State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Intertidal invertebrates
At the Schaapen Island sites, the Dwarf cushion-star Parvulastra exigua was locally common in
moist cracks and rock-depressions, as were the false limpets Siphonaria serrata and S. capensis.
At Schaapen Island East, the upper mid-shore was characterized by distinct bands of Ulva and B.
glandula (Figure 8.12). In contrast, alive barnacles were largely absent from the mid shore at
Schaapen Island West although some empty shells still attached to the rock were encountered.
Instead, at this site a tube-building polychaete was common. This tubeworm was deeply
embedded in a compact matrix of sand, maybe cemented so compact by some secretion of the
worm (Figure 8.12). This sand-worm mixture covered the mid shore in large patches, making up
to 12% of the biotic cover there.
With increasing wave force, the mid shore was dominated by filter feeders, specifically M.
galloprovincialis and B. glandula (Figure 8.12). The latter was particularly abundant at the semiexposed
site Iron Ore Terminal with 75% cover. Algal presence was generally low with some
cover by the ephemerals Ulva spp. and Porphyra capensis, as well as the seaweeds Caulacanthus
ustulatus and Nothogenia erinacea. Mobile animals included the limpets Scutellastra granularis,
Siphonaria serrata, and the tiny periwinkle Afrolittorina knysnaensis nestling in amongst the
barnacles. The scavenging whelk Burnupena spp. was encountered in low numbers at most sites.
Differences in community structure were most pronounced at the low shore where the
energy of waves is most effective. Generally, biotic cover within a shore increased towards the
low shore, but cover also increased among the shores with intensifying wave force (from 28% at
the low shore at Jetty to 84% at Marcus Island). At the very sheltered sites, faunal cover was very
low with some mussel and mixed barnacle cover (B. glandula, Amphibalanus amphitrite and
Notomegabalanus algicola). At Dive School, the two indigenous mytilids, Aulacomya ater and
Choromytilus meridionalis, as well as the alien M. galloprovincialis co-occurred, albeit at very low
densities. Algal cover was only slightly higher, consisting primarily of encrusting Ralfsia verrucosa,
the foliose seaweeds Gigartina polycarpa, Nothogenia erinacea and the green ephemeral alga
Ulva spp. Mobile animals included the limpet Cymbula granatina, the winkle Oxystele tigrina,
Parvulastra exigua, and the sea urchin Parechinus angulosus, often found in groups in pools or
crevices hidden under pieces of shell or gravel (Figure 8.6). Few large specimens of the false plum
anemone Pseudoactinia flagellifera were also encountered there.
At the sheltered Schaapen Island sites, the ground cover was dominated by a diverse
array of up to 20 different algae species. Most common were ‘pink’ encrusting corallines (a
variety of species), followed by foliose seaweeds such as Gigartina polycarpa, Aeodes orbitosa,
Mazzaella capensis, Gymnogongrus glomeratus, Ulva sp., and a low growing turf-forming mixture
of fine red algae (Figure 8.6). Particularly at Schaapen Island West, the mid-shore sand-worm
mixture extended down into the low intertidal, often surrounding and intertwined with, algal
stands. Occasionally, the sand had washed away and the thin stiff tubes of the polychaetes
emerged (Figure 8.6).
Burrowing in this sandy substrate were dense colonies of the red-chested sea cucumber
Pseudocnella insolens, often numbering >350 individuals per 0.5m 2 (Figure 8.6). Sessile
invertebrates were rare but mobile animals included the limpets Fissurella mutabilis and Cymbula
granatina, the cushion star Parvulastra exigua, the winkle Oxystele tigrina and the scavenging
whelk Burnupena spp.
The semi-exposed site Iron Ore Terminal was still characterized by algae, in particular
encrusting species, as well as Sarcothalia stiriata, Mazzaella capensis, Hypnea spicifera,
Nothogenia erinacea, Plocamium spp., Ulva spp. and near the infratidal zone the kelp Laminaria
pallida (Figure 8.6). Mussels and barnacles were present but with low cover, the latter primarily
represented by the giant barnacle Austramegabalanus cylindricus (Figure 8.6). Very common was
the pear-shaped limpet Scutellastra cochlear, followed by S. barbara and Cymbula granatina.
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