First description of larvae of Acanthodraco dewitti in the Ross Sea, Antarctica

Six postlarval and an adult bathydraconid were collected in Terra Nova Bay, Ross Sea, during January-February 1988 and February 1998, respectively. The adult was identified as Acanthodraco dewitti Skóra, 1995 (type locality South Shetland Islands), a species not recorded in the Ross Sea. The postlarvae may be those of A. dewitti. The morphology and pigmentation patterns of the postlarvae are described and compared with those of other bathydraconids.     

Feeding habits of <Emphasis Type="Italic">Bathydraco marri</Emphasis> (Pisces,Notothenioidei, Bathydraconidae) from the Ross Sea,Antarctica

In comparison with other bathydraconids, all species of the genus Bathydraco are poorly known from an ecological perspective. The diet of juvenile Bathydraco marri Norman, 1938 was studied for the first time in specimens collected in the southwestern Ross Sea during summer 1998. Fish were collected in a single otter trawl catch at 330–340 m depth. The stomach content analysis showed that this species fed exclusively on crustaceans. Overall, 20 prey taxa were identified to genus or species level. Mysids, amphipods and copepods were the most important prey in decreasing order of importance. Other prey, such as Euphausia superba, isopods and tanaids were eaten occasionally and in very small amounts. A multivariate analysis was applied to feeding data to assess ontogenetic or sex-related changes in diet. No difference was detected between sexes, whereas diet of small and large fish differed in some degree. An ontogenetic shift from small and pelagic crustaceans such as copepods to benthic–benthopelagic prey such as amphipods and mysids was observed. Relating present results with published data on physiological characteristics of B. marri, it was possible to infer their feeding behaviour and mode of life. Like other bathydraconids, this species appeared to be an inactive and sluggish fish, which relied on more or less motile benthic or epibenthic prey adopting a “sit and wait” feeding strategy. On the other hand, smaller fish seem to be more active, feeding also on pelagic prey such as copepods that can be seasonally abundant, thus reducing the intraspecific competition for food.     

Aspects of the biology of the icefish Dacodraco hunteri (Notothenioidei, Channichthyidae) in the Ross Sea, Antarctica

On the basis of five specimens, the icefish Dacodraco hunteri (Notothenioidei, Channichthyidae) is documented for the first time in the Ross Sea, Antarctica. Meristic counts and morphometric measurements are provided for this small, streamlined, laterally compressed species. D. hunteri has a weakly ossified skeleton with considerable cartilage in the skull. It has a partially persistent notochord and reduced amounts of bone in the vertebral column since the centra are incompletely constricted. Its weight in seawater averages only 1.28% of its weight in air and, as one of the lightest notothenioids, D. hunteri is probably a permanent inhabitant of the water column. The diet consists of relatively large specimens of the pelagic nototheniid fish Pleuragramma antarcticum. Accepted: 27 September 1998     

Cytogenetics of the bathydraconid fish Gymnodraco acuticeps (Perciformes, Notothenioidei) from Terra Nova Bay, Ross Sea

In the framework of the I.C.E.FISH (International Collaborative Effort on Antarctic Fish Adaptive Evolution) project, during the 1998-1999 season at the Italian shore-based Terra Nova Bay Station, the broad fields of adaptation and evolution of the fish suborder Notothenioidei were tackled through the integration of many disciplines. As a representative contribution of I.C.E.FISH, a cytogenetic study of the bathydraconid fish Gymnodraco acuticeps is reported. The Bathydraconidae is a heterogeneous notothenioid taxon whose intra-family relationships are very uncertain. The conventional karyotype and the location of nuclear ribosomal genes, by means of fluorescence in situ hybridisation, contributed to species-specific characterisation and provided the basis for comparative analyses. The karyotype of G. acuticeps consists of 48 chromosomes (2 metacentric, 2 submetacentric and 44 acrocentric); major ribosomal cistrons correspond to a large region in a single chromosome pair. Mapping of the available karyotypic data on a molecular phylogenetic tree provided information on chromosomal diversification during the cladogenesis of the bathydraconids.     

Chromosomal studies on ten species of notothenioid fishes (Notothenioidei: Bathydraconidae,Channichthyidae, Nototheniidae)

The results of a cytogenetic study conducted with banding and in situ hybridization techniques using ribosomal and telomeric probes on various species belonging to three families (Bathydraconidae, Channichthyidae and Nototheniidae) of the perciform suborder, Notothenioidei, are reported. The heterochromatin distribution and composition, nucleolar organiser and localisation of telomeric sequences seem to indicate that both in karyologically conservative families such as channichthyids and in families exhibiting greater karyological variability, certain DNA fractions like ribosomal genes and centromeric and telomeric DNAs are prone to some variability. This could play an important role in favouring or hampering chromosome rearrangements.     

Some biological characteristics of early larvae Dacodraco hunteri (Notothenioidei: Channichthyidae) in the western Ross Sea

Ichtyoplankton surveys were carried out in the western Ross Sea by the R/V Italica in the austral summer 1996 and 1997–1998 to study species composition and spatial distribution of larval stages of fish. One of the most abundant icefish caught was Dacodraco hunteri, a poorly known channichthyid inhabiting the high-Antarctic Zone. Based on 382 yolk-sac larvae and 13 preflexion larvae, the study was focused to estimate spatial distribution and abundance, as well as diet and growth rate. The pigmentation pattern and some morphometric measurements were also recorded for comparative purposes. The specimens were caught in relatively restricted areas located in Terra Nova Bay and north of the Ross Ice Shelf on the Challenger and Joides Basins. The standardized abundance of early larvae ranged between 0.03 and 1.72 individuals 10⁻³ m³ in 1996 and 0.16–4.53 individuals 10⁻³ m³ in 1997–1998, respectively. Fitting a linear model to the mean length increase in larvae collected in subsequent catch dates, the growth rate was estimated to be approximately 0.11 mm/day. Based on back calculation of growth rate and presumed hatch size of 11 mm, larval hatching probably took place in mid-December. Diet of preflexion larvae consisted exclusively of larvae of the pelagic nototheniid Pleuragramma antarcticum, a key species of the high-Antarctic pelagic food web. Hence, D. hunteri probably plays a more important role than previously thought in the pelagic community of the Ross Sea.     

The chromosomal complement of the artedidraconid fish Histiodraco velifer (Perciformes: Notothenioidei) from Terra Nova Bay, Ross Sea

The karyotype of Histiodraco velifer from the Antartic Ocean was analyzed using various banding methods and in situ hybridization with a telomeric probe. A male and a female had a diploid set of 46 chromosomes (6 submetacentric + 40 acrocentric, FN = 52); the nucleolar organizer was CMA3-positive and was located on the short arm of a medium-sized submetacentric pair. All chromosomes stained uniformly with DAPI, whereas C-banding revealed heterochromatic blocks that were mostly located centromerically and telomerically and were resistant to ALUI digestion. The substantial identity of the karyotype of H. velifer with that of the other artedidraconids investigated so far suggests that chromosome changes must have played a less than significant role in the speciation among the lineages of this fish family endemic to Antarctica.     

Diversification of brain and sense organ morphology in Antarctic dragonfishes (Perciformes: Notothenioidei: Bathydraconidae)

In the subzero shelf waters of Antarctica, fishes of the perciform suborder Notothenioidei dominate the fish fauna and constitute an adaptive radiation and a species flock. The 16 species of dragonfishes of the family Bathydraconidae live from surface waters to nearly 3,000 m and have the greatest overall depth range among notothenioid families. We examined the anatomy and histology of the brain, retina, and cephalic lateral line system of nine bathydraconid species representing 8 of the 11 known genera. We evaluate these data against a cladogram identifying three clades in the family. We provide a detailed drawing of the brain and cranial nerves of Gymnodraco acuticeps and Akarotaxis nudiceps. Bathydraconid brain morphology falls into two categories. Brains of most species are similar to those of generalized perciforms and some basal notothenioids (Class I). However, brains of deep-living bathydraconids (members of the tribe Bathydraconini minus Prionodraco) have a reduced telencephalon and tectum that renders the neural axis visible - the stalked brain morphology (Class II). All bathydraconids have duplex (rod and cone) retinae but there is considerable interspecific variation in the ratio of cones:rods and in the number of cells in the internal nuclear layer. Retinal histology reflects habitat depth but is not tightly coupled to phylogeny. Although the deep-living species of Bathydraconini have rod-dominated retinae, the retinae of some sister species are photopic. An expanded cephalic lateral line system is also characteristic of all members of the Bathydraconini as exemplified by Akarotaxis. This morphology includes large lateral line pores, wide membranous canals, hypertrophied canal neuromasts, and large anterodorsal lateral line nerves, eminentia granulares, and crista cerebellares. The saccular otoliths are also enlarged in members of this tribe. Neural diversification among bathydraconids on the Antarctic shelf has not involved the evolution of sensory specialists. Brain and sense organ morphologies do not approach the specialized condition seen in primary deep-sea fishes or even that of some secondary deep-sea fishes including sympatric non-notothenioids such as liparids (snailfishes) and muraenolepidids (eel cods). The brains and sense organs of bathydraconids, including the deep-living species, reflect their heritage as perciform shorefishes.     

Phylogeny of Antarctic dragonfishes (Bathydraconidae,Notothenioidei, Teleostei) and related families based on their anatomy and two mitochondrial genes

Although Antarctic teleosts of the suborder Notothenioidei are well studied, the status of some families remains unclear because of limited taxonomic sampling and sometimes poor statistical support from molecular phylogenies. It is true for the Bathydraconidae, the sister-family of the famous haemoglobin-less icefishes, the Channichthyidae. The present study is aimed at clarifying bathydraconid phylogeny and the interrelationships of higher notothenioid families, taking nototheniids as the outgroup. For this purpose, about 300 positions in the mitochondrial control region, 750 positions in the cytochrome b, and a matrix of morphological characters were employed for separate and simultaneous phylogenetic analyses. We conclude that (1) molecular data strongly support the split of bathydraconids into three clades, here called the Bathydraconinae (Bathydraco, Prionodraco, Racovitzia), the Gymnodraconinae (Gymnodraco, Psilodraco, Acanthodraco), and the Cygnodraconinae (Cygnodraco, Gerlachea, Parachaenichthys). Interrelationships between these three and the Channichthyidae remain unclear. Molecular data support neither paraphyly nor monophyly of the bathydraconids, while morphology leads to the monophyly of the family based on the synapomorphic loss of the spinous dorsal fin; (2) The Channichthyidae, the Harpagiferidae, and the Artedidraconidae are monophyletic families; (3) the phylogeny of the haemoglobin-less channichthyids is completely resolved and congruent with the conclusions of based on anatomical characters; (4) The present molecular results as well as other molecular studies favour the hypothesis that harpagiferids are the sister-group of artedidraconids, though our morphological matrix puts harpagiferids as the sister-group of all other families on the basis of a single character. With regard to harpagiferid relationships, it is interesting to notice that, when analysed simultaneously, morphological characters are not automatically "swamped" within molecular ones: in the tree based on the simultaneous analysis of all available data, morphological characters impose their topology on molecules.     

Picoplankton BIOMASS in the Ross Sea (Antarctica)

Summary Spatial distribution of picoplankton in the Ross Sea was studied. The authors discuss the biomasses of various picoplanktonic-sized fractions and of bacterial cells between 0.2 and 2.0 m capable of growing on Marine Agar 2216 (Difco). Picoplankton having a cellular diameter cf between 1.0 and 2.0 m (PP1) generally predominate, accounting for 73% of the whole picoplankton biomass. However, smaller cells (PP2) can represent 28% of the picoplankton biomass at depths corresponding to 1% of surface light. These results are in good agreement with those found in the coastal regions of McMurdo Sound (Fuhrman and Azam 1980) and in other areas of the Antarctic seas where total bacterioplankton was studied (Hanson et al. 1983b; El-Sayed 1987; Lancelot et al. 1989). Biomasses of total picoplankton (TPP) are not correlated with any of the environmental parameters studied. The PP1 is correlated with O₂ and silicates and PP2 is correlated with O₂, phosphates temperature and nitrates. Aerobic heterotrophic biomasses are correlated with O₂ and salinity.     

Organic matter composition in coastal sediments at Terra Nova Bay (Ross Sea) during summer 1995

We illustrate the spatial and vertical distribution of sediment phytopigments and organic matter biochemical composition at Terra Nova Bay (Ross Sea) during summer 1995. Coastal sediments displayed high phytopigments concentrations associated with huge amounts of labile organic matter largely dominated by proteins. This result was opposite to previous observations in the same area. Such comparison suggested that whilst organic matter quantity in the sediments depended upon the vertical input from the water column, temporal changes in its biochemical composition were related to benthic processes. As considerably high concentrations of biopolymeric organic carbon were found even at 6-cm depth and according to the “loss type” functioning of the coastal waters of the Ross Sea, we stress the summer time occurrence in coastal sediments of an important organic matter burial. Accepted: 24 October 1999     

Larval stages of the Antarctic dragonfish Akarotaxis nudiceps (Waite, 1916), with comments on the larvae of the morphologically similar species Prionodraco evansii Regan 1914 (Notothenioidei: Bathydraconidae)

The notothenioid family Bathydraconidae is a poorly understood family of fishes endemic to the Southern Ocean. There is especially little information on Akarotaxis nudiceps, one of the deepest-dwelling and least fecund bathydraconid species. Using genetic and morphological data, we document and describe the larval stages of this unique species, offer a novel characteristic to distinguish it from the morphologically similar bathydraconid Prionodraco evansii and use the sampling locations to infer a possible spawning area of A. nudiceps along the western Antarctic Peninsula. These results provide important baseline information for locating, identifying and studying the biology of A. nudiceps, an important component of the Southern Ocean ecosystem.     

Sea urchins, sea stars and brittle stars from Terra Nova Bay (Ross Sea, Antarctica)

Although echinoderms constitute some of the most conspicuous taxa of the Antarctic benthic communities, the echinoderm fauna of Terra Nova has not been described yet. The present study provides the first species list of echinoids, ophiuroids and asteroids from Terra Nova Bay (30–500 m depth) and describes the depth distribution of these species. Preliminary observations of the summer reproductive condition of some of the species are also included.     

First occurrence of Caprella scaura Templeton, 1836 (Crustacea: Amphipoda) on off-coast fish farm cages in the Mediterranean Sea

The non-indigenous caprellid Caprella scaura Templeton, 1836, native to the western Indian Ocean, was firstly recorded in the Mediterranean Sea in 1994, and all Mediterranean populations discovered to date are related to shoreline areas. A total of ten fish farms were sampled off the coasts of Spain (4), Italy (1), Croatia (2), Greece (1) and Malta (2). This is the first time that C. scaura has been reported from off-coast areas. Reproducing populations have been detected in fouling communities of three tuna farms off the coast of Croatia and Malta, which also signifies the first confirmed record of this species in both countries. The occurrence of successfully established and thriving populations of C. scaura Templeton, 1836 at floating off-coast fish farms underlines the importance of these structures as stepping stones in the species.