Identification of the Relationship Between Environmental Features and Copepod Abundances in the Kuroshio Waters Adjacent to Eastern Taiwan Using Generalized Additive Models

Spatial distribution patterns of copepod abundances were analyzed in relation to environmental variables in the Kuroshio waters adjacent to eastern Taiwan. Generalized additive models (GAMs) were applied to examine the relative influence of environmental factors on copepod abundance collected from 2005 to 2008 in this region. To construct a GAM, relationships were analyzed for physical and biotic variables (season, chlorophyll-a concentration, temp at 5 m, temp at 100 m, temp differences between 5 m and 100 m, salinity at 5 m). Stepwise GAM building revealed the relative importance of the variables in explaining the variance in copepod abundance. The variables ranked (1) season, (2) chl-a concentration, (3) temp_100 m, (4) sal_5 m, (5) temp_5 m and (6) temp_diff in decreasing order. Time series of copepod abundance standardized for physical and biotic factors quantified in the GAM implied a seasonal trend, which was highest in summer-autumn period and lowest in winter. The spatial pattern of copepod abundance was characterized by noticeable high abundances associated with higher chlorophyll-a concentration, lower temperature at 5 m and lower salinity at 5 m in the northwestern (121.5-122°E, 23.5-24.5°N) and southwestern (121-121.5°E, 22-23°N) nearshore region of the study area.