Bay of Ambaro (Madagascar) - Ecology

Comparatively, coral and rocky reefs are the richest habitat of the area in terms of fish diversity while seagrass and pure sand-rubble substrates are poor. Silty bays harbor poorer fish communities although several species are unique to this environment. The area is home to multiple species including fish and shrimps, holothurians, mollusks, etc. On the muddy seafloor, numerous small demersal species (Leiognatidae, Mullidae, etc.) coexist with shrimps. Very little is known about these species in this area. However, juveniles of most of the fish species are found in coastal areas and the adults seaward further. On the continental shelf, from isobaths 10m to the edge of the continental shelf, where no commercial trawl or net fishery occur, 5 species, Gazza minuta, Leiognathus equula, Leiognathus splendens, Secutor insidiator and Upeneus sulphureus, aggregating on sandy-muddy seabeds, dominate the fish community. The Indian mackerel, Rastrelliger kanagurta, is the main small pelagic fish species encountered. It is thus difficult to separate biological indicators and management strategies as fisheries mainly target a single group of species, namely shrimp.
In the mid 1990s, the trawl fishing ground experienced an infestation of urchins resulting in a significant reduction in shrimp catch. Even though no direct correlation was found with the massive bycatch dumped at sea, urchins are known for colonising degraded habitats.
27 species of shark and holothurians also used to be common in the area, but as a consequence of intensive exploitation, their populations have been depleted. Of the 463 species of reef fish belonging to 191 genera and 65 families recorded in the area, about 30 species are confined to Madagascar and adjacent regions including Mozambique, East Africa, Comoro Islands, St. Brandon’s Shoals, and the Mascarene Group, 8 species are presently known only to occurin Madagascan waters (Pseudochromidae: Halimuraenoides isostigma, Pseudochromis sp.1, Pseudochromis sp.2; Plesiopidae: Plesiops malalaxus; Pomacentridae: Amphiprion latifasciatus, Pomacentrus atriaxillaris, Pomacentrus caeruleopunctatus; Labridae: Paracheilinus hemiaeniatus; Gobiidae: Flagellogobius fourmanoiri), and 4 other species are known to occur only in Madagascar and the Comoros/Saint Brandon’s Shoals.