MEPS 436:29-50 (2011)  -  DOI: https://doi.org/10.3354/meps09210

ABSTRACT: During the 1960s and early 1970s, the open system of the Rhine-Meuse estuary with a continuous salinity gradient was converted into a series of stagnant fresh water lakes separated by sluices from the North Sea coastal region ‘Voordelta’. For the last 50 yr, the macrozoobenthic communities have been monitored intensively, and a large dataset is available on the responses of macrozoobenthic communities to strong disturbances (e.g. transitions in salinity, currents and dynamics) and gradual changes (e.g. changes in pollution and nutrient levels). The current study analyzes patterns and developments in macrozoobenthic compositions in terms of community descriptors (e.g. density, richness, evenness and diversity) and proportional distributions over feeding guilds (suspension feeders, deposit feeders, surface deposit feeders, herbivores, omnivores and predators). We compare historic and present situations and show that communities respond in similar ways (viz. peaking densities co-occurring with decreasing richness and diversity) to large disturbances and that the distribution over the feeding guilds indicates the state of the environment. Although the historic communities showed signs of system deterioration (mainly due to pollutants and nutrients), and at present, exotic species are abundant in the region, historic data were found to be valuable as a reference for what can be expected on the macrozoobenthic level following estuary restoration. This study showed the value of an undisturbed estuary in terms of total macrozoobenthic diversity compared to the series of fresh water lakes now separated from the Voordelta system and raises questions about future plans for a regulated salt water inlet that will be restricted to only 11.5 km inland.

KEY WORDS: Benthic communities · Species diversity · Feeding guilds · Quality indicators · ­Reference state · Salinity gradient · Multi-dimensional scaling