Nitrogen fixation and release of fixed nitrogen by Trichodesmium spp. in the Gulf of Mexico

During a 3‐yr study in the Gulf of Mexico, we measured dinitrogen (N2) fixation and nitrogen (N) release by Trichodesmium and compared these rates with water column N demand and the estimated N necessary to support blooms of Karenia brevis, a toxic dinoflagellate that severely affects the West Florida shelf. Net and gross N2 fixation rates were compared in simultaneous incubations using δ15N2 uptake and acetylene reduction, respectively. The difference between net and gross N2 fixation is assumed to be an approximation of the rate of N release. Results demonstrate that Trichodesmium in the Gulf of Mexico are fixing N2 at high rates and that an average of 52% of this recently fixed N2 is rapidly released. Calculations suggest that observed densities of Trichodesmium can provide enough N to support moderately sized K. brevis blooms. Based on other studies where δ15N2 and acetylene reduction were compared directly, it appears that N release from Trichodesmium is common but varies in magnitude among environments. In addition, carbon (C) and N‐based doubling times for Trichodesmium vary among studies and environments. Comparing gross N2 fixation and C fixation directly, C‐based doubling times exceeded N‐based doubling times, which suggests an imbalance in elemental turnover or a failure to fully quantify Trichodesmium N use

Interactions Between Zooplankton and Karenia brevis in the Gulf of Mexico.

Blooms of the toxic dinoflagellate K. brevis are common in the Gulf of Mexico, yet no in situ studies of the interactions between zooplankton and K. brevis in the Gulf of Mexico have been conducted. Zooplankton numerical abundance, biomass and taxonomic composition of nonbloom and K. brevis bloom stations within the ECOHAB study area were compared. At nonbloom stations, the most important determinant species were Parvolcalanus crassirostris, Oithona colcarva and Paracalanus quasimodo at the 5-m isobath and P. quasimodo, O. colcarva and Oikopleura dioka at the 25-m isobath. There was considerable overlap between the 5 and 25-m isobaths, with 9 species contributing to the top 90% of numerical abundance at both isobaths. Within K. brevis blooms Acartia tonsa, Centropages velificatus, Temora turbinata, Evadne tergestina, O. colcarva, O. dioika, and P. crassirostris were consistently dominant. Variations between non-bloom and bloom assemblages were evident, including variations in numerical abundance and biomass and the reduction in numerical abundance of 3 key species. Calculated grazing pressure proved insufficient to terminate K. brevis blooms, despite occasional grazing hot spots

Harmful algal blooms and eutrophication : examining linkages from selected coastal regions of the United States

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Harmful Algae 8 (2008): 39-53, doi:10.1016/j.hal.2008.08.017.Coastal waters of the United States (U.S.) are subject to many of the major harmful algal bloom (HAB) poisoning syndromes and impacts. These include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), ciguatera fish poisoning (CFP) and various other HAB phenomena such as fish kills, loss of submerged vegetation, shellfish mortalities, and widespread marine mammal mortalities. Here, the occurrences of selected HABs in a selected set of regions are described in terms of their relationship to eutrophication, illustrating a range of responses. Evidence suggestive of changes in the frequency, extent or magnitude of HABs in these areas is explored in the context of the nutrient sources underlying those blooms, both natural and anthropogenic. In some regions of the U.S., the linkages between HABs and eutrophication are clear and well documented, whereas in others, information is limited, thereby highlighting important areas for further research.Support was provided through the Woods Hole Center for Oceans and Human Health (to DMA), National Science Foundation (NSF) grants OCE-9808173 and OCE-0430724 (to DMA), OCE-0234587 (to WPC), OCE04-32479 (to MLP), OCE-0138544 (to RMK), OCE-9981617 (to PMG); National Institute of Environmental Health Sciences (NIEHS) grants P50ES012742-01 (to DMA) and P50ES012740 (to MLP); NOAA Grants NA96OP0099 (to DMA), NA16OP1450 (to VLT), NA96P00084 (to GAV and CAH), NA160C2936 and NA108H-C (to RMK), NA860P0493 and NA04NOS4780241 (to PMG), NA04NOS4780239-02 (to RMK), NA06NOS4780245 (to DWT). Support was also provided from the West Coast Center for Oceans and Human Health (to VLT and WPC), USEPA Grant CR826792-01-0 (to GAV and CAH), and the State of Florida Grant S7701617826 (to GAV and CAH)

Lagrangian Particle Tracking of a Toxic Dinoflagellate Bloom within the Tampa Bay Estuary

A coastal risk assessment system simulates the basic physical mechanisms underlying contaminant transport in Tampa Bay. This risk assessment system, comprised of a three-dimensional numerical circulation model coupled to a Lagrangian particle tracking model, simulates the transport and dispersion of a toxic dinoflagellate bloom. Instantaneous velocity output from the circulation model drives the movement of particles, each representing a fraction of a K. brevis bloom, within the model grid cells. Hindcast simulations of the spatial distribution of the K. brevis bloom are presented and compared with water sample concentrations collected during the peak of the bloom. Probability calculations, herein called transport quotients, allow for rapid analysis of bay-wide K. brevis transport showing locations most likely to be impacted by the contaminant. Maps constructed from the transport quotients provide managers with a bay-wide snapshot of areas in Tampa Bay most at risk during a hazardous bloom event

Influence of Extreme Storm Events on West Florida Shelf CDOM Distributions

Colored Dissolved Organic Matter (CDOM) distribution and signatures provide vital information about the amount and composition of organic material in aquatic environments. This information is critical for deciphering the sources and biogeochemical pathways of organic carbon, and thus vital to the understanding of carbon cycling and budgets. Waters of the West Florida Shelf are heavily influenced by many river systems on Florida\u27s Gulf Coast that, to the first order, control CDOM distributions on the shelf. Three storm events during 2004 and 2005 (Hurricane Charley, Hurricane Wilma, and a Winter Storm) profoundly altered the typical distribution of CDOM fluorescence and absorption properties on the Southern West Florida Shelf. Seasonal surveys revealed that changes in the underwater light field as a result of major hurricanes and resuspension events are linked closely with a number of factors prior to a storm\u27s passing such as the presence of persistent blooms, rainfall and discharge. Additionally, storm track and wind direction were found to play a significant role in CDOM signatures

Long-term evaluation of three satellite ocean color algorithms for identifying harmful algal blooms ( Karenia brevis) along the west coast of Florida: A matchup assessment

We present a simple algorithm to identify Karenia brevis blooms in the Gulf of Mexico along the west coast of Florida in satellite imagery. It is based on an empirical analysis of collocated matchups of satellite and in situ measurements. The results of this Empirical Approach is compared to those of a Bio-optical Technique – taken from the published literature – and the Operational Method currently implemented by the NOAA Harmful Algal Bloom Forecasting System for K. brevis blooms. These three algorithms are evaluated using a multi-year MODIS data set (from July, 2002 to October, 2006) and a long-term in situ database. Matchup pairs, consisting of remotely-sensed ocean color parameters and near-coincident field measurements of K. brevis concentration, are used to assess the accuracy of the algorithms. Fair evaluation of the algorithms was only possible in the central west Florida shelf (i.e. between 25.75°N and 28.25°N) during the boreal Summer and Fall months (i.e. July to December) due to the availability of valid cloud-free matchups. Even though the predictive values of the three algorithms are similar, the statistical measure of success in red tide identification (defined as cell counts in excess of 1.5 × 10 4 cells L −1) varied considerably (sensitivity— Empirical: 86%; Bio-optical: 77%; Operational: 26%), as did their effectiveness in identifying non-bloom cases (specificity— Empirical: 53%; Bio-optical: 65%; Operational: 84%). As the Operational Method had an elevated frequency of false-negative cases (i.e. presented low accuracy in detecting known red tides), and because of the considerable overlap between the optical characteristics of the red tide and non-bloom population, only the other two algorithms underwent a procedure for further inspecting possible detection improvements. Both optimized versions of the Empirical and Bio-optical algorithms performed similarly, being equally specific and sensitive (~ 70% for both) and showing low levels of uncertainties (i.e. few cases of false-negatives and false-positives: ~ 30%)—improved positive predictive values (~ 60%) were also observed along with good negative predictive values (~ 80%)

First Record of a Fish-Killing \u3cem\u3eGymnodinium\u3c/em\u3e sp Bloom in Kuwait Bay, Arabian Sea: Chronology and Potential Causes

Significant natural and aquaculture fish deaths in Kuwait Bay occurred from September to October of 1999 and were attributed to a bloom of the dinoflagellate Gymnodinium sp. A chronology of the bloom event suggests that a period of low winds and stable water-column structure preceded the bloom. Maximum cell concentrations of Gymnodinium sp. (\u3e6 x 10(6) cells l(-1)) were also immediately preceded by a more than 20-fold increase in mean inorganic nitrogen concentrations (up to 60 muM) and elevated inorganic phosphate concentrations. This, combined with elevated inorganic and organic nutrient concentrations within the bloom, suggests that coastal nutrient eutrophication was Likely to have contributed significantly to bloom development and support. Termination of the Gymnodinium sp. bloom coincided with a bloom of the non-toxic ciliate Mesodinium rubrum, which appeared as large red patches in Kuwait Bay. While no adverse human health effects were associated with the bloom, closure of shellfish and selected finfish (largely mullet Liza macrolepis) markets resulted in significant economic losses to the region. The occurrence of this toxic algal bloom event, the first within the Arabian Sea, highlights the need for monitoring and research programs in the Arabian Sea and Kuwait Bay that focus on nutrients and eutrophication, in addition to oil related pollution issues

Evidence for Dissolved Organic Nitrogen and Phosphorus Uptake During a Cyanobacterial Bloom in Florida Bay

Florida Bay, a shallow, seagrass-dominated bay in southern Florida, USA, receives significant nutrient inputs and has experienced seagrass losses and microalgal blooms within the last several decades. Inorganic nutrient inputs have been well characterized, but the role of organic nutrients, specifically of dissolved organic nitrogen (DON) and organic phosphorus (DOP), in supporting microbial processes in the bay is unknown. In this study various techniques were used to assess the importance of these nutrients along a transect in Florida Bay when a cyanobacterial bloom occurred in the central region in November 2002. These techniques included measurements of ambient particulate and dissolved nutrients, enzyme (urease and alkaline phosphatase) activities, and experiments to determine rates of N-15 uptake (nitrate, ammonium, urea, and amino acids over a period of 0.5 h) and long-term (48 h) changes in microbial biomass and N-15 natural abundance in enrichment bioassays. The cyanobacterial bloom in central Florida Bay was associated with the highest concentrations of DON and DOP, whereas the microflagellate- and diatom-dominated eastern bay region was associated with the highest concentrations of inorganic nutrients. The zeaxanthin: chlorophyll a ratio (an indicator of the relative contribution of cyanobacteria to phytoplankton biomass) was positively correlated with the rate of uptake of urea, and negatively correlated with the rate of uptake of inorganic nitrogen. The opposite pattern was observed for the fucoxanthin: chlorophyll a ratio (indicative of relative diatom biomass) and the peridinin: chlorophyll a ratio (indicative of relative photosynthetic dinoflagellate biomass), suggesting that different algal groups were using different N substrates. Biomass responses in the bioassay experiments showed that phytoplankton (as chlorophyll a) responded to DON additions in the western region and to DOP additions in the eastern region, but heterotrophic bacteria, in contrast, responded to DOP additions in the west and DON additions in the east. These findings thus demonstrate the potential for different sources of N, including DON, to stimulate different components of the algal community, and for the phytoplankton and bacteria to respond differently to N and P

Brevetoxin persistence in sediments and seagrass epiphytes of east Florida coastal waters

► A Karenia brevis bloom developed in the Intracoastal Waterway along the east Florida coast in summer 2007. ► In summer 2008 brevetoxins were found in sediments of the northern Intracoastal Waterway. ► Brevetoxins were also found in summer 2008 within seagrass epiphytes in the southern Intracoastal Waterway. ► Generally, brevetoxins were present in either sediments or seagrass epiphytes at any station. A bloom of Karenia brevis Davis developed in September 2007 near Jacksonville, Florida and subsequently progressed south through east Florida coastal waters and the Atlantic Intracoastal Waterway (ICW). Maximum cell abundances exceeded 10 6 cells L −1 through October in the northern ICW between Jacksonville and the Indian River Lagoon. The bloom progressed further south during November, and terminated in December 2007 at densities of 10 4 cells L −1 in the ICW south of Jupiter Inlet, Florida. Brevetoxins were subsequently sampled in sediments and seagrass epiphytes in July and August 2008 in the ICW. Sediment brevetoxins occurred at concentrations of 11–15 ng PbTx-3 equivalents (g dry wt sediment) −1 in three of five basins in the northern ICW during summer 2008. Seagrass beds occur south of the Mosquito Lagoon in the ICW. Brevetoxins were detected in six of the nine seagrass beds sampled between the Mosquito Lagoon and Jupiter Inlet at concentrations of 6–18 ng (g dry wt epiphytes) −1. The highest brevetoxins concentrations were found in sediments near Patrick Air Force Base at 89 ng (g dry wt sediment) −1. In general, brevetoxins occurred in either seagrass epiphytes or sediments. Blades of the resident seagrass species have a maximum life span of less than six months, so it is postulated that brevetoxins could be transferred between epibenthic communities of individual blades in seagrass beds. The occurrence of brevetoxins in east Florida coast sediments and seagrass epiphytes up to eight months after bloom termination supports observations from the Florida west coast that brevetoxins can persist in marine ecosystems in the absence of sustained blooms. Furthermore, our observations show that brevetoxins can persist in sediments where seagrass communities are absent