Spatio-temporal Variability of Acartia clausi (Copepoda, Calanoida) Population Structure, Abundance, Body Length, and Biomass in a Tropical Coastal Lagoon (Grand-Lahou, Côte d’Ivoire)

Raphaël N’Doua Etilé,Georges Kassi Blahoua,Théophile Aké Bédia,Paul Essetchi Kouamelan,Valentin N’Douba

doi:10.18483/ijsci.1296

Abstract

The spatial and seasonal variations of Acartia clausi population structure, abundance, biomass and body length variation in relationship to environmental variables were investigated in the Grand-Lahou lagoon at 21 stations from January to December 2004. A. clausi abundance, biomass and body (prosome) length showed considerable seasonal and spatial variation. On average, total population abundance and biomass obtained during the dry season (Mean: 7.11 ind/l and 9.08 µgC/l respectively) were higher than that those which have gotten during the wet season (Mean: 2.98 ind/l and 2.76 µgC/l respectively). The same tendency was registered for prosome length of all development stages, with 275-1000 µm during the dry season versus 225-975 µm during the wet season. A. clausi population (without the nauplii) was dominated by copepodids stages in all seasons. During the dry season, on average, copepodids stages constituted 76.65% of total density and 52.98% of total biomass. During the wet season, copepodids stages represented 92.23% of total density and 72.42% of total biomass. In the adults stages, on average females (F) were more numerous than males (M), with a sex ratio (M/F) of 0.75. However, males were slightly more abundant than females during the dry season (February to April and September) with sex ratio (M/F) range from 1.10 to 1.46. Correlation on data of this study analyses showed that spatio-seasonal variations of A. clausi abundance, Biomass and Body length were mainly linked to water salinity, pH, transparency and dissolved oxygen, phosphates and nitrates concentrations.

Highlights

Zooplankton plays a major role in the functioning and the productivity of aquatic ecosystems through its impact on the nutrient dynamics and its key position in the food webs
Significant differences between dry and wet seasons were found for different parameters studied (ANOVA, p < 0.05), excepted for dissolved oxygen (ANOVA, p > 0.05)
Data from the present study shows that Acartia clausi is constantly present in Grand-Lahou lagoon with maximal density and biomass during the dry season and in Tadio and Niouzoumou lagoon during the wet season

Summary

Introduction

Zooplankton plays a major role in the functioning and the productivity of aquatic ecosystems through its impact on the nutrient dynamics and its key position in the food webs. Besides most zooplanktonic organisms can have herbivorous detritivorous diet and exert a strong grazing impact on the phytoplanktonic (Atienza et al, 2016) and protoplankton (Londsale et al, 2000) biomass. They constitute a food source for organisms of the upper trophic levels such as planktivorous fish larvae and carnivorous invertebrates as chaetognaths (Reiss et al, 2005). Copepods are probably the most numerous multicellular on the earth (Mauchline, 1998) They are distributed throughout the ocean and their margins extend into freshwaters. According to Boyer (2012) who makes a literature review on the Acartiidaes, it represents a family very extensively widespread being part of the 10 families of copepods the most observed on the

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