DIVERSITY, DISTRIBUTION, AND ENVIRONMENTAL NICHES OF GELATINOUS ZOOPLANKTON SPECIES OF QATAR PELAGIC ECOSYSTEMS

Abstract

Gelatinous zooplankton are integral key components of marine ecosystems throughout the world, where they most often play an influential role in trophic dynamics, nutrient cycling, and ecosystem stability overall. In general, extreme environmental conditions in the Arabian Gulf and specifically off Qatar, characterized by high temperatures, elevated salinity, and low nutrient availability, introduce challenging conditions and unique niches for marine life. The present study focuses on the diversity and distribution of gelatinous zooplankton in the pelagic ecosystem of Qatar in relation to abiotic and biotic factors, with a description of the environmental niches for dominant species in terms of oceanographic (Sea Surface Temperature and Sea Surface Salinity) and trophic conditions (Chlorophyll-a and Zooplankton Dry Weight). Monthly samplings of gelatinous zooplankton were performed between February 2023 and January 2024 at seven coastal and four offshore stations around Qatar. A total of 22 gelatinous zooplankton species were identified. The dominating species were Oikopleura dioica, Diphyes chamissonis, Sagitta bipunctata, Flaccisagitta enflata, and Thalia democratica. The environmental parameters monitored during the study presented a marked seasonality: peak SST as high as 35°C and salinity values as high as over 50 PSU during summer. Such extremity in the environmental variables has affected the diversity and abundance of the zooplankton gelatinous community. The Cumulative Frequency Method used to build the dominant species ecological niches has shown that the relative tolerance of dominant species to environmental variables is very variable, ranging from species with a very broad ecological niche to those with a rather specialized one. In this framework, the present study highlights the adaptation of gelatinous zooplankton to the extreme pelagic environment of Qatar.