Algal Toxins Alter Copepod Feeding Behavior

Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod’s feeding appendages–a “sampling beating” that has short durations (<100 ms) and involves little fluid entrainment and a longer duration “grazing beating” that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod’s grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod’s feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods

Ensemble models with uncertainty analysis for multi-day ahead forecasting of chlorophyll a concentration in coastal waters

201903 bcrcVersion of RecordPublishe

Species specificity and potential roles of Karlodinium micrum toxin

Karlodinium micrum is a toxic mixotrophic dinoflagellate that has been responsible for fish kills in coastal environments worldwide. The role that karlotoxins play in the life history of K. micrum is unknown, but maycontribute to its bloom-forming ability. We tested the hypothesis that karlotoxins could inhibit the growth of other protists depending on the sterol composition of target cell membranes. We also examined the effect of toxin addition on feeding rates of K. micrum on a flagellatedprey, Storeatula major. Dose-dependent effects of isolated karlotoxin (KmTX2) were tested in growth bioassays (24–48h) of K. micrum, three raphidophytes (Heterosigma akashiwo, Fibrocapsa japonica andChattonella subsalsa), two cryptophytes (S. major and Pyrenomonas salina), and the dinoflagellates Amphidinium carterae, Pfiesteria piscicida and P. shumwayae. Growth of K. micrum, P. salina, A. carterae and P. piscicida were not affected by karlotoxin additions up to 1 000ng ml–1. Other organisms showed growth inhibition at concentrations between 500ng ml–1 and 1 000ng ml–1. Predation by K. micrum on S. major was significantly higher in the presence of 25ng ml–1 KmTX2. Theresults are consistent with a role for karlotoxin in allelopathic inhibition of competitors and/or prey immobilisation depending on sterol composition

Marine microalgae attack and feed on metazoans

Free-living microalgae from the dinoflagellate genus Karlodinium are known to form massive blooms in eutrophic coastal waters worldwide and are often associated with fish kills. Natural bloom populations, recently shown to consist of the two mixotrophic and toxic species Karlodinium armiger and Karlodinium veneficum have caused fast paralysis and mortality of finfish and copepods in the laboratory, and have been associated with reduced metazooplankton biomass in-situ. Here we show that a strain of K. armiger (K-0688) immobilises the common marine copepod Acartia tonsa in a density-dependent manner and collectively ingests the grazer to promote its own growth rate. In contrast, four strains of K. veneficum did not attack or affect the motility and survival of the copepods. Copepod immobilisation by the K. armiger strain was fast (within 15 min) and caused by attacks of swarming cells, likely through the transfer and action of a highly potent but uncharacterised neurotoxin. The copepods grazed and reproduced on a diet of K. armiger at densities below 1000, cells ml(−1), but above 3500 cells ml(−1) the mixotrophic dinoflagellates immobilised, fed on and killed the copepods. Switching the trophic role of the microalgae from prey to predator of copepods couples population growth to reduced grazing pressure, promoting the persistence of blooms at high densities. K. armiger also fed on three other metazoan organisms offered, suggesting that active predation by mixotrophic dinoflagellates may be directly involved in causing mortalities at several trophic levels in the marine food web

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, NO(2) + NO(3)), 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

Environmental forcing of phytoplankton in a Mediterranean estuary (Guadiana Estuary, southwestern Iberia): a decadal of anthropogenic and climatic influences

Phytoplankton seasonal and interannual variability in theGuadiana upper estuarywas analyzed during 1996–2005, a period that encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton succession, with early spring diatom blooms and summer–early fall cyanobacterial blooms, was apparently driven by changes in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited mode in the near future

A prospective, case–control study on the lipid profile and the cardiovascular risk of menopausal women on oestrogen plus progestogen therapy in a northern Italy province

Purpose To evaluate the effects of oestrogen plus progestogen therapy (EPT) on the lipid metabolism of menopausal patients. Methods We conducted a prospective study on 223 patients with clinical and blood chemistry diagnosis of menopause, who were eligible for hormone therapy and a follow-up period lasting at least 5 years. We selected a control group. Patients attended annual or 6-monthly visits for the duration of the 5-year follow-up period. For each patient, total-cholesterol, HDL-cholesterol, LDL-cholesterol and triglyceride values were considered at the first visit and after 5 years. We compared these values of the above parameters in relation to time and EPT and the repercussions that the presence/absence of replacement therapy had in terms of lipid profile alteration between the groups studied. Results Of the 223 patients eligible for enrolment, 178 made up the study group (EPT Group) and 45 made up the control cohort (N-EPT-Group). At the first visit, median value was (EPT-Group vs. N-EPT-Group): cholesterol was 240 versus 226 mg/dL, LDL-cholesterol 169 versus 174 mg/dL, HDL-cholesterol 60 mg/dL in both groups, triglyceride 125 versus 92 mg/dL (p:n.s). Five years later, median value was (EPT-Group versus N-EPT-Group): cholesterol 225 versus 236 mg/dL (p < 0.001), LDL-cholesterol 125 versus 184 mg/dL (p < 0.001), HDL-cholesterol 64 versus 68 mg/dL (p:n.s.), triglyceride 72 versus 94 mg/dL (p:n.s.). No adverse effects of EPT were observed. Conclusions Thorough risk/benefit assessment, associated with initially low doses and without rigid cutoffs, particularly when started early, EPT can be made a valid means of cardiovascular prevention, specifically because it positively alters the lipid profile of menopausal women