Diet and feeding strategies of mesopelagic fishes in the western Mediterranean

• Published in: Progress in oceanography 2015-06, Vol.135, p.1-17
• Main Authors: Bernal, Ainhoa, Olivar, M. Pilar, Maynou, Francesc, Fernández de Puelles, M. Luz
• Format: Article
• Language: English
• Subjects: Adults; Argyropelecus hemigymnus; Copepoda; Cyclothone braueri; Diets; Elongation; Euphausiid; Feeding; Fish; Hygophum; Lampanyctus crocodilus; Lampanyctus pusillus; Marine; Myctophum punctatum; Night; Ostracoda; Stomach; Strategy
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2015.03.005

•Trophic ecology of mesopelagic fishes in the Mediterranean Sea was investigated.•Broad diet overlap was found among most fish species.•Main differences in feeding patterns were due to voracity and vertical segregation.•The degree of prey selectiveness and diet specialisation was low in most fishes.•It might be related to the low fish diversity for the mesopelagic assemblage. Myctophids, gonostomatids and sternoptychids are the most abundant teleosteans worldwide and constitute an important assemblage of the mesopelagic ecosystem, functioning as vehicles of energy and matter through trophic webs. This study concentrates on the trophic ecology of the most abundant mesopelagic fishes of the western Mediterranean (WM) based on stomach content analysis. The myctophids (in this study: Benthosema glaciale, Ceratoscopelus maderensis, Lobianchia dofleini, Myctophum punctatum, Hygophum benoiti, Hygophum hygomii, Lampanyctus crocodilus, Lampanyctus pusillus and Notoscopelus elongatus) perform extensive diel migrations across the water column, between the surface to as deep as 1000m, interacting with plankton and micronekton at multiple depths, and generally feeding in the epipelagic layers at night. In contrast, the gonostomatids Cyclothone braueri, Cyclothone pygmaea, and the sternoptychid Argyropelecus hemigymnus remain below epipelagic layers, feeding at different times throughout the day and night. The diet composition, trophic niche breadth and prey selectivity of 11 of these fish species were determined for juvenile and adult individuals from two surveys performed in December 2009 and July 2010 in the western Mediterranean Sea. The number of prey items varied among species, e.g. Myctophum punctatum was the species with the highest feeding intensity, reaching ca. 700 prey items in a stomach, whereas the mean number of prey in Cyclothone braueri was low (usually 1 or 2 prey per stomach). A dietary shift towards larger prey was evident from juveniles to the largest and oldest adult individuals, despite trophic niche breadths did not increase with body length for any of these mesopelagic species. The diets of the small gonostomatids, sternoptychid and early juveniles of myctophids were dominated by non-calanoid copepods, ostracods, and other small zooplankton, whereas medium-sized myctophids, e.g. L. dofleini or H. benoiti, preyed mainly on calanoids. The oldest stages of L. crocodilus and N. elongatus fed mostly on macrozooplankton and micronekton. There was high