Distribution patterns of striped mullet Mugil cephalus in mangrove creeks, Zanzibar, Tanzania

Spatial and seasonal variations in density of striped mullet Mugil cephalus were investigated in four mangrove creeks in Zanzibar, Tanzania, during a one-year cycle. Fish were collected monthly in the lower, intermediate and upper reaches of each creek using a beach-seine net. All fish collected were juveniles between 2 and 16 cm standard length. The density of juvenile mullet differed significantly among the creeks, but the spatial patterns within them were consistent with higher densities upstream in three of the creeks. Generally, small mullet (2–10 cm) were more abundant in the upper reaches compared to the lower and intermediate reaches. Seasonal patterns were weak, although mullet densities were high during the period of heavy rains (March–May). Principal component analysis showed that a muddy substrate with microphytobenthos was positively correlated with high mullet densities, although site-specific variables such as shallow water depth and water clarity were also significantly correlated. Our findings suggest that the densities of juvenile striped mullet vary among sites and creeks in response to refuge availability from turbid, shallow water and the accessibility of food from benthic microalgae. Keywords: East Africa; marine embayment; Mugil cephalus; population density; spatial and seasonal variationAfrican Journal of Marine Science 2010, 32(1): 85–9

The use of clear-water non-estuarine mangroves by reef fishes on the Great Barrier Reef

Within the tropics, mangroves and coral reefs represent highly productive biomes. Although these habitats are often within close proximity, the role and importance of mangrove habitats for reef fish species remains unclear. Throughout the Indo-Pacific, reef fish species appear to have few links with estuarine mangrove habitats. In contrast, clear-water non-estuarine mangrove habitats throughout the Caribbean support many reef fish species and may be fundamental for sustaining reef fish populations. But how important are clear-water non-estuarine mangroves for reef fishes within the Indo-Pacific? Using visual surveys during diurnal high tide, the fish assemblages inhabiting clear-water mangrove and adjacent reef habitats of Orpheus Island, Great Barrier Reef, were recorded. Of the 188 species of fishes that were recorded, only 38 were observed to inhabit both habitats. Of these, only eight were observed more than five times within each habitat. These observations provide little indication that the clear-water mangroves are an important habitat for reef fish species. In addition, although based on just a 3-month survey period, we found little evidence to suggest that these areas are important nurseries for reef fish species. The clear-water mangroves of Orpheus Island may, however, provide an additional foraging area for the few reef fish species that were observed to utilize these habitats during high tide. The difference in the importance of clear-water mangroves for reef fishes within this study compared with clear-water mangrove counterparts within the Caribbean is surprising. Although only preliminary, our observations would support suggestions that the patterns reflect the different hydrological characteristics and evolutionary histories of these two biogeographic regions

Mangrove timber use as an ecosystem service in the Colombian Pacific

Mangroves provide ecosystem services for local communities. However, in coastal systems it is yet unknown how human settlements are directly interacting with mangroves. We assessed the use of mangroves as an ecosystem service at Málaga and Buenaventura bays, on the Colombian Pacific coast, by interviewing local communities and examining the impact of mangrove harvest on the structure of the forest, an often overlooked effect. Results showed that mangroves are mainly harvested for their wood. Rhizophora spp. are the main source of wood for fuel purposes, whereas Mora oleifera (Triana ex Hemsl.) Ducke, a mangrove associate, provides 100% of the wood used for the construction of stilt houses. The selective extraction of these species has altered the composition and structure of the forest. Sample sites undergoing harvest have relatively low densities of mangroves; however, one site at Quebrada Valencia shows signs of copious regeneration (>9000 seedlings/ha). Due to the importance of mangroves for the subsistence of coastal communities, and the threat that mangroves are exposed to in Colombia, the management of mangroves should be a priority. Managers must address the sustainability of critical species as part of conservation strategies in order to maintain ecosystem services for local communitie