BACKGROUND:Previous flatworm phylogenetic research has been carried out analysing 18S and 28S DNA markers. Through this methodology, Mariplanellinae subfamily has been recently re-classified as Mariplanellida status novus. This new classification implied that 3 genera belonged to Mariplanellida: Mariplanella, Lonchoplanella and Poseidoplanella. In this study, we aim to clarify some of the relationships within Rhabdocoela analysing 18S and 28S DNA markers of a total of 91 species through Maximum Likelihood and Bayesian Inference methodologies. A total of 11 species and genera, including Lonchoplanella, from the island of Sylt are included and had not previously been involved in any molecular phylogenetic analyses.RESULTS:Our phylogenetic results support Mariplanellida as an independent group within Rhabdocoela and its status as an infraorder. Our study suggests that Lonchoplanella axi belongs to Mariplanellida. Within Rhabdocoela, Haloplanella longatuba is nested within Thalassotyphloplanida, instead of Limnotyphloplanida. Within Kalyptorhynchia, the taxon Eukalyptorhynchia turned out to be paraphyletic including members of Schizorhynchia. These results also support the position of the genus Toia separate from Cicerinidae.CONCLUSIONS:Lonchoplanella axi belongs to Mariplanellida, whose status as infraorder is herein confirmed. The genus Toia belongs separate from Cicerinidae. Further research is needed to clarify the phylogenetic relationships of Hoploplanella. Most of the species, genera and families included in this study with more than one terminal are monophyletic and well supported. Adding gene markers and complementary morphological studies will help to clarify those relationships that remain uncertain.

Introduction Any measure of ecological stability scales with the spatial and temporal extent of the data on which it is based. The magnitude of stabilization effects at increasing spatial scale is determined by the degree of synchrony between local and regional species populations. Methods We applied two recently developed approaches to quantify these stabilizing effects to time series records from three aquatic monitoring data sets differing in environmental context and organism type. Results and Discussion We found that the amount and general patterns of stabilization with increasing spatial scale only varied slightly across the investigated species groups and systems. In all three data sets, the relative contribution of stabilizing effects via asynchronous dynamics across space was higher than compensatory dynamics due to differences in biomass fluctuations across species and populations. When relating the stabilizing effects of individual species and sites to species and site-specific characteristics as well as community composition and aspects of spatial biomass distribution patterns, however, we found that the effects of single species and sites showed large differences and were highly context dependent, i.e., dominant species can but did not necessarily have highly stabilizing or destabilizing effects on overall community biomass. The sign and magnitude of individual contributions depended on community structure and the spatial distribution of biomass and species in space. Our study therefore provides new insights into the mechanistic understanding of ecological stability patterns across scales in natural species communities.

A shallow subtidal area in the northern Wadden Sea was monitored over 17 years (from 2003 to 2019) for sediment parameters and macrobenthic fauna. Due to the sheltered position of the study area, sediment composition remained rather stable with only minor annual and seasonal variations in sediment granulometry. An intermittend storm (‘Kyrill’) had no significant effect on sediment composition parameters; the construction of an artificial dune along the southern border of the study area had minor transient but no lasting effects on sediment composition. Faunal species richness and total abundance showed the typical seasonality with minimum abundance in late winter and a peak after recruitment in summer. Variations between years in autumn (post-recruitment) abundances were best explained by the number of days with a seawater temperature <1°C during the preceding winter. Temperature during other seasons, salinity, chlorophyll concentration and NAO showed no significant correlations with total abundance, nor did storm (‘Kyrill’) or construction of the artificial dune. Within-site faunal variability was best explained by water depth and velocity of the tidal currents while sediment granulometry was of minor importance. However, the amount of bivalve shell detritus mixed with the sandy sediment proved to be the strongest covariant of species numbers, total abundance, and species-specific abundances. At the sediment surface, shells provide the only anchorage for epibenthic species which in turn attract associated fauna. Shells inside the sediment hamper movement of infaunal predators and epibenthic predators are handicapped in rooting about for prey. Thus, shell material is a highly significant structural factor for the macrozoobenthos in these shallow waters. In a future with increasing ocean acidification, the availability of benthos as a food source for higher trophic levels will depend on the balance between pH-driven shell destruction and the compensatory power of shell-building species.

Over the past 70 years, numerous authors studied the platyhelminth fauna near the island of Sylt in the eastern North Sea, each with a specific focus on varying aspects of ecology, morphology or systematics, and most of them dealing with a single habitat type. These data are combined with new data to get a comprehensive view of species richness, the distribution of individual species across tidal levels and sediment types and the resulting communities. So far, 398 platyhelminth species have been recorded around Sylt island, plus a still growing number of unidentified or undescribed species, in particular from subtidal waters. The distribution over habitat types (as defined by sediment types and tidal level) is described for the known species. Neighbouring habitat types overlap in species composition, and faunal composition changes continuously over environmental gradients. The number of species recorded per habitat type mirrors the sampling intensity and varied between some 20 species in poorly studied habitats and 150 in the well-studied intertidal sand flats. Corrected for variations in sampling intensity, platyhelminth species richness showed no significant differences between sediment types and only moderate variation over tidal levels. On a larger spatial scale, three faunal assemblages can be differentiated: the supratidal harbours brackish-water species (mesohaline in the upper and polyhaline in the lower supratidal), the intertidal polyhaline-marine species with a wide tolerance of variations in physical factors and the subtidal marine (± stenohaline) species. With respect to sediment type, mud and sand dwellers are well separated in the supra- and subtidal belt but less in the intertidal. Provided these rules are general, I conclude platyhelminth species richness in a given section of coastline mainly depends on the ranges of environmental factors covered. Nineteen new species encountered during this study are described.

We describe a new genus of dalytyphloplanid rhabdocoels, with seven new species. Orostylis gen. nov. has a unique combination of characters including the presence of a sclerotised stylet, an anteriorly positioned male copulatory organ with the male genital pore in the buccal cavity, and the absence of an oviduct. The ovary empties directly into the intestinal lumen. Orostylis dohae sp. nov., Orostylis asinaraensis sp. nov., Orostylis caecus sp. nov., Orostylis distortus sp. nov., Orostylis donanae sp. nov., Orostylis gallicus sp. nov., and Orostylis timucuorum sp. nov. are distinguished from each other by the structure of the sclerotised parts of the male copulatory organ. Molecular and morphological evidence place the new genus in Neodalyellida Willems et al. 2006, and similarities with other taxa are discussed.

An extensive data set of macrozoobenthos from the eastern North Sea was evaluated in order to describe the distribution of infaunal species with respect to water depth and median grain size of the sediment. The resulting data are presented for 134 species, in 104 species abundance correlated significantly with water depth, with most species decreasing in abundance towards the hydrographically turbulent shallow areas. This suggests hydrography is a limiting factor for most of the species in this area while very few species only seem to favour the turbulent side of the gradient. With respect to median grain size, two thirds of the species showed significant abundance variations and one third did not. Most of the latter species were either represented by rather poor data or are known to be highly motile. Thus, true sediment generalists seem to be few. Conversely, no species was exclusively restricted to a single sediment type. Significant depth × sediment type interaction terms in a regression model indicate that abundance distribution over sediment types varied with depth level in 60% of the species, indicating that these populations were restricted to a part of their species-specific tolerated ranges in the study area. Hence, the distributional patterns over water depth and sediment types shown here represent realised niches. These data may help to locate populations and, in the light of global change, may serve as a baseline for future comparisons.

Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore extraction site. We studied the long-term effects of sand extraction on bathymetry, geomorphology, habitats and benthic fauna. Sand extraction created dredging holes about 1 km in diameter and up to 20 m below the ambient seafloor level. Directly after dredging the superficial sediment layer, inside the pits was dominated by coarse sand and stones. Hydroacoustic surveys revealed only minor changes of bathymetry > 35 years after sand extraction. Obviously, backfill of the dredging pits was very slow, at a rate of a few millimeters per year, presumably resulting from low ambient sediment availability and relatively calm hydrodynamic conditions despite high wave energy during storms. Thus, a complete backfill of the deep extraction sites is likely to take centuries in this area. Hydroacoustic surveys and ground truthing showed that the backfilled material is mainly very fine sand and mud, turning the previously coarse sand surface into a muddy habitat. Accordingly, grab samples revealed significant differences in macrozoobenthos community composition, abundance and species density between recently dredged areas (< 10 years ago), recovery sites (dredging activity > 10 years ago) and undisturbed sites (control sites). Overall, dredging turned the original association of sand-dwelling species into a muddy sediment association. Since re-establishment of disturbed benthic communities depends on previous reestablishment of habitat characteristics, the low sedimentation rates indicate that a return to a pre-dredging habitat type with its former benthic community and habitat characteris- tics is unlikely. Since coarse sand is virtually immobile in this area, a regeneration towards pre-dredging conditions is also unlikely without human interference (e.g., mitigation measures like depositing coarse material on the seafloor to restore the sessile epifauna).

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.

Ongoing erosion at coasts, beaches and dunes accompanied by a climate change-induced sea-level rise requires extensive protection measures. At the Island of Sylt (SE North Sea) beach nourishments were conducted for almost 50 years to protect the exposed western coast against erosion. Since 1984, the materials for the sand replenishments were dredged from an offshore excavation site approx. 7 km west off Sylt in the German Bight. In this study, we investigate the long-term effects of sand extraction on the local geomorphology, the associated benthic habitats and fauna. Hydroacoustic surveys and grab sampling revealed that after more than 35 years changes in bathymetry (with dredging pits of down to ~15 m below sea floor) and also changes in habitat characteristics are still present. Additionally, the sediment and benthic faunal compositions have changed. A comparison between dredged areas and undisturbed seafloor revealed significant differences in mud content (increasing), the number of individuals and species of macrozoobenthic organisms (decreasing). This indicates that the benthic communities in the dredging areas are in a persistent successional stage. Mud-loving species (e. g. Notomastus latericeus and Kurtiella bidentate) profit from the changed habitats, however sand-preferring organisms (e.g. Pisione remota and Aonides paucibranchiata) largely disappeared. Because of the slow backfill rates, we conclude that a complete backfill of the deep dredging pits is likely to take centuries. The same is expected to apply for the regeneration of the benthic communities. However, since rather coarse-to-medium sand was removed from this area and re-accumulation of this Pleistocene material is not possible because of weak transport rates, a re-establishment of benthic communities that prefer coarser sand seems to be unlikely. Since benthic communities are strongly linked to the habitat characteristics, habitat mapping using hydroacoustic techniques is an efficient and cost-effective measure to monitor the state of regeneration in this study site.

Most of our planet’s biodiversity is still unknown, particularly in the sea. Although around the island of Sylt in the North Sea, the small zoobenthos (meiofauna) has been studied intensively since the 1950s, repeating previous surveys revealed an unexpected wealth of new species in addition to the 330 species of free-living microturbellarians (non-parasitic Platyhelminthes) already known from this area. Extrapolation from well-known to less-known habitat types suggests that a total of some 520 Platyhelminth species should be expected around this island, about 670 in the North Sea ecoregion, and 830 in the ‘Northern European Sea’ ecoprovince. Assuming that the other biogeographic provinces of the planet harbour a similar diversity, a total of some 20,000 marine microturbellarian species is estimated for the global shelf zones. Less than 10% of these are known by now. As a contribution to fill that gap, ten new taxa are described: Coelogynopora minuta n. sp., Coelogynopora sopottehlersae n. sp., Cirrifera paraculeata n. sp., Boreocelis fragilis n. sp., Postbursoplana noldti n. sp., Promesostoma wehrenbergi n. sp., Ptyalorhynchus oculatus n. sp., Acrorhynchides canaliculatus n. sp., Dactyloplana n. gen., and Dactyloplana tridigitata n. sp.

Based on the past 150 years of research and ongoing time-series observations we give a comprehensive overview of marine species composition around the island of Sylt in the eastern North Sea. A total of 2758 species is listed according to the categories microplankton (591 species), zooplankton (137), nekton (118), benthic microflora (158), benthic macroflora (125), benthic micro-and meiofauna (1204), benthic macrofauna (509), birds and mammals (91), and neobiota (39). Plants account for a third of the species, most (85%) of them are microscopic Chromista. Among animals, 60% of the species are micro- and meiofauna though this faunal component is still insufficiently known. These figures are similar to records from the southern North Sea and therefore may by typical for temperate climate sedimentary coastal areas. A comparison with the total of marine species suggests that the small benthic fauna may be severely understudied over most of the world. Analysis of global change depends on sound baseline data and species inventories like this can assist in the detection of biodiversity changes. They emphasise rare species and the full range of local habitats while time-series measurements usually rely on a few selected habitats and biotic components to generate a very general picture of the state of an ecosystem.

Trawling is one of the most damaging activities for fauna living at the ocean resulting in simultaneous pulse and chronic impacts on benthic communities on multiple spatio-temporal scales. Recently, high quality Vessel Monitoring by Satellite (VMS) data provides spatio-temporal information of swept area by fishery trawlers. Using this huge amount of information in combination with about 20 environmental descriptors, we aim to tease apart the effect of species endogenous features (i.e. dispersal capability) and exogenous factors (i.e. environmental conditions) on the fauna responses to fishery and its related spatial scales. We analyse data of 300 grab-samples taken in the German Bight (North Sea), encompassing 140 macrobenthic species collected on a regular grid over an area of about 8000 km2. We use Moran Eigenvector Maps to model patterns of potential connectivity between locations and shed light on which spatial scales fisheries, environmental characteristics, and macrobenthos are linked. Finally, we show maps of fauna response to fishery. We argue that despite the importance of proper quantification of fishing pressure and other human activities, shedding light on the effects and response to such activities is crucial for a sound understanding of the processes that shape ecosystems and diversity distribution

Climate change and species introductions strongly changed macrobenthic community composition in the North Sea during past decades. To find out whether there was a similar change in meiofauna, I re-examined a semi-exposed sandy beach of the Island of Sylt that had been intensively studied between 1965 and 1975. These previous studies provide the baseline for temporal change. As before, the analysis of species composition focused on Platyhelminthes. Minor change in the physical properties of the beach during the past decades was compensated for by including two adjoining beaches, one slightly more sheltered and the other slightly more exposed. In due consideration of somewhat differing sample size, platyhelminth species richness barely changed over the past 50 years, and the numerical dominant species were still the same. However, roughly 10% of the 220 species found during this study were not previously recorded from the Island of Sylt. Thirteen are new to science though unpublished records indicate that half of them already occurred previously. Seven species described from elsewhere were recorded for the first time in the Sylt area. Based on their known geographical range, none of these can be unambiguously assigned an immigrant or introduced species. I conclude that (1) the platyhelminth fauna displayed high temporal stability over the past 50 years, and (2) though this beach is among the best studied in the world, a rate of 10% new species indicates our knowledge on the diverse meiofauna is still relatively poor. Seven new species of Platyhelminthes are described and three re-described: Coelogynopora multispina n. sp., Pseudostomum gracilis Westblad 1955, Nesite ptychoperoides n. gen. n. sp., Haplovejdovskya scilliensis Faubel & Warwick 2005, Haloplanella magnarhabdita n. sp., Haloplanella spiralis n. sp., Moevenbergia oculifagi n. sp., Coronhelmis inaequalis n. sp., Proxenetes inflatus den Hartog 1966, and Diascorhynchus falconis n. sp.

Exposed sandy coasts are predominantly physically controlled environments where benthic communities are structured by the independent response of species to the physical environment, with minimal biological interactions (swash exclusion hypothesis). This prevalence of physical control may be regarded as a typical property of exposed coastal areas. In an offshore direction, the importance of wave effects on the benthos will diminish until a depth is reached where they are no longer significant [wave exclusion hypothesis (WEH)]. This loss of a coastal property may be used to define an offshore depth limit of the coastal zone. We used a large set of benthos data from the SE North Sea to test whether an offshore limit of the coast can be clearly recognised despite strong small-scale variability and how this limit would vary seasonally and from year to year. In accordance with WEH, both species density and total abundance of macrobenthos were low in the surf zone, strongly increased with depth, and averaged over all sampling dates became relatively constant below 30 m depth. Seasonally, these gradients were weaker during summer recruitment than during autumn. Species richness, by contrast, showed no significant difference with depth. In single years, the depth of the turning point from increasing abundances to constant abundances varied between 20 and 31 m (equivalent to 40–80 km off the coastline) depending on wave height. We conclude that this zone can be derived from benthic community gradients.