Thallus pruning does not enhance survival or growth of a wave-swept kelp

• Published in: Marine biology 2020-03, Vol.167 (4), Article 52
• Main Authors: Burnett, Nicholas P., Koehl, M. A. R.
• Format: Article
• Language: English
• Subjects: Algae; Autumn; Biomedical and Life Sciences; Breaking; Coastal ecosystems; Correlation analysis; Forces; Freshwater & Marine Ecology; Fronds; Growth; Growth rate; Herbivores; Herbivory; Hydrodynamics; Intertidal environment; Kelp; Life Sciences; Long-term effects; Marine & Freshwater Sciences; Marine biology; Microbiology; Morphology; Neurosciences; Oceanography; Original Paper; Pruning; Storms; Surveying; Survival; Thalli; Thallus; Velocity; Winter storms; Wounds; Zoology
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-020-3663-5

Kelp are ecologically important in wave-swept habitats because their thalli provide food and habitat to many other organisms. Fronds of kelp thalli can be broken off by hydrodynamic forces that exceed frond strength, especially if the fronds are weakened by wounds inflicted by herbivores. Previous studies hypothesized that breaking benefits some kelp by reducing their size and the risk of dislodgement by large hydrodynamic forces, but we know little about the long-term effects of breaking on kelp growth and survival. Here, we used the intertidal kelp Egregia menziesii to study the relationship between the breaking of the kelp’s fronds ("pruning") and the kelp’s growth and survival. By surveying kelp pruning and herbivore wounds on fronds for 24 months at intertidal sites in northern California we found that pruning was positively correlated with herbivory. We also measured growth rates and long-term survival of kelp to determine if they were correlated with kelp pruning or size. For kelp of any size, heavy pruning led to reduced growth rates in every season except autumn. Contrary to suggestions in the literature that pruning enhances kelp survival, we found that heavily pruned kelp were less likely than lightly pruned kelp to survive winter storms, and heavy pruning led to reduced long-term survival. Thus, the reduction in growth rate caused by pruning of E. menziesii , which renders kelp unable to recover from tissue loss, appears to be more important to long-term survival of this strong perennial kelp than is the danger of being swept away by waves.