MEPS 509:127-136 (2014)  -  DOI: https://doi.org/10.3354/meps10876

ABSTRACT: Understanding the factors that control the performance and abundance of important community members such as ecosystem engineers is critical for understanding ecosystem dynamics in a changing climate. Oscillation of the moon’s declination over 18.6 yr periods directly affects emersion time in intertidal systems. Here we document the direct influence of this predictable emersion time cycle on the cover of the dominant intertidal kelp and ecosystem engineer Saccharina sessilis. Field surveys over 14 yr showed large changes in the kelp canopy (between a maximum of 84% and a minimum of 21% cover) that were tightly linked to changes in annual emersion time. In laboratory experiments, we found evidence of a mechanistic link between emersion and S. sessilis canopy cover, as even short exposure to realistic low-tide conditions reduced physiological performance and caused substantial biomass loss. Our field data show a strong negative relationship between annual emersion time and kelp canopy cover. The emersion time cycle had cascading effects on the community, as shown by a strong positive correlation between kelp canopy cover and the abundance of the chiton Katharina tunicata, a major herbivore that depends on the canopy for shade. Recognizing the effects of natural, decadal-scale cycles on habitat-modifying species is an especially important step in achieving an understanding of the ecological consequences of climate change.

KEY WORDS:  Celestial mechanics · Ecosystem engineer · Emersion time · Habitat modification · Kelp · Maximum quantum yield · Rocky intertidal zone · Sub-lethal stress