Search

Abstract: Many members of the benthic fauna of the Antarctic continental shelf share close phylogenetic relationships to the deep-sea fauna adjacent to Antarctica and in other ocean basins. It has been suggested that connections between the Southern Ocean and the deep sea have been facilitated by the presence of a deep Antarctic continental shelf coupled with submerging Antarctic bottom water and emerging circumpolar deep water. These conditions may have allowed ‘polar submergence’, whereby shallow Southern Ocean fauna have colonised the deep sea and ‘polar emergence’, whereby deep-sea fauna colonised the shallow Southern Ocean. A recent molecular study showed that a lineage of deep-sea and Southern Ocean octopuses with a uniserial sucker arrangement on their arms appear to have arisen via polar submergence. A distantly related clade of octopuses with a biserial sucker arrangement on their arms (historically placed in the genus Benthoctopus) is also present in the deep-sea basins of the world and the Southern Ocean. To date their evolutionary history has not been examined. The present study investigated the origins of this group using 3133 base pairs (bp) of nucleotide data from five mitochondrial genes (12S rRNA, 16S rRNA, cytochrome c oxidase subunit I, cytochrome c oxidase subunit III, cytochrome b) and the nuclear gene rhodopsin from at least 18 species (and 7 outgroup taxa). Bayesian relaxed clock analyses showed that Benthoctopus species with a high-latitude distribution in the Southern Hemisphere represent a paraphyletic group comprised of three independent clades. The results suggest that the Benthoctopus clade originated in relatively shallow Northern Hemisphere waters. Benthoctopus species distributed in the Southern Ocean are representative of polar emergence and occur at shallower depths than non-polar Benthoctopus species. [Copyright &y& Elsevier]

The importance of the euchaetid copepod Paraeuchaeta antarctica in the subantarctic pelagic ecosystem was quantified in the coastal waters of the Golfe du Morbihan at Kerguelen Islands by comparing food samples from two diving seabirds with concurrent net samples taken within the predator foraging area. Paraeuchaeta antarctica occurred in very high densities (up to 30 individuals m−3 and 96 mg dry weight m−3) in the water column, being more abundant in the deepest part of the gulf than in shallow waters or at the more offshore shelf stations. The common diving petrel feeds almost exclusively on crustaceans, its diet being dominated by the amphipod Themisto gaudichaudii (52% by number and 84% by reconstituted mass) and P. antarctica (33% and 16%, respectively). Rockhopper penguins preyed upon crustaceans and fish, with four taxa being important, namely T. gaudichaudii (37% and 23%, respectively), Euphausia vallentini (24% and 41%), postlarval fish (10% and 24%), and P. antarctica (13% and 3%). Paraeuchaeta antarctica dominated numerically in 21% of the diving-petrel food samples and in 12% of penguin samples. The two bird species segregated by preying upon different developmental stages of P. antarctica, diving petrels fed equally on CV of both sexes and CVI♀, while penguins fed on CVI♀ only. Comparison of P. antarctica found in net and food samples indicated no prey selection by common diving petrels that caught the different copepod stages in proportion to their availability in the water column. On the other hand, the diving performance of penguins, which is better than that of the petrels (mean maximum dive depths 69 m for penguins versus 32 m in petrels), allows them to catch CVI♀ in deeper waters, probably near the bottom. Our study shows that P. antarctica is a major component of the coastal macrozooplankton community and a significant prey for two species of diving seabirds inhabiting Kerguelen. This is also the first record of a copepod species as a prey for penguin, and the first to highlight P. antarctica in the food of austral seabirds. [ABSTRACT FROM PUBLISHER]

Abstract: During the last 30 years, at-sea studies of seabirds and marine mammals in the oceans south of the Subtropical Front have described an association with major frontal areas. More recently, the advancement in microtechnology has allowed the tracking of individuals and investigations into how these marine predators actually use the frontal zones. In this review, we examine 1) the relative importance to apex predators of the different frontal zones in terms of spatial distribution and carbon flux; 2) the processes that determine their preferential use; and 3) how the mesoscale dynamics of frontal structures drive at-sea foraging strategies of these predators. We review published results from southern waters and place them in a broader context with respect to what has been learned about the importance of fronts in oceans farther north. Some fronts constitute important boundaries for seabird communities in southern waters. At a mesoscale the maximum values of seabird diversity and abundance correspond to the location of the main fronts. At-sea surveys show a strong curvilinear correlation between seabird abundance and sea surface temperatures. High mean species richness and diversity for whales and seabirds are consistently associated with the southern water mass boundary of the Antarctic Circumpolar Current, the Subtropical Front and the Subantarctic Front; in the case of the Polar Front mean seabird densities are more variable. At small-scales, variation in seabird occurrence has been directly related to the processes at fronts in a limited number of cases. A significant positive relation was found between some plankton feeding species and frontal temperature gradient–phytoplankton variables. Telemetric studies have revealed that several apex predators (penguins, albatrosses, seals) perform long, directed foraging trips either to the Subtropical front or Polar Front, depending on locality. Seabirds with low flight costs, such as albatrosses, are able to reach fronts at long distances from colonies, showing variable foraging strategies as a function of the distances involved. Diving birds such as King penguins, that travel at a higher cost and lower speed, rely on the predictable spatial distribution of mesopelagic fish found close to the Polar Front. They may use the currents associated with eddies as oceanographic cues in the active search for frontal zones. Once in these areas they dive preferentially in and below the depth of the thermocline where catches per unit effort are high. Elephant seals concentrate foraging activity principally inside or at the boundary of cyclonic eddies. These mesoscale features appear to offer exceptional productivity favourable for foraging by various diving top predators. The connection between biophysical parameters at fronts and predators is likely to be made through biological enhancement. Top predators appear to forage at locations where prey are advected by physical processes and others where prey are produced locally. Long-term research on at-sea distributions and demographic parameters of top predators are essential to assess the consequences of potential shift in front distributions in relation to global warming. Such environmental changes would add to the impact of fish extraction by the industrial fisheries on the southern food webs. [Copyright &y& Elsevier]