Exploring multi-scale relationships between geology and ecology in Northern and Central California’s intertidal habitats

We present a multidisciplinary, geological and ecological study that tests whether rock’s geologic characteristics and their spatial variations in the intertidal habitat is a significant determinant of the types and abundance of organisms that can settle, grow, and survive in a given intertidal location. To investigate these relationships we (1) produced high-resolution (~2cm to 5cm) digital elevation models (DEMs) of rock surfaces exposed in the intertidal zone using state-of-the-art terrestrial laser scanning (TLS). The geological surveys were conducted on outcrops representative of the most common rock types (igneous, sedimentary and metamorphic/mélange units) along the Central and Northern California and at the same locations as the long-running biodiversity program PISCO and the newly established Northern California marine protected areas (MPAs). (2) Conducted biodiversity surveys at the same sites using methods developed in the pacificrockyinterdal.org program. (3) Linked the geomorphological and community composition attributes for each site to determine the characteristic spatial coupling signature. To parameterize the geomorphology of the rock surface we analyzed the DEMs with a Matlab code that produces a triangular irregular network (TIN) model of the surface and calculates the ratio between the area of the Delaunay triangles and their interpolated surface within a moving window of variable size (ranging from cm to tens of meters). The value of the ratio expresses the rugosity of the rock surface at any given scale. Bivariate plots of rugosity vs. window size offer, for the first time, the opportunity to quantitatively determine the spectral distribution of rock surface complexity over multiple scales, correlate rugosity with specific geologic features (e.g. fracture spacing, bedding) and allow statistical testing of the spatial relationships between community composition and geology (e.g. spectral coherence tests).