DIEL VERTICAL MIGRATION OF PLANKTONIC CRUSTACEAN POPULATIONS IN THE IZVORU MUNTELUI BICAZ RESERVOIR

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1 DIEL VERTICAL MIGRATION OF PLANKTONIC CRUSTACEAN POPULATIONS IN THE IZVORU MUNTELUI BICAZ RESERVOIR Mihai-Georgel ERHAN Al. I. Cuza University Iaşi, Faculty of Biology, Bd. Carol I A, 7 Iaşi, Romania, ermikero@yahoo.com Abstract. The diel vertical migration of the planktonic crustacean populations from the Izvoru Muntelui Bicaz reservoir has been studied by several researchers who have had different opinions about the presence of this phenomenon in the reservoir. The majority of the researchers have shown that DVM (diel vertical migration) phenomenon is present at the majority of planktonic crustacean species but in the same time there are data which are putting under doubt the presence of DVM in the Izvoru Muntelui Bicaz reservoir. It has been observed that the direction and amplitude of DVM are not the same for all the planktonic crustacean species. In this paper we are presenting the results obtained after the analysis of zooplankton samples taken in September. We concluded that the presence of planktonic crustacean populations DVM cannot be neither confirmed nor infirmed, so further complex researches are needed. Keywords: crustacean populations, species, diel vertical migration, reservoir. Rezumat. Migraţia nictemerală a populaţiilor de crustacee planctonice din lacul de acumulare Izvoru Muntelui Bicaz. Migraţia zooplanctonului şi a populaţiilor de crustacee planctonice, a fost studiată de o serie de cercetători, dar mai există semne de întrebare asupra existenţei acestui fenomen în lacul de acumulare Izvoru Muntelui Bicaz. S-a observat că nu toate organismele zooplanctonice se comportă la fel, mai ales în ceea ce priveşte sensul şi amplitudinea migraţiilor efectuate în decurs de de ore. În această lucrare sunt prezentate observaţiile şi concluziile rezultate în urma analizei probelor de zooplancton prelevate în luna Septembrie. Prezenţa fenomenului migraţiei nictemerale la populaţiile de crustacee planctonice din lacul de acumulare Izvoru Muntelui Bicaz nu poate fi confirmată, dar nici infirmată. Cuvinte cheie: populaţii de crustacee, specii, migraţie nictemerală, lac de acumulare. Introduction The phenomenon through which the planktonic crustacean populations are concentrating at the surface of the water during the night and descending towards the bottom of the reservoir during the day time, ascending again towards the superficial layers of water in the evening and descending to the bottom of the reservoir at dawn is called diel vertical migration or DVM. This is the main type of DVM, but there are species that are migrating in the opposite direction meaning from the bottom of reservoir to the superficial layers of water during the day and vice versa during the night. The DVM is characterised by two types of motion: ascending and descending of the organisms. While the ascension of the organisms is an active type of motion the descending process can be passive due to the fact that organisms are denser than the water. Another characteristic of DVM is their amplitude, which varies very much because of the different swimming speed of the organisms and not only. The amplitude of DVM is very small for rotiferans (less than m) and very big for planktonic crustaceans (up to m) (Pourriot, 199). Also there are species that are not migrating. The amplitude of DVM can be limited by the presence of toxic cyanobacteria at the surface of the water or by the lack of O in the bottom water layers. The DVM can be also influenced by the weather, wind and water temperature.

2 Mihai-Georgel Erhan It is considered that the triggering factor of DVM is light because researchers noticed that the organisms are presenting phototactic behaviour when the intensity of light decreases or increases. The diel vertical migration of the planktonic crustacean populations from the Izvoru Muntelui Bicaz reservoir has been studied by several researchers who have different opinions about the presence of the phenomenon in this lake. The majority of researchers (Rujinschi & Rujinschi, 197; Miron & Grasu, 19; Miron et al., 193) have shown that DVM phenomenon is present at the majority of planktonic crustacean species but in the same time there are data which are putting under doubt the presence of DVM in the Izvoru Muntelui Bicaz reservoir (Mustaţă et al., 1999). Material and Methods In this paper we are presenting the observations and conclusions resulted from the analysis of data gathered after the analyses of the zooplankton samples taken in September. The sampling point was placed half way between the fish aquaculture farms. The sampling was made using a plankton net according to Apstein used for vertical sampling on water layers. The samples were temporary fixed with 9% alcohol. In the laboratory a second filtration process was made. During this second filtration process all the water from the samples was eliminated and the samples were permanently fixed with 9% alcohol, followed by the identification of taxa and the counting of the organisms. Because the samples contained a very large number of organisms we have extracted four sub-samples with a volume of ml from each of the samples using a Hensen pipette. The sampling was made in four essential moments of a day - at noon (1: pm), in the evening (: pm) at midnight (1. am) and in the morning (. am). The sampling was made in these moments of a day because these moments are characterised by different light intensities and it is known that most of the zooplanktonic organisms present a phototactic behaviour. Results and Discussion In the Tables 1- we have presented the medium values obtained after counting four sub-samples for each sample. The results are presented also using graphics because this type of presentation offers a better view of the situation. In the following graphics are presented the results obtained during this study but without those for species Leptodora kindtii Focke and Bosmina longirostris Müller the data obtained for these species are not relevant. Table 1. Vertical distribution of the planktonic crustacean populations at 1. pm. Fam. Cyclopidae (variae taxa) 1 11 Eudiaptomus gracilis Sars Diaphanosoma orghidani Negrea Daphnia sp. (variae taxa) 1 Bosmina longirostris Müller - - Leptodora kindtii Focke Total

3 Table. Vertical distribution of the planktonic crustacean populations at. pm. Fam. Cyclopidae (variae taxa) 1 11 Eudiaptomus gracilis Sars 1 9 Diaphanosoma orghidani Negrea 3 3 Daphnia sp. (variae taxa) 3 7 Bosmina longirostris Müller Leptodora kindtii Focke Total 1 19 Table 3. Vertical distribution of the planktonic crustacean populations at 1. am. Fam. Cyclopidae(variae taxa) Eudiaptomus gracilis Sars Diaphanosoma orghidani Negrea 1 9 Daphnia sp. (variae taxa) Bosmina longirostris Müller Leptodora kindtii Focke Total Table. Vertical distribution of the planktonic crustacean populations at. am. Fam. Cyclopidae (variae taxa) 3 Eudiaptomus gracilis Sars Diaphanosoma orghidani Negrea 3 31 Daphnia sp. (variae taxa) Bosmina longirostris Müller Leptodora kindtii Focke Total pm - m - m - 3m 3 - m Figure 1. Vertical distribution of Cyclopidae at 1: pm. density(no. of organisms) 3. pm - m - m - 3m 3 - m depth(m) Figure. Vertical distribution of Cyclopidae at :. pm.

4 Mihai-Georgel Erhan am - m - m - 3m 3 - m Figure 3. Vertical distribution of Cyclopidae at 1: am am - m - m - 3m 3 - m Figure. Vertical distribution of Cyclopidae at : am. From the analysis of the figures 1-, we can observe that the distribution of this group on water layers it corresponds to a normal DVM pattern just in the evening, midnight and morning (: pm, 1: am, : am) because at noon (1: pm) the situation is very different from the normal DVM pattern, meaning that although a big part of the organisms are in the inferior water layers the biggest part of them is concentrated at the water surface in the superior layer ( m). 1. pm m - m - 3m 3 - m Figure. Vertical distribution of Eudiaptomus gracilis Sars at 1: pm. 3 3 : pm - m - m - 3m 3 - m Figure. Vertical distribution of Eudiaptomus gracilis Sars at : pm : am - m - m - 3m 3 - m Figure 7. Vertical distribution of Eudiaptomus gracilis Sars at 1: am. 3 : am - m - m - 3m 3 - m Figure. Vertical distribution of Eudiaptomus gracilis Sars at : am. Studying distribution of Eudiaptomus gracilis Sars species we can observe that is the same situation like in the case of Cyclopidae family. The difference is that in the inferior water layers at 1: pm there are fewer organisms than in the previous situation.

5 1 1: pm - m - m - 3m 3 - m Figure 9. Vertical distribution of 1: pm. density (no. organisms) 1. pm - m - m - 3m 3 - m Figure. Vertical distribution of : pm. 1. am. am density (no. organisms) m - m - 3m 3 - m Figure 11. Vertical distribution of 1: am. density (no. organisms) 1 - m - m - 3m 3 - m Figure 1. Vertical distribution of : am. The analysis of data obtained for Diaphanosoma orghidani Negrea and Daphnia sp. reveals the same situation like in the previous two cases. 1. pm. pm m - m - 3m 3 - m m - m - 3m 3 - m Figure 13. Vertical distribution of Daphnia sp. at 1: pm. Figure 1. Vertical distribution of Daphnia sp. at : pm.

6 Mihai-Georgel Erhan 1. am. am m - m - 3m 3 - m m - m - 3m 3 - m Figure. Vertical distribution of Daphnia sp. at 1: am. Figure 1. Vertical distribution of Daphnia sp. at : am. 1. pm. pm m - m - 3m 3 - m m - m - 3m 3 - m Figure 17. Vertical distribution of planktonic crustacean populations at 1: pm. Figure 1. Vertical distribution of planktonic crustacean populations at : pm am - m - m - 3m 3 - m Figure 19. Vertical distribution of planktonic crustacean populations at 1: am. 3. am - m - m - 3m 3 - m Figure. Vertical distribution of planktonic crustacean populations at : am. For a better visualisation of the obtained results and also for finding out if the results obtained at the level of taxa are reflected from the general point of view we have determined the general percentage distribution of the planktonic crustacean populations on water layers. The individual analysis of the presented graphics shows that the distribution of the planktonic crustacean populations on water layers it corresponds to a normal DVM pattern just in the evening, midnight and morning (: pm, 1: am, : am) because at noon (1: pm) the situation is very different from the normal DVM pattern, meaning that although a big part of the organisms are in the inferior water layers the biggest part of them is concentrated at the water surface in the superior layer ( m). This is also the result obtained during the individual analysis of taxa.

7 The comparative study of the graphics in all the mentioned cases including the general view of the planktonic crustacean species distribution reveals an interesting phenomenon, meaning that although normally in the time period between 1: pm and : pm the organisms should be migrating from the bottom of the reservoir towards the water surface the real direction is opposite. So, all the organisms which have been concentrating at the surface during the day are migrating down in the evening. In the time period between : pm and 1: am the direction of migration changes again and the organisms are concentrating again at the water surface which determines the normal DVM pattern found at 1: am. The time period between 1: am and : am is characterised by a normal migration direction from the surface to the deeper water layers. The last studied time period is that between : am and 1: pm and what we can observe is that the direction of migration is changing again, instead of going down the organisms are migrating towards the water surface and the pattern discovered at 1: pm is opposite than the normal DVM pattern. Should be mentioned that during the sampling period, the environment conditions were relatively unstable with clouds and clear sky (has influence over the light intensity), strong wind, big waves, small amount of precipitation. The water temperature has varied between 1 and 1 C. Conclusions Almost all taxa are presenting a very large number of individuals in the superficial water layer ( m) at noon (1: pm) which is the opposite situation than in a normal DVM pattern. The individual analysis of the graphics shows that, at : pm, 1: am and : am, the distribution pattern is a normal DVM pattern. The planktonic crustacean species are moving constantly on vertical of water column, but the amplitude of these moves varies from one taxa to another and it is influenced by the environmental conditions like water temperature, wind, light intensity, water chemistry, etc. Some of the taxa, that we found, had very low density (Leptodora kindtii Focke and Bosmina longirostris Müller). The presence of planktonic crustacean populations DVM couldn t be neither confirmed nor infirmed so further complex researches are needed, researches which should take in consideration the influence generated by the presence in the area of two fish aquaculture farms, the swimming speed of each taxa, the amplitude of the migrations and environment conditions (water temperature, light intensity, water chemistry, water mixing due to air movement, etc.). Also the further researches should take in consideration an extension of the study area towards those lake areas where the human influenced is minimal. References Miron, I. et al., 193. Lacul de acumulare Izvorul Muntelui Bicaz. Monografie limnologică. Editura Academiei R. S. R., Bucureşti, p. Miron I., Grasu, M., 19. Zoplanctonul lacului de acumulare Bicaz în al III lea an de la formarea sa. Analele Ştiinţifice ale Universităţii Al. I. Cuza Iaşi, Secţiunea II a. Biologie, X (): 7. Mustaţă, Gh. et al Dinamica nictemerală a zooplanctonului din lacul Izvoru Muntelui Bicaz în condiţiile anului 199. Lucrările simpozionului Lacurile de acumulare din România, : 9. Pourriot, R., Meybeck, M., 199. Limnologie Générale. Masson Editeur, 9 p. Rujinschi, R.-I., Rujinschi, C., 197. Unele aspecte privind dinamica nictemerală a zooplanctonului din secţiunea Rugineşti, lacul Bicaz. Lucrările Staţiunii Stejarul : 7.