Near- and Offshore Macrofauna Communities and Their Physical Environment in a South-Eastern North Sea Sandy Beach System

Ingrid Kröncke,Thomas H Badewien,Alexander Bartholomä,Anne-Christin Schulz,Oliver Zielinski,Lydia R Becker

doi:10.3389/fmars.2018.00497

Abstract

The aim of the study is to compare spatial variation of macrofauna communities in the near- and offshore zone of the beach system of the island of Spiekeroog (German North Sea) in order to environmental parameters such as hydrodynamics and sediment type. The analysis of hydroacoustic backscatter signals have been used to classify the sea bottom characteristics in terms of surface roughness. Sampling was carried out in May 2014. Samples were taken along a 3.4 km transect in north-south direction. The analyses of the spatial distribution structure of the environmental parameters and the macrofauna communities revealed a clear zonation of the transect line into an inner, outer nearshore, and offshore zone. The inner nearshore was exposed to high hydrodynamic energy with a high variability in sediment composition, a lack of biogenic structures, lowest taxa numbers, but a considerably high diversity (Shannon Wiener index). The hydrodynamic conditions in the nearshore zone were more stable. Sediment distribution was homogenous. Taxa number and abundances increased and polychaete species such as Magelona johnstonii, Spiophanes bombyx, and Lanice conchilega characterized the community. In the offshore zone, taxa number and abundances increased even further. Lanice conchilega dominated the community. While current velocities of the bottom layers decreased, mud contents slightly increased.

Highlights

Sandy beach ecosystems constitute an important transition zone between continental and marine zones (Bergamino et al, 2011)
Looking at current velocities within the two layers, differences in depth ( z) and in current velocity ( u), as well as differences in temperature ( t), salinity ( s), and direction of outflowing low tide waters, we identified five hydrodynamic groups (A-E), which were significantly separated by similarity profile test (SIMPROF) (p < 0.05)
The analysis of the spatial distribution structure of the environmental parameters and the macrofauna communities revealed a classical zonation of a sandy beach system in nearand offshore zone along the transect

Summary

Introduction

Sandy beach ecosystems constitute an important transition zone between continental and marine zones (Bergamino et al, 2011). Hydrodynamic parameters in combination with topographic features force beach systems into a range of different morphodynamic types (Brown and McLachlan, 1990; Short, 1996; Defeo and McLachlan, 2005; Defeo et al, 2009; Nel et al, 2014). These types range from microtidal reflective (narrow and steep) to macrotidal ultradissipative (wide and flat) extremes (Short, 1996; Schlacher et al, 2008; Nel et al, 2014). In between those extremes and are defined as intermediate state (Defeo and McLachlan, 2005)

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