The georgian Black sea shelf’s macrozoobenthos and its ecological state

UDC 574.587

E. Mikashavidze

State Environmental Agency, Black SeaMonitoringCenter,
Water Ecology and Fisheries Laboratory, Batumi, Georgia, eteri-mikashavidze@rambler.ru

МАКРОЗООБЕНТОС ЧЕРНОМОРСКОГО ШЕЛЬФА ГРУЗИИ
И ЕГО ЭКОЛОГИЧЕСКОЕ СОСТОЯНИЕ

Е. Микашавидзе

Государственное управление экологии, Центр мониторинга Черного моря
Лаборатория водной экологии и рыболовства, Батуми, Грузия, eteri-mikashavidze@rambler.ru

Ecological state of our planet is not the identical. This one has survive dramatic changes during the last decades causing by growing anthropogenic factors on the level of big and small ecosystems. These changes have been revealed on each component including macrozoobenthos species. Integral analyze of benthic organisms’ rentable using gives the chance to expose the ,,hot” spot originated by human impact. This helps to determine environmental ecological index and makes real prognoses for the correction. Determination of shelf’s hydrofauna including identification of specific composition, also recognition their place and role in biocenoses structure, basic studying the ecological conditions give an opportunity to get deep into biological knowledge and thus make recommendations for obstacle unwilling changes.

Therefore, it was studied the macrozoobenthos biodiversity of Georgia’s shelf in 1978–2008. According to research the shelf is presented by following basic sediments: sand, silty sand, shelly silt, silt. Average annual shelf’s bottom hydrochemical data is following: maximal temperature –23°C on 5–10 m isobath in summer and minimal – 8–8,7°С on 100–150 m isobath in winter. maximal salinity on the depth 150 m was 18 %0 and the minimal 13,9 %0 was in bottom layers of rivers Chorokhi and Kodori. Quantity of soluble oxygen and carbon dioxide is in proportion with productivity of trophyc chain. According to hydrochemical analysis of oxygen diluted index was revealed 64–81 % in bottom waters of Ochamchire and Gudauta. This data appoints to down level of turbulence and marks out the number of attached macrofauna. There is noted the sharp seasonal difference between regions. Due to researches It may be conclude that shelf’s hydrochemical regime makes good conditions for hydrobionts for growth, reproduction and diversity.

On Georgia’s shelf (Sarfi – Gudauta) due to long term monitoring macrozoobenthos specific systematic structure composes 2 kingdoms, 12 types, 16 classes, 42 orders, 93 familia and 185 species. Among them from the type of Tubemakers dominate Polychaeta including Errantia and Sedentaria forms. From Sedentaria Polychaeta subclass it were observed 28 species and Errantia Polychaeta – 33 ones. Mollusks were presented by two classes: Gastropoda – 23 species and Bivalvia – 30 species. The shelf of Georgia is offered by Arthropoda especially Branchiata counting 50 benthic species, where decapoda dominates (20 species). The benthic biodiversity of Georgia’s shelf is caused by ,,Mediterranization” process.

In annotate list of benthic fauna there is notable development of bottom fauna, showing the domination of Polychaeta (61 species). This is 33 % of whole zoobenthic species. Due to specific diversity, mollusks are on the second level (53 species) – 29 %, Gastropoda – 13 % (23 species) and Bivalvia – 16 % (30 species). Crustaceans compose 27 % with 50 species dominating Decapoda and Amphipoda (16–20 species). Among Polychaeta there was registered Errantia and Sedentaria species. From Errantia 29 species were revealed and from Sedentaria – 32 species. Mollusks were presented by Gastropoda – 23 species and Bivalvia – 30 species. Crustaceans exist of Decapoda with 20 species.

Living organisms are compactly related to each other and make biotic communities – biocenoses. According to previous years data (Kiseliova, 1981; Kiseliova et al., 1963, 1966) the Georgian shelf is presented by following biocenoses: 1) Chamelea gallina; 2) Pitar rudis +Nephthys cirrosa; 3) Callianassa truncate+ Nephthys cirrosa; 4) Amphiura stepanovi+Terebellides stroemi+Modiolus phaseolinus.

On the base of Georgia’s shelf soil and inhabiting macrozoobenthos species there is divided two main ecological groups: stenoedaphic and everyedaphic. To stenoedaphic species belong lytophiles, fsamophiles and helophiles.

In benthic diversity the main thing for ecological grouping is sediments’ form, well observed during ecological groups’ determination on Georgia’s shelf. Fsamophiles dominate with 66 species, and lytophiles have small number – 26 species. In coastal ecosystem macrozoobenthos represents the chain of substance and energy biotic rotation. Spatial sustainability and comparison long term live of macrozoobenthos organisms and their communities make them as an object for studying of sea changes. This will help us to determine Biological quality index – BQI .Thus we evaluated the Georgian shelf’s ecological state (Wilson et al., 1985). The research region’s stable zone composes 93,75 % of the whole area, opportunistic one – 6,25 %, but there wasn’t revealed abiotic zone. Due to data base, BQI equals to 8,66, which appoints to freshness of research region. BQI makes a control on pollution of bottom precipitations, also macrozoobenthos specific composition, quantity, biomass and specific number change’s dynamic as well.

Macrozoobenthos specific diversity studying is notable appointed to industrial fish food stock determination, especially for Sturgeon nourishment (Mikashavidze et al., 1981, 1990, 1998). We used materials collected in Anaklia bottom waters– contents (stomach and guts) of about 110 Sturgeon (1978–1980) and seasonal samples collected in benthal of Sufsa-Ochamchire bottom waters. Nowadays The Black sea shelf’s zone is strongly stressed by anthropogenic impact. Also irrational fishing is cleared provoked sharp decreasing of Sturgeon stock.

From macrozoobenthos species observed in research region, by food value the benthic fauna was distinguished 17 species (table 1), among them were following taxons: Polychaeta (Terebellides stroemi Sars, 1861; Nephthys cirrosa Ehlers, 1868; Heteromastus filiformis (Claparede,1864); Glycera capitata Oersted,1843; Melinna palmata Grube,1869); Crustacea (Callianassa truncata Giard et Bonnier 1890; Brachynotus sexdentatus Risso, 1827; Diogenes pugilator (Roux,1828); Paramysis agigensis Bacescu, 1940); Mollusks (Tritia reticulata (Linne,1758); Chamelea gallina (Linne, 1758); Mytilus galloprovincialis Lam., 1819; Pitar rudis (Poli, 1791); Plagiocardium simile (Milachevitch, 1909); Donacilla cornea (Poli, 1791); Polititapes aurea (Gmelin, 1790)); and Echinodermata (Amphiura stepanovi Djakonov, 1954).

During selection index calculation, we didn’t use 3 fish species (Trachurus trachurus (L.), Mullus barbatus ponticus Essip. and Engraulis encrassicholus ponticus Alex) being in Sturgeons’ digestive system. Selection index for invertabrates is the same. The high selection index was fixed in T. stroemi, from Crustaceans– C. truncata and from Mollusks – P. rudis and Ch. gallina. According to Sturgeons’ food stock the high density was revealed in Polychaeta 60 egz./m2 – 40 % of whole population. The next one is mollusk – 27 egz./m2 – 21,5 % of the whole number. Crustaceans were 14 egz./m2. The high density is characterized for mollusks – Ch. gallina made the same named biozenose.

Table 1. The macrozoobenthic role in nourishment of Sturgeon on the Georgian Black sea shelf

Benthicfauna

Quantity, egz./m2

Biomass g/m2

Food spectr, %

Food inten­sivity, %

Selection index

numb

mass

numb

mass

Polychaeta

Terebellides stroemi

12

2,0

20,00

4,37

0,44

2,1

1,6

Nephthys cirrosa

25

4,82

2,52

4,37

0,44

0,2

0,6

Heteromastus filiformis

4

8,63

2,50

1,09

0,11

0,13

0,4

Glyceracapitata,

4

5,20

2,50

0,53

0,05

0,8

0,07

Melinna palmate

15

0,02

2,50

0,03

0,003

0,8

1,0

Total

60

20,7

30,02

10,39

1,04

4,03

3,67

Mollusks

Tritia reticulata

4

1,0

2,50

0,82

0,08

0,7

0,5

Chamelea gallina

12

10,7

12,48

22,43

2,24

1,3

1,5

Mytilus galloprovincialis

4

4,70

2,50

2,45

0,25

0,7

0,3

Pitar rudis

4

4,80

29,95

44,77

4,48

9,3

6,8

Plagiocardium simile

1

0,20

2,51

0,80

0,08

3,1

2,6

Donacilla cornea

1

0,02

2,50

0,05

0,005

3,1

1,6

Polititapesaurea

1

0,01

2,50

0,03

0,003

3,1

3,0

Total

27

21,59

54,94

71,35

7,14

21,3

16,3

Crustaceans

Callianassa truncata,

8

20,4

4,99

16,30

1,63

0,2

5,8

Brachynotus sexdentatus

1

0,08

2,50

0,27

0,03

3,1

2,7

Diogenes pugilator,

1

0,70

2,50

0,27

0,03

3,1

0,2

Paramysis agigensis

4

0,06

2,50

0,05

0,005

0,7

0,6

Total

14

21,2

12,49

16,89

1,69

7,1

9,3

            Amphiurastepanovi

24

9,6

2,56

1,37

0,14

2,8

5,4

Total

226

73

35,23

34,67

 

From Polychaeta preveal T. stroemi and N. cirrosa, and from Crustaceans the major part of macrozoobenthic diversity takes C. truncata (8 egz./m2), which is 57 % of the whole number. On the Georgian Black sea coastal region macrozoobenthic gives 4,8 thousand tones biomass in Sturgeons’ basic biotop a year. This is rather sufficient for nourish of Sturgeon distributing in that region. In selection index of Sturgeon dominate mollusks (21,3), with biomass – 16,3. Sturgeon eat the following species: T. stroemi, C. truncata, Ch. gallina and P. rudis. Hence, selection index for Sturgeon is determined not the quantity of some organisms, but an opportunity to obtain of benthos organisms for users.


Zoocenosis — 2009
Біорізноманіття та роль тварин в екосистемах: Матеріали V Міжнародної наукової конференції. – Дніпропетровськ: Ліра, 2009. – С. 71-73.

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