Low Densities of the Ghost Crab Ocypode quadrata Related to Large Scale Human Modification of Sandy Shores

Sandy beaches are the most common ecosystems of coastal regions and provide direct and indirect essential services for millions of people, such as coastal protection, fishing, tourism, and recreational activities. However, the natural habitats of sandy shores are being modified at rates never experienced before, making beaches key monitoring sites of marine ecosystems worldwide. The ghost crab species Ocypode quadrata is the most conspicuous crustacean of sandy beaches along the Western Atlantic coast and has been successfully used as an indicator of anthropogenic disturbance and environmental variability. To investigate the potential role of a “triple whammy” [(1) urbanization; (2) use of resources; (3) decreasing resilience] on the most common bioindicator of sandy shores, we compiled a dataset including 214 records of burrows density from 94 microtidal sandy beach sectors covering a range of over 65° of latitude. The response of burrows density to synergetic effects of human modification of natural systems and environmental changes was investigated using linear models. We used the cumulative Human Modification (HMc) index, a standardized geographic projection of changes of natural systems, as a predictor of urbanization, industrialization and use of resources. The predictor wave energy, tidal range and temperature (sea surface and air) were included as potential effects of climate changes. Literature review showed records mainly concentrated at sub-tropical and temperate regions. HMc values were clearly negatively related to burrows density, thereby supporting an effect of modification of natural habitat at large spatial scale. Sea surface temperature and air temperature were positive related with density and the lack of a general pattern of the relationship between burrows density, interactions between wave energy and tide range, supported unclear patterns reported at regional scales. Finally, we argue that ghost crabs are valuable targets for protection actions on sandy beaches that can benefit coexisting species and provide natural habitat conservation.

Beach-dune modelling in support of Building with Nature for an integrated spatial design of urbanized sandy shores

The long-term physical existence of sandy shores critically depends on a balanced sediment budget. From the principles of Building with Nature it follows that a sustainable protection of sandy shores should employ some form of shore nourishment. In the spatial design process of urbanized sandy shores, where multiple functions must be integrated, the knowledge and the prediction of sediment dynamics and beach-dune morphology thus play an essential role. This expertise typically resides with coastal scientists who have condensed their knowledge in various types of morphological models that serve different purposes and rely on different assumptions, thus have their specific strengths and limitations. This paper identifies morphological information needs for the integrated spatial design of urbanized sandy shores using BwN principles, outlines capabilities of different types of morphological models to support this and identifies current gaps between the two. A clear mismatch arises from the absence of buildings and accompanying human activities in current numerical models simulating morphological developments in beach-dune environments.

Urban dunes

Sandy shores worldwide suffer from coastal erosion due to a lack of sediment input and sea-level rise. In response, coastal sand nourishments are executed using ‘Building with Nature’ techniques (BwN), in which the sand balance is amplified and natural dynamics are instrumental in the redistribution of sand, cross- and alongshore. These nourishments contribute to the growth of beaches and dunes, serving various design objectives (such as flood safety, nature, and recreation). Nevertheless, human interference (such as buildings and traffic) along urbanized sandy shores may have significant, yet poorly understood, effects on beach and dune development. Better insight is required into the interplay of morphological, ecological and urban processes to support Aeolian BwN processes for dune formation and contribute to the sustainable design of urbanized coastal zones. This paper aims to bridge the gap between coastal engineering and urban design by formulating design principles for BwN along urbanized sandy shores, combining nourishments, natural dune formation and urban development on a local scale to strengthen the coastal buffer. The first part of the paper analyses sedimentation processes in the (built) sea-land interface and identifies spatial mechanisms that relate coastal occupation to dune formation. Hence a preliminary set of design principles is derived by manipulating wind-driven sediment transport for BwN dune formation after nourishment. In the second part of the paper, these principles are applied and contextualized in two case-studies to compare their capability for BwN in different coastal profiles: the vast, rural, geomorphologically high dynamic profile of a mega-nourishment (Sand Motor); versus the compact, highly urbanized, profile(s) of a coastal resort (Noordwijk). Conclusions reflect on the applicability of BwN design principles within different coastal settings (dynamics, urbanity) and spatial arrangements facilitating BwN dune formation.

URBAN DUNES: PROMOTING BWN DUNE FORMATION AT NOURISHED BEACHES THROUGH SPATIAL DESIGN

Sandy shores offer a multitude of ecosystem services; regulating- (e.g. protection against flooding), production- (e.g. drinking water) and cultural services (e.g. recreation), all depending on the quality of supporting services (e.g. natural balances of water, nutrients and sediment). For sandy shores especially, the long-term physical existence is depending on the sediment balance. Therefore, based on Building with Nature (BwN) principles, sediment balances and -dynamics represent essential components of any spatial design of sustainable urbanized sandy shores. Examples of such design are nourishments where the sand balance of the system is amplified and natural dynamics distribute sediment ashore. This approach is used in the Netherlands to compensate for coastal erosion with a total yearly nourishment volume of 12 million m3 of sand. Typical magnitudes of individual nourishments are 1 to 2 million m3, whereas the Sand motor is an experimental mega nourishment of 20 million m3. After nourishment, the sediment is transported by natural processes (waves, tide, wind etc) contributing to the growth of dunes. The question is how to support this dune development, not just to improve the coastal safety, but also the combined use with other urban & ecological programs in the coastal zone. In this contribution we discuss spatial design principles and their influence on the transport of sediment for the formation of dunes; supporting flood safety, urban and landscape qualities. This requires an interplay of nourishment, directed sediment transport in the beach-dune interface and the desired buffer capacity established by the dunes. Depending on the preferred defence strategy (seaward, landward or consolidating) different spatial interventions can be made to enhance dune formation after nourishment.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/fNnVkDS1Gig