V V Murina - Occurrence of the bathypelagic larvae of the polychaete - страница 1
МОРСЬКИЙ ЕКОЛОГІЧНИЙ ЖУРНАЛ
V. V. Murina1, d. Sc. (Biol.), A. E. Kideys2, Ph. d., F. Ustun3, B. Toklu4
1Institute of Biology of the Southern Seas, National Academy of Sciences of Ukraine, Sevastopol, Ukraine 2 Institute of Marine Sciences, Middle East Technical University, Erdemli, Icel, Turkey 3 Sinop Faculty of Fisheries, 19 Mayis University, Sinop, Turkey 4 Faculty of Fisheries, Cukurova University, Balcali, Adana, Turkey
OCCURRENCE OF THE BATHYPELAGIC LARVAE OF THE POLYCHAETE, VIGTORNIELLA ZAIKAI IN THE SOUTHERN PART OF THE BLACK SEA
The bathypelagic larvae of the polychaete, Vigtorniella zaikai, were found in the southern part of the Black Sea for the first time. The findings were made in the depths from 85 - 110 to 150 - 180 m at 14 stations. Maximum density (119 ind m-3) of the larvae was registered in suboxic zone (<10mM dissolved oxygen content, DOC), immediately above the hydrogen sulphide seawater layer. Vertical distribution of pelagic larvae of other polychaetes associated with V. zaikai was also studied. The deepest seawater layer adjoining redox zone was inhabited by V. zaikai, Protodrilus sp. and the larvae of Phyllodocidae gen. sp. These taxa compose the bathypelagic polychaetes fauna.
Key words: Polychaeta, Vigtorniella zaikai, bathypelagic larvae, Black Sea
The first finding of the bathypelagic larvae of Vigtorniella zaikai was made by M. Kisseleva  over 50 years ago. Studying the samples of plankton taken from the deep-water areas of the Black Sea, M. I. Kisseleva had found formerly unknown larvae and tentatively defined them as trochophora "C" and nechtochaeta "B" without identifying the species, genus and family. Later, Murina  gave a detailed description of these larvae based on examination of more recent samples collected from deep-water locations of the Black Sea. She suggested that the "B" and "C" larvae were two different developmental stages of one and the same species, and identified them as Pelagobia serrata Southern, 1909. The smaller, sphaerical trochophora larva is 220 ц in diameter, and the larger, 5-segment nectochaeta - 700 ц in length. Later, Kisseleva  had re-identified P. serrata as a new taxon, Victoriella zaikai (fam. Chrysopetalidae). However, a genus of Protozoa had early been given the same generic name
Victoriella; therefore, Kisseleva  had to rename her finding as Vigtorniella.
Description of the new taxon of Polychaeta was based on examination of the larvae, which were brought by the adult polychaetes, V. zaikai, grown by V. I. Zaika in the laboratory and fed for a year on benthic diatoms and organic matter. Pelagic larvae for the experiment were collected alive from 100 - 130 depth at a deep-sea station located in the central Black Sea. The holotype of V. zaikai Kisseleva, 1992, is 1000 ц in length and consists of10 segments. As to the distribution of V. zaikai in the Black Sea, it is noteworthy that the larvae have never been found in the depths 0 - 50 (75) m either in coastal seawater or in the open sea. Numerous samples were collected during research expeditions to different locations of the Black Sea and thoroughly studied [6, 7, 8] and the obtained results allowed to have outlined the entire distribution area of this pelagic larva. However,
© V. V. Murina, A. E. Kideys, F. Ustun, B. Toklu, 2006
the seawater above the continental slope of Turkey has not been investigated until the present study.
Materials and methods. Samples of zooplankton were collected on 16 stations during the research cruise of the R/V Knorr in the Black
Sea in the south-western (Table 1) and in southeastern (Table 2). The pelagic larvae of V. zaikai were found on 14 stations (Fig. 1). Samples of meroplankton were collected with a Nansen net with 135 j mesh size.
Fig. 1 The stations of the R/V «Knorr» at which the pelagic larvae of Vigtorniella zaikai were found during the Black Sea cruise in April 1998 (•) and in May - June 2001 (+)
Рис. 1 Схема станций, на которых найдены пелагические личинки Vigtorniella zaikai во время исследований в Черном море э/с «Knorr» в апреле 1998 г. (•) и в мае - июне 2001г. (+)
Results. Larvae of V. zaikai were found at 11 of 13 stations made during the expedition on board of the R/V Knorr (Table 1). At stations 5 and 8 located in shallow seawater areas (the depths of 112 and 38 m, respectively) the larvae were absent in the samples collected from the 30 -0 and 100 - 0 m depths. At station 11, where the depth was 2168 m, the total numbers measured in the sampled seawater layer (0 -130 m) was the highest - 250 ind. (Table 1).
Meroplankton was studied using samples collected from 13 stations. For the majority of the stations the pelagic larvae of the bivalve mollusc, Mytilus galloprovincialis, were the most abundant component of meroplankton. Second in the 58 prevalence were polychaete larvae which divided into two communities. The first community was represented by the neritic warm-water larvae of Harmothoe aff. reticulata, Pholoe synophthalmica, Phyllodoce maculata, Microspio meznikowianus, and the second by the bathypelagic cold-water larvae of Vigtorniella zaikai, Protodrilus sp. and larvae of the family Phyllodocidae not identified to species. At stations 6 and 8, planulas of Hydroidea were enormously abundant. The rest of the meroplankton -Polititapes aures (Bivalvia), Morhensternia (=Rissoa) parva (Gastropoda), Upogebia pusilla (Decapoda) and Balanus improvisus (Ciripedia) -were only rarely found.
Table 1 The numbers of Vigtorniella zaikai and other meroplankton (ind.m and % of the total abundance in the sample, respectively) in the zooplankton samples from the Western Black Sea (R/V "Knorr", May - June 2001) Табл. 1 Численность личинок Vigtorniella zaikai и других организмов меропланктона (экз.м и в % от общего числа в пробе) в пробах зоопланктона из западной части Черного моря (НИС"Knorr", май - июнь, 2001 г.)
Table 2 Vertical distribution of Vigtorniella. zaikai larvae in the South-eastern Black Sea (R/V "Knorr"; April,
Табл. 2 Вертикальное распределение личинок Vigtorniella zaikai в юго-восточной части Черного моря
(НИС "Knorr", апрель 1998)
Max depth, m
H2S, zone depth, m
Seawater layer, m Density of V. zaikai ind m3, (% from total meroplankton)
M 15 R 45
120 - 145
145 - 180
125 - 150 5.2 (8.7)
150 - 185 58.6 (99)
M 30 V 45
85 - 110
110 - 140
85 - 110 2.8 (2.3)
110 - 140 119 (9.2)
L 30 T 28
125 - 150 1.2 (12)
150 - 180 43.7 (96)
125 - 150
150 - 180
Seawater layer, m Other species of meroplankton
120 - 145 Phyllodocidae g. sp.
Protodrilus sp. Harmothoe sp._
125 - 150 Protodrilus sp. Harmothoe sp._
85 - 110 Protodrilus sp. Harmothoe sp.
85 - 110
Phyllodocidae g. sp.
125-150 Phyllodocidae g. sp.
Protodrilus sp. Harmothoe sp.
125 - 150
Protodrilus sp. Harmothoe sp._
145 - 180
150 - 185
110 - 140 Phyllodocida
e g. sp.
110 - 140
150 - 180 Phyllodocida
e g. sp.
150 - 180 Absent
At stations 7 and 11, the share that V. zaikai contributed to the total abundance of larvae was highest (Table 1).
Remarkably interesting data were obtained from examination of samples collected during the Black Sea expedition (the R/V Knorr, April 1998) from the 25 m thin seawater layer in the locations with maximum depths of 400, 500
and 2200 m (Table 2). Two stations, M15R45 and
L30T28, were located in the close proximity to the southern coast of the Black Sea (fig.).
Meroplankton was collected through the entire seawater column by depths beginning from the 0-25-m layer and deeper. Not a single larva of V. zaikai had been found in three subsurface layers down to 85 - 110 m depth as well as in the samples taken at 13.00 at the deep-water station M30V45 from the final, 85 - 110-m deep, layer
As regards vertical distribution, V. zaikai occupied the depth with the upper boundary going at 85-110 m depth at the deep-water station M30V45; at two other, relatively shallow-water, stations it descended deeper (Table 2). The lower depth of the occurrence had not been determined because the samples of zooplankton were collected only down to hydrogen sulphide zone. It should be noted that the lower depth at which these polychaetes occurred depended upon the station; the difference was especially pronounced between the depth of 140 m at the open-sea station M30V45 and the depth of 180 m at two stations in the coastal zone of sea water. It is noteworthy that maximum density of the larvae of V. zaikai (119 ind.-3 was regularly measured in the oxycline overlying the hydrogen sulphide zone (Table 2). The obtained estimate is slightly greater than the early record of 113 ind.m3 , and has been the acknowledged maximum for V. zaikai in the Black Sea as yet.
Vertical distribution of the pelagic larvae of companion polychaete species was studied, too. Trochophores, metatrochophores and nectochaetes (fam. Phyllodocidae g. sp), all developmental stages of Harmothoe sp. (H aff. reticulata) and
nectochaetes Protodrilus sp. (fam. Protodrilidae) inhabited the seawater layer of 120 - 145 m. In greater depths (145 - 180 and 150 - 185 m) only the larvae of Phyllodocidae g.sp. no identified to species and Protodrilus sp. were found. M. I. Kisseleva  suggested that the larvae of Protodrilus sp. were a new species. From the typical P. flavocapitatus they differed in that their trunk was 2 - 3 times smaller as usual, the eyes were often absent, the adhesive organs unusually shaped, and eggs smaller and more numerous. Probably, this taxon should be given name in honour of M. I Kisseleva, but this hypothesis requires more detailed study. It is noteworthy that larvae of other polychaetes associated with V. zaikai were mostly solitary and rarely found. Presumably, the larvae of V. zaikai, Protodrilus sp. and Phyllodocidae g. sp., are the polychaetes which have evolved the tolerance for the oxygen-deficient environment.
During the 45th expedition of the R/V
Professor Vodyanitsky, along with Protodrilus sp. different developmental stages and adults of the benthic form of V. zaikai were found in the narrow depth range (117 - 151 m) in the northwestern Black Sea (. These findings have confirmed the early hypothesis about the occurrence of adult V. zaikai in the interface layer (120 - 150 m) between the aerobic oxic and the anaerobic anoxic (hydrogen sulphide) zones along the continental slope . Maximum density (9140 ind.m-2) of the adults of V. zaikai was registered at the depth of 139 m. It is noteworthy that the polychaetes inhabited the 1 - 2-cm thick uppermost layer above grey silty mud .
Early, a hypothesis was advanced about a benthic transition belt going along the Black Sea and populated by the polychaetes V. zaikai and Protodrilus sp. However, only one location has been detected in the Black Sea as yet that is, probably, because in taking samples for the investigation special box-corer and multicorer were used .
Discussion. The trochophores and nectochaetes of V. zaikai occur in the depths from
50 - 75 to 200 -250 m  under the temperature of 6.3 - 9.0 °C, the salinity of 18.2 - 21.1%o, in the presence of hydrogen sulphide and low DOC (0.18 - 0.25 and 0.05 - 0.06 ml/l, respectively). Maximum density of the larvae (113 ind.m-3) was measured in the sample taken with a water bottle from the 111 - 96-m layer (st. 4632, the maximum depth of 2062 m) during the expedition of the R/V "Mikhail Lomonosov" in 1985. The proportion between the trochophores at junior developmental stages and the nectochaetes at senior stages was 38 : 75.
Experiments were conducted to learn more about the survival rate, nutrition and oxygen consumption rate in V. zaikai kept under oxygen deficiency and in the presence of hydrogen sulphide [9, 10, 11]. Results of the investigation point out that ubder those conditions V. zaikai can survive for a longer time than other zooplankton, e.g. Copepoda (adults of Oithona nana, juvenile stages of Pseudocalanus elongatus and Calanus euxinus). Larvae of V. zaikai exhibited highest resistance to the adverse environment, staying alive for 5 hours under the concentration of hydrogen sulphide greater than 1.6 ml/l and DOC lesser than 0.3 ml/l.
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2. Kiseleva M. I. The distribution of polychaete larvae in plankton of the Black Sea // Proc. Sevastopol Biol. Station. 1959. - 12: 160 - 167 (in Russian).
3. Kiseleva M. I. A new genus and species of the family Chrysopetalidae (Polychaeta) from the Black Sea // Zool. J. - 1992. - 71, no 11. - P. 128 -132 (in Russian).
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Морський екологічний журнал, № 2, Т. V. 2006
Two opposite opinions have been offered to explain why some mesozooplankton organisms concentrate in the redox zone: Sorokin  suggested that this is owing to the feeding selectivity of the mesozooplankton feeding on thiobacteria, while Vinogradov and Flint  rejected the very possibility that the mesozooplankton might consume the production of thiohaemosynthesis.
The findings of numerous dense populations of mesozooplankton, including copepods and the larvae of polychaetes, in the redox zone have allowed to hypothesise about a "false bottom" situated at a local oxycline in the depth of oxic zone , i.e. in the lower depth limiting the vertical distribution of the dominant mesozooplankton organisms. For example, copepods can migrate through seawater column, ascending from the depth to the layers more enriched with dissolved oxygen [14, 15]. Unlike copepods, the larvae of V. zaikai rare have been found in the subsurface overlying the 50 - 75 m depth, their dense populations are the major component of bathypelagic fauna in redox zone of the Black Sea.
Zool. J. - 1998. - 77, no 5. - P. 533 - 539 (in Russian).
6. Murina V. V. On finding the pelagic polychaete larvae in the Black Sea // Zool. J. - 1986. - 65, no 10. - 1575 - 1580 (in Russian).