EU-US ECOHAB. EC-NSF Cooperative Activity in Environmental Research: In Situ Holographic Measurements of Particle Distributions and Small Scale Turbulence in Thin Layers

Johns Hopkins University, Baltimore MD

Investigators

Abstract

This project was submitted under the EU-US Cooperative Activity on the Ecology and Oceanography of Harmful Algae. The U.S. PIs will join colleagues from France, Ireland, Spain and UK to study the physics and biology of thin layers with concentrated Harmful Algal Bloom (HAB). Serious problems in Europe are caused by contamination of farmed shellfish with Diarrheic Shellfish Poisoning (DSP) toxins produced by the dinoflagellate genus Dinophysis. The existence of thin layers with high Dinophysis concentration has come to light recently, but the information is sporadic because the layers can be present at any depth, and due to sampling difficulties with standard instruments. In the case of Dinophysis, the concentration does not depend solely on nutrition, but also on interactions between physics, life cycle and behavior. This study will determine the hydrodynamic (e.g. local flow structure, turbulence, stratification, small gyres and pycnoclines), biological (e.g. growth, nutrition and mortality) and chemical environment leading to the build up, maintenance and population dynamics of Dinophysis in thin layers. The field tests will take place under a variety of hydrodynamic regimes in the Rias of Galicia (NWSpain), the estuarine plume zones of the Atlantic coast of France, and in the bays of southwestern Ireland. All are shellfish production areas with history of harvest closures due to contamination with DSP toxins. The Johns Hopkins group will focus on small-scale biophysical and particle-particle interactions. By deploying a submersible holocamera, augmented with a digital holographic cinematography, they will observe and measure processes and interactions occurring at the critical scales of 10 mm to 10 cm. Automated data analysis tools will enable the investigators to process a large database under various conditions that will be used for parameterizing the behavior of Dinophysis. The results will include: i. The spatial and size distributions of different classes of particles. Particles larger than 10 mm are detected, and shapes can be defined in particles larger than 30 mm. ii. The nearest neighbor distance (NNS) within the same species, and between species, including predators and prey; iii. The instantaneous 3-D velocity distributions within the sample volume, which is used for calculating the local velocity, strain rate, vorticity, dissipation rate and turbulence intensity; iv. The swimming behavior (speed, trajectory, direction) of Dinophysis in its local environment; v. Direct observations on behavior, feeding and grazing of Dinophysis; vi. Conditional statistics of concentration, NNS and behavior based on local physical and biological parameters; Intellectual Merit: Progress in understanding of population dynamics of different phytoplankton species, including Dinophysis, requires detailed knowledge of their in-situ concentrations, behavior, and biophysical interactions. This project will deploy a new but proven/developed technology in the ocean in order to obtain detailed and unique insight on the interaction of dinoflagellates with their local biophysical environments. The results will illuminate processes affecting the formation and maintenance of thin layers containing Dinophysis. Broader Impacts. Socio-Economic Issues: HAB adversely affect health, tourism, fisheries and food production in the coastal ocean, causing closure of fisheries, illness and even death. This project will obtain essential information to develop such understanding of the importance of bio-physical mechanisms in the formation of some HABs. Education of future Scientists: Studies of biophysical interactions in the ocean require background in biology, fluid mechanics, and instrumentation. This project will support one such student in an interdisciplinary training program.