Acceleration loggers reveal fine-scale heterogeneity in wave exposure along an open coast

Abstract

Wave action shapes species distributions and ecological interactions within the intertidal- and shallow-subtidal zone. Empirical estimates of wave exposure within these zones are limited by logistical constraints and/or cost. Hydrodynamic models of wave action poorly resolve fine-scale heterogeneity in wave energetics that are important for biology. We used cost-effective accelerometers to continuously measure fine-scale wave exposure across 12 locations (i.e., two depth strata at each of six sites), over sixteen consecutive months. We categorised wave exposure at each of our sites a priori (as ‘exposed’ or ‘sheltered’) based on shore topography. We compared in situ measurements of acceleration with a nearby wave rider buoy and evaluated variation in water acceleration and frequency of large wave events among sites and between depths. Wave height data significantly correlated with accelerometer data confirming accelerometers sufficiently measure wave action. Our analyses indicate significant fine-scale variation in acceleration, and differences in timing and frequency of large wave events during the study period. In situ acceleration had limited correspondence with shore-based (a priori) assessments of wave exposure. These results demonstrate the spatial and temporal differences in water acceleration on the Wellington south coast and highlight the limitations of surface topography to predict fine-scale wave action. This study also emphasizes the need for fine scale wave action measurements to better explain patterns in intertidal/shallow subtidal organism traits.