Biological diversity and seasonal variation of mesozooplankton in the south eastern Black Sea coastal ecosystem

YILDIZ Ilknur, FEYZIOGLU Ali Muzaffer
Faculty of Marine Sciences, Karadeniz Technical University, Trabzon, Turkey

 

Abstract

In this study, the seasonal distribution of mesozooplankton was investigated between 1999 and 2006 in a station located in the South Eastern Black Sea Region. A total of 40 cruises were done within the South Eastern continental shelf throughout this period in order to collect mesozooplankton samples. A total of 11 mesozooplankton species were identified. The highest abundance of species were 67770 ind/m2 (Penilia avirostris), 50048 ind/m2 (Sagitta setosa), 42143 ind/m2 (Oikopleura dioica), 27987 ind/m2 (Acartia clausi), 25792 ind/m2 (Oithona similis), 24806 ind/m2 (Pseudocalanus elongatus), 12094 ind/m2 (Paracalanus parvus), 11697 ind/m2 (Calanus euxinus). Calanus euxinus and Pseudocalanus elongatus were determined as cold water species having high abundance in winter and early spring. The species of Acartia clausi and Oithona similis were assessed as species observed in all seasons. According to the Bray-Curtis similarity index, the copepod species shows seasonal difference. The summer and early autumn was found to be different than other sampling periods in terms of population structure. The results of this study will form a basis for long-term mesozooplankton monitoring studies in the Black Sea coastal ecosystem.

Keywords:      Black Sea, Zooplankton, Copepod, Seasonal Dynamic, Abundance

 

 

Introduction

One of the most important environmental factors that control commercial fish stocks showing great fluctuations all the year is food supply. Fish larvae start life as ichthyoplankton and they were fed on zooplankton during initial feeding periods. The food of zooplankton is constituted by phytoplankton [12]. Zooplankton has a key role in the pelagic food chain for energy transfer to upper energy level [27, 16, 17]. Many organisms of commercial importance in many parts of the world depend mostly on copepods as a food source at the planktonic larvae stage [28]. Anchovy (Engraulis encrasicolus), which is the most important fish species in the Black Sea ecosystem, feed in winter when they form a shoal consisting of Calanus helgolandicus and Acartia calusi which are abound. These two calanoid copepod species are of great importance in the energy cycle of the Black Sea ecosystem [21].

Studies concerning the planktonic organisms which are greatly important in food chain in the Black Sea are usually based on discrete sampling in the western and northern territories and in certain periods [6, 21, 8, 14, 48]. In particular, this provides an opportunity to explain the long-term seasonal dynamics of zooplankton populations. The regime shifts occurring in the Black Sea in the last 20 years have had important effects on zooplankton and fishery. At the beginning of the 1990s, a decrease was observed in production of second and third trophic levels in marine ecosystems on the world. The Black Sea was negatively affected by global warming after the mid-90s. This effect caused decreases in phytoplankton and zooplankton abundance [33]. The changes observed throughout the Black Sea continued after the 2000s. The coastal ecosystem belonging to the South Eastern Black Sea, in particular, is still under the influence of these changes. No data about time series belonging to coastal ecosystem in mesozooplankton abundance was available until the end of the 1990s. There are still no data on the annual zooplankton abundance, diversity and species composition so far. This caused a significant insufficiency in the interpretation of the ecosystem.

The aim of this study was to reveal the change in seasonal structure of mesozooplankton throughout the years in the South Eastern Black Sea coastal ecosystem and also proved data about the annual zooplankton abundance, diversity and species composition in the region. Moreover, it was also the aim to eliminate the shortage of data on the time series between 1999 and 2006. The data which belongs to former periods were also used. In this context, it is intended to present the changes in planktonic structure due to regime shifts and climate change on a global level, which has been frequently discussed in recent years. In addition, the study presents the difference between the South Eastern Black Sea and South Western Black Sea in terms of composition of species and the point at which the Eastern Black Sea coastal ecosystem comes under the Mediterranization process.

 Materials and Method

Study area and sample collection

The Black Sea is the biggest anoxic marine environment on the world. The maximum depth of the Black Sea is 2200 m. Its surface area and volume is 4.2 x 105 km2 and 5.3 x 105 km3, respectively.  The Black Sea is almost isolated from the oceans of the world. It has a limited connection to the Mediterranean Sea via Turkish Straits system and the Sea of Marmara. Strong density stratification prevents vertical mixing. The oxygenated upper layer reaches up to 150 meters. The water mass at the lower layers (only 13% of the sea volume) is anoxic and contains hydrogen sulphide.  A temporary halocline separates oxic and anoxic waters [36]. There is a well-determined oxygen-minimum zone (OMZ) between these waters. General cyclonic circulation of the Black Sea appears as wind effect [32]. Along with this, the Batumi anticyclone is located on the South Eastern part of the Black Sea. This anticyclone provides the continuity of coastal currents [23].

In order to collect mesozooplankton samples in the South Eastern Black Sea, 40 cruises were done between 1999-2006 to the station 15 nautical miles from the coast and located at the coordinates of 41°11′ 15” N- 40º 14′ 15” E (Figure 1).  The station was always visited between 11:00 and 14:00 h local time. The depth near the permanent station is about 780 m. All tows were made by vertical hauls between from the different depth layers beginning of anoxic layer to the surface in the southeastern part of the Black Sea. Beginning of the anoxic water bodies was determined according to sigma-t values. If sigma-t values are greater than 16.2, water bodies were considered to be anoxic [4]. A plankton net, Kahlsico (75 cm mouth diameter and 75µm aperture size), was used for plankton sampling. Because adequate sampling early copepodit stages of small species like Pseudocalanus elongatus, Paracalanus parvus, requires mesh sizes of 61 and 35 µm respectively [16]. Hydro-bios digital 5 digits flowmeter was used for the calculation of seawater filtered [47].

Figure 1

Figure 1. Sampling station

Collected samples were transferred into 1 litre plastic jars. They were fixed with formaldehyde buffered with borax having a final concentration of 4%. The samples were concentrated in jars for quantitative analyses, depending on the density. Counting was done under Olympus BH2 stereomicroscope using a Bogorov–Rass counting chamber. Counting was repeated on 8 sub-samples [16]. In the identification of copepod and the cladocera species, general anatomy, P4, P5, a1 and urosome structure were taken into account. Mauchline et al. (1998) and Johnson and Allen (2005) were used for identification of the species. CTD parameters were measured in-situ by using General Oceanic Idronaut 316 CTD.

Marine ecologists use the Bray-Curtis index to explain the similarities and differences between samples [54]. In order to examine the mesozooplankton population in the Eastern Black Sea coastal ecosystem, copepod, the most common group, was used as the base. The Bray-Curtis index was utilized to reveal the differences and similarities of this group throughout the year. In order to determine the similarity of sampling periods throughout the year, the Bray-Curtis similarity index was calculated by the equation below:

formula

s:  number of core taxa present in the sampling period i and j

nik: number of individual in taxon k in the sampling period i

njk: number of individual in taxon k in the sampling period j

 Result

 Environmental Parameters

In order to determine the environment in which mesozooplankton organism live the variation in temperature and salinity with respect to depth is given by graphs (Figure 2).

Figure 2

Figure 2. Monthly average temperature (°C), salinity (‰) and density (sigma-t kgm-3) profiles in the Black Sea.

It was determined in CTD profiles obtained during the study that the variation in water temperature with respect to depth is statistically significant for all seasons, except winter (p<0.05). The surface water temperature ranged from 8.5°C to 28.3°C in the region of concern. The thermocline layer was observed at depths of 15-25 m in spring whereas in summer and autumn it was observed at depths of 25-45 m. This shows that the mixing layer moved to higher depths in summer and autumn. It was observed in the temperature profile that the temperature did not change after a depth of 100 m. Moreover, the Cold Intermediate Layer (CIL) was encountered at a depth between 35- 75 m.  According to our sigma-t profile, beginning of anoxic zone water bodies was 155- 162 meter depth summer and winter sampling periods respectively.

The salinity profiles measured within the study area are given in Figure 2. It was determined that the salinity of 17 ‰ measured at surface showed a gradual change and it reached 21.2 ‰ at the depth of 200 m. The measurements showed that the average salinity of 17.6 ‰ at the surface rose to 19 ‰ at 100 m and to 21.2 ‰ at 200 m.

Monthly sigma-t profiles used in expressing seawater density are given in Figure 2. The Sigma-t value in the surface waters is lower in the summer months than in winter months. The average sigma-t value was 9.6 kg m-3 whereas it increased to 14.3 kg m-3 in winter months. The sigma-t profile up to 50 m, which varies greatly by season, did not reveal a statistically significant change after 50 m. It reached 16.6 kg m-3 after 200 m., Anoxic zone starts at the Sigma-t value of 16.2 kg m-3 and varies between 120 and 130 m, throughout the year depending on the seasons.

 Mesozooplankton abundance and distribution

Eleven species in nine systematic groups were identified as belonging to the mesozooplankton during the study. Three of these groups belong to Arthropoda, 3 to Mollusca and 3 to Cnidaria phylum. Chordata, Chaetognatha and Annelida phylum were represented by one group. Seven species in the Copepoda group and two species in the Cladocera group of Arthropoda were determined.  The Appendicularia and Chaetognatha groups were represented by one species. The Bivalvia, Cirripedia, Decapoda, Gastropoda, Polychaeta and Hydrozoa groups were evaluated as Meroplankton. The systematic groups, to which these species belong, and their abundance are presented in Table I.

Table I. Average annual abundance of zooplankton species determined at the station of concern in 1999, 2000, 2001, 2002, 2005 and 2006 (individual/m2).

Table I

Differences were observed in terms of mesozooplankton abundance (p<0.05). The lowest abundance was determined in 1999 (Figure 3). Three blooms were observed in summer (June), autumn (September) and winter (December). The maximum mesozooplankton abundance was reached in September with 360.130 ind/m2. Copepods were observed in all sampling periods. In addition, it was seen that the copepod group had its maximum value in terms of abundance in December. The copepods were determined as 73.638 ind/m2 (Figure 4). The Cladocera species were the second dominant group in September.  The number of organisms belonging to this group reached up to 90.409 ind/m2.

The highest Mesozooplankton abundance was determined in August 2000 (Figure 3). In this period, the number of organism in water column reached 1.350.211 ind/m2. The Copepoda species were continuously observed in the year 2000 (Figure 4). The highest value of Copepoda was determined in May as 136.382 ind/m2. In samplings done in 2000, the Cladocera species were encountered only at the end of summer.

The periods in 2001 when mesozooplankton abundance was the highest in 2001 were determined as April (995.300 ind/m2), August (1.484.004 ind/m2) and December (989.126 ind/m2) (Figure 3). The Copepoda group was the dominant group during the sampling period (Figure 4). This group had its maximum value in terms of abundance in December with 185.662 ind/m2. The number of organisms of the Cladocera species, however, reached its maximum in August. The Cladocera abundance reached up to 261.091 ind/m2 in this period.

The samplings done in 2002 cover the winter, spring and summer seasons. The highest abundances were determined in January (1.090.344 ind/m2), February (170.475 ind/m2) and June (828.584 ind/m2) (Figure 3). The Copepoda species were regularly observed in the samples taken (Figure 4). The Copepoda became dominant in 2002 and reached to 269.046 ind/m2 in February. While the Cladocera species were not observed in the winter or spring months, the highest value was determined in August as 7.280 ind/m2.

In 2005, sampling was done in February, April, May and June. The highest mesozooplankton number was determined in May with 1.280.717 ind/m2 (Figure 3). In this sampling period, the Copepoda group had its maximum value in April with 170.184 ind/m2 (Figure 4).

Mesozooplankton abundance was the highest in June 2006 (Figure 3). Oikopleura diocia of Appendicularia was the group with the highest abundance in the water column with 178.493 ind/m2 organisms in June (Figure 4). The Copepoda species was again observed in all samples and became the second dominant group of 2006. It was seen that the Copepoda group reached 85.325 ind/m2 in 2006. The Cladocera species reached 24.623 ind/m2 in June.

Figure 3

Figure 3. The variation in total mesozooplankton abundance and temperature with respect to years

Figure 4

Figure 4. Seasonal abundance values of the mesozooplankton groups of Copepoda, Cladocera, Chaetognatha, Appendicularia and Meroplankton species in 1999, 2000, 2001, 2002, 2005 and 2006 (ind/m2)

Figure 5

Figure 5. Similarity index values of the Copepoda group in 1999, 2000, 2001, 2002, 2005 and 2006

The results of similarity index applications for Copepods are presented in Figure 5. Population structure showed similarities between the other periods and July 1999 (%23), and August-September 2000 (%53), July 2001 (%57), May-June 2002 (%63), June 2005 (%78) and September 2006 (%52). Those sampling months create a difference due to a low similarity rate in these periods. Thus, the copepod group has a significantly different population structure in July compared to the other months of 1999.  This difference was observed because the Paracalanus parvus species and copepodit stages of the species had been encountered in July. However, the reason for the difference observed at the end of summer in similar applications in 2000 was because Oithona similis, Harpacticoid copepod and the copepodit stages of other copepod species had reached higher numbers than other months. Since Calanus euxinus was highly abundant though the numbers of other species decreased in July 2001, the copepod group displayed a different population structure. By the decrease in the numbers of copepod species in May and August 2002 this period created characteristic differences. A similar situation is valid for June 2005. The difference in September 2006 can be explained by the increase in the abundance of Acartia clausi and Centropages ponticus species.

Table II. Seasonal distributions abundance of Copepoda species with respect to years during the sampling period (ind/m2)

Table II

Discussion

Environmental parameters

The surface temperature in the Black Sea shows seasonal and spatial variations. Sea surface temperature in the winter period (February-March) decreases down to an average of 6-7°C (Figure 2). Temperature gradient showing spatial differences is given as 8-9°C in southern parts and 2-3°C in northern parts. Sea surface temperature having an average of 20-22°C in summer months increases up to 24-25°C along the east and south coasts. No anomalies were observed during the sampling done between 1999 and 2006. Yearly temperature variations in the sea surface remained within the seasonal temperature limits found in previous studies [34]. The seasonal thermocline layer changed between 15 and 25 m, starting from spring to mid-summer. The change from mid-summer to the end of autumn was between the depths of 25 and 45 m. The surface mixed layer in the winter season reached a depth of 75 m whereas yearly water temperatures showed no change after a depth of 100 m (Fig 2).

The difference in salinity observed between the surface waters and deep waters is one of the most characteristic properties of the Black Sea. Low salinity and density in surface waters and high salinity and density cause stagnation of deep waters. This situation leads to the existence of hydrogen sulphide (H2S) in circular cyclonic stream edges (periphery) at depths of 160-200 m in regions close to coast and at depths of 80-120 m in central parts of the Black Sea [51].

The salinity of surface water changes between 17 ‰ and 18 ‰ in Black Sea (Figure 2). Even though changes with respect to months were observed in salinity, it was not statistically significant (P<0.05).

The composition and seasonal distribution of Mesozooplankton species

Zooplankton is the most important component of the food chain in sea and oceans. Copepods are the most important zooplanktonic group, which constitutes the primary food supply of fish larvae, and some fishes having high economic value. The other important groups are Cladocera, Cirripedia, Polychaeta, Chaetognatha, Appendicularia and Meroplankton. In our study, a total of 11 zooplankton, group 7 of which belonged to the copepod group, were identified (Table I, Table II). Acartia tonsa and Pontella mediterrenea species found in previous studies in the Sinop region were not encountered in the study [46, 48]. In our study, different from Ustun’s (2005) study performed to determine the composition and distribution of zooplankton in the Central Black Sea, Harpacticoid copepod abundance was also identified.

It is seen that species diversity in the South Eastern Black Sea Region is lower than the Marmara and Western Black Sea. In the samples obtained during the study, seven copepods and two cladocera species were identified and Evadne nordmani, Evadne spinifera and Pleopis polyphemoides species (Cladocera) which are present in Western Black Sea were not observed. Furthermore, Aetideus sp., Ctenocalanus vanus, Metridia lucens, Microcalanus pusillus, Oncaea media, Oncaea minuta, Oncaea subtilils and Scolecithricella sp. species which are among Mediterranean species were not encountered in the South Eastern Black Sea ecosystem, either. It was reported that Mediterranean-origin mature zooplanktonic organisms died within 24 hours as the salinity decreased below 18 ‰ [18]. This situation explains why Mediterranean-origin species in the plankton cannot be found moving away from the straits in the Black Sea.

During the 10-year sampling at Mediterranean, important interannual variability emerged when the total zooplankton abundance was considered [5]. The copepods were the most abundant group as in Black Sea. Three higher peaks were determined in mesozooplankton during the annual cycle in both marine environment (Black Sea and Mediterranean). Monthly zooplankton abundance data indicated that the highest peaks were found during the first part of cool years, and the lowest values during second part [5]. According to literature, annual peaks of similar taxonomic groups take place almost the same periods in the Mediterranean and Black Sea.

The bloom of mesozooplankton was determined in every season in studies performed on the middle part of Black Sea Anatolian Coast (Sinop). It was reported that the most important of these blooms were observed in the autumn and winter months [46, 48]. Zooplankton bloom periods were affected by phytoplankton seasonality and population structure [25]. Phytoplankton population of East and West Black Sea shows differences at community structure in the same periods [49, 10]. So, when the present data compared with the literature [48] it was observed that Western and Eastern Black Sea showed differences in zooplankton peak seasons at the same period.

In this study performed between 1999 and 2006, the mesozooplankton abundances changed with respect to the years. Depending on the temperature and phytoplankton intensity, peaks were identified in the summer season of 2000-2001, at the beginning of the spring of 2005, and in summer season of 2006 (Figure 3).  Seasonal variations in biomass of different zooplankton groups occur together with seasonal variations in phytoplankton, bacterioplankton and water temperature [25].

The contribution of Cladocera to autumn bloom in 1999 was very high (90.409 ind/m2). When the seasons are compared, as seen from Table1 and Figure 4, the group is showed differences for 1999 (p< 0.05). The Penilia avirostrist species, in particular, reached a high abundance. The abundance of this group, when it is high, plays an important role in the food chain in the transportation of organic matter to higher levels [37, 45, 2]. The studies performed showed that P. avirostrist feed mostly on nanoplankton (2-20 µm). Furthermore, it was emphasized that they also feed on dinoflagellate and diatoms which are bigger in size [2]. Thus, cladocera play an important role in the re-joining of nutrients in water columns at the upper levels into the cycle [3]. The bloom in autumn of 1999 occurred through the high abundance of Sagitta setosa (82.618 ind/m2) and Copepod group (36.976 ind/m2) (Figure 4). Copepods are the primary food source of Sagitta setosa (Feigenbaum, 1991). In this period, high copepod abundance was followed by breeding and the growth of Sagitta setosa. It is known that the most important factors affecting the growth of S. setosa in the Black Sea are temperature and food supply [7]. Therefore, the high abundance of Sagitta setosa was affected by the existence of appropriate food intensity previous month.

The high abundance of the P. avirostrist of Cladoceras caused the bloom to occur at the end of the summer in 2000 and 2001 (Table I and, Figure 4). It was reported in research that cladoceran are intermittently present in the marine environment all the year round and after a rapid decrease following a very high abundance they disappeared from the plankton [35, 43, 26, 50]. The factors that control the abundance of this group are not clear despite the studies performed up to now. According to some researchers, temperature variation in the year plays an important role in the population dynamics of P. avirostrist [35].

The blooms of the 2001 winter (December), 2002 winter (January-February) and 2005 winter and spring were caused by the high abundance of the copepod group (Figure 4 and 6). Oithona similis of the cyclopoid copepods contributed most to the mesozooplankton abundance in May 2001 (49.959 ind/m2, Table II). Although Oithona similis is cold-water species and represents the cold water copepod in the Black Sea [15], it was also observed in the hot seasons through the year during the sampling period.

This is because, the species is also batyplanktonic organism, therefore, it is possible to find it in deep water during the summer. As a result, it was observed the vertical tow samples in each sampling period. In 2002, however, Acartia clausi, which is the euryhaline and eurythermal species, was an important species of winter bloom due to high abundance in February. Moreover, A. clausi species were continuously identified in samplings in our study. A. clausi species are abundant in hot and warm seas and observed within plankton all year. It is known as a species which can survive in such negative environmental conditions [13, 14]. Thus, it is a species continuously observed in the regions which are under the influence of continental climate. The Mediterranization process has an important place in the enrichment of Black Sea copepod fauna. This process was investigated in detail by Kovalev et al. (1998). A total of 60 copepod species originating from the Mediterranean Sea were identified. It was stated that among these species Microcalanus pusillus, Aetideus armatus, Euchaeta marina, Metridia lucens and Oncaea obscura species were new records for the straits region of the Black Sea between 1995 and 1997. Our study area lies within a region far from the straits. Not observing the species identified by Kovalev et al. (1998) in our region shows that the Eastern Black Sea region is not under the influence of Mediterranization.

Five copepod species, Calanus helgolandicus, Paracalanus parvus, Pseudocalanus elongatus, Acartia clausi and Oithona nana, were identified in a study performed in Inland Port of Sinop in the Black Sea [53]. In another study, again performed in Sinop in the Black Sea, a total of 27 zooplankton species were identified. Seasonal distribution and composition of zooplankton was comparatively investigated between 2002 and 2004. It was reported that six of the identified zooplankton species were in the copepod group [48]. Among these copepod species Calanus euxinus, Acartia clausi, Pseudocalanus elongatus, Paracalanus parvus and Centropages ponticus were identified in the South Eastern Black Sea coastal ecosystem. In our study, different to the species identified in the Black Sea, Oithona nana species were not encountered. However, Oithona similis species was identified. Oithona brevicornis species in the Northern Black Sea was reported as a new record in 2001 [55]. However, this species was not yet identified in the South Eastern Black Sea in field studies we have performed.

In our study, while mesozooplankton abundance belonging to 1999-2000 was lower, it was observed that average mesozooplankton abundance increased by a few times. This is parallel to the findings of Finenko et al. (2003). The pressure of M. leidyi on zooplankton was very high before 2000. After the 2000s, M. leidyi fed on zooplankton was brought under control by the introduction of B. ovata, which is the predator of M. leidyi, into the Black Sea ecosystem.  This situation brings about an increase in mesozooplankton amounts [41]. The increase after 2000 in general mesozooplankton abundance, particularly in copepod nauplii, observed in our study can be explained by Beroe ovata, which brought M. leidyi under control. The physical parameters revealing a dynamic structure during the year do not show big differences between years. It seems that the reason species composition and abundance differs with respect to years is food supply and prey-predator relationship.

When the density of Mnemiopsis declined in 1992–1993, zooplankton abundance began to rise. In 1996, the abundance of zooplankton, particularly copepoda which is the basic food for anchovy, increased significantly [39]. According to the data presented here, it is clearly seen that the increase in zooplankton abundance continued from 1996 to 2002 and copepod abundance reached the its peak level in 2002 reflecting the increase in the anchovy catch on the Turkish Black Sea fishery ( Fig 6). This period coincides with the highest anchovy catch in the Turkish Black Sea fishery. Anchovy were caught 385.000 tons during this period [44]. So it can be said that the anchovy catch is partly depends on to copepod abundance.

Figure 6

Figure 6. Anchovy production during the sampling period

It was reported that in the distribution of Calanus euxinus and Pseudocalanus elongatus in the Black sea that they are cold water species and started to reproduce in late autumn [1]. In our study, high abundance of Calanus euxinus and Pseudocalanus elongatus were determined in winter and at the beginning of spring. It was reported that these species, called cold water species were dominant in the upper part of the mixed layer of the Black Sea ecosystem and the abundance increased in the winter [52]. The species observed in the late summer and autumn blooms in the Eastern Black Sea are cladocera species, Acartia clausi and Oikopleura dioica. These species are called eurythermic mesozooplankton species. These species observed in the study area were also reported by Shiganova (2005) in offshore waters of the Black Sea. Additionally, blooms of Penilia avirostrist from cladoceras, Centropages ponticus from copepods and Sagitta setosa from Chaetognathas were observed in mid-summer and at the beginning of autumn. Since Oithona similis is a eurythermic species, high abundance was identified in all seasons. Paracalanus parvus, which is another eurythermic species, was identified in the sampling periods and in all seasons, except summer in the South Eastern Black Sea ecosystem.

According to our results, despite the species diversity changes, the most important mesozooplankton group in the region is copepoda. The cladocera group is seen only during the summer period. Calanus euxinus and Pseudocalanus elongatus have been specified as cold water species. The eurothermic species of Acartia clausi has been observed all year. In the light of the obtained data, the Mediterranization process has not been observed in the South Eastern Black Sea coastal ecosystem until 2006. It has been determined that South Eastern Black Sea region is affected in a similar way from the changes in the global scale. Monitoring studies should be given importance in order to put forth the dynamic structure of the ecosystem.

Acknowledgements

This study was supported by the Karadeniz Technical University Scientific Research Fund under project code 2003.117.001.4.  The authors also wish to thank the crew of R/V KTU DENAR-1 for their assistance in sampling.

 

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Table Legends

Table I. Average annual abundance of zooplankton species determined at the station of concern in 1999, 2000, 2001, 2002, 2005 and 2006 (individuals/m2).

table 1

 Table II. Seasonal distributions of Copepoda species with respect to years during the sampling period (ind/m2).

table 2

Figure Legends

Figure 1. Sampling station

Figure 2. Monthly average temperature (°C), salinity (‰) and density (sigma-t kgm-3) profiles in the Black Sea.

Figure 3. The variation in total mesozooplankton abundance and temperature with respect to years

Figure 4. Seasonal abundance values of the mesozooplankton groups of Copepoda, Cladocera, Chaetognatha, Appendicularia and Meroplankton species in 1999, 2000, 2001, 2002, 2005 and 2006 (ind/m2)

Figure 5. Similarity index values of the Copepoda group in 1999, 2000, 2001, 2002, 2005 and 2006

Figure 6. Anchovy production during the sampling period

figure 6

Figure 1.

 

figure 1

Figure 2.

figure 2

Figure 3.

figure 3

Figure 4.

figure 4

Figure 5.

figure 5

Figure 6.