Biophysical Survey of Mafia Island Marine Reserves

Several areas of coral reef habitat have been observed within the borders of
NIMR. The major areas of scleractinian coral are on the western and southern sides of
Nyororo Island, along the reef drop-off extending from the north-west of the reserve area
down to the north-east, on deeper reef sites in the eastern section of the reserve, and in
scattered patches within the lagoonal area at the centre of the reserve. These consist of a
range of reef types supporting differing coral communities. Along the western side of
Nyororo Island, and in parts along the shallow areas of the northern reef edge, are
branching Acropora dominated communities. These communities are typical of those
found in more exposed environments with higher levels of water flux. The deeper sites in
the eastern section consist primarily of very large massive corals. Massive growth forms
also tend to dominate the reef framework on the lagoon and back reef sites, but the
communities here also support other coral species and include columnar and branching
forms.
a) Benthic Composition
The reef habitats observed on the reef flat and slope on the western side of the
island (Site 2) have the highest exposure to anthropogenic influences. This is manifested
in some damage occurring, particularly on the reef flat, with large areas of broken
branching and foliaceous coral. However, this site still has high levels of scleractinian
coral cover (Figure 4), especially on the deeper parts of the reef and on areas further
away from the fishing camp, and supports an abundant fish population. As with all the
reef areas assessed, there is a high coverage of soft corals (Figure 4). The scleractinian
coral community on this reef consists primarily of branching Acropora as well as large
areas of foliaceous corals (Figure 5).
Bleaching, primarily of branching Acropora species on the shallow reef flat, was
observed on two visits. Water temperature during this period was an average of
approximately 34°C. In addition, some bleached colonies had suffered partial mortality,
most likely as a result of the bleaching event.