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Seagrass ‘fairy circles’ on the Isles of Scilly

Published online by Cambridge University Press:  13 June 2022

Richard M. Warwick Open the ORCID record for Richard M. Warwick [Opens in a new window]
Richard M. Warwick*
Affiliation:
Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PL1 3DH, UK Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute, Murdoch University, 90 South St, Murdoch, Western Australia 6150, Australia
*
Author for correspondence: Richard M. Warwick, E-mail: [email protected]
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Abstract

Perfectly circular patches bare of vegetation in otherwise continuous swards of seagrass, and perfect circles of seagrass with lush fringes of shoots on the outer margins but with virtually bare centres, have both attracted popular attention as ‘fairy circles’ or ‘fairy rings’ in view of the folklore surrounding the supernatural origins of their terrestrial fungal counterparts. Aerial photographic and satellite surveys show that, on the Isles of Scilly, circles of Zostera marina of the second type occur sporadically, with exceptionally prolific clusters in specific localities associated with the colonization of bare substratum after disturbance, gradually disappearing over the period of this study at one site and appearing at another. Their abundance is the highest recorded anywhere in the world. Early suggestions that they represent seaweed growth on the stones of ancient hut-circles, submerged for centuries as a result of sea-level rise, are refuted. It is argued that they result from the unrestricted clonal growth of genets arising from individual Zostera seedlings, expanding equally in two dimensions and colonizing vacant habitat, with the older central shoots senescing and dying. Diameters of the circles constitute a stepwise increase in size, and the growth increments may represent a similar rate of seasonal growth in consecutive years, implying a linear rhizome growth rate of ~2.5 m year−1, which would be exceptional for Zostera marina, but which is supported by an observation on circles exposed on a low spring tide and would be an evolutionary adaptation for rapid recolonization in such a physically disturbed environment.

Keywords

Circle sizeclonal rhizome growthgenet ageIsles of Scillyphysical disturbancerecolonizationseedling productionZostera marina
Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 102 , Issue 1-2 , March 2022 , pp. 63 - 68
Copyright
Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of Marine Biological Association of the United Kingdom

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