Interaction between water flow and oxygen deficiency on growth in the infaunal brittle star Amphiura filiformis (Echinodermata : Ophiuroidea)

Interactions between 'oxygen concentration' (normoxia: >80% oxygen saturati on, and hypoxia: 18% oxygen saturation) and 'water flow velocity' (low: 0.1 cm s(-1), and moderate: 0.5 cm s(-1)) were studied on growth rates in the brittle star Amphiura filiformis in a flow-through aquaria system. Effects of 'sublethal predation' on growth rates were investigated as 'number of am putated arms' (1 and 3 arms) and 'amputation of the disk'. A significant in teraction between oxygen concentration and water how velocity was observed in mean arm regeneration rate, but in both flow velocities higher mean arm regeneration rates were observed in normoxia compared to hypoxia. In hypoxi a a positive response in arm regeneration rate was observed in moderate flo w compared to low flow velocity. In normoxia, however, no response to flow velocity was observed. The latter observation indicates that Amphiura filif ormis is able to maintain the ventilation of the burrow at low flow velocit ies. but in low oxygen concentrations hydrodynamic forces seem to affect gr owth. A significant interaction between oxygen concentration and disk amput ation was observed in both arm and disk regeneration rates, indicating that the disk is the major organ for gas exchange in this species. The number o f arms amputated, however, did not affect mean arm regeneration rate. The r esults obtained in this study suggest that the secondary production in subt idal infaunal populations could be negatively affected by low oxygen concen trations and that this response is even more negative in combination with l ow flow velocities in the near-bottom water. (C) 2000 Elsevier Science B.V. All rights reserved.