Spatial zonation of zooplankton in the northwestern Arabian Sea: A multivariate approach

Abstract

Latitudinal variation in abundance, diversity, dominance pattern and zonation of the major groups of zooplankton was studied n the coastal waters of northwestern Arabian Sea, between 25°44' N and 10°44' N. Maxwell Boltzmann Statistic and multivariate approach by factor analysis adopting varimax rotation was used for grouping of the plankton. Maxwell Boltzmann test resulted in significant clustering tendency during day and night with relatively high values during night. The value of the index based on the proportional abundance of all the groups considered together in each quadrat, decreased gradually from Gulf of Aden to off Karachi along the Pakistan Coast with maximum value in the Saudi Arabian Coast. But the index evaluated for each taxon, implied a significant positive correlation with the variation (%) in the spatial distribution, having high value in the Saudi Arabian Coast due to nutrient enrichment of the surface by upwelling and decreases towards north during day. Thus, the zooplankton taxa are not randomly or uniformly distributed but have a patchy distribution with degree of patchiness much more than that given by the theoretical distribution. Significant inverse relationship was observed between the value of the index and the total variance explained by the significant factor groups of the zooplankton taxa. The zooplankton samples represented single continuously varying plankton population rather than separate and distinct populations thereby ruling out the possibility of any sudden and unpredictable changes in the plankton population during the transitional period, March to June in the coastal regions of the Northwestern Arabian Sea. Day collections are more diverse than the night collections with relatively high equality in the spatial distribution.