Haploniscus astraphes, Brökeland, Wiebke & Svavarsson, Jörundur, 2017

Brökeland, Wiebke & Svavarsson, Jörundur, 2017, Distribution of haploniscids (Isopoda, Asellota, Haploniscidae) in Icelandic waters, with description of Haploniscus astraphes n. sp. from the Iceland basin and the Southeast Atlantic Ocean, Zootaxa 4231 (3), pp. 301-326 : 321-324

Distribution of Haploniscidae at the Greenland-Iceland-Faeroe Ridge

Ten species of the Haploniscidae were sampled during the BIOICE expeditions in the GIF area ( Table 1, Figs 10– 12 ), eight species of Haploniscus and one species each of genera Antennuloniscus and Chauliodoniscus . By far the most frequent species was Haploniscus bicuspis with 11,410 specimens sampled at 136 stations ( Table 1). H. foresti and A. simplex were also fairly frequent, occurring at 19 and 12 stations, with 1375 and 1816 specimens, respectively. Haploniscus aduncus occurred at ten stations, while Chauliodoniscus armadilloides was reported from 7 stations. The remaining species were found at one to four stations only, i.e. Haploniscus astraphes , H. ampliatus , H. angustus , H. hamatus , and H. spinifer .

The only species occurring north of the Greenland-Iceland-Faeroe Ridge were Haploniscus bicuspis and H. angustus . Haploniscus ingolfi is the only other haploniscid species previously reported from the Nordic Seas ( Wolff 1962; Svavarsson 1988), but was not found is this study.

H. bicuspis and H. angustus were the only haploniscid species occurring at depths shallower than the saddle depth at 840 m on the Ridge and seem to be able to cross the shallow sills of the Greenland-Iceland-Faeroe Ridge and thus colonize the waters all around Iceland . Haploniscus bicuspis has been reported to be adapted to cold conditions around 0°C ( Hansen 1916; Wolff 1962), and was here reported in many instances from temperatures below zero (as low as -0.86°C), but even at temperatures as high as 7.11° C. Accordingly, the species was found in a variety of water masses, such as the warm Modified North Atlantic Water ( MNAW), the deep Labrador Sea Water (LSW) and the Iceland Sea Overflow Water ( ISOW) south of Iceland, and even in the cold Norwegian Sea Deep Water ( NSDW) in the deep north.

The remaining species are confined to areas south of the Greenland-Iceland-Faeroe Ridge ( Figs 10 – 12 ) and also to depths greater than 1200 m, holding higher (>2°C) bottom temperatures ( Table 1). H. astraphes and H. ampliatus occurred only in the LSW, while H. hamatus and H. spinifer occurred only in the ISOW. Haploniscus aduncus , H. foresti , Antennuloniscus simplex and Chauliodoniscus armadilloides occurred, however, in both ISOW and LSW.

The Greenland-Iceland-Faeroe Ridge is presumably one of the most pronounced barriers of species distribution in the world oceans. This is the only extensive, shallow ridge crossing the Atlantic Ocean in an easterly-westerly direction, separating the Nordic Seas and the Arctic Ocean from the North Atlantic proper. The deepest connections between these oceans are the Denmark Strait (~ 620 m) in the Greenland-Iceland Ridge and the Faroe Bank Channel (~ 840 m) southwest of the Faeroe Islands ( Hansen & Østerhus 2000). North of the ridge bottom temperatures are low, being nearly -0.9°C in the deepest parts. The cold overflow water passing the ridge mixes with warmer water masses resulting in higher bottom temperatures south of the ridge.

Most commonly benthic species living in the area have their distributional limits at the ridge, e.g. desmosomatid and nannoniscoid asellote isopods ( Brix & Svavarsson 2010); anthuridean isopods ( Negoescu & Svavarsson 1997), valviferan isopod ( Stransky & Svavarsson 2006), amphipods ( Weisshappel 2001) and pectinoid bivalve molluscs ( Dijkstra et al. 2009). It is still poorly known how the ridge and the different associated water masses shape the distribution of the species in question; whether this is by the strong thermal gradient, by the presence of water masses of subzero temperatures being difficult to adapt to, or simply by the physical presence of the ridge itself. Svavarsson et al. (1993) concluded that the diversity of the Arctic deep-water fauna was low due to the isolating effects of the ridge and the associated water masses.

Although haploniscid isopods are known throughout the world oceans, the Nordic Seas and the Arctic Ocean are poor of haploniscid species ( Svavarsson et al. 1993). Apparently, the physical presence of the ridge limits the distribution of most of the haploniscid species towards the north, due to the deep occurrence of most of the species seen here.

Most of the haploniscids listed here have been found in the northernmost part of the Atlantic Ocean. Haploniscus astraphes n. sp., however, shows an extensive distribution, from the south side of the Greenland- Iceland Ridge to the Guinea Basin, South Atlantic and the Angola Basin. Whether these really belong to the same species remains to be evaluated using molecular methods.

Figures

FIGURE 10. Distribution of haploniscid species around Iceland (BIOICE localities): A, Haploniscus astraphes n. sp. (dot), H. ampliatus (triangle) and H. hamatus (square); B, H. aduncus; C, H. angustus.

FIGURE 11. Distribution of haploniscid species around Iceland (BIOICE localities): A, H. bicuspis; B, H. foresti; C, H. spinifer.

FIGURE 12. Distribution of haploniscid species around Iceland (BIOICE localities): A, Antennuloniscus simplex; B, Chauliodoniscus armadilloides.