Unique spicules may confound species differentiation: taxonomy and biogeography of Melonanchora Carter, 1874 and two new related genera (Myxillidae: Poecilosclerida) from the Okhotsk Sea

Sponges are amongst the most difficult benthic taxa to properly identify, which has led to a prevalence of cryptic species in several sponge genera, especially in those with simple skeletons. This is particularly true for sponges living in remote or hardly accessible environments, such as the deep-sea, as the inaccessibility of their habitat and the lack of accurate descriptions usually leads to misclassifications. However, species can also remain hidden even when they belong to genera that have particularly characteristic features. In these cases, researchers inevitably pay attention to these peculiar features, sometimes disregarding small differences in the other “typical” spicules. The genus Melonanchora Carter, 1874, is among those well suited for a revision, as their representatives possess a unique type of spicule (spherancorae). After a thorough review of the material available for this genus from several institutions, four new species of Melonanchora, M. tumultuosa sp. nov., M. insulsa sp. nov., M. intermedia sp. nov. and M. maeli sp. nov. are formally described from different localities across the Atlanto-Mediterranean region. Additionally, all Melonanchora from the Okhotsk Sea and nearby areas are reassigned to other genera; Melonanchora kobjakovae is transferred to Myxilla (Burtonanchora) while two new genera, Hanstoreia gen. nov. and Arhythmata gen. nov. are created to accommodate Melonanchora globogilva and Melonanchora tetradedritifera, respectively. Hanstoreia gen. nov. is closest to Melonanchora, whereas Arhythmata gen. nov., is closer to Stelodoryx, which is most likely polyphyletic and in need of revision.

SEISMICITY of the NORTH-EAST of RUSSIA in 2015

The results of seismic monitoring of the Magadan oblast, the Chukotka Autonomous okrug, and the shelves of the adjacent seas (Okhotsk, Chukchi, Bering, and East Siberian seas) are considered. There were 14 seismic stations working in the region. The new station “Gadlya” was opened on the Okhotsk sea coast. The catalog includes information about 290 earthquakes with energy classes KR=4.4–12.6. As usual, most of them (93 %) are localized in the Kolyma region. The total seismic energy released within the region’s borders was ΣЕ=4.6341012 J. According to the earthquake energy completeness map Кmin built for the region, minimal energy level of earthquakes, Кmin=5.0, is provided at two areas near the Susuman and Magadan stations. The station network can register without omissions the earthquakes with Kmin≥8 at the Okhotsk sea and Kolyma areas, with Kmin≥10.6 in the Chukotka area. In 2015 three earthquakes with intensities I=2–4 by MSK-64 scale were felt in settlements of North East of Russia. The 2015 strongest earthquake occurred on June 1 at 10h53m with KR=12.6 (MPSP=4.9), h=31 km in the Kolyma area. A maximum shaking intensity of I=4 was observed in Omsukchan settlement (∆=132 km). In March 2015 a swarm of 29 weak earthquakes with KR=6.2–9.8 occurred northeast of Talaya settlement. Epicenters of Kolyma area earthquakes were plotted on the tectonic zoning map of the Magadan region. Most earthquakes are confined to the main deep faults oriented in the northeastern and sublatitudinal directions. All hypocenters are located within the Earth's crust. The seismicity level of the North-East of Russia in 2015 according to the “SOUS09” scale was assessed as "background average" for the observation period from 1968 to 2015. Spatially, all earthquakes in the North-East of Russia are traditionally concentrated within the major seismogenic belts – Chersky, North-Okhotsk, and Trans-Beringian.

Controls on Terrigenous Detritus Deposition and Oceanography Changes in the Central Okhotsk Sea Over the Past 1550 ka

The Okhotsk Sea, which connects the high latitude Asian continent and the North Pacific, plays an important role in modern and past climate changes due to seasonal sea ice coverage and as a precursor of the North Pacific Intermediate Water. The long-term glacial-interglacial changes of sea ice coverage and its impacts on terrigenous transport and surface primary productivity in the Okhotsk Sea remain, however, not well constrained. Base on the paleomagnetic, rock magnetic, micropaleontological (diatom), and geochemical studies of the marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth: 1,123 m) taken in the central Okhotsk Sea, we reconstruct the terrigenous sediment transport and paleoceanographic variations during the past 1550 thousand years (kyr). Seventeen geomagnetic excursions are identified from the paleomagnetic directional record. Close to the bottom of the core, an excursion was observed, which is proposed to be the Gilsa event ∼1550 thousand years ago (ka). During glacial intervals, our records reveal a wide extension of sea ice coverage and low marine productivity. We observed ice-rafted debris from mountain icebergs composed of coarse and high magnetic terrigenous detritus which were derived from the Kamchatka Peninsula to the central Okhotsk basin. Still during glacial intervals, the initiation (i.e., at ∼900 ka) of the Mid-Pleistocene Transition marks the changes to even lower marine productivity, suggesting that sea-ice coverage became larger during the last 900 ka. During interglacial intervals, the central Okhotsk Sea was either devoid of sea-ice or the ice was at best seasonal; resulting in high marine productivity. The weaker formation of Okhotsk Sea Intermediate Water, lower ventilation, and microbial degradation of organic matter depleted the oxygen concentration in the bottom water and created a reduced environment condition in the sea basin. The freshwater supplied by snow or glacier melting from Siberia and Kamchatka delivered fine grain sediments to the Okhotsk Sea. During the stronger interglacial intervals after the Mid-Brunhes Transition (i.e., Marine Isotope Stages 1, 5e, 9, and 11), strong freshwater discharges from Amur River drainage area are in association with intensified East Asian Summer Monsoon. This process may have enhanced the input of fine-grained terrigenous sediments to the central Okhotsk Sea.

Helminth fauna of spawning pacific herring Clupea pallasii from the Taui population (Tauiskaya Guba Bay, Okhotsk Sea)

Parasites of spawning pacific herring (Clupea pallasii Valenciennes in Cuvier et Valenciennes, 1947) from the Taui population are explored on the samples caught on two spawning grounds located in the Ola lagoon and Amakhton Bay (Tauiskaya Guba Bay, Okhotsk Sea), and 17 species of helminthes are found, including 6 trematodes, 5 cestodes, 4 nematodes, and 2 acanthocephalans. Some differences in species composition of helminthes and their infestation were found between these estuarine and marine spawning grounds. In the Ola lagoon, 16 species of helminthes were identified, including 5 species of cestodes, whereas only 13 species of helminthes, including 3 species of cestodes, were found in the Amakhton Bay. The Taui population of herring is distinguished from the Okhotsk and Gizhiga-Kamchatka populations by presence of nematodes Hysterothylacium aduncum, l, and Ascorophis pacificus with rather high rates of invasion (occurence = 52.9 %; mean abundance = 4.16) and trematode Bucephaloides spp. On the other hand, the herring from the Taui population has common dangerous parasites with other populations in the Okhotsk Sea, as trematode Brachyphallus crenatus and nematode Anisakis spp. (larvae), with high degree of infestation.