Biophysical Survey of Mafia Island Marine Reserves

industry as it is highly regarded for its natural beauty, good diving and snorkelling, and
the presence of black tip sharks and turtles. The coral reef extends for over 2.5km around
the east and north of the island at a distance of around 1km, and encloses shallow
seagrass beds. At its maximum the coral reef is 100m wide. There is a channel (4 to 6m
deep) running from the north-west of the reserve area towards NIMR. The channel area
begins at the north-western extent of the coral reef and is approximately 0.5km in width.
To the north of the reef, near the channel, is a small patch reef surrounded by sand
substrates. The western side of the island is experiencing rapid erosion of the shoreline.
According to anecdotal evidence, the island has reduced in width by nearly two-thirds
over the past ten years. As testimony to this, there are many large tree trunks lying in the
water and on the beach along the western shore.
The reef at SIMR is comprised of a mixed coral community based on an eroded
coral rag and sandstone base. A discernable reef edge is present along most of the reef
with a short vertical section often present on the deepest reef margins from 5m down to
10-12m deep. In places the coral reef is replaced by rubble slopes running down from the
shallow seagrass habitats to the outer reef edge. They generally are no more than 30m in
width. The conditions experienced at SIMR were less turbid than those observed at
MBIMR, but visibility was still generally low and the reef was primarily dominated by
soft corals (21.32% +/- SE 1.95%). The main growth morphologies of scleractinian corals
were found to be massive (4.88% +/- SE 0.66%), and branching (5.32% +/- SE 1.41%).
In addition, all other growth forms were recorded, but at less than 1% average cover. On
the deeper reef margins, particularly at the north-eastern corner of the reef where it is at
its widest, large Porities colonies were found, many of them over 4m in diameter.
Fish abundance on the reef at SIMR was not at the same level as observed on
coral rich habitats at sites in NIMR, but there was greater diversity of species. The most
abundant reef fish observed on the coral reef at SIMR were Dash and Dot Goatfish
(Parupeneus barberinus) and Striped Bristletooth (Ctenochaetus striatus). Five species of
butterfly fish were recorded, including Redfin (C. trifasciatus), which are commonly
associated with coral rich habitats, and Vagabond (C. vagabundus), which are found in
turbid ‘dead’ sites. In total, 32 of the 55 reef fish species looked for were recorded on