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The biological and physical processes contributing to planktonic thin layer dynamics were examined in a multidisciplinary study conducted in East Sound, Washington, USA between June 10 and June 25, 1998. The temporal and spatial scales characteristic of thin layers were determined using a nested sampling strategy utilizing 4 major types of platforms: (1) an array of 3 moored acoustical instrument packages and 2 moored optical instrument packages that recorded distributions and intensities of thin layers; (2) additional stationary instrumentation deployed outside the array comprised of meteorological stations, wave-tide gauges, and thermistor chains; (3) a research vessel anchored 150 m outside the western edge of the array; (4) 2 mobile vessels performing basin-wide surveys to define the spatial extent of thin layers and the physical hydrography of the Sound. We observed numerous occurrences of thin layers that contained locally enhanced concentrations of material; many of the layers persisted for intervals of several hours to a few days. More than one persistent thin layer may be present at any one time, and these spatially distinct thin layers often contain distinct plankton assemblages. The results suggest that the species or populations comprising each distinct thin layer have responded to different sets of biological and/or physical processes. The existence and persistence of planktonic thin layers generates extensive biological heterogeneity in the water column and may be important in maintaining species diversity and overall community structure.

Anderson, J. T., Holliday, D. V., Kloser, R., Reid, D. G., and Simard, Y. 2008. Acoustic seabed classification: current practice and future directions. – ICES Journal of Marine Science, 65: 1004–1011. Acoustic remote sensing of the seabed using single-beam echosounders, multibeam echosounders, and sidescan sonars combined and individually are providing technological solutions to marine-habitat mapping initiatives. We believe the science of acoustic seabed classification (ASC) is at its nascence. A comprehensive review of ASC science was undertaken by an international group of scientists under the auspices of ICES. The review was prompted by the growing need to classify and map marine ecosystems across a range of spatial scales in support of ecosystem-based science for ocean management. A review of the theory of sound-scattering from seabeds emphasizes the variety of theoretical models currently in use and the ongoing evolution of our understanding. Acoustic-signal conditioning and data quality assurance before classification using objective, repeatable procedures are important technical considerations where standardization of methods is only just beginning. The issue of temporal and spatial scales is reviewed, with emphasis on matching observational scales to those of the natural world. It is emphasized throughout that the seabed is not static but changes over multiple time-scales as a consequence of natural physical and biological processes. A summary of existing commercial ASC systems provides an introduction to existing capabilities. Verification (ground-truthing) methods are reviewed, emphasizing the difficulties of matching observational scales with acoustic-backscatter data. Survey designs for ASC explore methods that extend beyond traditional oceanographic and fisheries survey techniques. Finally, future directions for acoustic seabed classification science were identified in the key areas requiring immediate attention by the international scientific community.

Thin layers of plankton are recurrent features in a variety of coastal systems. These layers range in thickness from a few centimeters to a few meters. They can extend horizontally for kilometers and have been observed to persist for days. Densities of organisms found within thin layers are far greater than those above or below the layer, and as a result, thin layers may play an important role in the marine ecosystem. The paramount objective of this study was to understand the physical processes that govern the dynamics of thin layers of zooplankton in the coastal ocean. We deployed instruments to measure physical processes and zooplankton distribution in northern Monterey Bay; during an 11 d period of persistent upwelling-favorable winds, 7 thin zooplankton layers were observed. These zooplankton layers persisted throughout daylight hours, but were observed to dissipate during evening hours. These layers had an average vertical thickness of 1.01 m. No layers were found in regions where the Richardson number was < 0.25. In general, when the Richardson number is < 0.25 the water column is unstable, and incapable of supporting thin layers. Thin zooplankton layers were also located in regions of reduced flow. In addition, our observations show that the vertical depth distribution of thin zooplankton layers is modulated by high-frequency internal waves, with periods of 18 to 20 min. Results from this study clearly show an association between physical structure, physical processes and the presence of thin zooplankton layers in Monterey Bay. With this new understanding we may identify other coastal regions that have a high probability of supporting thin layers. KEY WORDS: Thin layer · Physical processes · Transport · Zooplankton · Coastal circulationResale or republication not permitted without written consent of the publisher

We measured the distribution of hydrographic parameters, currents, phytoplankton fluorescence, suspended sediments and zooplankton in axial transects through the Chesapeake Bay estuarine turbidity maximum (ETM) seasonally (May, July and October 1996) and over tidal cycles within seasons. Zooplankton abundance was estimated with a 6-frequency, Tracor Acoustical Profiling System (TAPS-6) at the same vertical (0.25 to 0.50 m) and horizontal (0.5 to 1.5 km) resolution as hydrographic parameters and suspended sediments. The general pattern exhibited in axial transects through the Chesapeake Bay ETM is that sediments, fluorescence and zooplankton are in higher concentrations up-Bay of the salt wedge (defined as the intersection of the 1 isohaline with the bottom). The salinity front appears to trap these particles in the upper portion of Chesapeake Bay. The highest acoustically determined zooplankton biomass generally occurred near the bottom, at the toe of the salt wedge. The convergence zone associated with this feature concentrates sediments and zooplankton (primarily the copepod Eurytemora affinis). Advection appeared to dominate changes in zooplankton abundance during time series studies at a fixed station in the ETM. Zooplankton biomass at the fixed ETM station increased/decreased with the tidal excursion of the salt wedge. Water column zooplankton concentrations and the vertical distribution of zooplankton biomass appeared to be influenced by currents. We often found that during maximum ebb and flood tidal currents, zooplankton biomass and sediments in the mid and upper water column increased. Thus the hydrodynamic processes that resuspend, advect and trap suspended sediments in the ETM likely have the same effects on zooplankton. The ETM of the Chesapeake Bay appears to act as an entrapment zone for zooplankton. The lack of diel vertical migration, carrying eggs until they are ready to hatch, possible reduced predation by visual predators in the turbid waters, and the ability to consume phytoplankton, protozoa and detritus all may allow Eurytemora to persist at high concentrations in the Chesapeake Bay ETM. KEY WORDS: Zooplankton · Estuarine turbidity maximum zone · Chesapeake Bay Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 213: [215][216][217][218][219][220][221][222][223][224][225][226][227] 2001 to 30 km along the N/S axis of the bay (Fig. 1). The location of the ETM varies seasonally and at shorter time scales due to variations in freshwater input and wind-forcing. The ETM region of the Chesapeake Bay has a mean volume of approximately 2.63 km 3 and a mean depth of 4 m. Almost all of the freshwater input to the ETM region comes from the Susquehanna River. At the average Susquehanna River flow of 1100 m 3 s -1 , the freshwater replacement time of the ETM region is approximately 1 mo. Suspended sediment concentrations in the ETM are generally 40 to 80 mg l -1 higher than concentrations upstream or downstream of the ETM, with the largest concen...

A 1-km 2 area located 2 km off the Florida Panhandle (30 22 6 N; 86 38 7 W) was selected as the site to conduct high-frequency acoustic seafloor penetration, sediment propagation, and bottom scattering experiments [1]. Side scan, multibeam, and normal incidence chirp acoustic surveys as well Manuscript

Relationships among microplankton composition, copepod diet, and egg production are examined with data from gut content analysis of copepods from California coastal waters and from the Irish Sea, feeding and egg production experiments on Acartia tonsa off southern California, and egg production measurements on copepods from a subtropical estuary (Port Everglades, Florida), temperate shelf waters (southern California, Irish Sea), and the open ocean (Gulf Stream). The copepod species studied appeared to feed preferentially on dinoflagellates and microzooplankton relative to diatoms. Patterns of variability in egg production conform, generally, to changes in dinoflagellate and microzooplankton biomass, but seem to be independent of changes in diatom biomass.

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