Epiphytism, biofouling, seagrass, Bryozoa , biodiversity, sample-based data set, ecological traits, Mediterranean Sea

In the marine environment, the term “epiphyte” is defined as: “all micro- or macro-organism living attached on a plant substrate” (Steel and Bastow Wilson 2003). The seagrass Posidonia oceanica L. Delile, commonly known as Neptune grass, is an endemic species of the Mediterranean Sea that hosts a distinctive and diverse epiphytic community, dominated by various macroalgal and animal organisms (Boero et al. 1985; Mazzella et al. 1989; Peres and Picard 1964; Van Der Ben 1971). Among epiphytic animals fixed on seagrass substrates, cheilostome bryozoans are often the most abundant and diverse taxa (Balata et al. 2007; Lepoint et al. 1999; Nesti et al. 2009; Pardi et al. 2006). Some species, like Electra posidoniae Gautier, are strictly found on Neptune grass leaves (Gautier 1961; Lepoint et al. 2014b; Matricardi et al. 1991). Due to this important contribution, cheilostome bryozoan diversity has received particular attention (Balduzzi et al. 1983; Gautier 1961; Harmelin 1973; Hayward 1975; Kocak et al. 2002; Lepoint et al. 2014a), but quantitative data are often lacking and seasonal variability is less often documented than spatial variability. This spatio-temporal variability was assessed quantitatively in Lepoint et al. (2014a) and the occurrence and abundance data set resulting from this study was made freely available on the GBIF portal as a sample-based data set. Biological and ecological features of the leaves’ community are also presented and discussed in Lepoint et al. (2014a). Trophic ecology of Electra posidoniae, an obligate epiphyte of P. oceanica, are discussed in Lepoint et al. (2014b). Scale community data were only published in the GBIF data set but not discussed.

The data set is a sample-based data set (n = 103 sampling events), recording occurrence (n = 1234) and abundance of cheilostome Bryozoa (n = 6488 counted colonies) settled as epiphytes on leaves and scales of the seagrass P. oceanica. Sampling encompasses an entire annual cycle (from November 2002 to December 2003) (n = 5 sampling seasons) and six sampling depths (7, 10, 15, 20, 25, 30 m). The data set package is composed of two data files: the former describing sampling events and the latter reporting occurrence and abundance of bryozoan colonies.

The data were collected during a postdoctoral project (G.L.) entitled: ”Nitrogen dynamics and ecology of the epiphyte community in a Posidonia oceanica seagrass bed”.

The Posidonia seagrass beds are one of the most important ecosystems in the Mediterranean coastal zone. Seagrass beds are in regression in many areas of the world, while the reasons of such regression are complex and often poorly understood. The epiphyte community constitutes an important component of the seagrass meadow. Variability in epiphyte community composition and/or biomass may sometimes be linked to anthropogenic disturbance and used as monitoring tool (Mabrouk et al. 2013; Martinez-Crego et al. 2010; Piazzi et al. 2004). This argues for more fundamental studies of the seagrass ecosystem functioning and epiphyte biodiversity.

The general objective of this project was to study the dynamics of nitrogen in the epiphyte community of the Posidonia leaves in relation with its ecology and its spatio-temporal structure.

Sampling and experiments were performed in Revellata Bay (Corsica, France), near the STARESO oceanographic station between 2002 and 2004. Samples were taken at a reference site (depth 10 m) followed by our laboratory since the 1970s, as well as along a permanent transect (7 to 35 m depth). At the level of a Posidonia shoot, particular attention was given to the spatio-temporal evolution of the structure of the epiphytic community. Specific composition of sessile fauna (mainly Bryozoa) was established at 7, 10, 15, 20, 25 and 30 m depth (Lepoint et al. 2014a). Temporal dynamics and trophic ecology of the dominant species Electra posidoniae was studied using seasonal sampling and isotopic approach (Lepoint et al. 2014b). Finally, we have measured experimentally the nitrogen uptake by different epiphytic macroalgae components (Lepoint et al. 2007). Complementary information about the epiphytic community of P. oceanica in Revellata Bay may be also found in, for example, Dalla Via et al. 1998; Jacquemart and Demoulin 2006; Lepoint et al. 1999; Michel et al. 2015; Pête et al. 2015.

GL conceived the sampling design, performed the sampling and performed identification of specimens. LNM and AH formatted and published the dataset. LNM, GL & AH wrote the paper.

We sincerely thank the staff of the oceanographic station STARESO (Calvi, Corsica) for their welcome and their logistic help, and particularly Sylvain Plaza for his diving assistance. We acknowledge Björn Berning who reviewed this ms and made valuable recommendations. G.L. is presently Research Associate at Fonds National de la Recherche Scientifique (FRS-FNRS), and benefited during this study of a postdoctoral fellowship from FRS-FNRS. This study was financed by a FRS-FNRS contract (FRFC 2.45.69.03) and the Action de Recherche Concertée 10/533 (French-speaking Community of Belgium). We also warmly thank the Belgian Biodiversity Platform (BELSPO, Belgium) that convinced and formed us to valorise and share such data set for biodiversity study purpose. This paper is MARE paper number 325.