Horizontal gradient in fish assemblage structures in and around a seagrass habitat: some implications for seagrass habitat conservation |
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Authors: | Masahiro Horinouchi |
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Institution: | (1) Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatsucho, Matsue, Shimane 690-8504, Japan |
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Abstract: | Horizontal gradients in fish assemblage structures in and around a seagrass habitat were evaluated by visual observations.
The assemblage structures clearly differed between open microhabitats lacking seagrass, i.e., nearby sand and the area adjoining
the outer margin of the seagrass bed (referred to as “outer gap”), and microhabitats with seagrass within the overall seagrass
bed, although not differing among the latter microhabitats, including both edge and core portions. Such open microhabitats
were found to be not always inferior, but nearly equal to or even sometimes greatly superior in fish species’ diversity and/or
abundance to the microhabitats with seagrass. In particular, the outer gap was always ranked first in total species’ number
and had outstanding abundance in spring. Similar open microhabitats adjoining seagrass walls facing the sand patch within
the seagrass bed (referred to as “inner gap”) in spring were also characterized by higher fish species and individual numbers.
The 11 most abundant fishes showed four discrete distribution patterns (three recognized herein and one implied by precedent
studies), such contributing to a horizontal gradient in the fish assemblage structure. While no fishes showed a preference
for the edge or core of the seagrass bed, group-forming juveniles of several species favored gap microhabitats, suggesting
that, in addition to the traditionally recognized edge and core microhabitats, the concept of gap microhabitats should be
included in seagrass conservation ecology. |
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Keywords: | Seagrass-fish assemblage structure Edge Core Gap Conservation |
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