David L. Mackas

The seasonal cycle revisited: interannual variation and ecosystem consequences

The annual seasonal cycle accounts for much of the total temporal variability of mid- and high-latitude marine ecosystems. Although the general pattern of the seasons repeats each year, climatic variability of the atmosphere and the ocean produce detectable changes in intensity and onset timing. We use a combination of time series data from oceanographic, zooplankton and seabird breeding data to ask if and how these variations in the timing of the spring growing season affect marine populations. For the physical environment, we develop an annual index of spring timing by fitting a non-linear 2-parameter periodic function to the average weekly SST data observed in British Columbia from 1 January to the end of August each year. For each year, the phase parameter describes the timing of seasonal warming (the timing index) and the amplitude parameter describes the magnitude of the temperature increase between the fitted winter minimum and summer maximum. For the zooplankton, which have annual and strongly synchronous cycles of biomass, productivity, and developmental sequence, we use copepodite stage composition to index the timing of the annual maximum. For seabirds, we examine (1975–1999) the timing of hatching, nestling growth performance, and diet for four species of alcids at Triangle Island, British Columbia’s largest seabird colony and the world’s largest population of the planktivorous Cassin’s auklet. Temperature, zooplankton, and seabirds have all shown recent decadal trends toward ‘earlier spring’, but the magnitudes of the timing perturbations have differed from variable to variable and from year to year. Recent (1996–1999) extreme interannual variation in spring timing and April SST helped to facilitate a mechanistic investigation of oceanographic features that affect the reproductive performance of seabirds. Our results demonstrate a significant negative relationship between the annual spring timing index (and April mean SST) and nestling growth rates for both Cassin’s auklet and rhinoceros auklet. Nestling growth rates were significantly lower in early, warm years. We demonstrate that low growth rates of Cassin’s auklet occurred when copepod

Marine plankton phenology and life history in a changing climate: current research and future directions

Increasing availability and extent of biological ocean time series (from both in situ and satellite data) have helped reveal significant phenological variability of marine plankton. The extent to which the range of this variability is modified as a result of climate change is of obvious importance. Here we summarize recent research results on phenology of both phytoplankton and zooplankton. We suggest directions to better quantify and monitor future plankton phenology shifts, including (i) examining the main mode of expected future changes (ecological shifts in timing and spatial distribution to accommodate fixed environmental niches vs. evolutionary adaptation of timing controls to maintain fixed biogeography and seasonality), (ii) broader understanding of phenology at the species and community level (e.g. for zooplankton beyond Calanus and for phytoplankton beyond chlorophyll), (iii) improving and diversifying statistical metrics for indexing timing and trophic synchrony and (iv) improved consideration of spatio-temporal scales and the Lagrangian nature of plankton assemblages to separate time from space changes.

Zooplankton Distribution and Dynamics in a North Pacific Eddy of Coastal Origin: I. Transport and Loss of Continental Margin Species

Zooplankton from coastal/continental margin environments can be transported long distances seaward into the subarctic North Pacific by the large (100–200 km diameter) anticyclonic eddies that form annually in late winter along the eastern margin of the Alaska Gyre. One recurrent region for eddy formation is off the southern tip of the Queen Charlotte Islands (near 52°N 132°W). Eddies from this source region (termed ‘Haida eddies’) propagate westward into open ocean waters during the subsequent 1–3 years, often to about 140°W, occasionally to mid gyre. Each eddy contains a core of anomalously low density water, and produces an upward doming of the sea surface detectable by satellite altimetry, thereby aiding repeated ship-based sampling. The zooplankton community in the eddies is a mixture between shelf/slope species (transported from the nearshore formation region) and subarctic oceanic species (which colonize the eddy from the sides and below). This paper reports sequential observations (late winter, early summer and fall seasons of 2000, and early summer and fall of 2001) of the abundance and distribution of continental-margin zooplankton in the Haida eddies that formed in late winters of 2000 and 2001. Shelf-origin species declined in abundance over time. Species that appeared to have a continental slope origin sometimes declined but sometimes persisted and flourished. Transport and retention within the eddy appeared to be especially effective for species that undergo diel vertical migration.

“Seamount effects” in the zooplankton community near Cobb Seamount

Abstract Oceanic seamounts often support large nektonic stocks. Since the mid-1950s it has been believed that this high productivity results, in part, from biological response to the physical interaction between oceanic currents and the abrupt topographic profiles represented by most seamounts. The “classic theory” for the production/maintenance of seamount nektonic stocks suggests that (i) the combination of localized upwelling and the trapping/concentrating action of closed anticyclonic vortices (i.e. Taylor cones) enhance local primary production, (ii) thereby promoting local secondary productivity that, (iii) supports local nektonic populations. Here we test one element of this theory: whether proximity to a shallow seamount is associated with changes in zooplankton abundance and species composition. Zooplankton samples were collected near Cobb Seamount, a shallow ( 100 m and is not an effective retention mechanism. Total zooplankton abundance did not vary significantly on- versus off-seamount. However, using a variety of nonparametric multivariate techniques we demonstrate that a “seamount effect” on zooplankton-community composition is detectable up to 30 km from the seamount summit. This effect is superimposed on (and locally much stronger than) the expected slow decline in resemblance as between-sample geographic distance increases. Possible mechanisms by which this effect operates include: differential growth or reproduction, differential mortality and behavioral or migratory effects. The on-off seamount differences are accounted for largely by the increased relative abundances of two fast-growing opportunists, doliolids (Dolioletta sp) and larvaceans (Oikopleura sp.), near Cobb Seamount. Predation pressure from seamount fish and active avoidance of the seamount by zooplankton may also play a role in generating the seamount effect. The absence of an effective trapping mechanism and the fact that total zooplankton abundance does not increase near the seamount lead us to conclude that the bottom-up model of localized energy transfer proposed under the “classic hypothesis” is incorrect for Cobb Seamount: nektonic stocks at Cobb Seamount (and, possibly, other shallow seamounts) are more likely supported by flow-through (i.e. advected) rather than local production.

Zooplankton community composition along the inner portion of Line P during the 1997-1998 El Nino event

The 1996-1999 zooplankton samples from oceanic waters off southern British Columbia provide time series descrip- tions of biomass and community composition before, during, and immediately after the 1997-1998 El Nino event. Our most frequent sampling (every month in 1998 and three to four times per year in other years) was off southern Van- couver Island, and extended seaward from the shelf-break to approximately 200 km offshore along and adjacent to the inner third of the long-term Line P/Station P section (48°30-49°N, 126-130°40W). El Nino-associated changes in the zooplankton community were most apparent over the shelf-break and slope, and weaker further offshore. At the nearshore portion of this line (P03-P06), the 1997-1998 differences from long-term seasonal averages included both lower total biomass and shifts in community composition (reduced abundance of endemic boreal-temperate species, increased abundance of mid-California neritic and oceanic species). Toward the seaward end of the section (P08-P12), changes of zooplankton species composition were much less apparent, and the main signal associated with the 1997- 1998 event was an early and narrow spring peak of Neocalanus spp. Although most extreme in 1998, both the nearshore and offshore sets of anomalies were continuations of trends that had developed progressively off British Columbia through the 1990s. A few taxa, normally endemic to southern parts of California Current and previously absent or very rare off British Columbia, appeared in our samples in 1997-1998 and persisted through summer of 1998 and at some locations into 1999. The changes observed over the continental slope of Vancouver Island were very similar to the observations of 1970s versus late 1990s differences in the zooplankton of the central Oregon coast continental shelf (PICES Sci. Rep., 10 (1999) 45; Prog. Oceangr. (2002)), suggesting that there was alongshore continuity of both oceanic forcing and zooplankton response. Crown Copyright  2002 Published by Elsevier Science Ltd. All rights reserved.

From Sea to Sea: Canada's Three Oceans of Biodiversity

Evaluating and understanding biodiversity in marine ecosystems are both necessary and challenging for conservation. This paper compiles and summarizes current knowledge of the diversity of marine taxa in Canadas three oceans while recognizing that this compilation is incomplete and will change in the future. That Canada has the longest coastline in the world and incorporates distinctly different biogeographic provinces and ecoregions (e.g., temperate through ice-covered areas) constrains this analysis. The taxonomic groups presented here include microbes, phytoplankton, macroalgae, zooplankton, benthic infauna, fishes, and marine mammals. The minimum number of species or taxa compiled here is 15,988 for the three Canadian oceans. However, this number clearly underestimates in several ways the total number of taxa present. First, there are significant gaps in the published literature. Second, the diversity of many habitats has not been compiled for all taxonomic groups (e.g., intertidal rocky shores, deep sea), and data compilations are based on short-term, directed research programs or longer-term monitoring activities with limited spatial resolution. Third, the biodiversity of large organisms is well known, but this is not true of smaller organisms. Finally, the greatest constraint on this summary is the willingness and capacity of those who collected the data to make it available to those interested in biodiversity meta-analyses. Confirmation of identities and intercomparison of studies are also constrained by the disturbing rate of decline in the number of taxonomists and systematists specializing on marine taxa in Canada. This decline is mostly the result of retirements of current specialists and to a lack of training and employment opportunities for new ones. Considering the difficulties encountered in compiling an overview of biogeographic data and the diversity of species or taxa in Canadas three oceans, this synthesis is intended to serve as a biodiversity baseline for a new program on marine biodiversity, the Canadian Healthy Ocean Network. A major effort needs to be undertaken to establish a complete baseline of Canadian marine biodiversity of all taxonomic groups, especially if we are to understand and conserve this part of Canadas natural heritage.

Does blending of chlorophyll data bias temporal trend

Arising from D. G. Boyce, M. R. Lewis & B. Worm 466, 591–596 (2010)10.1038/nature09268; Boyce et al. replyPhytoplankton account for about half of global and nearly all of marine primary productivity; consequently, any widespread drop in phytoplankton biomass would almost certainly have severe ecological consequences. Boyce et al. have reported strong (∼1% per year) and sustained declines in marine phytoplankton biomass at local, regional and global scales. However, I suggest that some or much of their reported declines are attributable to bias between the two data types used by Boyce et al.. Although real changes may have occurred, their proper quantification requires removal of the bias component.

Cross-shore separation of adult and juvenile euphausiids in a shelf-break alongshore current

Abstract Euphausiids are an important component of the zooplankton in boundary current upwelling regions, including the Pacific Northwest continental margin. Many aspects of euphausiid distribution and ecology in this region are well known. However, some features of their spatial and temporal distribution are less understood: • How and why euphausiids aggregate near the shelf-break upwelling center. • How and why there is (within an alongshore band of high abundance of all stages) spatial segregation of adults and larvae. • Why, despite spatial association with upwelling, euphausiid abundance off Vancouver Island is weakly or negatively correlated at interannual time scales with upwelling intensity. To address these, we made km-resolution surveys of adult, juvenile, and larval euphausiid horizontal distributions, water properties, and currents across the Vancouver Island shelf break in mid-to-late spring of two successive years. Survey timing was before (1997) and after (1998) the spring transition to upwelling conditions, and near the annual spring reproductive peak. In both years, early developmental stages occupied an alongshore band that was offset from the late juveniles and adults. The direction of the offset differed between the two surveys. Early life history stages (larvae and early juveniles) were shoreward of adults in April 1997 (downwelling-conditions), but seaward of adults in May 1998 (upwelling-conditions). Separation distance (order 5–10 km) was consistent with expected differences in cumulative wind-driven (and vertically-sheared) cross-shore transport of surface-dwelling larvae and early juveniles vs. transport of diel migratory late juveniles and adults. Separation direction was consistent with recent history of winds and Ekman transport—shoreward during poleward winds, and seaward into blue water (and usually into a strong equatorward current) during equatorward winds.

Comparison of multifrequency acoustic and in situ measurements of zooplankton abundances in Knight Inlet, British Columbia

An investigation of midwater zooplankton aggregations in a coastal fjord was conducted in November 2002. This study focused on quantitative comparisons between a calibrated, three-frequency (38, 120, and 200 kHz) vessel-based echo-sounder, a multinet towed zooplankton sampler (BIONESS), and a high-resolution underwater camera (ZOOVIS). Daytime layers of euphausiids and amphipods near 70-90-m depth were observed in lower parts of the inlet, especially concentrated by tidal flows around a sill. Quantitative backscatter measurements of euphausiids and amphipods, combined with in situ size and abundance estimates, and using an assumed tilt-angle distribution, were in agreement with averaged fluid-cylinder scattering models produced by Stanton and Chu [ICES J. Mar. Sci. 57, 793-807, (2000)]. Acoustic measurements of physonect siphonophores in the upper inlet were found to have a strong 38-kHz scattering strength, in agreement with a damped bubble scattering model using a diameter of 0.4 mm. In relatively dense euphausiid layers, ZOOVIS abundance estimates were found to be a factor of 2 to 4 higher than the acoustic estimates, potentially due to deviations from assumed euphausiid orientation. Nocturnal near-surface euphausiid scattering exhibited a strong (15 dB) and rapid (seconds) sensitivity to vessel lights, interpreted as due to changing animal orientation.

Response of Euphausia pacifica to small-scale shear in turbulent flow over a sill in a fjord

Zooplankton in the ocean respond to visual and hydro-mechanical cues such as small-scale shear in turbulent flow. In addition, they form strong aggregations where currents intersect sloping bottoms. Strong and predictable tidal currents over a sill in Knight Inlet, Canada, make it an ideal location to investigate biological behaviour in turbulent cross-isobath flow. We examine acoustic data (38, 120 and 200 kHz) collected there during the daylight hours, when the dominant zooplankters, Euphausia pacifica have descended into low light levels at ∼90 m. As expected, these data reveal strong aggregations at the sill. However, they occur consistently 10–20 m below the preferred light depth of the animals. We have constructed a simple model of the flow to investigate this phenomenon. Tracks of individual animals are traced in the flow and a variety of zooplankton behaviours tested. Our results indicate that the euphausiids must actively swim downward when they encounter the bottom boundary layer (bbl) to reproduce the observed downward shift in aggregation patterns. We suggest that this behaviour is cued by the small-scale shear in the bbl. Furthermore, this behaviour is likely to enhance aggregations found in strong flows at sills and on continental shelves.