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

State of Saldanha Bay & Langebaan Lagoon 2011
Intertidal invertebrates
Table 8.2.
Site
SIMPER results listing the species that contribute >5% to the dissimilarity between 2010 and
2011 at each site. The % cover data are averages across the six replicates per site, and are on
the fourth-root transformed scale.
Species
2010
%cover
2011
%cover
Contribution
%
Average
dissimilarity
Dive School Balanus glandula 0.0 1.13 8.64 33.2
Gigartina polycarpa 1.17 0.38 6.35
Jetty Balanus glandula 0.0 1.39 11.78 46.5
Amphibalanus amphitrite 1.26 0 10.70
Ralfsia verrucosa 1.27 0.74 5.49
Ulva spp. 1.03 0.51 5.42
Schaapen East Blue green algae 1.76 0.86 6.30 43.8
Schaapen West Blue green algae 1.85 0.0 9.45 41.3
Iron Ore Terminal Amphibalanus amphitrite 1.24 0.0 8.62 32.2
Gigartina polycarpa 0.92 0.0 6.42
Sarcothalia stiriata 0 0.85 5.92
Austromegabalanus
cylindricus
0.11 0.86 5.30
Lynch Point Red turf 0 0.75 4.61* 34.1
North Bay Laminaria pallida 0 0.77 4.75* 35.0
Marcus Island Blue green algae 1.05 0.0 5.97 31.3
* Note that at these sites none of the species contributed >5% to the dissimilarity. The species with the highest contribution
is thus listed.
From the temporal pattern displayed by the rocky shore communities, it is evident that at
none of the sites there is a directional change in community composition that would indicate a
persistent change, such as for example the arrival or loss of a species. Rather the communities show
temporal fluctuations, reflecting for example dominance of ephemerals over one or more years (e.g.
Schaapen West and Marcus Island). Ephemeral algae typically show strong temporal variation in
their abundances (Griffin et al. 1999, Maneveldt et al. 2009). They generally have short life-cycles
and dense populations are therefore only temporarily. Recruitment and survival success is also
strongly related to environmental conditions that will vary from year to year. Ephemeral
assemblages also vary in their species distribution and density according to the successional stage of
the shore or patch on the shore. For example, limpet exclusion experiments on the south-western
Cape resulted in an immediate recruitment of blue-green algae and Porphyra, which were after a
couple of months replaced by Ulva spp. This green alga in turn, was then replaced by encrusting and
corticated algae with time (1-2 years, Maneveldt et al. 2009). Changes in ephemeral algae cover over
the years are thus likely to be a natural seasonal and interannual phenomenon, and there is no
reason to assume anthropogenic influences.
187
ANCHOR
e n v i r o n m en t a l