This study explores the relation between sediment composition and intertidal macrobenthos populations in the Zwin nature reserve (Belgium and The Netherlands), a tidal lagoon that is included in the Ramsar list of wetlands of international importance and has been designated as Natura 2000 area, among others due to its function as wintering habitat for shorebirds that feed upon macrobenthic invertebrates. Species response models show highest biomass of these prey species in organically enriched cohesive sediments and a distinct decline in probability of occurrence for most species in coarse sediments. Further, the biomass of macrobenthos declined between 2003 and 2010 in the extensive low intertidal inlet channel concurrent with the coarsening of the sediment over time in this hydrodynamically stressed habitat. In contrast, macrobenthos biomass increased in a sheltered shallow intertidal habitat that acted as a catchment area for finer sediments, therefore facilitating the succession towards a higher elevated habitat with salt marsh vegetation establishment. Hence, spatio-temporal sediment dynamics decreased site quality for intertidal predators due to a reduction in feeding areas over time, and a change in physical sediment properties that alter the macrobenthos species occurrence and population biomass. This study thus illustrates that sediment transport dynamics may affect the functioning of coastal shallow soft-sediment habitats, like coastal lagoons. The presented macrobenthos species response models provide a tool to assist in management actions that enable the conservation of cohesive low intertidal habitats that provide a high food supply to shorebirds, fish and macrocrustaceans

Summary1. Beach nourishment, the placement of sand onto a sediment-starved stretch of coast, is widely applied as a soft coastal protection measure because of its reduced ecological impact relative to hard coastal protection. In order to predict effects on the intertidal sandy beach ecosystem, we developed a simulation model that integrates species envelope-based projections for the dominant macrobenthos species and mechanistic food web modules for higher trophic levels. 2. Species envelopes were estimated by using Bayesian inference of species' biomass relationships according to the three determining abiotic variables: intertidal elevation, median grain size and total organic matter, obtained from multiple sampling campaigns along the Belgian coast. Maximum potential abundance of higher trophic levels represented by birds, shrimp and flatfish were estimated based on their derived trophic relationship with macrobenthos. 3. After validation, we demonstrated that unlike nourishment slope, sediment grain size strongly determines beach-level species richness and production, with strong deterioration in species richness after nourishment with coarse sediment (>300 lm). Patterns for higher trophic levels do not follow the changes in macrobenthos abundance and biomass. 4. Synthesis and applications. The optimal grain size range for nourishment of fine-grained beaches is 200-300 lm. This modelling approach shows that the impact assessment of beach nourishment needs to include the evaluation of different species richness and biomass variables. Focusing solely on the potential abundance of species from higher trophic levels might lead to deceptive conclusions due to the dominance of opportunistic prey species.

Population dynamics and zonation of the amphipods Bathyporeia pilosa and B. sarsi, co-occurring on some beaches, were studied through monthly sampling of eight cross-shore transects along the Belgian coast (October 2003-October 2004. Their biomass and production were assessed for the Wrst time. Abundance and biomass of B. pilosa were ten times higher along western ultradissipative transects than along slightly more reXective, eastern transects. For B. sarsi (less prominent), diVerences between the two westernmost transects (2-5£ higher) and all others were observed, whereas P/B ratio was comparable for all. B. pilosa could reach two times higher abundance and biomass and higher levels of production (max B. sarsi = 7,580 g m ¡2 y ¡1 ; max B. pilosa = 16,040 g m ¡2 y ¡1 ), while the species was nearly absent from the eastern transects. Continuous reproduction and recruitment with three relative peaks of the latter (February, July, October) were observed. Fecundity showed parallel temporal variation for both species, peaking in February and September-October. Interestingly, the July relative "recruitment" peak could not be explained by relative abundance of gravid females or fecundity, but was probably caused by adult mortality. Both species displayed comparable gonad production (B. pilosa: P g = 0.73 mg/ind year; B. sarsi: P g = 0.71 mg/ind year), but B. pilosa produced fewer yet larger embryos. Peak abundances were found at 436 § 25 SD cm (B. pilosa) and 357 § 40 SD cm (B. sarsi) above MLLWS, corresponding to a 40-62 m cross-shore distance between the peaks of both species. The occupied cross-shore range was larger for B. sarsi than for B. pilosa (35-54 m), for females than for males (15-23 m), and for adults than for juveniles of B. pilosa (5-8 m). Both species displayed many comparable life history features. DiVerences in abundance and biomass may be related to beach morphodynamics and zonation.

Macrofaunal sediment selectivity considerations for beach nourishment programmes. Published in: Marine Environmental Research 84:10-16Joke Van Tomme is the first author of this article. Sarah Vanden Eede helped with the experimental work, the analysis of the results and the finalisation of the manuscript.Chapter 4 -Macrofaunal sediment selectivity considerations for beach nourishment programmes 84 AbstractNowadays, beach nourishment is widely considered as a better alternative compared to the construction of hard structures to protect a sandy coast against detrimental erosive effects, both from an ecological and an engineering perspective. The rare studies conducted on the ecological impact of beach nourishment are short-term, post hoc monitoring investigations of the benthic macrofauna. Little is known of the biological processes during and after nourishment. To allow swift recolonization after nourishment, the characteristics of the nourished beach have to match the habitat demands of the benthic macrofauna. The sediment preference of the key intertidal species Scolelepis squamata, Eurydice pulchra, Bathyporeia pilosa and Bathyporeia sarsi, which dominate many West European sandy beaches, was investigated through laboratory experiments, both in single-species as well as combined-species treatments. While the former aimed at developing guidelines for impact mitigation of beach nourishment, the latter aimed at elucidating the role of biotic interactions in sediment preference.Results of the experiments indicated that Bathyporeia pilosa and Eurydice pulchra prefer the finest sediment, while Bathyporeia sarsi had a broader preference and also occurred in medium-coarse sediments. However, the sediment preference of Eurydice pulchra for fine sediments was not confirmed by other field and experimental studies. The polychaete Scolelelpis squamata had the broadest preference and even showed a high occurrence in coarse sediments that are not naturally occurring on the sandy beaches where the animals were caught for this experiment. However, this polychaete is a cosmopolitan species, not only occurring on fine-grained beaches, but also on coarse-grained beaches worldwide. The preferences imply that beach nourishment with coarse sediment will have a major effect on Bathyporeia pilosa while effects of coarse sediments on Scolelepis squamata will be minor. Finally, interspecific competition with the sympatrically occurring amphipod Bathyporeia sarsi was found to change the sediment selection of the amphipod Bathyporeia pilosa towards the coarser sediments where Bathyporeia sarsi occurred in lower frequencies.

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