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Coastal upwelling regions represent less than 2% of the marine biosphere's volume. Nonetheless, local biogeochemical processes have a considerable impact on the structure and functioning of the global oceans. In this study we characterize the evolution of biogeochemical properties during the upwelling seasons of 2009 and 2010 in the coastal ecosystem off central Oregon (west coast of USA). Both years displayed similar cumulative upwelling favorable winds and total input of preformed nutrients into the midshelf despite of their marked differences in the timing of the onset of the upwelling season, its duration and the number of upwelling relaxation events. However, these differences in upwelling forcing induced inter-annual variability in oxygen and nitrogen deficiencies, particulate matter accumulation and nutrient regeneration. Our results suggest that the summer evolution of nitrogen loss and oxygen depletion over the shelf does not follow a simple relationship with the cumulative upwelling index. We hypothesize that other factors, such as the intensity and persistence of the upwelling, which affect the residence time of water masses over the continental shelf, play a key role in the cumulative effect of biological processes leading to hypoxia in these coastal environments.

Micronekton in deep-scattering layers around the Hawaiian Islands undergo diel migrations with both vertical and horizontal components. We sought to determine whether resource availability provides an adaptive explanation for this migration. We simultaneously measured the spatio-temporal patterns of micronekton, using acoustics and imaging optics, and of their potential zooplankton prey, using net tows, acoustics, and optics. Zooplankton biomass, density, and total abundance were higher at night than prior to sunset at nearshore sites, whereas relatively little diel variation was observed offshore. All measures of zooplankton availability were 5 to 6 times higher nearshore than offshore during nighttime hours when migrating micronekton species were nearshore. There was no significant nearshore-offshore gradient in zooplankton prior to sunset, leading to 2 possible explanations for the day-night patterns in zooplankton: benthic emergence and vertical migration coupled with horizontal motion. Analysis of taxonomic patterns from net tows did not support the benthic emergence hypothesis. All 3 zooplankton assessment techniques supported the conclusion that zooplankton distribution could favor horizontal migration by micronekton given the pressures for micronketon to be in deep water during daylight to avoid predators. Recently pub- lished work has shown that small animals (2 to 10 cm in length) in scattering layers comprised of micronekton travel distances of at least 11 km roundtrip each night, often against currents, to obtain these increased food resources. The length and likely cost of the journey provides some insight about the importance of the potential feeding gains.

The marine phytoplankton species Phaeocystis pouchetii often forms large blooms of gelatinous colonies during spring in north temperate, boreal, and Arctic waters. The macroscopic colonies in such blooms develop originally from free-swimming solitary cells that shed their flagella, secrete a gelatinous membrane, and undergo repeated cell divisions within an enlarging colony membrane. However, the essential first steps in this process have not been described in situ, and hence the factors controlling initiation of colony blooms are poorly understood. Studies were con- ducted in mesocosms in a western Norway fjord to document the development of small young colonies under simulated and ambient conditions, resulting in 2 novel perspectives: (1) The critical early stages of colony bloom formation may occur in a relatively brief window in time. The rate of for- mation of young colonies from solitary cells was faster in nutrient-fertilized compared to unfertilized mesocosms, but this only happened after a period of diatom growth in the mesocosms and subse- quent increases in P. pouchetii colony abundance. Then, small percentages of solitary cells were mathematically necessary to account for observed colony numbers. (2) Initial formation of new young colonies occurred during the dark period of the ambient springtime diel light cycle, and patterns of colony accumulation implied rapid multiple cell divisions within colonies during the dark period, a process termed phased ultradian growth. Such an evolutionary strategy of rapid change from single cells to multi-cell colonies would be advantageous as a means of minimizing grazing losses during the critical period of size transition from microscopic free-swimming cells that are susceptible to microzooplankton and viruses, to larger colonies that are susceptible to metazoan zooplankton but relatively impervious to viruses and microzooplankton. The combined results offer a new insight into colony proliferation: colony blooms do not necessarily require a long period of constant conversion of solitary cells into colonies, but rather may be the product of punctuated, rapid life cycle transforma- tions and ultradian growth of young colonies.

Calanoid copepod eggs have a robust, chitinous outer chorion, which makes field-collected, formaldehydefixed eggs difficult to penetrate with stains or molecular probes. Egg development studies in copepods have involved physical, chemical, and enzymatic treatments to remove the chorion. We present an efficient, onestep method for staining copepod eggs with the fluorescent nucleic acid stains DAPI and PicoGreen®. Nuclei in treated eggs are clearly visible for examination and counting with compound and confocal microscopy, so that eggs can be rapidly classified with respect to developmental stage. The method is effective for eggs of Calanus, Metridia, and Centropages. Both stains were effective after 24-h exposure for eggs that were fixed from several days to 8 years. Early stages are distinguished by complete counts of nuclei. A blastula phase and gastrulation are distinctive. Calanus pacificus and Calanus marshallae embryos spend more than half the development period in the later ‘gray ball’ and limb bud stages. Stage classification by this method is useful for studies of copepod egg mortality in the field.

In high latitude planktonic ecosystems where the prymnesiophyte alga Phaeocystis pouchetii is often the dominant primary producer, its importance in structuring planktonic food webs is well known. In this study we investigated how the base of the planktonic food web responds to a P. pouchetii colony bloom in controlled mesocosm systems with natural water enclosed in situ in a West Norwegian fjord. Similar large (11 m 3 ) mesocosm studies were conducted in 2 successive years and the dynamics of various components of the planktonic food web from viruses to mesozooplankton investigated. In 2002 (4 to 24 March), 3 mesocosms comprising a control containing only fjord water; another with added nitrate (N) and phosphate (P) in Redfield ratios; and a third with added N, P, and cultured solitary cells of P. pouchetii, were monitored through a spring bloom cycle. In 2003 (27 Feb- ruary to 2 April) a similar set of mesocosms were established, but cultured P. pouchetii was not added. As expected, during both years, addition of N and P without addition of silicate resulted in an initial small diatom bloom followed by a colonial bloom of P. pouchetii (600 to 800 µg C l -1 ). However, the hypothesis that addition of solitary cells of P. pouchetii would enhance subsequent colony blooms was not supported. Interestingly, despite the large production of Phaeocystis colonial material, little if any was transferred to the grazing food web, as evidenced by non-significant effects on the biomass of micro- and mesozooplankton in fertilized mesocoms. Separate experiments utilizing material from the mesocosms showed that colonies formed from solitary cells at rates that required only ca. 1% con- version efficiencies. The results are discussed from the perspective of future research still required to understand the impact of life cycle changes of this enigmatic phytoplankter on surrounding ecosystems.

Most cells experience an active and variable fluid environment, in which hydrodynamic forces can affect aspects of cell physiology including gene regulation, growth, nutrient uptake, and viability. The present study describes a rapid yet reversible change in cell morphology of the marine dinoflagellate Ceratocorys horrida Stein, due to fluid motion. Cells cultured under still conditions possess six large spines, each almost one cell diameter in length. When gently agitated on an orbital shaker under conditions simulating fluid motion at the sea surface due to light wind or surface chop, as determined from digital particle imaging velocimetry, population growth was inhibited and a short-spined cell type appeared that possessed a 49% mean decrease in spine length and a 53% mean decrease in cell volume. The reduction in cell size appeared to result primarily from a 39% mean decrease in vacuole size. Short-spined cells were first observed after 1 h of agitation at 20 8 C; after 8 to 12 d of continuous agitation, long-spined cells were no longer present. The morphological change was completely reversible; in previously agitated populations devoid of long-spined cells, cells began to revert to the long-spined morphology within 1 d after return to still conditions. During morphological reversal, spines on isolated cells grew up to 10 m m·d 2 1 . In 30 d the population morphology had returned to original proportions, even though the overall population growth was zero during this time. The reversal did not occur as a result of cell division, because singlecell studies confirmed that the change occurred in the absence of cell division and much faster than the 16-d doubling time. The threshold level of agitation causing morphology change in C. horrida was too low to inhibit population growth in the shear-sensitive dinoflagellate Lingulodinium polyedrum. At the highest level of agitation tested, there was negative population growth in C. horrida cultures, indicating that fluid motion caused cell mortality. Small, spineless cells constituted a small percentage of the population under all conditions. Although their abundance did not change, single-cell studies and morphological characteristics suggest that the spineless cells can rapidly transform to and from other cell types. The sinking rate of individual long-spined cells in still conditions was significantly less than that of short-spined cells, even though the former are larger and have a higher cell density. These measurements demonstrate that the long spines of C. horrida reduce cell sinking. Shorter spines and reduced swimming would allow cells to sink away from turbulent surface conditions more rapidly. The ecological importance of the morphological change may be to avoid conditions that inhibit population growth and potentially cause cell damage.