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Shallow coastal systems act as nursery habitat for many species of fish and macroinvertebrates. Juveniles of these species may show selective use of certain habitat types over others, but the degree of such selectivity is not well studied for many species. Analysis of habitat selectivity is often hindered by inherently different gear types used in the habitats examined, which may not allow for direct comparison between the habitats. Here, we carry out nekton catches in the fringing marsh, using fyke nets, and in the adjacent seagrass habitat, using trawls, in the northern Gulf of Mexico to assess the relative use of the two habitats by the juveniles of six widespread important species. To resolve issues of gear comparability between fyke nets and trawls, we develop a habitat use index (HUI S) . The results reveal a consistent trend where, in relation to pinfish, speckled sea trout shows slightly higher (from 8.4 to 66.9 times); American silver perch and brown shrimp show moderately higher (from 2.3 to 369.4 times); and blue crab and white shrimp show greatly higher (from 90.6 to 2366.4 times) use of marsh over seagrass habitat. Thus, while similar in direction, differences in the use of marsh over seagrass habitat in relation to pinfish were more pronounced in some sites. We propose an index that can resolve issues of gear comparability and improve our understanding of coastal habitat selectivity by fish and macroinvertebrates. [ABSTRACT FROM AUTHOR]

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0-18.8 %), and four had high cover (83.8-97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems. [ABSTRACT FROM AUTHOR]