The bedforms that are the result of the dynamics of the Wadden Sea, have considerable effects on the life of the seafloor. Dutch researchers have developed a method that can map bedforms that have a large influence on species occurrences. Understanding the interactions between bedform dynamics and species can help in identifying sensitive parts of the Wadden Sea.

Benthic life underwater
At first glance, a tidal flat may seem but a bare area. However, on- and in the seafloor lives an entire community of polychaetes, shellfish and crustaceans. Where we know a lot about the intertidal of the Wadden Sea, much less is known about the parts that are always submerged. Therefore, within the Waddenmosaic program research is conducted specifically aimed at understanding the areas that never fall dry during low tide: the subtidal Wadden Sea.

From bare flat to megaripple
The Wadden Sea is a highly dynamic system. Currents, tide and sediment (i.e. sand, clay, pebbles) synergistically form a hilly landscape that moves across the bottom of the Wadden Sea. Ranging from small sand ripples to large sand waves with in between megaripples of about 20 meters in length and half a meter high. Many species on the seafloor cannot cope with the change in landscape that these bedforms cause: a centimeter deposition of sediment can already be devastating. Hence, most species cannot survive in an area with megaripples due to the fast movement of these bedforms. Despite the large influences of megaripples on the occurrence of many species, the current mapping techniques do not reveal these bedforms.

Mapping sensitive areas
The renowned journal Remote Sensing in Ecology and Conservation published a study from a team of Dutch scientists from Waddenmosaic. They described how to map these bedforms, that have such large influences on the occurrences of species. The researchers combined the new seafloor map with data from an earlier sampling campaign to reveal relationships between natural dynamics and the occurrence of species. Mostly mobile and resilient species that can quickly move through the sediment can be found in areas with megaripples, whereas in less dynamic areas mostly sensitive species can be found like cockles and mud snails. Understanding the interactions between natural dynamics and the occurrence of different species can help in identifying the more sensitive areas in the Wadden Sea. Besides, it can help future research in elucidating the cumulative effects of natural- and anthropogenic seafloor disturbance, to help further improve underwater nature.

Schematic overview

Left: In calm areas – without megaripples – mostly less mobile and filter-feeding species can be found. For example cockles and soft-shell clams, but also the common ragworm.

Middle: In areas with less strong megaripple formation, only highly mobile filter-feeding species, such as the Atlantic jackknife clam, and less mobile deposit-feeding species, like the armoured bristleworm, can be found.

Right: In highly dynamic areas with strong megaripple formation only the most highly mobile deposit-feeders and scavengers can be found, such as sand digger shrimp and certain ragworms.