Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume (C : vol) and nitrogen to volume (N : vol) relationships. Cellular C and N content ranged from 48 to 3.0 ϫ 10 4 pgC cell Ϫ1 and 11 to 2,656 pgN cell Ϫ1 for cells ranging in volume from 180 to 2.8 ϫ 10 5 m 3 . C and N density in dinoflagellates decreased significantly with increasing cell volume. C : N ratios ranged from 3.44 to 6.45. C : vol and N : vol in dinoflagellates are significantly related as expressed by the equations pgC cell Ϫ1 ϭ 0.760 ϫ volume 0.819 and pgN cell Ϫ1 ϭ 0.118 ϫ volume 0.849 . Previously published data were combined to compare C : vol relationships in different phylogenetic protist groups, including chlorophytes, chrysophytes, prasinophytes, and prymnesiophytes. Our analysis indicated differences between the C : vol relationships available for ciliates. A new C : vol relationship for diatoms was established (pgC cell Ϫ1 ϭ 0.288 ϫ volume 0.811 ). Dinoflagellates are significantly more C dense than diatoms. Except for diatoms, we found few significant differences between C : vol relationships of different phylogenetic groups. Consequently, one C : vol relationship for taxonomically diverse protist plankton excluding diatoms was determined (pgC cell Ϫ1 ϭ 0.216 ϫ volume 0.939 ). In the combined data set, carbon density was not constant but decreased significantly with increasing cell volume. Using constant C : vol conversion factors for plankton over large size ranges will cause systematic errors in biomass estimates.

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A B S T R A C TAlong the Pacific coast of North America, from Alaska to Mexico, harmful algal blooms (HABs) have caused losses to natural resources and coastal economies, and have resulted in human sicknesses and deaths for decades. Recent reports indicate a possible increase in their prevalence and impacts of these events on living resources over the last 10-15 years. Two types of HABs pose the most significant threat to coastal ecosystems in this ''west coast'' region: dinoflagellates of the genera Alexandrium, Gymnodinium, and Pyrodinium that cause paralytic shellfish poisoning (PSP) and diatoms of the genus Pseudo-nitzschia that produce domoic acid (DA), the cause of amnesic shellfish poisoning (ASP) in humans. These species extend throughout the region, while problems from other HABs (e.g., fish kills linked to raphidophytes or Cochlodinium, macroalgal blooms related to invasive species, sea bird deaths caused by surfactant-like proteins produced by Akashiwo sanguinea, hepatotoxins from Microcystis, diarrhetic shellfish poisoning from Dinophysis, and dinoflagellate-produced yessotoxins) are less prevalent but potentially expanding. This paper presents the stateof-knowledge on HABs along the west coast as a step toward meeting the need for integration of HAB outreach, research, and management efforts.Published by Elsevier B.V.

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[1] River Influences on Shelf Ecosystems (RISE) is the first comprehensive interdisciplinary study of the rates and dynamics governing the mixing of river and coastal waters in an eastern boundary current system, as well as the effects of the resultant plume on phytoplankton standing stocks, growth and grazing rates, and community structure. The RISE Special Volume presents results deduced from four field studies and two different numerical model applications, including an ecosystem model, on the buoyant plume originating from the Columbia River. This introductory paper provides background information on variability during RISE field efforts as well as a synthesis of results, with particular attention to the questions and hypotheses that motivated this research. RISE studies have shown that the maximum mixing of Columbia River and ocean water occurs primarily near plume liftoff inside the estuary and in the near field of the plume. Most plume nitrate originates from upwelled shelf water, and plume phytoplankton species are typically the same as those found in the adjacent coastal ocean. River-supplied nitrate can help maintain the ecosystem during periods of delayed upwelling. The plume inhibits iron limitation, but nitrate limitation is observed in aging plumes. The plume also has significant effects on rates of primary productivity and growth (higher in new plume water) and microzooplankton grazing (lower in the plume near field and north of the river mouth); macrozooplankton concentration (enhanced at plume fronts); offshelf chlorophyll export; as well as the development of a chlorophyll ''shadow zone'' off northern Oregon.

Microzooplankton grazing and phytoplankton growth rates were measured with the dilution technique during spring, summer and fall in the oligotrophic Sargasso Sea near Bermuda. Phytoplankton growth rates estimated from changes in chlorophyll a ranged from 0.2 to 0.8 d-' and grazing rates from undetectable to 0.8 d-'. Grazing rates approximately balanced or exceeded growth rates, except on 1 date when no grazing was detected. The results support the view that phytoplankton in the subtropical oligotrophic gyres are growing at high, but sub-maximal, rates and are grazed to low stable blomass levels. Chlorophyll grazing rates in the surface mixed layer could be related to ambient chlorophyll levels by a Michaelis-Menten model with a grazing threshold. The close correspondence between the apparent feeding threshold level and the observed lower limit of chlorophyll concentration in the surface water of the Sargasso Sea suggests that the lower biomass limit may be related to threshold feeding behavior of the grazer community.

The Pacific Northwest (PNW) shelf is the most biologically productive region in the California Current System. A coupled physical-biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of PNW shelf waters using realistic hindcasts and model experiments that omit outflow from the Columbia River and Strait of Juan de Fuca (outlet for the Salish Sea estuary). Outflow from the Strait represents a critical source of nitrogen to the PNW shelf-accounting for almost half of the primary productivity on the Vancouver Island shelf, a third of productivity on the Washington shelf, and a fifth of productivity on the Oregon shelf during the upwelling season. The Columbia River has regional effects on the redistribution of phytoplankton, but does not affect PNW productivity as strongly as does the Salish Sea. A regional nutrient budget shows that nitrogen exiting the Strait is almost entirely (98%) of oceanorigin-upwelled into the Strait at depth, mixed into surface waters by tidal mixing, and returned to the coastal ocean. From the standpoint of nitrogen availability in the coastal euphotic zone, the estuarine circulation driven by freshwater inputs to the Salish Sea is more important than the supply of terrigenous nitrogen by rivers. Nitrogen-rich surface waters exiting the Strait follow two primary pathways-to the northwest in the Vancouver Island Coastal Current and southward toward the Washington and Oregon shelves. Nitrogen flux from the Juan de Fuca Strait and Eddy Region to these shelves is comparable to flux from local wind-driven upwelling.

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