Meroplankton Of Eastern Mediterranean And Western Black Sea
MEROPLANKTON OF EASTERN MEDITERRANEAN AND WESTERN BLACK SEA
G.-V.V. Murina
Institute of the Southern Seas, National Academy
of Sciences of Ukraine, Sevastopol
For the first time a study was carried out on the similarities and differences in the meroplankton in two interconnected basins - the Eastern Mediterranean and the Western Black Sea. The qualitative and quantitative distribution of the larval meroplankton were studied during the expedition on the R/V "Academic Kovalevskii", in autumn 1984.
In the Aegean Sea, 135 zooplankton samples were taken from 12 stations at depths ranging between 44 and 1075 m. The distance from the nearest coast varies from 7 to 101,4 sea miles. Maximal density of the pelagic larvae 3020ind/ m2 was received in the Thermaikos Bay.
In the Western Black Sea 52 samples from 9 stations were collected near the Bosporus and 60 samples from 11 stations were make in the coastal waters of Bulgaria. The distance from nearest coast varies from 17 to 45 sea miles. The maximal number of the pelagic larvae 48 460 ind/m2 were received near Bulgarian coast.
There is considerable difference in the taxonomic composition of meroplankton between the Mediterranean and the Black Sea, the Mediterranean being richer in fauna (table 1). This is due to the great drop in salinity from 35 to 18%. These typical stenohaline taxons such as Priapulida, Echiura, Brachiopoda, Cephalopoda, Crinoidea, Enteropneusta, Stomatopoda, present in abundance in the Mediterranean Sea, are not found in the Black Sea. Some taxons as Sipuncula, Ophiuroidea, Asteroidea, Echinoidea, Holothuroidea and Scaphopoda are represented in the Black Sea only 1-8 species. The higher diversity in the Mediterranean is exemplified by the presence of larvae such as ophiopluteus, echinopluteus, auricularia, doliolaria, pentactula, bipinnaria, brachiolaria, pelagosphaera, tornaria etc.
The dominating groups in the Aegean Sea were the veligers of Gastropoda and Bivalvia, nectochaetes of Polychaetes and ophiopluteus of
Ophiuroidea. About 45% of the total number of pelagic larvae were Gastropoda veligers and were found at Bruker Bank (depth 130m). At Thermaikos Bay, half of the larvae were ophiopluteus, with a density of 98ind./m3 (25-10m layer). The larvae of Bivalvia, Gastropoda and Polychaeta were represented more or less equally in zooplankton samples taken at station 7 miles off Saloniki (1075 m depth).
In the Black Sea, Bivalvia larvae comprised 91-98% of the total number of meroplankton. The predominance of the veliger Mytilaster lineatus is a distinguishing feature of the summer-autumn meroplankton of the Black Sea. The density of M. lineatus veligers reached a maximum of 1718 ind/m3 at Bulgarian coastal waters (25-10m layer over the depth of 45m). The predominance of the larvae Polychaeta as exception to the rule was observed at the deep-water (depth 1050 m, the layer 125-100m). The dominant species was presented by the trochophore and nectochaete of Vigtorniella zaikai (fam. Chrysopetalidae). V. zaikai inhabit usually the deep layers at the low temperatures (6,33-8,96ºC). The distribution of these cryophilic larvae in the Black Sea is very wide. They have the extraordinary ability to spend a long time in the cyclonic gyres of the Black Sea.
There are some free-swimming larvae having the active predatory behaviour, for example Chaetopterus variopedatus and Plyllochaetopterus socialis (fam. Chaetopteridae). The most part of invertebrate\’s larvae is sestonophages, filterables by type of food. They make the diurnal migration depending on diurnal dynamic of phytoplancton feeding upon microscopic algae as their main food.
In order to determine characteristics of meroplankton vertical distribution let\’s analyze the results of the diurnal (twenty-four-hour) station in Aegean and Black Sea. The diurnal change of the vertical distribution of total meroplankton density was investigated over the Johnston bank (depth 75m). Maximum larvae number-57 ind/m3 was marked in the morning by 8-hour sample in 10-0 m layer. In the Black Sea maximum larvae number-1086 ind/m3 was noted in 20-hour sample also in 10-0 m layer.
Essential influence on the meroplankton number has temperature. This fact is proved by the observation made at a diurnal station over the Bruker bank. Samples from the upper 25-5 m layer are taken very often, every 5m. According growing the depth temperature of the water falls from 23ºC on surface to 15ºC in the 100-75 m layer. The highest larvae density was observed in the upper warm layer (10-0 m). The maximum density of larvae was marked at 16 o\’clock (4 p.m.) and at midnight (24 o\’clock). In the deepest cold layer the larvae occurred very rare (single specimen) or as a rule they absent. Temperature of water of the upper layer (0-5 m) varies faintly from 22.5ºC at 4p.m to 23.2 at 4 a.m.
Table 1. Taxonomic composition of the meroplankton from Eastern Mediterranean and Western Black Sea during the autumn 1984
Taxon
East Medeterranian
West Black Sea
1
2
3
Class Nemertini
single
single
Class Turbellaria
single
single
Class Phoronidae
single
single
Class Polychaeta
-
Family Hesionidae
3
-
Fam. Chrysopetalodae
2
20
Fam. Chatopteridae
6
-
Fam. Disomiidae
34
-
Fam. Ariciidae
single
-
Fam. Phyllodocidae
single
35
Fam. Sigalionidae
single
4
Fam. Nereidae
single
4
Fam. Spionidae
20
177
Fam. Nephthydidae
single
5
Fam. Capitellidae
single
16
Fam. Polynoidae
single
7
Fam. Oweniidae
single
4
Fam. Sabellariidae
single
single
Fam. Amphictenidae
single
single
Fam. Protodrilidae
single
single
Class Echiura
single
-
Class Sipuncula
5
-
Class Bivalvia
52
1332
Class Gastropoda
60
54
Class Bryozoa
single
10
Class Phoronidea
single
2
Class Crustacea
Suborder Cirripedia
2
19
Order Decapoda
5
9
Phylum Echinodermata
Class Ophiuroidea
100
-
Clas Echinoidea
9
-
Class Holoturoidea
2
-
Phylum Hemichordata
Class Enteropneusta
single
-
Note: “single”- single occurrence; “34” -maximal density specimens in m3
“ - “- absence of specimens
It is very important to compare the space-temporal distribution of the principal group\’s larvae concerning of high taxons habitants of the Aegean and Western Black Sea. For Aegean Sea we used the material, received on September 22-23 over Bruker Bank (depth 130 m). Five layers of water were caught by 17ºC in the surface layer and 22ºC in the deepest one 100-75 m.
Bivalvia veligers concentrate in the upper layer during the twenty-four hours in the upper layer 10-0 m. They have very rare occurrence or may be absent in the deepest layer 100-75 m. Maximal density 19 sps /m3 is marked in the morning and at midnight.
The Gastropoda veligers are more numerous than Bivalvia ones. The great bulk of larvae concentrate in the surface layer 5-0 m from 16 to 24 o\’ clock. The maximal density 58 sps/ m3 is observed in the morning.
The Polychaeta larvae are less numerous than mussels ones, They concentrate in the upper layers (10-0 m). Maximal density 22 sps/m3 is noticed in the surface layer (5-0 m) in the morning.
The Echinodermata larvae concentrate in the upper layers as well. They are presented with echinopluteus (Echinoidea), auricilaries, doliolaries and pentactules (Holothuroidea) and ophiopluteus (Ophiuroidea). The latter are the dominanted group. Maximal density of Echinodermata larvae is 16 sps/m3 in the upper layer (5-0 m) in the morning.
The space-temporal distribution of the Black Sea principal taxons of meroplankton has the following feature. We used the material collected at the station N 46 over 150 m depth (44o 45’ N, 31o 45’ O).
Bivalvia veligers concentrate in two upper layers during the twenty-four hours. They have the rare occurence in the deepest layer 100-75 m. Maximal density 1058 ind /m3 was marked in the 10-0 m layer in the morning. The dominant species of larvae was veligers of Mytilaster lineatus.
The Gastropoda veligers in comparison Bivalvia occured during usually very rare, exception of 16 and 20 hour. The great bulk of larvae 51 and 25ind/m3 concentrates in the surface layer 10-0 m). The dominant species of larvae was veligers of Bittioum reticulatum.
The Polychaeta larvae are less numerous than Bivalvia ones. They did not form the great crowd (accumalations). The dominant species of larvae were the nectochetes of Prionospio malmgreni (fam. Spionidae). This species inhabits widely the coastal shallow zone of the Black Sea.
Conclusion. The qualitative and quantitative distribution of the larval meroplankton in two interconnected basins - the Eastern Mediterranean and the Western Black Sea were studied during the expedition on the R/V "Academic Kovalevskii", in autumn 1984. There is considerable difference in the taxonomic composition of meroplankton. The Mediterranean meroplankton has more richest fauna as Black Sea one. The pelagic larvae of the Western Black Sea are more numerous as the Eastern Mediterranean ones. The dominant groups of Mediterranean meroplankton are larvae of Gastropoda and Echinodermata. The meroplankton of the coastal zone of the Western Black Sea contains mainly Bivalvia larvae, in particular Mytilaster lineatus veligers. The meroplankton of the deepsee bathyal zone consist of Polychaeta larvae, chiefly trochophores and nectochaetes Vigtorniella zaikai. Analyse of the meroplankton vertical distribution in the Aegean Sea and Western Black Sea reveals the prevalence of the main part of larvae to the upper layer of the waters.
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