Abstract
Reefs, mangroves and seagrass biotopes often occur in close association, forming a complex and highly productive ecosystem that provide significant ecologic and economic goods and services. Different anthropogenic disturbances are increasingly affecting these tropical coastal habitats leading to growing conservation concern. In this field-based study, we used a visual census technique (belt transects 50 m x 2 m) to investigate the interactions between fishes and microhabitats at the Mamanguape Mangrove-Reef system, NE Brazil. Overall, 144 belt transects were performed from October 2007 to September 2008 to assess the structure of the fish assemblage. Fish trophic groups and life stage (juveniles and adults) were recorded according to literature, the percent cover of the substrate was estimated using the point contact method. Our results revealed that fish composition gradually changed from the Estuarine to the Reef zone, and that fish assemblage was strongly related to the microhabitat availability, as suggested by the predominance of carnivores at the Estuarine zone and presence of herbivores at the Reef zone. Fish abundance and diversity were higher in the Reef zone and estuary margins, highlighting the importance of structural complexity. A pattern of nursery area utilization, with larger specimens at the Transition and Reef Zone and smaller individuals at the Estuarine zone, was recorded for Abudefduf saxatilis, Anisotremus surinamensis, Lutjanus alexandrei, and Lutjanus jocu. Our findings clearly suggests ecosystem connectivity between mangrove, seagrass and reef biotopes, and highlighted the importance of Mamanguape Mangrove-Reef System as a priority area for conservation and research, whose habitat mosaics should be further studied and protected.
Highlights
Reefs, mangroves and seagrass beds are the major coastal habitats in tropical areas (Nagelkerken et al, 2000; Ikejima et al, 2003; Mumby et al, 2004; Mumby et al, 2008; Nagelkerken & Faunce, 2008; Nagelkerken et al, 2008)
Considering the Mamanguape Mangrove-Reef system, with the presence of estuary and reefs as adjacent ecosystems and exposed to similar environmental conditions, this study addressed the following questions: (1) are there differences in the fish assemblages distributed along the estuarine-reef gradient? (2) how does microhabitat availability influence the spatial distribution of fishes? (3) does structural complexity, inferred by rugosity, influence fish assemblage composition? (4) based on the ontogenetic distribution of fishes, is there indication of connectivity between the Mamanguape mangrove estuary and the adjacent rocky reef ecosystem?
In addition to the fish species found within the area covered by transects, we recorded the presence of four other species along the margins of the Estuarine zone: Antennarius sp., Gymnothorax funebris, Sphoeroides greeleyi, and Strongylura sp
Summary
Mangroves and seagrass beds are the major coastal habitats in tropical areas (Nagelkerken et al, 2000; Ikejima et al, 2003; Mumby et al, 2004; Mumby et al, 2008; Nagelkerken & Faunce, 2008; Nagelkerken et al, 2008). Many studies have long discussed the nursery role of mangroves and estuaries (Ogden & Gladfelter, 1983; Arrivillaga & Baltz, 1999; Nagelkerken et al, 2000; Ikejima et al, 2003; Mumby et al, 2004; Nagelkerken & Faunce, 2008), and how juvenile fish use habitats like seagrass beds and small, protected patch reefs before venturing out to large reefs. Some studies have suggested that current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of adjacent reefs (Mumby et al, 2004; Mumby & Hastings, 2008)
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