Small‐scale macrobenthic community structure along asymmetrical sand waves in an underwater seascape

Chiu H. Cheng,Bas W. Borsje,Sarah O'Flynn,Karline Soetaert,Tom Ysebaert,Olivier Beauchard

doi:10.1111/maec.12657

Abstract

AbstractSand waves are dynamic and regular bedforms that are ubiquitous in sandy shelf seas. However, information about the ecological characteristics (e.g., benthic community structure) and their spatial variability within these habitats is very limited. To address this knowledge gap, we undertook a field campaign in summer 2017 to investigate the macrofaunal community composition of a sand wave area off Texel (Dutch part of the North Sea). Sand waves in this area were asymmetrical, with longer gentle slopes that were approximately double in length to the shorter steep slopes. The benthic distribution along the different parts of these sand waves was assessed by collecting a large number of box cores within a transect line (~1 km). We show considerable variability in the individual, biomass and taxon densities, which were all significantly higher on the steeper slopes of the sand waves. These results are consistent with the trends observed in both the abiotic parameters and video analysis that were measured in two recent studies at the same study area. Our results provide valuable insight into the small‐scale patterns of variability in asymmetrical dynamic bedform environments, where gentle slopes seem to be primarily controlled by physical forces, while steep slopes are more under biotic control.

Highlights

In many coastal regions worldwide, the sandy seabed is seldom static or flat, but oftentimes, many types of bedforms can be found, as is the case in the Dutch sector of the North Sea (Borsje, de Vries, et al, 2009)
We showed that the morphology of the asymmetrical sand waves have a profound effect on the benthic community structure, as seen in the individual, biomass and taxon densities
Our results suggest that sampling resolution is another important aspect that must be considered, especially for dynamic environments such as asymmetrical sand waves

Summary

Introduction

In many coastal regions worldwide, the sandy seabed is seldom static or flat, but oftentimes, many types of bedforms can be found, as is the case in the Dutch sector of the North Sea (Borsje, de Vries, et al, 2009). These include the largest sand banks of up to 10 km in length and 30 m in height, down to small sand ripples that are on the order of tens of cms in length and several cms in height; in between this range are several intermediaries such as megaripples (up to 10 m long, tens of cm in height) and sand waves (100– 1,000 m long, up to 10 m high; Morelissen et al, 2003) Though development of these bedforms are largely driven by hydrodynamic and physical (e.g., sedimentary) processes, other factors such as benthic organisms are believed to play an important role in shaping the sedimentary and hydrodynamic conditions of these environments (Borsje et al, 2009; Damveld et al, 2019). This is the case for the meso-scale sand waves, which are the focus of this study here.

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Conclusion