Biophysical Survey of Mafia Island Marine Reserves

C. MBIMR
MBIMR is the smallest of the three reserve areas. In addition to the island itself,
there are extensive shallow seagrass habitats, deep seagrass habitat, and a soft coral
dominated reef. The shallow seagrass beds cover the entire area between the reef and the
island, an area extending for more than 3km 2 . The reef curves around the east and north
of the island at a distance of 1km, and is situated on a highly eroded coral rag and
sandstone base which extends for over 2km in length.
The coral reef habitats which were found in MBIMR are dominated by soft corals
(31.55% +/- SE 0.88%) with a very low coverage of scleractinian corals (7.55% +/- SE
1.33%). This is likely to be due to the turbid environmental conditions frequently
experienced at MBIMR which result in very low light levels and high sedimentation.
Scleractinian corals found were mainly massive, sub-massive, and encrusting forms. Due
to its diversity of benthic organisms MBIMR supports an abundant community of benthic
invertebrates. This includes Crown Of Thorn Starfish (COTS) which is in contrast to the
other surveyed sites. COTS were found on just over half of the transects completed at
MBIMR (0.53 +/- SE 0.13), whereas only a single COTS was recorded on all transects
completed for the other two reserves.
The shallow and deep seagrass habitats in MBIMR are both extensive, and
ecologically rich. Five species of seagrass were identified from the shallow habitats. The
seagrass habitats provide important nursery sites which supports fish populations,
particularly juvenile Emperors. In addition, they have relatively high numbers of
commercially important species such as edible sea cucumbers and cowries.
Sites found to be of particularly conservation importance are:
• The shallow seagrass habitats found at MBIMR form a unique and diverse
ecosystem which supports many invertebrate species at risk from over-collection.
The sites examined do not appear to be subject to more than minimal levels of