Abstract

The differential use of nursery habitats by grunts and snappers (Haemulidae and Lutjanidae) across a complex coastal seascape was examined using a cross-shelf habitat (CSH) framework. The framework explicitly defined structural bottom types, cross-shelf physical strata, and associated spatial features on scales ranging from 0.01 m2 to 1x103 km2. These habitat attributes were combined using matrices which integrated an axis representing structural bottom types with an axis representing physiographic cross-shelf strata. The framework identified 10 cross-shelf strata, most encompassing over 15 natural bottom types for the shelf area of Biscayne Bay, Florida. The resulting matrices contained 169 cells which represent potential cross-shelf habitats. The hypothesis that utilization of cross-shelf habitats by grunts and snappers was uniform was not supported by 30 years of prior literature or museum materials, and new field surveys of the Biscayne Bay area. In terms of bottom types, newly settled stages of Lutjanus griseus and Anisotremus surinamensis (< 20 mm SL) were not recorded from hard structures and seagrasses, respectively. Distributions of newly settled Lutjanus synagris were broader; they occurred in both grassbeds and on hard structures. Structurally-identical habitats were often used differently based on their cross-shelf positioning. Habitat utilization patterns ranged from opportunistic to highly specialized. For example, L. synagris was estimated to use approximately 64 cross-shelf habitats for settlement, while A. surinamensis used 10. Opportunistic use of structural habitats at settlement characterized seven of 21 grunt and snapper species. The CSH framework facilitated nursery area identification on several spatial scales and may provide a template for identifying habitats essential for fish production.

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