Material matters: a thermal habitat suitability model of shoreline infrastructure in an urban harbor

Ecological engineering efforts on coastal infrastructure have been associated with positive effects on species richness and abundance in urban intertidal ecosystems, but the mechanisms underlying these effects are yet unknown. The current study explores the distribution of high temperature extremes on coastal infrastructure as a potential mechanism driving epibiotic community biodiversity. A Noah Land Surface Model previously adapted for mussel beds was modified for this study to approximate physical and thermal properties of materials commonly used in coastal armoring. Hourly temperature, tide and solar elevation data for Boston, MA, USA were used to simulate temperatures on a total of twelve model surfaces representing concrete, granite and steel bulkheads with north, east, south and west surface orientations, over a period of 5 years from 2014-2018. Results show that including material thermal properties and surface orientation as model inputs improves predictive power for bulkhead temperature over using air temperature or sea surface temperature alone, and specifically highlight the influence of material in producing temperatures in excess of thermal limits for local species. Significant differences in the duration and intensity of high temperatures among model surfaces demonstrate that substitution of material choices to mitigate thermal extremes can be considered most important on south- and west-facing surfaces, somewhat important on east-facing surfaces, and least important on north-facing surfaces. A species assessment of intertidal epibiota on bulkheads in Boston Harbor was conducted to validate model predictions for habitat suitability based on surface orientation and substrate material. Ultimately, these results suggest that temperature is a mechanism to explain differences in epibiotic community identity on coastal infrastructure and that similar modelling efforts could be undertaken as the basis for eco-design considerations.