|Spatial variation of intertidal macrofauna on a sandy ocean beach in Australia|
James, R.J.; Fairweather, P.G. (1996). Spatial variation of intertidal macrofauna on a sandy ocean beach in Australia. Est., Coast. and Shelf Sci. 43(1): 81-107
In: Estuarine, Coastal and Shelf Science. Academic Press: London; New York. ISSN 0272-7714, more
|Authors|| || Top |
- James, R.J.
- Fairweather, P.G.
Spatial variation of macrofauna on a sandy beach was examined simultaneously over two scales across-shore (among and within zones) and three nested scales along-shore over the entire length of the beach. Prior to the main study, pilot studies were performed to determine: (1) the relative efficiency, accuracy and precision of combinations of core size, depth of sampling, and sieve mesh size; and (2) the likely distribution of macrofauna across-shore so that stratification of sampling in the main study would be meaningful. From this, three zones were defined across-shore, namely: (1) the high-shore zone which extended 10 m downshore of the drift line and was dominated by two species of isopod; (2) the mid-shore zone which extended across the beach from the bottom of the high-shore zone to the top of the swash zone and was dominated by the glycerid polychaete Hemipodus sp.; and (3) the swash zone which contained more species than the other two zones and was dominated by amphipods, Hemipodus sp., the bivalve Donax deltoids and a species of cumacean. In the main study, multivariate analyses confirmed that assemblages of macrofauna varied significantly among zones despite smaller scale variation within zones and along-shore variation. Significant along-shore variation was detected in assemblages of macrofauna from each zone and occurred at different scales for different zones. Only assemblages in the swash zone showed a pattern of along-shore variation that was consistent with a gradient in wave exposure along the beach. Univariate analyses showed that significant variation in populations of individual taxa occurred at both large and small scales. Significant variation was detected across-shore within zones for nearly all variates and this demonstrated the importance of formally assessing variation within zones when making comparisons among zones. Significant variation was also detected along-shore in analyses of particular taxa, and interactions of across- and along-shore variation also occurred. These results illustrate the necessity of considering both across- and along-shore variation for describing spatial patterns in assemblages or individual species of macrofauna. Unfortunately, sampling a single transect across a beach, which is common in many published descriptions of spatial patterns, will not provide an adequate nor representative description of the macrofauna of that beach because this approach fails to consider all important sources of variation and confounds large- and small-scale variation. The authors conclude that a better understanding of small-scale variation, both along- and across-shore within beaches, is required in order to provide better descriptions of patterns, provide a basis for larger scale studies, allow unconfounded comparisons among beaches and, ultimately, to improve our understanding of the ecology of sandy beaches.