Spatial and temporal distribution of the benthos in the Mfolozi-Msunduzi Estuary, KwaZulu – Natal
The objectives of the study were to describe the subtidal component of the invertebrate benthic fauna and to investigate spatial and temporal distribution of the fauna. Samples were collected quarterly in 2009 to investigate seasonal patterns of the benthos of the system. Another aim of this study was to determine the benthic biomass of the Mfolozi – Msunduzi estuarine system. Results indicated that 23 taxa were recorded in 2009 with 18 and 15 taxa in the Mfolozi and Msunduzi Estuary, respectively. The most abundant species were the burrowing ocypodid crab Paratylodiplax blephariskios and the polychaete Dendronereis arborifera. These were followed by the polychaetes Ceratonereis sp., Prionospio sexoculata and the amphipods Corophium triaenonyx. Freshwater taxa, such as Simuliidae, Baetidae, Chironomidae and Ecnomidae were recorded in the upper reaches of the Mfolozi Estuary during summer, this was due to the area being dominated by freshwater inflow. No significant differences (p<0.05) were found between sampling seasons and between sampling sites with regard to the mean number of taxa, mean densities (N.m-2), species richness (D), species evenness (J') and species diversity (H'). The cluster and MDS ordination showed that the benthic fauna of the system could be separated into three most important clusters, the first of which comprised mostly of the Msunduzi sites, indicating that seasonal changes did not influence the community structure of the Msunduzi Estuary. the second group comprised mostly of the Mfolozi winter (June and August) samples while the third group comprised the Mfolozi summer (March and November) samples and this clearly showed that seasonal changes played a major role in structuring the benthic community in the Mfolozi Estuary. The SIMPER results indicated that P. blephariskios and D. arborifera were the taxa most responsible for structuring the benthic community in both the Mfolozi and Msunduzi Estuaries. BIOENV showed that the single variable most responsible for structuring the benthic assemblage in the system was sediment particle size, followed by sediment sorting coefficient and temperature. The best combination of environmental factors which played a role in the distribution and abundance of benthos were temperature, sediment particle size and the sorting coefficient. These results showed that sediment characteristics combined with natural seasonal variability (temperature), played the most important role in structuring the benthic community of the Mfolozi – Msunduzi system. In terms of biomass, P. blephariskios was the greatest contributor to the benthic biomass of the system, followed by D. arborifera. The mean benthic biomass at the Mfolozi sites was very low, with highest values recorded at the mouth of the system, while the highest mean benthic biomass at the Msunduzi sites was recorded at sites MS2 and MS1, while the biomass of the remaining sites was less than 50 mg.m-2. Seasonal variations were evident in the Mfolozi – Msunduzi system, with very low biomass of 1883 mg.m-2 dry weight in March, while the highest biomass was recorded in June (16827 mg.m-2 dry weight). The biomass decreased in August (13412 mg.m-2 dry weight) and again in November (12660 mg.m-2 dry weight).
Invertebrate benthic fauna, Fauna, Benthos
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