Seafloor Terrain Shapes the Three-dimensional Nursery Value of Mangrove and Seagrass Habitats

Abstract

Mangroves and seagrasses are important nurseries for many marine species, and this function is linked to the complexity and context of these habitats in coastal seascapes. It is also connected to bathymetric features that influence habitat availability, and the accessibility of refuge habitats, but the significance of terrain variation for nursery function is unknown. To test whether seafloor terrain influences nursery function, we surveyed fish assemblages from mangrove and seagrass habitats in 29 estuaries in eastern Australia with unbaited underwater cameras and quantified the surrounding three-dimensional terrain with a set of complementary surface metrics (that is, depth, aspect, curvature, slope, roughness) applied to sonar-derived bathymetric maps. Terrain metrics explained variability in assemblages in both mangroves and seagrasses, with differing effects for the entire fish assemblage and nursery species composition, and between habitats. Higher depth, plan curvature (concavity or convexity) and roughness (backscatter) were negatively correlated with abundance and diversity in mangroves and positively linked to abundance and diversity in seagrass. Mangrove nursery species (6 species) were most abundant in forests adjacent to flats with concave holes, rough substrates and low-moderate depths, whereas seagrass nursery species (3 species) were most abundant in meadows adjacent to deep channels with soft mounds and ledges. These findings indicate that seafloor terrain influences nursery function and demonstrate contrasting effects of terrain variation in mangroves and seagrass. We suggest that incorporating three-dimensional terrain into coastal conservation and restoration plans could help to improve outcomes for fisheries management, but contrasting strategies might be needed for different nursery habitats.

Fish and crustaceans provide early indicators of success in wetland restoration

“…We successfully detected changes to the composition, species richness and harvestable abundance of fish and crustacean assemblages with both BRUVS and fyke nets. This is a promising result because both sampling gears are commonly used in wetland research to monitor different components of the fish and crustacean assemblages (Hollingsworth & Connolly 2006; Olds et al 2012; Borland et al 2022b). For example, BRUVS target large and often less abundant fish and crustacean communities in deeper subtidal areas and fyke nets target small and juvenile fish and crustacean assemblages in shallow intertidal areas (Weaver et al 1993; Gladstone 2012).…”