzschia toxic cells and DA concentrations were detectable in the water column most of the time, they were often at low levels. A total of 82 California sea lions were found stranded in the Bay between 2004 and 2007 with acute or chronic signs associated with DA

Pulsed river water events can increase nutrient levels potentially translating into enhanced primary production, phytoplankton community shifts, and bloom formation. The Bonnet Carre Spillway is a managed river diversion which can be used to redirect a significant amount of Mississippi River water into Lake Pontchartrain, reducing the risks of flood in the downstream communities during runoff seasons. We investigated nutrient enrichment and consequent changes in phytoplankton biomass, including toxic species in Lake Pontchartrain during and after a 1-month Bonne Carre Spillway opening in 2008. Water samples were collected along a 30 km transect. A freshwater plume was found to have formed by the strong river input that had limited mixing with the lake during the opening. The plume and lake water gradually mixed together after the Spillway was closed, indicated by the reduction of the horizontal salinity gradient. The river pulse increased the lake nitrate and dissolved reactive phosphorus concentrations to more than five times the lake background in the plume stations. Nutrient concentrations decreased rapidly after the Spillway closure as the plume dissipated. Diatoms and chlorophytes dominated the system during the opening. After the Spillway closure, there was a shift over time from diatom dominance to toxic cyanobacteria dominance that corresponded to more stable, warmer, and nutrient-limited water conditions. Associated toxins were present and varied over time and space. Further research on the phytoplankton assemblages on the lake is needed in subsequent, non-Spillway opening years to evaluate the impact of river water pulses on the development of these toxic cyanobacterial blooms.

The neurotoxin domoic acid (DA) produced by the diatoms Pseudo-nitzschia has been responsible for deaths of marine mammals and birds in Monterey Bay, California, USA. In this study we examined links between DA-related strandings of the seasonally migratory California sea lion Zalophus californianus and regional occurrences of DA-producing diatoms using a decade-long time series. Results suggest a more complex pattern of stranding than anticipated, one not related simply to regional abundance of the toxin producers. Stranding patterns of sea lions exhibiting signs of acute DA toxicosis may be best explained by multiple causative factors including timing of toxic blooms with respect to the sea lion breeding cycle, adequacy of sea lion prey during the breeding season, as well as the geographic range of this pinniped outside of the breeding season. Three DA-related stranding events occurred in Monterey Bay in 1998, 2000 and 2007, when toxic DA blooms were pre- sent in the Bay and the California coast was experiencing El Nino/Southern Oscillation conditions. Foraging centers near the breeding site likely provided inadequate food for individuals, leading to northerly movement of these highly mobile predators to other geographic sites resulting in exposure to toxic DA-producing blooms. High toxic Pseudo-nitzschia and DA concentrations did not, however, result in DA-related stranding events in 2002, 2003 and 2004, when weaker than normal upwelling events were present in the Bay. Relative productivity of central versus southern California with respect to the breeding season thus appears to strongly influence the frequency of DA-related strand- ings in Monterey Bay, California.

Harmful algal blooms are an increasing problem for coastal waters world-wide. The presence of the toxigenic diatom genus Pseudo-nitzschia is of concern in the Gulf of Mexico, due to the potential for several species in this genus to produce the neurotoxin domoic acid (DA). Louisiana coastal waters are of particular interest due to the presence of both toxin-producing species of Pseudo-nitzschia and abundant potential vectors. While trophic transfer of DA to consumers has repeatedly occurred along the California coast, little is known about trophic transfer of recently detected DA in the Gulf of Mexico. In this study, the presence of DA was investigated in filter-feeding gulf menhaden (Brevoortia patronus) and in seawater where high abundances of these fish reside. Pseudo-nitzschia presence and enumeration was determined using light microscopy, species identification in seawater and gulf menhaden gut contents was conducted with transmission electron microscopy (TEM), and DA quantification in corresponding seawater and tissue samples was determined by competitive enzyme-linked immunosorbent assay (cELISA). Examination of the phytoplankton revealed the presence of four species of Pseudo-nitzschia: P. calliantha for the first time, P. pseudodelicatissima, P. pungens, and P. americana, with P. calliantha as the dominant Pseudo-nitzschia species. Low levels of DA were detected in both seawater and fish samples, with a significant correlation between the two (n = 22, p = 0.043). Thus, for the first time in the Gulf of Mexico, a potential vector of DA has been identified, revealing the possibility of DA contamination in coastal Louisiana food webs. Published by Elsevier B.V.

Toxin producing cyanobacteria commonly inhabit fresh waters and brackish estuaries, and blooms of these species may be escalating worldwide due to eutrophication. The most common cyanobacterial toxins occurring in fresh and brackish waters are microcystins (MC), which are known to accumulate in aquatic organisms. Prey preference for filter-feeding organisms, such as clams and mussels, make the blue crab, Callinectes sapidus, a candidate for microcystin contamination, therefore making this commercially important edible crab species a potential vector of these toxins to humans. The present study was conducted in a hyper-eutrophic freshwater lake, Lac des Allemands, located in the Barataria estuary system of southeastern Louisiana, and was aimed at documenting the presence and abundance of toxic cyanobacteria and assessing microcystin concentrations in surface water and blue crabs taken from this region. Microcystis sp. were the dominant cyanobacteria, with alternating blooms of Microcystis and Anabaena spp. occurring during the 8-month study. Enzyme-linked immunosorbent assay (ELISA) was used to evaluate concentrations of microcystins from surface water and hepatopancreas, viscera, and muscle tissues of blue crabs. The highest concentration of microcystins found in surface water (1.42 μg MC l−1) was above the tolerable daily intake (TDI) guideline for microcystins in drinking water (1.0 μg MC l−1) set by the World Health Organization (WHO). Highest concentration of microcystins occurring in crab tissue were 820 μg MC kg−1 in hepatopancreas, 65 μg MC kg−1 in viscera, and 105 μg MC kg−1 in muscle, which were close to or exceeding the WHO-TDI guidelines for human consumption (0.04 μg MC kg−1 body weight day−1) based on human body weight and amount of crab tissue consumed. This study documents the presence of microcystins in both surface water and blue crab tissue and therefore, demonstrates the potential for Microcystis and Anabaena blooms to produce toxins that may be accumulated in the tissues of blue crabs and transferred to higher level consumers, including humans.

Over the past decade diatom blooms of domoic acid (DA)-producing Pseudo-nitzschia spp. have been responsible for numerous marine mammal and bird mortalities in Monterey Bay, CA. One possible toxin vector is the market squid, Loligo opalescens , a small pelagic mollusk that plays an important role in the near-shore food web of the California Current ecosystem as a favored vertebrate prey species. This study examined the trophic link between toxic Pseudo-nitzschia and L. opalescens using toxin and stomach content analyses of animals collected from Monterey Bay, CA in 2000. Receptor binding assay data (confirmed by tandem mass spectrometry), demonstrated the presence of DA in squid during a toxic Pseudo-nitzschia event, with P. australis frustules observed in stomach samples. Though DA levels were low ( −1 tissue) in L. opalescens during the study period, it is now clear that this potent neurotoxin can occur in squid and is likely delivered through its krill prey species, which are known to retain DA after feeding on toxic Pseudo-nitzschia . Our findings suggest that further study of the relationship between Pseudo-nitzschia blooms and DA contamination of squid is warranted to better evaluate the potential health risk to humans and wildlife associated with this major commercial seafood species and important prey item.

Krill are important grazers on diatoms and critical prey items for many high level carnivores in Monterey Bay and elsewhere along the California coast. Here, some of the higher level consumers have recently been shown to be severely affected by the toxin, domoic acid (DA), a secondary metabolite of some species of the diatom Pseudo-nitzschia. To understand the potential role of krill in vectoring DA from diatoms to large predators, several grazing experiments were conducted. Field-collected Euphausia pacifica and Thysanoessa spinifera were fed on a diet of toxic and non-toxic Pseudo-nitzschia species. Gut evacuation rates of krill and CHN analysis of the algae were obtained concurrently to determine gut residence time and nutritional value of the food. Our results from a short-term (6 h) grazing experiment demonstrated that both E. pacifica and T. spinifera consumed toxic Pseudo-nitzschia multiseries but the responses of the two krill species differed to a degree, with E. pacifica having the higher weight-specific feeding rate. Results from a longer-term (24 h) grazing experiment showed that E. pacifica had a different, interrupted grazing pattern and showed no immediate ill effects when consuming toxic P. multiseries as contrasted with its more constant feeding pattern on non-toxic Pseudo-nitzschia pungens. We show that toxin loads in krill digestive tracts, estimated from feeding rates and gut residence time measured here, match the observed body burdens of DA measured in field-collected krill during toxic blooms. Such data are important for predicting toxin transfer from krill to higher trophic levels during blooms of toxic algae. As an example of this transfer, we show the vulnerability of a krill-feeding seabird, Cassin's Auklet (Ptychoramphus aleuticus) to DA likely vectored by krill during toxic Pseudo-nitzschia blooms.

Over the past decade, blooms of the domoic acid (DA) producing diatom Pseudo- nitzschia have been responsible for numerous deaths of marine mammals and birds in Monterey Bay, California. Euphausiids (krill) are important members of the local zooplankton grazer community and comprise the primary diet of squid, baleen whales, and many seabirds. Krill are thus a key potential vector for the transfer of DA to higher trophic level organisms in Monterey Bay. A better understand- ing of the quantitative trophic interactions and body burden of DA in krill is required to predict whether they can act as an effective vector for this neurotoxin. Here we report results of toxin analy- ses and gut content examinations of krill Euphausia pacifica collected from Monterey Bay in 2000. Corresponding counts of toxic Pseudo-nitzschia species in the water and their cellular DA concen- trations were also obtained at the collection sites. Toxin analysis by receptor binding assay demon- strated that DA in krill tissue varied between 0.1 to 44 µg DA equiv. g -1 tissue (confirmed by tandem mass spectrometry), with levels corresponding to the abundance of toxic Pseudo-nitzschia species present in the water. The occurrence of Pseudo-nitzschia australis frustules in the digestive tract of E. pacifica verified that a toxic species of this diatom was an important part of their diet and thus impli- cated this phytoplankter as the source of DA. These findings provide compelling evidence for the role of krill as a potential transfer agent of the phycotoxin DA to higher trophic levels in marine food web.

the edges of the inlet. The net flux of total suspended sediment out of the bay was determined to be 8800 t of which 20% was organic matter, demonstrating a significant source of organic matter to the base of the coastal ocean detrital food chain. The time evolution and net fluxes of water, and suspended sediments showed that the net flow resembles conventional estuarine circulation patterns with net outward flow on the surface and shallow ends of the inlet and with net inward flow in the center and at the bottom of the center of the inlet. The west side has a much larger outward flow than the east side while the east side is fresher. These differences suggest that the Louisiana Coastal Current from around the Bird’s Foot Delta derived from the mixing of shelf water with the Mississippi River freshwater may have entered the bay. This must have been mostly from the east side during the survey, which resulted in a smaller outward flow on the eastern side. A numerical experiment further confirmed this assumption and the model was verified by field observations on 5 May 2010.