Download PDF - Anchor Environmental

3.4 Vegetation
There are four main vegetation communities associated with the Uilkraals Estuary: macroalgae,
submerged macrophytes, reeds and sedges, and salt marsh.
Heydorn & Bickerton (1982) recorded 13 species of semi-aquatic plants in and around the
Uilkraals Estuary. These included Crassula glomerata, Plantago carnosa, triglochin bulbosum,
Scirpus littoralis, Sebaea minutiflora, Sebaea albens, Spergularia marginata, Cotula eckloniana,
Chenolea diffusa, Samolus deis and Limonium scabrum.
Macroalgae
Macroalgae can be indicative of water quality and nutrient enrichment. Macroalgae may be
intertidal (intermittently exposed) or subtidal (continually submerged) and can be attached to
hard or soft substrata or they may float (Adams et al. 1999). Opportunistic macroalgae are
found in temporary closed estuaries like the Uilkraals as they can tolerate fluctuating salinities.
During a survey in 1981 the filamentous algae Enteromorpha and Cladophora were recorded in
the estuary and Ulva beds were present under the road bridge (Heydorn & Bickerton 1982).
Enteromorpha and Cladorphora belong to the family Chlorophyta, and are often found to
extend further into estuaries due to their salinity tolerance (Adams et al. 1999).
Submerged macrophytes
The high macrophyte diversity in the Uilkraals Estuary is of conservation importance. There
are approximately 2 ha of submerged macrophytes in the estuary, which provide an important
habitat for invertebrates and juvenile fish. Submerged macrophytes are plants rooted in both
soft subtidal and low intertidal substrata, which are completely submersed for most states of
the tide (Adams et al. 1999). Submerged macrophyte beds support diverse and abundant
invertebrate and juvenile fish communities (Whitfield 1984, 1989). Primary productivity of
submerged macrophytes is high and on par with the most productive plant habitats in marine
and terrestrial ecosystems (Day 1981, Fredette et al. 1990). Adams et al. (1999) found in saline
waters in the region, Zostera capensis is prevalent. Submerged macrophytes are important in
their provision of food for epifaunal and benthic invertebrate species as well as nursery areas
for juvenile fish through the provision of food, shelter and protection (Adams et al. 1999).
Salt marsh
Salt marshes in estuaries are a source of primary production and provide habitat and food for a
variety of faunal species (Adams et al. 2006). The degree of tidal flushing is important in
determining how much nutrients they release into the water column (Childers & Day 1990).
An open mouth is important as this maintains the intertidal salt marsh community. Salt marsh
plants are distributed away from the water’s edge along an inundation gradient (Figure 13).
Intertidal salt marsh occurs between the limits of the high and low tide ranges, while supratidal
marsh occurs above the intertidal zone and is only normally flooded during spring tide and
Uilkraals Estuary Situation Assessment
23
Anchor Environmental