Abstract
Ecosystems are linked by the movement of organisms across habitat boundaries and the arrangement of habitat patches can affect species abundance and composition. In tropical seascapes many coral reef fishes settle in adjacent habitats and undergo ontogenetic habitat shifts to coral reefs as they grow. Few studies have attempted to measure at what distances from nursery habitats these fish migrations (connectivity) cease to exist and how the abundance, biomass and proportion of nursery species change on coral reefs along distance gradients away from nursery areas. The present study examines seascape spatial arrangement, including distances between habitats, and its consequences on connectivity within a tropical seascape in Mozambique using a seascape ecology approach. Fish and habitat surveys were undertaken in 2016/2017 and a thematic habitat map was created in ArcGIS, where cover and distances between habitat patches were calculated. Distance to mangroves and seagrasses were significant predictors for abundance and biomass of most nursery species. The proportions of nursery species were highest in the south of the archipelago, where mangroves were present and decreased with distance to nurseries (mangroves and seagrasses). Some nursery species were absent on reef sites farthest from nursery habitats, at 80 km from mangroves and at 12 km from seagrass habitats. The proportion of nursery/non‐nursery snapper and parrotfish species, as well as abundance and biomass of seagrass nursery species abruptly declined at 8 km from seagrass habitats, indicating a threshold distance at which migrations may cease. Additionally, reefs isolated by large stretches of sand and deep water had very low abundances of several nursery species despite being within moderate distances from nursery habitats. This highlights the importance of considering the matrix (sand and deep water) as barriers for fish migration.
Highlights
Ecosystems are linked by the movement of organisms across habitat boundaries and the arrangement of habitat patches can affect species abundance, biomass and composition (Baguette et al 2013)
Using a seascape ecology approach, the present study aims to: 1) examine changes in fish abundance, biomass and species composition on tropical reefs along geographical distance gradients away from nursery areas; and 2) identify distance thresholds away from nursery habitats where abundances and biomasses of nursery fish species abruptly decline in a Mozambican archipelago
In 2001, its boundaries were extended to encompass the current area of 1430 km2, including seagrass beds, coral reefs and terrestrial environments
Summary
Ecosystems are linked by the movement of organisms across habitat boundaries and the arrangement of habitat patches can affect species abundance, biomass and composition (Baguette et al 2013). These movements are often caused by changes in animal needs in terms of food and shelter and may result in ontogenetic changes of habitat use. This can lead to spatial separation between juveniles and adults within populations (Werner and Gilliam 1984). Little is known about seascape thresholds in marine systems, it is a potential factor in structuring marine communities and lends important information for ecosystem-based management
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