Relevant Scales in Zooplankton Ecology: Distribution, Feeding, and Reproduction of the Copepod Acartia Hudsonica in Response to Thin Layers of the Diatom Skeletonema Costatum

We investigated the interaction of the copepod Acartia hudsonica in relation to thin layers of the diatom Skeletonema costatum. Thin layers have recently received much attention, since they are common and persistent features in the water column, often overlooked by traditional sampling methods. Their frequent abundance in coastal oceans and the high biomass associated with them has led to the assumption that they are important grazing sites of calanoid copepods. We employed 2-m tall tower tanks that allowed us to simulate thin layers. Three variables representative of three time scales were considered: the distribution of copepods in the tanks (time scale of minutes), fecal pellet production as a proxy for ingestion rate (time scale of hours), and egg production rate (time scale of \u3e12 h). A. hudsonica responded significantly but very little to the thin layers in terms of their distribution. Given a choice, there was a slightly higher tendency to swim through a patch of diatoms than to swim around it. Fecal pellet production was slightly lower in the thin-layer treatments than in the homogeneous controls. Egg production was not influenced by differential distribution of diatoms in the tanks, which indicated that the copepods dealt equally well with patchy food as when the same numbers of cells were available in a homogeneous distribution. Time series experiments showed that ingested carbon is integrated over time scales of \u3e12 h. Therefore, small-scale fluctuations of food in space and time do not necessarily translate into small-scale fluctuations in reproductive output

Feeding ecology of juvenile Pacific salmon (Oncorhynchus spp.) in a northeast Pacific fjord: diet, availability of zooplankton, selectivity for prey, and potential competition for prey resources

We investigated the feeding ecology of juvenile salmon during the critical early life-history stage of transition from shallow to deep marine waters by sampling two stations (190 m and 60 m deep) in a northeast Pacific fjord (Dabob Bay, WA) between May 1985 and October 1987. Four species of Pacific salmon—Oncorhynchus keta (chum) , O. tshawytscha (Chinook), O. gorbuscha (pink), and O. kisutch (coho)—were examined for stomach contents. Diets of these fishes varied temporally, spatially, and between species, but were dominated by insects, euphausiids, and decapod larvae. Zooplankton assemblages and dry weights differed between stations, and less so between years. Salmon often demonstrated strongly positive or negative selection for specific prey types: copepods were far more abundant in the zooplankton than in the diet, whereas Insecta, Araneae, Cephalapoda, Teleostei, and Ctenophora were more abundant in the diet than in the plankton. Overall diet overlap was highest for Chinook and coho salmon (mean=77.9%)—species that seldom were found together. Chum and Chinook salmon were found together the most frequently, but diet overlap was lower (38.8%) and zooplankton biomass was not correlated with their gut fullness (%body weight). Thus, despite occasional occurrences of significant diet overlap between salmon species, our results indicate that interspecific competition among juvenile salmon does not occur in Dabob Bay

Effects of warm water intrusions on populations of macrozooplankton on Georges Bank, Northwest Atlantic

Author Posting. © The Authors, 2004. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 25 (2005): 143-156, doi:10.1016/j.csr.2004.07.028.As part of the Georges Bank/North West Atlantic GLOBEC (Global Ocean Ecosystems Dynamics) Program, macrozooplankton and micronekton were collected on 30 Broad Scale Survey Cruises between January – June, 1995 –1999, using a 10 m2 MOCNESS (3mm mesh). The objective of this study is to examine the effects of warm water intrusions on populations of macrozooplankton, namely Salpa spp., Phronima spp., Neomysis americana, and Crangon septemspinosa, on Georges Bank. Salpa spp. and Phronima spp. showed a large degree of horizontal co-occurrence, being found predominantly in Upper Slope/Gulf Stream Water and Georges Bank/Gulf of Maine Water. Abundances of these taxa showed striking interannual variability, and were only abundant on the southern flank and in the Northeast Channel in late spring/early summer of 1995 and 1999, periods during which AVHRR imagery and hydrographic data showed the presence of warm water intrusions. These intrusions seemed to have little effect on the distribution of other macrozooplankton (e.g., Neomysis americana and Crangon septemspinosa). Warm water intrusions can directly affect Salpa spp. and Phronima spp. populations by advecting them onto Georges Bank, although other, more resident populations, especially those inside the 100m isobath, seem to be little affected by such intrusions.Additional thanks goes to Tom Niesen and Stan Williams for their advice on data analysis and interpretation. This work was supported by NSF award No. OCE96-17209 and NOAA award No. NA66GP0356 to S. M. Bollens provided from the US GLOBEC Northwest Atlantic/Georges Bank Program, a joint program of the National Science Foundation and the National Oceanic and Atmospheric Administration

Beyond Eutrophication: Vancouver Lake, WA, USA as a Model System for Assessing Multiple, Interacting Biotic and Abiotic Drivers of Harmful Cyanobacterial Blooms

Eutrophication of lakes and reservoirs has contributed to an increase in the magnitude and frequency of harmful cyanobacterial blooms; however, the interactive effects of nutrient availability (eutrophication) and other abiotic and biotic drivers have rarely been comprehensively studied in the field. We undertook an eight-year (2005–2013) research program that assessed the interaction of multiple factors driving cyanobacterial blooms in Vancouver Lake, a large, shallow eutrophic lake in Washington, USA. Our program consisted of nearly continuous monthly or weekly monitoring of water quality and plankton community composition over eight years, as well as multiple zooplankton grazing experiments over three years. We found a relatively consistent seasonal succession of phytoplankton and zooplankton assemblages, and a pattern of interacting factors influencing cyanobacterial bloom dynamics. Typically, a combined effect of decreased dissolved inorganic nitrogen (N), a sudden increase of dissolved inorganic phosphorus (P), and a cascading effect of zooplankton grazing created a ‘perfect storm’ of conditions that promoted the rapid proliferation of cyanobacteria over the two to three weeks before a bloom. At the blooms’ peaks, cyanobacterial carbon biomass reached as high as 20 µg L−1, with total [chl a] often exceeding 750 µg L−1. In the weeks following the blooms’ peaks, [PO4-P] and [NH4-N] dropped and copepod feeding rates fell to near zero, whereas microzooplankton grazing rates reached their maxima. Microzooplankton grazing impact, combined with low nutrient availability, then drove down cyanobacteria abundance. Vancouver Lake serves as a model for understanding multiple, interacting drivers of cyanobacterial bloom dynamics in shallow, temperate lakes, and is therefore an important system in which to investigate new questions related to the science and management of harmful algal blooms

Modeling the trophic impacts of invasive zooplankton in a highly invaded river.

The lower Columbia River (Washington and Oregon, USA) has been heavily invaded by a large number of planktonic organisms including the invasive copepod Pseudodiaptomus forbesi and the planktonic juveniles of the invasive clam, Corbicula fluminea. In order to assess the ecological impacts of these highly abundant invaders, we developed a multivariate auto-regressive (MAR) model of food web dynamics based upon a 12-year time-series of plankton community and environmental data from the Columbia River. Our model results indicate that plankton communities in the lower Columbia River are strongly impacted by the copepod P. forbesi at multiple trophic levels. We observed different ecological effects across different life stages of P. forbesi, with nauplii negatively impacting ciliates and autotrophs, and copepodite stages negatively impacting Daphnia and cyclopoid copepods. Although juvenile C. fluminea were highly abundant in the summer and autumn of each year, our best fit MAR model did not show significant C. fluminea impacts. Our results illustrate the strong ecological impact that some zooplankton invaders may cause within rivers and estuarine systems, and highlight the need for further research on the feeding ecology of the planktonic life-stage of C. fluminea. Overall, our study demonstrates the manner in which long-term, high resolution data sets can be used to better understand the ecological impacts of invasive species among complex and highly dynamic communities

Thin layer formation during runaway stratification in the tidally dynamic San Francisco Estuary

During the course of a year, we repeatedly collected high-resolution vertical fluorometer data timed to coincide with a specific state during the tidal cycle. The time (end of the ebb during neap tide) and the location (a deep channel half-way between the Golden Gate and the point of tidally averaged bottom salinity of 2 psu) were chosen with the goal to observe runaway stratification. We consistently found at least one pronounced chlorophyll peak in the water column; however, the vertical location of these peaks varied within three types including surface, bottom and subsurface maxima. Our results showed that heterogeneity of chlorophyll in the water column and thin layer formation do occur in systems that are characterized by high tidal flow speeds thus resulting in patchy prey fields for zooplankton that migrate in tidal cycles through the water column. Using these chlorophyll profiles, approximate calculations suggested that only during the spring phytoplankton bloom did all layers of the water column provide sufficient food for maximum egg production of the San Francisco Estuary copepod Acartia sp