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Abstract
Estuarine hypoxia (<4.0 mg O2/litre) caused by eutrophication has been linked to mass mortality of fish and Crustacea. However, there is little information on the hypoxia tolerance of New Zealand's estuarine mysid shrimps and/or if these species exhibit behavioural and physiological responses to low dissolved oxygen. Laboratory experiments demonstrated the native mysid shrimp Tenagomysis novae‐zealandiae was tolerant of dissolved oxygen levels of 4.0 mg O2/litre and 1.5 mg O2/litre, but very sensitive to levels <0.5 mg O2/litre. Mortality occurred within 22 min when dissolved oxygen levels decreased to 0.5 mg O2/ litre, although the 7 h LC50 value for T. novae‐zealandiae was calculated to be 1.11 mg O2/litre. There was a clear relationship between T. novae‐zealandiae activity and decreasing dissolved oxygen levels. Reduced activity appears to be a strategy of T. novae‐zealandiae to tolerate moderate hypoxia (4.0 and 1.5 mg O2/litre). However, this behaviour was unsuccessful at 0.5 mg O2/litre, as all test organisms demonstrated erratic behaviour and escape responses immediately before loss of equilibrium and mortality.