Spatial and temporal variation in fish community structure of a marine embayment in Zanzibar, Tanzania

Abstract

Spatial and temporal variation in the fish community structure were studied in a tropical non-estuarine embayment in Chwaka Bay, Zanzibar (Tanzania). Fish samples were collected bi-monthly (at each spring low tide) for 1 year (November 2001-October 2002) from a range of bay habitats ranging from mangroves deep inside the bay to seagrass beds close to the mouth of the bay. Additionally, environmental variables were examined to determine their relationship with the fish community structure. Being a non-estuarine embayment, the environmental variables as well as the fish community structure in each habitat remained relatively constant for most part of the year; however, a marked decline was observed during the rainy period (April-May). Significant variations in fish community variables (density, biomass and species richness) and in water temperature and salinity were observed during the rainy season in all habitats, with larger changes in the mangrove and mud/sand flats habitats than in the seagrass beds. Seasonal variations in water clarity and dissolved oxygen were not significant, though. Many species disappeared from the mangrove and mud/sand flats habitats during the rainy season and those which persisted showed a remarkable decrease in density. Moreover, the results indicate that mangroves were the preferred settling habitats for Gerres filamentosus, Gerres oyena, Lethrinus lentjan and Monodactylus argenteus, especially during the dry period (DecemberFebruary) before the rainy season. This observation is contrary to what has been reported from some other tropical regions where greater abundance and species richness was observed during the rainy season. A significant relationship was found between density of fish and temperature, salinity and turbidity. Since salinity was the most Handling editor: J. A. CambrayElectronic supplementary material The online version of this article (123 conspicuously changing environmental variable with seasons, we propose that salinity, alone or in combination with low visibility and temperature, was probably the most important environmental factor structuring the fish assemblage in the mangrove and mud/sand flats habitats, particularly during the rainy season.

Rapid changes in fish utilization of mangrove habitat in Western Madagascar

“…(a few here), emperors (a dominant), and monos (another dominant. Fish density and biomass decreased from January to February (Lugendo et al 2007), similar to our observations. Species richness increased slightly from Wetlands Ecol Manage (2009) 17:345-354 351 January to February and then decreased during the rainy season; this was attributed to altered salinity.…”

“…In Zanzibar, barracuda (Sphyraena barracuda) (Walbaum) recruits decreased from January to February, while the pickhandle barracuda, S. jello, increased in the present study. Lugendo et al (2007) noted an increase in small monos and a decrease in larger individuals from January to February, which was observed here. Four of the seven species they studied had recruits in the mangroves in January and February, which corresponds to this study in which monos, surgeons, butterflyfish and emperor recruits appeared in late January.…”

Distribution of fish among Avicennia and Sonneratia microhabitats in a tropical mangrove ecosystem in South China

“…The height and biomass of pneumatophores as well as canopy shade (presented as relative light intensity both inside and outside the vegetated area) were important factors influencing species richness, density, and biomass in our study, suggesting that pneumatophores and trees might provide refuge for fish to escape predation (Laegdsgaard and Johnson 2001). Besides, studies have shown relationships between fish assemblages and water salinity (Barletta et al 2005, Lugendo et al 2007), water temperature (F elix et al 2017), access to creeks (Meynecke et al 2008, Krumme et al 2014, and habitat heterogeneity (F elix et al 2017), etc. At the Avicennia site, structure of pneumatophores had impacts on all measured fish variables, with pneumatophore height showing positive effect but pneumatophore biomass showing negative effect.…”

The Impact of Mangrove Prop-Root Epibionts on Juvenile Reef Fishes: A Field Experiment Using Artificial Roots and Epifauna

“…All replicates of the study were performed during the wet season; fish abundance in inshore habitats usually peaks on a seasonal basis (Stoner 1986;Barietta et al 2003;Lugendo et al 2007). …”