Climate-related sediment load has severe impacts on the early life-stages of commercially important high-latitude kelp species

Kelp are likely to experience significant impacts due to ongoing climate change. Changes in sediment load as a result of glacial melt will have a major influence on coastal systems over the coming decades. Bull kelp ( Nereocystis luetkeana ) and ribbon kelp ( Alaria marginata ) are both species of commercial and ecological importance. In this study, fertile specimens were collected from Juneau, Alaska. Spores produced were cultivated over 30 days in four sediment treatments: 0 g/L, 0.21 g/L, 0.42 g/L, and 0.84 g/L. Sediment was obtained from the Mendenhall Glacier watercourse in Juneau, Alaska, and was mostly between 63 μm and 2 mm grain size. Germination and growth of both species were lower in sediment treatments at and above 0.42 g/L, although A. marginata appeared to be resilient to low levels of sediment load. Sediment levels at 0.42 g/L and above negatively impacted germination in A. marginata , while germination in N. luetkeana was negatively impacted by all sediment-added treatments. In terms of gametophyte size, A. marginata gametophytes at 20 days were largest in the control, smaller in the 0.21 g/L and 0.42 g/L treatments, and smaller still in the 0.84 g/L treatment. N. luetkeana gametophytes at 20 days were larger in the control treatment than in other treatments. Gametophyte density in both species was negatively impacted by all sediment treatments. Sediment load from late fall through early spring, when kelp gametophytes are present on the benthos, may have severe implications for the persistence and survival of wild kelp populations in glaciated regions. • Germination and gametophyte growth is impacted by added sediment. • A. marginata appears resilient to low levels of sediment load. • Gametophyte density in both species is negatively impacted by added sediment. • Sediment load may have implications for the survival of wild kelp populations in glaciated regions.