Dynamics of epibenthic copepods in relation to environmental factors and phytoplankton abundance in tropical river, estuarine and coastal environments

Abstract

Changes in epibenthic copepod populations markedly affect the population of benthic dwelling animals in rivers, estuaries and marine ecosystems. Unfortunately, studies focusing the environmental influence on the structure of epibenthic copepods are lacking. This study addresses the deficit of information focusing the environmental factors that affect the structure of epibenthic copepods in various lotic environments. The copepods community and environmental variables in water 0.3 m above the bottom of four areas (from 10 km upstream of the Kuantan River mouth to 5 km offshore) were studied monthly over one-year. The study area is characterised by a hot equatorial climate with the monsoon (more-rainy summer, October–March) and the non-monsoon (less-rainy summer, April–September). Totally forty-three species of copepods on thirteen groups were recorded, with harpacticoid copepod groups being dominant in all sampling zones except the upstream zone, where freshwater copepods were dominant and harpacticoid copepods were absent. The total abundance of copepods was greater at the coast and estuary than at the river. Phytoplankton density, salinity, total suspended solids (TSS) and dissolved oxygen (DO) significantly influenced the abundance of epibenthic copepod groups, but their influence on copepods was zone-specific. At the coastal and the estuarine zones, harpacticoid copepod groups were positively influenced by the abundance of phytoplankton, whereas the other copepod groups were negatively influenced by the TSS. The influence of TSS on cyclopoid and calanoid copepods was dependent on the density of phytoplankton with a higher density reducing the impact of TSS. At the downstream, harpacticoid copepod groups were positively influenced by the abundance of phytoplankton, DO and salinity while the other copepod groups were positively influenced by DO and salinity and negatively influenced by TSS. At the upstream, freshwater copepod groups were positively influenced by the DO concentration and negatively influenced by the salinity while, other copepod groups were positively influenced by both DO and salinity. Other environmental variables had a weak and insignificant influence on the densities of observed copepod groups. Both monsoon and non-monsoon seasons equally influenced the observed copepod groups. The observed results need to be regularly monitored to changing tropical environments for better elucidating the ecology of various groups of epibenthic copepods associated with the climate change and various anthropogenic activities.