Research - Jeannette E. Zamon

General research interests

Over the next five years I hope to investigate food web dynamics associated with complex topographies in the ocean (e.g. features such as reefs, sills, archipelagos, canyons). I would like to understand how fluid flows affect biological productivity and the foraging behavior of predators. In particular, I see four broad categories of techniques that will be relevant to this research:

analysis of nutrients and biological production
analysis of fluid flows and water mass structure
analysis of predator movement and behavior patterns
analysis of predator time-energy budgets

Because I forsee using physical and biological oceanographic techniques to answer questions about behavior and food web ecology, I see this as interdisciplinary, collaborative work appealing to physical and biological oceanographers, ecologists, and behaviorists. Tidal currents and complex topographies are common features of nearshore environments, therefore knowledge gained should be broadly applicable to different geographic regions.

Fig 1. Water mass and biological structure associated with a sill in Cattle Pass, San Juan Channel. To the right, water is stratified (two-layers with different water properties); to the left, water is well-mixed from top to bottom.

Ultimately, the goal of this work would be to answer the following types of questions:

What roles do in situ vs. advected production play in supporting upper trophic levels in these areas?

Which current flow features are associated with or create good feeding habitats for predators, and how do those features enhance foraging success?

How does energy intake and foraging success of predators near complex topography compare to that in surrounding habitat not affected by topography-current interactions?
How important is complex topography as habitat to keystone planktivorous forage fish species, such as herring and sandlance?

Summary of doctoral research

Recent advances in oceanographic instrumentation are leading to a better understanding of the structure of current flows over complex topographies. However, the biological consequences of these flow features are not well known. Several studies suggest tidal currents interacting with small-scale topographic relief may create spatially or temporally predictable increases in plankton density which are important to plankton predators¹.

Fig 2. Study site in the San Juan Islands, Washington. The 'x' marks indicate zooplankton sampling stations. Flooding tides run from south to north; ebbing tides run from north to south. The Pacific Ocean lies at the western opening of Juan de Fuca.

My dissertation tests the hypothesis that tidal currents control energy flow to planktivorous consumers and top predators by creating predictable spatial and temporal patterns in plankton distributions. The objectives of this study were to determine whether or not

tidal currents cause changes in the densities of plankton consumed by fish
fish distributions track changes in zooplankton densities in time and space
fish predators change their feeding behavior to track changes in fish distributions

I used temperature-salinity profiles, surface drifters, nets, downward-looking acoustics, and behavioral observations to examine correlations among tidal phase, plankton distributions, fish distributions, and feeding activity of top predators.

Fig 3. Paracalanus and Pseudocalanus copepods, typical prey for sandlance and herring.

Work I completed at Friday Harbor Marine Laboratories, San Juan Island, WA demonstrated incoming tidal currents were associated with significant, predictable increases in near-surface plankton densities. Numerically dominant copepods were of the genera Pseudocalanus and Paracalanus, and Corycaeus. For sampling locations within the main tidal current, median copepod densities were significantly greater during floods than ebbs. For the sampling location outside of the main current, median densities were not significantly different between tides. Density differences were probably caused by the upwelling of deep copepod aggregations from Juan de Fuca Strait.

The tidal increases in plankton abundance attracted plankton-eating fish (Pacific sandlance, Ammodytes hexapterus; Pacific herring,Clupea harengus) to feed near current jets.

The fish aggregations in turn attracted abundant seabirds (the most common summer birds being rhinoceros auklets, Cerorhinca monocerata; common murres, Uria aalge; pelagic cormorants, Phalacrocorax pelagicus; glaucous-winged gulls, Larus glauscesens; Heerman's gulls, Larus heermani) seals (harbor seals, Phoca vitulina), and other fish predators (salmon species, Oncorhynchus spp.; spiny dogfish, Squalus acanthias) to feed in the same areas. In contrast, significantly less feeding activity was found on the outgoing tide. The patterns in plankton distributions, fish distributions, and feeding behavior are consistent within and among three years of study. The end result is energy seems to be "pumped" into the community during the incoming tide.

Conversion of numerical plankton densities to biomass estimates showed that advected secondary production available to consumers could be of a similar order of magnitude as in situ primary production. Tidal advection of plankton from Juan de Fuca therefore plays a significant role in structuring fish distribution and behavior, as well as in controlling energy flow to top predators. The energy subsidy brought in by the tides may explain why the San Juan and Gulf Islands, and other geographic regions with similar interactions between tidal currents and physical complexity in topography, are able to support large, diverse populations of marine life. This work also highlights the importance of small-scale flows to individual foraging behavior.

Fig 4. Feeding flock in San Juan Channel. The gulls are tracking a school of fish which has been trapped against the surface by diving rhinoceros auklets² (below) and murres.

¹For example, Alldredge and Hamner (1980). Recurring aggregation of zooplankton by a tidal current. Estuarine and Coastal Marine Science 10:31-37; Bray (1981). Influence of water currents and zooplankton densities on daily foraging movements of blacksmith, Chromis punctipinnis, a planktivorous reef fish. Fishery Bulletin 78(4): 829-841;Braune and Gaskin (1982). Feeding ecology of nonbreeding larid populations off Deer Island, New Brunswick. Auk 99:67-76; Wolanski and Hamner (1988). Topographically controlled fronts in the ocean and their biological influence. Science 241: 177-181

²Auklet photo courtesy of Cornell Laboratory of Ornithology slide collection.

Summary of master's research

The development of relatively inexpensive hydroacoustic technology in the 1980s and 1990s made an important new tool available to aquatic biologists. Acoustic data can provide continuous, real time, non-invasive information on the distribution, relative abundance, absolute abundance, size, and species of aquatic organisms - from the size of copepods (a few mm) to fishes (centimeters) to whales (tens of meters). These distributional data can be used to answer questions about how changes in the distribution of prey organisms are related to changing physical features in the ocean, or how predator distribution and behavior relate to prey distributions.

Fig. 1. Acoustic image of a 1852 x 1852 x 100 m volume of ocean. Krill density is represented in a color scale from black (zero) to red (over 150 krill m³); penguin location and abundance (2-20 individuals) is indicated with white peaks. The bottom panel represents a 180-degree rotation of the top image.

As a master's student at Cornell University, I learned how to apply basic hydroacoustic techniques to questions about the foraging behavior of marine predators. My thesis examined three-dimensional structure in Antarctic krill (Euphausia superba) aggregations, and the implications of that structure for krill availability to chinstrap penguins (Pygoscelis antarctica). Results showed significant depth differences in the degree of krill aggregation, with krill less aggregated in deeper layers than shallow layers. Surface distributions of penguins were associated with the edges of krill aggregations. There was a statistically significant association of the penguin distribution with krill in the depth layer that coincided with mean penguin dive depths. This work illustrated the importance of considering all three dimensions of variation in prey density to diving predators - when prey biomass is integrated over the whole water column, edge effects and depth-dependent associations are masked. The tendency for predators to aggregate over the edges of aggregations may also explain why many studies have not found signficant correlations between marine predators and highest prey densities.

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