Potential effects of an invasive seaweed (Caulerpa cylindracea, Sonder) on sedimentary organic matter and microbial metabolic activities

Abstract

Caulerpa cylindracea (Sonder), among the most successful marine bio-invaders on a global scale, poses severe threats to biodiversity. However, the effects of this seaweed on the quantity and the biochemical composition of sedimentary organic matter are still poorly known. Since the whole set of sedimentary features affects the availability of substrates for benthic microbial communities, we: i) investigated the biochemical composition of sediments colonized and not-colonized by C. cylindracea, and ii) compared the metabolic patterns of the microbial communities associated with C. cylindracea and in the sediments colonized and not-colonized by the seaweed. Our results show that C. cylindracea can influence the quantity and biochemical composition of sedimentary organic matter (OM), and that microbial populations associated with colonized sediments do have specific metabolic patterns and degradation capacities. Caulerpa cylindracea can also influence the metabolic patterns of the microbial community specifically adapted to degrade compounds released by the seaweed itself, with possible consequences on C cycling.

Below‐ground processes control the success of an invasive seaweed

“…Sediments colonized by C. cylindracea were characterized by biopolymeric C contents higher than those observed in bare and P. oceanica sediments, and this is primarily due to the higher protein and carbohydrate contents when compared with the native habitats. This result is consistent with previous studies conducted in the Adriatic Sea (Pusceddu et al., ; Rizzo et al., ) and confirms that the presence of C. cylindracea is associated with a higher quantity of organic substrates that could support the growth of benthic heterotrophs. However, the contribution of phytopigment to biopolymeric C in sediments colonized by the invasive alga was lower than that observed in either bare or seagrass sediments.…”

“…Such effects may result from native seagrasses and C. cylindracea differing in the nutritional quality of organic detritus (and therefore in its degradation rates), which, in turn, varies with the relative importance of lipids, proteins and carbohydrates (Pusceddu, Dell'Anno, Fabiano, & Danovaro, ). Moreover, previous studies have suggested that the presence of this alga could modify benthic microbial communities composition (Rizzo, Pusceddu, Stabili, Alifano, & Fraschetti, ), as well as patterns of bacterially mediated organic matter diagenesis, and that these changes could be among the reasons for the modifications of metazoan meiofauna communities (Pusceddu et al., ). Thus, whilst the resistance to invasion of intact seagrass beds, such as those of Posidonia oceanica , has largely been attributed to above‐ground processes (e.g.…”

Under the canopy: Community-wide effects of invasive algae in Marine Protected Areas revealed by metabarcoding

“…Thus, a complex pattern of direct and indirect effects emerges; however, few works have addressed the impacts on the smaller components of the communities like the present study. There is evidence that the three species can affect mobile epifaunal components Guerra-García et al, 2012;Bedini et al, 2015), and in sediment communities C. cylindracea can affect meiofaunal composition and sediment characteristics (Pusceddu et al, 2016;Rizzo et al, 2017). To our knowledge, only Bulleri et al (2017), using an experimental approach, showed that the transplant of C. cylindracea to canopyremoval plots did not alter the structure of the understory assemblages of algae and sessile invertebrates, a result in agreement with our findings, albeit based only on visual censuses of macrobenthic taxa.…”

Propagule composition regulates the success of an invasive seaweed across a heterogeneous seascape

“…Positive effects of −F+R on +F+R could be explained by below‐ground processes, which have so far received little regard in the success of marine macrophytes in marine sediment systems, despite them being some of the most invasive species in the world (but see Gribben et al, ; Gribben et al, ). In Caulerpales, rhizoids are root‐like structures associated with specific bacteria that enhance carbon, nitrogen (including amino acids) and phosphorous uptake from the substratum (Arnaud‐Haond et al, ; Chisholm, Dauga, Ageron, Grimont, & Jaubert, ; Rizzo et al, ). Thus, 22‐cm long −F+R fragments, by virtue of their high number of rhizoid clusters, may have enhanced the success of +F+R fragments allowing a more rapid conditioning of the sediment microbiota without, at least in the first stages of establishment, reducing light levels.…”

“…promote a microbial community that alters sediment biochemical processes (e.g. sulphur cycling) and/or may release metabolites that benefit their own performance to the detriment of their native competitors (Gribben et al, , ; Rizzo, Pusceddu, Stabili, Alifano, & Fraschetti, ). Thus, seaweed fragments with high rhizoid numbers could overcome biotic resistance.…”