Effects of sediment on spore performance as a potential constraint on kelp distribution

Kelp habitats contribute to marine productivity and diversity, making understanding the constraints on their distribution important. In the Gulf of St. Lawrence, Alaria esculenta occupies a subset of Saccharina latissima's range. Since tolerance to sedimentation by early life stages was suggested to cause this contrasting distribution, we tested the influence of sediment levels on spore attachment and development. For both species, the proportion of attached spores that developed decreased with increasing sediment. However, spore attachment and gametophyte density increased with sediment concentration but only for Saccharina. At the maximum sediment level examined, spore attachment and gametophyte densities of the two species were similar, contrary to the idea that sediment effects on early life stages explain differences in adult distribution. Further investigation, particularly with higher sediment loads, is required to confirm this conclusion. As turbidity is increasing globally, understanding the mechanisms underpinning changes in seaweed distribution will facilitate appropriate local-scale management.