Species - area relationships for sandy beach macrobenthos in the context of intertidal width

The marine species richness (MSR) recorded in 159 sandy beach surveys was analysed in relation to beach width (W). MSR is the number of macrobenthic species collected in a standard intertidal transect survey, excluding insects. Beach width (W) was estimated by dividing the spring tide range [m] by the beach face slope, to give a value in [m]. The relationship between MSR and W was best described by a semilog (exponential) model, which was highly significant: MSR = -5.2 + 10.8 log W. The fit of a power model (MSR = cWz) was also significant. The steep slope of the curve for a power model (z=0.49) suggests that beaches function as isolated rather than contiguous habitats and that the nature of the habitat becomes more benign as beaches widen. There are some latitudinal effects, with tropical beaches displaying a higher species-area relationship for any beach width than other regions.