Dredging fundamentally reshapes the ecological significance of 3D terrain features for fish in estuarine seascapes

Hayden P Borland,Nicholas L Ortodossi,Christopher J Henderson,Andrew D Olds,Marcus Sheaves,Rod M Connolly,Ben L Gilby,Bob Gorissen,Simon J Pittman,Ashley J Rummell

doi:10.1007/s10980-021-01394-5

Abstract

ContextLandscape modification alters the condition of ecosystems and the structure of terrain, with widespread impacts on biodiversity and ecosystem functioning. Seafloor dredging impacts a diversity of flora and fauna in many coastal landscapes, and these processes also transform three-dimensional terrain features. The potential ecological significance of these terrain changes in urban seascapes has, however, not been investigated.ObjectivesWe examined the effects of terrain variation on fish assemblages in 29 estuaries in eastern Australia, and tested whether dredging changes how fish associate with terrain features.MethodsWe surveyed fish assemblages with baited remote underwater video stations and quantified terrain variation with nine complementary metrics (e.g. depth, aspect, curvature, slope, roughness), extracted from bathymetry maps created with multi-beam sonar.ResultsFish diversity and abundance were strongly linked to seafloor terrain in both natural and dredged estuaries, and were highest in shallow waters and near features with high curvature. Dredging, however, significantly altered the terrain of dredged estuaries and transformed the significance of terrain features for fish assemblages. Abundance and diversity switched from being correlated with lower roughness and steeper slopes in natural estuaries to being linked to features with higher roughness and gentler slopes in dredged estuaries.ConclusionsContrasting fish-terrain relationships highlight previously unrecognised ecological impacts of dredging, but indicate that plasticity in terrain use might be characteristic of assemblages in urban landscapes. Incorporating terrain features into spatial conservation planning might help to improve management outcomes, but we suggest that different approaches would be needed in natural and modified landscapes.

Highlights

Urbanisation is the leading form of landscape modification globally, with most ecosystems having been transformed to support the needs of an ever-growing human population (Seto et al 2012; Song et al 2018)
Fish abundance was highest near convex terrain features that were steep and soft
Landscape modification alters the condition of ecosystems and the structure of terrain features, and this can lead to declines in biodiversity and ecosystem functioning (Heery et al 2017; Berger-Tal and Saltz 2019)

Summary

Introduction

Urbanisation is the leading form of landscape modification globally, with most ecosystems having been transformed to support the needs of an ever-growing human population (Seto et al 2012; Song et al 2018) This intense form of landscape modification is typically associated with habitat loss and degradation, pollution, the introduction of pest species, and in some extreme cases, changes in regional climate (Kowarik 2011; Pickett et al 2011). These negative consequences of urbanisation have significant and widespread impacts on the composition of floral and faunal communities, and can lead to declines in biodiversity, productivity, the rate and distribution of ecological functions and ecosystem services (Johnson and Munshi-South 2017; Berger-Tal and Saltz 2019). There has been considerable research into the impacts of habitat loss, landscape fragmentation and species translocation in urban environments, both on land and in the sea (Pickett et al 2011; McCauley et al 2015), but the potential ecological consequences of intense terrain modification are rarely studied in coastal waters (Borland et al 2021)

Objectives

Methods

Results

Conclusion