和歌山県田辺湾滝内及び内ノ浦の潮間帯のコアマモ群落におけるベントス群集

抄録

To examine effects of seagrass Zostera japonica on benthic animals, community structures of the benthos was compared among two Z. japonica meadows and a bare sandy area on intertidal flats at Takinai and Uchinoura, Tanabe Bay, Wakayama Prefecture, Japan, from August, 2004, to July, 2005. The mean number of species (N/0.0625 m²) was higher in the Z. japonica meadows (Takinai: 18.5-26.8, Uchinoura: 16.0-28.7) than in the bare sandy area (6.0-13.5). In addition, higher mean densities (N/m²) and mean wet weight (g/m²) of benthic animals were found in the seagrass meadow (Takinai: 6,408-10,763 and 147.0-533.5, respectively; Uchinoura: 1,632-9,061 and 162.0-562.0, respectively) than in the bare sandy area (368-1,424 and 12.1-49.1). Almost all of the species (82.5%) collected from the bare sandy area were also present in the Z. japonica meadows. Appearance rate and abundance of the benthic species were different between the Z. japonica meadows at Takinai and Uchinoura. The number of gastropod species was lower at Uchinoura than at Takinai, but the reverse was true for gastropod abundance. Although the number of species was higher in seagrass meadows than in the bare sandy area, the lower density of benthos at the latter site resulted in a higher evenness value (J') there than in the Z. japonica meadows, and the diversity index (H') at all three sites was, therefore, similar. Lower evenness in the Z. japonica meadows is also related to the notable dominance of certain species, such as Pullucina pisidium and Cirriformia tentaculata. From these results, it is concluded that Z. japonica meadows provide a valuable and hospitable environment for benthic animals, especially infauna, in sandy and muddy bottoms in the intertidal zone.