Who lives in a pear tree under the sea? A first look at tree reefs as a complex natural biodegradable structure to enhance biodiversity in marine systems

Hard substrates play an important role in global marine systems as settlement surface for sessile reef-forming species such as corals, seaweeds, and shellfish. In soft-sediment systems, natural hard substrates such as stones, bedrock and driftwood are essential as they support diverse assemblages of reef-associated species. However, availability of these hard substrates has been declining in many estuaries and shallow seas worldwide due to human impacts. This is also the case in the Dutch Wadden Sea, where natural hard substrates have gradually disappeared due to burial by sand and/or active removal by humans. In addition, driftwood that was historically imported from rivers has been nullified by upstream logging and coastal damming of estuaries. To investigate the historic ecological role of wood presence in the Wadden Sea as settlement substrate and fish habitat, we constructed three meter high artificial reefs made of felled pear trees. Results demonstrate that these reefs rapidly developed into hotspots of biodiversity. Within six months, the tree-reefs were colonized by sessile hard substrate associated species, with a clear vertical zonation of the settled species. Macroalgae and barnacles were more abundant on the lower parts of the reef, while bryozoans were more dominant on the upper branches. In addition, six fish species were observed on the reefs, while only two species were caught on sandy control sites. Moreover, the abundance of fish on the reefs was five times higher. Individuals of the most commonly caught species, the five-bearded rockling Ciliata mustela, were also larger on the reef. These patterns also hold true for common prawn, Palaemon serratus, which were also larger and ten times more numerous on the reefs. Present findings indicate that the reintroduction of tree-reefs as biodegradable, structurally complex hard substrates can increase local marine biodiversity in soft-sediment systems within relatively short time scales.</p

Publisher correction:Resource landscapes explain contrasting patterns of aggregation and site fidelity by red knots at two wintering sites

[This corrects the article DOI: 10.1186/s40462-018-0142-4.].</p

The seafloor from a trait perspective:A comprehensive life history dataset of soft sediment macrozoobenthos

Biological trait analysis (BTA) is a valuable tool for evaluating changes in community diversity and its link to ecosystem processes as well as environmental and anthropogenic perturbations. Trait-based analytical techniques like BTA rely on standardised datasets of species traits. However, there are currently only a limited number of datasets available for marine macrobenthos that contain trait data across multiple taxonomic groups. Here, we present an open-access dataset of 16 traits for 235 macrozoobenthic species recorded throughout multiple sampling campaigns of the Dutch Wadden Sea; a dynamic soft bottom system where humans have long played a substantial role in shaping the coastal environment. The trait categories included in this dataset cover a variety of life history strategies that are tightly linked to ecosystem functioning and the resilience of communities to (anthropogenic) perturbations and can advance our understanding of environmental changes and human impacts on the functioning of soft bottom systems

Mutual facilitation between foundation species Mytilus edulis and Lanice conchilega promotes habitat heterogeneity on tidal flats

Foundation species that modify their habitat can facilitate other species, including other foundation species. Most studies focus solely on a single foundation species, overlooking such facilitation cascades. In this study, we investigated the interactions between the two coastal foundation species Mytilus edulis (blue mussel) and Lanice conchilega (sand mason worm). We investigated whether these species engage in facilitative interactions or if their association simply reflects a shared ecological niche on the soft-sediment intertidal flats of the Dutch Wadden Sea. To do so, we performed species distribution modeling, manipulative field experiments, and field surveys. We found a positive association between both foundation species, with a 2.45 times higher occurrence of both species compared to a random distribution. In addition, these species partially occupied the same ecological niche. We demonstrated that L. conchilega provided settlement substrate for M. edulis spat, increasing densities by 400 times compared to bare plots. Furthermore, M. edulis reefs facilitated L. conchilega occurrence in the wake of the reef. Biogenic reef development revealed that this interspecific facilitation resulted in spatial habitat heterogeneity. Therefore, we conclude that interspecific facilitation can significantly enhance the occurrence of these two important intertidal foundation species. Acknowledgment of such complex facilitation interactions has an untapped potential for improving the success of restoration and conservation programs.</p

Field Report: Anna Plains and Roebuck Bay Benthic Invertebrate Mapping 2016

This project has been funded by the Department of Parks and Wildlife partnership with BHP Billiton “Eighty Mile Beach and Walyarta Conservation Program”, with in-kind support from NIOZ and Wetland Research & Management This report was produced at the Broome Bird Observatory in late October 2016. Abstract 1. This is a report on repeat surveys on the state of the benthic invertebrates at two internationally important areas of intertidal mudflats in northwest Australia (Roebuck Bay and Eighty Mile Beach) during October 2016. In the period 6-19 October 2016, we mapped the invertebrate macrobenthic animals (those retained by a 1 mm sieve) at the main intertidal sites of West Kimberley, WA: Eighty Mile Beach and Roebuck Bay. We revisited almost the entire intertidal area along Eighty Mile Beach that was ‘benthically’ mapped in October 1999. The benthic animals of the northern mudflats of Roebuck Bay had been mapped in 1997, 2000, 2002, and 2006; we revisited as many as possible of these previously established sampling stations along the northern shore. 2. Our team comprised close to 100 participants with greatly varying levels of experience, though similarly high motivation and enthusiasm. At Eighty Mile Beach we visited 816 sampling stations laid out in a grid of 200 m intersections over 7 separate areas along ca. 75 km of beach (from 10 km north of the Anna Plains Station beach access to 65 km south). In the northern part of Roebuck Bay, we visited 534 sampling stations also laid out in a grid with 200 m intersections (but with distance of 400 m in the southeast). We made notes on the surface features on the mud, including the presence or absence of seagrass and various macrofauna. In the course of digging up, sieving, and sorting the mud samples from all stations, we identified and measured 32,500 individual invertebrates. We tried to identify all animals groups up to the level of species if possible, all on the basis of morphological differences. These species were often given field names, as time and means (literature or access to internet) did not allow us to always attach a proper scientific name. In addition, it is very likely that some of the species are still undescribed. Animals were preserved on ethanol for a more thorough scientific identification at a later date. 3. This time we surveyed two very distinct sections of the West Kimberley coast. Roebuck Bay represents a true embayment that is semi-enclosed by mangroves along the eastern, and some of the western shores, and by cliff and pindan woodlands in the north. Eighty Mile Beach stretches over 200 km along the open Indian Ocean facing northwest. In this environment, the intertidal mud- and sandflat area stretches from 1-5 km wide from shore to sea and is enclosed by sand dunes and a few mangroves. Despite the two systems being very important as nonbreeding areas for the same species of long-distance migrant shorebirds, their geomorphology and ecology are very distinct. 4. At both areas the biodiversity of benthic animals was very high compared with other intertidal soft sediment areas across in the world. In Roebuck Bay, 368 species were found, and at Eighty Mile Beach 156 species, providing a total of 433 species/taxa. The most diverse group were the Polychaeta with 167 species, followed by Crustacea (74), Bivalvia (59), Gastropoda (59), and Echinodermata (35). All other groups total less than 12 species. 5. The two areas have 92 species in common, which in the case of Eighty Mile Beach means that 60% of the species also occur in Roebuck Bay. Major groups not found at Eighty Mile Beach were Asteroidea, Brachiopoda, Hirudinea, Oligochaeta, Platyhelminthes, Polyplacophora, and Pycnogonida. Most of these groups were also rare in Roebuck Bay, but the absence of Brachiopoda (lamp-shells) and Pycnogonida (seaspiders) at Eighty Mile Beach came as a surprise. Some species, including two species of Spionidae (Polychaeta) common at Eighty Mile Beach were either absent or extremely rare at Roebuck Bay. Furthermore, a small seacucumber with dark coloured spots all over its body, another larger seacucumber Paracaudina chilensis, two bivalve species of the genus Tellina, and two species of anemones were not found in Roebuck Bay. Yet, Roebuck Bay had many more species (277) not found at Eighty Mile Beach, the most common of these was the relatively large bivalve Tellina piratica, followed by the smooth tusk shell (Laevidentalium lubricatum), and the polychaete family Sternaspidae. 6. The large difference in biodiversity between Roebuck Bay and Eighty Mile Beach may be caused by different factors. Roebuck Bay has a greater variety of sedimentary habitats than Eighty Mile Beach. Eighty Mile Beach is completely exposed to the waves of Indian Ocean, while Roebuck Bay is protected by the peninsula on which Broome is situated. Therefore, notorious ‘ecosystem engineers’ such as the seagrasses occur quite extensively on the intertidal area of Roebuck Bay, but are not found at Eighty Mile Beach. These seagrass mats of Halodula uninervis and Halophila ovalis form special habitat for e.g. the little snail Smaragdia souverbiana. The influence of Broome city by episodic sewage and fertilizer releases, of which blooms of the cyanobacteria Lyngbya are an indication, can may well have a negative influence; opportunistic widespread species other than Lyngbya may of course benefit from the additional nutrient inputs. 7. Local communities and the land-owners actively participated in both expeditions. Several DPAW ranger groups (Yawuru, Karajarri and Nyangumarta) joined the sampling and also aided in the identification of species. Angela Rossen (WAMSI) spearheaded a biodiversity project that involved pupils from Cable Beach Primary School. We believe that we have raised wide awareness and generated considerable enthusiasm for the ecology of a unique contribution of northwest Australia to the world. 8. Based on their outstanding universal values, we recommend that the WA government consider an application of the joint marine reserves of Eighty Mile Beach and Roebuck Bay for World Heritage Status, thus joining China and South Korea in acknowledging and protecting this shared heritage

Space–time analyses of sediment composition reveals synchronized dynamics at all intertidal flats in the Dutch Wadden Sea

Intertidal mudflat systems are shaped by geological processes and an interplay of hydrodynamics, sediment availability and ecological processes. All around the world these systems are affected by relative sea level rise (RSLR), changing climate and by human activities such as sediment nourishments, dredging, hydrological engineering and bottom trawling. These kinds of perturbations cause changes in morphology and sediment composition which may cause shifts in the composition, spatial distribution and productivity of benthic communities. We analysed the spatial and temporal variability of the sediment grain size of more than 900 km2 intertidal flats in the Dutch Wadden Sea in the period 2009–2019. The large scale coverage was achieved by yearly grid sampling at more than 4000 stations. Spatial panel data models were used to analyse changes in median grain size and mud content between years and to estimate the effects of resuspension due to wind and the accumulation of silt during summer. We show that between years the sediments of the intertidal flats changed synchronously throughout the study area and that the flats became coarser during the period 2011–2015 and muddier again between 2015 and 2019. The system wide changes and the absence of clear local deviations leads to the hypothesis that a large scale factor like changing hydrodynamic regime (e.g. due to RSLR), variability in the composition of suspended sediment in the North Sea or changing microphytobenthic productivity were causally involved in the coarsening of intertidal flats. Our data and analysis provides a base for further scientific enquiry but longer time series on higher temporal resolution of both sediment data and the physical and ecological environment are required. Models simulating the environment may provide further insight into possible development of sediment composition of the intertidal flats of the Wadden Sea

Ragworms (<i>Hediste diversicolor</i>) limit eelgrass (<i>Zostera marina</i>) seedling settlement:Implications for seed-based restoration

Seagrasses are globally declining and multiple restoration efforts are undertaken to reverse these losses. However, these efforts have proven to be challenging, facing a variety of bottlenecks. We studied how predation by macroinvertebrates may form a potential bottleneck for seed-based seagrass restoration. Specifically, we questioned if the omnivorous common ragworm (Hediste diversicolor) may act as a predator on eelgrass (Zostera marina) seeds and whether that could affect seed-based eelgrass restoration trials. In a controlled lab experiment, we studied (1) how seedling establishment was affected by ragworm biomass (0, 2, 8 g DW m−2), (2) if the absence or presence of an additional or alternative high-protein food source (Sanikoi ® Gold Protein Plus, 52% protein) prevented potential seed predation by ragworms and (3) how ragworm size (small: 0.0029 g and 3.3× bigger: 0.0095 g DW ragworm−1) affected eelgrass seedling establishment. Additionally, we questioned (4) if ragworms may provide a bottleneck for annual eelgrass restoration experiments in the Dutch Wadden Sea by combining data from a large-scale benthic survey (SIBES, Netherlands Institute for Sea Research (NIOZ), Texel) with an existing eelgrass habitat suitability map. We found that &gt;2 g DW m−2 ragworms completely hampered eelgrass seedling establishment, even when fed an additional, protein-rich, food source. Ragworms only seemed to target sprouted seeds rather than intact seeds. Additionally, sprouted seed consumption by ragworms was size-dependent: sprouted seeds escaped predation by smaller ragworms even when present in high biomass (2 g DW m−2). By extrapolating our findings to the field, we showed that 52.8% of the potential eelgrass growth sites in the Dutch Wadden Sea overlap with impeding ragworm biomass (≥2 g DW m−2). By consuming sprouted eelgrass seeds, ragworms may consequently strongly impede seed-based eelgrass restoration efforts, especially since both species have highly overlapping distributions. We thus provided novel insights into an unknown bottleneck for seed-based eelgrass establishment, which may have restoration implications. Especially for annual eelgrass that fully depends on successful seedling establishment for their persistence and survival.</p