Fig. 1
Relationships between intertidal height (in dm from MTL) and a the proportion (in %) of the samples taken at that level revealing a certain high numerical density of large (shell length >22 mm) cockles, and b species richness of macrozoobenthos (in number of species per 0.045 m2). Data of late-summer sampling of 100-m sections of 12 transects of 1 km each on Balgzand. Levels of mean low tide (LTL), mean tide (MTL) and mean high tide (HTL) indicated. Numbers of 100-m sections at each height indicated along horizontal axis of lower graph. a Data of entire 38-year (1970–2007) period of observation, showing relationships for different cockle densities: (solid squares) >50 m−2 (open circles) >100 m−2, (solid triangles) >200 m−2, and (open squares) >500 m−2. Standard errors shown only for values of upper line (>50 large cockles m−2). b Averages (with 1 SE) of the 28-year (1980–2007) section-mean numbers of macrozoobenthic species found (for example: 3 sections were located at MTL with 28 observation each and the pictured point of 9.4 was the average of three 28-year means)