Conclusions and discussion

1. Abundance and fragmentation patterns of the habitat-forming macroalga Lithophyllum byssoides (Lamarck) Foslie along the Iberian Peninsula Atlantic coast P. Veigaa,b, M. Rubala,b, E. Cacabelosc, J. Moreirad and I. Sousa-Pintoa,b a Department of Biology, Faculty of Sciences, University of Porto, Portugal. b Laboratory of Coastal Biodiversity, Centre of Marine and Environmental Research CIMAR/CIIMAR, University of Porto, Portugal c Centro Tecnológico del Mar-Fundación CETMAR, C/ Eduardo Cabello s/n, 36208, Vigo, Spain d Departamento de Biología (Zoología), Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain Introduction • Lithophyllum byssoides (Lamarck) Foslie is an habitat-forming calcareous alga well known in the Mediterranean coasts (Solera, 1991) where it can form massive reefs. However, this species is also common on the intertidal Atlantic shores of the Iberian Peninsula. • Lithophyllum byssoides, as other calcareous macroalgae do, can form tri-dimensional crusts (Figs. 1, 2) providing ecological niches for a diverse range of invertebrates (Chenelot et al., 2011). Despite its importance as habitat-forming species, there is a lack of information about many of its basic ecological features on the Atlantic coast. • Aim: to fill gaps in the understanding of key ecological features of L. byssoides, such as distribution and fragmentation patterns, along the Atlantic coast of the Iberian Peninsula. Fig. 1. Patch of Lithophyllum byssoides. Fig. 2. Mussels living on a patch of Lithophyllum byssoides. Methods Results • Study area: encompassed the Galician (NW Spain) and Portuguese coasts following a fully nested hierarchical sampling design. • The coast was divided in five regions (Fig. 3A): A Mariña, Costa da Morte, North Portugal, Central Portugal and South Portugal; these regions were defined by different oceanographic regimes and separated from each other by 100s of km. • Within each region, three rocky shores (Fig. 3A), separated by 10s of km, were selected. • Within each of these shores, three sites, separated by 10s of m, were randomly selected. 3A AM CM Rinlo 44ºN Llas Burela Barrañán N Malpica 3B 43ºN Muxía 42ºN Oia Moledo NP Viana 41ºN 3C 40ºN Peniche CP 39ºN Ribeira de Ilhas Magoito 38ºN Oliveirinha SP Almograve Zambujeira 37ºN 3D 12ºW 11ºW 10ºW 9ºW 8ºW 7ºW Figure 4. Mean ± SD of percentage of cover, volume, patch cohesion, patch density and total area of L. byssoides. Figure 3. Location of the 15 studied shores along the Atlantic coast of the Iberian Peninsula. AM: A Mariña; CM: Costa da Morte; NP: North Portugal; CP: Central Portugal; SP: South Portugal (A). 50x50 cm quadrats to estimate percentage of cover of L. byssoides (B). 10x10 cm quadrats to estimate volume of L. byssoides(C). 50x50 quadrats to take pictures of L. byssoides and estimate its structural complexity and fragmentation (D). Table 1. Analysis of variance on the percentage of cover, volume, patch cohesion, patch density and total area of L. byssoides. ns = not significant; s = significant; *P < 0.05; **P < 0.01; ***P < 0.001. • Sampling: At each site 5 random independent quadrats (50x50 cm) were selected • to estimate the percentage of cover of L. byssoides (Fig. 3B) • to estimate volume, patches of L. byssoides were scraped (10x10 cm) (Fig. 3C). • to take pictures (Fig. 3D) and estimate the total area, patch density and patch cohesion (Godet et al. 2011). • Data analysis: Significant differences on the considered variables were examined by means of a 3-way nested analysis of variance (ANOVA) with three factors: region (5 levels, fixed), shore (3 levels, random, nested in area) and site (3 levels, random, nested in location and area) (n=5). Conclusions and discussion • We can conclude that L. byssoides showed homogenous patterns of abundance and fragmentation along different studied regions of the Atlantic coast of the Iberian Peninsula despite their different oceanographic regimes (i.e. differences on temperature, upwelling frequency and intensity). • At the scales of shore and sites, however, significant variability was found for all the studied variables except for patch density at the scale of shore. • It is remarkable the low values of all variables in the Moledo shore in North Portugal (Fig. 4), where the edible mussel, Mytilus galloprovinciallis, is extremely abundant. • Mussels, barnacles and L. byssoides are sessile habitat-forming organisms that can compete among each other for space at the same tidal level. • The lowest abundance of L. byssoides where mussels are exceptionally abundant points out that competition for space could be a major driver of the abundance and fragmentation pattern for the former. • According to data obtained from scrapped samples, L. byssoides commonly overgrowths barnacles but not mussels (Fig. 2). REFERENCES: Solera J.S. 1991. Lazaroa12: 43-51; Chenelot H. et al. 2011. Marine Biodiversity 41: 413-424; Godet L. et al. 2011. Estuarine, Coastal and Shelf Science 92: 472-479. ACKNOWLEDGEMENTS: P. Veiga (SFRH/BPD/81582/2011) and M. Rubal (SFRH/BDP/81567/2011) were supported by postdoctoral grants awarded by Fundaçãopara a Ciência e Tecnologia (FCT, Portugal).