Deep refuges and warm adaptation at range edges: genomic insights from kelp forestsClimate Change Refugia

Antoine Minne^1,2, Melinda Coleman^1,3,4, David Wheeler³, Jacqueline Batley¹, Thomas Wernberg^1,2

¹University of Western Australia, Australia - ²Institute of Marine Research, Norway - ³New South Wales Department of Primary Industries, Australia - ⁴National Marine Science Centre, Australia

Adaptive differences among populations will play a key role in the persistence of future kelp forests. While differences in genetic composition are increasingly reported from distant kelp forests, similar studies from segregated adjacent populations are more rare. For example, deep reefs are often overlooked due to logistical constraints, despite their potential role as refuges that shield kelps from extreme surface temperatures. Moreover, information on how genetic differences translate into differences in phenotypic responses to temperature is often unknown.

Focusing on golden kelp forests (Ecklonia radiata) in Western Australia, a region affected by ocean warming and marine heatwaves, we reveals genomic insights into adaptive differences and connectivity across shallow (10-15m) and deep (30-50m) reefs in three regions spanning the species’ warm and cool range.

The majority of genomic variation was explained by differences between regions with neutral genomic variation showing no difference between depths, supported by high bi-directional gene flow. In contrast, there was significant levels of putative adaptive genetic differentiation between shallow and deep populations but only in the warm edge region, with high fixation of alternate alleles. Complementary findings from an experiment assessing the thermal performance of cultivated kelp gametophytes from four genomically defined populations supported this result. Unique phenotypic traits were observed only in cultivated gametophytes from the shallow warm-edge population, suggesting potential selection for environmental conditions that vary with depth. These findings open new avenues for genetically informed conservation approaches to meet the threat from ocean warming.