Relationship between species richness and morphodynamics in sandy beaches: what are the underlying factors?

Abstract

One of the most documented generalisations in sandy beach ecology is the trend for species richness of macroinvertebrates to decrease along a morphodynamic gradient from the dissipative to the reflective condition. This widely documented pattern remains unexplained, because the responsible ecological factors and underlying biological processes are still unknown. It has been proposed that swash condition, which changes significantly along the morphodynamic gradient, is the key limiting factor underlying this biological pattern. In this study, I suggest that 2 other physical factors could also be involved: sediment grain size and erosion-accretion dynamics. This proposal is supported by a 2 yr study of 12 sandy beaches in Chile, which showed that grain size becomes coarser, erosion-accretion dynamics more intense, and swash frequency and velocity increase as morphodynamic conditions change from dissipative to reflective extremes. I propose that these 3 environmental factors, although physically interrelated, may have independent influences on different biological processes or species. I suggest therefore that the reduction of species towards the reflective extreme is caused by increasing environmental severity, which is generated by the action (of at least) the 3 physical factors mentioned above. This proposal constitutes the hypothesis of 'multicausal environmental severity', which agrees with the large interspecific variability in the life history and ecological traits of sandy beach communities, since it admits that species with different characteristics could be controlled by different limiting factors. Thus, the present hypothesis provides a more general and flexible framework for investigating the relationship between species richness and morphodynamics in sandy beaches.

Interrelationships of bacteria, meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park, NW Italy)

“…This finding is in T sediment temperature, S salinity, Eh redox-potential, Chl-a chlorophyll a concentration, PHP phaeopigments concentration, CPE chloroplastic pigment equivalent, POC particulate organic carbon concentration, MD median grain size, r 1 inclusive graphic standard deviation, s k skewness coefficient, Prt proteins, Cho carbohydrates, TBN total bacteria number, q w harmonic rank coefficient accordance with the multicausal environmental severity hypothesis, which admits that species with different characteristics are controlled by different limiting factors (Brazeiro 2001). Taxon-specific responses to environmental variables may well be the reason for the different patterns revealed by the multivariate analyses.…”

Ecological impact of coastal defence structures on sediment and mobile fauna: Evaluating and forecasting consequences of unavoidable modifications of native habitats

“…coast orientation, shelf extent, bathymetry) (Short and Wright, 1983). This shore morphodynamic gradient seems to determine some characteristics of the benthic macrofauna, such as the well-known relationship existing between a trend in decreasing macroinvertebrate species richness along a gradient from dissipative to reflective shore conditions (Brazeiro, 2001). Thus, any artificial coastal defence structure, which includes Low Crested Structures (LCS) built to prevent coastline erosion, will impact softbottom benthic assemblages by altering both hydrodynamic and sedimentary characteristics of the surrounding habitats.…”

Spatial and temporal changes in interstitial meiofauna on a sandy ocean beach of South America

“…Hydrodynamic stress plays an important role in controlling spatial patterns of meiofauna density and community structure (Covazzi et al, 2001). Exposed marine beaches have been defined as physically stressful environments (McLachlan, 1983;Rodil & Lastra, 2004) and thus the best way to understand population variability in these ecosystems is by documenting responses to abiotic factors (Jaramillo & McLachlan, 1993;Brazeiro, 2001). …”