The Effects of Reduced Oxygen Content on Predation and Siphon Cropping by the Brown Shrimp, Crangon crangon

Abstract

Abstract. Aquarium experiments were performed to test for critical oxygen levels in relation to the predation efficiency of C. crangon. Short‐term (60 h) experiments where done in normoxia (> 95%). 50, 40.30, and 20% oxygen saturation with the amphipod Bathyporeiapilosa as prey. A significantly reduced predation rate was detected at 30% oxygen. Sublethal effects of C. crangon on adult Macoma balthica (mainly by siphon cropping) were studied by measuring the condition of the clams (morphometric, somatic, and biochemical). To test for these effects experiments were conducted under normoxia and moderate hypoxia (40% oxygen); Condition and siphon indices revealed no change in condition after a 3‐week exposure to moderate hypoxia, while a significant reduction in the condition of adult clams was found in both normoxia and hypoxia when subjected to siphon cropping by C. crangon. No enhanced siphon cropping could be detected due to hypoxia.The results indicate that C. crangon is able to maintain its predatory role until a level of 30% oxygen in short‐term exposure. After a 20% oxygen level, however, the abiotic stress alters the functional role of C. crangon as a predator, indicating a threshold of 20–302 oxygen for the normal functioning of the predator‐prey food webs.