Analysing long-term change in small benthos: geomorphological dynamics affects method selection

Werner Armonies

doi:10.1186/s10152-019-0533-y

Abstract

In the tidal inlets of the northern Wadden Sea, species composition of selected taxa of the small benthos is compared to a study performed some 35 years before, using the same methods and sampling the same sites. Site-by-site comparisons suggest a dramatic change in community composition at a local scale. However, geomorphology is highly dynamic in this area, and sediment composition, water depth, or both, had changed during the intermediate decades in most of the sites. Since most of the species are limited to a single sediment type, a habitat approach was used for an alternative analysis of the data. This contradicted the idea of dramatic change but revealed relatively high stability of species composition at a regional scale, indicating that local change cannot be up-scaled to larger areas in this highly dynamic environment. Instead, a habitat approach is more adequate though increasing environmental dynamics requires increasing sampling effort. As a by-product of this study, 8 new taxa of Platyhelminthes are described: Karlingia septentrionalis n. sp., Paracalviria diadema n. sp., Kataplana macrobursalia n. sp., Adenorhynchus compositus n. sp., Litucivis simplex n. sp., Scoliopharyngea magnaspina n. sp., Promesostoma convolutum n. sp., and Gnathorhynchus rostellatus indivisus n. spp.

Highlights

Due to the natural variability of environmental and climatic factors as well as to human interference, habitats and their associated communities are subject to change over time
Where sound background data are available, the degree of change can be analysed by repetition of a previous study using the same methods, and sampling the same sites, which may be an efficient method to reduce random variability when temporal changes are the target [1]. This worked quite well in the analysis of temporal change in the small benthos of a semi-exposed tidal beach that had been morphologically stable over the past
Sea are such a highly dynamic zone, where dislocations of the tidal channels and interspersed sand banks result in bathymetric changes up to 20 m within 10 years [3]

Summary

Introduction

Due to the natural variability of environmental and climatic factors as well as to human interference, habitats and their associated communities are subject to change over time. Sea are such a highly dynamic zone, where dislocations of the tidal channels and interspersed sand banks result in bathymetric changes up to 20 m within 10 years [3]. This caused no major problems in analyses of historic change in the larger epibenthic fauna [4, 5] because dredging always integrates over the dredged distance and the habitat types therein, and because mobility determines the spatial scales over which the densities of benthic organisms are associated with substrate variability [6]. Since species vary in the preferred ranges of environmental factors, a site characterised by “fine sand, 12 m depth” in a previous mmons.org/licenses/by/4.0/

Methods

Results

Conclusion