Spatial distribution and habitat preferences of demersal fish assemblages in the southeastern Weddell Sea (Southern Ocean)

Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose fam- ily, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dol- loidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepi- dorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni)

Ecological assessment of anthropogenic impact in marine ecosystems: The case of Bagnoli Bay

none13noPollutants alter marine systems, interfering with provisioning of ecosystem services; understanding their interaction with ecological communities is therefore critical to inform environmental management. Here we propose a joint compositional- and interaction-based analysis for ecological status assessment and apply it on the benthic communities of the Bagnoli Bay. We found that contamination differentially affects the communities’ composition in the bay, with prokaryotes influenced only by depth, and benthos not following the environmental gradient at all. This result is confirmed by analyses of the community structure, whose network structure suggest fast carbon flow and cycling, especially promoted by nematodes and polychaetes; the benthic prey/predator biomass ratio, adjusted for competition, successfully synthesise the status of predator taxa. We found demersal fish communities to separate into a deep, pelagic-like community, and two shallow communities where a shift from exclusive predators to omnivores occurs, moving from the most polluted to the least polluted sampling units. Finally, our study indicate that indices based on interspecific interactions are better indicators of environmental gradients than those defined based on species composition exclusively.embargoed_20220311Hay Mele B.; Russo L.; Crocetta F.; Gambi C.; Dell'Anno A.; Danovaro R.; Guglielmo R.; Musco L.; Patti F.P.; Riginella E.; Tangherlini M.; Ribera d'Alcala M.; D'Alelio D.Hay Mele, B.; Russo, L.; Crocetta, F.; Gambi, C.; Dell'Anno, A.; Danovaro, R.; Guglielmo, R.; Musco, L.; Patti, F. P.; Riginella, E.; Tangherlini, M.; Ribera d'Alcala, M.; D'Alelio, D

Life history traits of Notothenia rossii and N. coriiceps along the southern Scotia Arc

Notothenia coriiceps and Notothenia rossii are two widespread nototheniid fishes, that live sympatrically along the southern Scotia Arc from South Georgia to the South Shetland Islands. In this sector of the Southern Ocean, they experienced different exploitation rates in the past and exhibit different habitat and food preferences as adult. Aiming to evaluate the influence of these factors in shaping life history traits of these species, we compare the reproductive investment and the age structure between the species and in N. rossii, between populations inhabiting different areas. Based on histological analyses, the two species share the same pattern of gamete development in both sexes. The potential fecundity was similar and was positively related to fish size in both species, being relatively high with respect to other notothenioids and in terms of egg size at deposition. Based on sagittal otolith readings, the growth rate and maximum age recorded differed significantly between the two species. Notothenia rossii exhibited a higher growth rate and a comparatively lower maximum age than N. coriiceps. Similarly, N. rossii attained sexual maturity at the same age but at a larger size than N. coriiceps. At the intraspecific level, no differences in life history traits were observed between the populations of N. rossii collected from different areas. Consistent with the different levels of fishing pressure exerted on these species and their low resilience, a recent significant decrease over time in the maximum fish size and related reproductive potential has been observed only in the overexploited populations of N. rossii

Comparative analysis of otolith morphology in icefishes (Channichthyidae) applying different statistical classification methods

The genus Chionodraco includes three morphologically similar species, two of them (C. hamatus and C. myersi) living sympatrically in the Eastern Antarctica, and the third one (C. rastrospinosus) being distributed in the Western Antarctica along the southern Scotia Arc. The few overlapping diagnostic characters are often useless for the right taxonomic identification of three species, complicated by the presence of hybrids between them. In the present study, we tested the discrimination power of sagittal otolith shape as a tool to distinguish among these closely related species. An array of shape indices and elliptic Fourier descriptors were individually obtained from sagittal otoliths and analysed using three different models for species classification: Linear Discriminant Analysis (LDA), Random Forest (RF) and K-nearest neighbour (KNN). According to the characteristics of the adopted metric (precision), none of the methods resulted to be the absolute best approach as the performance largely varied with the species. The overall precision was 63 %, 66 % and 70 % for LDA, RF and KNN respectively, so that KNN can be considered the best classifier model. As expected, C. myersi was the best recognized species by all classifier models, consistently with its morphological and phylogenetic difference from the other two species. Taking into account the observed pattern of otolith morphology of the three species and their own geographical distribution, we were able to evaluate the role of genetic, endogenous or environmental components in influencing otolith size and shape

Reproductive traits and age of barbeled plunderfishes from the Weddell Sea

The genus Pogonophryne is the most species-rich genus of barbeled plunderfishes (Artedidraconidae) and includes more than 25 poorly known species endemic to the Southern Ocean. In this study, we provide new data on the age and reproductive traits of some species of Pogonophryne from the southern Weddell Sea, inferred through otolith reading and histological analyses of gonads. Individual age estimates ranged between 16 and 18 years for Pogonophryne barsukovi and Pogonophryne immaculata and between 10 and 22 years for Pogonophryne scotti. As is commonly found in notothenioids, P. barsukovi followed a group-synchronous type of ovarian development, with pre-vitellogenic and vitellogenic oocytes forming two well-separated egg-size groups. A single spawning female in the sample produced 3c1097 eggs and 7.9 eggs g-1. The sample of P. immaculata consisted exclusively of developing males, with testes composed of cysts of spermatogonia, spermatocytes and spermatids. Pogonophryne scotti was the most abundant species, including relatively small males at immature or developing stages of gonad development. Larger females were regressing, being characterized by ovaries with postovulatory follicles and atretic oocytes. Based on the macroscopic and histological analyses of gonads, the spawning season would take place in autumn for P. barsukovi and P. immaculata and in spring-early summer for P. scotti

Aspects of the biology of the Antarctic dragonfish Gerlachea australis (Notothenioidei: Bathydraconidae) in the Weddell Sea, Antarctica

The Antarctic dragonfish Gerlachea australis is one of the most common bathydraconid species within the fish community of the Filchner Depression in the Weddell Sea. Nevertheless, several biological aspects of this species remain poorly known. The aim of this study was to provide new data on its population structure in terms of size, sex and age through sagittal otolith readings, as well as some reproductive traits based on macroscopic and histological analyses of gonads. The sex ratio in the sampled population was 1:1, with males being significantly smaller than females. Both sexes attained maximum age estimates of 14 years. Based on a von Bertalanffy growth model, females showed a higher asymptotic length than males at a comparable growth rate, thus reaching a higher growth performance. The spawning season was spread over a relatively long period, lasting at least from late December through late February. The reproductive effort in terms of fecundity and egg size diameter was similar to that of other bathydraconids, ranging from 739 to 1260 eggs/female and 3.2 mm after hydration, respectively. The fish size at first spawning (TL50) was 18.5 and 22.5 cm in males and females, corresponding to 80% of their maximum size. G. australis exhibited a combination of life history traits found in other high-Antarctic notothenioids, such as long gametogenesis, large eggs associated with low fecundity, relatively rapid body growth until reaching a delayed sexual maturity, moderate longevity and maximum size, and overall low growth performance

Biological parameters of the High-Antarctic icefish, Cryodraco antarcticus (Channichthyidae) from the South Shetland Islands

Despite their wide distribution around the Antarctic continent, the life strategies of the long-fingered icefish Cryodraco antarcticus have been rarely investigated and are not well understood. The aim of this paper was to provide more insights on the demographic characteristics of the population living off the South Shetland Islands, focusing attention on key biological traits such as age and growth and the reproductive cycle. Individual age and reproductive status were assessed through the microstructural analyses of sagittal otoliths and histological analysis of gonads, respectively. The sex-balanced sampled population consisted of juvenile and adult fishes covering a wide size range. Both sexes had positive allometric growth, although males exhibited smaller maximum size and lower body condition than females. Fish longevity was comparable between sexes, being 16 and 18 years in males and females, respectively. Applying the von Bertalanffy growth model to length-at-age estimates, males consistently reached lower maximum asymptotic size at a faster rate than females. Based on the gametogenic process, the spawning period was inferred to occur from late summer to early autumn. As commonly found in icefishes, females devoted a great investment to reproduction as gonadosomatic index, egg size, and fecundity. A single female (62 cm TL) spawned about 7730 eggs as large as 3\u20134 mm. Considering also the results of previous studies conducted in other areas, this species is characterized by a long-lasting pelagic juvenile phase and adults share similar life strategies across the range of their spatial distribution, suggesting the possibility of a single panmictic circum-Antarctic population

Biological parameters of the High-Antarctic icefish, Cryodraco antarcticus (Channichthyidae) from the South Shetland Islands

Despite their wide distribution around the Antarctic continent, the life strategies of the long-fingered icefish Cryodraco antarcticus have been rarely investigated and are not well understood. The aim of this paper was to provide more insights on the demographic characteristics of the population living off the South Shetland Islands, focusing attention on key biological traits such as age and growth and the reproductive cycle. Individual age and reproductive status were assessed through the microstructural analyses of sagittal otoliths and histological analysis of gonads, respectively. The sex-balanced sampled population consisted of juvenile and adult fishes covering a wide size range. Both sexes had positive allometric growth, although males exhibited smaller maximum size and lower body condition than females. Fish longevity was comparable between sexes, being 16 and 18 years in males and females, respectively. Applying the von Bertalanffy growth model to length-at-age estimates, males consistently reached lower maximum asymptotic size at a faster rate than females. Based on the gametogenic process, the spawning period was inferred to occur from late summer to early autumn. As commonly found in icefishes, females devoted a great investment to reproduction as gonadosomatic index, egg size, and fecundity. A single female (62 cm TL) spawned about 7730 eggs as large as 3\u20134 mm. Considering also the results of previous studies conducted in other areas, this species is characterized by a long-lasting pelagic juvenile phase and adults share similar life strategies across the range of their spatial distribution, suggesting the possibility of a single panmictic circum-Antarctic population

Demersal fish assemblages in the southeastern Weddell Sea

Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose family, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dolloidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepidorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni)

Food partitioning and diet temporal variation in two coexisting sparids, Pagellus erythrinus and Pagellus acarne

22 pages, 4 figures, 4 tablesResource partitioning in two congeneric sparids, pandora Pagellus erythrinus and axillary seabream Pagellus acarne, was investigated using stomach content analysis integrated with data on stable isotopes (δ15N and δ13C). The study was carried out on coastal muddy bottoms in the Gulf of Castellammare (southern Tyrrhenian Sea, western Mediterranean Sea) in seasons (autumn, November 2004; winter, March 2005; spring, early June 2005), at depths between 50 and 100 m. Stomach content analysis suggested low trophic niche overlap between the two species. Pagellus erythrinus mainly preyed on strictly benthic organisms (polychaetes, brachyuran crabs and benthic crustaceans). Although it consumed benthic prey, P. acarne preferred suprabenthic prey such as peracarid crustaceans from the benthic boundary layer a few metres above the bottom. The two species showed different isotopic values, with P. erythrinus exhibiting higher δ15N and more enriched δ13C than P. acarne, in accordance with its marked benthic behaviour and high predation on carnivore polychaetes. Significant temporal variability in both diet and isotopic values caused trophic differences between the two species. The autumn and winter diet differed from the spring diet and the trophic levels of both species increased from autumn and winter to spring, in accordance with variations in food availability and changes in prey δ15N and δ13C. These temporal variations may be linked to an increase in energy requirements for reproduction, together with the differing availability of preferred prey throughout the year. Significantly, lower δ13C was recorded in fishes collected in winter (March), suggesting the influence of river inputs as a source of particulate organic matter in this zone after the flooding season. In conclusion, these sympatric congeneric fish species displayed clear food partitioning throughout the temporal scale analysedSamples from the Gulf of Castellammare analysed in this study were collected with the permission of the Italian Ministry of Agriculture and Forestry (Project No. 6A84/2003). The authors wish to thank all the participants in field work and all the staff at CNR-IAMC of Castellammare del Golfo, particularly C. Romano, who helped with polychaete identification. Special thanks to S. Vizzini (Univ. of Palermo-IT) for help with isotope analysis and to H. Main for revising the EnglishPeer reviewe