Abstract:
Projections suggest that global climate change is warming and changing the salinity
of brackish waters (e.g., lagoons, estuaries), with impacts on nursery and feeding
habitats for fish and other organisms. This study evaluated the response of
mesozooplankton - responsible for energy transfer to higher trophic levels - to the
combination of these climate change factors. It was conducted using samples from
the Volta estuary. A field study on transects indicated that, in terms of species
composition, mesozooplankton of the area were dominated by copepods (68%)
followed by decapods (25%), cladocerans (4.5%) and rotifers (0.5%); these were
related to chlorophyll-a concentration, temperature and dissolved oxygen of the
estuary. Combined impacts of warming and changes in salinity were assessed on
two cosmopolitan mesozooplankton - Temora Stylifera and Paracalanus parvus -
using microcosm experiments involving different levels of salinity (22, 21, 25, 29
and 30 ppt) and warming (+0, +2 and +4 °C). Combination of these factors could
explain ≈74% of the variations in egg production rate (EPR) by Temora; EPR of
the copepod decreased (70%) with each degree of warming. In contrast, only feacal
pellet production (FPP) by Paracalanus could be related to the combination of the
two climate change factors; FPP decreased by ≈56% when the copepod was
exposed to increasing temperature and salinity. It can therefore be said that different
species of estuarine mesozooplankton respond differently to the combined impacts
of surface warming and salinity changes expected under global climate change
