Pengaruh Coastal Upwelling di Utara Kontinen Papua dan Gelombang Ekuatorial Rossby Terhadap Produktivitas Perairan dan Perikanan Tuna di Barat Pasifik Warm Pool.

Abstract

The Western Pacific Warm Pool (WPWP) waters is oligotrophic waters due to the existence of high salinity barrier layer which complicate mixing between low nutrient surface water with pycnocline layer. However, these waters able to supply more than 25% word tuna catches that dominated by Skipjack tuna (Katsuwonus pelamis), Yellowfin tuna (Thunnus albacares), Bigeye tuna (Thunnus obesus), and Albacore (Thunnus alalunga). This ability is thought to be influence by coastal upwelling in the north of Papua continent and equatorial Rossby wave event during ENSO. This study aims to examine the mechanism and influence of coastal upwelling and equatorial Rossby wave on primary productivity and tuna fisheries in the WPWP waters during ENSO. The study using exploratory methods by combining the methods of remote sensing satellite, mooring (Triton Buoy Mooring & ARGO Drifter), Nasa Ocean Biogeochemical Model (NOBM), and tuna fishing using Purse seine fleet. The study results showed that coastal upwelling in the north of Papua continent produced in response to the westerly wind and anomalies (WWBs) through the mechanisms of the Ekman transport, NGCC and NGCUC anomalies, and advection of equatorial Rossby wave (the north pole propagation) from the east of phillipines curved to coastal and oceanic waters north of Papua continent during west moonson. Under the influnce of coastal upwelling, enhancement of primary productivity of oceanic waters occurs through Ekman transport and NGCC and NGCUC anomalies which concentrate upwelling water masses and nutrient rich of coastal waters around the equator. The new nutrient input caused by Rossby waves occur through rototiller effect of Rossby wave which lifted nitracline and deep chlorophyll-a maximum (DCM) to the mixed layer (MLD) at the crest of the main wave and sink the low nutrien surface water and DCM deeper in the trough wave. Increased of primary productivity in surface waters is shown by the high concentration of chlorophyll-a and total chlorophyll (phytoplankton blooming) in the area of disturbance. The calculation result of coastal upwelling contribution to increased of primary productivity in coastal and oceanic waters are 73% and 68%. This value is higher than contribution of equatorial Rossby wave (<40%) in WCPW waters during ENSO either or other oligotrophic waters. It is caused by (a) upwelling of nitracline and DCM only reach shallow depth on the base of MLD and within range of SeaWIFS optical depth zone (25 – 40 m) while largest proportion of high chlorophyll-a concentration below both of the depth, (b) a high concentration of dissolved iron (FeD) in the waters during the ENSO restrictive the growth of specific microphytoplankton,and (c) a high consumtion rate of Diatom group by mesozooplankton are abundance in the upwelling area. Waters response as a result of these mechanisms is also shown by increased abudance of Cyanobacteria and Coccolithophores phytoplankton group in the area of new nutrient input and simultaneously dominate phytoplankton fluorescence in the waters. On the contrary, Diatom and Chlorophytes phytoplankton group have a low abudance. It is caused by high grazing rate of mesozooplankton such as copepoda and high concentration of FeD in the waters restrictive the growth both of phytoplankton group. Consequently, the waters are dominated by mesozooplankton and high abundance of biomass micronekton available as tuna food (prey) in distrubance region. The result of the synthesis previous research also showed that a high abundance of Cyanobacteria (especially genus Prochlorococcus) in DCM related to high biomass micronekton in the layer. Thus, tuna with high energy requirements tend to be present in areas with high concenration of prey such as distrubance region and in DCM. This situation is reflected by high abudance and catch rate (CPUE) of tuna in the oceanic waters affected by coastal upwelling and Rossby wave either or both of mechanism simultaneously during the west season. Tuna fishing also takes place during the east seasonal in oceanic waters corresponded with the occurrence of thermal front and chlorophyll-a front that is associated with high abundance of Cyanobacteria and Coccolithophores phytoplankton groups. Under the influence of equatorial Rossby wave, tuna fishing in the oceanic waters significanlly occured at the crest wave, on the contrary in the trough wave tuna fishing occurred with a low percentage of presence and only relies on the high abundance of micronekton in DCM. Based on this relationship between the abudance of Cyanobacteria group which dominate phytoplankton fluorescence and the abudance of prey, the members of microbial loop and chlorophyll-a can be used as biological indicators to determine potential tuna fishing ground using remote sensing satellite methods in WPWP waters.