The sandy seabed of shallow coastal shelf seas displays morphological patterns of various dimensions. The seabed also harbors a rich ecosystem. Increasing pressure from human‐induced disturbances necessitates further study on drivers of benthic community distributions over morphological patterns. Moreover, a greater understanding of the sand ripple distribution over tidal sand waves may improve morphological model predictions. Here we analyzed the biotic abundance and ripple morphology in sand wave troughs and crests using video transects. We found that both the epibenthos and endobenthos are significantly more abundant in sand wave troughs, where ripples are less abundant and more irregularly shaped. Finally, we show that camera systems are relatively quick and effective tools to study biotic spatial patterns in relation to seabed morphology.

The behavior of asymmetrical bedforms, which include many tidal sand waves, is challenging to understand. They are of particular interest since they are mostly located within areas prone to offshore engineering activities. Most experimental investigations regarding asymmetrical bedforms consider the riverine environment, are limited to a single sand wave or a few scattered ones, and focus only on differences between crest and trough. Hardly any information is available on sediment compositional changes along asymmetrical tidal sand waves, despite their abundance offshore. An asymmetrical sand wave field located off the coast of Texel Island in the North Sea was studied in June and October 2017. A total of 102 sediment samples were collected over two seasons along a single transect that covered five complete sand waves to measure the grain size composition, organic carbon concentration, chlorophyll-a (chl-a) concentration, and sediment permeability. We found significant variations in these sediment parameters between the sand wave trough, crest, and gentle and steep slopes, including a difference in permeability of more than 2-fold, as well as a difference in median grain size exceeding 65 µm. Based on these characteristics, a sand wave can be divided into two discrete halves: gentle slope + crest and steep slope + trough. Our results indicate a distinct sediment-sorting process along the Texel sand waves, with a significant difference between the two halves of each sand wave. These data could serve as input for process-based modeling of the link between sediment-sorting processes and seabed morphodynamics, necessary to design offshore engineering projects.

The taxonomy of the Afrotropical and Malagasy Paraparatrechina fauna is revised for the first time. Thirteen species are revealed, of which eight are described as new: P. brunnella LaPolla & Cheng; P. concinnata LaPolla & Cheng; P. gnoma LaPolla & Cheng; P. myops LaPolla & Fisher; P. ocellatula LaPolla & Fisher; P. oreias LaPolla & Cheng; P. splendida LaPolla & Cheng; P. umbranatis LaPolla & Cheng. An identification key to the worker caste is provided.

Sand 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.

Innovative techniques are needed to assess oyster performance in flat oyster reef restoration projects. A valve gape monitor, a device that continuously measures opening and closing of live bivalves, can potentially be used as an effective method to determine survival and behaviour of the European flat oyster Ostrea edulis. The method has been successfully used in combination with a number of bivalve species to investigate valve gape activity in response to environmental factors. In this study, eight O. edulis were equipped with valve gape sensors in order to relate gape to environmental conditions such as food availability. Valve gape activity was monitored under controlled laboratory conditions, with and without food, in a concrete basin in the Oosterschelde and in the field (Voordelta, Dutch North Sea). Under controlled laboratory conditions, oysters clearly responded to changes in food availability. Starved oysters closed their valves significantly longer than oysters that received food, and the relative gape width in fed oysters was larger. In the concrete basin (Oosterschelde), a positive correlation between valve opening and Chlorophyll-a was found. Additionally, valve gape activity and tidal movement appeared to be linked. When exposed to a full tidal cycle (Voordelta), a negative correlation between valve opening and Chlorophyll-a was found. However, there was no correlation between valve gape and current velocity. In autumn, longer periods of inactivity were seen, but when valves opened, the valve gape was larger. These data indicate that valve gape can provide valuable information on behaviour (gape frequency and gape width), but also show that it is not necessarily a good proxy for feeding rate. Nevertheless, these results show that the gape monitor can be used to determine the natural behaviour of flat oysters under field conditions, and that gape opening provides information on behaviour and the stress response of bivalves to environmental conditions.