De gevolgen van de compartimentering van de Zuidwest-Nederlandse zoute en brakke wateren voor de diversiteit van bruin- en roodwieren

This study examines the development of brown and red algal species richness and distribution in the Southwest Netherlands’ saline and brackish waters following the execution of the Delta Hydrotechnical Works. These works have produced a de facto compartmentalisation of the formerly more or less continuous estuarine area. We now have a saline tidal sea arm (Oosterschelde), saline and brackish stagnant lakes (Grevelingen and Veerse Meer, respectively), as well as remnants of the estuarine habitat (Westerschelde, Nieuwe Waterweg). A comparison of the recent situation with the one that existed before any great alterations took place shows: 1. Species richness of the marine flora on this (regional/local) scale is largely dependent on salinity. 2. An overall rise in number of species of brown and red algae is apparent. Among the ten distinguished sectors of the SW Netherlands the steepest rises occurred in the tidal saline Oosterschelde and the stagnant saline Grevelingen, probably caused by the now continuously high salinity and clear water. 3. A great impact of alien imports (‘exotics’) is visible in the sheltered Oosterschelde and Grevelingen, a much smaller impact on the exposed North Sea coast and in the estuarine brackish Westerschelde. 4. There is not much indication of reductions in species areas, in the red algae rather the reverse seems true. 5. This study demonstrates a case where human interference has produced an increased species diversity in the marine environment by creating more diverse habitats. As such it is merely a continuation of a process that has been going on in the SW Netherlands during the last few centuries.