Spatially distributed water quality responses to freshwater discharge in a tropical estuary, Hilo Bay, Hawai'i.

Hilo Bay, Hawai'i, is an estuary of great importance to its neighboring coastal community, but it is threatened by impaired water quality indicated by excessive turbidity and chlorophyll a associated with river discharges of sediments and nutrients. The Wailuku River in the western half of the bay is the primary source of freshwater discharge, hypothesized here to form a surface water-dominant half of the bay with different water quality traits than the groundwater-dominant, eastern half of the bay where the spring-fed Wailoa River discharges. The water quality of both halves of the bay over different flow conditions of the Wailuku River is examined in this study using spatially distributed water quality sampling which collects hundreds of samples in either half of the bay at a distance of about every 40 m. The dense sample shows significant differences between the two halves of the bay, with greater salinity dilution and turbidity in the surface water-dominant area. Both salinity and turbidity have a predictable relation to discharge, with salinity decreasing and turbidity increasing in higher flow conditions. Chlorophyll a, however, has a more complex relation to discharge, as chlorophyll a concentrations are greatest in high-flow conditions, but this may be because the water quality samples were collected in different seasons. Furthermore, significantly greater chlorophyll a concentrations in the groundwater-dominant half of the bay in low-flow conditions show that discharge may be spuriously correlated to chlorophyll a, and further studies of the effects of surface water discharge on chlorophyll a concentrations are warranted.

Enterococcus exceedances related to environmental variability at New Jersey ocean beaches.

Microbial pollution at ocean beaches is a global public health problem that can be exacerbated by excessive rainfall, particularly at beaches adjacent to urban areas. Rain is acknowledged as a predictive factor of Enterococcus levels at NJ beaches, but to date no study has explicitly examined the link. Here, five beaches (156 observations) in Monmouth County, NJ, with storm drain outflows present were sampled for Enterococcus and water quality during dry and wet periods. Hypotheses included (1) beaches differ in Enterococcus levels, (2) Enterococcus is present year-round, and (3) Enterococcus exceedances could be modeled based on environmental parameters. Beaches showed significantly different median Enterococcus levels, with site SEA2 (Neptune Blvd. in Deal, NJ) lower than others and site SEA4 (South Bath Ave. in Long Branch, NJ) higher than the other sites. Elevated Enterococcus levels were detected at water temperatures from 6.5 to 22.2 °C. Multiple linear regression models identified rainfall (+), water temperature (+), and water level (-) as related to Enterococcus concentrations levels at these beaches. For the purpose of simulating the efficacy of different monitoring strategies, a hindcast model of Enterococcus abundance based on historic rainfall, water temperature, and water level data was produced. Results indicated that once-per-week sampling detected ~14% (e.g., 1/7) exceedance events, while sampling during summer alone detected ~ 50% of annual exceedance events. Models of Enterococcus exceedance based on readily available environmental time series have the potential to supplement and improve Enterococcus monitoring at NJ beaches.

Spatial analysis of water quality parameters in Hilo Bay, Hawai'i, using a combination of interpolated surfaces and hot spot analysis.

Hilo Bay estuary, located on the northeastern side of Hawai'i Island, experiences variability in water quality parameters due to its numerous water inputs. This estuary experiences influxes of water from three sources: groundwater to the east, marine water from the north, and surface water from the Wailuku River to the west. High rainfall and river flow impacts Hilo Bay's water quality including salinity, turbidity, and chlorophyll a concentration. Here, maps of Hilo Bay water quality were examined to assess spatial patterns of these important parameters. Exploring the patterns of these water quality parameters by creating inverse distance weighted (IDW) interpolation surfaces of survey points and clusters based on hot spot analyses during low- and high-flow conditions showed statistically significant differences in spatial water quality in Hilo Bay. Water quality maps after a storm show (1) an overall decrease in salinity, (2) a river plume from the Wailuku River associated with a turbidity hot spot, and (3) a chlorophyll a hot spot offset from the river plume in the center of the bay. Using spatial analysis to analyze water quality throughout the entirety of Hilo Bay before and after storm events can lead to a better understanding of how this ecosystem is affected during these types of events, and furthermore, adopting this method of sampling and analysis allows for a greater representation of water quality all over the bay and can improve the monitoring of water quality in this important ecosystem.

Seasonal to Inter-Annual Variability of Primary Production in Chesapeake Bay: Prospects to Reverse Eutrophication and Change Trophic Classification.

Estuarine-coastal ecosystems are rich areas of the global ocean with elevated rates of organic matter production supporting major fisheries. Net and gross primary production (NPP, GPP) are essential properties of these ecosystems, characterized by high spatial, seasonal, and inter-annual variability associated with climatic effects on hydrology. Over 20 years ago, Nixon defined the trophic classification of marine ecosystems based on annual phytoplankton primary production (APPP), with categories ranging from "oligotrophic" to "hypertrophic". Source data consisting of shipboard measurements of NPP and GPP from 1982 to 2004 for Chesapeake Bay in the mid-Atlantic region of the United States supported estimates of APPP from 300 to 500 g C m-2 yr-1, corresponding to "eutrophic" to "hypertrophic" categories. Here, we developed generalized additive models (GAM) to interpolate the limited spatio-temporal resolution of source data. Principal goals were: (1) to develop predictive models of NPP and GPP calibrated to source data (1982 to 2004); (2) to apply the models to historical (1960s, 1970s) and monitoring (1985 to 2015) data with adjustments for nutrient loadings and climatic effects; (3) to estimate APPP from model predictions of NPP; (4) to test effects of simulated reductions of phytoplankton biomass or nutrient loadings on trophic classification based on APPP. Simulated 40% decreases of euphotic-layer chl-a or TN and NO2 + NO3 loadings led to decreasing APPP sufficient to change trophic classification from "eutrophic' to "mesotrophic" for oligohaline (OH) and polyhaline (PH) salinity zones, and from "hypertrophic" to "eutrophic" for the mesohaline (MH) salinity zone of the bay. These findings show that improved water quality is attainable with sustained reversal of nutrient over-enrichment sufficient to decrease phytoplankton biomass and APPP.

Long-term trends, current status, and transitions of water quality in Chesapeake Bay.

Coincident climatic and human effects strongly influence water-quality properties in estuarine-coastal ecosystems around the world. Time-series data for a number of ecosystems reveal high spatio-temporal variability superimposed on secular trends traceable to nutrient over-enrichment. In this paper, we present new analyses of long-term data for Chesapeake Bay directed at several goals: (1) to distinguish trends from spatio-temporal variability imposed by climatic effects; (2) to assess long-term trends of water-quality properties reflecting degradation and recovery; (3) to propose numerical water-quality criteria as targets for restoration; (4) to assess progress toward attainment of these targets. The bay has experienced multiple impairments associated with nutrient over-enrichment since World War II, e.g., low dissolved oxygen (DO), decreased water clarity, and harmful algal blooms (HAB). Anthropogenic eutrophication has been expressed as increased chlorophyll-a (chl-a) driven by accelerated nutrient loading from 1945 to 1980. Management intervention led to decreased loading thereafter, but deleterious symptoms of excess nutrients persist. Climatic effects exemplified by irregular "dry" and "wet" periods in the last 30+ years largely explain high inter-annual variability of water-quality properties, requiring adjustments to resolve long-term trends. Here, we extend these analyses at a finer temporal scale to six decades of chl-a, Secchi depth, and nitrite plus nitrate (NO2 + NO3) data to support trend analyses and the development of numerical water-quality criteria. The proposed criteria build on a conceptual model emphasizing the need to distinguish climatic and human effects in gauging progress to reverse eutrophication in estuarine-coastal ecosystems.

Variable climatic conditions dominate recent phytoplankton dynamics in Chesapeake Bay.

Variable climatic conditions strongly influence phytoplankton dynamics in estuaries globally. Our study area is Chesapeake Bay, a highly productive ecosystem providing natural resources, transportation, and recreation for nearly 16 million people inhabiting a 165,000-km(2) watershed. Since World War II, nutrient over-enrichment has led to multiple ecosystem impairments caused by increased phytoplankton biomass as chlorophyll-a (chl-a). Doubled nitrogen (N) loadings from 1945-1980 led to increased chl-a, reduced water clarity, and low dissolved oxygen (DO), while decreased N loadings from 1981-2012 suggest modest improvement. The recent 30+ years are characterized by high inter-annual variability of chl-a, coinciding with irregular dry and wet periods, complicating the detection of long-term trends. Here, we synthesize time-series data for historical and recent N loadings (TN, NO2 + NO3), chl-a, floral composition, and net primary productivity (NPP) to distinguish secular changes caused by nutrient over-enrichment from spatio-temporal variability imposed by climatic conditions. Wet years showed higher chl-a, higher diatom abundance, and increased NPP, while dry years showed lower chl-a, lower diatom abundance, and decreased NPP. Our findings support a conceptual model wherein variable climatic conditions dominate recent phytoplankton dynamics against a backdrop of nutrient over-enrichment, emphasizing the need to separate these effects to gauge progress toward improving water quality in estuaries.

Ichthyotoxic Karlodinium veneficum (Ballantine) J Larsen in the Upper Swan River Estuary (Western Australia): Ecological conditions leading to a fish kill.

Ichthyotoxic Karlodinium veneficum has become a persistent problem in the eutrophic Swan River Estuary (SRE) near Perth, Western Australia. Karlotoxin (KmTx) concentrations and K. veneficum were sampled from March to July 2005, spanning a bloom confirmed by microscopy and genetics (ITS sequence), and a fish kill coincident with end of the bloom. The objective of this study was to investigate K. veneficum cell and toxin dynamics, and water quality conditions, leading up to the bloom and fish kill in this estuarine system. Abundance of K. veneficum increased as diatom abundance decreased over a 3-month period (Jan-Mar) preceding the bloom. Low freshwater flow to the SRE characterized the bloom initiation period, while elevated seasonal flows altered water quality and preceded the end of the bloom and fish kill. The bloom of K. veneficum was localized over a bottom layer of hypoxic water in a stratified water column. Low nitrate levels, DIN:DIP (mol) near unity, and particulate C:N:P of K. veneficum-rich water samples were consistent with nitrogen limitation of phytoplankton. A KmTx 2 congener was present in the concentration range 0-1052 ng KmTx mL-1, levels that were sufficient to kill larval fish in the laboratory within 4 h. A KmTx cell quota of 2.8 pg KmTx cell-1 was estimated for the bloom, which is moderately high for the species. Gill histopathology of fish from this fish kill showed signs of damage similar to those caused by KmTx in the lab. Results from this study suggest that conditions in the SRE, including elevated K. veneficum abundance and KmTx cell quotas, as well as hypoxia in the upper SRE, likely contribute to seasonal fish kills observed in this system.

A dinoflagellate exploits toxins to immobilize prey prior to ingestion.

Toxins produced by the harmful algal bloom (HAB) forming, mixotrophic dinoflagellate Karlodinium veneficum have long been associated with fish kills. To date, the perceived ecological role for toxins has been relief from grazing pressures. Here, we demonstrate that karlotoxins also serve as a predation instrument. Using high-speed holographic microscopy, we measure the swimming behavior of several toxic and nontoxic strains of K. veneficum and their prey, Storeatula major, within dense suspensions. The selected strains produce toxins with varying potency and dosages, including a nontoxic one. Results clearly show that mixing the prey with the predatory, toxic strains causes prey immobilization at rates that are consistent with the karlotoxins' potency and dosage. Even prey cells that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in pure suspensions, as quantified by their velocity, radii of helical trajectories, and direction of helical rotation. When mixed with prey, all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely, the nontoxic control strain does not alter its swimming and does not affect prey behavior. In separate experiments, we show that exposing prey to exogenous toxins also causes prey immobilization at rates consistent with potency. Clearly, the toxic predatory strains use karlotoxins as a means of stunning their prey, before ingesting it. These findings add a substantiated critical understanding for why some HAB species produce such complex toxin molecules.

STRAIN VARIATION IN KARLODINIUM VENEFICUM (DINOPHYCEAE): TOXIN PROFILES, PIGMENTS, AND GROWTH CHARACTERISTICS(1).

Karlodinium veneficum (D. Ballant.) J. Larsen strains, 16 from the U.S. Atlantic eastern seaboard and two from New Zealand (CAWD66 and CAWD83), were used to characterize toxin profiles during batch culture. All 18 strains were determined as the same species based on ITS sequence analyses, a positive signal in a chloroplast real-time PCR assay and pigment composition. Five karlotoxin 1 (KmTx 1) containing strains were analyzed from the Chesapeake Bay, and 10 karlotoxin 2 (KmTx 2) strains were analyzed from Florida to North Carolina. One strain (MD5) from the Chesapeake Bay produced no detectable toxin. The two cultures from New Zealand contained both novel karlotoxins with lower masses and earlier elution times. Toxin type did not change during batch culture, although the KmTx phenotype did change in some strains under extensive (months) phototrophic growth in replete media. KmTx cell quota did not change during batch culture for most strains. The mass spectrum for every KmTx examined showed a pattern of multiple coeluting congeners within each HPLC peak, with masses typically differing by 16 amu. KmTx congeners tested showed nearly a 500-fold range in specific hemolytic activity, with KmTx 1 (typically occurring at lower cellular levels) most hemolytic and CAWD66 toxin least hemolytic, while KmTx 2 and the CAWD83 toxin had similar intermediate specific activity. Despite morphological, genetic, and photopigment indicators consistent with species homogeneity among the 18 strains of K. veneficum, the high degree of toxin variability suggests different functional roles among strains that likely coexist in situ.

ENVIRONMENTAL MODULATION OF KARLOTOXIN LEVELS IN STRAINS OF THE COSMOPOLITAN DINOFLAGELLATE, KARLODINIUM VENEFICUM (DINOPHYCEAE)(1).

We examined the influence of N or P depletion, alternate N- or P-sources, salinity, and temperature on karlotoxin (KmTx) production in strains of Karlodinium veneficum (D. Ballant.) J. Larsen, an ichthyotoxic dinoflagellate that shows a high degree of variability of toxicity in situ. The six strains examined represented KmTx 1 (CCMP 1974, MD 2) and KmTx 2 (CCMP 2064, CCMP 2283, MBM1) producers, and one strain that did not produce detectable karlotoxin under nutrient-replete growth conditions (MD 5). We hypothesized that growth-limiting conditions would result in higher cell quotas of karlotoxin. KmTx was present in toxic strains during all growth phases and increased in stationary and senescent phase cultures under low N or P, generally 2- to 5-fold but with some observations in the 10- to 15-fold range. No karlotoxin was observed under low-N or low-P conditions in the nontoxic strain MD 5. Nutrient-quality (NO3 , NH4 , urea, and glycerophosphate) did not affect growth rate, but growth on NH4 produced 2- to 3-fold higher cellular toxicity and a 50% higher ratio of KmTx 1-1:KmTx 1-3 in CCMP 1974. CCMP 1974 showed higher cellular toxicity at low salinity (≤5 ppt) and high temperature (25°C). Our results suggested that given the presence of a toxic strain of K. veneficum in situ, the existence of environmental conditions that favor cellular accumulation of karlotoxin is likely a significant factor underlying K. veneficum-related fish kills that require both high cell densities (10(4) · mL(-1) ) and high cellular toxin quotas relative to those generally observed in nutrient-replete cultures.