The Sea of Marmara is an inland sea, located entirely within the borders of Turkey, which connects the Black Sea with the Aegean Sea through the Turkish strait system. The İstanbul and Çanakkale Straits provide a balance between the water supply and evaporation in the Sea of Marmara (Özsoy et al. 1995). The widest part (80 km) of the sea is located in the north-south direction and the longest one (280 km) in the east-west direction (Beşiktepe et al. 1994)
The Sea of Marmara has been the subject of various studies since the 18th century. The first study on benthic invertebrates inhabiting the Sea of Marmara was carried out by Forsskâl (1775), who reported
The objective of the study was to investigate the taxonomy and ecology of mollusk species inhabiting
The benthic material investigated in the present study was collected from the Sea of Marmara in 2012, at 14 sites at a depth ranging from 0.2 to 0.5 m (Fig. 1; Table 1). Samples were collected using a quadrate sampler 20 x 20 cm. At each site, three replicates were collected for community analysis and an additional water sample was collected for chemical analysis. The material was wet-sieved onboard using a 0.5 mm mesh and was stored in jars containing 4% seawater-formalin solution. In the laboratory, the material in jars was washed with water and the maximum height of the
Map of the study area
Coordinates, sampling dates, depth range and location of the sampling sites
Sites | Coordinates | Date | Depth (m) | Localities | |
---|---|---|---|---|---|
Latitude | Longitude | ||||
1 | 40°01.650'N | 26°19.950'E | 25.09.2012 | 0.2 | Çanakkale, Güzelyalı |
2 | 40°17.483'N | 26°36.933'E | 26.09.2012 | 0.2 | Çanakkale, Suluca |
3 | 40°08.000'N | 26°21.417'E | 06.10.2012 | 0.2 | Çanakkale, Havuzlar |
5 | 40°23.900'N | 26°52.633'E | 26.09.2012 | 0.2 | Çanakkale Şevketiye |
6 | 40°28.083'N | 27°16.250'E | 26.09.2012 | 0.2 | Karaburun |
7 | 40°35.617'N | 27°32.800'E | 28.09.2012 | 0.5 | Island of Marmara |
8 | 40°28.050'N | 27°42.583'E | 27.09.2012 | 0.2 | Erdek |
9 | 40°36.317'N | 27°40.067'E | 28.09.2012 | 0.5 | Island of Marmara |
13 | 40°32.417'N | 28°47.300'E | 30.09.2012 | 0.5 | Bozburun |
14 | 40°39.567'N | 29°09.200'E | 01.10.2012 | 0.2 | Koru |
19 | 41°01.117'N | 29°00.550'E | 03.10.2012 | 0.5 | Üsküdar |
24 | 40°57.917'N | 27°57.400'E | 04.10.2012 | 0.5 | Ereğli |
25 | 40°51.983'N | 27°27.633'E | 05.10.2012 | 0.5 | Kumbağ |
26 | 40°36.500'N | 27°05.817'E | 05.10.2012 | 0.5 | Şarköy |
The salinity, temperature and dissolved oxygen concentration were measured in the field using a SCT meter (YSI 100) and an oxygen meter (YSI 55). Water samples were collected for chemical analysis and transferred immediately to the laboratory. Nutrients, chlorophyll
Bellan Santini's dominance index (D, Bellan Santini, 1969) and Soyer's frequency index (F, Soyer, 1970), wet weight (total biomass value; B), Shannon-Weaver diversity (H'; Shannon & Weaver, 1949) and Pielou's evenness (J’; Pielou, 1975) indices were calculated for each species and each site. These community parameters were processed on the map using the SURFER software. The correlation between community parameters (number of species and individuals, total wet weight, diversity and evenness indices) and environmental parameters were determined by
Pearson's correlation analysis with a significance level of p & 0.05. Cluster analysis based on the Bray–Curtis similarity index (group average technique) was used to group the sampling sites. SIMPER analysis was applied to determine the percentage contribution of species to the similarity and dissimilarity within each group formed as a result of the cluster analysis. Canonical correspondence analysis (CCA) was carried out to analyze the relationship between the assemblages of mollusks and the environmental factors. Prior to the cluster analysis, the raw data were transformed using the transformation of yji = log (xji + 1). Monte Carlo permutations were applied to determine the significance of the ordination axes. The statistical analyses were carried out using PRIMER 6, STATISTICA 7.0 and Canoco 4.5 software packages.
The specimens identified in this study were deposited in the Museum of Faculty of Fisheries, Ege University (ESFM), İzmir, Turkey.
The analysis of the benthic material collected at 14 sites revealed a total of 30 mollusk species and 18 468 individuals belonging to three classes (Polyplacophora, Gastropoda and Bivalvia) (Table 2). The class Gastropoda was represented by the largest number of species and individuals (22 species and 7611 individuals), followed by Bivalvia (7 species and 10 854 individuals) and Polyplacophora (1 species and 3 individuals). The identified mollusk species belonged to 13 different families, of which Rissoidae, Mytilidae and Pyramidellidae were represented by the largest number of species: 10, 5 and 3, respectively
List of the species and total number of individuals at the study sites with their dominance (D%) and frequency values
K1 | K2 | K3 | K5 | K6 | K7 | K8 | K9 | K13 | K14 | K19 | K24 | K25 | K26 | D% | F% | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
POLYPLACOPHORA | ||||||||||||||||
Lepidochitona cinerea(Linnaéus, 1767) | 0.02 | 4.76 | ||||||||||||||
GASTROPODA | ||||||||||||||||
Steromphala adansonii(Payraudeau, 1826) | 38 | 0 | 10 | 23 | 68 | 124 | 8 | 12 | 24 | 4 | 17 | 0 | 129 | 3 | 2.49 | 66.67 |
Jujubinus striatus(Linnaéus, 1758) | – | – | 1 | 0.01 | 2.38 | |||||||||||
Tricolia pullus pullus(Linnaéus, 1758) | 17 | 2 | 4 | – | – | 15 | – | 29 | 12 | 2 | 1 | 2 | 149 | 89 | 1.74 | 45.24 |
Homalopoma sanguineum(Linnaéus, 1758) | – | – | – | – | – | – | 3 | – | – | – | – | – | – | – | 0.02 | 2.38 |
Bittium reticulatum(da Costa, 1778) | 10 | 18 | – | – | – | 5 | 1224 | 1 | – | – | – | – | 7 | 7 | 6.89 | 35.71 |
Cerithidium submammillatum(De Rayneval & Ponzi, 1854) | – | – | – | – | – | – | 245 | – | – | – | – | – | – | – | 1.33 | 2.38 |
3 | 0.02 | 2.38 | ||||||||||||||
41 | – | 43 | 0.45 | 11.90 | ||||||||||||
– | – | 1 | 0.01 | 2.38 | ||||||||||||
27 | 4 | 2 | – | – | 4 | 3 | – | – | – | – | – | – | – | 0.22 | 19.05 | |
– | – | – | – | – | – | 41 | – | – | – | – | – | – | – | 0.22 | 2.38 | |
54 | – | 7 | – | – | – | – | – | – | – | – | – | – | – | 0.33 | 9.52 | |
5 | 0.03 | 2.38 | ||||||||||||||
119 | 108 | 75 | 43 | 87 | 354 | 116 | 36 | 2648 | 22 | 14 | – | 835 | 566 | 27.20 | 85.71 | |
2 | 0.01 | 2.38 | ||||||||||||||
0.01 | 2.38 | |||||||||||||||
– | 2 | – | 3 | – | 11 | – | – | – | – | 1 | – | 0.10 | 16.67 | |||
– | – | – | 1 | 9 | – | – | – | – | – | – | – | – | – | 0.10 | 7.14 | |
– | – | – | – | – | – | – | 1 | – | – | – | – | – | – | 0.01 | 2.38 | |
– | – | – | – | 1 | – | – | – | – | – | – | – | 0.01 | 2.38 | |||
6 | – | 0.03 | 4.76 | |||||||||||||
– | – | – | – | – | – | 1 | – | – | – | 0.01 | 2.38 | |||||
BIVALVIA | ||||||||||||||||
1 | 0.02 | 4.76 | ||||||||||||||
11 | 22 | 1 | 10 | 32 | 8 | 98 | 1815 | 108 | 38 | 9 | 42 | 144 | 1113 | 18.69 | 71.43 | |
182 | 95 | – | 12 | 5 | 80 | 253 | – | 146 | 30 | 47 | 99 | 242 | 5784 | 37.77 | 69.05 | |
19 | 15 | – | 1 | 1 | 59 | 19 | 18 | 149 | 8 | 1 | – | 22 | 7 | 1.73 | 47.62 | |
90 | 1 | 5 | – | – | 4 | – | – | 2 | – | – | – | – | – | 0.55 | 19.05 | |
1 | 0.01 | 2.38 | ||||||||||||||
– | – | – | – | – | – | 3 | – | – | – | – | – | – | – | 0.02 | 4.76 | |
*– new record for the fauna of Mollusca in the study area |
The dominant species in the area were
According to the frequency index value, four species were found to have continuous distribution in the area. The most frequent species were
The mean number of species, the number of individuals, wet weight values and values of the diversity and evenness indices at the sampling sites are presented in Figures 2 and 3. Site K1 showed the highest mean number of species (11 species), followed by sites K8 (9 species) and K25 (7 species). Site K26 showed the highest mean mollusk density (63 083 ind. m~2), while the lowest mean density (758 ind. m–2) was found at site K19. The highest mean wet weight, i.e. biomass (34.3 g m–2), was recorded at site K8, followed by sites K25 (21.8 g m–2) and K9 (19.5 g m–2) (Fig. 2).
The mean number of mollusk species (S), the mean number of individuals per m2 (N) and the mean biomass of mollusks g m–2 (B) at the sampling sites
Mean values of the diversity index (H') and of the evenness index (J') at the sampling sites
The highest mean value of the diversity index (H' = 2.7) was determined at site K1 and the lowest one (H' = 0.5) – at site K9. The highest mean values of the
evenness index were determined at sites K1 and K19 (J' = 0.8), whereas the lowest ones at sites K5, K13 and K 26 (J' = 0.3) (Fig. 3).
Pearson's correlation analysis revealed that the values of the evenness index were negatively correlated with temperature (pr = –0.53) and pH (pr = –0.59), but positively correlated with Chla (pr= 0.69; p & 0.05; Table 3). There was also a correlation between the values of the diversity index, pH (pr= –0.55) and Chla (pr = 0.57; p & 0.05) (Table 3).
Pearson's correlation coefficients between the environmental variables and community parameters. Statistically significant values (
Number of species | Number of individuals | | Wet weight | Evenness index | Diversity index | |
---|---|---|---|---|---|
Salinity | 0.45 | –0.06 | –0.14 | 0.18 | 0.37 |
Temperature | 0.13 | 0.37 | 0.44 | –0.32 | |
Oxygen | 0.00 | 0.06 | 0.05 | –0.33 | –0.19 |
pHins | –0.18 | 0.40 | 0.35 | ||
Chla | 0.22 | –0.20 | –0.36 | ||
Total nitrogen | 0.05 | –0.18 | 0.23 | –0.27 | –0.03 |
Phosphorus | –0.01 | 0.48 | 0.06 | –0.31 | –0.26 |
Silicate | –0.07 | –0.27 | –0.20 | 0.44 | 0.16 |
Max. thallus height | 0.15 | 0.20 | 0.44 | 0.32 | 0.20 |
Epiphyte wet weight | 0.25 | 0.20 | 0.21 | –0.07 | –0.08 |
Algae wet weight | 0.01 | 0.05 | 0.16 | 0.05 | 0.08 |
Based on the Bray-Curtis similarity index, two species assemblage groups (A and B) were clustered with values higher than 50% (Fig. 4). Group A included sites K1 and K3 with an average similarity of 58% and group B comprised sites K8, K5, K6, K14, K19, K9, K2, K26, K13, K7 and K25, showing an average similarity of 64%.
Dendrogram indicating similarities and dissimilarities of the sampling sites
Species contributing most to the species assemblages of
Similarity | Dissimilarity | ||||
---|---|---|---|---|---|
Associations | A | B | A–B | A–K24 | B–K24 |
% similarity and dissimilarity | 58% | 64% | 53% | 76% | 54% |
13 | 14 | 9 | 16 | ||
10 | |||||
16 | 11 | ||||
8 | |||||
12 | 10 | 9 | |||
20 | |||||
17 | 9 | 8 | |||
13 | 14 | ||||
11 | 8 | 9 |
CCA showed that the environmental factors affect the distribution of the mollusk species (Table 5; Fig. 5). The first two canonical axes showed high values of correlation between the species and environment (r = 0.999 and 0.994 for axes 1 and 2). CCA axes 1 and 2 explained 30.8% and 25.5% of the relationship between the species and environment respectively, amounting to 56.3% in total. The Monte Carlo test showed that all canonical axes were statistically significant (F = 4.652;
Biplot of CCA performed on the total abundance of all species in samples and environmental variables (arrows): T – temperature; O – oxygen; pHi – pH; Chl
Results of canonical correspondence analysis. Statistically significant values (
Environmental variables | Axis 1 | Axis 2 |
---|---|---|
Temperature | –0.401 | |
Oxygen | 0.413 | 0.237 |
pH | –0.021 | –0.053 |
Chlorophyll |
–0.301 | 0.115 |
Total nitrogen | 0.555 | |
Phosphorus | –0.501 | 0.208 |
Silicate | 0.303 | –0.084 |
Maximum thallus height | –0.203 | |
Epiphyte wet weight | –0.047 | 0.039 |
Algal wet weight | –0.222 | |
Eigenvalues | 0.703 | 0.585 |
Species-environment correlations | 0.999 | 0.994 |
Cumulative percentage variance of species data | 29.6 | 54.2 |
Cumulative percentage variance of species-environment relation | 30.8 | 56.3 |
One of the findings of the present study is the rissoid
The present study is the first comprehensive work focusing on the mollusk species associated with
Due to the lack of detailed studies on the assemblages of mollusks inhabiting
Compared to other algae species
The findings of the present study are consistent with the results obtained by Russo (1997), Pitacco et al. (2014) and Chiarore et al. (2017), who found that the Gastropoda class was represented by the largest number of species and individuals, followed by Bivalvia and Polyplacophora. Similarly, Pitacco et al. (2014) indicated that Rissoidae and Mytilidae associated with
In the present study,
The present study showed a significant positive correlation between the values of the diversity and evenness indices and Chl
According to CCA, total nitrogen and temperature were important environmental variables contributing to the distribution of the mollusk species in the study area. These results are consistent with those reported by Kurt Şahin et al. (2017) and Açık (2017), who found positive correlations between soft-bottom polychaetes assemblages and sipunculans and temperature. According to Sánchez-Moyano et al. (2000), the assemblage of mollusks with macroalgae was correlated with organic matter. In addition, it is known that
In conclusion,