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Marine Ecology Progress Series

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MEPS 431:205-213 (2011)  -  DOI:

Fish herbivory leads to shifts in seagrass Posidonia oceanica investments in sexual reproduction

S. Planes1,*, N. Raventos2,3, B. Ferrari1,4, T. Alcoverro2

1USR 3278, CNRS-EPHE, Centre de Biologie et d’Ecologie Tropicale et Méditerranéenne, Université de Perpignan,
66860 Perpignan Cedex, France
2Department of Marine Ecology, Centre d’Estudis Avançats de Blanes (CEAB-CSIC), C/ Acceso a la Cala St. Francesc 14,
17300 Blanes, Girona, Spain
3Present address: ARGOMARIS Private Foundation, Port of Mataró, Local DC/5C, 08301 Mataró, Spain
4Present address: Agence des Aires Marines Protégées, Mission pour le parc marin de la Cote Vermeille, Passage du Vieux Port, BP 05, 66660 Port-Vendres, France

ABSTRACT: Although the dominant ecological paradigm considers herbivory to play an insignificant role in seagrass ecosystems, past herbivore densities were high enough to result in significant reduction of seagrass growth. To study the long-term impact of sustained and intense herbivory on seagrass meadows, we compared morphological, population and reproductive (flowering) parameters of Posidonia oceanica meadows inside a Marine Protected Area (MPA; where herbivore fish populations are very high) with unprotected meadows. In addition, we evaluated short-term seagrass responses by manipulating herbivore access to seagrass plots with caging experiments conducted inside the MPA. The density and individual sizes of the herbivorous fish Sarpa salpa were greater in the MPA, with a biomass 10 times higher than in unprotected areas. Fish bite marks on leaves were 50% more abundant inside the MPA. Shoot surface, rhizome sugar content and flower density were 80, 20 and 70% lower in the MPA, respectively, but shoot density was 30% higher in protected ­meadows than in unprotected meadows. The caging (fish exclusion) experiment generally corroborated these results, although the caging period was probably too short to produce changes in shoot density. P. oceanica responded to severe biomass removal by herbivores (80% of the photosynthetic biomass) and consequent reductions in carbon storage in the rhizome by reducing sexual reproduction (flowering intensity) and by gradually increasing clonal growth (increasing shoot density). This plasticity suggests an evolutionary adaptive mechanism to deal with historically high herbivore numbers and is evidence of the importance of herbivory as a controlling process in the structuring and functioning of seagrass meadows in the past.

KEY WORDS: Herbivory · Seagrass · Posidonia oceanica · Mediterranean Sea · Sexual reproduction · Marine protected areas · Fish

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Cite this article as: Planes S, Raventos N, Ferrari B, Alcoverro T (2011) Fish herbivory leads to shifts in seagrass Posidonia oceanica investments in sexual reproduction. Mar Ecol Prog Ser 431:205-213.

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