Ecological Status of the Boka Kotorska Bay at Mariculture Areas, Montenegro

Aleksandra Huter1, Dragana Drakulović1, Branka Pestorić1, Danijela Joksimović1, Milica Mandić1

 

1 University of Montenegro - Institute of Marine Biology, Dobrota bb, Kotor, Montenegro; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

Abstract

During the investigated period, significant impacts of precipitation and freshwater input on temperature and salinity values were observed in most parts of the Boka Kotorska Bay. Freshwater input also had an impact on nutrient and chlorophyll concentration during the investigated period. The recorded values of phytoplankton are characteristic for oligo-mesotrophic areas. Species that are characteristic for nutrients enriched areas were also recorded. The presence of species that prefer areas rich in nutrients as well as the presence of toxic species, although in smaller numbers, indicate changes that should not be neglected.

Keywords: Boka Kotorska Bay, nutrients, phytoplankton, chlorophyll a.

Introduction

 

In comparison with other parts of the Adriatic Sea, The Boka Kotorska Bay represents a specific and unique environment, with its geographic position, abiotic and biotic environmental factors, and therefore also in the living world. The sea enters deep into the continent through two narrow channels (Kumbor and Verige), after which there is an open bay with an extension of about 36 km2, where the main shellfish farms are located.

Due to the surrounding karst relief, the bay can be considered as one of the main freshwater inputs in the southern Adriatic Sea (Bellafiore et al., 2011). During research conducted by Bellafiore et all. (2011) the bay was identified as a Region of Freshwater Influence. The freshwater input coming from the numerous sources present in the bay can strongly modify temperature, salinity and current patterns (Bellafiore et al., 2011).

Precipitation carries a large amount of suspended particles that affect the ecological conditions in sea water, like water color, translucency, salinity, density, etc.

During periods of massive/most intensive influx of terrestrial waters the surface sea water (0-2 m in depth) in the Bay of Kotor is characterized by very low salinity (3.24 ‰). The presence of terrestrial waters in the outer part of the Boka Kotorska Bay is considerably smaller, therefore, the decrease in salinity is less pronounced. During the summer months, when evaporation is high and inflow of land waters is significantly reduced, the maximum salinity values on the surface are: in the Bay of Kotor 35,46 ‰, in Bay of Tivat 37,39 ‰ and in the Bay of Herceg Novi 37,67 ‰. Variations in the bottom layers are less pronounced. For example, in the Kotor Bay, where the oscillations of salinity are largest in the surface layers, the difference between maximum and minimum salinity is 32.22 ‰, while in the deeper layers this difference is only 10.39 ‰ (Regner et al., 1998).

Transparency of seawater varies greatly and ranges from 3 m to 16 m (Regner et al., 1998). Transparency correlates with the density of phytoplankton, but can also be dependant on the amount of inorganic and organic particles, as well as the homogeneity of the upper layers.

Oceanographic conditions in the Boka Kotorska Bay depend on the submarine freshwater inputs as well as the degree of wind exposure. All of these factors influence the power and direction of surface currents as well as the bottom currents, and the vertical distribution of temperature and salinity.

Sea current streams can be divided into two layers, showing a surface outflow circulation and a bottom inflow circulation. The fresh water inflow causes estuarine circulation in the winter time, while winds cause the same during the summer months. However in the summer time, there is an equal possibility of inflow and outflow circulation in both layers. During the other parts of the year a clear two-layer streaming can be detected with outflow circulation in the surface layers and an equal and opposite current flowing along the bottom (Bellafiore et al., 2011).

 

Materials and Methods

Monitoring of the sea water quality for mariculture in the Boka Kotorska Bay implies monthly sampling of water at 11 farms (Figure 1). This paper presents results for the period from January 2016 to May 2016.

 

fig01
Figure 1: The Boka Kotorska Bay with marked samping locations.

 

  1. Institute of marine biology – IBM, Dobrota, Kotor Bay
  2. The mussel farm, Ljuta, Kotor Bay
  3. The oyster and mussel farm, Orahovac, Kotor Bay
  4. The seabream, seabass and mussel farm, Orahovac-Guskić, Kotor Bay
  5. The mussel farm, Lipci, Kotor Bay
  6. The mussel farm, Morinj, Kotor Bay
  7. The mussel farm Sv. Neđelja, Tivat Bay
  8. The mussel farm, Obala Đurašević, Tivat Bay
  9. The mussel farm, Ostrvo Cvijeća, Tivat Bay
  10. The mussel farm, Kukuljina, Tivat Bay
  11. The seabream and seabass farm, Stoliv, Kotor Bay

Seawater sampling for hydrographic analysis was carried out using a Niskin bottle (Hydro Bios, Germany) with a volume of 5 L at a depth of 0.5 m. The values of basic physical and chemical parameters were measured in situ using Multi Line 4 automatic probes, WTW, while the chemical parameters were determined by standard spectrophotometric methods. The basic physical and chemical parameters included: temperature, salinity, oxygen concentration, oxygen saturation, electroconductivity, transparency, pH, and determination of nutrient concentration (nitrite - NO2, nitrate - NO3, silicate - SiO4, phosphate - PO4, total phosphorus and total nitrogen). Absorbance was detected on a Perkin Elmer UV/VIS spectrophotometer (Lambda 2 – Markham, Canada), at a different wavelength for each nutrient.

Phytoplankton was sampled in January and April with 5 L Niskin bottles and then preserved in 250 ml bottles using a 2% neutralized formaldehyde solution. Cells were indentified and enumerated using a Leica DMI4000 B inverted microscope in subsamples of 25 ml after 24 h of sedimentation, following Utermӧhl (Utermöhl, 1958). Enumeration was carried out using phase contrast and bright field illumination at magnifications of 100, 200 and 630 x. The larger size fraction - microplancton (cells> 20μm) was analyzed to the species using the appropriate keys applied for this area (Cupp, 1943; Dodge, 1985; Hasle and Syvertsen 1996; Jorgensen1920). Microphytoplankton were used as indicators of eutrophication, both their presence and their density. Smaller size fraction - nanoplankton (cells <20μm) is shown as the total amount in the investigated positions. The amount of phytoplankton (microplancton and nanoplankton) is expressed through numerical values per the seawater volume unit (number of cells/L) at the investigated positions.

Photosynthetic pigments play a major role in biochemical processes in the marine environment. Chlorophyll a is often a measured biochemical parameter in oceanographic research because it reflects primary production and the degree of eutrophication in marine ecosystems.

Samples for concentration of chlorophyll a analysis were first filtered through Whatman GF/F filters ø 4.7 cm and 0.7 µm pore size, and then the pigment was extracted in 90 % acetone. Finally, chlorophyll a concentrations were determined on a Perkin Elmer spectrophotometer by measuring the absorbance at four wavelengths, and calculated according to Jeffrey et al (1997).

 

Results and Discussion

Analysis of basic physical parameters showed the seawater temperature in the surface layer ranged from 5.5ºC at Institute of Marine Biology Kotor (IMBK) station in January, up to 19.9ºC as the measured maximum at Sveta Nedjelja in May. Salinity values, as well as temperature varied depending on the sampling area as well as the sampling period. During the investigated period, there were numerous periods of rain, which had a significant effect on salinity. The lowest values of salinity were found at the Orahovac location (stations Orahovac-Cogi and Orahovac), 0.4 ‰ and 0.6 ‰, where a strong influence of fresh water inflow from underground sources and springs during the rainy season was observed. The values of salinity during the winter and spring months are shown in Figure 2 (a,b). During this period the oxygen concentration and saturation was uniform or slightly increased in relation to the usual values. Maximum oxygen value was measured at IMBK in April (12.53 mg/L). The maximum oxygen saturation was measured at the same station and was 132%. Increased oxygen concentration at most locations was the result of accelerated production in the upper water layers. The average water transparency was 7m, while the pH values ranged from 8.07 to 8.34.

 

fig02a     fig02b
Figure 2: Salinity values at samping stations during a) winter months and b) spring months.

 

In the winter period (January, February, March) the concentration of nutrients was higher than in the spring period (April, May). The measured values of nutrients in the surface layer were slightly increased. Maximum concentrations of nitrite ions were measured at locations in Tivat Bay, at the Ostrvo Cvijeća station, where the highest measured values of nitrite during the entire investigated period, reached up to 4.465 μmol/L (Figure 3. a). From January to March, due to high precipitation, the concentration of nitrate ions increased at Lipci where the maximum concentration was 187.67 μmol/L as well as at Orahovac where the value of nitrate ions reached 185.31 μmol/L during January (Figure 3. b).

 

fig03a     fig03b
Figure 3: Values of a) nitrite ions and b) nitrate ions at the samping stations.

 

At all the investigated stations the determined values of total nitrogen were uniform and the maximum was measured in January at the Tivat Bay station, Obala Đurašević (794.46 μmol / L). The highest concentrations of silicate ion were measured also in Tivat Bay, Ostrvo Cvijeća (1085.13 μmol/L in March and 623.14 μmol/L in January) and the lowest values were measured at Orahovac during April (86.22 μmol/L).

Phosphate concentration ranged from 0.414 μmol/L measured in February at the Obala Đurašević station with a maximum of 73.369 μmol/L measured in March at Ostrvo Cvijeća, which were the maximum recorded values of phosphate concentration in the Boka Kotorska Bay. Also the total phosphorus concentrations were the highest in Tivat Bay during the entire period of investigation. The maximum values were measured in January and May at Stoliv (22.95 μmol/L) and Ostrvo Cvijeća (23.03 μmol/L), while the lowest concentrations were measured at Orahovac during February (2.92 μmol/L).

The obtained results indicate that some of the stations (Ostrvo Cvijeća, Orahovac, Lipci), particularly pronounced during the winter time, had slightly or significantly higher nutrition values than other locations due to the large inflow of fresh water and abundant precipitation.

In January, the abundance of microplankton was very low and ranged from 102 to 103 cells/L. The highest abundance of the microplankton was at station Kukuljina (4.30 x 103 cells/L). Abundance of microplankton was higher in Tivat Bay compared to Kotor Bay. The lowest abundance of microplankton was at station IMBK, reached only 400 cells/L, as well as at stations Orahovac and Stoliv where were less than 440 cells/L. The highest abundance of nanoplankton - smaller phytoplankton fraction was at the Kukuljina (1.39 x 105 cells/L), while the lowest abundance was at the Orahovac-COGI station (8.46 x 104 cells/L) (Figure 4).

 

fig04
Figure 4: Abundance of microplankton and nanoplankton (number of cells/L) in the investigated areas in January 2016.

 

From the microplankton, diatoms were dominant at all stations. They were present throughout the whole year in phytoplankton assemblages. Diatoms were more abundant in a colder period, linking this phytoplankton group with a colder period of year, the period of lower salinity and temperature, while dinoflagellates dominate in a warmer period of the year as they prefer higher salinity and temperature and lower turbulence of water masses.

The highest abundance of diatoms were found in Kukuljina station (3.98 x 103 cells/L), where the microplankton was the most abundant, confirming that diatoms were the major part of microplankton assemblages. Increased number of diatoms was also at stations Lipci and Obala Đurašević (3.66 x 103 cells/L). The lowest abundance of diatoms was found at the Ostrvo Cvijeća (160 cells/L) (Figure 5). Dinoflagellates were less abundance in comparison to dominant diatoms and its highest abundance was found at station Ostrvo Cvijeća where reached to 440 cells/L. The lowest number of dinoflagellates was found at stations Dražin Vrt and Lipci where their number reached only 40 cells/L. Dinoflagellates were not recorded in Orahovac, Orahovac-COGI, Stoliv and Ljuta stations. Coccolithophorids and silicoflagellates have only been recorded on three stations (Ljuta, Lipci and Ostravo Cvijeća). At station Ostrvo Cvijeća, the abundance of coccolithophorids and silicoflagellates reached 160 cells/L (Figure 5).

 

fig05
Figure 5: The abundance of microplankton groups (diatoms, dinoflagellates, coccolitophorids and silicoflagellates) in the investigated areas during January 2016.

 

Of all diatoms dominated in January, the most abundant species were: Navicula spp., Pleurosigma elongatum, Pseudo-nitzschia spp., Thalassionema nitzschioides. The dominant dinoflagellates species were: Gyrodinium fusiforme, Prorocentrum micans, Tripos kofoidii. The species from the genus Pseudo-nitzschia spp. reached 103 cells/L, while the species from genus Navicula spp. and Thalassionema nitzschioides were present in almost all stations but not in high abundances. The dinoflagellate Prorocentrum micans reached the value of 240 cells/L, while the other species were present in lower density. Toxic dinoflagellates were not recorded.

Based on the results of the phytoplankton analysis for the April, the highest number of microplankton as the larger size fraction of phytoplankton assemblages was found at the IMBK station reached to 8.92 x 104 cells/L. The results of the phytoplankton analyses showed that in the Kotor Bay values of phytoplankton were higher than in the Tivat Bay. At Stoliv and Ljuta stations, the abundance of microplankton were higher and reached up to 6.69 x 104 cells/L and 6.73 x 104 cells/L respectively. The minimum recorded value of microplankton was found at the Sveta Nedjelja station where reached to 2.43 x 104 cells/L (Figure 6). Also, in Kotor Bay the values of nanoplankton (smaller size phytoplankton fraction) were usually higher compared to the Tivat Bay. The maximum abundance of nanoplankton was found at the IMBK station reached to 2.98 x 105 cells/L. Increased number of nanoplankton was also found at Stoliv and Lipci stations (2.48 x 105 cells/L and 2.52 x 105 cells/L respectively). The minimum abundance of nanoplankton was determined at the Sveta Nedjelja (1.89 x 105 cells/L) station where the microplankton abundance was the lowest (Figure 6).

 

fig06
Figure 6: Abundance of microplankton and nanoplankton (number of cells/L) in the investigated areas in April 2016.

 

Diatoms were dominant in almost all investigated area during April, with the exception of IMBK station where dinoflagellates dominated. The maximum value of the diatoms were found at Ljuta station (4.12 x 104 cells/L), while at the Obala Đurašević and IMBK stations it was also increased (3.3 x 104 cells/L and 3.19 x 104 cells/L respectively). The minimum abundance of diatoms was recorded at the Orahovac (1.75 x 104 cells/L), where microplankton was also lower. The dinoflagellates values were lower and ranged from 103 to 104 cells/L. The highest number of dinoflagellates was recorded at the IMBK station reached value of 5.73 x 104 cells/L, where it was the dominant group. The lowest number of dinoflagellates was found at the Sveta Nedjelja where the number of 1.56 x 103 cells/L was recorded. The number of coccolithophorids ranged from 103 to 104 cells/L. The highest number was recorded at the Stoliv station and was 1.41 x 104 cells/L. Coccolithophorids was not recorded at the IMBK station (Figure 7).

 

fig07
Figure 7: Abundance of microplanktonic groups (diatoms, dinoflagellates, coccolithophorids and silicoflagellates) in the investigated areas in April 2016.

 

Microphytoplankton (larger size fraction) were dominated by diatoms in all stations, while dinoflagellates were less abundant. Most of the diatoms species were represented by Chaetoceros affinis, Ch. diversus, Licmophora paradoxa, Melosira nummuloides, Navicula spp., Pleurosigma elongatum, Pseudo-nitzschia spp., and Thalassionema nitzschioides. Dominant species of the dinoflagellates were: Prorocentrum micans, Gymnodinium spp., Gonyaulax polygrama, Gyrodinium fusiforme and Tripos muelleri. Pseudo-nitzschia spp., Navicula spp., and Thalassionema nitzschioides were dominant in all positions, but species of Navicula spp. and Thalassionema nitzschioides were less abundant compared to the species Pseudo-nitzschia spp. The species Chaetoceros affinis and Ch. diversus, reachet up to 103 cells/L in positions where they were present. Dinoflagelate Prorocentrum micans was present in most positions and reached a number of 103 cells/L.

Toxic dinoflagellate Prorocentrum cordatum was present in almost all positions with a abundance of 104 cells/L (1.1 x104 cells/L at Lipci and Ljuta stations). Toxic dinoflagellate Dinophysis acuminata (up to 80 cells/L), D. acute (up to 40 cells/L), D. fortii (up to 40 cells/L) and Lingulodinium polyedra (up to 80 cells/L) were recorded in certain positions but in low abundance. Dinoflagellate species Gyrodinium fusiform was also found and reached up to 103 cells/L.

In January the concentration of chlorophyll a were very low in all examined stations. The minimum value was recorded at the IBM station (0.045 mg/m3), while the highest value was obtained at the Ostrvo Cvijeća station reached to 1.027 mg/m3. All investigated area can be classified into the lower or higher mesotrophic region according to the Siokou and Pagou (2000) classification specific for the region of the Eastern Mediterranean.

In February there was slightly higher value of chlorophyll a than in the previous month. Maximum concentration of chlorophyll a was measured at the IBM station in Kotor Bay where reached up to 3.219 mg/m3 classified this location as a eutrophic area. The minimum concentration of chlorophyll a was recorded at the Sveta Nedjelja station (0.746 mg/m3), Tivat Bay. During the period of abundant precipitation, and thus increasing of phytoplankton abundance as a result of the nutrient enrichment higher values of chlorophyll a concentrations are expected. According to Siokou and Pagou (2000), IBM and Ljuta stations belong to eutrophic areas, while other stations were highly mesotrophic (Figure 8).

 

fig08
Figure 8: Spatial distribution of chlorophyill a from January to April.

 

For the whole investigated period in Mart it was recorded the highest values of chlorophyll a concentration. A maximum value of 6,118 mg/m3 of chlorophyll a was recorded at Lipci and this station was classified as eutrophic area. Concentrations of chlorophyll a found in all stations were characteristic for eutrophication ecosystems, except Kukuljina station. Kukuljina was categorized into a highly mesotrophic area according to the categorization (Siokou and Pagou 2000).

The highest value recorded in April was at IBM station where reached up to 2.400 mg/m3 of chlorophyll a and only this area could be categorized as eutrophic zone. Most of the stations compared to the concentration of chlorophyll a are classified as higher mesotrophic areas, while the localities as Obala Đurašević and Kukuljina were the lower mesotrophic areas.

During the May there was two sampling periods (Figure 9). The investigated area, based on the concentration of chlorophyll a, showed mainly the characteristics of the eutrophic ecosystems (Siokou and Pagou 2000). The highest concentration of chlorophyll a were found at the IBM station where reached up to 5.221 mg/m3 (Figure 9). During the May the station Obala Đurašević indicated characteristics for the mesotrophic area more than the eutrophic area according to the categorization for the coastal areas of the Eastern Mediterranean (Siokou and Pagou 2000).

 

fig09
Figure 9: Spatial distribution of chlorophyill a at May.

 

During the researching period we did not found concentration of chlorophyll a characteristic for the oligotrophic areas.

According to the classification for the ecosystem status based on the concentration of chlorophyll a (Siokou and Pagou, 2000; Pagou,2000), total phytoplankton abundance and subsequently supplemented with concentration of nutrients by Ignatiades et al. (1992) and Karydis (1999) and aligned with the WFD (Simboura et al., 2005) water quality of coastal ecosystems in the Mediterranean can be described as high (up to 0.200 mg/m3), good (up to 0.400 mg/m3), moderate (up to 0.600 mg/m3), low (up to 2.100 mg/m3) and very low (over 2.100 mg/m3) quality.

Analysis of the chlorophyll a concentrations during January described the investigated area as lower to higher mesotrophic (Figure 10 b). During February and April sampling period, based on the measured chlorophyll a concentration the largest part of the Boka Kotorska Bay showed the characteristics of the mesotrophic area. According to concentration of chlorophyll a measured in March and May the bay was described mainly as eutrophic area (Figure 10 b). However, in Tivat Bay stations as Obala Đurašević and Kukuljina (Figure10 a) during the five-months showed concentrations of chlorophyll a below 2.100 mg/m3, that classified them as the better water quality sites compared to the other investigated area. The presented results of chlorophyll a are in accordance with previously reported for Zrmanja esuary (Burić et al., 2007) and for Boka Kotorska Bay (Krivokapić et al., 2011), where the peak of chlorophyll a was noticed in late winter and spring with increasing solar radiation and when the water column was rich with regenerated nutrients.

 

fig10a     fig10b
Figure 10: Box plot of chlorophyll a concentration a) by localities (1-IBMK, 2-Ljuta 3-Orahovac, 4-Orahovac-COGI, 5-Drazin vrt, 6-Lipci, 7-Sveta Nedjelja, 8-Obala Đurašević, 9-Ostrvo Cvijeća, 10-Uvala Kukuljina 11-Stoliv), b) by months.

 

Conclusions

During the investigated period a significantly lower values of water temperature and salinity were recorded at the most stations due to their specific position near the sources of fresh water and due to intensive precipitation.

According to values of chemical parameters in the period of January to May, aligned with the Statute for Classification and Categorization of Surface and Groundwater (official journal MNE, No. 2/07 of 29 October 2007), can be assumed that the quality of the seawater corresponded to the class of water that can be used for shellfish farming.

We were found that the abundance of phytoplankton varied depending on the external environment conditions. The abundance of phytoplankton was exceptionally low in January and reached a value of 103 cells/L, while in April the abundance of microplankton were higher and reached 104 cells/L. The observed values were characteristic for the oligo-mesotrophic areas (Kitsou and Karydis 2001, 2002). However a large number of dominant species (Chaetoceros affinis, Melosira nummuloides, Pseudo-nitzschia spp. and Thalassionema nitzschioides) were characteristic for areas rich in nutrients (Revelante and Gilmartin, 1980; 1985; Pucher-Petković and Marasović, 1980) as already been noticed in the Kotor Bay (Drakulović et al., 2010) with differences in a dominance of some species.

The presence of dinoflagellates is important because some are known to produce toxins. This study revealed toxic species as Dinophysis acuminata, D. acuta, D. fortii, Lingulodinium polyedra and Prorocentrum cordatum. This is serious because even at low concentrations of just over 103 cells/L, dinoflagellate Dinophysis spp is harmful for humans (Marcaillou-Le Baut et al., 1993). Also it should be emphasized increasing number of toxic dinoflagellates Prorocentrum cordatum with abundance of 1.1 x 104 cells/L. The presence of the phytoplankton species that prefer areas rich in nutrients and presence of potentially toxic and toxic species such as Pseudo-nitzschia spp and Dinophysis although still with a small abundance indicate changes that must not be neglected. Thus, in the future, this region may become a eutrophic area where toxicity events can be expected. In accordance with these results are the values of chlorophyll a, which are also indicate that the area had mesotrophic characteristics with the tendency to become the eutrophic during spring months.

 

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