SPATIAL HETEROGENEITY, BIOMASS AND SIZE STRUCTURE OF PLANKTON OF THE INDIAN-OCEAN - SOME GENERAL TRENDS

Data from surveys carried out in 1982 and 1990 in the Arabian Sea, and the South and North Sub-equatorial Divergence regions of the Indian O cean were used to analyse the spatial distribution and the size spectr a of zooplankton in relation to primary production and hydrophysical d ynamics on a scale of hundreds of kilometres. Spatial heterogeneity of biomass distributions increased with the size of organisms from phyto plankton to macrozooplankton. The zooplankton abundance spectra change d with hydrodynamic regimes of water dynamics (cyclonic, anticyclonic eddies, frontal zones) and could be approximated by linear regressions in logarithmic scale. From values of the normalised spatial variance of plankton biomass components (phyto-, meso-, macroplankton) it is co ncluded that heterogeneous 'fields' of predators exist on more uniform 'fields' of prey. Biomass ratios of phytoplankton (chlorophyll a), mi crozoo-, mesozoo- and macrozooplankton form an inverted pyramid of bio mass in the studied regions. Maximal slopes for zooplankton abundance size spectra have been observed in regions of maximum primary producti on, i.e. in regions of high primary production the smallest zooplankto n dominate the total zooplankton. This is also true for regions of hig h phytoplankton turnover. The ratio of primary production to herbivore production indicates that the highest efficiency of transfer from aut otrophs to heterotrophs is carried out by the smaller zooplankton. The ratio of primary production to zooplankton biomass increases as the s pectrum slope of the zooplankton abundance increases. This means that the ratio increases when small mesoplanktonic organisms become more do minant amongst the mesoplankton size range. Both types of relationship s can be approximated by diminishing non-linear equations. The values of these 2 ratios can change an order of magnitude on a scale of hundr eds of kilometres.