Document: LIS-3-80-6

Responses of an estuarine fish community to small frequent versus large infrequent disturbances.

EBY, L.A.* and L.B.CROWDER

Duke University Marine Lab Beaufort NC 28516 USA ¹

Abstract:
The role of disturbance in influencing ecosystems is well recognized in ecology. Disturbances span a range of extent, duration, frequency, and while the understanding of small frequent disturbances is rapidly advancing, the ecological effects of large infrequent disturbances are not well understood. During three years (1997-1999) of seasonal sampling of the fish community and water quality in a North Carolina estuary, the system experienced periodic hypoxia, occurring on the scale of days to weeks and meters to kilometers, throughout the summer. In the fall of 1999, North Carolina experienced several hurricanes and major flooding in coastal rivers and estuaries. In September, record high inflows into the Neuse reduced salinities in most of the estuary to 0 ppt. Lower estuarine areas, where deeper bottom salinities remained above 0 ppt, experienced stratification and bottom waters became hypoxic. We evaluated predictions, based on our experiences with small frequent disturbances, for the responses of the fish community (e.g., abundance, diversity, habitat utilization, and rate of return) to this flooding. Although these events occur at very different scales, they have many similar attributes. For example, many species experienced a threshold response where catches of most fish species drop an order of magnitude in the disturbed area. Predictions failed more often in estuarine areas where fish were exposed to multiple stresses (unlike in our small frequent disturbances).

Keywords: estuarine, disturbance, flooding, hypoxia, fish

This abstract is being presented at: 8:30 AM in session:
Oral Session #57: Ocean-Going Fish and Mammals.