Comparison of trophic spectrum in the blackspot seabream, Pagellus bogaraveo (Brünnich, 1768), between cold-water coral habitats and muddy bottoms in the central Mediterranean

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Highlights

  • Diet of P. bogaraveo in the central Mediterranean.

  • Comparison of the diet P. bogaraveo between muddy bottoms and CWC habitats.

  • Teleosts and crustaceans dominated in the diet on the muddy bottoms while teleosts in CWC habitats.

  • The trophic level was higher in CWC habitats than on the muddy bottoms.

  • A habitat effect is observed on the diet of P. bogaraveo.

Abstract

The present study represents the first documentation of the trophic spectrum of the deep-water bony fish Pagellus bogaraveo in two different habitats in the central Mediterranean Sea: muddy bottoms (MB) and cold-water coral (CWC) habitats. A total of 133 stomachs were collected on MB and 39 in CWC habitats. The feeding habit of P. bogaraveo was different in the two investigated habitats. A lower number of prey categories were found in CWC habitats (15) than on MB (36). Teleostei (%PSIRI = 38.29) and Crustacea (%PSIRI = 36.49) were the most important prey in MB. The taxon of Anellida was the most abundant in number and the third in importance. In CWC habitats Teleostei were the most abundant prey (%PSIRI = 62.03) and Ophiuroidea were the second important ones. Ontogenetic dietary variation was evident in both habitats. The comparison of the diet between the habitats was carried out considering two samples of specimens with overlapping sizes, 21 on MB and 18 in CWC habitats, ranging between 192 and 280 mm total length (TL) from the former habitat and 184 and 271 mm TL from the latter. Dietary differences were significant as shown both by Morisita's index and PERMANOVA. The habitat in which the species lives would seem to affect the trophic strategies of P. bogaraveo. The trophic niche breadth examined for comparable sized samples showed how P. bogaraveo was more generalist on MB (Bi = 0.406) and a little bit more specialist in CWC habitats (Bi = 0.301). P. bogaraveo resulted to occupy a higher position in the trophic web of the CWC habitats compared to that on MB.

Introduction

The blackspot seabream, Pagellus bogaraveo (Brünnich 1768), is a bony fish distributed in the North-East Atlantic and in the Mediterranean, between the continental shelf and slope (Whitehead et al., 1986). Ontogenetic habitat shifts are characteristic of this species, with the juveniles mainly located in shallower waters on muddy bottoms (MB) and larger fishes often associated with offshore outcrops and banks (Mytilineou et al., 2013; Orsi Relini and Fida, 1992; Pinho et al., 2014; Santos et al., 2019). Indeed, it seems that larger individuals of this fish are more abundant in particular habitats less accessible to trawling such as cold-water coral (CWC) habitats, canyons and seamounts (Afonso et al., 2012; Chilari et al., 2006; D'Onghia et al., 2011, 2012, 2015a, 2015b; Fabi et al., 2002, 2004; Mytilineou et al., 2013; Relini et al., 1999; Whitehead et al., 1986).

The studies carried out in the Santa Maria di Leuca (SML) CWC province and in the Bari Canyon (BC) proved that these sites, characterized by living colonies of cold-water corals, mainly Madrepora oculata and Lophelia pertusa, seem to be attractive habitats for this fish (D'Onghia et al., 2010; 2011; 2012; 2015a; 2015b; 2016; 2017; Sion et al., 2019). In particular, comparing coral versus non coral habitats in the SML CWC province, P. bogaraveo was exclusively collected in the former habitat using longline (D’Onghia et al., 2012). This fish was found preferentially distributed inside the BC where it was the most often observed fish species using a baited lander (D'Onghia et al., 2015b) and exclusively collected inside the canyon using longline (Sion et al., 2019). Groups of up to 40 individuals of P. bogaraveo were attracted to the bait and were shown in single frames, exhibiting typical gregarious behaviour. The individuals were observed both exploring the area and feeding actively on the bait, in the water column and on the seabed (D'Onghia et al., 2015b).

In general, the effect of SML coral mound topography and canyons on local circulation of water masses can enhance the abundance and the diversity of marine organisms through the transport of different types of food resources and the presence of complex physical habitats (D'Onghia et al., 2011; 2015a). Both SML CWC and BC can be hot spots of endemic species and can provide spawning and recruitment sites for benthic and benthopelagic organisms (Colloca et al., 2015; D'Onghia et al., 2015a). Indeed, the presence of cold-water corals increases the complexity of the habitat and the availability of shelter for spawners and their recruitment (e.g. Buhl-Mortensen et al., 2010; Costello et al., 2005; D'Onghia et al., 2010, 2015a,b; Henry et al., 2013; Husebo et al., 2002; Fabri et al., 2014; Mastrototaro et al., 2010; Roberts et al., 2009; Ross and Quattrini, 2007; Söffker et al., 2011). Although P. bogaraveo is mostly captured in Mediterranean fishing grounds on the shelf (Chilari et al., 2006; Spedicato et al., 2002), the almost exclusive finding of adults in the SML CWC province and BC could be due both to their preferential distribution linked to the presence of corals and the virtual absence of fishing in these two sites (D'Onghia et al., 2010; 2011; 2012; 2016; Vassallo et al., 2017).

The feeding habits and diet composition of this species have been little studied. Some information is available from the Azores (North-eastern Atlantic), where the diet of blackspot seabream consisted of a wide variety of organisms dominated by fishes, among which the principal prey were myctophids (Morato et al., 2001). Blackspot seabream also fed on several invertebrates, such as thaliaceans and ophiuroids (Morato et al., 2001). Also in the eastern Ionian Sea the fishes were the most important prey for the species. The tunicate Pyrosoma sp. followed by the giant red shrimp Aristaeomorpha foliacea were secondary prey items (Mytilineou et al., 2013).

To date there is neither information for the central Mediterranean, particularly for the southern Adriatic and North-western Ionian, nor for different types of habitats where the species lives.

The aim of this paper is to investigate the trophic spectrum of the blackspot seabream Pagellus bogaraveo in two different habitats of the central Mediterranean, MB and CWC, evaluating how the size of individuals and the type of habitat can affect their feeding pattern.

Section snippets

Feeding intensity and diet composition

In order to investigate the diet of P. bogaraveo in different habitats, a total of 172 stomachs were collected in the central Mediterranean from 2013 to 2019 between 38 and 668 m in depth. In particular, 133 stomachs were collected during the MEDiterranean International Bottom Trawl Survey (MEDITS) experimental trawl surveys (Spedicato et al., 2019) carried out on MB from Otranto to Capo Passero (Geographical Sub-Area 19, GSA 19) from June 2013 to July 2019, while 39 stomachs were collected in

Feeding intensity and diet composition

Diet analysis performed on stomachs of 133 individuals of P. bogaraveo ranging between 90 and 350 mm TL (Fig. 2a) sampled on MB in a depth range of 38–668 m showed that 15 of them were empty with a vacuity index very low, equal to 11.3% (Table 2). The few empty stomachs observed were found in specimens between 120 and 230 mm TL, while both the smallest and largest specimens had full stomachs (Fig. 2a).

A total of 39 stomachs belonging to specimens ranging between 184 and 378 mm TL (Fig. 2b) were

Discussion

The present results on the feeding ecology of Pagellus bogaraveo provide a new contribution towards the understanding of the marine food web in two different habitats, MB and CWC (Capezzuto et al., 2020).

All the samples considered in the analysis carried out in this paper were sufficient for the description of P. bogaraveo diet. Only for the length class >250 mm on MB and the length class 151–250 mm on CWC habitats, the low number of samples did not allow to reach the asymptote in the

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study benefited from data recorded during the MEDITS surveys within the Data Collection Framework (DCF), the Ricerca ITaliana per il MARE (RITMARE) and COCONET (Towards COast to COast NET works of marine protected areas - from the shore to the high and deep sea -, coupled with sea-based wind energy potential) projects.

Crescenza Calculli was supported by the PRIN2015 project “Environmental processes and human activities: capturing their interactions via statistical methods (EPHASTAT)”

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