Macrofaunal assemblages associated with the sponge Sarcotragus foetidus Schmidt, 1862 (Porifera: Demospongiae) at the coasts of Cyprus and Greece

Abstract Background This paper describes a dataset of macrofaunal organisms associated with the sponge Sarcotragus foetidus Schmidt, 1862, collected by scuba diving from two sampling sites: one in Greece (North Aegean Sea) and one in Cyprus (Levantine Sea). New information This dataset includes macrofaunal taxa inhabiting the demosponge Sarcotragus foetidus and contributes to the ongoing efforts of the Ocean Biogeographic Information System (OBIS) which aims at filling the gaps in our current knowledge of the world's oceans. This is the first paper, to our knowledge, where the macrofauna associated with S. foetidus from the Levantine Basin is being recorded. In total, 90 taxa were recorded, from which 83 were identified to the species level. Eight of these species are new records for the Levantine Basin. The dataset contains 213 occurrence records, fully annotated with all required metadata. It is accessible at http://lifewww-00.her.hcmr.gr:8080/medobis/resource.do?r=organismic_assemblages_sarcotragus_foetidus_cyprus_greece

The sponge Sarcotragus foetidus Schmidt, 1862 ( Fig. 1) belongs to the class of Demospongiae and, more specifically, to the subclass of Keratosa, i.e. sponges with skeleton comprised of spongin fibers (order Dictyoceratida, family Irciniidae).
This particular sponge species has an extensive network of small and large channels and cavities, and thus allows a variety of benthic invertebrates to inhabit them. Its surface is characterized by conules of 2-3 mm height, which are 10-15 mm apart from one another. The main skeleton is composed by a reticulate network of primary (ca. 100-200 µm in diameter) and secondary (ca. 50-100 µm in diameter) fibres (Manconi et al. 2013). Interestingly, this species was even mentioned by Aristotle, who had named it "Aplysias", meaning that it cannot be cleaned and used as a bath sponge, although its external morphology resembles to that of common bath sponges (Voultsiadou and Vafidis 2007).

General description
Purpose: This dataset includes species found associated with the demosponge S. foetidus. The sample sponges were collected from Greece (Linaraki, Sithonia, Halkidiki) and Cyprus (Milouria, Kissonerga, Pafos). Sampling in Cyprus was conducted in January of 2003 and August of 2003 and 2007, at depths between 5 and 10 meters. Sampling in Greece was conducted in February and July of 2003, in depths between 14 and 17 meters.

Study area description:
Samples were collected from one location at the coast of Halkidiki (Greece) and one location at the coast of Cyprus (Fig. 2). The two study sites can be distinguished based on their trophic state index. North Aegean Sea can be characterized as mesotrophic to eutrophic (Kyriakidis et al. 2015), in contrast to the oligotrophic Levantine Basin (Duineveld et al. 2000). Both study sites are rocky shores dominated by different species of photohilic algae, thus no obvious differences in the sponge associated fauna can be attributed to differences in the substrate type.

Linaraki:
The sampling site is located on the peninsula of Sithonia, in the North Aegean Sea (Fig. 3a). It is a moderately exposed rocky shore with a photophilic algal assemblage dominated by Ellisolandia elongata.

Milouria:
The sampling site is located close to the town of Pafos (Southwest Cyprus) (Fig. 3b. It is an exposed rocky shore with a photophilic algal assemblage dominated by the the non-indigenous species Palisada perforata. a b Figure 2.
Geographical location of the study area indicating the sampling stations.

Sampling methods
Study extent: Samples were collected at single time points. Three sponges were collected in the winter and two in the summer season from Greece. In addition, three sponges were collected in the winter and four sponges (one in 2003 and three in 2007) in the summer season from Cyprus.
Sampling description: Samples were collected by scuba divers. Each sponge was first covered with a plastic bag and was subsequently detached from the substrate, manually, with a knife. Once ashore, formalin was added in every sample to a final concentration of 5% and the samples were stored in jars.
Upon return to the laboratory, the epifauna of each sponge was collected initially. The formalin solution contained in the plastic bags was filtered through a 0.5 mm mesh size sieve in order to collect epifaunal organisms that were detached from surface of the sponges. Then, the surface and volume of each sponge was measured. Sponge volume was measured by water displacement. Afterwards, sponges were cut in smaller pieces and the animals found in the sponge channels were collected.
Quality control: All scientific names were standardised against the World Register of Marine species using the Taxon Match tool. Taxon names were also kept in the dataset as they had been originally recorded, with a reference to the currently accepted name.  The contribution of the different phyla found in the samples is shown in the figures below (Figs 4,5,6,7,8,9).      In Cyprus samples, Arthropoda was the phylum with the higher representation, both in summer (Fig. 4) and winter samples (Fig. 5). This was evident also when all the samples were included in the analysis, independent of season (Fig. 6). Interestingly, the increased abundance of Echinodermata in the summer (Fig. 4) was substantially reduced in the sponges collected during winter (Fig. 5).

Geographic coverage
However, the macrofaunal assemblage associated with the sponges collected from Greece was different; Arthropoda were still highly abundant, especially in the summer samples (Fig. 7), but other taxa such as Annelida and Mollusca showed also very high abundances and dominated the winter assemblages (Fig. 8). Overall, independently of season, the importance of the latter two phyla differentiated the sponges collected from the two locations (Fig. 9).
The aforementioned differences in the sponge associated macrofauna are also depicted on the MDS plot (Fig. 10), where it is apparent that the sponge samples cluster per country and season (ANOSIM: R = 0.811, p < 0.01).
Only 9 macrofaunal species out of the 83 were found to exist in both winter and summer sponge samples from Cyprus. On the contrary, sponges from Greece had 26 species in common when the two seasons were compared. Overall, when the species lists from the sponges collected from Greece and Cyprus were compared, there were 21 species common for both locations ( Fig. 11; Table 3).   Table 3.
Species found in common between the samples. *: non-indigenous species (ÖZTOPRAK et al. 2014, Pancucci-Papadopoulou et al. 2005). **: identification questionable for individuals from Cyprus (may be in fact Phascolosoma (Phascolosoma) stephensoni) (Açik 2014   This publication refers to the most recent version of the dataset available through the IPT server or MedOBIS. Future changes to the dataset due to quality control activities might change its content or structure. Christos Arvanitidis, Dr. Eva Chatzinikolaou and Dr. Vasilis Gerovasileiou, for their valuable comments and suggestions.