The Intertidal Communities on Dissipa-tive Beaches at Risk for Sea Level Rise—The Relationship of Beach Mor-phodynamics and Species Range.

Sea-level rise is likely to cause significant physical changes to beaches in the higher latitudes, resulting in steeper beaches with larger particle sizes. These physical changes have implications for beach invertebrate communities, which are determined largely by sediment particle size, and hence for ecosystem function. Previous studies have explored the relationships between invertebrate communities and environmental variables such as particle size, beach slope, and exposure to wave action. Yamanaka et al. (2010) quantified the abundance of meiofauna and macrofauna across a range of beaches in the UK. The authors confirmed the predominant role of beach physical factors in determining infaunal species composition on the less wave-dominated beaches typically found over much of the European coastline. The more dissipative beaches, or the flat beaches with finer particles and gentler slopes, had a higher density of organisms, but a smaller range of species richness. If predictions that accelerated sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–> will move beaches towards a more reflective morphodynamic state are correct, this could lead to potential adverse consequences for ecosystem functioning through the declining abundance of benthic organisms between 0.3 and 1mm in size. —Michelle Schulte
Yamanaka, T., Raffaelli, D., White, P.C.L., 2010. Physical determinants of intertidal communities on dissipative beaches: Implications of sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–>. Estuarine, Coastal and Shelf Science 88, 267–278.

The authors utilized various indices of beach morphodynamic state to quantify the physical characteristics of beaches in three different estuarine locations on the east coast of the UK that experience different tidal ranges, slopes, and range of particle size. The three contrasting field sites in the UK are the Humber estuary, the Ythan estuary, and the Firth of Forth. Five or six sampling sites were selected within each locality, restricted to a short area of the outer estuary or coastal site in order to minimize any potentially confounding effects of salinity<!–[if supportFields]> XE “salinity” <![endif]–><!–[if supportFields]><![endif]–>. At each station, a cylindrical core was pushed into the sediment to the depth of 10 cm on a randomly chosen surface to sample macrofauna, meiofauna, and sediment. Macrofauna were separated from sediment using a 500 µm mesh, preserved in 70% ethanol<!–[if supportFields]> XE “ethanol” <![endif]–><!–[if supportFields]><![endif]–>, identified to species level, and counted using a microscope. Meiofauna were separated from sediment using a 64 µm mesh, preserved in ethanol, and stained with Rose Bengal, identified to the lowest possible taxon, and counted. Particle size was determined by dry sieving through a tower of mesh sieves. The slope at each sampling station was calculated by measuring the height and distance of the sample site. The exposure at each beach site was calculated using the index derived from wind velocity, direction, duration, and the effective fetch.
Yamanaka et al. created new indices to determine the morphodynamic state of the beach and the wave energy. A combination of non-metric Multi Dimensional Scaling (NMDS), and an eigenvector-based approach, DCA, was used, in conjunction with cluster analysis to explore the main trends and patterns in the data in terms of physical and biological variables of the sites. In addition, stepwise multiple linear regression was used to explore the relationships of abundance and number of species with morphodynamic state. One-way analyses of variance (ANOVA<!–[if supportFields]> XE “ANOVA” <![endif]–><!–[if supportFields]><![endif]–>) were used to test the importance of each independent variable, and also to test the difference of physical variables between the three areas.
The authors explored the relationships between beach fauna and morphodynamic variables, to test whether more dissipative beaches support a high abundance of macrofauna and meiofauna as well as higher macrofaunal species richness. The authors ask how these relationships may inform our understanding of the impacts of sea-level rise<!–[if supportFields]>XE “sea-level rise (SLR)”<![endif]–><!–[if supportFields]><![endif]–> on benthic community structure and function. They compared the differences in the physical characteristics of each of the beaches. Median particle size was not significantly different between estuaries, but beach slope and wave exposure differed significantly. The Humber had a much higher range of exposures and a shallower beach slope than the Ythan and the Forth.
The fauna within these three sites differed in their composition and abundance. There was more overlap in species composition between the Humber and the Ythan, despite an order of magnitude difference in abundance. For each scenario, the more dissipative beaches contained higher abundances of all fauna. So that dissipative beaches with finer particles and shallow slopes generally support a higher abundance of macrofauna.
However, for species richness, Yamanaka et al. found that less dissipative beaches generally support higher macrofaunal species richness. Both the Ythan and the Humber had lower species richness compared to the Forth, but differed markedly in the numbers of individuals recorded. The Forth had an intermediate number of macrofauna individuals but the most taxa represented. In addition, the authors found that the length of exposure to the sun and the beach slope affect the abundance of small, benthic organisms. There were no clear relationships between diversity indices and beach physical variables.
Yamanaka et al. confirmed the predominant role of beach physical factors in determining infaunal species composition on the less wave-dominated beaches typically found over much of the European coastline. All of the species recorded can be described as deposit feeders, filter feeders, or predators. Past studies illustrate that large polychaetes are disproportionately important for ecosystem processes such as nutrient cycling. Thus, functional diversity and compositional effects rather than species richness, may play an important role in driving ecosystem processes. A greater diversity of large species including polychaete species was found at more sheltered sites on the Ythan and the Forth. If sea-level rise<!–[if supportFields]>XE “sea-level rise (SLR)”<![endif]–><!–[if supportFields]><![endif]–> pushes beaches towards steeper slopes and coarser particles, as indicated in the study by Yamanaka et al., then the abundance of these larger species is likely to decline, with consequent reduction in ecosystem functioning.
In summary, the authors illustrate the validity of the trend that more dissipative beaches have a higher abundance of macrofauna and meiofauna compared to reflective beaches when analyzing less wave-dominated beaches. In addition, the authors suggest that sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–> could have a significant impact on ecosystem functioning in northern temperate beaches, through the effects of changing particle size and wave exposure on benthic species richness and abundance, especially the larger-bodied polychaetes. 

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