Impact of macroalgal blooms and wader predation on intertidal macroinvertebrates: experimental evidence from the Mondego estuary (Portugal).

The effect of macroalgal blooms and predation by wading on benthic macroinvertebrates was examined in the Mondego estuary, Portugal, during spring 1997. Introduced macroalgal cover and exclusion of predators were used to examine changes in density of macroinvertebrates using univariate and multivariate analyses. There was no evidence of changes in numbers of macroinvertebrates due to predation. Macroalgae were, however, responsible for a decrease in abundance of the worms Amage adspersa (Grube) and Streblospio shrubsolii (Buchanan), and a substantial increase in numbers of Capitella capitata (Fabricius). The density of the worm Hediste diversicolor (O.F. Müller) increased during the first month and decreased after 2 months, associated with macroalgal cover. There were no differences in abundances of macroinvertebrates between different depths. Overall, only polychaete species were affected by macroalgae. Multivariate analysis also showed clear differences in assemblages of macroinvertebrates due to the presence of macroalgae.