The investigations under the biological programme will be carried out jointly by two agencies. NIO will undertake studies on bacteria, micro- and meso -zooplankton, particulate organic carbon and quantification of export fluxes. NIO, jointly with Department of Marine Sciences & Marine Biotechnology of Goa University will carry out investigations on Primary production, New production and Ocean color. Goa University has a licensed and full fledged radioisotope laboratory.
Participants
M. Madhupratap Principal Investigator
N. Ramaiah Co-Principal Investigator
S. Raghukumar
C. Raghukumar
T. Suresh
National Institute of Oceanography, Dona Paula , Goa.
K.K.C. Nair
T.C.Gopalakrishnan
P.Haridas
Regional Centre, National Institute of Oceanography , Cochin
Usha Muraleedharan Principal Investigator
Goa University , Goa.
Background
Our knowledge and mindsets on marine ecology have undergone major changes during the past 20 years owing mainly to several efforts internationally on the world oceans. There are many regions of the ocean that are unique in their geography, biota, ecotype as well as in their influence exerted on global weather. The Bay of Bengal is one such region. It is probably a fact that the Bay of Bengal is the world's largest estuary when one considers its area north of 12° N. Unfortunately, unlike the attention received by the Arabian Sea, its west coast counterpart, the Bay is really under-studied and less understood, albeit being the sea on the other coast of our country! In addition, the number of cruises that were undertaken for studying the Bay of Bengal during the IIOE were very few. By a cursory look at Krey and Babenerd (1976) Atlas on phytoplankton, one can easily notice that there were no more than two cruises across the Bay (along the Indian coast) and that there is a clear lacuna of efforts in studying the northern Bay of Bengal. It will be, therefore, unwise to rely on such limiting data for any projections of biological productivity. Further, very little work - on phytoplankton ecology, chlorophyll concentration, primary production, annual cycles of bloom formation, zooplankton variability, bacterial abundance and production rates - has been done in the Bay as a follow up of IIOE. So, it is of immediate necessity to study the Bay for a better resolution of the biology of this ‘uniquely placed peculiar marine system'.
One of the questions that
needs to be addressed is the role of the Bay of Bengal in the biological
processes and in the overall biogeochemistry of the Indian Ocean. The
numerous chemical, geological as well as biological processes occurring
throughout the water column in the sea are, to a large extent, controlled,
influenced or moderated by the autotrophic fixation of carbon dioxide in
the euphotic zone. Essentially, the organic biomass in chlorophyll bearing
phytotoplankton acts as a major reservoir of carbonaceous, nitrogenous,
phosphorous and silicious nutrients as well as many micronutrients. They
trap these nutrients by assimilation into cellular material. Its dissimilation-through
exudation, herbivory, senility and death - leads to release of these nutrients.
In essence, the photosynthetic production in the upper layers is, thus,
a major player in the fate and distribution of very many biologically essential
elements. A fine-tuned understanding of the primary productivity potential
of the Bay is, therefore, needed for any effort aimed at delineating the
complexity of biogeochemical processes that are under constant influence
of an array of physical forcings. It is also apparent that the fish species
composition is very different in the Bay compared to that in the Arabian
Sea thus pointing to a different species composition at the lower strata
of the food web in the Bay. Being primary and/or secondary consumers, the
zooplankton account for almost a tenth of the marine biomass. And, in general,
all life sustaining elements also pass through these consumers. In this
process, these elements undergo rapid changes in their form and concentration.
Any biological investigation that has an interest in quantifying carbon
fluxes, like the one being planned for the Bay, needs an assessment of
secondary production by determining zooplankton biomass. Now that the microzooplankton
are understood to account for almost half the carbon quantities in terms
of biomass, a study that looks at their quantities and types will be helpful
in understanding the biological/ ecological processes in the Bay. The role
of bacteria in energy transfer, organic material degradation and nutrient(s)
regeneration in the marine environment is generally quite well understood.
Bacteria are the major links to many biological and non-biological events
in the oceans. Their catabolic potentials are the ones that govern the
fate and speed of organic material bio-transformation in the entire water
column as well as in the deep sediments. Their association with marine
aggregates and all types of particles in the sea influences dissolution
and downward transport of particles. As there have been no attempts for
understanding many of these events from the Bay, it will be important to
study the role and significance of bacteria by determining their abundance
and production .
Investigations on phytoplankton and primary production
For the Arabian Sea, data on primary production and phytoplankton composition, abundance and seasonal variations are available (see Bhattathiri et al.,1996; Sawant and Madhupratap, 1996 and references therein). Preliminary studies have also indicated the potential of some species as a source of commercially important products and mass culture (Muraleedharan et al., 1989). A systematic study was carried out during the premonsoon and monsoon periods of 1989 to evaluate the seasonal variations of chlorophyll a, carotenoids and phytoplankton numbers in the coastal waters of Goa, in relation to the rapidly fluctuating physical environment (Muraleedharan and Pant, communicated). Other studies to relate primary production in the Indian Ocean to hydrological structure are underway (Muraleedharan and Muraleedharan, unpublished). In the case of the Bay, these informations are sparse (Madhupratap and Parulekar,1993). However, a close coupling of physical processes and biological production is evident in coastal waters of both the Arabian Sea and the Bay of Bengal.
While processes through which nutrients might become available in the euphotic zone of the open ocean of the Bay are poorly understood, it is believed that regenerated nutrients may have an important role. There is a need to differentiate between production through recycling and new production, from both coastal and open waters. It is needless, therefore, to emphasize on the need for measuring the spatial and temporal variations in primary productivity and chlorophyll concentrations and estimating the extent of new production from the Bay, in order to assess its productivity potential/ carbon fixation rates.
Recent studies under the
JGOFS (India) Program have indeed contributed towards a better understanding
of the oceanic processes in the eastern Arabian Sea. We have used clean
techniques and the protocols for measuring primary production rates have
helped to obtain highly reliable data. This experience is vital and will
assist us to obtain an insight into the biology of the Bay .
Method
Sampling will be done from the euphotic zone at various depths and provinces of the Bay for measuring primary production. Chlorophyll concentrations in each of these samples will be determined following the JGOFS protocols as was done for the Arabian Sea studies. We will follow clean techniques, using replicates for light and dark bottles and in situ incubation procedures. Additional parameters such as phytoplankton cell counts and particulate organic carbon and nitrogen will be estimated using the CHN analyser. Using the satellite imageries ( now available through Sea WIFS), attempts will be made to relate the sea truth on pigment concentrations to the remotely sensed observations for the entire Bay. Chlorophyll concentrations will be measured by Fluorometer and also calibrated for in situ CTD fluorescence profiles
Investigations on New Production
The role of new production - the fraction of primary production due to the assimilation of nitrogenous nutrients reaching euphotic waters through either upwelling and/or land drainage - in the overall primary productivity of the Bay needs a clear and immediate understanding. This is particularly so owing to the voluminous inputs of land sediments containing many nitrogenous nutrients to the Bay. Based on our experiences of measuring new production from the Arabian Sea (unpublished results) we propose to measure incorporation of various nitrogenous nutrients (15N- ammonia, -urea and –nitrate), taking care to work out appropriate concentrations for experimental incubations. It should thus be possible to calculate the new production fraction of the primary production in the Bay. Samples from all locations from where we will measure primary production using 14C will be analyzed for new production.
Studies on Bacterioplankton
One of the most noticeable advances in ocean biology during the past decade has been the understanding of the role, importance of and contribution from bacterioplankton in the overall biological processes. Of particular interest in this regard are the organotrophic bacteria, the key players in cycling of all biologically essential elements. More importantly, they serve as food for nearly all groups of microzooplankton, the understanding of which has helped us to appreciate them as 'producers'. In addition, the mechanism(s) of their involvement in particle formation and/or utilization is/are currently drawing attention of marine scientists worldwide.
Studies on the role and abundance of bacterioplankton in the Arabian Sea have helped us to substantiate their role in the microbial loop (Madhupratap et al, 1996; Ramaiah et al 1996). The so-called 'stable biomass of mesozooplankton paradox' is, in all likelihood, driven by the bacterioplankton that abound and grow rather rapidly during periods of low primary production. Many more scientific experiments are needed in this direction. Thus, a considerable interest on bacterioplankton has been recently developed from our studies in the Arabian Sea during the JGOFS (India). In the case of the Bay of Bengal, however, not a single point of observation on bacterial production rates is available, although a recent study by Kumar et al (1998) did examine a few samples for abundance of bacterioplankton. In that study it was observed that there was a close relationship between bacterial abundance and concentration and sizes of transparent exopolymer particles (TEPs) in the deeper waters. While the TEPs are important in fuelling the bacterial respiration at such depths, the ability of bacteria to catabolize other nutrients in the deep is of special significance in the particle fluxes. As the biological events and processes would be influenced in the Bay to a larger extent by several different features already listed above, it would be important to decipher the different roles played by bacterioplankton by studying their abundance (both free-living as well as , particle and TEPs attached) and production rates.
Method
Water samples collected from various selected depths at all sampling locations will be analyzed for the following parameters:
Bacterial abundance through epifluorescence microscopy by following JGOFS protocols (1994)
Bacterial production rates in the upper 150m by measuring 3H-methyl-thymidine incorporation rates
Determination of microbial ATP concentration to estimate the stocks of bacterial carbon.
Bacterial association with
TEPs and its possible influence on the downward flux.
Studies on meso and microzooplankton
Secondary production in the world oceans is dominated by the herbivorous zooplankton. Together with their carnivorous cousins, they link the energy flow in the marine environment. They are rapid contributors to nutrient regeneration processes, besides accelerating the flux of organic carbon through migration and through their feces that is exported following ingestion, digestion and defecation. There are numerous studies from the Arabian Sea on zooplankton abundance, species composition and their distribution in space and time (see Madhupratap and Parulekar, 1993 for a review). Despite such a plethora of information from the west coast, there has been no follow up of zooplanktonology from the Bay. There is virtually no information on their vertical distribution, particularly from depths below 200m. Knowledge of their abundance and composition is specially required if we need to realize the modes of bio-transport of organic matter out of the euphotic zone in the Bay, which has already been shown to have a complex picture of material fluxes and sequestration in the deep sediments (Kumar et al 1998).
From the recently concluded JGOFS (India) Arabian Sea Program, it has been clearly established that the microzooplankton forms a sizeable fraction of the zooplankton standing stock/biomass. Most notably, the microzooplankton carbon is sometimes more than that of mesozooplankton (Gauns et al 1996). There is no study from the Bay that has examined the microzooplankton component. It should be interesting to work on this group to know their abundance, type and seasonal cycles as well as to decipher if, as is the case in the Arabian Sea, they have a role in microbial loop in the Bay. Apparently, many other questions also persist about the Bay biology owing to scanty information on the overall productivity potential and fisheries. It would be of good interest to the oceanographers to relate the secondary production in the Bay through a meaningful assessment of zooplankton biomass.
It is often believed that
the northern Indian Ocean is a single geographic area as no major differences
in the zooplankton faunal elements are yet reported between the Arabian
Sea and the Bay. However, it would be worthwhile to investigate the seasonal
cycles of both meso- and micro-zooplankton and their species composition.
In this regard investigations of Madhupratap (1987); Madhupratap and Haridas
(1990) are helpful as they reported increasing zooplankton diversity from
the neretic to oceanic and deep waters. As the microzooplankton composition
in the open waters of the Arabian Sea have begun to be understood, it will
further help if this group with regard to its composition and annual/seasonal
variability in the Bay, is also investigated.
Method
At each sampling station, diurnal and vertical hauls of multiple plankton net from bottom and up will be made for sampling mesozooplankton (200 m m mesh width) at predetermined depths. Five different samples from surface (mixed layer), thermocline, oxygen minimum zone (OMZ), stratified zone immediately below thermocline, and 500-1000m column will be collected for the following studies.
Biomass determinations and analyses for species composition of mesozooplankton and diurnal migration.
Estimation of mesozooplankton carbon content after size fractionation
Collection of microzooplankton
from upper 200m and analyses for species composition, biomass, carbon turnover
and grazing rates.
Sediment trap Studies
It is very essential to get
a direct handle to the actual export of carbon from the upper ocean. This
will be achieved by the deployment of sediment traps as was done in the
Arabian Sea studies.
Method
Floating sediment traps will
be deployed at two depths (just below the euphotic zone and at 300 m).
Exported matter will be collected in bottles which will be programmed to
give a time series data base (every 12h) for 4 to 5 days. These samples
will be analysed for carbon content and compared with productivity measurements.
References
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Gauns, M., R. Mohanraju and M. Madhupratap, Studies on the microzooplankton from the Central and Eastern Arabian Sea, Curr. Sci., 71, 874-877, 1996.
Kumar, D. M., V.V.S.S. Sarma, M. Ramaiah, M. Gauns and S.N. De Souza, Biogeochemical significance of transparent exopolymer particles in the ocean. Geophys. Res. Lett., 25, 81 – 84, 1998.
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Ramaiah, N., S. Raghukumar and M. Gauns, Bacterial abundance and production in the Central and Eastern Arabian Sea, Curr. Sci., 71, 878-882, 1996.
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