Environmental influences on zooplankton diversity in the Kavaratti lagoon and offshore, Lakshadweep Archipelago, India

Highlights

• Copepods are the most dominant zooplankton group observed in Kavaratti lagoon.

• Zooplankton density showed positive correlation with temperature and nutrients.

• Chlorophyll-a is an important predictor for copepod abundance and diversity.

• Zooplankton’s abundance and occurrence assessed by CCA and Shannon—Wiener-index.

• The species richness values of zooplankton indicated the ecological stress.

Abstract

The present study aimed to analyse the influence of physico-chemical properties on zooplankton assemblages and species diversity in a lagoon system. The study was carried out in coral reef lagoon of Kavaratti Island, Lakshadweep Archipelago, India during the monsoon of the year 2017. Zooplankton assemblages, distributed among 56 taxonomic units, were found to be dominated by copepods (63.27%, 34 taxa) followed by cladocerans (11.14%, 7 taxa), ostracods (9.87%, 2 taxa), ciliates (6.23%, 6 taxa), chaetognaths (4.32%, 3 taxa), leptomedusae, (1.25%, 1 taxa), and appendicularians (3.92%, 3 taxa). Copepods assemblages showed maximum density of 14326 ind m⁻³ from S1, in which leptomedusea was the lowest abundant taxa (284 ind m⁻³). Shannon–Wiener-index between 3.725–3.860 attested to the fact that the species diversity and richness predominated in lagoon than that in offshore. Canonical Correspondence Analysis revealed the environmental parameters influencing the abundance and occurrence zooplankton community in the study area.

Introduction

Coral lagoons are considered to be the most productive biologically diverse and complex ecosystems of the marine environment; and hence they are referred to as the marine equivalent of tropical rainforest (Ahmad et al., 2011, Anu et al., 2007, Jose et al., 2010, Pagano et al., 2017). Recently, the influence of environment on planktonic communities has been topical and many ecological studies have specifically focused on planktonic species diversity and distribution (Banerjee et al., 2018, Bersano and Salvador, 2017, Jacobsen et al., 2018, Thabet et al., 2018). Zooplanktons are a primary component of the aquatic food chain and play a significant role in the functioning of aquatic food webs (Abdullah et al., 2017). Previous studies suggest that zooplankton groups are good indicators of eutrophication, water quality, acidification of water bodies as well as turbidity of lakes and reservoirs (Coelho et al., 2015, Muylaert et al., 2006). Zooplankton species composition is responsive to changes in abiotic factors such as temperature, pH, salinity, dissolved oxygen, and heavy metal primarily due to the differences in physiological tolerance of the species (Wissel and Boeing, 2003). Zooplankton species depend upon the abundance of phytoplankton composition, predation efficiency, size prey selection of fish as well as nutrient enrichment (Coelho et al., 2015). Due to the population growth and overexploitation, the anthropogenic stress on the marine ecosystem, especially the coral reefs are degrading in an enormous speed (Baum et al., 2016).

Kavaratti lagoon of Lakshadweep Archipelago India is endowed with higher dynamics of zooplankton diversity and composition, as well as the higher rate of primary productivity and which depends up on the depth and area of this lagoon (Goswami and Goswami, 1990). Lakshadweep archipelago of India consists of several small oceanic islands and coral lagoons between latitude 10–12$°$N and longitude 72–74$°$E in the Arabian Sea. Atolls are another highly productive major type of coral reef ecosystem and characterized with prominent canter lagoon which shows distinctive peculiarities compared to the surrounding oceans in their autotrophic abundance (Goldberg, 2016, Michotey et al., 2012). The primary production rate of macro algae and seagrass in the lagoon of these islands was several times higher than that of phytoplankton productivity (Dhargalkar and Shaikh, 2000). For decades, many of the authors investigated zooplankton dynamics in the coastal lagoon and fresh water ecosystems and illustrated the vital role of zooplankton in food web structures by transferring carbon to the higher trophic levels of organism (Ziadi et al., 2015). The occurrence and distribution of plankton fauna limited by a wide range of environmental factors such as availability of light, pH, temperature, salinity and dissolved oxygen (Ahmad et al., 2014, Ahmad et al., 2011, Paturej et al., 2017). In addition, many researchers (Abdul et al., 2016, An et al., 2012, Cardoso et al., 2012) claimed that the availability of nutrients also have a significant impact on the abundance and structure of the zooplankton community. Zooplankton species can also affect the relative abundance of the phytoplankton biomass not only by grazing but also by the nutrient regeneration (Sinistro et al., 2007). Zooplanktons are primary consumers in pelagic ecosystems and function as the conduits of lipids from phytoplankton to fish (Gladyshev et al., 2010). Zooplankton species, being one of the most important biotic elements that can impact all the functional aspects of aquatic ecosystems including trophic networks, food chains, energy flow and the circulation of matter, hence occupy the central position of the pelagic zone of food webs (Dodson et al., 1997). Planktons are especially good indicators of climate change in the marine environment for several reasons like, small population size and short life span. However, few of them are commercially exploited (Hays et al., 2005). Studies on zooplankton taxa in the Kavaratti Island are limited (Goswami, 1990). Monitoring of the hydrochemical and biological components may provide important information about diversity and dynamics as well as the processes that modify the marine ecosystems. The present study, therefore, investigated coastal environmental parameters and their influence on species diversity, and abundance of zooplankton species using integrated in-situ sampling and GIS techniques.