Functioning Of The Sexual System In The Black Sea Mussels In Conditions Of Anthropogenic Influence
Functioning of THE sexual system in THE Black Sea mussels in conditions of anthropogenic influence
E.V. Kholodkovskaya, O.Yu. Kudinsky
Odessa Branch Institute of biology of Southern Seas, National
Academy of Sciences of Ukraine
The northwestern part of the Black Sea is subject to significant anthropogenic loading from drainage of Dnieper, Dnestr and Danube rivers, and also such industrial centers as Odessa and Nikolaev. The sexual system reacts first of all to negative changes of the environment to hydrobionts. The sexual cycle of the mussel Mytilus galloprovincialis Lmk..on all of its length from the coast of England up to Tunis has distinct stages (Lubet, 1959). It is closely connected to seasonal and environmental temperature conditions. The period of sexual rest in various geographical zones lasts from about one - four months and, as a rule, covers 100% of the specimens (Lubet et al., 1981,1986).
The sexual cycle of mussels in the researched area is complicated and is not quite distinct.The temperature limits at which the gonad of mollusks passes this or that stage of development, are wider, than those of M.galloprovincialis in other seas (Table). In contrast to the Mediterranean mussels, the period of sexual rest (Stage 0) occurs practically all year, never covering all of the population, even its significant part. Even in the periods following mass spawning (May, July, October - December), the number of mussels with dormant gonads does not exceed 5-12%.
Frequency of the Stage 0 grows (Р > 0,99) with drop in temperature, reaching a maximum at 2ºС. At other stages the correlation with temperature is not revealed.
Gametogenesis (Stages I and II) is also extended, varying from 0 up to 37%. Its bottom temperature limit is not 6-8ºС, as considered earlier, but like the temperature of freezing of water. Contrary to opinion, that temperatures of 16-18ºС stop gametogenesis, we registered this stage at 22ºC.
Frequency of other stages is:
Maturation of gametes (Stage IIIА1 and IIIА2) 0-66.7 %;
Spawning (Stage IIIВ) 0-62.5 %;
Restoration of gonads (Stage IIIС) 0-42.1 %;
The end of the sexual cycle (Stage IIID) 0-79.3 %.
Table 1. Temperature limits of stages of the sexual cycle of mussels in the northwestern part of the Black Sea
Stage of development
according to Lubet-Valli
Temperature of water, оС
From literature
data*
Personal data
The period of sexual rest (0)
Growth of acinous gland (1)
Gametogenesis (2)
The period of reproduction (3А1)
Sexual maturity (3А2)
Spawning (3В)
Restoration of gonad (3С)
The end of the sexual cycle (3D)
14-24
14-18
9-17
8-17
8-17
7-18
7-18
16-17
0-22
4-21
0-21
2-22
0-22
0-22
0-22
0-22
*Lubet et al., 1981; Lubet et al., 1986.
The maximum monthly average frequency in various years does not coincide. That is characteristic for all stages. Together with individuals in a condition of sexual rest, spawning specimens have been noted in the same samples. That is not observed more anywhere else on extensive areas for this species. All-the-year-round histological analysis has shown that in the limits of each sample there is certain heterogeneity in the condition of sexual glands of separate individuals, which is different in various months. October and November are mostly mosaic in structure, when the maximal range of heterogeneity (up to 8 sexual stages, on the average 5,9) is observed. August is most homogeneous - on the average 3.5 stages. The greatest number of mollusks with mature sexual products (Stage 3А2) is in July and August.
For an estimation of interpopulation synchronism we developed a special index (Kholodkovskaya, Kudinsky, 1996; 1999). The index of synchronism of the sexual cycle is calculated as the ratio of percentage of a modal stage in the sample to number of stages in the sample. The size of the index can change from 1,25, when all of eight stages are present in the sample in equal amounts which in practice is improbable. Up to 100, is noted when only one stage is present in the sample, which sometimes is observed in ecologically safe areas, such, as Crimea.
In the Odessa Bay, subject to significant anthropogenic loads, the average index of synchronism makes up 8.0, that is significant (Р> 0.999) which is lower, than in the Kara-Dag region – 18.0 (sample number exceeding more than 600 individuals). The given index is applicable in case of small samples (Kholodkovskaya, Kudinsky 2000). In mussels living in the Odessa Bay in area of release of fresh drainage waters, it is significantly (0,95) reduced in comparison with mollusks from adjacent water areas, where freshening is not observed (volume of sample number – 128 individuals).
As a measure of desynchronization also the Simpson index of diversity has been tested. The size of the index of diversity of sexual stages in the sample theoretically can change from 1 up to 8, coinciding with the number of stages. Practically this valuedoes not exceed 5.7.Such high values are noted in the Odessa Bay, while in the Kara-Dag region, where anthropogenic load is insignificant, the maximal value was 3.5, and in the Bolshoi Utrish Cape area – 2.7.
A similar degree of asynchronism of the sexual cycle testifies to instability and poor quality of the environment of mollusks in the northwestern part of the Black Sea. This is shown by a reduction in fertility, which we estimate in a gamete volume fraction (GVF). So, in the period proceeding mass emission of males and females mussels living near the coast of East Crimea, the GVF-index is 30-40% higher, than in mollusks, living in the northwestern part of the Black Sea in a similar phase of the sexual cycle. After the termination in this area of mass reproduction practically in all samples of mussels the gonad is free from sexual cells, which is reflected by average values of the GVF-index of 5 % in males and 1 % in females. In mussels of the Odessa Bay in the period after spawning these parameters made up 39 and 9%, correspondingly.
References
1. Lubet P. Recherches sur le cycle sexuel et l\’emission des gametes chez les Mytilides et les Pectinides (Moll. Bivalves). -Rev. Trav. Inst. Pêches marit.-1959.-23 (3).-P.387-548.
2. Lubet P., Gimazane J.-P., Prunus G. Etude du cycle de reproduction de Mytilus galloprovincialis (Lmk) (Moll. Lamellibranche) a la limite meridionale de son aire de repartition, comparaison avec les autres secteurs de cette aire. Haliotis, 11,1981.- P.157-170.
3. Lubet P., Aloni N, Karnaukhova N. Etude experimentale de l\’action de la temperature sur le cycle reproduction de Mytilus galloprovincialis Lmk.; comparaison avec Mytilus edulis L. // C.r. Acad. Sci. S.3. - 1986. - 303, N2. - P.507-512.
4. Kholodkovskaya E.V. Kudinsky O.Yu. Index of synchronism of maturation of mussel gonads as an instrument of ecological monitoring // Management and conservation of the northern-western Black Sea coast // Scientific publications Proceedings of the EUCC International Symposium.- Odessa, 1996.- P. 71-76.
5. Kholodkovskaya E.V. Kudinsky O.Yu. Use of criteria of synchronism of a sexual cycle of mytilids in ecological monitoring of the Odessa Bay // Ecological problems of the Black Sea: In Materials of OTSNTEI, Odessa, 1999.-P. 301-305 (in Russian).
6. Kholodkovskaya E.V. Kudinsky O.Yu. Criterion of synchronism of a sexual cycle of mytilids // Global system of monitoring of the Black Sea: fundamental and applied aspects. In Materials of National Academy of Sciences of Ukraine, МGI.- Sevastopol, 2000.- P. 157-161(in Russian)
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