Effects of elevated temperature on erosion of Saccharina latissima (Laminariales, sugar kelp) blades

The critical role of kelp as an ecosystem engineer (nutrient cycling, habitat formation) is well recognized but under threat. Recent declines in natural kelp populations worldwide have been linked to global warming-induced rising temperatures of the ocean. There is, however, a noticeable gap in knowledge about the effects of temperature on the erosion of (distal parts of) the kelp blades. This erosion process, where blades tissue is lost, is crucial to understanding kelp health and nutrient dynamics in marine ecosystems. This study aimed to quantify the erosion rate of Saccharina latissima (Laminariales, sugar kelp) blades and the subsequent release of total organic carbon and total nitrogen during erosion under naturally increased temperatures (from 16.1 °C to 22.5 °C) and further elevated temperatures (from 16.1 °C to 27.1 °C). A significant increase in the erosion rate of the distal parts of blades was observed in both temperature treatments. Substantial amounts (4.24 ± 0.31 mg cm⁻² of C and 0.32 ± 0.13 mg cm⁻² of N) of nutrients were released from S. latissima, especially under sub-lethal temperature conditions. Under further elevated temperatures, with a prolonged period of higher temperature and a maximum temperature of 27.1 °C, the effects were stronger, and erosion occurred along the edges of the whole blade. Our findings suggest that rising temperatures accelerate the erosion of S. latissima blades, highlighting a reason for the decline of kelp forests under climate change, as well as the potential impacts on nutrient cycling in the oceans.