Meiofauna associated with vermetid reefs: the role of macroalgae in increasing habitat size and complexity

Abstract

We present the first dataset of meiofauna associated with vermetid reefs (biogenic constructions of Mediterranean intertidal habitat) in two areas along the northern coast of Sicily, Italy. The vermetid reefs are characterized by a horizontal extension from the shore towards the open sea and can be divided into three zones (the inner margin, the cuvette zone and the outer margin) which differ in hydrodynamic features. We studied the spatial distribution of meiofauna along the horizontal axis of the vermetid reefs, investigating the communities inhabiting the sediment inside cuvettes (shallow pools inside the ''cuvette zone'') located between the inner and the outer margins of the reefs. We observed an increase in meiofaunal abundance from the inner to the outer part of the reef (from 1808 ± 80 to 2992 ± 512 ind. 100 cm-2) in both areas. Moreover, we studied meiofaunal communities associated with the most abundant macroalgae (Cystoseira sp., Jania rubens, Palisada perforata, Dictyota sp. and Padina pavonica) living on the reefs, investigating the influence of habitat size (biomass) and identity (complexity) of macroalgae. We found that meiofauna varied in abundance (from 446 ± 51 to 1758 ± 231 ind. 100 cm-2 on P. perforata and Cystoseira sp., respectively), on different macroalgae, and that the habitat size significantly influenced these abundances, but its effect was dependent on macroalgal identity. In fact, we observed a positive correlation between meiofaunal abundance and algal complexity (fractal dimension). The high algal cover in the ''cuvette zone'' of the reefs could contribute to make this zone more suitable for meiofauna, in particular close to the outer margin where we found more complex macroalgae (i.e. Cystoseira sp.). These results confirm that vermetid reefs, with their structural complexity, may play an important role in structuring benthic fauna in intertidal habitats.

Assessment of Structural and Functional Diversity of Mollusc Assemblages within Vermetid Bioconstructions

“…Our findings also demonstrate that the distance between the vermetid bioconstructions plays a major role in forming different assemblages from site to site, confirming the existence of a geographical variability of benthic fauna at medium spatial scale, possibly due to biogeographic factors associated with the local variation of the environmental parameters [40,51]. Moreover, macroalgae provide additional substrate for grazer gastropods, in agreement with Ape et al [52] who found a significant relation between meiofauna and algal community associated with vermetid bioconstructions.…”

Asymmetric effects of changes in the habitat‐forming algae Sargassum on different associated mobile faunas along São Paulo coast, Brazil

“…This general pattern is also consistent and has already been registered separately for each of the main associated groups: for mollusks, a higher abundance, species diversity, and functional diversity were observed for assemblages associated with morphologically more complex macroalgae (Chemello & Milazzo, 2002;Veiga et al, 2018;Barbosa et al, 2019 andDuarte et al, 2020); for crustaceans, similar results were found for amphipods in Sargassum beds, presenting higher abundance and diversity in association with higher biomass and/or more complex fronds (Carvalho et al, 2018;Kodama et al, 2020); and for polychaetes, a higher abundance and diversity was observed when in association with increased biomass of an invasive macroalgae (Box et al, 2010). These positive effects are also observed in smaller organisms, such as meiofaunal assemblages, which are influenced by the macroalgal cover (Ape et al, 2018;Hicks, 1980;Losi et al, 2018). Ape et al (2018) observed positive correlation between meiofaunal total abundance and habitat size, but its effect was dependent on macroalgal identity, with higher total abundance of meiofauna on alga that presented more complex architecture, in terms of both biomass and their fractal dimensions.…”

“…These positive effects are also observed in smaller organisms, such as meiofaunal assemblages, which are influenced by the macroalgal cover (Ape et al, 2018;Hicks, 1980;Losi et al, 2018). Ape et al (2018) observed positive correlation between meiofaunal total abundance and habitat size, but its effect was dependent on macroalgal identity, with higher total abundance of meiofauna on alga that presented more complex architecture, in terms of both biomass and their fractal dimensions. Thus, based on niche theory, which argues that more complex habitats provide more microenvironments or niches (Loke & Todd, 2016), and given the intimate relationship between the associated fauna and the algal substrate (Christie et al, 2009), it would be expected that fluctuations on the algal substrate would be followed by the fauna; however, this is not so obvious.…”

Sessile macrobenthos (Ochrophyta) drives seasonal change of meiofaunal community structure on temperate rocky reefs

“…Moreover, differences in macroalgal complexity could explain differences in meiofaunal community (Gibbons, 1988b;Warwick, 1994a, 1994b): more complex macroalgae increase meiofaunal abundance and diversity by offering a large number of habitats where to feed and live, a high variety of food resources, facilitating the amount of trapped sediment and detritus, and providing effective shelter against predation (Whatley and Wall, 1975;Hicks, 1980Hicks, , 1985Hull, 1997;Frame et al, 2007). The macroalgal size is another factor that influences the structure of meiofaunal assemblages (Hicks, 1980;Gunnill, 1982), but its effect seems to be dependent on macroalgal identity; this in turn may be attributable to differences of complexity between macroalgae (Veiga et al, 2016;Ape et al, 2018). The three-dimensionally shaped erect macroalgae belonging to Ochrophyta found in the present study showed a higher complexity compared to that of Rhodophyta, which were composed by a great number of encrusting algae, with a more bidimensional shape.…”

“…Most previous studies on hard bottom meiofauna focused on the phytal meiofauna, and especially to the fraction living on macroalgae, while the meiofauna associated with the surfaces beneath the algal canopy or to other sessile organisms has received little attention Griffiths, 1986, 1988;Gibbons, 1988aGibbons, , 1988bArroyo et al, 2004;Fraschetti et al, 2006;Danovaro et al, 2007;Logan et al, 2008;Russo et al, 2015;Ape et al, 2018). Moreover, most studies have been conducted in the intertidal and upper sublittoral zones (e.g.…”