Environmental Change Drives Declines in Kelp Abundance Across the Northwest AtlanticBroad-scale Spatial Patterns

Jarrett Byrnes¹, Amy Smith², Kira Krumhansl³, Sean Grace⁴, Robert Jarrett⁵, Katie MacGregor³, Karen Filbee-Dexter^6,7,8, Jennifer Dijkstra⁹, Douglas Rasher¹⁰, Colette Feehan¹¹, Robert Steneck⁵, Jon Witman¹², Alexis Wilkes¹

¹University of Massachusetts Boston, USA - ²Wesleyan University, USA - ³Fisheries and Oceans Canada, Canada - ⁴Southern Connecticut State University - ⁵University of Maine, USA - ⁶University of Western Australia, Australia - ⁷Laval University, Canada - ⁸Institute of Marine Research, Norway - ⁹University of New Hampshire, USA - ¹⁰Bigelow Laboratory for Ocean Sciences, USA - ¹¹Montclair State University, USA - ¹²Brown University, USA

Global analysis of kelp forest change conducted a decade ago showed considerable variation in rates of change across the globe. In the decade since data was collected for this effort – the last data point was from 2014 – considerable change has happened around the globe. Have trends in kelps changed as well? Further, in the initial effort, a number of regions either did not have data or had data that was not published. With more data, can we use causal analysis to assess drivers of change? Here we focus on the Northwest Atlantic, going from 30 to 311 studies and expanding to all ecoregions in the province. We show consistent declines across all areas, as opposed to previous results showing high ambiguity and even some increases. Using data derived from satellites and models of oceanographic properties in combinations with causal modeling techniques from Econometrics, we show that these declines are driven by a combination of changes in temperature, turbidity, and wave height - all factors linked to changes in the region influenced by climate change. Our results show not only synoptic change in the region, but clear causal links to shifts in climate.