MEPS 537:89-104 (2015)  -  DOI: https://doi.org/10.3354/meps11438

ABSTRACT: Recent declines and losses of highly productive and diverse kelp beds have been observed worldwide and linked to increases in ocean temperature. We investigated the impacts of 4 temperature treatments (11, 14, 18 and 21°C) on growth, net length change and mortality of the dominant kelp species in Nova Scotia: Saccharina latissima, Laminaria digitata and Agarum clathratum. Growth rates of A. clathratum were reduced at 18°C over 3 wk of exposure, and all species experienced negative net changes in length at this temperature. Exposure to 21°C led to tissue loss at least twice that observed at 11°C and mortality within the first 2 wk of exposure. Exposure to 21°C for 1 wk reduced blade tissue strength (breaking stress) and extensibility (breaking strain) by 40 to 70% in S. latissima and L. digitata, and all 3 species exhibited reduced strength after 3 wk exposure to 18°C. Histological examination of the blade tissue showed temperature-induced damage to the cellular structure of blades of S. latissima and L. digitata. A. clathratum displayed limited tissue damage and was less susceptible to temperature-induced tissue weakening and loss. Our findings provide a mechanism by which rising temperatures could contribute to observed population declines of kelp species.

KEY WORDS: Kelp · Climate change · Temperature · Saccharina latissima · Laminaria digitata · Agarum clathratum · Material properties · Growth rate