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Coastal upwelling is known for inducing nearshore primary production, which can be advected to the offshore environment through offshore Ekman transport. However, this nearshore−offshore phytoplankton link has been less characterized at the community level. This study focuses on two shelf and slope sites off Oregon during years of 2013−2017 to examine the shelf−slope covariations in diatom and dinoflagellate abundance and community structure at seasonal and annual timescales. In general, the temporal changes of diatom and dinoflagellate abundance were coherent between shelf and slope. However, some differences were also noticeable. For example, diatom and dinoflagellate bloom magnitudes were higher in 2017 and 2014 on the shelf, but were higher in 2014−2016 at the slope. Diatom abundance had a stronger shelf−slope correlation than dinoflagellate correlation particularly in spring. The community structure was significantly correlated between shelf and slope during the annual upwelling period and in spring season. Ekman transport and nutrients played a significant role in shaping the diatom abundance and community structure temporal patterns at the slope. This shelf−slope correlation study infers that the benefits of nearshore upwelling blooms to the offshore food chains are season dependent and under high interannual variability. [ABSTRACT FROM AUTHOR]

Filtration by adult Euphausia pacifica was measured before and during the upwelling season, using both “disappearance of chlorophyll” and “disappearance of cells” techniques. Results show that feeding rates and selectivity varied with food assemblages. Filtration rate (F) was best modeled by the Ivlev function: the average F on total Chl-a was 92 mL euphausiid−1 h−1, and 119 mL euphausiid−1 h−1 on microscopy cell counts. F averaged 36 for the <5 µm size fraction of Chl-a, 94 for the 5–20 µm fraction and 107 mL euphausiid−1 h−1 for the >20 µm fraction. The average F values were 155 and 163 mL euphausiid−1 h−1 for chain-diatoms and single diatoms, respectively, and115 and 137 mL euphausiid−1 h−1 for the <40 µm and >40 µm ciliates, respectively. Ingestion rates based on total Chl-a and size fractions, total cell counts and ciliates were significantly correlated using Hollings' models (P < 0.01). Maximum daily ration was 23% body C day−1 when a high food concentration (700 µC L−1) was available, but over the carbon range of 50–200 µg C L−1, daily ration averaged 4% body C day−1. Diatoms were consumed almost exclusively during blooms associated with summer upwelling events; larger types of ciliates and dinoflagellates were fed upon preferentially compared with their smaller counterparts. [ABSTRACT FROM PUBLISHER]

Stage duration is a key parameter in modeling population dynamics of stage-structured populations, however stage duration can be difficult to estimate accurately because calculations are based on survivors and fail to account for mortality. Here we show a method by which development time and stage duration can be adjusted after accounting for within-stage mortality. As an example, we use a previously published data set on stage-specific abundances of the euphausiid, Euphausia pacifica from four laboratory-incubated cohorts, raised from egg to juvenile stage. We used a stage-structured population model along with an inverse algorithm to estimate stage durations, both with and without considering mortality rates. Results suggest that the overall stage duration from egg to furcilia was ∼48 days when mortality was considered, and ∼60 days when mortality was not included. Stage-specific mortality rates were generally lower than 10% per day for those stages with relatively high mortality rates (egg and naupliar stages and furcilia VI–VII) and <4% for other developmental stages. However, the difference between the estimates with and without considering mortality rates did not show a clear relationship with stage-specific mortality rates. More robust models that can incorporate the variability in developmental pathways and physiological changes that occur during the molting process may be necessary to further investigate how age distribution within stage and mortality influence the estimation of stage duration. [ABSTRACT FROM PUBLISHER]

Morphology and biometry of eggs spawned by females of Euphausia pacifica, Thysanoessa spinifera and Thysanoessa inspinata were compared with eggs collected along the Oregon coast to identify the eggs in preserved samples to species level and to infer species spawning areas and intensity of spawning events in the field. The average chorion diameter (CD) and embryo diameter (ED) were significantly larger for E. pacifica than for T. spinifera. Euphausia pacifica eggs usually have a significantly greater perivitelline space, and the chorion is firm, transparent, smooth, elastic and completely spherical, while T. spinifera embryos are not completely spherical and typically are soft and sticky with particles attached. Eggs of the twitching stage embryo of T. spinifera have an elliptical shape, while those of E. pacifica are spherical to very slightly elliptical even after hatching as nauplii. The CD and ED of T. inspinata eggs were smaller than those of the other two species and they were transparent and spherical with a non-sticky chorion. Biweekly time series of eggs (identified to species), of nauplii + metanauplii and of ripe females collected along the Newport hydrographic line (44°40′N) during 1970–1972 show that E. pacifica and T. spinifera spawn mainly <40 km from the coast from March to October, but E. pacifica also spawns regularly at oceanic locations. A meta-analysis of the egg CD and ED values of 38 euphausiid species around the world indicates that these variables alone cannot be used to identify eggs to species, excepting specific regions where one or two broadcast spawners dominate the euphausiid assemblage. [ABSTRACT FROM PUBLISHER]

Valdés, L., Peterson, W., Church, K., and Marcos, M. 2009. Our changing oceans: conclusions of the first International Symposium on the Effects of climate change on the world's oceans. – ICES Journal of Marine Science, 66: 1435–1438. [ABSTRACT FROM PUBLISHER]

Peterson, J. O., and Peterson, W. T. 2008. Influence of the Columbia River plume (USA) on the vertical and horizontal distribution of mesozooplankton over the Washington and Oregon shelf. – ICES Journal of Marine Science, 65: 477–483.River plumes extending out over continental shelf waters have distinct frontal boundaries along their leading edges that concentrate highly buoyant particles, including zooplankton. The margin between the base of the plume and the underlying oceanic waters is often many times larger in spatial extent than the visible surface front, but the influence of this region of a river plume on the vertical and horizontal distribution of zooplankton is less well understood. Using a laser optical plankton counter (LOPC) and a conductivity–temperature–depth sensor (CTD) mounted to a rapidly undulating tow body, we examined the horizontal and vertical distribution of zooplankton proximate to the Columbia River plume, to study how plume waters affect zooplankton over the continental shelf. Overall, vertically integrated zooplankton abundance and biovolume was elevated close to “aged” plume waters. Zooplankton tended to aggregate near the surface close to river plume waters. When plume waters are present at the surface, zooplankton aggregations tended to be in the upper 10 m of the water column, compared with 25 m when the plume was not present. The presence of river plumes may be ecologically and energetically important to surface feeding planktivores such as larval and juvenile fish. [ABSTRACT FROM PUBLISHER]

Populations of the sand crab, Emerita analoga, are well established on the California coast. However, populations in Oregon occur sporadically and appear to be restocked by larvae drifting north from California. Due to increased northward transport in winter during El Niño events, we would expect that larval recruitment to northern populations should be higher during these periods. This hypothesis was tested by comparing larval abundances between non-El Niño and El Niño years, 1997 and 1998, respectively. In 1997, larval abundances and seasonality were similar to historical data from 1969–71. First zoeal (Z1) stage larvae were present during these summers, but in low numbers, indicating that E.analoga spawned off the coast of Oregon. In 1998, strong larval recruitment from the south occurred, demonstrated by a large number of fifth zoeal stage (Z5) larvae collected off Oregon in April and May. The large numbers of Z1 found in summer 1998 indicate that the Z5, which arrived from California earlier that spring, successfully recruited to adulthood and reproduced. These data indicate that Oregon E.analoga populations are probably dependent on larvae travelling from California in the Davidson Current. It follows that this species could be used as an indicator of coastal current fluctuations such as those seen during El Niño events. [ABSTRACT FROM PUBLISHER]

Measurements of hydrography, water transparency, chlorophyll (Chl) a and egg production rates (EPRs) by females of Calanus marshallae Frost, Calanus pacificus Brodsky, Eucalanus californicus Johnson, Epilabidocera longipedata Sato, Pseudocalanus mimus Frost, Centropages abdominalis Sato, Acartia longiremis Lilljerborg and Paracalanus parvus (Claus) were estimated at weekly intervals between 17 July and 2 September 1997. Production of eggs was determined in 24 h incubations to examine the effects of environmental variability on EPR, to detect the possibility of food limitation of EPR, and to evaluate the hypothesis that growth rates of females are size dependent. During the study, an anomalous downwelling event occurred, possibly in response to the 1997 El Niño, which allowed us to determine how El Niño events affect EPRs of coastal copepods. The larger copepods Calanus marshallae, Calanus pacificus and Centropages abdominalis showed the highest egg production and specific growth rates during the period of active upwelling (18 July-13 August, water temperatures 8-13°C, Chl a concentration 4.7-16.2 μ l-1 and water transparency 3-5 m). After 27 August, the 1997-98 El Niño arrived off Oregon, creating a downwelling situation. Upwelling winds ceased, the thermocline intensified, temperature and transparency increased (to >18°C and 16 m), and Chl a declined to <2 μg l-1. Densities of the common coastal species declined greatly as well. Paracalanus parvus became the dominant species, and Eucalanus californicus, Epilabidocera longipedata and Corycaeus anglicus became common in our samples. EPRs for the larger boreal copepods (Calanus and Centropages) declined greatly during El Niño;; the smaller copepods, Pseudocalanus mimus, A.longiremis and Paracalanus parvus, showed low but relatively constant egg production and specific growth rates during both upwelling and downwelling events. Over the entire study period, only three species produced eggs at its maximum rate (24-28 eggs female-1 day-1), Pseudocalanus mimus which averaged 4 eggs day-1. All other species had EPRs that were two or five times below their maximum EPR. Thus, EPRs were not related to body size, contrary to our expectations. Hatching success was variable among species. Values as low as 20-40% were found for all species at least once during the study period, suggesting that occasionally a substantial portion of egg production may not be viable. [ABSTRACT FROM PUBLISHER]

We examined the relationship between egg production rate (E) and pigment ingestion rate (I, from gut content corrected for 33% loss) for adult female Temora longicornis in Long Island Sound on 47 occasions. Linear regression of E on I [both variables expressed in mass of nitrogen (N) female−1 day−1] was: EN = 0.0016 + 0.770 × IN. The slope, 0.77, is the apparent gross efficiency of egg production, equivalent to the gross growth efficiency (GGE) assuming that females partition all nitrogen for growth into egg production. Published work suggests that a GGE of 0.37 would be expected for herbivorous copepods. The discrepancy between the expected value of 0.37 and observed value of 0.77 could result from unquantified losses of gut pigment or because T.longicomis ingested a significant amount of nitrogen by feeding as a carnivore. We suggest that if T.longicomis females derive all of their nitrogen for growth by feeding on phytoplankton, and if no correction for pigment loss is employed, then the gut pigment method underestimates pigment ingestion by no more than a factor of two. [ABSTRACT FROM PUBLISHER]