Re-evaluation of ‘paradox of mesozooplankton’ in the eastern Arabian Sea based on ship and satellite observations

Abstract

In the central and eastern Arabian Sea (EAS), biomass and production of phytoplankton are known to vary spatially and seasonally whereas, biomass of mesozooplankton (MSP) is reported to be constant. This apparent contradiction has been called 'Arabian Sea Paradox'. However, it is important to note that the paradox of MSP is based on a very limited seasonal data (from 5-7 locations). Therefore, we reconsidered the paradox of MSP based on intensive in-situ observations at 39 -40 locations in the EAS. In agreement with the known seasonal difference in phytoplankton standing stock in the EAS, we analysed the MSP data in two ways using two-way nested ANOVA. In 'basin scale' analysis, MSP data were analysed from the EAS were pooled and seasonal and inshore -offshore variations were analysed for the entire region. In 'regional scale' analysis, MSP data were analysed separately for (a) northern region (north of 15°N) and (b) southern regions (15°N and south of it). Satellite data of chlorophyll a, SST and wind speed were also analysed to show the major differences in oceanographic features in the northern and southern EAS. The analyses showed prominently high chlorophyll a (av. 1mg m ) in the southern region during most of the year mainly due to thermohaline stratification. The MSP biomass was distributed almost in a similar way as that of phytoplankton stock with statistically significant spatial and seasonal variations in the northern and southern regions. In this paper, we review the 'paradox of MSP' and present clear and new evidences to show that this concept is not logically applicable for EAS.

Measurement of marine productivity using 15N and 13C tracers: Some methodological aspects

“…The climatology, hydrography and circulation of the northern Indian Ocean have been described by many authors (e.g., Swallow 1984;Shetye 1999;Schott and McCreary 2001;Balachandran et al 2008;Jyothibabu et al 2010). Here we give a very brief description.…”

Why Gulf of Mannar is a Marine Biological Paradise?

“…Pre-Monsoon (March-May) and Northeast Monsoon (November -February) are low productive periods in the SEAS along the southwest coast of India ( Supplementary Figure 3). This situation is caused by surface layer stratification through solar heating during the Pre-Monsoon and the intrusion of low saline oceanic Bay of Bengal waters during the Northeast Monsoon 22 . Both these cause meagre nutrient availability in the upper euphotic column creating low phytoplankton biomass (chlorophyll-a) concentration 22 .…”

Why do satellite imageries show exceptionally high chlorophyll in the Gulf of Mannar and the Palk Bay during the Norteast Monsoon?

“…One such application is the use of satellite chlorophyll a (hereafter chlorophyll) to identify synoptic oceanographic features (Dwivedi et al 2006;Jyothibabu et al 2010;Rao et al 2011). However, it is fundamental that there are chances of misinterpretation of satellite chlorophyll in optically complex coastal waters (Sathyendranath et al 1989).…”