Coexistence of the reef-building coral &lt;em&gt;Cladocora caespitosa&lt;/em&gt; and the canopy-forming alga &lt;em&gt;Treptacantha ballesterosii:&lt;/em&gt; Description of a new Mediterranean habitat

Alèssia Pons-Fita,Diego K. Kersting,Enric Ballesteros,Jana Verdura,Jorge Santamaría

doi:10.3989/scimar.05018.11b

Coexistence of the reef-building coral <em>Cladocora caespitosa</em> and the canopy-forming alga <em>Treptacantha ballesterosii:</em> Description of a new Mediterranean habitat

Alèssia Pons-Fita, Diego K. Kersting + Show 3 more

Open Access

https://doi.org/10.3989/scimar.05018.11b

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Abstract

Shallow Mediterranean rocky environments are usually dominated by macroalgae, but the stony colonial zooxanthellate coral Cladocora caespitosa is able to build extensive banks in some particular areas. Although zooxanthellate corals and benthic macroalgae are expected to compete for light and space when overlapping in the same habitat, there is previous evidence that C. Caespitosa and Mediterranean macroalgae do not suffer from competitive exclusion when living together. Here we characterize a new and unique Mediterranean habitat where the reef-building coral C. Caespitosa and erect seaweeds of the order Fucales (Cystoseira s.l.) coexist. In this new habitat C. Caespitosa reaches 34% cover and densities of Cystoseira s.l. (mainly Treptacantha ballesterosii) are much higher than values reported from other sites. Interestingly, abundances of T. Ballesterosii and C. Caespitosa show a positive relationship, suggesting that some kind of facilitation mechanism is taking place. These findings challenge the theory of competitive exclusion between corals and macroalgae and launch a wide array of possible open discussions on coral-macroalgae interactions.

Highlights

The most distinct trait of tropical marine ecosystems is the presence of coral reefs build by zooxanthellate scleractinian corals
Fig. 5. – Size frequency distribution of Treptacantha ballesterosii starting at the class interval of 1 cm (n=2603)
We have identified and characterized a new Mediterranean habitat constituted by a mixture of C. caespitosa colonies and T. ballesterosii stands

Summary

Introduction

The most distinct trait of tropical marine ecosystems is the presence of coral reefs build by zooxanthellate scleractinian corals. The unique zooxanthellate coral that has the capacity to build extensive beds and banks (sensu Peirano et al 1998) is the Mediterranean pillow coral Cladocora caespitosa (Linné, 1767) (Zibrowius 1982, Morri et al 1994, Peirano et al 2001), which can be considered a habitat former in locations where colonies concentrate in high densities and reach large sizes (Kružić and Požar-Domac 2003, Kersting and Linares 2012) Due to their reduced distribution, small size and generally low colony densities, Mediterranean coral bioconstructions have not been studied as extensively as tropical coral bioconstructions have. All these relevant features urged IUCN to include this species in the Red List with the status “Endangered” (Casado-Amezúa et al 2015) and the species appears in the List of Endangered and Threatened Species of the Barcelona Convention (Annex II UNEP-MAP-RAC/SPA 2013)

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