Effects of hypoxia and organic enrichment on growth of the brittle stars Amphiura filiformis (O.F. Muller) and Amphiura chiajei Forbes

Effects of oxygen concentration (normoxia: > 8.0 mg O-2 l(-1) and hypoxia: 1.8-2.2 mg O-2 l(-1)) and organic enrichment (control: 0 g C m(-2), medium: 27 g C m(-2) and high: 55 g C m(-2)) were studied on arm regeneration sate in two infaunal brittle star species, Amphiura filiformis and Amphiura chi ajei, during. two-month period in a flow-through aquaria system. In both sp ecies arm regeneration rates were significantly higher in organic enriched aquaria compared to control aquaria. Hypoxia significantly decreased the ar m regeneration rate in Amphiura filiformis but did not affect the rate in A mphiura chiajei. The results suggest that Amphiura filiformis is more sensi tive than Amphiura chiajei to hypoxia. Analyses on growth and energy alloca tion in Amphiura filiformis were carried out on the main factors oxygen con centration, organic enrichment, and amount of arm loss that simulated suble thal predation. The effect of sublethal predation was measured as growth of one or three arms that were amputated at the start of the experiment. Sign ificant interactions between sublethal predation and organic enrichment, an d oxygen concentration and organic enrichment, were observed for arm regene ration in Amphiura filiformis. Arm regeneration rate in specimens with one arm amputated differed significantly between the three treatments of organi c enrichment, but no difference was found in specimens with three arms ampu tated. In normoxia, arm regeneration rates increased in both medium and hig h organic load compared to control. However, in hypoxia, a positive growth response was only observed in the treatment medium organic load. At the ter mination of the experiment, dry mass of disks was significantly higher in s pecimens with one regenerated arm compared with specimens with three regene rated arms. The response of Amphiura filiformis to sublethal predation indi cates also an ability to allocate energy between disk growth (reproductive investment) and arm regeneration (somatic growth). (C) 1999 Elsevier Scienc e B.V. All rights reserved.