Sponge Aquaculture Trials in the East-Mediterranean Sea: New Approaches to Earlier Ideas

Aquaculture trials were conducted in the East Aegean Sea with Dysidea avara and Chondrosia reniformis to test the possibility of growing these sponges in the vicinity of sea-based fish farms. Culturing sponges in the vicinity of fish farms may have two benefits: the sponges may grow faster due to an increased availability of organic food and the pollution caused by the fish farms is remediated by the filtering activities of the sponges. An initial trial was conducted to compare growth of the two sponge species under floating fish cages to growth in a natural, pristine environment. Explants of D. avara were grown suspended on nylon threads, explants of C. reniformis were grown in cages constructed of stainless steel. After being one year in culture, nearly 100% of all explants of D. avara survived. Growth was highest underneath the fish cages, but growth rates were low compared to earlier studies. For C. reniformis survival at the pristine site was 100%, and growth was estimated at 800% per year. All explants cultured underneath the fish cages died due to smothering with sediment. After the initial trial, a new, cost-saving and growth promoting method for D. avara was tested at the fish farm location. Explants were grown on PVC pins that were mounted into a metal frame. Growth of the sponges on the pins was eight times faster than that of sponges growing on threads. We conclude that culturing D. avara under floating fish cages is feasible when using the new methodolog

Oxygen dynamics and flow patterns of Dysidea avara (Porifera: Demospongiae)

The present publication presents oxygen properties and pumping behaviour of Dysidea avara. Oxygen profiles were measured near and inside the atrial space of the osculum with a Clark-type micro-electrode. Pumping sponges had profiles with oxygen concentrations marginally lower than that of the aquarium water. In contrast, diffusive profiles, with a clear boundary layer above the sponge surface, and oxygen penetrating only 0.5 mm into the sponge tissue, were typically that of a sponge which was not pumping. Diffusive oxygen flux at the sponge surface was 4.2 µmol O2 cm2 d1 and the calculated volumetric filtration rate was 0.3 cm3 water cm3 sponge min1. The oxygen concentration in the osculum was temporally fluctuating between 95 and 59% saturation at a frequency of approximately once per minute. The combination of static oxygen micro-electrode measurements and particle tracking velocimetry (PTV) allowed us to simultaneously observe fine-scale oxygen fluxes and oscular flow patterns in active sponges, even at extremely low pumping rates. Oscular oxygen concentration and flow were correlated but not always synchronous to the second. Particle tracking velocimetry was used to visualize the flow field around the sponge and to distinguish sponge-generated flow from the unidirectional current in a flow-cel