Feeding Habits of the Striped Red Mullet, Mullus Surmuletus in the Eastern Adriatic Sea
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ISSN: 0001-5113 ACTA ADRIAT., ORIGINAL SCIENTIFIC PAPER AADRAY 59 (1): 123 - 136, 2018 Feeding habits of the striped red mullet, Mullus surmuletus in the eastern Adriatic Sea Mišo PAVIČIĆ, Jasna ŠILJIĆ, Dajana BRAJČIĆ JURICA and Sanja MATIĆ-SKOKO* Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, P.O. Box. 500, 21000 Split, Croatia *Corresponding author: [email protected] Feeding habits of the striped red mullet, Mullus surmutetus in the eastern Adriatic Sea were investigated. Stomach contents of 203 specimens (11.5 - 32.9 cm TL) collected by bottom trawling were analyzed. Commonly accepted procedures were followed during the diet composition inspec- tion and standard keys were used for food items determination. Examinations showed that 39 iden- tified prey taxa belong to 11 major systematic groups: Crustacea, Gastropoda, Bivalvia, Pisces, Cnidaria, Echinodermata, Polychaeta, Nematoda, Bryozoa, Algae and Rhizaria. The predominant and preferred prey category was decapod crustaceans within all size categories and only in the largest individuals, the dominance of Bivalvia followed by Polychaeta and Crustacea were found. The largest individuals also showed more variety in consumption of different prey categories and a higher mean number of prey items in comparison with smaller fish. No significant differences in prey foraging between males and females (p>0.05) and regarding to season (p>0.05) were found. Feeding on such wide spectra of prey without significant variations regarding to sex and season suggests that the striped red mullets are able to adapt to shifts in spatio-temporal variations in the abundance of potential prey. Presence of detritus in the digestive tracts is highly related to its forag- ing behaviour on muddy detritic bottoms. Key words: feeding, Mullus surmuletus, Adriatic Sea INTRODUCTION Among fishes, goatfishes may provide important ecosystem services, including resus- The food web models are very valuable tools pension and the formation of mixed species in measuring species’ importance in an ecosys- foraging associations due to their very active tem (POLIS & WINEMILLER, 1995; BELGRANO et foraging behaviour with vigorous stirring up of al., 2005; DE RUITER et al., 2005). Although they sediments by their barbells and mouths (RAN- may become very complex resulting in uncertain DALL, 1967; GOLANI & GALIL, 1991; UIBLEIN, 1991; causal relationships between distinct species, MCCORMICK, 1995; KRAJEWSKI et al., 2006). These such models allow the estimation of the number characteristics of their resource use make the of indirect interactions between organisms of the goatfishes essential components of food webs in same or different trophic levels and evaluation coastal ecosystems. Goatfishes have relatively of the overall trophic ‘connectedness’ of a single rarely been considered in food web models, species within an ecosystem. especially at the level of single species (UIBLEIN, 124 ACTA ADRIATICA, 59 (1): 123 - 136, 2018 2007). The reason for this is probably derives resource use in the Adriatic Sea striped red mul- from insufficient information on their feeding let, Mullus surmuletus, with size-/age-/sex-relat- biology in the respective habitat/area, mostly ed change in pray foraging on typical muddy sandy bottoms adjacent to hard bottoms, includ- detritic bottoms. ing coral reefs. Despite the lack of biological information MATERIAL AND METHODS (AJEMIAN et al., 2016) the striped red mullet, Mullus surmuletus Linnaeus, 1758 is a very The total of 203 individuals of Mullus sur- important species from an economical and eco- muletus were caught using bottom trawls (40 logical point of view in the Mediterranean lit- mm square mesh size) at depths from 80 to toral benthic communities (STAGLIČIĆ et al., 2011) 160 m in the Jabuka Pit area (middle Adriatic: and highly exploited species by Mediterranean 43°35’30.20”N 15°45’35.38” E). The samples demersal (REŇONES et al., 1995; MEHANNA, 2009) were taken in December 2011 and through and small-scale (MATIĆ-SKOKO et al., 2011; GFCM, 2012 year in the following months: January, 2015; GFCM, 2017) fisheries. It is distributed in the February, March, April, May and October. After Eastern Atlantic Sea from the North Sea to Sene- being caught the specimens were immediately gal and throughout the Mediterranean and Black transported to laboratory for examination. All seas (WHITEHEAD et al., 1986). The striped red specimens were weighted to nearest 0.1 g and mullet is a bottom-dwelling species, inhabiting their total length (TL) measured to nearest mm. shallow soft bottoms, seagrass beds and rocky Sex of every fish was determined. The length- bottoms (LOMBARTE et al., 2000; BAUTISTA˗VEGA, weight relationship was expressed with equation 2008; TSERPES et al., 2002), usually between 10 W=aLb; where W is total body weight, L is total and 80 m. Spawning occurs in spring period length, while a and b are constants. The gonado- (AMIN et al., 2016). Striped red mullet becomes somatic index (GSI) was calculated using equa- mature after its first year for both sexes (AMIN tion GSI= (gonad weight/fish weight) * 100. et al., 2016). Like other goatfishes (HOLLAND All specimens (138) that contained prey et al., 1993; MEYER et al., 2000), M. surmuletus items were divided in 10 mm TL classes in order shows daily short-distance movements within to determine frequency and numerical abun- and among foraging and resting sites preying dance of a certain prey group in stomachs relat- on small benthic invertebrates such as shrimps, ed to fish size. For qualitative and quantitative amphipods, polychaetes, mollusks and benthic diet analysis, digestive tracts were weighed (wet fishes (LABROPOULOU et al., 1997; LOMBARTE et weight) and preserved in a 4% formaldehyde for al., 2000; MEHANNA, 2009). Seasonal migrations the examination of their contents. Afterwards, in and formation of spawning aggregations that are the laboratory, gut contents were identified and known for sympatric species red mullet, Mullus the number of empty stomachs was shown as barbatus (MACHIAS & LABROPOULOU, 2002) are the vacuity index (%VI). Stomach contents were not well expressed for M. surmuletus. Juveniles examined under a dissecting microscope using are often encountered on soft bottoms, seagrass reflected light. Each dietary item was identi- beds and at different depths than adults, reflect- fied to the lowest possible taxon, counted and ing both horizontal and vertical ontogenetic weighed to the nearest 0.01 g. Item weight was habitat shifts. While young show a tendency of obtained by wet weight method. All fragments forming groups, adults usually live solitary or in of some prey groups were put on previously smaller groups (JARDAS, 1996). weighed filter paper and left for a few hours Foraging behaviour and consequently diet at room temperature. Semidry filter paper was are not stable and may significantly change then weighed to a precision of 0.001 g. A true among different habitats, but also during life weight was obtained as the diference between history. The aim of this study is to investigate wet filter paper together with prey organisms ontogenetic shifts and seasonal fluctuations in and the known dry filter paper weight. The level Pavičić et al.: Feeding habits of the striped red mullet, Mullus surmuletus in the eastern Adriatic Sea 125 Table 1. Percent frequency of occurrence (%F), percent of total number (%N), percent of total weight (%W) and percent index of relative importance (%IRI) for food items in Mullus surmuletus Food items F (%) N(%) W(%) IRI(%) Crustacea 54.39 58.16 65.03 81.66 Non-identified Crustacea 23.91 29.27 40.32 76.54 Decapoda 2.90 6.50 4.52 1.47 Natania Palaemonetes 0.72 0.41 0.32 0.02 Penaeidae 0.72 0.81 0.18 0.03 Eucarida Galatheidae 4.35 2.44 2.44 0.98 Galathea squamiffera 1.45 0.81 0.32 0.08 Galathea strigosa 0.72 0.81 0.09 0.03 Munida rugosa 0.72 0.41 1.45 0.06 Leucosiidae Ilia nucleus 0.72 0.41 0.18 0.02 Ebalia sp. 0.72 0.41 0.18 0.02 Ebalia granulosa 0.72 0.81 0.32 0.04 Xanthidae 2.17 4.47 4.71 0.92 Xantho pilipes 0.04 0.031 0.009 0.088 Xantho poressa 0.72 0.41 0.18 0.02 Monodaeus couchii 0.72 0.41 0.23 0.02 Portunidae 2.90 2.44 1.13 0.48 Bathynectes longipes 0.72 0.41 0.36 0.03 Macropipus corrugatus 2.17 1.22 2.53 0.38 Macropipus pusilus 0.72 0.41 1.72 0.07 Liocarcinus arcuatus 0.72 0.41 0.23 0.02 Paguridae 0.72 0.41 0.54 0.03 Parthenopeidae 1.45 0.81 0.32 0.08 Grapsidae Pachygrapsus marmoratus 0.72 1.63 0.63 0.08 Pilumnidae Pilumnus hirtellus 1.45 0.81 0.27 0.07 Majidae Pisa nodipes 0.72 0.81 0.95 0.06 Amphipoda 0.72 0.41 0.90 0.04 Gastropoda 2.17 2.44 0.32 0.09 Non-identified Gastropoda 0.72 0.81 0.09 0.03 Nassariidae Hinia sp. 0.72 0.41 0.05 0.02 Cerithiidae Bittium reticulatum 0.72 1.22 0.18 0.05 Bivalvia 13.04 18.29 8.01 6.94 Non-identified Bivalvia 7.25 9.35 4.43 4.59 Limidae Limulata subovata 0.72 0.41 0.09 0.02 Pectinidae Palliolum incomparabile 0.72 0.41 0.05 0.02 Solemidae Solemya togata 4.35 8.13 3.44 2.31 Pisces 5.07 3.25 0.77 0.94 Cnidaria 1.45 0.81 0.14 0.06 Anthozoa 1.45 0.81 0.14 0.06 126 ACTA ADRIATICA, 59 (1): 123 - 136, 2018 Echinodermata 3.62 4.07 4.34 1.07 Echinoidea Regularia 0.72 0.41 0.09 0.02 Echinocyanus pusillus 2.90 3.66 4.25 1.05 Polychaeta 9.42 6.10 10.63 7.25 Non-identified Polychaeta 9.42 6.10 10.63 7.25 Nematoda 2.90 2.85 9.77 1.68 Bryozoa 2.17 1.22 0.36 0.09 Non-identified Bryozoa 1.45 0.81 0.32 0.08 Margaretta cereoides 0.72 0.41 0.05 0.02 Algae 2.90 1.63 0.23 0.25 Rhizaria 0.72 0.41 0.05 0.02 Foraminifera Elphidium crispum 0.72 0.41 0.05 0.02 of identification depended on the completeness by 124 male and 79 female individuals.