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Biofilm-dwelling protozoa are a primary component of microbiota and play important roles in the functioning of microbial food webs such as the mediation of carbon and energy flux from plankton to benthos in marine ecosystems. To demonstrate the vertical pattern of the protozoan communities, a 1-month baseline survey was carried out in coastal waters of the Yellow Sea, northern China. A total of 40 samples were collected using glass slides as artificial substrates at four depths: 1, 2, 3.5 and 5 m. A total of 50 species were identified, comprising seven dominant and eight commonly distributed species. Species richness and individual species abundances showed a clear decreasing trend down the water column from 1 to 5 m, although the former peaked at a depth of 2 m. Multivariate approaches revealed that protozoan community structure differed significantly among the four depths, except for those at 2 and 3.5 m. Maximum values of species richness, diversity and evenness generally decreased with depth although they peaked at either 2 or 3.5 m. These results suggest that water depth may significantly shape the community patterns of biofilm-dwelling protozoa in marine ecosystems.

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The wake structure behind a circular cylinder-pair of unequal diameters as a function of incident flow angle α (0 • α 180 • ) has been investigated using the particle image velocimetry technique. The Reynolds number Re, centerto-center spacing ratio (P/D) and diameter ratio (d/D) are kept constant at 1200, 1.2 and 2/3, respectively. Instantaneous vorticity contours, mean flow fields and Reynolds shear stress contours are presented to elucidate the flow characteristics. The flow patterns behind the cylinder-pair change from that of a single bluff body to two vortex streets with increasing incident angle over the range of 0 • α 90 • , while the inverse phenomenon is observed when 90 • < α 180 • .

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The flow around two circular cylinders in tandem arrangement with different diameters has been investigated numerically. The upstream to downstream cylinder diameter ratio was kept constant at a value of d/D = 2/3 and the centre-to-centre distance was varied from 1.2D to 5D. The Reynolds number based on upstream cylinder diameter and free-stream velocity used in this study is equal to 200. Force coefficients and flow frequencies have been obtained from 2D fluid flow finite-element simulations. Single-wake shedding, reattachment and co-shedding regimes have been observed. The results show that, depending on initial perturbations, reattachment and co-shedding can be observed on a wide range of centre-to-centre distances (L/D ∈ [1.8, 3.8]), which defines the bi-stable flow range. The lower part of the bi-stable range is characterized by a lock-in phenomenon for which vortex-shedding from the upstream and downstream cylinders are synchronized when there are co-shedding flow conditions.