Using Novel Techniques to Differentiate the Effects of Macroalgae and the Physical Substrate on Associated SpeciesResistance, Resilience and Phase Shifts

Jennifer Dijkstra¹, Constance Tyler¹, Brandon O’Brien², Glenna Dyson¹, Kristen Mello-Rafter¹

¹University of New Hampshire, USA - ²Kutztown University, USA

The spatial extent of foundational kelp forests is declining as a result of multiple stressors, including warming ocean temperature and introduced species. This has led to a regime shift in which community functional traits of height, complexity and interstitial volume are vastly different from the original community. However, the relationship between various macroalgae communities, the physical substrate, fishes, lobsters and crabs is yet unresolved. In areas of kelp decline in the southwestern Gulf of Maine, increasing signs indicate macroalgae communities will emerge as low, complex turf-dominated macroalgae systems. Yet kelp beds in this region are not the giant or even mid-level kelp forests observed elsewhere, they are also low-lying, prompting further study on the role of kelps for associated species. Here, we assess the relative contributions of the substrate’s physical structure and that of the foundation species to associated species by employing novel Structure-from-Motion (SfM) photogrammetry. By leveraging the advantages of this technique and incorporating methods adapted from other remote sensing fields, we can distinguish the roles of macroalgae and of the physical substrate in supporting fishes, and adult crabs, and lobsters. Our initial results revealed variable contributions of foundation species and terrain attributes to the distribution of fishes, but not the distribution of crabs or lobsters. Gaining a clearer understanding of the individual effects of habitat components—foundation species and physical substrate—will enhance our ability to predict the impacts of shifting benthic communities.