Long-term changes in the abundance and community structure of net-phytoplankton in Oshoro Bay, Hokkaido [Japan]
2010
Fukui, D., Hokkaido Univ., Hakodate (Japan). Faculty of Fisheries Sciences | Kitatsuji, S. | Ikeda, T. | Shiga, N. | Yamaguchi, A.
Phytoplankton samplings with 0.1 mm mesh nets were made bi-weekly or monthly at Oshoro-Bay, western Hokkaido, during 1984 through 2004 (21 years). Sea surface temperature (SST), specific gravity (SG) and transparency (TRANS) were also determined at each sampling. Daylight length (DAYLIGHT) was available from Homepage of Meteological Agency. Throughout the study period, the abundance of phytoplankton ranged from 5.2 to 179,682 cells/L (grand mean: 3,037) in which centric diatoms were most abundant (mean: 79.5% of the total), followed by pennate diatoms (17.0%) and dinoflagellates (3.5%). The total number of species identified was 99 for centric diatoms, 35 for pennate diatoms and 23 for dinoflagellates. From a cluster analysis based on Bray-Curtis similarity index, phytoplankton communities were classified into five groups. With regards to long-term patterns, the regime shift (cool to warm) that occurred in 1989/1990 in the broader Northern Hemisphere was detected in the anomalies of SST and the total phytoplankton abundance, but was not reflected in the data for SG, TRANS or phytoplankton community structure. Rather, partial autocorrelation analysis for environmental factors (SST, SG, TRANS and DAYLIGHT) and phytoplankton abundance, and a cluster analysis for phytoplankton community structure revealed that the most predominant pattern was seasonal, reflecting local climate events with 12-month cycles.
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