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Vertical and Horizontal Variability of Chlorophyll-a and Its Relationship with Environmental Parameters in the Waters of Sangihe and Talaud Islands, North Sulawesi, Indonesia

1Research Center for Oceanography, National Research and Innovation Agency (BRIN), Indonesia, Indonesia

2Research Center for Oceanography, National Research and Innovation Agency, Indonesia

3Fisheries Department, Faculty of Agriculture, Gadjah Mada University, Indonesia

4 Marine Science Department, Sriwijaya University, Indonesia

5 Research Center for Applied Microbiology, National Research and Innovation Agency, Indonesia

6 Polar Biological Oceanography, Alfred Wegener Institute, Germany

7 Marine Biology Department, Bremen University, Germany

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Received: 27 Sep 2023; Revised: 21 Dec 2023; Accepted: 7 Jan 2024; Available online: 5 Mar 2024; Published: 27 Mar 2024.

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Abstract

The chlorophyll-a is an important biological parameter that could act as a proxy to indicate the abundance of phytoplankton and the primary productivity of an aquatic ecosystem. This paper investigates the vertical and horizontal variability of chlorophyll-a in the waters of Sangihe and Talaud Islands, Indonesia, and its correlation with water environmental parameters. In this study, the distribution of chlorophyll-a, temperature, salinity, and nutrients (NO3 and PO4) from the surface to a depth of 200 m (photic zone) was measured at 29 research stations. The results showed that the distribution of chlorophyll-a in the waters of the Sangihe-Talaud Islands was varied vertically and horizontally. The waters around the Sangihe Islands generally exhibited a higher chlorophyll-a distribution and shallower Deep Chlorophyll Maxima compared to the water around the Talaud Islands. The concentration of chlorophyll-a varied between 0.0017 and 1.2155 mg.m-3, with most of the water column in Sangihe-Talaud considered oligotrophic, although some stations or depths were mesotrophic or slightly eutrophic. The maximum chlorophyll-a concentration was found in the sub-surface layer at depths between 46 and 101 m. The low N:P ratio (<16) and N:Si ratio (<1) indicate that the water columns of Sangihe-Talaud, up to a depth of 200m, were N-limited. Based on the GAM analysis, chlorophyll-a concentration in Sangihe-Talaud waters was primarily regulated by temperature, salinity, and the N:P ratio, with weak influence from phosphate and the N:Si ratio. The analysis also suggests that primary productivity in Sangihe-Talaud is sensitive to temperature changes, indicating its vulnerability to future warming events.

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Keywords: Celebes sea; deep chlorophyll maxima; generalized additive model; Mollucas sea; nutrients
Funding: Research Center for Oceanography, National Research and Innovation Agency (BRIN), Indonesia; Fisheries Department, Faculty of Agriculture, Gadjah Mada University, Indonesia; Marine Science Department, Faculty of Mathematics and Natural Science, Sriwijaya

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