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Article Excerpt
Feeding pits created by rays may directly or indirectly affect the numbers of meiofauna. We examined the recovery rates of meiofauna inside feeding pits in both intertidal and subtidal areas. Cores were taken inside and immediately outside each pit. Numbers of total meiofauna, nematodes, and other meiofauna found within intertidal pits were significantly reduced following pit formation; the numerically dominant nematodes were reduced by 64%. Recovery to background levels occurred by 48 hours. Numbers of meiofauna in subtidal pits were either unaffected by the feeding activity of rays or differences were undetected due to rapid recovery within 24 h. This is the first study in which comparisons have been made concurrently in adjacent subtidal and intertidal areas.
Keywords: meiofauna, nematodes, fish, feeding, rays, disturbance
INTRODUCTION
Small benthic organisms such as meiofauna comprise one of the most abundant groups of organisms in soft-bottom communities (1) and have been shown to be important food resources for estuarine fishes and crustaceans (2, 3, 4, 5, 6, 7, 8, 9). The abundance and composition of benthic meiofaunal communities may be affected directly through feeding by higher trophic level organisms or indirectly through disturbance to the sediments that results from feeding activity (10, 11, 12, 13, 14, 15). Physical disturbance from factors such as hydrology affect sediment dynamics and composition, and may also influence the structure of meiofaunal communities (16, 17).
Fishes such as Leiostomus xanthurus Lacepede 1802 (spot), Fundulus heteroclitus Linnaeus 1766 (mummichog) and Platichthys stellatus Pallas 1788 (starry flounder), as well as crustaceans such as Palaemonetes pugio Holthuis 1949 (grass shrimp), have been shown to impact benthic meiofaunal communities either through direct feeding or disturbance (5, 7, 11). In fact, disturbance accounted for most of the mortality of nematodes in a study of spot feeding and accounted for over 30% of the mortality of copepods (17). However, predation by juvenile spot has been found to be non-selective and was not a significant source of meiofaunal mortality in some areas (18). Sediment disturbance caused by rays has been documented in various parts of the world (19). Rhinoptera bonasus Mitchill 1815 (cownose ray) have been documented to destroy eelgrass beds of Zostera marina Linnaeus 1753 replacing that habitat with unstable sand (20). Rays have been shown to reduce harpacticoid copepods in subtidal pits (21) and other meiofauna in intertidal feeding pits (14, 15), despite the fact that the rays are seeking food items such as crabs, other crustaceans (22), and mollusks (22, 23).
Recovery time of meiofauna depends on various factors including location, duration, intensity, and size of disturbance. In repeatedly disturbed large areas, such as dredged sites, recovery could take years (24). Similarly, in large-scale nodule mining areas, meiofaunal numbers were reduced post disturbance (25). Dernie et al. (26) noted that the recovery time of a benthic community significantly increased if disturbance intensity was increased. Vanaverbeke et al. (27) found that nematode communities may be altered due to frequent sand extraction. In areas of small-scale disturbance, previous studies have demonstrated that recovery of benthic organisms was fairly rapid following disturbance, usually within 24 h in many parts of the southeastern United States (16, 21, 28). In a study of subtidal pits formed by the Atlantic stingray Dasyatis sabina in Florida, nematodes took about 96 hours to recover (29). In our previous intertidal research, we found that the numbers of nematodes, ostracods, and oligochaetes were reduced in ray feeding pits immediately following feeding pit formation, but they recovered within 48 h (14). However, the timing of feeding pit formation affected recovery time (15). Numbers of meiofauna in pits that were formed earlier in the summer season recovered approximately 24 h faster than pits formed later in the season. This may be the result of the negative cumulative effect of repeated disturbance of the sediments, which may reduce the population size of possible recolonizers in the area. For polychaetes, Reise (30) noted a significant decrease in numbers after eight days of repeated human disturbance (raking) in a sandy...
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