Diversity and Density of Zooplankton in Active and Non-Active Fishing Zones off Kollam, Southwest Coast of India
Chiragkumar Katira *
Department of Aquatic Environment Management, Kerala University of Fisheries and Ocean Studies, Panangad-682506, Keralam, India.
Arun Konduri
Department of Aquatic Environment Management, Kerala University of Fisheries and Ocean Studies, Panangad-682506, Keralam, India.
Omdevsinh Vala *
Department of Aquaculture, Kerala University of Fisheries and Ocean Studies, Panangad-682506, Keralam, India.
Sagar Khara
Department of Aquaculture, Kerala University of Fisheries and Ocean Studies, Panangad-682506, Keralam, India.
*Author to whom correspondence should be addressed.
Abstract
Zooplankton constitute a fundamental component of marine pelagic ecosystems, serving as a critical trophic link between primary producers and higher trophic levels, including commercially important fish species. Understanding the distribution and abundance of zooplankton is essential for elucidating ecosystem processes and supporting ecosystem-based fisheries management. The present study investigated the diversity, composition, and density of zooplankton communities in active fishing zones (FZs) and adjacent non-fishing zones (NFZs) off Kollam, Keralam, along the southwestern Arabian Sea, a region of considerable ecological and economic significance.
Sampling was conducted monthly from November 2019 to February 2020 across near-shore, coastal, and offshore waters. Active fishing zones were identified using the Indigenous Traditional Knowledge (ITK) of local fishers in conjunction with acoustic observations from a GPS-coupled fish finder, whereas non-fishing zones were selected from nearby areas lacking active fishing operations and visible fish aggregations. Zooplankton samples were collected using a 200 µm mesh plankton net, preserved in 4% buffered formalin, and analysed using a Sedgwick–Rafter counting cell and standard taxonomic identification keys.
A total of 53 zooplankton taxa were recorded during the study period, contributing valuable baseline information on zooplankton biodiversity from the coastal waters off Kollam. Total zooplankton density ranged from 422 to 503 ind. m⁻³, with the highest density observed at FZ-1 during November and the lowest at NFZ-3 during December. Copepods constituted the dominant component of the zooplankton assemblage in both fishing and non-fishing zones, accounting for 49.6–72.1% of total abundance, followed by decapod larvae (9.7–24.4%) and chordates. Two-way analysis of variance (ANOVA) revealed significant spatial and temporal variations in zooplankton density among sampling zones and months. However, a consistent distinction between fishing and non-fishing zones was not evident, as elevated zooplankton densities occurred in both zone categories during different sampling periods.
The results indicate that temporal environmental variability exerts a stronger influence on zooplankton distribution than fishing-zone status alone in the coastal waters off Kollam. The study enhances understanding of plankton–fish trophic interactions in the southwestern Arabian Sea and provides a scientific foundation for future investigations on fish aggregation processes, marine ecosystem dynamics, and ecosystem-based fisheries management.
Keywords: Zooplankton, fishing zones, non-fishing zones, copepods, coastal ecosystem, Arabian Sea, Kollam, ecosystem-based fisheries, abundance