Determinants of Caulerpa racemosa distribution in the north-western Mediterranean

Abstract

Predicting community susceptibility to invasion has become a priority for preserving biodiversity. We tested the hypothesis that the occurrence and abundance of the seaweed Caulerpa racemosa in the north-western (NW) Mediterranean would increase with increasing levels of human disturbance. Data from a survey encompassing areas subjected to different human influences (i.e. from urbanized to protected areas) were fitted by means of generalized linear mixed models, including descriptors of habitats and communities. The incidence of occurrence of C. racemosa was greater on urban than extra-urban or protected reefs, along the coast of Tuscany and NW Sardinia, respectively. Within the Marine Protected Area of Capraia Island (Tuscan Archipelago), the probability of detecting C. racemosa did not vary according to the degree of protection (partial versus total). Human influence was, however, a poor predictor of the seaweed cover. At the seascape level, C. racemosa was more widely spread within degraded (i.e. Posidonia oceanica dead matte or algal turfs) than in better preserved habitats (i.e. canopy-forming macroalgae or P. oceanica seagrass meadows). At a smaller spatial scale, the presence of the seaweed was positively correlated to the diversity of macroalgae and negatively to that of sessile invertebrates. These results suggest that C. racemosa can take advantage of habitat degradation. Thus, predicting invasion scenarios requires a thorough knowledge of ecosystem structure, at a hierarchy of levels of biological organization (from the landscape to the assemblage) and detailed information on the nature and intensity of sources of disturbance and spatial scales at which they operate.

Resistance and facilitation by native algal communities in the invasion success of Undaria pinnatifida

“…At this stage of invasion, competitive effects through canopy shading, pre-emption of primary substratum and overgrowth may compromise the ability of an invader to establish viable populations (Britton-Simmons 2006, Scheibling & Gagnon 2006, Dunstan & Johnson 2007, Valentine et al 2007, Thomsen et al 2009). Conversely, disturbances that create gaps in natural communities may allow invasion (Valentine & Johnson 2003, Edgar et al 2004, Valentine & Johnson 2004, Incera et al 2010, and particular types of benthic cover may actually facilitate invasion (Bulleri & BenedettiCecchi 2008, Bulleri et al 2009, Bulleri et al 2011. Unfortunately, in terms of management and in-depth understanding of processes, many of them are context-dependent (Thomsen et al 2011).…”

Demography and population biology of the invasive kelp Undaria pinnatifida on shallow reefs in southern New Zealand

“…However, at least part of its success seems to be related to the wide variety of substrata onto which it can recruit. Eighty-seven percent of autumn recruits appeared among the branches of turfing corallines (Thompson, 2004), which preclude effective population recruitment of many fucoids (Bellgrove et al, 2010;Schiel and Lilley, 2011) and can facilitate macroalgal invasions (Bulleri and Benedetti-Cecchi, 2008;Bulleri et al, 2009Bulleri et al, , 2011. These coralline patches may retain some moisture and provide 'safe sites' for microscopic gametophytes and sporophytes, and may well account not only for much of Undaria's localized success but also for how its microscopic stages survive over summer.…”

Habitat traits and patterns of abundance of the purple sea urchin, Paracentrotus lividus (Lamarck, 1816), at multiple scales along the north Portuguese coast

“…This variable was estimated in each replicate quadrat through a simplified adaptation of the method described in Bulleri et al (2011). Five out of the twenty-five sub-quadrats of the sampling frame overlapped to each replicate were selected at random and the depth of the substratum (i.e.…”