Evelyn Lessard | UW - Academia.edu (original) (raw)

Papers by Evelyn Lessard

... Langue / Language. Anglais Revue : Multilingue Editeur / Publisher. Gauthier-Villars, Paris, ... more ... Langue / Language. Anglais Revue : Multilingue Editeur / Publisher. Gauthier-Villars, Paris, FRANCE (1985-1994) (Revue) Mots-clés anglais / English Keywords. Thallophyta. ; Algae. ;Growth rate. ; Time variation. ; Spatial variation. ; Population dynamics. ; Biomass. ; ...

Handbook of Methods in Aquatic Microbial Ecology, 2018

Marine Ecology Progress Series, Nov 17, 2006

As part of the Pacific Northwest ECOHAB project, we measured clearance rates and feeding selectiv... more As part of the Pacific Northwest ECOHAB project, we measured clearance rates and feeding selectivity of calanoid copepods off the coast of Washington State, USA, during fall of 2003. We tested the hypothesis that copepods discriminate amongst prey, particularly against the toxic diatoms Pseudonitzschia spp. in natural assemblages from this highly productive, upwelling environment. Seven grazing experiments were conducted across and along the shelf using the copepods Calanus pacificus, Metridia pacifica, Acartia longiremis and a small community assemblage dominated by Acartia spp., with minor contributions from Pseudocalanus spp., Paracalanus spp. and Oithona spp. Three general patterns emerged from our experiments. First, all copepods, except A. longiremis in 1 experiment, showed neutral preference or discriminated against Pseudo-nitzschia, but preference did not appear related to cellular domoic acid concentrations. Second, the dominant prey biomass contributors in each experiment were cleared at low rates relative to other prey types. In most cases the dominants were the diatom Thalassiosira spp. or the autotrophic dinoflagellates Ceratium spp. and Prorocentrum spp. The third pattern was high preference for microzooplankton. High clearance on microzooplankton can result in trophic cascades, which were evident in our size-fractionated chlorophyll data. These patterns indicate that copepods could have both direct and indirect effects on the plankton community composition on the Washington coast. However, our estimates of total potential grazing suggest that copepod grazing impact on Pseudo-nitzschia populations is negligible.

Harmful Algae, Sep 1, 2010

We conducted field and laboratory experiments to determine whether the Pseudo-nitzschia-derived m... more We conducted field and laboratory experiments to determine whether the Pseudo-nitzschia-derived metabolite, domoic acid (DA), functions as a microzooplankton grazing suppressant. Using the seawater dilution technique in natural plankton communities along the Pacific Northwest coast, we found no significant relationship between dissolved DA and microzooplankton grazing rate on Pseudo-nitzschia spp. Dilution experiments amended with either 50 or 80 nM dissolved DA also showed no evidence that microzooplankton community grazing was affected by DA. The relationship between Pseudo-nitzschia spp. intracellular DA and microzooplankton grazing was less clear. On a subset of data where small Pseudo-nitzschia spp. cells dominated community composition, an apparent negative relationship between intracellular DA and microzooplankton grazing was observed. However, we provide evidence that this relationship is a microzooplankton response to Pseudo-nitzschia spp. growth rate, rather than cellular DA. In laboratory experiments, two diatom-consuming dinoflagellates, Protoperidinium excentricum and P. pellucidum, were fed single and mixed diets of a toxic and non-toxic Pseudonitzschia species and an optimal prey, Ditylum brightwellii. P. excentricum did not grow or ingest either the toxic or non-toxic Pseudo-nitzschia. However, P. pellucidum grew as well on the toxic Pseudo-nitzschia multiseries as it did on D. brightwellii, but did not grow on the non-toxic Pseudo-nitzschia pungens. Both dinoflagellates were capable of growing if Pseudo-nitzschia spp. diets were mixed with D. brightwellii. Addition of dissolved DA also had no negative effect on dinoflagellate growth when fed the optimal diatom diet. We conclude that domoic acid has no functional role in deterring microzooplankton grazing or growth rates. Further, our findings highlight the difficulty of defining the complex mechanisms that regulate predator and prey interactions within microplankton food webs.

Journal of Experimental Marine Biology and Ecology, Oct 1, 1996

The efficacy of DAPI (2,4-diamadino-6-phenylindole), a fluorescent DNA-specific stain, to live-st... more The efficacy of DAPI (2,4-diamadino-6-phenylindole), a fluorescent DNA-specific stain, to live-stain protists was evaluated for use as tracers in laboratory studies of feeding by larval pollock, Therugru chalcogrumma (Pallas). At 4 kg. ml-', DAPI effectively live-stained all eight species of heterotrophic protists examined. DAPI also stained four species of autotrophic protists although staining was more variable. No toxic effects of DAPI were detected. DAPI did not appear to alter the swimming behavior of stained protists. Further, the growth rates of a ciliate, Euplotes sp. and an autotrophic flagellate, Rhodomonas salinu (Wislouch) Hill and Wetherbee, exposed to DAPI, did not differ significantly from growth in controls. When DAPI-stained Euplotes sp. were presented to larval pollock, ingested cells were easily seen in larval guts. This is the first report of ingestion of an aloricate ciliate by larval pollock. The lack of toxicity of DAPI and the easy visualization of ingested DAPI-stained protists, make this method a useful new tool for examining the ingestion of protists by metazoa and other protists.

Aquatic Microbial Ecology, 2005

We measured growth rates and starvation survival capacity of 3 thecate heterotrophic dinoflagella... more We measured growth rates and starvation survival capacity of 3 thecate heterotrophic dinoflagellate species (Protoperidinium conicum, P. depressum, P. excentricum; Peridiniacea: Dinophyceae), isolated from surface waters in Puget Sound, Washington, USA. Feeding on the diatom Ditylum brightwellii, the 3 species achieved maximum specific growth rates of 1.13, 0.21 and 0.33 d-1 respectively. Maximum growth rates were observed at prey concentrations between 50 and 280 µg C l-1. Prey concentrations < 20 µg C l-1 supported only negative or low growth rates. Predators survived in the presence of 11 phylogenetically diverse phytoplankton species for several days, but only the diatom D. brightwellii supported measurable predator growth. Grazing rates of up to 6 µg C l-1 (22 D. brightwellii) Protoperidinium-1 d-1 were calculated from limited data. All species were able to starve for extended periods; P. depressum survived up to 71 d at diatom prey concentrations <1 µg C l-1. This extended starvation survival provides Protoperidinium species with a distinct advantage when prey availability is heterogeneous in time or space. Our results suggest that resistance to starvation could affect Protoperidinium's energy allocation and could help explain previously observed dominance of Protoperidinium species in wintertime plankton communities despite low phytoplankton-prey concentrations. The viability of Protoperidinium species in the absence of prey has important implications for their function as both predators of phytoplankton and prey for zooplankton.

Limnology and Oceanography, 2009

The Juan de Fuca eddy is a toxic ''hot spot.'' Domoic acid (DA) was detected in the eddy during e... more The Juan de Fuca eddy is a toxic ''hot spot.'' Domoic acid (DA) was detected in the eddy during each of six cruises over a 4-yr study, although Pseudo-nitzschia abundance and toxin concentrations were highly variable. During the September 2004 eddy bloom, Pseudo-nitzschia spp. exceeded 13 3 10 6 cells L 21 , and particulate DA reached 80 nmol L 21. Of the .10 species of Pseudo-nitzschia identified in this region, those coincident with the most toxic blooms are P. cf. pseudodelicatissima, P. cuspidata, P. multiseries, and P. australis. However, the presence of any particular species could not be used as an indicator of toxicity because of the high level of variability in intracellular DA in field assemblages. Pseudo-nitzschia cells were typically associated with blooms of other diatom taxa but also were coincident with blooms of euglenoids and dinoflagellates in the eddy region. Pseudo-nitzschia always comprised ,17% of the total carbon biomass, thereby rendering remote sensing an unsuitable means for predicting toxigenic Pseudo-nitzschia blooms in this region. Our results support the hypothesis that the Juan de Fuca eddy region and not the nearshore zone is the primary initiation site for toxic blooms of Pseudo-nitzschia affecting the Washington coast. Although particulate DA was observed near the edges of the Columbia River plume, whether toxin can be produced in situ in plume water is not resolved. No first-order predictive relationships were found for either Pseudo-nitzschia abundance or DA concentration and environmental data from all six cruises. Domoic acid (DA), produced by species of the diatom genus Pseudo-nitzschia, was first recognized as a biotoxin to humans when over 100 people became severely ill after consuming mussels harvested near Prince Edward Island, Canada, in 1987 (Wright et al. 1989). Most of the known toxic events in North America since that time have occurred on the U.S. West Coast, where DA was first implicated in the illness and death of brown pelicans and Brandt's cormorants in Monterey Bay, California, in 1991 (Work et al. 1993). In October 1991, about 1 month following the toxic bloom of Pseudo-nitzschia in California, DA concentrations above the regulatory limit were found in the edible parts of Pacific razor clams (Siliqua patula) and Dungeness crabs (Cancer magister) on the Washington coast (Wekell et al. 1994). In 1998, the deleterious effect of DA on the health of marine mammals, in particular, California sea lions (Zalophus californianus), was confirmed for the first time along the West Coast (Scholin et al. 2000),

Aquatic Microbial Ecology, 1999

The growth, grazing, and cell volume of Strombidinopsis multjaurls, a large (-100 pm) coastal pla... more The growth, grazing, and cell volume of Strombidinopsis multjaurls, a large (-100 pm) coastal planktonic cil~ate, IS affected by food concentration and temperature. Using growth and grazlng data, we modelled small-scale bloom dynam~cs between the clliate and ~t s prey. Growth expenments were conducted at 13°C on S. niultiauris fed the 10 pm d~noflagellate Gymnodiniurn simplex; changes in cell numbers and cell volume were monitored. Ingestion rate was measured by 3 methods (uptake of fluorescently labelled latex beads, heat-killed, fluorescently labelled G nmplex; and I4C-labelled G. simplex). Growth rate vprsus food concentration followed a rectangular hyperbolic response, with a maxlmum of p = 0 6 d ' above 104 prey ml-l (480 ng C ml-l), below 1.3 X 10"l-' (62 ng C ml-l), mortality occurred. Cell volume followed a rectangular hyperbolic response to food concentration, and showed a doubling in size between zero and maxmum prey levels. Grazing rate initially ~ncreased with food concentration and was then inhib~ted at levels >10"rey ml-l. The cil~ate ~ngested 14C-labelled live prey at higher rates than either dead or artificial prey at subsaturating concentrations; above saturating concentrations, ingestion rates were similar for the 3 prey types. The maximum observed grazlng rate was 35 prey cihate ' h-' Growth rate and cell volume were measured under steady-state conditions at 9 temperatures between 3 5 and 22°C: clliates died at 3.5 and 5"C, growth rate increased hnearly to a maximum of p = 0.9 d-l at 15"C, did not change between 15 and 20°C, and decreased at 22°C. Cell volume ~ncreased between 5 and 10°C and decreased between 10 and 22°C. The population dynamlcs model revealed that the ciliate was able to control the dinoflagellate population. Over the 20 d model simulation, virtually no predator-prey cycle occurred when prey growth rates were p < 0.2 d-' As prey growth rate was increased bloom dynamics became apparent, with a minunum duration of-10 d for a bloom to begin and end at a prey growth rate of p = 0.65 d-l. During these simulated blooms ciliates reached maxlmum levels of 35 cells n~l-' , and prey reached levels of 1.7 X 104 cells ml-', slmilar to numbers found in a typical coastal bloom. Our data and model suggest that ciliates and their prey produce episodic, short-term blooms, and we recommend that these events be evaluated more carefully in the field and be incorporated into models. KEY WORDS. Blooms. Cell volume. Grazing rate. Growth rate. Microzooplankton. Mortality rate. Ohgotnch ciliate. Plankton. Temperature response

Marine Biology, 1985

A dual-isotope method was developed to measure grazing rates and food preferences of individual s... more A dual-isotope method was developed to measure grazing rates and food preferences of individual species of heterotrophic dinoflagellates from natural populations, collected from the Slope, Gulf Stream, and Sargasso Sea and from a transect from Iceland to New England, in 1983. The isotope method measures the grazing rates of microzooplankton which cannot be separated in natural populations on the basis of size. Tritiated-thymidine and 14Cbicarbonate were used to label natural heterotrophic and autotrophic food, respectively. Nine oceanic dinoflagellate species in the genera Protoperidinium, Podolam?as, and Diplopsalis fed on both heterotrophic and autotrophic food particles with clearance rates of 0.4 to 8.0/~1 cell-1 h-1, based on 3H incorporation, and 0.0 to 28.3 #1 cell-1 h-a, based on 14C incorporation. Two dinoflagellate species, Protoperidinium ovatum and Podolampas palmipes, fed only on 3H-labelled food particles. Several species of dinoflagellates fed on bacteria (< 1 pm) which had been prelabelled with 3H-thymidine, The clearance rates of heterotrophic dinoflagellates and ciliates were similar and within the range of tintinnid ciliate clearance rates reported in the literature. As heterotrophic dinoflagellates and ciliates can have comparable abundances in oceanic waters, we conclude that heterotrophic dinoflagellates may have an equally important impact as microheterotrophic grazers ofphytoplankton and bacteria in oceanic waters.

Our long-term goals are to quantify and predict how rapidly and effectively various functional gr... more Our long-term goals are to quantify and predict how rapidly and effectively various functional groups of zooplankton aggregate to and exploit localized, transient resource concentrations, such as those represented by thin layers. We are particularly interested in the consequences of transient resource concentrations for the dynamics of planktonic communities over large space and time scales. OBJECTIVES The objectives of this study are: (1) To quantify the degree to which micro-planktonic predators recruit to and exploit thin layers of phytoplankton resources in thin layers. (2) To document the effects of high resource levels within thin layers on micro-predator reproduction and dispersal, and the trophic impacts of these predators on phytoplankton and other biotic components of thin layers. (3) To synthesize these observations into a predictive modeling framework that translates from observations of individual cells at small space and time scales into an understanding of biologicalphysical interactions on the much larger space and time scales of oceanographic features such as thin layers. APPROACH Our approach has been to develop and deploy two novel sampling methods intended to quantify in situ micro-plankton dynamics.

Deep-sea Research Part Ii-topical Studies in Oceanography, Dec 1, 2016

Two extended pulsed feeding experiments, following the spring bloom period, investigated lipid re... more Two extended pulsed feeding experiments, following the spring bloom period, investigated lipid retention in the prominent Bering Sea euphausiid (krill) Thysanoessa raschii. These experiments occurred during late spring and early summer of 2010. Concurrent taxonomic analysis of the natural algal community allowed prey type to be linked to lipid composition of the natural communities. In late spring, experimental periods of feeding followed by starvation showed an overall decrease in total lipid for T. raschii. In early summer, no consistent trend was observed for total lipid with the visible presence of storage lipid in some animals. Polar lipids, as phospholipids, were the dominant krill lipid class in both experiments constituting Z 88% of total lipid, and triacylglycerols reached a maximum of 5% of total lipid. The sterols cholesterol and brassicasterolþdesmosterol comprised 98-99% of total sterol abundances in T. raschii throughout both experiments, even after feeding periods when alternative sterols (i.e. the algal sterol 24-methylenecholesterol) accounted for up to 39% of sterols in potential food particles. Cholesterol abundance and concentration increased during both incubations, likely due to the metabolism of dietary sterols. Major fatty acids observed in krill included C14:0n, C16:0n, C16:1(n-7), C18:1(n-7), C18:1(n-9), C20:5(n-3), and C22:6(n-3) with the diatom-attributed C16:1(n-7) decreasing in abundance and concentration during starvation. Low concentrations of the dinoflagellate-derived sterol and a novel C28:8 PUFA, typically found in dinoflagellates and prymnesiophytes, indicated predation on protozooplankton in early summer when diatom abundances were low. The stability of lipid distributions over periods of starvation and intermittent feeding suggest that fatty acid and sterol biomarkers present in this polar euphausiid principally reflect long-term diet history rather than short-term feeding episodes.

Deep-sea Research Part Ii-topical Studies in Oceanography, Dec 1, 2016

Euphausiids are an important component of the eastern Bering Sea marine ecosystem. We synthesized... more Euphausiids are an important component of the eastern Bering Sea marine ecosystem. We synthesized information on the ecological roles of two species, Thysanoessa raschii, which predominates over the Middle and Inner Shelf Domains, and T. inermis, which predominates over the Outer Shelf Domain. Although estimates of

Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2012

Euphausiids are an integral part of the Bering Sea ecosystem, linking primary production to upper... more Euphausiids are an integral part of the Bering Sea ecosystem, linking primary production to upper level trophic levels as both consumers and prey. Species native to this region extend over a range of geographic provinces and serve as a critical component of the movement of energy through the food web. As one facet of the BEST-BSIERP Bering Sea program, we determined the proximate composition and essential allometric relationships of multiple species of euphausiids collected over three years in the eastern Bering Sea. Three euphausiid species were examined: Thysanoessa inermis, Thysanoessa raschii, and Thysanoessa longipes. While the three species were similar with respect to size, T. inermis had the highest average wet and dry weights per size class, as well as highest carbon and caloric concentrations. Among the three species, T. inermis and T. longipes had similar lipid concentrations, with T. longipes showing higher average lipid concentrations. Empirical equations were developed to describe fundamental relationships between length, weight, PC/PN, and calorie and lipid content for the three species over the full range of sizes encountered in the study area. Such relationships increase our understanding of how euphausiids contribute to the carbon budget and energy input in the eastern Bering Sea system and help to define realistic parameters for ongoing and future modeling efforts.

Journal of Geophysical Research, 1990

An interdisciplinary study of the entrainment of shelf and slope waters in the Gulf Stream front ... more An interdisciplinary study of the entrainment of shelf and slope waters in the Gulf Stream front was undertaken in October 1985 northeast of Cape Hatteras. Fifteen hydrographic transects of the Gulf Stream front and of the shelf water intrusion known as Ford water were completed in 2• days with a towed undulating profiler, the SeaSoar, equipped with a conductivity-temperature-depth probe and a fluorometer. Upstream sections within 50 km of the shelf break show entrainment of surface and subsurface waters along the northern edge of the high-velocity Gulf Stream. The low-salinity core, first observed at 70 m, is subducted to > 100 m. The subsurface Ford water is also at a maximum in chlorophyll, fluorescence, and dissolved oxygen and contains a distinct diatom assemblage of nearshore species. Productivity rates in the Ford water may be equivalent to those in slope waters. Expendable current profilers yield an estimated transport for subsurface shelf waters of 1 to 5 x 105 m 3 s-1 and indicate that vertical shear at the depth of maximum static stability is typically 2 x 10-2 s-1. A bulk Richardson number is estimated over vertical scales of several meters by combining SeaSoar density profiles with velocity shear from concurrent expendable current profiler deployments. The minimum values are generally > 1, and only infrequently are they at or below the 0.25 threshold for shear instability. The presence of double-diffusive processes around the low-salinity core of Ford water is indicated by elevated conductivity Cox numbers. The stability parameter "Turner angle" shows that low-salinity Ford water and its associated T-S property front are sites of double-diffusive mixing, given general agreement between the distributions of Turner angle and Cox number. We conclude that double-diffusive processes are more important than shear flow instability in governing cross-isopycnal mixing. However, downstream transit times are so swift that no measurable change or decay occurs in the Ford water. This explains the occurrence of distinct shelf water phytoplankton species within the low-salinity waters downstream of Cape Hatteras. ment. While the filaments occur both at the surface and at depth (-•50-100 m), it is not clear how they are connected in

Journal of Marine Research, Sep 1, 1994

ABSTRACT

Applied and Environmental Microbiology, Mar 1, 1983

The survival of natural populations of Escherichia coli and enterococci in sewage was measured in... more The survival of natural populations of Escherichia coli and enterococci in sewage was measured in large-volume diffusion chambers in an estuary and a salt marsh. The 5-liter chambers, with polycarbonate membrane sidewalls, were found to be suitable for up to week-long experiments. Decay rates, measured

Dissolved oxygen (O2) and temperature recorded from 2018-2020 from a sensor array that measures p... more Dissolved oxygen (O2) and temperature recorded from 2018-2020 from a sensor array that measures pH, pCO2, temperature, salinity, dissolved oxygen, chlorophyll, turbidity, and current velocity at Friday Harbor Laboratories Ocean Observatory (FHLOO).

Journal of Plankton Research, 1996

We surveyed springtime biomass and abundance of the >20 nm microprotozoa in surface waters of the... more We surveyed springtime biomass and abundance of the >20 nm microprotozoa in surface waters of the SE Bering Sea and Shelikof Strait, Alaska. This study was part of the Fisheries Oceanography Coordinated Investigations (FOCI) program examining processes which affect the recruitment variability of walleye pollock (Theragra chalcogramma). Microprotozoa are a potential prey resource for larval pollock which has not been previously examined. In both areas, the >20 (im microprotozoa were predominantly dinoflagellates and ciliates. At the time of sampling (May 1990 in Shelikof Strait and April 1992 in the SE Bering Sea), the spring diatom bloom was under way in Shelikof Strait, but not in the SE Bering Sea. Heterotrophic dinoflagellates dominated the microprotozoan assemblage in Shelikof Strait, but not in the SE Bering Sea. In the SE Bering Sea. total microprotozoan abundances ranged from 300 to 6233 organisms 1 ' and biomass from 0.58 to 9.73 jig C I 1. In Shelikof Strait, abundance and biomass were higher, ranging from 850 to 14 960 organisms 1' and from 1.29 to 70.73 jig C I ', respectively. These biomass levels are comparable to those reported from other coastal and oceanic regions. Microprotozoan biomass levels were sufficient to support the estimated metabolic needs of first-feeding larval walleye pollock. It remains to be shown whether larval pollock use this resource.

... Langue / Language. Anglais Revue : Multilingue Editeur / Publisher. Gauthier-Villars, Paris, ... more ... Langue / Language. Anglais Revue : Multilingue Editeur / Publisher. Gauthier-Villars, Paris, FRANCE (1985-1994) (Revue) Mots-clés anglais / English Keywords. Thallophyta. ; Algae. ;Growth rate. ; Time variation. ; Spatial variation. ; Population dynamics. ; Biomass. ; ...

Handbook of Methods in Aquatic Microbial Ecology, 2018

Marine Ecology Progress Series, Nov 17, 2006

As part of the Pacific Northwest ECOHAB project, we measured clearance rates and feeding selectiv... more As part of the Pacific Northwest ECOHAB project, we measured clearance rates and feeding selectivity of calanoid copepods off the coast of Washington State, USA, during fall of 2003. We tested the hypothesis that copepods discriminate amongst prey, particularly against the toxic diatoms Pseudonitzschia spp. in natural assemblages from this highly productive, upwelling environment. Seven grazing experiments were conducted across and along the shelf using the copepods Calanus pacificus, Metridia pacifica, Acartia longiremis and a small community assemblage dominated by Acartia spp., with minor contributions from Pseudocalanus spp., Paracalanus spp. and Oithona spp. Three general patterns emerged from our experiments. First, all copepods, except A. longiremis in 1 experiment, showed neutral preference or discriminated against Pseudo-nitzschia, but preference did not appear related to cellular domoic acid concentrations. Second, the dominant prey biomass contributors in each experiment were cleared at low rates relative to other prey types. In most cases the dominants were the diatom Thalassiosira spp. or the autotrophic dinoflagellates Ceratium spp. and Prorocentrum spp. The third pattern was high preference for microzooplankton. High clearance on microzooplankton can result in trophic cascades, which were evident in our size-fractionated chlorophyll data. These patterns indicate that copepods could have both direct and indirect effects on the plankton community composition on the Washington coast. However, our estimates of total potential grazing suggest that copepod grazing impact on Pseudo-nitzschia populations is negligible.

Harmful Algae, Sep 1, 2010

We conducted field and laboratory experiments to determine whether the Pseudo-nitzschia-derived m... more We conducted field and laboratory experiments to determine whether the Pseudo-nitzschia-derived metabolite, domoic acid (DA), functions as a microzooplankton grazing suppressant. Using the seawater dilution technique in natural plankton communities along the Pacific Northwest coast, we found no significant relationship between dissolved DA and microzooplankton grazing rate on Pseudo-nitzschia spp. Dilution experiments amended with either 50 or 80 nM dissolved DA also showed no evidence that microzooplankton community grazing was affected by DA. The relationship between Pseudo-nitzschia spp. intracellular DA and microzooplankton grazing was less clear. On a subset of data where small Pseudo-nitzschia spp. cells dominated community composition, an apparent negative relationship between intracellular DA and microzooplankton grazing was observed. However, we provide evidence that this relationship is a microzooplankton response to Pseudo-nitzschia spp. growth rate, rather than cellular DA. In laboratory experiments, two diatom-consuming dinoflagellates, Protoperidinium excentricum and P. pellucidum, were fed single and mixed diets of a toxic and non-toxic Pseudonitzschia species and an optimal prey, Ditylum brightwellii. P. excentricum did not grow or ingest either the toxic or non-toxic Pseudo-nitzschia. However, P. pellucidum grew as well on the toxic Pseudo-nitzschia multiseries as it did on D. brightwellii, but did not grow on the non-toxic Pseudo-nitzschia pungens. Both dinoflagellates were capable of growing if Pseudo-nitzschia spp. diets were mixed with D. brightwellii. Addition of dissolved DA also had no negative effect on dinoflagellate growth when fed the optimal diatom diet. We conclude that domoic acid has no functional role in deterring microzooplankton grazing or growth rates. Further, our findings highlight the difficulty of defining the complex mechanisms that regulate predator and prey interactions within microplankton food webs.

Journal of Experimental Marine Biology and Ecology, Oct 1, 1996

The efficacy of DAPI (2,4-diamadino-6-phenylindole), a fluorescent DNA-specific stain, to live-st... more The efficacy of DAPI (2,4-diamadino-6-phenylindole), a fluorescent DNA-specific stain, to live-stain protists was evaluated for use as tracers in laboratory studies of feeding by larval pollock, Therugru chalcogrumma (Pallas). At 4 kg. ml-', DAPI effectively live-stained all eight species of heterotrophic protists examined. DAPI also stained four species of autotrophic protists although staining was more variable. No toxic effects of DAPI were detected. DAPI did not appear to alter the swimming behavior of stained protists. Further, the growth rates of a ciliate, Euplotes sp. and an autotrophic flagellate, Rhodomonas salinu (Wislouch) Hill and Wetherbee, exposed to DAPI, did not differ significantly from growth in controls. When DAPI-stained Euplotes sp. were presented to larval pollock, ingested cells were easily seen in larval guts. This is the first report of ingestion of an aloricate ciliate by larval pollock. The lack of toxicity of DAPI and the easy visualization of ingested DAPI-stained protists, make this method a useful new tool for examining the ingestion of protists by metazoa and other protists.

Aquatic Microbial Ecology, 2005

We measured growth rates and starvation survival capacity of 3 thecate heterotrophic dinoflagella... more We measured growth rates and starvation survival capacity of 3 thecate heterotrophic dinoflagellate species (Protoperidinium conicum, P. depressum, P. excentricum; Peridiniacea: Dinophyceae), isolated from surface waters in Puget Sound, Washington, USA. Feeding on the diatom Ditylum brightwellii, the 3 species achieved maximum specific growth rates of 1.13, 0.21 and 0.33 d-1 respectively. Maximum growth rates were observed at prey concentrations between 50 and 280 µg C l-1. Prey concentrations < 20 µg C l-1 supported only negative or low growth rates. Predators survived in the presence of 11 phylogenetically diverse phytoplankton species for several days, but only the diatom D. brightwellii supported measurable predator growth. Grazing rates of up to 6 µg C l-1 (22 D. brightwellii) Protoperidinium-1 d-1 were calculated from limited data. All species were able to starve for extended periods; P. depressum survived up to 71 d at diatom prey concentrations <1 µg C l-1. This extended starvation survival provides Protoperidinium species with a distinct advantage when prey availability is heterogeneous in time or space. Our results suggest that resistance to starvation could affect Protoperidinium's energy allocation and could help explain previously observed dominance of Protoperidinium species in wintertime plankton communities despite low phytoplankton-prey concentrations. The viability of Protoperidinium species in the absence of prey has important implications for their function as both predators of phytoplankton and prey for zooplankton.

Limnology and Oceanography, 2009

The Juan de Fuca eddy is a toxic ''hot spot.'' Domoic acid (DA) was detected in the eddy during e... more The Juan de Fuca eddy is a toxic ''hot spot.'' Domoic acid (DA) was detected in the eddy during each of six cruises over a 4-yr study, although Pseudo-nitzschia abundance and toxin concentrations were highly variable. During the September 2004 eddy bloom, Pseudo-nitzschia spp. exceeded 13 3 10 6 cells L 21 , and particulate DA reached 80 nmol L 21. Of the .10 species of Pseudo-nitzschia identified in this region, those coincident with the most toxic blooms are P. cf. pseudodelicatissima, P. cuspidata, P. multiseries, and P. australis. However, the presence of any particular species could not be used as an indicator of toxicity because of the high level of variability in intracellular DA in field assemblages. Pseudo-nitzschia cells were typically associated with blooms of other diatom taxa but also were coincident with blooms of euglenoids and dinoflagellates in the eddy region. Pseudo-nitzschia always comprised ,17% of the total carbon biomass, thereby rendering remote sensing an unsuitable means for predicting toxigenic Pseudo-nitzschia blooms in this region. Our results support the hypothesis that the Juan de Fuca eddy region and not the nearshore zone is the primary initiation site for toxic blooms of Pseudo-nitzschia affecting the Washington coast. Although particulate DA was observed near the edges of the Columbia River plume, whether toxin can be produced in situ in plume water is not resolved. No first-order predictive relationships were found for either Pseudo-nitzschia abundance or DA concentration and environmental data from all six cruises. Domoic acid (DA), produced by species of the diatom genus Pseudo-nitzschia, was first recognized as a biotoxin to humans when over 100 people became severely ill after consuming mussels harvested near Prince Edward Island, Canada, in 1987 (Wright et al. 1989). Most of the known toxic events in North America since that time have occurred on the U.S. West Coast, where DA was first implicated in the illness and death of brown pelicans and Brandt's cormorants in Monterey Bay, California, in 1991 (Work et al. 1993). In October 1991, about 1 month following the toxic bloom of Pseudo-nitzschia in California, DA concentrations above the regulatory limit were found in the edible parts of Pacific razor clams (Siliqua patula) and Dungeness crabs (Cancer magister) on the Washington coast (Wekell et al. 1994). In 1998, the deleterious effect of DA on the health of marine mammals, in particular, California sea lions (Zalophus californianus), was confirmed for the first time along the West Coast (Scholin et al. 2000),

Aquatic Microbial Ecology, 1999

The growth, grazing, and cell volume of Strombidinopsis multjaurls, a large (-100 pm) coastal pla... more The growth, grazing, and cell volume of Strombidinopsis multjaurls, a large (-100 pm) coastal planktonic cil~ate, IS affected by food concentration and temperature. Using growth and grazlng data, we modelled small-scale bloom dynam~cs between the clliate and ~t s prey. Growth expenments were conducted at 13°C on S. niultiauris fed the 10 pm d~noflagellate Gymnodiniurn simplex; changes in cell numbers and cell volume were monitored. Ingestion rate was measured by 3 methods (uptake of fluorescently labelled latex beads, heat-killed, fluorescently labelled G nmplex; and I4C-labelled G. simplex). Growth rate vprsus food concentration followed a rectangular hyperbolic response, with a maxlmum of p = 0 6 d ' above 104 prey ml-l (480 ng C ml-l), below 1.3 X 10"l-' (62 ng C ml-l), mortality occurred. Cell volume followed a rectangular hyperbolic response to food concentration, and showed a doubling in size between zero and maxmum prey levels. Grazing rate initially ~ncreased with food concentration and was then inhib~ted at levels >10"rey ml-l. The cil~ate ~ngested 14C-labelled live prey at higher rates than either dead or artificial prey at subsaturating concentrations; above saturating concentrations, ingestion rates were similar for the 3 prey types. The maximum observed grazlng rate was 35 prey cihate ' h-' Growth rate and cell volume were measured under steady-state conditions at 9 temperatures between 3 5 and 22°C: clliates died at 3.5 and 5"C, growth rate increased hnearly to a maximum of p = 0.9 d-l at 15"C, did not change between 15 and 20°C, and decreased at 22°C. Cell volume ~ncreased between 5 and 10°C and decreased between 10 and 22°C. The population dynamlcs model revealed that the ciliate was able to control the dinoflagellate population. Over the 20 d model simulation, virtually no predator-prey cycle occurred when prey growth rates were p < 0.2 d-' As prey growth rate was increased bloom dynamics became apparent, with a minunum duration of-10 d for a bloom to begin and end at a prey growth rate of p = 0.65 d-l. During these simulated blooms ciliates reached maxlmum levels of 35 cells n~l-' , and prey reached levels of 1.7 X 104 cells ml-', slmilar to numbers found in a typical coastal bloom. Our data and model suggest that ciliates and their prey produce episodic, short-term blooms, and we recommend that these events be evaluated more carefully in the field and be incorporated into models. KEY WORDS. Blooms. Cell volume. Grazing rate. Growth rate. Microzooplankton. Mortality rate. Ohgotnch ciliate. Plankton. Temperature response

Marine Biology, 1985

A dual-isotope method was developed to measure grazing rates and food preferences of individual s... more A dual-isotope method was developed to measure grazing rates and food preferences of individual species of heterotrophic dinoflagellates from natural populations, collected from the Slope, Gulf Stream, and Sargasso Sea and from a transect from Iceland to New England, in 1983. The isotope method measures the grazing rates of microzooplankton which cannot be separated in natural populations on the basis of size. Tritiated-thymidine and 14Cbicarbonate were used to label natural heterotrophic and autotrophic food, respectively. Nine oceanic dinoflagellate species in the genera Protoperidinium, Podolam?as, and Diplopsalis fed on both heterotrophic and autotrophic food particles with clearance rates of 0.4 to 8.0/~1 cell-1 h-1, based on 3H incorporation, and 0.0 to 28.3 #1 cell-1 h-a, based on 14C incorporation. Two dinoflagellate species, Protoperidinium ovatum and Podolampas palmipes, fed only on 3H-labelled food particles. Several species of dinoflagellates fed on bacteria (< 1 pm) which had been prelabelled with 3H-thymidine, The clearance rates of heterotrophic dinoflagellates and ciliates were similar and within the range of tintinnid ciliate clearance rates reported in the literature. As heterotrophic dinoflagellates and ciliates can have comparable abundances in oceanic waters, we conclude that heterotrophic dinoflagellates may have an equally important impact as microheterotrophic grazers ofphytoplankton and bacteria in oceanic waters.

Our long-term goals are to quantify and predict how rapidly and effectively various functional gr... more Our long-term goals are to quantify and predict how rapidly and effectively various functional groups of zooplankton aggregate to and exploit localized, transient resource concentrations, such as those represented by thin layers. We are particularly interested in the consequences of transient resource concentrations for the dynamics of planktonic communities over large space and time scales. OBJECTIVES The objectives of this study are: (1) To quantify the degree to which micro-planktonic predators recruit to and exploit thin layers of phytoplankton resources in thin layers. (2) To document the effects of high resource levels within thin layers on micro-predator reproduction and dispersal, and the trophic impacts of these predators on phytoplankton and other biotic components of thin layers. (3) To synthesize these observations into a predictive modeling framework that translates from observations of individual cells at small space and time scales into an understanding of biologicalphysical interactions on the much larger space and time scales of oceanographic features such as thin layers. APPROACH Our approach has been to develop and deploy two novel sampling methods intended to quantify in situ micro-plankton dynamics.

Deep-sea Research Part Ii-topical Studies in Oceanography, Dec 1, 2016

Two extended pulsed feeding experiments, following the spring bloom period, investigated lipid re... more Two extended pulsed feeding experiments, following the spring bloom period, investigated lipid retention in the prominent Bering Sea euphausiid (krill) Thysanoessa raschii. These experiments occurred during late spring and early summer of 2010. Concurrent taxonomic analysis of the natural algal community allowed prey type to be linked to lipid composition of the natural communities. In late spring, experimental periods of feeding followed by starvation showed an overall decrease in total lipid for T. raschii. In early summer, no consistent trend was observed for total lipid with the visible presence of storage lipid in some animals. Polar lipids, as phospholipids, were the dominant krill lipid class in both experiments constituting Z 88% of total lipid, and triacylglycerols reached a maximum of 5% of total lipid. The sterols cholesterol and brassicasterolþdesmosterol comprised 98-99% of total sterol abundances in T. raschii throughout both experiments, even after feeding periods when alternative sterols (i.e. the algal sterol 24-methylenecholesterol) accounted for up to 39% of sterols in potential food particles. Cholesterol abundance and concentration increased during both incubations, likely due to the metabolism of dietary sterols. Major fatty acids observed in krill included C14:0n, C16:0n, C16:1(n-7), C18:1(n-7), C18:1(n-9), C20:5(n-3), and C22:6(n-3) with the diatom-attributed C16:1(n-7) decreasing in abundance and concentration during starvation. Low concentrations of the dinoflagellate-derived sterol and a novel C28:8 PUFA, typically found in dinoflagellates and prymnesiophytes, indicated predation on protozooplankton in early summer when diatom abundances were low. The stability of lipid distributions over periods of starvation and intermittent feeding suggest that fatty acid and sterol biomarkers present in this polar euphausiid principally reflect long-term diet history rather than short-term feeding episodes.

Deep-sea Research Part Ii-topical Studies in Oceanography, Dec 1, 2016

Euphausiids are an important component of the eastern Bering Sea marine ecosystem. We synthesized... more Euphausiids are an important component of the eastern Bering Sea marine ecosystem. We synthesized information on the ecological roles of two species, Thysanoessa raschii, which predominates over the Middle and Inner Shelf Domains, and T. inermis, which predominates over the Outer Shelf Domain. Although estimates of

Deep-sea Research Part Ii-topical Studies in Oceanography, Jun 1, 2012

Euphausiids are an integral part of the Bering Sea ecosystem, linking primary production to upper... more Euphausiids are an integral part of the Bering Sea ecosystem, linking primary production to upper level trophic levels as both consumers and prey. Species native to this region extend over a range of geographic provinces and serve as a critical component of the movement of energy through the food web. As one facet of the BEST-BSIERP Bering Sea program, we determined the proximate composition and essential allometric relationships of multiple species of euphausiids collected over three years in the eastern Bering Sea. Three euphausiid species were examined: Thysanoessa inermis, Thysanoessa raschii, and Thysanoessa longipes. While the three species were similar with respect to size, T. inermis had the highest average wet and dry weights per size class, as well as highest carbon and caloric concentrations. Among the three species, T. inermis and T. longipes had similar lipid concentrations, with T. longipes showing higher average lipid concentrations. Empirical equations were developed to describe fundamental relationships between length, weight, PC/PN, and calorie and lipid content for the three species over the full range of sizes encountered in the study area. Such relationships increase our understanding of how euphausiids contribute to the carbon budget and energy input in the eastern Bering Sea system and help to define realistic parameters for ongoing and future modeling efforts.

Journal of Geophysical Research, 1990

An interdisciplinary study of the entrainment of shelf and slope waters in the Gulf Stream front ... more An interdisciplinary study of the entrainment of shelf and slope waters in the Gulf Stream front was undertaken in October 1985 northeast of Cape Hatteras. Fifteen hydrographic transects of the Gulf Stream front and of the shelf water intrusion known as Ford water were completed in 2• days with a towed undulating profiler, the SeaSoar, equipped with a conductivity-temperature-depth probe and a fluorometer. Upstream sections within 50 km of the shelf break show entrainment of surface and subsurface waters along the northern edge of the high-velocity Gulf Stream. The low-salinity core, first observed at 70 m, is subducted to > 100 m. The subsurface Ford water is also at a maximum in chlorophyll, fluorescence, and dissolved oxygen and contains a distinct diatom assemblage of nearshore species. Productivity rates in the Ford water may be equivalent to those in slope waters. Expendable current profilers yield an estimated transport for subsurface shelf waters of 1 to 5 x 105 m 3 s-1 and indicate that vertical shear at the depth of maximum static stability is typically 2 x 10-2 s-1. A bulk Richardson number is estimated over vertical scales of several meters by combining SeaSoar density profiles with velocity shear from concurrent expendable current profiler deployments. The minimum values are generally > 1, and only infrequently are they at or below the 0.25 threshold for shear instability. The presence of double-diffusive processes around the low-salinity core of Ford water is indicated by elevated conductivity Cox numbers. The stability parameter "Turner angle" shows that low-salinity Ford water and its associated T-S property front are sites of double-diffusive mixing, given general agreement between the distributions of Turner angle and Cox number. We conclude that double-diffusive processes are more important than shear flow instability in governing cross-isopycnal mixing. However, downstream transit times are so swift that no measurable change or decay occurs in the Ford water. This explains the occurrence of distinct shelf water phytoplankton species within the low-salinity waters downstream of Cape Hatteras. ment. While the filaments occur both at the surface and at depth (-•50-100 m), it is not clear how they are connected in

Journal of Marine Research, Sep 1, 1994

ABSTRACT

Applied and Environmental Microbiology, Mar 1, 1983

The survival of natural populations of Escherichia coli and enterococci in sewage was measured in... more The survival of natural populations of Escherichia coli and enterococci in sewage was measured in large-volume diffusion chambers in an estuary and a salt marsh. The 5-liter chambers, with polycarbonate membrane sidewalls, were found to be suitable for up to week-long experiments. Decay rates, measured

Dissolved oxygen (O2) and temperature recorded from 2018-2020 from a sensor array that measures p... more Dissolved oxygen (O2) and temperature recorded from 2018-2020 from a sensor array that measures pH, pCO2, temperature, salinity, dissolved oxygen, chlorophyll, turbidity, and current velocity at Friday Harbor Laboratories Ocean Observatory (FHLOO).

Journal of Plankton Research, 1996

We surveyed springtime biomass and abundance of the >20 nm microprotozoa in surface waters of the... more We surveyed springtime biomass and abundance of the >20 nm microprotozoa in surface waters of the SE Bering Sea and Shelikof Strait, Alaska. This study was part of the Fisheries Oceanography Coordinated Investigations (FOCI) program examining processes which affect the recruitment variability of walleye pollock (Theragra chalcogramma). Microprotozoa are a potential prey resource for larval pollock which has not been previously examined. In both areas, the >20 (im microprotozoa were predominantly dinoflagellates and ciliates. At the time of sampling (May 1990 in Shelikof Strait and April 1992 in the SE Bering Sea), the spring diatom bloom was under way in Shelikof Strait, but not in the SE Bering Sea. Heterotrophic dinoflagellates dominated the microprotozoan assemblage in Shelikof Strait, but not in the SE Bering Sea. In the SE Bering Sea. total microprotozoan abundances ranged from 300 to 6233 organisms 1 ' and biomass from 0.58 to 9.73 jig C I 1. In Shelikof Strait, abundance and biomass were higher, ranging from 850 to 14 960 organisms 1' and from 1.29 to 70.73 jig C I ', respectively. These biomass levels are comparable to those reported from other coastal and oceanic regions. Microprotozoan biomass levels were sufficient to support the estimated metabolic needs of first-feeding larval walleye pollock. It remains to be shown whether larval pollock use this resource.