The intertidal system of the estuary of the River Humber has local seagrass beds that provide feeding and wintering areas for over 133,000 waders and wildfowl. It is rich in invertebrate communities. The estuary also provides for breeding birds, grey seals and natterjack toads. Spurn Point at the tip of the Spurn peninsula is made of hard glacial moraine so is less liable to erosion than areas further north on the Holderness coast. The Spurn peninsula is a beach with dunes which moves in response to the action of the waves. The wave action removes sand from the east of the beach and deposits it on the western side. The coast is influenced mainly by wave action but in the estuary the processes are driven by the power of the tides. The incoming tidal currents carry more sediment into the estuary than the ebb tides carry out. The estuary is shallow because of this constant deposition. Isostatic recoil is, however, causing the area to sink at the rate of 3 mm annually and global warming is making the sea level rise. The combined effects of these processes mean that the sea in the estuary may be half a metre higher by the year 2050. A large area around the estuary consists of land which lies below the present high-water mark. Flood defences offer only a short-term and local answer and may actually increase the long-term risks. Managed realignment of the coast by setting back the coastal defences will provide new intertidal habitats and harness natural equalising processes and is the preferred long term solution. There is archaeological evidence to suggest that the first settlers in Holderness arrived in the Neolithic era when the plain was still very wet and most likely consisted of a mixture of marshes, lakes, islands and woodland. As the sea level changed and the area became drier it was progressively cleared of trees and the higher drier parts were initially favoured for settlement. The Domesday survey reveals that in the reign of Edward the Confessor there were 45 different freeholders having land in Holderness. The name of Holderness may be derived from the Danish "hold" which was the name given in that language to a nobleman with considerable territorial possessions. The "ness" part generally refers to a prominentary, or nose-shape, either in a river or jutting from a coastline. After the Norman Conquest of England the extensive Lordship of Holderness was given by King William I to Drogo de la Beuvrière, a Flemish supporter.