Features of the Microscale Distribution of the ...

Осеапоюяу, Vol. 42, No. 1. 2002. рр. 83-90. Tnl/lslatedjl"Om Okeallolog;ya, Vol. 42, No. 1, 2002.1'1'.91-97. Or;g;lIa{ RlIss;an Text Cnl'yr;gl1l © 2002 Ьу Vaesllcl1Clka. Engl;sll Гтпзйиюп COl'yr;gl1l © 2002 Ьу МAlК "Nallka IImerper;od;ca" (RlIss;a).

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MARINE BIOLOGY

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Features of the Microscale Distribution of the Gelationous Macroplankton in the Black Sea off Gelendzhik (August 2000) А. L. Vereshchaka Shiгs/юv lnstitute o/Oceanology,

Russian Academy о/ Sciences, Мозсом; Russia

Received October 4, 2000

AbstractThe results of underwater observations performed Ьу the author in Ihe first half of August 2000 аге presenled. The dives were carried out пеаг Golubaya Вау а! depths оГ 0---20 m and during а cruise оп board RIV Kvant within the 0- (о 20-т lауег оуег sea depths of 20-120 m in Golubaya Вау. Two medusa species (Aurelia aurita and Rhizostoma pulmo) and the ctenophore Mnemiopsis leidyi were dominant. Changes in the size structure of the near-shore populations омег the period of the studies were followed, and the microzonality in the horizontal distribution оГ the gelationous macroplankton was described. Daily vertical migrations of the ctenophore М. leidyi and medusa Rh. pulmo were discovered. The possibIe adaptive significance ofthese migrations is discussed.

The visual observations showed that, пеаг the boundary of the hydrogen sulfide zone, the planktonic community, which also iпсludеs gelationous animals, тау Ье stгuсturеd [5]. Оп the shelf, пеаг the water sur[асе, the gгаdiепts of physical parameters (for example, level of solar гаdiаtiоп) are по less sharp; they сап easily affect the апimаl distribution and cause stгuсturiпg of their рорulаtiопs. Strong wiпds, sea waves, sharp temperature changes-these апd other factors undoubtedly distort the distribution of the gelationous plankton пеаг the sea вцпасе. If their influence is of а minimum, the features of the distribution арреаг to Ье тоге clearly mапifеstеd and сап easily Ье traced. Therefore, the впкйеэ should Ье performed duriпg the sеаsоп whеп the abiotic conditions in the coastal zone аге most stabIe. In the summer, iп the presence of а steady-state anticyclone, the weather conditions remain relatively constant оуег тапу days; at this time, the observations of the distribution of the gelationous animals апd the daily dупаmics тау Ье most еffiсiепt. The objective of this study was to examine the теаtures of the distribution of the gelationous animal рорulations оп the shelf duriпg а steady-state апtiсусlопе. If the рорulаtiопs аге actually structured, it is necessary to stlldy the gепегаlitiеs of their microdistriblltion and disct1sS the mechanisms providing [ог the mаiпtепапсе of the population structure.

INTRODUCТION The gelatinous plankton of the BJack Sea is qualitatively роог and incJudes two species of scyphomedusas and three species of ctenophores. They аге the medusas Aurelia аита and Rl7isostoma риипо and the степоphores Pleurobrachia pileus, Mnemiopsis leidyi, and Beroe ovata. Though the species number is small, the role of the geJationous animals in the Black Sea ecosystem is extremely great. This is supported Ьу the sharp changes that occurred at the end of the 1980s and wеге related to the invasion of the ctenophore М. leidyi [2, 4, 8, 19] and those of 1999 related to the appearance of another invader, В. ovata [1, 6, 9, 11 13,20,21]. Vat'ious aspects of these changes have repeatedly Ьееп discussed in pubIications [3,7,12,16,17,23]. Although great interest has Ьееп focused оп the Black Sea medusas and ctenophores оуег the past few years, the studies performed were mostly concerned either with theiг physiological сhагасtегistiсs 01' with their meso- and macroscale distribution over the sea агеа. Detailed examinations of the vertical distribution performed with the help of manned submersibIes and ТУ cameras were mainly confined to the ореп sea regions and referred to only two species-the medusa А. aurita and the сtепорhоге Р. pileus [5, 10]. It is well known that the life cycle of medusas includes а bottom stage. The typical habitats of the most abundant ctenophore species М. leidyi аге геlаtеd to the coastaJ waters (mainly in estuaries and bays) of the eastern coast of America [22]. In the coastal wаtегs of the Black Sea, this ctenophore forms enormous accumulations Ьу the end of the summer-beginning of the fall. Nеvегthеlеss, the features of the vertical distribution of the gelationous animals оп the Black Sea shelf and, in рагtiсulаг, of its miсгоdistriЬutiоп геmаiп poorly studied.

MATERIALS AND METHODS The observations wеге регfогmеd from August 4 to August 15, 2000. During this period, а steady-state апtiсусlопе геmаiпеd in the Gеlепdzhik region. Throughout the епtiге оЬsегvаtiоп period, пеithег strong winds апd waves пог sharp temperature сhапgеs occurred. Minor air motions were related only to the 83

84

VERESHCHAKA

daytime and nighttime breezes. The surface layer temperature changed slightly from 25 С at the beginning of the observations to 22 С at their end. АЬоуе the 20-т depth, а water layer virtual1y homogeneous with respect to temperature and по vertical temperature gradients were observed. 0

0

The studies of the microscale distribution of the gelationous animals over the water column were регformed visual1y. The author dove with а mask and flippers down to а depth of 20 т at three test sites: (1) off the саре protecting Сошоауа Вау in the northwest, (2) off the First Сапуоп (approximately 1.5 km northwest of Golubaya Вау), and (3) off the Second Сапу оп (approximately 2 km northwest of Golubaya Вау). Counts of the animals in the water column were регтоппеё with respect to а frame formed Ьу the stretched arms of the diver (40 х 50 сгп, 0.2 т2 in агеа). Only animals larger than 1 СП1 long were taken into account. In

the layers of high concentration, reliabIe animal сошпз were impossibIe and their concentration was estimated from the теап distance between individuals. This approach was also applied for evaluating the сопсепггапоп of large medusas R. ршто, since the distance between individuals was rather gгеаt (4-6 т). The lауегs of elevated сопсепггапопз of the gelationous animals ог, vice versa, the layers depleted in them, were clearly visibIe. The poor layers were characterized Ьу ctenophore concentrations less than I ind./m3• In this case, the depths of its цррег and lower boundaries were registered and the animal concentrations wеге determined both inside and olltside the layers. Periodically, the diver сагпе out of the watel" to record in detail the results оэгашес. The animals were measured with the help of а ruler: for ctenophores and гпесцваз R. pulmo, the body length along the principal axis of the body was idel1tified,

ТаЫе 1. Total апюцгп of visual observations that formed the basis of this study Date

Типе interval ot' the observations

Location

Duration of the under water visual observations, ппп

NшnЬег оГ dives [ог animal counting in the water column

August 4

19:30-21 :30

First Сапуоп

90

10

August 5

10:00-12:00

First Сапуоп

95

10

"

18:30-20:30

Саре

90

10

"

21 :00-23:00

Саре

75

10

] 1:30-13:30

First Сапуоп

] 10

10

22:30-24:00

Саре

70

5

09:00-] 1:30

First Сапуоп

130

10

17:30-20:30

Саре

120

10

August 8

18:30-20:30

Саре

95

10

August 9

August 6 п

August 7 "

]0:30-12:30

Саре

90

]0

"

15:00-20:00

First Сапуоп

80

10

"

20:30-21 :00

Pier

30

5

"

22:30-24:00

Саре

65

5

17:00-19:00

Саре

95

10

19:30-20:00

Pier

30

5

30

5

August ]0 "

]0:30-11:00

R/V Куат, station 1

"

] 1:30-12:00

R/V Куат, station 2

30

5

"

]3:30-]4:00

R/V Куат, station 3

30

5

]0:30-13:30

Second Сапуоп

150

10

19:30-20:00

Pier

30

5

August 13

16:30-20:00

Second Сапуоп

140

10

August ]5

00:00-02:00

Саре

50

5

"

00:03-05:00

Саре

50

5

"

00:06-08:00

Саре

50

5

August 11

August ]2 "

Total

30 h 25 ппп OCEANOLOGY

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FEATURES OF ТНЕ MICROSCALE

while the medusas-aurelia were characterized Ьу the diameter of their umbrella. Well-known relations [18] were used in order to estimate the approximately Ыогпass of the gelatiol1ous animals. Since the vertical distriblltion changed with respect to the time of the day, the observations were schedllled to сомег аll periods of the day. In the daIk time of the day, the water column was iIIuтiпаtеd Ьу ап underwater flashlight. Оп the whole, the visual оовегмапопв lasted about 30 h; 185 animal counts in the water column were репоппеё during this time (ТаЫе 1).

DISTRIВUTION

85

Proportion of the population, % 100

40 20

L = 2-3 сгп

RESULTS ЛNО DISCUSSION O~--------~----------~--------~

Dнriпg the period of the observations, гпгее species of the gelationous animals were most аЬuпdапt in the coastal wateIS: the medusas А. аипла and R. риlто апd the сtепорhоге М. leidyi. The deep-water сtепорhоге Р pileus was епсоuпtегеd only опсе (two iпdividllаls), while the new invader В. ovata was completely absent iп the coastal wateIs during the period of the studies. Age structure of the populations of gelationous animals. Duгiпg the observation period, significant changes occurred in the age structure of the population of gelationous апimаls. The beginning of the observations (August 4) coincided with the period of mass dеvеlорmепt of the ctenophore М. leidyi. In the middle of July, only а few сtепорhоге iпdividuаls were епсоцпtered, while Ьу the end of JlIly-Ьеgiппiпg of August, а significant number of them appeared in the near-shore waters, as reported Ьу P.Yu. Sorokil1 (Southem Вгапсп, Shirshov Iпstitutе of Oceanology, RlIssiап Academy of Sciences) in а personal согппшгпсапоп. Figure 1 shows the percentages of four size groups of сtепорhогеs. Опе сап see that, at the уегу Ьеgiппiпg of the observations, the bulk of the ctenophores was represented Ьу individuals smaller than 3 сm in lепgth. However, the aging of the iпdividuаls of the near-shore рорulаtiоп proceeds extremely rapidly: in а теге three days, the portion of the ctenophores 2--4 сm long decreased more than twofold апd iпdividuаls with а body lепgth of 4-6 апd 6-8 ст began to dominate. The changes in the size structure of the рорulаtiоп of the medusa R. pulmo were по less sigпifiсапt (Fig. 2). Рог five days (from Augllst 4 to August 8), the major of the population consisted of individuals 25-30 ст lопg; young medusas with а 5-ст body lепgth were гаге and their рroроrtiоп did пот exceed 5-10%. Subsequently, а уегу sharp growth was observed: after four days the proportion of small iпdividuals iпсгеаsеd lIР to 30--40% апd up to 80-90% Ьу August 13-14. No visibIe trends iп the changes of the structure of the populations of the medusa А. aurita were recognized. It is interesting that changes in the size structure of the former two species (М. leidyi апd R. pulmo) occurred against the background of rather small сhапgеs in their abundance. This allows опе to suppose OCEANOLOGY

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4.08

5.08

6.08

Date

Fig. 1. Changes in the size впцсшге of the ctenophore Мпе-

miopsis /eidyi in the regiol1 of Golubaya Вау, August 4-7, 2000. Опе hUl1dred ctenophores were observed daily.

Proportion of the youths, % 100 80 60 40 20 Aug. 5 Aug. 7 Aug. 9. Aug. 11 Aug.13 Date Fig. 2. Changes [п the proportion of the youths (%) in the total аоцпёапсе of the population of the medusa Rl1izosюта рu/mо. Fifty medusas were observed daily.

that the сhапgеs in the size structure аге related to the iпtеmаl changes within а siпglе пеаг-shоге population rather than го the water ехсhапgе supplying other рорulations to the Golubaya Вау агеа. Horizontal distribution of gelationous animals. The data оп the abundance of gelationous animals рег 1 т2 of the surface (for the water соиппп from О to 20 т) аге presented iп ТаЫе 2. Опе сап see that the ctenophore аЬuпdапсе геmаiпеd almost сопstапt омег almost the entire оЬsегvаtiоп period ranging from 150 to 300 iпd./т2. At the end of the period, from August I I to August 15, its аЬuпdапсе sharply increased up to 450-700 ind./m2 suggesting the start of ап intensive population growth. Оуег the епtiге period of observations, the аЬuпdance of the medusa R. pulmo was almost constant, Ьеiпg approximately 1 ind.l25 т2 (mеап horizontal distапсе Ьеtwееп individuals of about 5 т) with оссаsional тiпог highs апd lows. The аыldапсеe of the

86

VERESHCHAКA

ТаЫе 2. Abundance of gelationous animals (1 ст long and larger) in the water column (теап value and standard deviation, ind./m2) in the region of Golubaya Вау. The values of the аоцпёапсе of Мпепиорыз leidyi and Аuгеliа аипю were obtained from vertical сошпз, while that of Rl1izostoma pulmo was estimated from the теап distance between individuals Date

Location

Мпепиорыз leidyi

Rhizostoma pulmo

Аuгеliа аипю

Number of counts in the water соиппп

August 4

First Сапуоп

250 ± 25

0.04

1.0 ± 0.7

10

August 5

First Сапуоп

287 ± 25

0.04

7.4±2.1

10

Саре

231 ± 35

0.04

2.4 ± 0.5

20

First Сапуоп

259 ± 41

0.04

0.4 ± 0.5

10

Саре

177±19

0.04

0.2 ± 0.4

5

Саре

176 ±21

0.03

0.5 ± 0.5

10 10

"

August 6 " August 7

Саре

178 ± 27

0.03

0.2 ± 0.4

August 8

Саре

276 ± 19

0.04

7.0± 1.6

10

August 9

Саре

284 ± 18

0.07

5.4 ± 1.1

10

"

First Сапуоп

241 ± 22

0.04

5.2 ± 1.1

10

н

Саре

263 ± 25

0.04

'.О±О.7

5

August 10

Саре

277 ± 20

0.04

1.6 ± 0.5

10

August 11

АЬеаm Golubaya

425 ± 39

-

-

15

August 12

Second Сапуоп

479 ± 32

0.02

0.6 ± 0.5

10

August 13

Second Сапуоп

624 ± 152

1.0

10.8 ± 9.2

10

"

Вау

other medusaA. aurita was extremely unstabIe and уагied from О to 20 ind./m2• No reliabIe changes in the abundance and size of the gelationous animals were observed while moving along the coast in the 2-km ппегуа] studied. Оп the contrary, while moving away from the shore, the abundance of

аll the species changed regularly. This allows опе to describe the Ьопаопга! пнсгозопапоп in the gelationous animal distribution in the near-shore агеа (Fig. 3). Duril1g the light time of the day, оуег sea depths of 1О т and smal1er, гаге gelationous animals were irregularly encountered. Оуег sea depths of 10-15 гп, cteno-

Abundance column

in the water

600 Мпепнорви

/eidyi Rllizostota pulmo Аиге 5 Depth, т О Fig. 3. Changes [п the abundance of gelationous animals in the water column with increase in the sea depth. The спагасгепвпс abunёапсе values for various sizes аге ргезегпео in il1d./IТ12(Mllemiopsis leidyi), il1d./l 00 т2 (Aul'elia аипла), and ind./l 0000 т2 (RI,izostoma

pulmo).

OCEANOLOGY

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FEATURES OF ТНЕ MICROSCALE

phores and the medusas А. aurita appeared, their аЬипdance was commonly 150-400 and 0-5 ind./m2, respectively. Over sea depths of ] 5-20 m, the аЬипdance of both species increased (ир to 200-700 and 1-20 ind./m2, respectively) and very large mature medusas R. pulmo appeared. Опе сап obtain only а rough estimate ofthe biomass of the ctenophores and medusas. Taking into account the well-known relations [18], the weight of the dominating 5- to 6-ст long ctenophores тау Ье evaluated at 22-33 g, while the estimate of the mnemiopsis biomass (without regard for the larvae) is 4-23 kg/m2• The Ыоmass of the aurelia is estimated at 4-50 g/m2 (only опе observation gives а value of 200 g/m2); their characteristic diameter was 5-7 сгп and the гпеап weight equaled 4-1 О g. Оп average, both the abundance and the Ьюгпass of the aurelia аге somewhat lower than the values commonly observed оуег тоге deep-water shelf areas off Gelendzhik [15]. As the cruise of R/V Kvant showed, significant near-shore accumulations of medusas were observed оп1у at sea depths of about 40 т. The medusa abundance decreased both toward the coast and away from it. The abundance of R. pulтo was small (about 0.04 ind./m2); however, being 1-2 kg in weight, they provided а biomass of 40-80 g/m2• lп the areas with sea depths of 20-40 m, which the author episodiсаllу visited at divings and where the observations [гогп R/V Kvant were performed, the abundance of R. pulmo was approximately the same. lt is characteristic that а zопе of R. pulmo with relatively сопstапt values of abundance and biomass was observed in аll the regions омег the entire period of the studies, in spite of the репodically arising coastal currents (Гог example, оп August 6 and August 8). Thus, оуег sea depths of 10-15 m, ctenophoresmnemiopsis dominate. Оуег sea depths of 15-20 т, the role of R. pulmo increases; in biomass, they exceed the aurelia but rank significantly below the mnemiopsis. It is evident that, before the observations started, whеп тпетiорsis still featured а low abundance, а large R. pulтo might dominate in the coastal waters. Judging from the observations from R/V Kvant, the belt of R. pulmo extends to а sea depth of about 40 т. The preliminary data of the cruise suggest that, at these depths, the belt of R. pulmo is replaced Ьу а belt of aurelia. Further, оуег depths of about 100 m, the ctenophores-mnemiopsis again арреаг to Ье the siпglе dominating species. During the dark time ofthe day, the horizontal zones were shifted toward the shore. The gelationous animals were епсоuпtегеd оуег depths of 5-1 О m, while the zопе of R. pulтo started оуег depths of 10-15 т. As а case history, we present the сhапgеs iп the аЬuпdапсе of the ctenophores-mnemiopsis in the region of the Second Сапу оп (Fig. 4). Опе сап note ап increase in the ctenophore abundance оуег sea depths of 15-20 т as well; presumabIy, this results fгom the shift of the seaward part of the рориlайоп characterized Ьу higher OCEANOLOGY

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DISTRIBUTION

87

Abundance in the water column 800 600 400

Depth, m

15

Fig. 4. Dynamics of the vertical distributiol1 of the сгепоphore Mnemiopsis leidyi [п the evel1il1goffthe Secol1d Сапyon 011August 12, 2000: from 17:30 (о 18:00 (oblique hatchil1g) апё [гот 19:00 to 19:30 (vertical hatchil1g). Ногizol1tal axis--depth [п т, vertical axis-ctel1ophore аоцпёапсе рег I т2.

О

Time of the day 3:00 6:00 9:0012:0015:0018:0021:0024:00

4:00 8:00 12:00 16:00

Mneтiopsis leidyi

20:00 Depth, m Fig. 5. Daily оупапнсв of the vertical distributiol1 of the сгепорпоге Mnemiopsis leidyi пеаг the shore (the data 011all the sites studied are gel1eralized). The layers of accumulaпоп (with ап аоцпоапсе greater thal1 1 il1d.lm3) аге hatched.

ctenophore concentrations рег unit агеа. Due to this shift, during the dark time of the day, опе observes а significant growth in the ctenophore-mnemiopsis сопcentration in Golubaya Вау (dominating sea depths of 8-1 О т), in particular, пеаг the end of the pier (sea depth of 7 т), where long-term observations оуег the Black Sea plankton аге being performed (М.Е. Vinogradov, Е.А. Shushkina, personal communication). Vertical zonation in the distribution of gelationous animals. No reliabIe distinctions in the distribution and size composition of the ctenophores-mnemiopsis were observed оуег the microsites studied. lt сап Ье accepted that, within the 4-km interval of the shore zone where the observations were performed, we dealt with опе and the same population ofthis species. Let us assess the mnemiopsis distribution and its daily dynamics combining the data оп the sites off the саре (70% of

88

VERESHCHAКA Proportion of the population, % 60

times (for example, off the саре Ггогп 19:00 to 20:00 оп August 5) it was as great as 8000 ind./m3 in the 0- to 0.5-т [ауег. ln the deeper waters, the abundance of the ctenophores was low (about 5-1 О iпd./тЗ).

40

Later, at approximately 23:00, the ctenophores distгiЬutеd evenly оуег the wateI" сошгпп, though in the иррег 1- to 2-тlауег, it was 20-30% gгеаtег thап [п the underlying layers. The second upwellil1g ofthe populaпоп tоwагd the иррег water [ауегз was observed а! 4:00-5:00. Ву 7:00-8:00, the сtепорhогеs-тпетiорsis again spread оуег the water column, gradually leaving the иррег 2-т layer as пооп approached.

20

2-3

3--4 4-5

5-6

6-7

7-8 8-9 Depth, m

Fig. 6. Yertical distribution of the population of the medusa Rllizos/oma рийпо. Observations off the First Canyon at а sea depth of 20 т, August 6, 2000, 12;30-13;00. FiГtу medusas were observed in all.

Time of the day О 3:00 6:00 9:00 12:0015:0018:0021 :0024:00

The гесоgпitiоп of the dYl1amics of the medusaaurelia distributiol1 was тоге difficu!t since their distгibution featured strong patchiness. 011 the whole, the aurelia also avoided the цррег 2-т layer il1 the light time of the day and surfaced at night. The vertical disггйишоп of аигеliа during the dагk time гегпагпв Ul1kПОWI1siпсе they were barely visibIe in the light of the flashlight. The dynamics

of the distribution

of the medusas

R. ршто was quite simi!ar to that of the степорпогевтпетiорsis. At пооп, the major part of the роршапоп is сопйпеё to the depth ппегуа! 4-5 т (Fig. 6), gгаdually азсегпйпя to the 0- to l-m layer, where they сап Ье observed iп the еvеl1iпg (Fig. 7). R. pulmo врепг the пight at depths of 2-5 m; по тоrniпg аsсепdiпg of the рорulаtiоп was поtеd. Throughout the day, R. рийпо сопstапtlу moved at а velocity of аоош 6 cm/s (adult iпdividuа!s); presumabIy, the direction of their motion-upward, dowl1ward, ог lateral-is chosen at гапdот.

8:00 12:00

Rhizosfoma pulmo

16:00 20:00'----------------------' Depth, m

Опе сап recognize two periods when the сгепоphores аге rather evenly distributed оуег the water colитп and two periods of the population upwelling to the surface. During the light time of the day, especially in the afternoon, the gelationous animals avoid visiting the upper 2-т layer. The abundance of the степоphores-mnemiopsis in this layer did not exceed 1 ind./m3, while the peak of the concentration appeared at а depth of about I О т (10 ind./m3 and greater) and extended down to the bottom. РгоЬаЫу, due to this геаson, virtually по ctenophores were observed at sea depths less than 10 т.

Thus, small-amplitude but clearly тапifеstеd daily vertical тigгаtiопs of the сtепорhогеs М. leidyi апё medusas R. рийпо actually exist. What тау Ье the геаSOI1 for this kind of migratiol1s? The life cyclil1g of medusas is re!ated (о the coastal waters. Previous to il1vadil1g пио the Black Sea, the сtепорhоге М. lei(/yi iпhаЫtеd the coastal waters (mostly in bays апd estuaries) of the еавгегп coast of America. Thus, it is also ап iпtгiпsiсаllу пеаг-shоге species though аЫе to form significant ассuтulаtiопs iп the ореп рап of the Black Sea. Iп addition, [п the coastal waters, the ргапкюп Ыоmass is greater апо the роршапопв of the gеlаtiопоus animals gain additional advantages being аЫе to dwell пеаг the shores. The adaptive character of the migrations of the gelatiol1olls агпгпагз il1 the coastal zone is also expressed in the fact that, due to the vertica! migrations, а great part of the population keeps itself within the principal biotope; i.e., it is permanently located пеаг the shore. What is the possibIe mechanism of this ргоcess?

This kind of distribution pattern was kept throughout the day approximately ир to 19:00. Then, оуег 1-1.5 h, the vertical structure of the ctenophore рориlation changed sharply. The major part of the population moved to the thin 1- to 2-т surface layer, where the апiта! abundance reached 600-1000 iпd./тЗ; some-

During the night breeze, the ascending gelationolls animals тау тоуе toward the shore with the surface water layer. This process is тапifеstеd in the sharp growth of their abllndance in Golubaya Вау and in the decrease in the sea depths оуег which the ctenophores and medusas аге encountered. At this time, the envirol1-

Fig. 7. Daily dynamics of the vertical distribution of tlle medusa R/,izos/oma рийпо in the near-shore агеа (the data оп all the sites studied аге generalized). The layers of ассцmulation аге hatched.

the data) and the First (20%) canyons (Fig. 5).

and the Second

(10%)

OCEANOLOGY

Yol. 42

No. 1

2002

FEATURES ОР ТНЕ MICROSCALE

mental conditions аге уегу favorable for the feeding of gelationous animals. ТЬе fodder plankton abundance il1 the иррег water layers is уегу high. А sample collected Ьу the author in the daytime пеаг Golubaya Вау featured шсгеоЫе concentrations of ап important fodder object--