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

Abstract

Context Landscape 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. Objectives We 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. Methods We 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. Results Fish 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. Conclusions Contrasting 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.

Seascape genetics in a polychaete worm: Disentangling the roles of a biogeographic barrier and environmental factors

“…Such variables play an essential role in the performance and survival of species with planktonic larval stages, especially for those who inhabit rocky shores. Furthermore, three‐dimensional features, such as curvature profile, can cause widespread impacts on biodiversity and functional traits (Borland et al, 2022; Demopoulos et al, 2018), since it influences water flow dynamics across the surface. These assumptions are related to how geomorphic metrics can distinguish different benthic communities, even for polychaetes (De Leo et al, 2014), showing again that environmental heterogeneity, rather than only the geographic distance, is responsible for the genetic differentiation (Harley & Helmuth, 2003).…”

Restoration promotes ecological functioning through greater complementarity

“…BRUVS were deployed in a stratified manner at 16 locations in the Yandina Creek wetlands to capture change across the entire drainage channel and tidal gate network, and at 10 random locations in each control wetlands over nine monitoring events ( n = 414). Each BRUVS was positioned simultaneously at least 200 m apart and comprised of a high‐definition GoPro Hero camera, mounted on a 5 kg weight, and with a 0.5‐m arm supporting a bait bag filled with 500 g of pilchards ( Sardinops sagax ) (Gladstone 2012; Borland et al 2022 a ). All deployments lasted for 1 hour and were done within 2 hours of high spring tides to maximize visibility and the extent of wetland inundation and standardize for effects of tidal variation.…”

“…mortality of pre-existing plant and animal communities), greater connectivity and improved accessibility to unoccupied ecological niche space (Duncan et al 2019;Olson et al 2019). Urban structures and terrain variation have previously elicited similar supplementation effects on the ecological functions performed by many generalist fish species in modified estuaries (Olds et al 2018;Borland et al 2022aBorland et al , 2022b. It is anticipated as biophysical (i.e.…”

Fish and crustaceans provide early indicators of success in wetland restoration

“…On each sampling event, BRUVS were deployed at 16 sites in the Yandina Creek wetlands, and at 10 sites in each reference wetland ( n = 46 per event). BRUVS were comprised of a high‐definition GoPro Hero‐5 camera and filmed at 1,080 pixels, 30 frames per second, and with a wide field of view (14 mm) and then mounted on a 5 kg weight, with a bait bag filled with 500 g of pilchards ( Sardinops sagax ) that was held 0.5 m in front of the camera on a PVC pipe (Olds et al 2018; Borland et al 2022a). All BRUVS deployments lasted for 1 hour and were completed within 2 hours either side of spring high tides to standardize for potential effects of tidal variation.…”