Effects of elevated temperature and sedimentation on grazing rates of the green sea urchin: implications for kelp forests exposed to increased sedimentation with climate change

Sea urchin grazing rates can strongly impact kelp bed persistence. Elevated water temperature associated with climate change may increase grazing rates; however, these effects may interact with local stressors such as sedimentation, which may inhibit grazing. In Alaska, glacial melt is increasing with climate change, resulting in higher sedimentation rates, which are often associated with lower grazer abundance and shifts in macroalgal species composition. The short-term effects of elevated temperature and sediment on grazing were investigated for the green sea urchin, Strongylocentrotus droebachiensis (O.F. Müller, 1776), in Kachemak Bay, Alaska (59° 37′ 45.00″ N, 151° 36′ 38.40″ W) in early May 2017. Feeding assays were conducted at ambient temperature (6.9–9.8 °C) and at 13.8–14.6 °C with no sediment and under a high sediment load. Grazing rates significantly decreased in the presence of sediment, but were not significantly affected by temperature. Along with sediment impacts on settlement and post-settlement survival, grazing inhibition may contribute to the commonly observed pattern of decreased macroinvertebrate grazer abundance in areas of high sedimentation and increased sedimentation in the future may alter sea urchin grazing in kelp forests.