Collaborators: Andone Lavery (WHOI), Peter Wiebe (WHOI)
The primary focus in the lab at present is on the ecology of euphausiids in the northwest Atlantic Ocean. Euphausiids, or krill, are a common group of crustaceans in pelagic marine ecosystems, notable among zooplankton for their strong swimming capabilities and, in certain species, for the formation of dense aggregations. As a result of these characteristics, the spatial and temporal distribution of euphausiids is highly variable, and this ‘patchiness’ in euphausiid distribution is thought to be instrumental in determining their availability to predators. In the Gulf of Maine, limited observations suggest that euphausiids can be locally abundant and an important prey item for a number of predators, including marine mammals and commercially-important fish. Overall, however, relatively little is known about the interaction of biological and physical processes leading to variability in the distribution and abundance of euphausiids in the Gulf of Maine region.
Our long-term goal is to understand the bio-physical factors determining euphausiid patchiness and availability to higher predators across scales, focusing on the Gulf of Maine as a model region. To that end, we are currently pursuing a series of inter-related projects:
Biological and Physical Determinants of Euphausiid Aggregation, Behavior, and Interaction With Higher Predators at an Abrupt Topographical Feature in the Gulf of Maine
Large, deep, and dense euphausiid aggregations have been reported in a number of regions of abrupt topography in the world’s oceans, including in the Gulf of Maine. We seek to address the hypothesis that the formation and variability of such aggregations relate to the interaction of physical concentration mechanisms with local topography and with plasticity in diel vertical migration and active aggregative behaviors, focusing on the northern flank of Georges Bank as a model study region. This hypothesis will be addressed through a field program employing a comprehensive array of sensors, including both conventional narrowband and recently-developed broadband acoustic systems to sample the euphausiids, and a variety of other acoustic, optical, net, and other sampling devices to quantify their physical and biological environment. Repeat surveys in the fall of 2010 will be conducted, timed to capitalize on known or likely variations in the flow field, food availability, light levels, and predation.
Euphausiid behavior and physical aggregation mechanisms in the canyons of the New England continental shelf break
The continental shelf break represents a frontier region in current understanding of the dynamics of the western North Atlantic Ocean and its inhabitants, and this project is motivated by the hypothesis advanced in the literature that large aggregations of euphausiids found in the canyons of the New England shelf break play an important role in subsidizing the productivity of commercial fish and squid stocks in shallower reaches of the shelf. Canyons also appear to constitute particularly important habitat for certain whales. We seek to understand the biological and physical processes that lead to the formation, persistence, and availability to predators of these euphausiids aggregations. To achieve this objective, in the summer of 2010 we will conduct acoustic and net surveys both within and away from Atlantis Canyon, southwest of Georges Bank, timed to coincide with a shelf break cetacean survey conducted by the Northeast Fisheries Science Center. By addressing the bio-physical factors that lead to the aggregation of euphausiids and that determine their availability to higher predators in these canyon regions, we seek to take a necessary first step towards defining the essential habitat of fish and whale predators on euphausiids and quantifying their interaction for the development of ecosystem-based management models.
Spatial and Temporal Variability in the Broad-Scale Distribution of Euphausiids in the Gulf of Maine
We are drawing upon existing datasets to characterize the distribution, abundance, and aggregation structure of euphausiids in the Gulf of Maine region at broad spatial scales and seasonal inter-annual temporal scales, in relation to bathymetric features, hydrographic conditions, and climate indices. The relevant datasets include:
(1) Measurements of zooplankton abundance/biomass (including euphausiids) made with nets during bimonthly GoM surveys (1977-2008) by the MARMAP and ECOMON programs, provided by Jon Hare of the Northeast Fisheries Science Center (NEFSC).
(2) Measurements of the frequency of occurrence of euphausiids in fish stomach content samples collected during NEFSC fish stock assessment surveys of the GoM (1973-2008), provided by Jason Link of NEFSC.
(3) Data collected during fall acoustic surveys for herring on the northern flank of Georges Bank (1999-2009), provided by Mike Jech of NEFSC.
(4) Multi-sensor datasets collected during surveys of the deep basins of the Gulf of Maine conducted during the falls of 1997-1999 under the Georges Bank GLOBEC program.