Results and discussion

Three colonies of Uschakovia gorbunovi were collected in Svalbard waters (two in the Barents Sea and one in the northern part of the Greenland Sea), while one was collected in the Makarov Strait, an area situated between Franz Josef Land and Novaya Zemlya in the northeastern Barents Sea (Figure 1).

Figure 1. Records of Uschakovia gorbunovi. Pink circle – initial finding by Kluge (Reference Kluge and Buynitskiy1946) in the East Siberian Sea, orange diamonds – initial findings by Kluge (Reference Kluge and Buynitskiy1946) in the Kara Sea, red triangles – present findings in the northern Barents Sea (the numbers correspond to those in Table 1).

According to the initial description by Kluge (Reference Kluge and Buynitskiy1946, Reference Kluge1962), a colony of Uschakovia gorbunovi is erect and arises from an ancestrula that is anchored by rhizoids, which then leads to the emergence of several founding zooids that exhibit the same ability to develop rhizoids. This erect, branched part of the colony develops from either one zooid or a compact sequence of linking zooids, which display an extraordinary degree of elongation. The branches of autozooids are grouped in alternating pairs and triads, before transitioning into a quadriserial configuration and subsequently undergoing bifurcation. This primary branch divides several times, creating a cluster of four to six branches. Autozooids possess a long, tubular, proximal gymnocyst that expands distally to surround an elongated opesia. Outward-facing zooids are equipped with a bipartite opesia, wherein the distal part is covered by a frontal membrane that surrounds operculum, and the proximal part is composed of the swollen bases of a pair of long, partially cuticular spines. In contrast, the inward-facing zooids show no spines, but they have an elongated opesia. Avicularia arise from the proximal gymnocyst of both zooid types; the subrostral chamber is significantly elongated and expands distally, forming a terminally hooked, acute rostrum. The presence of ovicells remains unidentified within this species.

Unlike Kluge (Reference Kluge and Buynitskiy1946), who recorded a fully developed colony (as suggested from his initial description and illustration), we were able to photograph a small colony consisting of either a young developing colony (according to its small size) or a fully developed colony with only one linking zooid (Figure 2).

Figure 2. Uschakovia gorbunovi Kluge, Reference Kluge and Buynitskiy1946 from the Barents Sea, 2017. (a) – general colony view, scale bar 5 mm, (b) – distal part of the colony, scale bar 0.5 mm, (c) – details of the colony, scale bar 0.5 mm.

Founding zooids, spines, and ancestrulae were likely missed during grab sampling – a process that may preclude successful collection of intact, delicate colonies of deep-water bryozoans with thinly calcified zooids. Unfortunately, the other three colonies found in the study area were severely damaged and also exhibited small sizes.

The length of our photographed colony was 5 mm. The lengths of the other colonies were 8 mm (No. 1), 4 mm (No. 3), and 4.5 mm (No. 4). Kluge (Reference Kluge1962) did not provide the total length of his colonies, while Cook (Reference Cook2001) described a colony with a length of 10 mm in the waters of the Faroe Islands and noted that the maximum length of the colonies from the Faroes was 15 mm. The zooids of the Barents Sea colony were yellowish in colour, with a length ranging from 0.75 to 0.87 mm and a width of 0.25 mm. These measurements coincide with the range observed by Kluge (Reference Kluge1962): 0.75–1.40 mm in length and 0.25 mm in width. Cook (Reference Cook2001) revealed autozooids lengths ranging from 0.76 to 0.83 mm.

Kluge reported that Uschakovia gorbunovi is a high-Arctic species that occurs at temperatures ranging from −0.90 to −1.40°C, while Micael et al. (Reference Micael, Denisenko, Gíslason, Guðmundsson, Kukliński and Rodrigues2022) recorded this species at −1.8 to −6.0°C. Our findings fall within this range (Table 1).

The frequency of Atlantic water inflows into high-latitude regions of the Barents Sea has been increasing (Frolova et al., Reference Frolova, Lyubina, Dikaeva, Akhmetchina and Frolov2007; Matishov et al., Reference Matishov, Moiseev, Lyubina, Zhichkin, Dzhenyuk, Karamushko and Frolova2012; Kortsch et al., Reference Kortsch, Primicerio, Fossheim, Dolgov and Aschan2015; Dvoretsky et al., Reference Dvoretsky, Vodopianova and Bulavina2023), resulting in stronger ocean currents and wind forcing (Matishov et al., Reference Matishov, Matishov and Moiseev2009, Reference Matishov, Moiseev, Lyubina, Zhichkin, Dzhenyuk, Karamushko and Frolova2012), may facilitate the range extensions of bryozoans. This phenomenon has been observed in both high and lower latitude areas of the Barents Sea over the past decade (Evseeva et al., Reference Evseeva, Ishkulova and Dvoretsky2022; Evseeva and Dvoretsky, Reference Evseeva and Dvoretsky2023, Reference Evseeva and Dvoretsky2024; Dvoretsky and Dvoretsky, Reference Dvoretsky and Dvoretsky2024). It can be hypothesized that Uschakovia gorbunovi was transported into the Barents Sea through the influx of cold Arctic waters from the Kara Sea between Franz Josef Land and Novaya Zemlya. This current then flows westward across the northern Barents Sea along the eastern slope of the Spitsbergen Bank, where it merges with the East Spitsbergen Current (Jakobsen and Ozhigin, Reference Jakobsen and Ozhigin2011). This circulation pattern provides a plausible explanation for the new distribution records of this bryozoan in the northern part of the Barents Sea. However, there emerges a question concerning the lack of early findings of Uschakovia gorbunovi in Svalbard waters, particularly since the species was discovered in the Faroe Islands based on a collection made in 1987. The bryozoan fauna in the shallow-water Svalbard area has been extensively studied (Gulliksen et al., Reference Gulliksen, Palerud, Brattegard and Sneil1999; Gontar et al., Reference Gontar, Hop and Voronkov2001; Kukliński, Reference Kukliński2002; Palerud et al., Reference Palerud, Gulliksen, Brattegard, Sneli, Vader, Prestrud, Strøm and Goldman2004). Uschakovia gorbunovi, which prefers deeper waters, was not found in collections prior to 2005, possibly due to insufficient sampling efforts in the open sea waters near the Svalbard Archipelago. Several bryozoan species have expanded their range through boat bottoms, ship hulls, and ballast water tanks (López Gappa et al., Reference López Gappa, Carranza, Gianuca and Scarabino2010; Ryland et al., Reference Ryland, Bishop, De Blauwe, El Nagar, Minchin, Wood and Yunnie2011; Loxton et al., Reference Loxton, Wood, Bishop, Porter, Spencer Jones and Nall2017; Anderson et al., Reference Anderson, Peterson and Andres2022). However, this pathway is only relevant for coastal species. In the case of the deep-water Uschakovia gorbunovi, a more likely scenario is their distribution via mobile benthic species, such as the invasive snow crab Chionocetes opilio. This species was first recorded in the Barents Sea in 1996 (Dvoretsky and Dvoretsky, Reference Dvoretsky and Dvoretsky2015), and adult snow crabs reached the Kara Sea in 2012 (Zimina, Reference Zimina2014). The migration of snow crabs in the opposite direction may have promoted the range extension of Uschakovia gorbunovi into the Barents Sea. Previous research has shown that snow crabs are suitable hosts for deep-sea bryozoans (Savoie et al., Reference Savoie, Miron and Biron2007) and that invasive crabs can contribute to the spread of their epibionts within the new area of occurrence (Dvoretsky and Dvoretsky, Reference Dvoretsky and Dvoretsky2022, Reference Dvoretsky and Dvoretsky2023).

Our study provides a basis for further monitoring of bryozoan fauna in Arctic seas under changing environmental conditions and a reference point for tracking the range expansion of bryozoans at high latitudes.