Inter-Research
Marine Ecology Progress Series

ABSTRACT: A series of field and laboratory experiments examined the factors that control fish-assemblage structure in barrier islands ponds on the Eastern Shore of Virginia. We investigated why surf-zone fishes, which are introduced to the island ponds during periodic wash-over events, are unable to persist for extended periods. We simulated over-wash events by collecting fishes from the shallow surf-zone and introducing them into 0.56 m² field enclosures. During summer months, surf-zone fishes typically died within 24 h. Levels of dissolved oxygen and temperature frequently exceeded the tolerance limits of the surf-zone fishes (demonstrated in a series of laboratory experiments), suggesting that these variables were responsible for fish mortality. In non-summer months, when dissolved oxygen and temperature stresses were ameliorated, surf-zone fishes could survive for months in the ponds. We conducted field-enclosure experiments at 3 fish densities in order to evaluate the survival and condition of a common surf-zone fish, Membras martinica (the rough silverside): (1) 8 M. martinica (14 fish m^-2), (2) 16 M. martinica (28 fish m^-2), and (3) 8 M. martinica + 8 Fundulus heteroclitus (28 fish m^-2). After approximately 1 mo during the spring, fall and winter, survival and condition of fishes in Treatments 2 and 3 were significantly reduced, suggesting that biological interactions were an important cause of surf-zone fish mortality. A temporal environmental stress gradient may result in seasonally varying importance of abiotic and biotic structuring factors.

KEY WORDS: Marsh pond · Fish · Competition · Seasonal · Dissolved oxygen · Community structure · Barrier Island · Virginia

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Published in MEPS Vol. 207 (2000) on November 22
Print ISSN: 0171-8630; Online ISSN: 1616-1599. Copyright © Inter-Research, Oldendorf/Luhe, 2000