Abstract
One of the most important contributions of crustose coralline algae (CCA) to some coral reefs is their structural role in sunlit habitats, but in the Atlantic southernmost coral reef, Abrolhos, these algae are also important components of living communities covering larger areas than corals. Little is known about their competence in occupying reef space and consequently their ecological role. This work compared two CCA species along reef sites and habitats and their responses to different irradiance levels. To study colonization, epoxy discs were placed at four sites and three habitats (reef base, reef flat and reef edge). Crustose coralline individual pieces were glued onto epoxy discs and their relative growth was estimated. Productivity responses to irradiance levels found on reef habitats was measured on incubated samples. In general, CCA were less abundant than filamentous algae and non-calcareous crusts. Crustose algae showed no seasonal or spatial pattern in cover, contrasting with erect algae that differed in biomass among sites depending on season. Differences among habitats were only found for CCA. The dominant coralline Porolithon onkodes was more productive and grew faster than Lithophyllum stictaeforme at high irradiance level and both species were inhibited at low light. Dominance of P. onkodes in shallow and sunlit reefs was explained by its preference for high-light environments.
Highlights
This study aims to describe the early colonization and growth of crustose coralline algae (CCA) on the reef flat, edge and base of sheltered and exposed sites in summer and winter, testing the responses of the two most common coralline species to different light levels
The most common erect seaweeds found on colonization disks were filamentous algae (Cladophora dalmatica, Sphacelaria tribuloides, Polysiphonia scopulorum, Ceramium byssoides), foliose algae (Enteromorpha flexuosa, Padina gymnospora, Colpomenia sinuosa, Dictyota ciliolata, Dictyota mertensii, Dictyota menstrualis), non-calcareous crusts and calcareous coralline crusts
P. onkodes can be regarded as a plant adapted to high light environments and L. stictaeforme adapted to low light ones, where saturations levels are around 500 and 150 μmol m−2 s−1, respectively (Lüning, 1990)
Summary
The crustose coralline algae (CCA, Corallinales Rhodophyta) on coral reefs can cover large areas, such as in the Africa (McClanahan et al, 2001b), Australia (Fabricius and De’ath, 2001), Caribbean (Adey and Vassar, 1975; McClanahan et al, 2001a; Williams and Polunin, 2001), Fiji (Littler and Littler, 1997), Hawaii (Vroom et al, 2005), and Brazil (Figueiredo, 1997; Gherardi and Bosence, 2001; Villas-Bôas et al, 2005). Studies have confirmed that together with corals, CCA are important components of the reef framework in shallow environments exposed to strong wave action in the Caribbean (Macintyre, 1997) and Brazilian reefs (Kikuchi and Leão, 1997; Leão and Dominguez, 2000; Gherardi and Bosence, 2001; Leão and Kikuchi, 2001; Lei et al, 2018). Morphological characteristics of coralline algae indicate adaptations to many environmental and biological factors, such as wave exposure, light intensity, sediment deposition, competition, and herbivory (Steneck, 1986, 1988; Steneck and Dethier, 1994). Herbivorous fishes play key roles in the carbon and energy flux of food webs and are considered some of the primary determinants of the benthic structure (Clements et al, 2009). Herbivorous fish assemblages, dominated by surgeonfishes (Acanthuridae) and parrotfishes (Labridae: Scarini), are widely regarded for their importance in the control of the settlement, growth, and spread of benthic seaweeds (Steneck, 1988; Horn, 1989)
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