Fluid motion and solute distribution around sinking aggregates. II. Implications for remote detection by colonizing zooplankters

Marine snow aggregates are colonized by copepods, and encounter rates infer red from observed abundances of colonizers are high. We examined the potent ial for hydromechanical and chemical remote detection. The fluid disturbanc e generated by a sinking aggregate was described by solving the Navier-Stok es' equation for a sinking sphere at Reynolds numbers typical of marine sno w (up to 20). Fluid deformation rate, the component of the flow that can be perceived by copepods, attenuates rapidly, and detection distances estimat ed from knowledge of the hydromechanical sensitivity in copepods are insuff icient to account for the observed abundances of colonizers. We next solved the advection-diffusion equation to describe the chemical trail left by a leaking and sinking aggregate. The plume is long and slender and may be det ected by a horizontally cruising copepod. From the model of the plume and l iterature-based estimates of size-dependent aggregate leakage rates of amin o acids, we estimate that a threshold sensitivity to amino acids of 0.4 x 1 0(-7) M is required to account for observed abundances of colonizers. This is consistent with knowledge of the amino acid concentrations needed to eli cit behavioral responses in copepods.