Quantifying natural rocky shore biogeomorphic interactions to inform eco-engineering designs for urban coasts.

 

 

The interplay between topographic complexity (aka. Geomorphology) and ecological communities is of growing interest by ecologists in the rapidly growing field of eco-engineering. This work brings a biogeomorphological lens to these studies, examining the influence of lithology and different types of geomorphic features found on rocky coasts. Geomorphic features such as pools, pits, cracks, crevices and ledges vary spatially and are closely linked to geological contingency and this in turn effects on rocky shore biodiversity (species richness, abundance and community composition). We studied these interactions in four ways: (1) a comparative study of rock mass and rock material properties at four sites in Scotland to establish the role of rock type and geomorphic feature type on ecology, (2) a comparison of two lithologies (limestone and sandstone) at the same site to identify the importance of rock type and geomorphic feature type on ecology (3) a further study integrating Terrestrial Laser Scans of geomorphic complexity overlain with ecological variables (species richness and mobile species abundance) to create a model of rocky shore species density in relation to geomorphic features and (4) a study of species density at the Glamorgan coast, Wales, comparing the effects of one geological factor – low and high density jointing (crevices and cracks) within the same bed layer. Species richness and abundance was found to significantly differ with rock type and the presence of geomorphic features on each shore, with deep pools being the optimal habitat type with regards to these ecological variables. The higher abundance of species in pools and crevices (depending on site) highlights that the presence of larger-scale features such as pools, crevices and ledges are important for the survival of intertidal species as crevices can function as refuge from predators and wave stress and pools can reduce desiccation stress at low tide.  Features that performed well in attracting higher species richness or abundance, which were ledges, deep pools and crevices, were examined in greater depth. Pits were also examined due to their common use as retrofitted ecological enhancement on coastal infrastructure (Firth et al., 2014b; Hall et al., 2018; Loke et al., 2017; Martins et al., 2010), where generalised linear models were used to examine the significance of width, depth and water holding % on species richness and abundance for each feature, allowing us to make quantitatively based assessment of which feature types are most ecologically optimal.  This greater provision of habitat through increased surface area, increased protection and greater variety of surface topography suggest that complex rock types and associated landform features/geomorphic features are more likely to have higher species richness and abundance, particularly when compared to adjacent areas of shore platforms that lack this geomorphic complexity.  These natural rocky shore biogeomorphology findings can be used to optimise future eco-engineering designs, enriching the design process and considerations for improving ecological outcomes on urbanised coasts. It also allows us to bring in geomorphic features, and thus rocky shore geomorphology into urban landscapes, enriching human interactions with geomorphology as well as ecology.