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

Dive School
Jetty
Schaapen East
Schaapen West
Iron Ore Jetty
Lynch Point
North Bay
Marcus Island
State of Saldanha Bay & Langebaan Lagoon 2011
Intertidal invertebrates
Figure 8.15. Temporal changes of evenness and Shannon-Wiener diversity indices (mean ± SE) from 2005 to
2011 at the eight rocky shore sites. (DS = Dive School, J = Jetty, SE = Schaapen East, SW =
Schaapen West, IO = Iron Ore Terminal, L = Lynch Point, NB = North Bay, M = Marcus Island).
2D Stress: 0.19
2005
2008
2009
2010
2011
Figure 8.16. Multi-dimensional scaling (MDS) plot of the rocky shore communities at the eight study sites
from 2005 to 2011. The circles delineate a 40% similarity level.
Another seaweed that had declined in abundance was Gigartina polycarpa at Dive School
and Iron Ore Terminal, whereas Sarcothalia stiriata increased at the latter site. Changes in barnacle
cover had also contributed to dissimilarities, specifically at the two very sheltered boulder beaches
Dive School and Jetty, where B. glandula was absent in 2010 but present in 2011, while the striped
barnacle Amphibalanus amphitrite occurred in 2010 at Jetty and Iron Ore Terminal but not in 2011.
In general though, average dissimilarities between the years per site were low, indicating that
temporal differences in rocky shore communities were small (Table 8.2).
Temporal variations in abundance of functional groups at the eight study sites are illustrated
in Figure 8.17. At the two sheltered boulder beaches Dive School and Jetty, filter feeders and
ephemerals had slightly decreased while corticated algae and grazers had increased with time. In
2011, however, algae other than encrusting were sparse. At Schaapen East, filter feeders depicted
an increasing and ephemerals a decreasing trend, while encrusting corallines fluctuated strongly. At
Schaapen West, biotic cover had steadily increased until 2010, especially encrusting corallines and
ephemerals. The latter group had drastically declined by 2011, reducing the overall cover. Iron Ore
Terminal and Lynch Point remained relatively constant over time, with only minor variations in
encrusting coralline and ephemeral cover at Lynch Point. At North Bay, there was a drastic increase
in filter feeders until 2010, remaining at the same level in 2011. Corallines and ephemerals again
showed slight temporal fluctuations. At Marcus Island, ephemeral algae had greatly increased from
2005 to 2009 while at the same time corticated algae and filter feeders declined. The substantial
ephemeral cover resulted in an overall greater biotic cover in 2009. In 2010, ephemerals had
somewhat reduced but returned again 2011.
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