Influence of habitat corridors on dispersal success, predation induced mortality and colonization of estuarine macrofauna in seagrass

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Title: Influence of habitat corridors on dispersal success, predation induced mortality and colonization of estuarine macrofauna in seagrass
Author: Darcy, Meaghan Christian
Advisors: David B. Eggleston, Committee Chair
Abstract: A habitat corridor is a landscape feature that is hypothesized to promote dispersal between habitat patches that would otherwise be isolated, and promote population persistence. Habitat corridors have not been widely explored in marine and estuarine systems. We used artificial seagrass units (ASUs) placed on unstructured sediment in Middle Marsh and Drum Shoals, Back and Bogue Sounds, North Carolina to create seagrass patches (1m2 and 4m2) separated by bare sediment or connected by additional ASUs, which made up a habitat corridor. We assessed the interactive effects of habitat corridor (presence or absence) and interpatch distance (5m or 10m), as well as the ratio of corridor width to patch width upon dispersal of grass shrimp, Palaemonetes sp., and bay scallops, Argopecten irradians in seagrass. We conducted mark-recapture experiments where marked grass shrimp or bay scallops were placed in one patch from each treatment (donor patch). Regardless of the presence of a habitat corridor, interpatch distance, or ratio of corridor width to patch width, dispersal between seagrass patches for grass shrimp and bay scallops did not significantly vary. There was, however, a significant site effect with the number of scallops successfully dispersing between seagrass patches significantly higher at Drum Shoals than at Middle Marsh. The small spatial scales of this study and the perception of a homogeneous environment may explain the lack of a dispersal response by grass shrimp. Site-specific differences in bay scallop dispersal may have been due to varying flow at the two study sites. Tethering experiments were conducted concurrently with dispersal experiments to assess the interactive effects of habitat corridor and interpatch distance, as well as perimeter to area ratio, on predation-induced mortality of bay scallops. Habitat corridor, interpatch distance or perimeter to area ratio did not significantly influence predation-induced mortality of scallops; however, there was a significant site by interpatch distance interaction. Predation rates were greater in patches separated by 10m at Middle Marsh than at Drum Shoals, whereas predation was greater in patches separated by 5m at Drum Shoals than at Middle Marsh. The lack of predation response to habitat corridors may have been due to a prey refuge in size (the scallops used in this study were relatively large, 35mm-50mm), or relatively low replication (N = 5) or another biotic or environmental factor not measured during this study. Colonization experiments were conducted to assess the interactive effects of habitat corridor and interpatch distance upon the colonization of estuarine macrofauna in seagrass. Neither mean density nor species diversity of estuarine macrofauna, nor mean density of individual taxonomic groups was significantly influenced by the presence of habitat corridors or by interpatch distance. Mean densities of slow-, intermediate-, and rapid-level dispersers were also not significantly influenced by the presence of habitat corridors or interpatch distance. The lack of community-level response may be explained by the interaction of hydrodynamics and its influence on the perception of a homogeneous or heterogeneous environment by dispersing organisms. Although habitat corridors may promote animal movement between habitat patches in terrestrial systems and for certain marine predators, the results from the present study do not confirm that habitat corridors are used by estuarine macrofauna for dispersal or colonization at relatively small spatial (10s of m) and temporal (hours to one month) scales. The coupled effects of hydrodynamics and habitat use should be considered when investigating distribution and abundance patterns of organisms with different dispersal abilities.
Date: 2003-11-21
Degree: MS
Discipline: Marine, Earth and Atmospheric Sciences
URI: http://www.lib.ncsu.edu/resolver/1840.16/395


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