Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques
Lawson, Gareth L.
MetadataShow full item record
KeywordUnderwater acoustics; Marine zooplankton; Nathaniel B. Palmer (Ship) Cruise NBP01-03; Nathaniel B. Palmer (Ship) Cruise NBP01-04
The physical and biological forces that drive zooplankton distribution and patchiness in an antarctic continental shelf region were examined, with particular emphasis on the Antarctic krill, Euphausia superba. This was accomplished by the application of acoustic, video, and environmental sensors during surveys of the region in and around Marguerite Bay, west of the Antarctic Peninsula, in the falls and winters of 2001 and 2002. An important component of the research involved the development and verification of methods for extracting estimates of ecologically-meaningful quantities from measurements of scattered sound. The distribution of acoustic volume backscattering at the single frequency of 120 kHz was first examined as an index of the overall biomass of zooplankton. Distinct spatial and seasonal patterns were observed that coincided with advective features. Improved parameterization was then achieved for a theoretical model of Antarctic krill target strength, the quantity necessary in scaling measurements of scattered sound to estimates of abundance, through direct measurement of all necessary model parameters for krill sampled in the study region and survey period. Methods were developed for identifying and delineating krill aggregations, allowing the distribution of krill to be distinguished from that of the overall zooplankton community. Additional methods were developed and verified for estimating the length, abundance, and biomass of krill in each acoustically-identified aggregation. These methods were applied to multifrequency acoustic survey data, demonstrating strong seasonal, inter-annual, and spatial variability in the distribution of krill biomass. Highest biomass was consistently associated with regions close to land where temperatures at depth were cool. Finally, the morphology, internal structure, and vertical position of individual krill aggregations were examined. The observed patterns of variability in aggregation characteristics between day and night, regions of high versus low food availability, and in the presence or absence of predators, together reinforced the conclusion that aggregation and diel vertical migration represent strategies to avoid visual predators, while also allowing the krill access to shallowly-distributed food resources. The various findings of this work have important implications to the fields of zooplankton acoustics and Antarctic krill ecology, especially in relation to the interactions of the krill with its predators.
Submitted to the MIT Department of Biology and the WHOI Biology Department in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2006
Showing items related by title, author, creator and subject.
Martin Traykovski, Linda V. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1998-02)Work on the forward problem in zooplankton bioacoustics has resulted in the identification of three categories of acoustic scatterers: elastic-shelled (e.g. pteropods), fluid-like (e.g. euphausiids), and gas-bearing (e.g. ...
The ecology of colonial radiolarians : their colony morphology, trophic interactions and associations, behavior, distribution, and the photosynthesis of their symbionts Swanberg, Neil Ralph (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1979-08)Colonial radiolarians (Spumellaria) are among the most common and abundant large zooplankton, but they have been little studied by modern biologists. Colonies were found on 98% of epipelagic diving stations in the period ...
Limits of Nematoscelis megalops in the northwestern Atlantic in relation to Gulf Stream cold core rings. I, Horizontal and vertical distributions Wiebe, Peter H.; Boyd, Steven H. (Woods Hole Oceanographic Institution, 1979-01)The hydrographic limit of the distribution of Nematoscelis megalops in the Northwestern Atlantic Ocean is usually marked by the abrupt changes in water properties across the Gulf Stream. There are, however, isolated but ...