Understanding the Role of Macroalgal Complexity and Allelochemicals Production in Invasive and Non-Invasive Macroalgae in the North-Western Adriatic Sea: Effect on the Associated Communities

Abstract

Highly diverse microphyto and meiobenthic communities are associated with large-sized marine macroalgae. Both morphological traits and allelochemical responses of macroalgae affect the composition of these communities, but the relative importance of these factors remains incompletely understood. In this study we investigated the microphytobenthic and meiobenthic communities associated with some native macroalgae and a non-indigenous species (Sargassum muticum) of the north-western Adriatic Sea. These seaweeds were sampled in two coastal sites subjected to different impacts. The possible effects of the structural complexity of the macroalgae and the potential role of allelochemicals (specifically polyunsaturated aldehydes, PUAs) on the associated communities were examined using univariate and multivariate analyses. The results indicate that distinct assemblages were associated with the macroalgae collected at the two different sites. Differences in microphytobenthic communities could be ascribed to differences in the macroalgal morphological traits and in their PUAs production. Conversely, variation of the meiobenthic community seemed to be related mainly to differences in the macroalgal communities at the two sites. This apparent inconsistency between the two analyzed communities suggests that microphytobenthos and meiofauna were differently shaped by the environmental habitat provided by macroalgae in the two sites, that are subjected to different environmental conditions and human activities. Overall, these results indicate that interactions between organisms belonging to different trophic groups (e.g., microphytobenthos and meiofauna) should be investigated in detail to better understand the global role of macroalgae as habitat formers on coastal ecosystems, especially in the case of large-sized introduced species.

Macroalgal features and their influence on associated biodiversity: implications for conservation and restoration

“…A few studies have found that algal structural complexity had little influence on e.g. invertebrate species richness (Russo, 1990;Dijkstra et al, 2017) or abundance (Russo, 1990;Lenzo et al, 2023), while others have found that these relationships change temporarily. According to Da Rocha et al (2006), similar assemblages could be associated with structurally different macroalgae, but complexity still have an influence on the biology of the dominant groups of invertebrates.…”

“…Structural complexity has also been linked to a prominent group of red coralline algae, the Rhodoliths (Harvey and Bird, 2008;Stelzer et al, 2021;Neves and Costa, 2022). They create a porous habitat that enhances individual and bed physical complexity (Gabara et al, 2018, Cerqueira Veras et al, 2020, Goodsell et al (2004) 23 , Gunill (1982) 24 , Hacker and Steneck (1990) 25 , Harvey and Bird (2008) 26 , Hauser et al (2006) 27 , Hooper and Davenport (2006) 28 , Hughes (2010) 29 , Hull (1997) 30 , Karr (2011) 31 , Kelaher and Castilla (2005) 32 , Leite and Turra (2003) 33 , Lenzo et al (2023) 34 , Lilley and Schiel (2006) supporting significantly higher diversities than non-living beds or adjacent bare sediments (Robinson, 2015;Stelzer et al, 2021;Neves and Costa, 2022), or even some kelp beds (Schoenrock et al, 2018). Along with complexity, the depth (shallow or deep, in tropical or polar latitudes, respectively; Mikhaylova et al, 2019;Cerqueira Veras et al, 2020) and density of these beds also contribute to biodiversity.…”

“…As the bulk of the information summarized in Table 1 indicates, most research to date shows that macroalgae and the habitats they create contribute to an increase in at least some measure of biodiversity. While those increases range widely from weak to very strong, and the influence of non-native seaweeds or other factors add an additional level of complexity (e.g., Veiga et al, 2016;Lutz et al, 2019;Ndhlovu et al, 2021;Lenzo et al, 2023), seaweeds generally improve rather than hinder associated communities. The most consistent promoter of faunal diversity seems to be the complexity of identifiable features within a seaweed itself (e.g., branching or holdfast morphology; Hacker and Steneck, 1990;Hauser et al, 2006;Lutz et al, 2019: Velasco-Charpentier et al, 2021 or the complexity achieved by the presence of several individuals or species coming together into a discernable habitat (Best et al, 2014;Tano et al, 2016).…”