Lanternfish

Abstract: The diets of six of the main seabird species (two petrels, two albatrosses, two penguins) breeding at Bird Island, South Georgia were studied simultaneously during the chick-rearing period in 1986. For five species, Antarctic krill Euphausia superba was the main food (39–98% by mass); grey-headed albatrosses took mainly the ommastrephid squid Martialia hyadesi (71%) and only 16% krill. The size of the krill taken was similar between seabird species, although there were small but significant differences between penguins and the other species. Sex and reproductive status of krill, however, was different between all seabird species, reflecting some combination of differences in foraging ranges, selectivity by predators, or differences in escape responses of krill. For the krill-eating species, the rest of the diet varied substantially between species, comprising Martialia and nototheniid fish (blackbrowed albatross and, along with lanternfish, white-chinned petrel), lanternfish and amphipods (Antarctic prion and macaroni penguin), and icefish (gentoo penguin). Long-term data on breeding success and information on diet in 5–10 other years suggest that in 1986 seabird diet and reproductive performance was indicative of a year of good availability of krill around South Georgia. In such circumstances, ecological segregation between krill-eating species appears to be maintained chiefly by differences in foraging range and feeding methods, which are reviewed. This situation is rather different from the few studies of seabird communities elsewhere, where prey type and size are believed to be the main mechanisms of dietary segregation.

Abstract: Recent data from research cruises and explorator fishing in the Antarctic Polar Frontal Zone (APFZ) of the Scotia Sea, together with data from dietary studies of Antarctic vertebrate predators, have revealed a large, previously overlooked trophic system in the Southern Ocean (Fig. 1). The upper trophic levels of this open-ocean epipelagic community are exceptional in that they contain no fish species. Fishes are replaced by cephalopods, including the ommastrephid squid, Martialia hyadesi. This squid preys on mesopelagic m.yctophids (lanternfish), which feed largely on copepods. We identify here a geographically distinct, Antarctic, open-ocean food chain which is of importance to air breathing predator species but where Antarctic krill, Euphausia superba, is absent. This system is probably prevalent in areas of higher primary productivity, especially the Scotia Sea and near the peri-Antarctic islands. Squid stocks in the APFZ may have potential for commercial exploitation, but they, and the predators they support, are likely to be sensitive to overfishing. Squid have a short, semelparous lifecycle, so overfishing in a single year can cause a stock to collapse.

Abstract: Myctophids are among the most abundant fishes in the world׳s ocean and occupy a key position in marine pelagic food webs. Through their significant diel vertical migrations and metabolism they also have the potential to be a significant contributor to carbon export. We investigated the feeding ecology and contribution to organic carbon export by three myctophid species, Benthosema glaciale , Protomyctophum arcticum , and Hygophum hygomii , from a structurally and ecologically unique ecosystem- the Mid-Atlantic Ridge (MAR). Similar to the results of previous studies, the diet of these fishes was primarily copepods and euphausiids, however, gelatinous zooplankton was identified in the diet of B. glaciale for the first time. Ridge section and time of day were significant explanatory variables in the diet of B. glaciale as determined by canonical correspondence analysis, while depth was the only significant explanatory variable in the diet of P. arcticum. Daily consumption by MAR myctophids was less than 1% of dry body weight per day and resulted in the removal of less than 1% of zooplankton biomass daily. Although lower than previous estimates of carbon transport by myctophids and zooplankton in other areas, MAR myctophid active transport by diel vertical migration was equivalent to up to 8% of sinking particulate organic carbon in the North Atlantic. While highly abundant, myctophids do not impart significant predation pressure on MAR zooplankton, and play a modest role in the active transport of carbon from surface waters.