Macrobenthic Secondary Production in the Intertidal Zone of the Ria Formosa—a Lagoon in Southern Portugal

Production and biomass of the macrobenthic intertidal fauna of a sand flat, a Zostera noltii bed, and a mud flat in the Ria Formosa, Southern Portugal were examined over an annual cycle. The following values were obtained for secondary production P (g ash free dry weight m-2 a-1) and average biomass (g ash free dry weight m-2)—the value in brackets with the epibenthic predator Carcinus maenas included: sand flat: P=32•5 (34•4); =15•2 (15•4); P/ =2•14 (2•23); Zostera noltii bed: P=54•2 (57•6); =16•7 (17•2); P/ =3•24 (3•35); mud flat: P=54•7 (71•5); =22•4 (25•1); P/ =2•44 (2•85). Biomass varied markedly with minimum values during winter and maxima in spring/summer reflecting highest macrobenthic production during spring and summer months. Production and biomass were much more diverse on the sand flat and in the Zostera bed compared to the mud flat. This was interpreted as being due to differences in grain size characteristics between the sand flat and the mud flat and a caging effect of Zostera leaves. Production figures are discussed with reference to the main food sources of the species. It is concluded that detritus must be of outstanding importance for the production processes in the Ria Formosa.