Yu N Tokarev - Influence of seamounts at the atlantic ocean on modification of the bioluminescence and plankton characteristics - страница 1

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МОРСЬКИЙ ЕКОЛОГІЧНИЙ ЖУРНАЛ

УДК 577.472(262.5):591.148:574.52

INFLUENCE OF SEAMOUNTS AT THE ATLANTIC OCEAN ON MODIFICATION OF THE BIOLUMINESCENCE AND PLANKTON CHARACTERISTICS

© Yu. N. Tokarev 1, E. P. Bityukov 1, R. Williams 2

1 Institute of Biology of the Southern Seas (IBSS), 335011, Sevastopol, Ukraine (e-mail: tokarev@ibss.iuf.net) 2 Centre for Coastal Marine Science, Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK

(e-mail: bw@mail.pml.ac.uk)

Поступила 13 февраля 2003 г.

The bioluminescence and plankton characteristics in the euphotic layer over 11 seamounts in the Atlantic Ocean were studied. Investigations were carried out along the axis of flow over the mounts. Bathyphotometric measurements (1606 casts) were taken from 2 m to 100 m depths at 87 stations over the various seamounts with a vertical resolution of 1 m. Plankton samples were taken with Juday nets and submersible electric pumps with 36 m3-•h-1 performance. The bioluminescence characteristics varied over seamounts with different geomorphological features. The hydrodynamic gyres, created by the bottom elevations, and the upwelling of water with biogenic elements, also seem to have effects on the quantitative characteristics of the plankton. The largest changes in the structure and intensity of the bioluminescence field were observed in the regions of large geomorphological formations. For example, over mountains at greater depth in the North Atlantic Ocean (Slozhnaya, Mayskaya, Hecate sea mounts) changes were observed between 5 and 16 km from their peaks, while in the regions of comparatively shallow bank, such as Valdivia, changes were seen up to distances of 100 km. The influence of sharppicks sea mounts (Meteor and Irving, Udachnaya bank) on the bioluminescence field and distribution of plankton was not so evident. For example, the effects of the Meteor and Irving mountains were observed only over their peaks, with the intensity of bioluminescence exceeding the background levels by 1.5 to 3 times. The same effect was observed over the Udachnaya bank that was being characterised by higher productivity. In the region of Valdivia bank, which has a depth similar to the Meteor and Irving sea mounts (about 250 m) the bioluminescence intensity, in the upper 100 m layer increased over 20 times if compared with the open ocean.

Key words: Atlantic Ocean, seamounts, bioluminescence, plankton

Исследованы распределения планктона и биолюминесценции в эвфотическом слое над 11 подводными возвышенностями Атлантического океана. Исследования проводились вдоль оси течения над возвышенностями. Батифотометрические измерения (1606 зондирований) проводились от 2 до 100 м глубины с вертикальным разрешением в 1 м на 87 станциях над различными поднятиями. Планктонные пробы отбирались с помощью сети Джеди и погружаемых электрических насосов производительностью 36 м3-ч-1. Характеристики биолюминесценции варьировали над поднятиями различной геоморфологии. Степень влияния порождаемых поднятиями дна гидродинамических вихрей, обусловливающих подъёмбогатых биогенными элементами глубинных вод, на количественные характеристики планктона оказалась также различной. Наибольшие изменения структуры и интенсивности поля биолюминесценции выявлены в районе крупных геоморфологических образований. Так, над более глубоководными возвышенностями (горы Сложная, Майская, Хекате) эти изменения зарегистрированы на расстояниях 5 - 16 км от их вершин, в то время как в районе сравнительно мелководной банки Вальдивия - до 100 км. Влияние островершинных поднятий (горы Метеор, Эрвинг, банка Удачная) на поле биолюминесценции и распределение планктона выражено существенно меньше. Так, воздействие гор Метеор и Эрвинг прослеживается только над самими вершинами поднятий, причём интенсивность биолюминесценции здесь не более чем в 1.5 - 3 раза превышала фоновые. Аналогичный эффект наблюдался в районе банки Удачная, отличавшейся высоким продукционным потенциалом. В то же время в районе банки Вальдивия, с аналогичными горам Метеор и Эрвинг глубинами (около 250 м), интенсивность биолюминесценции в слое 0 - 100 м увеличивалась в сравнении с фоновыми акваториями до 20 раз.

Ключевые слова: Атлантический океан, подводные возвышенности, биолюминесценция, планктон

Against a background of low level production in the oligotrophic waters of the Atlantic Ocean there are regions of enhanced production associated with submarine crests and seamounts [1]. The level of our knowledge on the hydrological and biological situations in these regions is still limited [13].

Seamounts disturb the flows passing over them and cause changes in the structure of the surrounding waters [10, 12]. In general a flow meeting a seamount causes upwelling of deep waters, which in turn causes biological enrichment of the surface layers. In particular, gyres created by sea mounts, named Proudman-Taylor piles, have been observed in the Pacific Ocean, where local water circulation were associated with their slopes. These circulations lead to an increase of primary production and general enhancement of the trophic chain [7, 9].

For this reason the Former Soviet Union carried out a series of complex studies of the pelagic communities over seamounts with different geomorphological features, geographical location and hydrological state in the Atlantic Ocean. The objectives were to examine the influence of these regions on the biological structure and production of the pelagic community [6].

Materials and Methods. The studies were conducted on board R/V "Professor Vodyanitsky" in January and August -September, 1982 to the southern and north­eastern regions of the Atlantic Ocean. Using a standard programme, we investigated 11 seamounts of different characters (Fig.^ and

Table 1).

Investigations of meso- and small-scale spatial structure of the bioluminescence field was one element of this complex programme [2, 4, 5, 14]. Bathyphotometric, temperature and salinity soundings were taken from a drifting ship every 3 minutes to a depth of 100 m along the transects at 1 m vertically and 30 to 60 m horizontally resolutions, depending on the speed of the drifting vessel [16]. Approximately 30 soundings were taken at each station along the transects. This allowed to determine the statistical characteristics of the bioluminescent field intensity, temperature and salinity on different scales of their distribution [15].

A special device was employed, which limited the astronomical component of luminescence and provided a constant level of mechanical stimulation of bioluminescents. Profiles were conducted with a speed of 1 m-sec-1.

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Measurements of bioluminescence of plankton organisms were carried out only at night and began 2 hours after sunset. This permitted to exclude the influence of daylight on the rhythm of light emission of plankton luminescents and their vertical migration. Together with bioluminescence measurements, temperature and salinity of the studied layer, speed of drift of the vessel, force and direction of wind have been considered.

The meso-scale structure of the bioluminescent field was determined by integration between stations. The transects with measurements of bioluminescence were situated every 18 to 22 km along the axis, passing over the summit. The number of stations analysed in each transect varied from 4 to 15 over the 11 seamounts (Table 1).

Zoo- and phytoplankton samples were taken by Juday net with 112 цгп mesh size in the 0-100 m and 0-150 m layers, as well as bacterioplankton and phytoplankton samples were taken by submersible electric pumps with 36 m3-h-1 performance in the upper 30 m layer (Table 2). Phytoplankton were sampled also with a rosette of 5-l water bottles, fixed 1 m higher than the bathyphotometer, from intense bioluminescence layers and standard horizons. The water samples were filtered with 0.45 цгп pore diameter filters, after which the numbers ofг

Influence of Seamounts at the Atlantic Ocean ...

Лорський екологічний журнал, № 1, Т. II. 2003

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testaceous dinophyte algae were counted. These dinoflagellates    are    the    most important bioluminescence component of marine phytoplankton [8].

Table. 2. Characteristics of plankton in separate layers over seamounts: in 0 - 100 m layer, * - in 0 - 30 m layer; ** - in 0 - 150 m layer

Табл. 2. Характеристики планктона в отдельных слоях над поднятиями: в слое 0 - 100 м, * - в слое 0 - 30 м; ** - в слое 0 - 150 м

Seamount

Bacterioplankton

Phytoplankton

Mesozooplankton

 

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Biomass

mg.m-3

Number thdsclm-3

Biomass

mg.m-3

Number

m-3

Biomass mgm-3

Hecate

2058*

201*

22.2

12.9

422**

25.2**

Dobraya, Slozhnaya,

1974*

177*

23.3

18.3

1706**

25.5**

Mayskaya

 

 

 

 

 

 

Irving

894

83

11.7

5.0

331**

9 6**

Meteor

713

71

15.6

10.7

251

12.5

Sierra-Leone

903

89

9.2

6.1

285**

16.6**

Udachnaya

668

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Yu N Tokarev - Influence of seamounts at the atlantic ocean on modification of the bioluminescence and plankton characteristics