Effects of hypoxia on movements and behavior of selected estuarine organisms from the southeastern United States

Hypoxia, or low dissolved oxygen, remains a common occurrence in estuarine waters as human activity in coastal areas expands. Fish kills, probably the most recognized indicator of these and other water quality problems, have significantly increased in recent years in many Southeastern United States estuaries. While entire aquatic communities are impacted by changes in avai lable oxygen, estuarine organisms serve as appropriate indicators of these changes as they exhibit complex physiological and behavioral responses to h ypoxia. The consequences of hypoxia for these species depend on their abili ty to detect and avoid areas of low dissolved oxygen. We conducted a series of two-way, replicated choice experiments with juvenile spot (Leiostomus x anthurus), pinfish (Lagodon rhomboides), croaker (Micropogonias undulatus), menhaden (Brevoortia tyrannus), white mullet (Mugil curema), mummichog (Fu ndulus heteroclitus), and brown shrimp (Penaeus aztecus) to determine their ability to detect and avoid specific levels of hypoxia. Additional data on organisms' movement patterns, aquatic surface respiration, and ventilation rates were collected. All species tested could detect and avoid 1 mg l(-1) dissolved oxygen. The hypoxia avoidance response differed among species, a s some species exhibited an avoidance threshold while others exhibited a gr aded avoidance response. These data supply baseline information necessary t o assess how some mobile estuarine organisms respond behaviorally to oxygen concentrations, and to understand how hypoxia more broadly impacts fish po pulations and estuarine community health. (C) 2000 Elsevier Science B.V. Al l rights reserved.