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

Abstract

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 m 2 , 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).

Reproductive traits and age of barbeled plunderfishes from the Weddell Sea

“…Pogonophryne scotti was the most common species within the genus, consistent with the results obtained during a recent seabed imaging survey conducted in the Weddell Sea (La Mesa et al 2019). Notably, the lack of large adult males in the samples could be related to their spatial segregation during parental egg guarding, as described in the northern Weddell Sea in the same period (February–March) (Jones & Near 2012).…”

Parental care and reproductive strategies in notothenioid fishes

“…The male cleans the nest free of sand and debris by vibrating the anal fin with intense and continuous waving movements, and then female laids the eggs in the cleaned nesting site (Ferrando et al., 2014). Underwater observations made by scuba divers (Kock, 2005; Kock et al., 2006) or by ROV (La Mesa et al., 2019; Pisano et al., 2010) documented the nesting behaviour of male Pagetopsis macropterus in the Ross and Weddell Seas (Figure 3h). As previously reported for other notothenioid species, egg masses are laid on the flat and cleaned surface of a large stone.…”

“…Each batch was laid on a large, flat rock as a single layer of about 2,500 eggs 3.4 mm diameter that were unevenly spaced and more contiguous in the centre but scattered in the periphery (Evans et al., 2005). More recently, a seabed imaging survey conducted in the Weddell Sea documented a specimen of Cygnodraco mawsoni guarding eggs on a flat dropstone on a substrate formed by a dense sponge spicule mat (Figure 3g; La Mesa et al., 2019). A large specimen of P. charcoti was observed close to its nest during scuba diving at Potter Cove (King George Island, South Shetlands).…”

“…As previously reported for other notothenioid species, egg masses are laid on the flat and cleaned surface of a large stone. As they provide a stable substrate and increase habitat heterogeneity on the seafloor, glacial dropstones are also used as nesting site by C. wilsoni in the west Antarctic Peninsula fjords (Ziegler et al., 2017) and in the northern and southern Weddell Sea (Figure 3i; Biebow et al., 2014; Kock et al., 2008; La Mesa et al., 2019). Batches of 500–600 eggs are deposited in adherent monolayers on the entire surface of flat stones of about 20‐cm diameter (Kock et al., 2008).…”

Neuromorphological disparity in deep-living sister species of the Antarctic fish genus Trematomus

“…As sister species, T. lepidorhinus and T. loennbergii share some of the behavioral, morphological and ecological parameters of their niche. Both species have been photographed perching within epibenthic communities of sessile suspension feeders (Gutt and Ekau 1996) as well as on the substrate in the Weddell Sea (La Mesa et al 2019). Based on ecomorphological data they have streamlined body morphology and are more adapted toward utilization of the water column than other trematomids (Klingenberg and Ekau 1996).…”