Environmental flow regimes for Dysidea avara sponges

Abstract

The aim of our research is to design tank systems to culture Dysidea avara for the production of avarol. Flow information was needed to design culture tanks suitable for effective production. Water flow regimes were characterized over a 1-year period for a shallow rocky sublittoral environment in the Northwestern Mediterranean where D. avara sponges are particularly abundant. Three-dimensional Doppler current velocities at 8-10-m depths ranged from 5 to 15 cm/s over most seasons, occasionally spiking to 30-66 cm/s. A thermistor flow sensor was used to map flow fields in close proximity ( approximately 2 cm) to individual sponges at 4.5-, 8.8-, and 14.3-m depths. These "proximal flows" averaged 1.6 cm/s in calm seas and 5.9 cm/s during a storm, when the highest proximal flow (32.9 cm/s) was recorded next to a sponge at the shallowest station. Proximal flows diminished exponentially with depth, averaging 2.6 cm/s +/- 0.15 SE over the entire study. Flow visualization studies showed that oscillatory flow (0.20-0.33 Hz) was the most common regime around individual sponges. Sponges at the 4.5-m site maintained a compact morphology with large oscula year-around despite only seasonally high flows. Sponges at 8.8 m were more erect with large oscula on tall protuberances. At the lowest-flow 14.3-m site, sponges were more branched and heavily conulated, with small oscula. The relationship between sponge morphology and ambient flow regime is discussed.