5.2.5 Zooneuston 



YUVENALY P. ZAITSEV, LEONID N. POLISCHUK. and BORIS G. ALEXANDROV 

 Department of Hydrobiology of Active Surfaces of the Sea. Institute of Southern Seas, Odessa, USSR 



Introduction 



Samples of zooneuston were taken at 33 stations in the 

 Bering Sea and at 14 stations in the Chukchi Sea (see scheme 

 with stations). The equipment for collecting zooneuston samples 

 included a two stage plankton-neuston net FNS-2 and a fish fry 

 trawl MNT (Zaitsev, 1971). A synchronous hauling of the 

 upper two microhorizons, the neuston layer (0-5 cm) and the 

 subneuston layer (5-25 cm) was performed. 



The MNT is a high speed equipment device for collecting 

 hydrobiological material (rate of trawling up to 3 m/sec) in the 

 0-25 cm layer. The PNS-2 was hauled at a distance of several 

 tens of meters at a velocity of 25 cm/sec. The volume of filtered 

 water was determined taking into consideration the time of 

 filtration and speed, as well as the working area of the net. 

 Ninety-four samples altogether were taken in the Bering and 

 Chukchi Seas. 47 samples each from the neuston layer and the 

 subneuston layers (Table 1). 



TABLE 1 



Zooneuston samples taken in the Bering and Chukchi Seas. 



The aiea of sampling embraced a large water mass including 

 the south part of the Chukchi Sea, Chirikov Gulf, and Gulf of 

 Anadyr of the Bering Sea, as well as the oceanographic East 

 and South Polygons. The most northerly station was situated 

 at a latitude of 68°39'7"N, the most southerly, 57°25'7"N. Thus 

 the study of zooneuston was carried out in the near polar and far 

 polar waters. 



As a result of the interaction of the ocean and atmosphere 

 on the ocean-atmosphere boundary, certain specific conditions 

 of life are created. One of the contours of the biotopes 6f the 

 halosphere is found here. The neuston population has much 

 species diversity and in the abundance of organisms, and plays 

 an important part not only in the life of the water layer, but in 

 the sea bottom, especially in the shelf zone (Zaitsev, 1971). 



The study of neuston in high latitude sea watens — in this 

 case, the Bering and Chukchi Seas — is important from many 

 points of view. First of all, the neuston of extreme north as well 

 as extreme south seas has not been studied. Secondly, the 



Bering and Chukchi Seas are known as background regions of 

 the World Ocean (Tsyban et ai, 1985), and thus neuston from 

 these waters will most certainly react to it (Zaitsev, 1986). 



The first preliminary investigations of zooneuston in the 

 Bering Seas were carried out in the summer of 1 962 ( Chebanov, 

 1965; Zaitsev, 1971). A more profound study of neuston was 

 performed by L. N. Polishchuk and B. G. Alexandrov under the 

 guidance of Yu. P. Zaitsev in July 1984. The same authors 

 studied zooneuston from 28 July to 31 August 1988 during the 

 Third Joint US-USSR Bering & Chukchi Seas Expedition on 

 board the research vessel (RA') Akademik Korolev. This was 

 the first time neuston was studied in the waters of the Chukchi 

 Sea. 



The animal population of the Bering and Chukchi Seas 

 differs in species composition and high density of populations 

 (Tables 2,3). 



It should be noted that because of specific natural conditions 

 in those seas, such as low temperatures, ice fomiation, lengthy 

 winter season, etc., only temporary forms of zooneuston 

 developed that were capable of terminating their ontogenesis 

 during the short period of hydrological summer. First of all, 

 these include the larvae of bottom invertebrates (bivalves, 

 gastropods, cirripeds, polychaetes, echinoderms, phoronides. 

 nemertines). decapod larvae, euphausiid larvae, juvenile fornis 

 of chaetoghaths, as well as early stages (eggs, nauplii, 

 copepodites ), the majority of copepods, the cladocerean Evadne 

 nordmanni , the pelagic polychaete Tomopteris pacifica, 

 pteropods (Clione limacina, Limacina helicina). tunicates 

 (Fritillaria borealis, Oikapleura labradoriensis). hydrozoans 

 (Taghkea octopunctata, Aglantha digitate, Obelia sp., 

 Pantaehogon haeckeli). and the siphonophore Dimophyes 

 arctica. 



Adult copepods such as Oncea borealis, Tortanus 

 discaudatus, Eurytemora pacifica. Acartia longiremis, and 

 Pseudocalanus minutus behaved like neustophils. The most 

 northern representative of the pontellid family Epilabidocera 

 amphitrites proved to be a typical neuston. 



The average number of organisms in the neuston layer in 

 the East Polygon amounted to 1 18,284 specimens/m', which is 

 about 4.5 times greater than the amount discovered here in the 

 summer of 1984. It is not difficult to give the reason for this 

 significant difference. As to the ratio of the abundance of 

 organisms in the neuston and subneuston layers, in 80% of the 

 cases, there were more in the former layer (Table 4). 



Tintinnids, pteropods, nauplius eggs and, early copepodite 

 stages of Copepoda (Ointhona siniilis, Acartia longiremis. 

 Pseudocalanus minutus, Eucalanus hungii). decapod larvae, 

 and juvenile polychaetes prevailed in the neuston layer. 



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