Introduction
As the most diverse members of the marine zooplankton are found in a wide range of environmental parameters, copepods play a significant role in the planktonic food web (Razouls et al., Reference Razouls, de Bovée, Kouwenberg and Desreumaux2019; Al-Mamun et al., Reference Al-Mamun, Akhtar, Rahman, AftabUddin and Modeo2020; Walter and Boxshall, Reference Walter and Boxshall2020). Despite their small size, they play a significant role in keeping water quality by controlling the growth of phytoplankton (Paturej and Kruk, Reference Paturej and Kruk2011). Population fluctuations of plankton depend on several environmental factors, including the monsoon as a prevailing wind and surface current (Srichandan et al., Reference Srichandan, Sahu, Panda, Baliarsingh, Sahu and Panigrahy2015).
The Chabahar Bay (Iran) is a small semi-tropical bay on the northeast coast of Gulf of Oman. Two distinct summer and winter monsoons and two inter-monsoonal periods (pre-monsoon [PRM] and post-monsoon [POM]), characteristic of the Asian monsoons (Wilson, Reference Wilson2000), affect the Arabian Sea and Gulf of Oman, including the coasts of Oman, Iran, Pakistan, and west coasts of India. Although the monsoons show a lower impact on the coasts of Iran (Caulfield, Reference Caulfield1990), it is associated with physical and chemical changes in the water.
The effects of environmental parameters on various aspects of zooplankton (Nour El-Din and AL-Khayat, Reference Nour El-Din and AL-Khayat2001; Smith and Madhupratap, Reference Smith and Madhupratap2005; Rezai et al., Reference Rezai, Amini and Kabiri2014; Al-Mamun et al., Reference Al-Mamun, Akhtar, Rahman, AftabUddin and Modeo2020; Amidi et al., Reference Amidi, Fatemi, Ghodousi and Javid2022) and copepods have been widely studied in various parts of Indian Ocean, including estuaries (Madhupratap, Reference Madhupratap1987; Paul et al., Reference Paul, Karan, Ghosh and Bhattacharya2019), various coastal regions of the Indian sub-continent (Saravanakumar et al., Reference Saravanakumar, Rajkumar, Serebiah and Thivakaran2007; Nawaz et al., Reference Nawaz, Sivakumar and Baskar2023), the Persian Gulf (Al-Yamani and Prusova, Reference Al-Yamani and Prusova2003; Al-Yamani and Khvorov, Reference Al-Yamani and Khvorov2007; Ali et al., Reference Ali, Al-Yamani and Khalaf2009), Arabian Sea and Gulf of Oman (Kazmi, Reference Kazmi2004; D'souza and Gauns, Reference D'souza and Gauns2018; Smith et al., Reference Smith, Criales and Schack2020), and exclusively Chabahar Bay (Fallahi et al., Reference Fallahi, Seraji and Dehghan2003; Peyghan et al., Reference Peyghan, Savari, Doustshenas, Sakhaee and Dehghan Madiseh2011; Fazeli et al., Reference Fazeli, Savari, Nabavi and Zare2013, Reference Fazeli, Zare, Nabavi and Sanjani2015; Hedayati et al., Reference Hedayati, Pouladi, Vazirizadeh, Qadermarzi and Mehdipour2017; Nazari et al., Reference Nazari, Mirshamsi, Sari, Aliabadian and Arbizu2018a, Reference Nazari, Mirshamsi, Sari and Aliabadian2018b). Going through the above literature, none of these has focused on the diversity and species richness of surface copepods in relation to the environmental factors, particularly in the Chabahar Bay, which has been dealt with in the current study, accordingly. In the present study, the changes of environmental parameters in different seasons on the distribution, density, abundance, and structure of the communities of surface copepods in Chabahar Bay have been investigated, and it is assumed that the environmental parameters, particularly temperature fluctuations, salinity, and pH, are the key factors in the distribution, abundance, and density of copepods.
Considered as a free zone, Chabahar Port is expected to develop further that may cause pollution. In addition to the lack of monitoring surveys in the Chabahar Bay, there is a need to gather environmental and biological data in this water body. This study aims to investigate the effects of regional development to provide ecological and taxonomic data for monitoring studies further.
Materials and methods
Study area
The Gulf of Oman is warm and mainly affected by the tropical climate due to its location in the north of the Tropic of Cancer. The Gulf of Oman is along the western side of the Arabian Sea in the northwestern part of the Indian Ocean. The surface waters of the Indian Ocean with relatively low salinity of the Gulf of Oman enter the Persian Gulf through the Strait of Hormuz. The surface waters of the Gulf of Oman are dominated by the oceanic water of the Indian Ocean, which flows along the coast of Iran mixed with some cool water transported during the northeast monsoon (NEM) from December to March. During June–September, upwelling continues along the southern coast of Oman (Arabian Sea), leading to a decrease in water temperature in the Gulf of Oman during summer. Chabahar Bay, located in southeast of Iran, has a moderate tropical climate with high relative humidity. The connection of Iran's waters to the Indian Ocean through the Gulf of Oman exposes the region to the monsoon winds of the Indian Ocean (Al-Hashmi et al., Reference Al-Hashmi, Piontkovski, Bruss, Hamza, Al-Junaibi, Bryantseva and Popova2019).
The zooplankton samples were collected during four periods, including December 2021 (POM), January 2022 (NEM), May 2022 (PRM), and September 2022 (southwest monsoon [SWM]). The sampling was conducted from the mid-night to dawn. Five stations (Figure 1) were selected in the Chabahar Bay based on costal activities such as vicinity to international port (st.1), local port (st.2), Tis fishing port (st.3), centre of Chabahar Bay as a less-disturbed location (st.4), and old fishing and goods port in the city coastal area (st.5). The geographical location of each was GPS marked (Table 1).
Figure 1. Sampling localities in Chabahar Bay, Gulf of Oman.
Table 1. Coordinates of each sampling locality in Chabahar Bay
Sampling method
The zooplankton samples were collected from the surface waters of Chabahar Bay using a Hydrobios® plankton net (30 cm aperture, 1.2 m total length, and 100 μm mesh size) equipped with a calibrated flowmeter for calculating the volume of filtered seawater. The net was towed horizontally at the water surface in five localities in the Chabahar Bay. All zooplankton samples (kept in 60 polyethylene containers of 300 cm3) were immediately fixed and preserved in a 4% solution of formaldehyde in seawater and then their volumes were adjusted to 300 ml (Omori and Ikeda, Reference Omori and Ikeda1984).
The environmental parameters including water surface temperature, salinity, pH, total dissolved solids (TDS), and dissolved oxygen (DO) were obtained in situ using a hand-held multiparameter probe Lutron® WA-2017SD for temperature, and ATi® R-pH instrument for other factors. At each station, water samples were collected in chlorophyll-a concentration. This was measured in a laboratory using a spectrophotometer UPLAB® at absorption wavelengths of 630, 647, and 664 nm following Jeffrey and Humphrey (Reference Jeffrey and Humphrey1975).
In the laboratory, three replicates of 1 ml plankton samples in preserving fluid from each locality and season were transferred into a counting cell instrument and copepod/zooplankton individuals were sorted and then counted under a compound microscope ZEISS and a stereomicroscope WILD M3. Only adult copepods were identified and named to the genus level. The zooplankton abundances were expressed as the number of individuals per cubic metre (ind. m−3) following Postel et al. (Reference Postel, Fock, Hagen, Harris, Wieb, Lenz, Skjoldal and Huntley2000). Identification of copepods was verified using available keys (Conway et al., Reference Conway, White, Hugues-Dit-Ciles, Gallienne and Robins2006; Al-Yamani et al., Reference Al-Yamani, Skryabin, Gubanova, Khvorov and Prusova2011; Prusova et al., Reference Prusova, Smith and Popova2011; Conway, Reference Conway2012; Richardson et al., Reference Richardson, Davies, Slotwinski, Coman, Tonks, Rochester, Murphy, Beard, McKinnon, Conway and Swadling2013). In the present study, the taxonomic nomenclature is adopted from the World Register of Marine Species (2024). The copepod diversity indices were calculated using the Shannon–Wiener diversity index ‘H′’ (Shannon and Wiener, Reference Shannon and Wiener1949), Margalef's species richness ‘D’ (Margalef, Reference Margalef1968), and Pielou's evenness ‘J′’ (Pielou, Reference Pielou1969).
Statistical analyses
To examine the normality of data, the Kolmogrov-Smirnov test was used. Then parametric tests were applied, as the data were normally distributed. Analysis of variance (ANOVA) using multiple comparison Tukey's b test was applied to find significant differences among mean annual abundances of copepod communities in and between each station and season using IBM SPSS Statistics software (Ver. 27). To determine the relationship between environmental parameters in different seasons and five sampling stations in the Chabahar Bay, principal component analysis (PCA) was performed. Temporal and spatial differentiation of the copepod communities among seasons and stations were visualized through non-metric multidimensional scaling (nMDS) and cluster analyses, which grouped copepod genera and assessed the similarities and differences between the stations and seasons of the year. Based on square root transformed genera abundances, the analysis used the Bray–Curtis similarity matrix to group season and stations. A similarity percentage contribution (SIMPER) analysis was performed for the observed differences of genera in different seasons and stations. The PCA, nMDS, cluster, and SIMPER analyses were performed using the PRIMER v6 statistical package (Clarke and Gorley, Reference Clarke and Gorley2006).
Results
Environmental factors
The environmental parameters (mean ± SE) in the Chabahar Bay in different seasons are presented in Table 2. The results revealed that the greatest average temperature was recorded in SWM (24.40 ± 0.13°C) and POM (24.40 ± 0.21°C) while the lowest was observed in NEM (22.60 ± 0.13°C) (N = 15; F = 31.294; P < 0.0005). The highest mean value of salinity was recorded in PRM (38.00 ± 0.00 psu) and the lowest was recorded in SWM (36.25 ± 0.07 psu) (N = 15; F = 76.99; P < 0.0005). The highest and lowest mean pH values were recorded as 8.17 ± 0.004 and 7.44 ± 0.12 in NEM and SWM, respectively (N = 15; F = 21.07; P < 0.0005). The highest and lowest mean DO values were recorded in NEM and SWM as 6.76 ± 0.13 and 3.60 ± 0.10 mg l−1, respectively (N = 15; F = 84.08; P < 0.0005). The highest and lowest mean TDS values were recorded in SWM and NEM as 56.93 ± 0.40 and 53.45 ± 0.46 mg l−1, respectively (N = 15; F = 20.90; P < 0.0005). The highest and lowest mean values of chlorophyll-a were recorded in POM and NEM as 0.89 ± 0.12 and 0.08 ± 0.01 μg ml−1, respectively (N = 15; F = 43.53; P < 0.0005). The results of ANOVA of environmental parameters in different seasons show that there is no significant difference between the average temperatures in SWM and POM, but there is a significant difference with other seasons (P < 0.0005). There is significant difference between the average salinity in pre-monsoon with other seasons (P < 0.0005). There is a significant difference between the average pH in NEM and other seasons (P < 0.0005). There is a significant difference between the average DO in NEM and other seasons (P < 0.0005). There is no significant difference between the average TDS in SWM, PRM, and POM, but there is a significant difference with NEM (P < 0.0005). Also, there is a significant difference between the average chlorophyll-a in POM and other seasons (P < 0.0005).
Table 2. Environmental parameter values (mean ± SE) in Chabahar Bay during the current survey
Unmatched letters in each column show a significant difference.
Zooplankton community composition
In the present study, 38 copepod genera were identified which belonged to five orders and 22 families. The results of the current survey revealed that the total population of zooplankton community was remarkably diverse and comprised of 66% copepods and 34% non-copepods (Figure 2).
Figure 2. Copepod community relative abundance (%) and other zooplankton groups in Chabahar Bay.
Abundance of copepods
The comparison of analyses of variances of mean copepod abundance showed the highest value as 393,005 ± 21,324 ind. m−3 in PRM (N = 469; F = 104.394; P < 0.0005). While in POM, the mean abundance of copepods was recorded as 38,792 ± 2339 ind. m−3 (N = 561; F = 104.394; P < 0.0005). In addition, the results of the ANOVA (Table 3) showed that there is a significant difference between the mean abundance of copepods in PRM and other seasons (P < 0.0005) (Table S1, Supplementary material).
Table 3. Mean abundance (ind. m−3) of copepods in different seasons in Chabahar Bay
N, number of individual of copepods.
The comparison of ANOVA of the five studied copepod orders showed that, regardless of copepod larvae, the highest annual mean abundance of copepods belongs to the Cyclopoida 291,266 ± 20,554 ind. m−3 (N = 835; F = 77.782; P < 0.0005) and Calanoida 261,497 ± 21,970 ind. m−3 (N = 1003; F = 77.782; P < 0.0005), while, the lowest mean abundance 794 ± 259 ind. m−3 (N = 3; F = 77.782; P < 0.0005) belongs to the Monstrilloida (Figure 3). The results of the ANOVA showed that there is no significant difference between the mean abundance of Cyclopoida and Calanoida, but there is a significant difference with other orders (P < 0.0005) (Table S2, Supplementary material).
Figure 3. Annual mean abundances (±SE) of different orders of copepods in Chabahar Bay.
The results of ANOVA among copepod orders in different seasons indicated that, regardless of copepod larvae, in POM the Calanoida with 16,005 ± 731 ind. m−3 (N = 231; F = 97.948; P < 0.0005) and Cyclopoida with 15,517 ± 1481 ind. m−3 (N = 258; F = 97.948; P < 0.0005) presented the highest mean abundance. Similarly, in the NEM, Cyclopoida with 85,808 ± 5900 ind. m−3 (N = 245; F = 105.772; P < 0.0005), in PRM, Cyclopoida with 141,205 ± 10,495 ind. m−3 (N = 173; F = 58.717; P < 0.0005), and in SWM, Calanoida with 75,993 ± 7441 ind. m−3 (N = 267; F = 51.872; P < 0.0005) demonstrated greater mean values (Figure 4). The results of the ANOVA showed that there is no significant difference between the mean abundance of Calanoida and Cyclopoida in POM, but there is a significant difference with other orders in this season (P < 0.0005). Also, there is a significant difference between the mean abundance of the Cyclopoida and other orders in the NEM and PRM. In the SWM, there is a significant difference between the mean abundance of the Calanoida and other orders (P < 0.0005) (Table S3, Supplementary material).
Figure 4. Mean abundance ± SE of different orders of copepods in different seasons in Chabahar Bay. POM, post-monsoon; NEM, northeast monsoon; PRM, pre-monsoon; SWM, southwest monsoon.
The comparison of differences in the mean abundance of copepod orders in different stations revealed that regardless of the copepod larvae, in the st.1 Cyclopoida with 120,643 ± 9952 ind. m−3 (N = 204; F = 67.128; P < 0.0005) and Calanoida with 109,568 ± 6963 ind. m−3 (N = 285; F = 67.128; P < 0.0005), in the st.2 Cyclopoida with 51,055 ± 4721 ind. m−3 (N = 173; F = 28.729; P < 0.0005), in the st.3 Cyclopoida with 54,943 ± 4377 ind. m−3 (N = 180; F = 70.129; P < 0.0005) and Calanoida with 46,404 ± 2700 ind. m−3 (N = 222; F = 70.129; P < 0.0005) were dominant. While, in the st.4 Calanoida with 32,307 ± 3931 ind. m−3 (N = 172; F = 39.016; P < 0.0005) and Cyclopoida with 24,812 ± 1101 ind. m−3 (N = 125; F = 39.016; P < 0.0005) and in st.5 Calanoida with 43,193 ± 3960 ind. m−3 (N = 176; F = 74.739; P < 0.0005) and Cyclopoida with 39,814 ± 2040 ind. m−3 (N = 153; F = 74.739; P < 0.0005) represented the highest mean abundance (Figure 5). The results of the ANOVA showed that in st.1 and st.3, there is no significant difference between the mean abundance of Cyclopoida and Calanoida, but there is a significant difference with other orders in these two stations (P < 0.0005). In st.2, there is a significant difference between the mean abundance of Cyclopoida and other orders (P < 0.0005). In st.4 and st.5, there is no significant difference between the mean abundance of Calanoida and Cyclopoida, but there is a significant difference with other orders in these two stations (P < 0.0005) (Table S4, Supplementary material).
Figure 5. Mean abundance ± SE of different orders of copepods in different stations in Chabahar Bay.
The comparison of means among copepod family members using ANOVA showed that, regardless of copepod larvae, the highest annual mean abundances were belonged to Oithonidae with 167,382 ± 11,089 ind. m−3 (N = 344; F = 147.324; P < 0.0005), Paracalanidae 73,777 ± 4487 ind. m−3 (N = 273; F = 147.324; P < 0.0005), Corycaeidae 59,823 ± 4229 ind. m−3 (N = 228; F = 147.324; P < 0.0005), and Temoridae 52,250 ± 3691 ind. m−3 (N = 166; F = 147.324; P < 0.0005). However, the lowest abundance values with 794 ± 259 ind. m−3 belonged to the Monstrillidae (N = 3; F = 147.324; P < 0.0005) (Figure S1, Supplementary material). The results of the ANOVA showed that there is no significant difference between the mean abundance of the Paracalanidae and Corycaeidae, as well as the Corycaeidae and Temoridae, but there is a significant difference between other families (P < 0.0005) (Table S5, Supplementary material).
The results of ANOVA in different seasons, by combining the all stations data, showed that regardless of copepod larvae, in POM, the Paracalanidae with 9099 ± 529 ind. m−3 (N = 73; F = 93.391; P < 0.0005; Figure S2A, Supplementary material), in NEM, Oithonidae with 52,061 ± 3817 ind. m−3 (N = 101; F = 178.836; P < 0.0005; Figure S2B, Supplementary material), in PRM, Oithonidae with 89,836 ± 4540 ind. m−3 (N = 85; F = 140.772; P < 0.0005; Figure S2C, Supplementary material) and in SWM, Temoridae with 21,068 ± 1962 ind. m−3 (N = 48; F = 37.264; P < 0.0005), Oithonidae with 20,105 ± 2318 ind. m−3 (N = 60; F = 37.264; P < 0.0005) (Figure S2D, Supplementary material) presented the highest mean abundance. The results of the ANOVA showed that there is no significant difference between the mean abundance of Temoridae and Oithonidae in SWM but there is a significant difference with others (P < 0.0005). Also, there is a significant difference between the mean abundance of dominant families with others (P < 0.0005) (Table S6, Supplementary material).
The comparison of the mean abundance of copepod families in different stations showed that, regardless of copepod larvae, the Oithonidae presented the highest values as follows: in st.1 (Figure S3A, Supplementary material) with 73,641 ± 4759 ind. m−3 (N = 74; F = 111.479; P < 0.0005), in st.2 (Figure S3B, Supplementary material) with 25,234 ± 1276 ind. m−3 (N = 70; F = 76.227; P < 0.0005), in st.3 (Figure S3C, Supplementary material) with 31,083 ± 3301 ind. m−3 (N = 78; F = 65.196; P < 0.0005), in st.4 (Figure S3D, Supplementary material) with 11,697 ± 839 ind. m−3 (N = 48; F = 38.591; P < 0.0005), and in st.5 (Figure S3E, Supplementary material) with 25,727 ± 1376 ind. m−3 (N = 74; F = 119.607; P < 0.0005). Also, the results of the ANOVA showed that there is a significant difference between the mean abundance of the Oithonidae with other families in stations (P < 0.0005) (Table S7, Supplementary material).
Comparison of ANOVA of means among different genera of copepods showed that, regardless of copepod larvae, the greatest annual mean abundance (Figure 6) belongs to the genera Oithona with 167,382 ± 11,089 ind. m−3 (N = 344; F = 202.964; P < 0.0005), Temora with 52,250 ± 3691 ind. m−3 (N = 166; F = 202.964; P < 0.0005), Paracalanus with 40,041 ± 2256 ind. m−3 (N = 142; F = 202.964; P < 0.0005), Acartia with 34,822 ± 3876 ind. m−3 (N = 115; F = 202.964; P < 0.0005), Euterpina with 34,313 ± 1542 ind. m−3 (N = 54; F = 202.964; P < 0.0005), and Oncea with 34,033 ± 2951 ind. m−3 (N = 137; F = 202.964; P < 0.0005). While the lowest value with 794 ± 259 ind. m−3 (N = 3 F = 202.964; P < 0.0005) belonged to the genus Cymbasoma. The results of the ANOVA showed there is a significant difference between the mean abundance of Oithona and Temora with other genera (P < 0.0005). There is no significant difference between the mean abundance of Paracalanus, Acartia, Euterpina, and Oncea genera, but there is a significant difference with other genera (P < 0.0005) (Table S8, Supplementary material).
Figure 6. Annual mean abundance ± SE of different copepod families in Chabahar Bay.
The results of ANOVA, by combining all the stations data in different seasons, showed that regardless of copepod larvae in POM the genus Paracalanus with 6135 ± 42 ind. m−3 (N = 42; F = 68.861; P < 0.0005), Oithona with 5380 ± 553 ind. m−3 (N = 98; F = 68.861; P < 0.0005) (Table 4) showed the highest mean abundance. In the NEM, the highest mean abundance belonged to the genus Oithona with 52,061 ± 3817 ind. m−3 (N = 101; F = 186.097; P < 0.0005). The genus Oithona with 89,836 ± 4540 ind. m−3 (N = 85; F = 169.026; P < 0.0005) had the highest mean abundance in PRM, and in SWM, genus Temora with 21,068 ± 1962 ind. m−3 (N = 48; F = 42.293; P < 0.0005) and Oithona with 20,105 ± 2318 ind. m−3 (N = 60; F = 42.293; P < 0.0005) represented the highest mean abundance. The results of ANOVA test showed that there is no significant difference between the mean abundance of Paracalanus and Oithona in POM but there is a significant difference with other genera in this season (P < 0.0005). In NEM and PRM, there is a significant difference between the genus Oithona and other genera (P < 0.0005). Also, in SWM, there is no significant difference between Temora and Oithona genera, but there is a significant difference with other genera in this season (P < 0.0005) (Table S9, Supplementary material).
Table 4. Annual mean abundance ± SE (ind. m−3) of different genera of copepods in different seasons in Chabahar Bay
POM, post-monsoon; NEM, northeast monsoon; PRM, pre-monsoon; SWM, southwest monsoon.
The comparison of differences of the mean abundance of copepod genera in different stations, ANOVA analyses showed that, regardless of copepod larvae, the genus Oithona in st.1 (Table 5) with 73,641 ± 4759 ind. m−3 (N = 74; F = 136.545; P < 0.0005), in st.2 with 25,234 ± 1276 ind. m−3 (N = 70; F = 81.877; P < 0.0005), in st.3 with 31,083 ± 3301 ind. m−3 (N = 78; F = 70.048; P < 0.0005), in st.4 with 11,697 ± 839 ind. m−3 (N = 48; F = 40.276; P < 0.0005), and in st.5 with 25,727 ± 1376 ind. m−3 (N = 74; F = 132.005; P < 0.0005) presented the highest mean abundances. The results of ANOVA showed that there are significant differences between the mean abundance of the genus Oithona and other genera of copepods in different stations (P < 0.0005) (Table S10, Supplementary material).
Table 5. Annual mean abundance ± SE (ind. m−3) of different genera of copepods in five stations in Chabahar Bay
Biodiversity indices
In the study of biodiversity indices, the results showed that the highest mean Shannon–Wiener diversity index (H′) values were observed in SWM (2.80 ± 0.04) and POM (2.65 ± 0.06), while the lowest values were calculated in NEM (2.33 ± 0.05) and PRM (2.39 ± 0.09) (N = 15; F = 10.94; P < 0.0005). The highest mean Margalef species richness indices (D) were observed in POM (2.23 ± 0.11) and SWM (2.09 ± 0.08). The lowest value (1.63 ± 0.14) was recorded in PRM (N = 15; F = 5.64; P < 0.002). The highest mean Pielou's evenness (J′) were calculated (Table 6) in SWM (0.90 ± 0.01) and POM (0.88 ± 0.01). The lowest value was calculated in NEM (0.76 ± 0.01) (N = 15; F = 37.22; P < 0.0005). The results of ANOVA showed that there is no significant difference between the mean Shannon–Wiener diversity index in SWM and POM, but there is a significant difference with NEM and PRM (P < 0.0005). There is no significant difference between the means of Margalef species richness indices in POM and SWM, but there is a significant difference in PRM (P < 0.002). There is no significant difference between the mean Pielou's evenness in POM and SWM, but there is a significant difference in PRM and NEM (P < 0.0005) (Table S11, Supplementary material).
Table 6. Biodiversity indices (mean ± SE) of copepods in different seasons at Chabahar Bay
S, total genera; H', Shannon–Wiener diversity index; D, Margalef's species richness; J′, Pielou's evenness.
Unmatched letters in each column indicate a significant difference.
Relationship between environmental parameters and copepod communities
The PCA revealed that the first two axes explained 65.8% of the total variation in environmental parameters, including temperature, salinity, DO, pH, TDS, and chlorophyll-a. The PCA results indicate that salinity was the most influential factor at the first station during the POM period, while chlorophyll-a had the greatest impact at the second and third stations. Both salinity and chlorophyll-a were the most significant factors at the fourth and fifth stations during POM. During the NEM, DO exerted a greater influence at all stations. In the PRM and SWM, salinity and TDS were the most important factors in the five stations, respectively (Figure 7).
Figure 7. PCA results based on environmental parameters in different seasons and stations in Chabahar Bay. P, post-monsoon; N, northeast monsoon; R, pre-monsoon; S, southwest monsoon. 1, st.1; 2, st.2; 3, st.3; 4, st.4; 5, st.5.
The relationship between environmental parameters and the most abundant copepod genera (Oithona, Temora, Paracalanus, Acartia, Euterpina, and Oncea) in different seasons is shown in Figure 8. The first two axes of the PCA express 85.2% of the overall changes in environmental parameters (temperature, salinity, DO, pH, TDS, and chlorophyll-a) in relation to these genera. The PCA results indicate that, during the PRM, salinity had the greatest influence on these genera.
Figure 8. PCA based on the relationship between environmental parameters and the most abundant studied genera in different seasons in Chabahar Bay. P, post-monsoon; N, northeast monsoon; R, pre-monsoon; S, southwest monsoon. Ac, Acartia; Pa, Paracalanus; Te, Temora; On, Oncea; Oi, Oithona; Eu Euterpina.
Cluster analysis and nMDS were employed to examine the similarity of copepod community abundance across different stations and seasons, as depicted in Figure 9. The cluster analysis revealed the highest degree of similarity (82.58%) between st.1 and st.4 during the NEM. Additionally, the nMDS analysis yielded a stress level of 0.06, indicating an excellent correspondence between the stations across different seasons.
Figure 9. Cluster analysis (A) and nMDS ordination plot (B) illustrating the spatial differentiation of copepod communities in different seasons and stations in Chabahar Bay. P, post-monsoon; N, northeast monsoon; R, pre-monsoon; S, southwest monsoon.
SIMPER analysis based on genera abundance data showed that the similarity between stations is mainly caused by the Paracalanus (contribution: 22.23%), Copilia (contribution: 11.18%), Bestiolina (contribution: 9.34%), and Agetus (contribution: 6.32%) in POM (1.27% average similarity). The similarity between the stations is due to the Clausocalanus (contribution: 24.54%), Oncaea (contribution: 12.95%), Pseudodiaptomus (contribution: 9.16%), and Copilia (contribution: 8.39%) in NEM (14.26% average similarity). The similarity between stations is because of Typhlamphiascus (contribution: 3.78%), Microsetella (contribution: 3.78%), Acartia (contribution: 3.72%), and Paramphiacella (contribution: 3.72%) in PRM (73.29% average similarity). The similarity between stations is due to the genera Cosmocalanus (contribution: 9.89%), Pontella (contribution: 9.26%), Cymbasoma (contribution: 6.31%), and Amphiascopsis (contribution: 5.72%) in SWM (35.42% average similarity) (Table 7).
Table 7. SIMPER analysis: contribution (%) of the most representative genera to similarity between seasons
Discussion
Environmental factors
The water quality of the Chabahar Bay has been affected by several factors in recent decades as a result of anthropogenic activities (Burt et al., Reference Burt, Coles, Lavieren, Taylor, Looker and Samimi-Namin2016; Agah et al., Reference Agah, Saleh and Jalili2021). By measuring the environmental parameters at the sampling site, differences in the abundance of zooplanktons are observed (Kang et al., Reference Kang, Hyun and Shin2010). Previous studies showed that physical and chemical factors such as temperature and salinity are related to changes in the abundance of zooplanktons. The effect of these factors on the abundance and diversity of zooplanktons has been demonstrated in several studies (ROPME, 2003, 2004; Tajevidi et al., Reference Tajevidi, Manochehri and Shapouri2015).
Temperature fluctuations as a fundamental feature of water conditions are important in regulating many physiological processes of marine organisms and therefore it is one of the most important characteristics of water quality in aquaculture (IEPA, 2001), as it controls water metabolism, and it determines the aquatic habitat area (Ding and Elmore, Reference Ding and Elmore2015). Due to the change in pH, salinity, and DO values in the waters of seashores, both in terms of time and geography, it is not possible to provide fixed guideline values for temperature (Agah et al., Reference Agah, Saleh and Jalili2021).
In the current study, the highest mean temperatures were recorded in SWM (24.40 ± 0.13°C) and POM (24.40 ± 0.21°C), while the lowest mean temperature was recorded in NEM (22.60 ± 0.13°C). In the previous studies conducted in the Chabahar Bay by Bordbar et al. (Reference Bordbar, Nasrolahi, Lorenz, Moghaddam and Burchard2024), the lowest (16°C) and highest (34°C) water surface temperature values were recorded in February and June, respectively. In another study, Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021) recorded the elevated temperature (33°C) in the SWM due to the weak thermal stratification caused by the monsoon waves and the high turbulence of the water. This thermal stratification occurs during POM and later disappears in NEM as a result of lower water surface temperature owing to vertical mixing.
In a study of Agah et al. (Reference Agah, Saleh and Jalili2021), the average temperature values were between 25.5 and 26.6°C in the Chabahar Bay in PRM and POM, respectively. Also, the results showed that the surface water temperature changes in PRM and POM inside the Chabahar Bay were relatively higher than other stations, which can be attributed to the less water exchange in the mouth of the semi-closed bay. According to the report of NOAA Coral Reef Watch (2019), the minimum and maximum annual changes in sea surface temperature in Chabahar Bay in 2017 were observed in February (22.8°C) and June (30.3°C) with an average of 25.7°C.
According to the results of the current study, the highest mean value of salinity was found in PRM (38.00 ± 0.00 psu) and the lowest in SWM (36.25 ± 0.07 psu). According to Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021), salinities fluctuate in Chabahar Bay, especially in hot seasons, which is affected by evaporation rate due to shallow depth, semi-closed environment, and limited water flow. In several studies, the measured salinity in Chabahar Bay was between 36.7 and 36.9 psu (Fazeli et al., Reference Fazeli, Marnani, Sanjani, Zare, Dehghana and Jahani2010), 36.6 and 36.7 psu (Agah et al., Reference Agah, Saleh and Jalili2021), and in the Omani waters (Emara, Reference Emara2010) in February and March at 36.7 psu.
The pH is an important indicator of water quality. The ideal pH for biological productivity is between 6.8 and 8.5 (CCME, 2003), and pH values less than 4 are harmful to aquatic life (Abowei, Reference Abowei2010). Seasonal changes in atmospheric carbon dioxide and phytoplankton activities can affect pH changes in different seasons (Agah et al., Reference Agah, Saleh and Jalili2021). The highest and lowest mean pH values in the present study were recorded in the NEM and SWM as 8.17 ± 0.004 and 7.44 ± 0.12, respectively. Similarly, Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021) reported that the lowest pH values were recorded in SWM which agree with the current study findings. In a study by Agah et al. (Reference Agah, Saleh and Jalili2021), the average pH value POM in Chabahar Bay was 8.18. Also, in a study by Fazeli et al. (Reference Fazeli, Savari, Nabavi and Zare2013), the highest (8.4) and lowest (8.2) pH values were reported in Chabahar Bay in NEM and SWM, respectively.
Low levels of DO are known as one of the main factors for the survival of fauna and flora in aquatic environments (Friedrich et al., Reference Friedrich, Janssen, Aleynik, Bange, Boltacheva, Çagatay, Dale, Etiope, Erdem, Geraga, Gilli, Gomoiu, Hall, Hansson, Holtappels, Kirf, Kononets, Konovalov, Lichtschlag, Livingstone, Marinaro, Mazlumyan, Naeher, North, Papatheodorou, Pfannkuche, Prien, Rehder, Schubert, Soltwede, Sommer, Stahl, Stanev, Teaca, Tengberg, Waldmann, Wehrli and Wenzhöfer2014). The highest and lowest mean DO values were recorded in NEM and SWM as 6.76 ± 0.13 and 3.60 ± 0.10 mg l−1, respectively. Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021) showed that DO values exhibit an increasing trend from spring to autumn. In the autumn, as stated by Naqvi (Reference Naqvi2006), with a decrease in temperature and the later weakening of thermal stratification, the blooming of phytoplankton occurs and accordingly the amount of DO increases. In the summer because of seasonal stratification, according to Al-Azri et al. (Reference Al-Azri, Piontkovski, Al-Hashmi, Goes and Do Gomes2010), it leads to a decrease in oxygen concentration and hypoxic conditions in different areas of the Gulf of Oman. A study of Abedi et al. (Reference Abedi, Seyfabadi, Saleh and Sari2022) showed the negative effect of hypoxia conditions in the summer on the abundance of mesozooplanktons in the Gulf of Oman.
In a study of Agah et al. (Reference Agah, Saleh and Jalili2021), the amount of DO in the water surface of Chabahar Bay was between 6.6 and 6.13 mg l−1 in POM, which was considered to be moderate to maintain aquatic biodiversity. In general, organic waste and other inputs of nutrients from wastewater, industrial, and agricultural discharges can lead to a decrease in oxygen levels in some marine areas (Khan and Mohammad, Reference Khan and Mohammad2014).
According to previous studies (Mohanty et al., Reference Mohanty, Sahu, Singhasamanta, Mahapatra, Panigrahy, Satpathy and Sahu2010; Al-Mamun et al., Reference Al-Mamun, Akhtar, Rahman, AftabUddin and Modeo2020), the seasonal and spatial changes of environmental factors such as TDS and DO have a key role in the seasonal cycle of zooplanktons, especially the composition and distribution of copepods. In the current study, the highest and lowest mean TDS values were recorded in SWM and NEM as 56.93 ± 0.40 and 53.45 ± 0.46 mg l−1, respectively. This is in agreement with the measured data of TDS in summer (37.06–36.6) and winter (35.7–32.64) by Amidi et al. (Reference Amidi, Fatemi, Ghodousi and Javid2022) in the northwestern and eastern Indian Ocean.
The highest and lowest mean values of chlorophyll-a were recorded as 0.89 ± 0.12 and 0.08 ± 0.00 μg ml−1 in POM and NEM, respectively. In a study by Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021), high levels (1.90–3.77) of chlorophyll-a in PRM and POM correspond to algal bloom, which is consistent with the findings of the current study. Also, in a study of Agah et al. (Reference Agah, Saleh and Jalili2021), the highest chlorophyll-a value was recorded at the level of 0.64 μg ml−1. In some studies (Al-Azri et al., Reference Al-Azri, Piontkovski, Al-Hashmi, Goes and Do Gomes2010; Piontkovski et al., Reference Piontkovski, Al-Azri and Al-Hashmi2011; Polikarpov et al., Reference Polikarpov, Saburova and Al-Yamani2016; Bordbar et al., Reference Bordbar, Nasrolahi, Lorenz, Moghaddam and Burchard2024) the high chlorophyll levels in the autumn correspond to the runoff after the SWM. In the analysis of the results of satellite data in the western parts of Gulf of Oman in 1997–2008, it was shown that the highest concentration of chlorophyll-a was in February during NEM and in July–September during SWM. In PRM, as shown by Piontkovski et al. (Reference Piontkovski, Al-Azri and Al-Hashmi2011), due to the lower density of phytoplankton, the concentration of chlorophyll-a was low.
Zooplankton community composition
In the current study, the seasonal diversity and spatiotemporal fluctuations of surface copepods of Chabahar Bay were investigated. As this study focuses exclusively on surface copepods, consequently certain zooplankton and copepod species may be underrepresented, and their distribution patterns cannot be comprehensively explored in this paper.
This resulted in the identification of five orders, 22 families, and 38 genera of copepods. Here, we reported higher diversity, compared to Fazeli et al. (Reference Fazeli, Zare, Nabavi and Sanjani2015) in which 20 genera were identified. This is possibly related to sampling at dark with more localities in the current study. In the current study, 66% of the total zooplankton community belonged to copepods and 34% to non- copepods. This is nearly similar to previous studies by Loqmani et al. (Reference Loqmani, Zabihi and Attaran Fariman2019) in Chabahar Bay.
Abundance of copepods
According to the results of the current study, the highest mean abundance of copepods was obtained in PRM. In another study at the Persian Gulf (Mohsenizadeh et al., Reference Mohsenizadeh, Haghshenas and Rabbaniha2016), the peak abundance of copepods was seen in spring and winter in Nayband Bay. In a study of Dos Santos et al. (Reference Dos Santos, Marques and Pires2023), the peak abundance of copepods in the northeastern Atlantic Ocean was also shown in spring. According to Al-Busaidi and Claereboudt (Reference Al-Busaidi and Claereboudt2023), variation in the number of copepods is possibly under the influence of factors such as plankton net mesh size, netting technique (vertical, horizontal, or oblique), nature of sampling sites (open water, semi-enclosed bay, or estuarine system), number of sampling sites, boat speed, and the number of samples.
In the current study, among the 38 genera of recorded copepods, 11 families and 17 genera belonged to Calanoida, five families and nine genera to Cyclopoida, four families and ten genera to Harpacticoida, one family and one genus to Monstrilloida, and one family and one genus to Canuelloida. In a study of Al-Busaidi and Claereboudt (Reference Al-Busaidi and Claereboudt2023) in the Gulf of Oman, the total number of copepod species was 50, of which 38 species belonged to Calanoida. While in the Arabian Sea, there were 57 copepod species, of which 44 (43%) were calanoids. Here in Chabahar Bay, 66 species of copepods were identified by Fazeli et al. (Reference Fazeli, Zare, Nabavi and Sanjani2015), of which 34 were calanoid species. In a previous study (Fazeli et al., Reference Fazeli, Savari, Nabavi and Zare2013), 48 copepods were recorded in Chabahar Bay, of which 32 species belonged to calanoids.
In Blanco-Bercial et al.'s (Reference Blanco-Bercial, Cornils, Copley and Bucklin2014) study, the Calanoida, Cyclopoida, and Harpacticoida are known as dominant taxa. Here, the annual copepod diversity included the highest frequency of Cyclopoida (35.2%), Calanoida (31.6%), Harpacticoida (12.9%), and less abundant Canuelloida (1.6%). Conversely, the least abundant taxon was Monstrilloida (0.1%). In a study by Mohsenizadeh et al. (Reference Mohsenizadeh, Haghshenas and Rabbaniha2016), zooplankton fluctuations in Nayband Bay were attributed to the seasonal cycle of rainfall. They also reported that Cyclopoida with 24% of total abundance was the dominant copepod group.
In the current study, the family Monstrillidae showed the lowest mean abundance among the studied families. In a study by Suárez-Morales and Grygier (Reference Suárez-Morales and Grygier2021), it was shown that the Monstrillidae is abundant and diverse in coastal habitats; similarly Suárez-Morales (Reference Suárez-Morales2001) reported a high abundance of this group in Caribbean coral reefs. At a Brazilian estuary, Leite et al. (Reference Leite, Pereira, Abrunhosa, Pires and Da Costa2010) demonstrated that the peak abundance of Monstrilloids was in the dry season, while these were absent in the rainy season.
The genera Oithona and Euterpina are typical members of the Arabian Sea zooplankton. Their presence seems to be associated with low oxygen areas (see Jyothibabu et al., Reference Jyothibabu, Balachandran, Jagadeesan, Karnan, Arunpandi, Naqvi and Pandiyarajan2018). In the current study, the genus Oithona was the most abundant taxon. The annual total abundance was 20.2% of total copepods. Also, in the NEM and PRM, these contributed with the highest mean abundance which agrees with previous a study by Al-Busaidi and Claereboudt in (Reference Al-Busaidi and Claereboudt2023). In their study, the abundance of Oithona in the Arabian Sea increased sharply with the onset of the SWM and continued towards the POM. In a study of Abedi et al. (Reference Abedi, Seyfabadi, Saleh and Sari2023), it was shown that the genus Oithona is abundant in the Persian Gulf and the Gulf of Oman in the summer and spring in a wider range of temperature and salinity. In Smith and Madhupratap's (Reference Smith and Madhupratap2005) study, regardless of the location, the NEM is associated with an increase in the abundance of cyclopoid, especially for the members of the genus Oithona.
The dominancy of the genus Oithona probably depends on more than one factor. Small species have a low metabolism, thus require limited energy (Kiørboe and Hirst, Reference Kiørboe and Hirst2014). Also, as Castellani et al. (Reference Castellani, Robinson, Smith and Lampitt2005) stated, lower metabolic requirements may increase the chances of survival and reproduction of the genus Oithona and results in a higher abundance. The ability of Oithona to survive when water conditions are unfavourable, may explain the abundance of members of this genus in marine environments worldwide (Turner, Reference Turner2004; Zamora-Terol and Saiz, Reference Zamora-Terol and Saiz2013). The members of the genus Oithona act as the main grazers of phytoplanktons, key components of the microbial loop, and prey for ichthyoplanktons and other larger pelagic carnivores. In their study, Abedi et al. (Reference Abedi, Seyfabadi, Saleh and Sari2023) demonstrated that the members of the genus Oithona are considered as bioindicator in the Persian Gulf and the Gulf of Oman.
In addition to the high annual frequency of Oithona, the other genera namely, Temora, Paracalanus (Calanoida), and Euterpina (Harpacticoida) show the highest mean abundance. This may be due to the high tolerance of Oithona to temperature and salinity changes (Nishida, Reference Nishida1985), the adaptive reproductive natures of Euterpina (Mantha et al., Reference Mantha, Muthaiyan, Narayana, Kareem, Hans-Uwe, Kandasamy and Jiang-Shiou2012), and the opportunistic behaviours of Temora (Madhupratap, Reference Madhupratap1987). Similar to the present study, in a previous study by Mwaluma et al. (Reference Mwaluma, Osore, Kamau and Wawiye2003), the genera Paracalanus and Temora were the most dominant copepod genera in Mida Creek in the Eastern Indian Ocean and according to Nakajima et al. (Reference Nakajima, Yoshidia, Othman and Toda2008), Paracalanus, Oithona, Microsetella, and Oncaea were dominant genera in Malaysia.
In the present study, the genus Temora was the most abundant calanoid in Chabahar Bay. This is similar to and agrees with previous observations in the Gulf of Oman (see Al-Azri et al., Reference Al-Azri, Piontkovski, Al-Hashmi, Goes and Do Gomes2010; Fazeli and Zare, Reference Fazeli and Zare2011; Piontkovski et al., Reference Piontkovski, Al-Maawali, Al-Manthri, Al-Hashmi and Popova2014; Fazeli et al., Reference Fazeli, Zare, Nabavi and Sanjani2015) and the Arabian Sea (Jemi and Hatha, Reference Jemi and Hatha2019). This planktonic and epipelagic genus is widely distributed in tropical, subtropical, temperate waters (Tseng et al., Reference Tseng, Kumar, Chen and Hwang2011) and lagoons (Almeida et al., Reference Almeida, Costa and Eskinazi-Sant'Anna2012) in high abundance. As stated by Chang et al. (Reference Chang, Doi, Nishibe, Nam and Nakano2014), this may be due to their feeding behaviour, when preferred diatoms become scarce and consequently these copepods shift to consume a variety of food items including heterotrophic nano-flagellates and tolerate periods with limited phytoplankton.
In the current study, the Canuelloida contributed with 1.6% of the copepod community. Their least abundance in the planktonic community, as stated by Wells (Reference Wells1980), may indicate that they mostly feed near the substrate.
In the current study, among the five study stations, the highest mean abundance of copepods was observed in the order: st.1 > st.3 > st.2 > st.5 > st.4. In their study, Keshavarzi et al. (Reference Keshavarzi, Ebrahimi and Moore2015) showed that some stations such as Shahid Kalantari Port, Tis fishing Port, and 7th Tir Port are affected by anthropogenic activities. The Shahid Beheshti, Shahid Kalantari, Tis, and 7th Tir Ports are located in the Chabahar Bay, and due to limited water circulation as a semi-closed bay, they trap shipping activity wastes. They also mentioned that most of the polluted stations, such as the 7th Tir Port, are located in the southeast of Chabahar Bay, and the pollution decreases northwesterly in the bay. Consequently, Keshavarzi et al. (Reference Keshavarzi, Ebrahimi and Moore2015) concluded that the areas such as 7th Tir Port is under higher potential risks for Chabahar Bay biota.
In a study by Loqmani et al. (Reference Loqmani, Zabihi and Attaran Fariman2019), the results of the one-way ANOVA showed no significant difference in terms of zooplankton density in different stations of each season. In their later study, Loqmani et al. (Reference Loqmani, Attaran Fariman and Zabihi2020) stated that the partial difference in the measured zooplankton density in different stations could be due to difference in the sampling time or presence of a warmer or cooler waterbody at the same time in the region.
Biodiversity indices
The three biodiversity indices showed moderate diversity of copepods (H′: 2.33–2.80) similar to previous studies from the Arabian Sea (Padmavati et al., Reference Padmavati, Haridas, Nair, Gopalakrishnan, Shiney and Madhupratap1998; D'souza and Gauns, Reference D'souza and Gauns2018) and Bay of Bengal (Fernandes, Reference Fernandes2008). The number of species varies depending on the stability of the environment (Margalef, Reference Margalef1958; Deevey, Reference Deevey1971). According to the results of the present study, similar to Fazeli et al. (Reference Fazeli, Savari, Nabavi and Zare2013), the lowest biodiversity index value was obtained in the NEM. Also, the highest and lowest species richness values were observed in the POM and PRM, respectively. According to Goswami et al. (Reference Goswami, Sarupria, Bhargava and Desai1992), in terms of location, the mean abundance and diversity of zooplankton showed an inverse correlation with the abundance of zooplankton and accordingly they found higher diversity in stations far from the coast due to the stable and prevailing environmental conditions which allow the plankton community to diversify.
Compared to the Gulf of Oman, diversity indices in the Persian Gulf are low (Ghanbarifardi and Malek, Reference Ghanbarifardi and Malek2009). Probably, the SWM and NEM in the Arabian Sea are the reason for the higher diversity indices in the Gulf of Oman. Upwelling of nutrient-rich deep waters of the Arabian Sea continues during the SWM along the southern coast of Oman at the Arabian Sea (Wiggert et al., Reference Wiggert, Hood, Banse and Kindle2005). During the POM, based on Fazeli et al. (Reference Fazeli, Savari, Nabavi and Zare2013), the species richness of mesozooplanktons gradually starts to increase.
Relationship between environmental parameters and copepod communities
In the current study, PCA results showed that environmental parameters such as pH, DO, temperature, salinity, and chlorophyll-a have a significant influence on semi-closed bays such as Chabahar Bay. Similarly, in a study of Amidi et al. (Reference Amidi, Fatemi, Ghodousi and Javid2022), the results of the PCA showed that electrical conductivity, temperature, salinity, and TDS had the greatest impact on stations in the Persian Gulf and the Indian Ocean. In a study of Ershadifar et al. (Reference Ershadifar, Ker, Kochaknejad, Qazilu and Beskele2021), the first two axes of the PCA test explained 85.6% of the variation in physicochemical parameters and chlorophyll in Chabahar Bay, with the first axis explained 63.9% of environmental changes, showing a positive correlation between temperature and salinity. The second axis explained 21.7% of changes, where temperature had a strong positive correlation and pH had a strong negative correlation. Abo-Taleb et al. (Reference Abo-Taleb, Ashour, El-Shafei, Alataway and Maaty2020) conducted a study in the northwest Red Sea, where PCA results showed that in colder seasons, there was a close correlation between DO and depth, while in warmer seasons, temperature and salinity were closely correlated. The first two axes of the PCA explained 29.9% of environmental parameter changes in cold seasons and 29.6% in hot seasons.
Copepod species are generally divided into three categories: thermophilic species, eurythermal species such as Acartia spp., Centropages spp., and halophilic tropical species (Zuo et al., Reference Zuo, Wang, Chen, Gao and Wang2006). In a study by Abedi et al. (Reference Abedi, Seyfabadi, Saleh and Sari2023) in the Gulf of Oman, canonical correspondence analysis (CCA) revealed that mesozooplankton abundance in summer and spring was significantly correlated with salinity, DO, and water temperature. Based on these results, the mesozooplankton communities in the Gulf of Oman are primarily influenced by the combined effects of temperature, salinity, and DO, which significantly impact their distribution during these seasons.
In a study of Nandy and Mandal (Reference Nandy and Mandal2020), CCA results indicated that temperature, pH, DO, salinity, and nutrients are the key environmental parameters in relation to spatial–temporal changes of zooplankton distribution. The results of this test across the four seasons of the study, a clear spatial distribution pattern of zooplankton populations was observed along the salinity gradient, suggesting that salinity plays a crucial role in explaining zooplankton dynamics, particularly on a spatial scale. Dorgham et al. (Reference Dorgham, El-Tohamy, Qin, Abdel-Aziz and El-Ghobashy2019) found in high salinity areas, species such as Oithona nana, O. plumifera, Euterpina acutifrons, and Paracalanus parvus were the most abundant species and had a relatively higher contribution. Pervious research has highlighted the significant influence of sea surface salinity, DO, and sea surface temperature on the diversity, distribution, and dominance of copepod species (Radhakrishnan et al., Reference Radhakrishnan, Sunny, Sivasankaran and Mahadevan2020). The effect of salinity and temperature on the presence of some high saline species such as Oncaea along the northeastern Arabian Sea is controlled by ocean currents (Radhakrishnan et al., Reference Radhakrishnan, Sunny, Sivasankaran and Mahadevan2020). Chew and Chong's (Reference Chew and Chong2011) study in Malaysia revealed that species such as Oithona simplex are correlated with higher salinity. Due to its ability to adapt to a wide range of salinity and temperature, Paracalanus crassirostris is the dominant species of the copepod community in the west coast of Peninsular Malaysia. It appears that salinity and chlorophyll-a are the two main factors controlling the diversity of copepods. Marques et al. (Reference Marques, Azeiteiro, Martinho, Viegas and Pardal2009) also demonstrated that the salinity of different water masses is closely related to the distribution pattern of zooplanktons. Yoshida et al. (Reference Yoshida, Toda, Md Yusoff and Othman2006) showed that Acartia pacifica prefers water with higher salinity and lower temperature. Similarly, Santhanam and Perumal (Reference Santhanam and Perumal2003) observed a positive correlation between salinity and the population density of Acartia and Oithona in the Vellar estuary on the southeast coast of the Indian Ocean.
The cluster analysis of the stations over 1 year reveals a high similarity of 82%, indicating no significant differences between the stations. Given considering the high similarity, it is likely that the stations, all located within the same study area, exhibit changes in similarity primarily due to seasonal variations and environmental parameters.
In the current study, the 38 genera of copepods studied accounted for cumulative contribution of >90% of the total community. According to a study of Abedi et al. (Reference Abedi, Seyfabadi, Saleh and Sari2022), SIMPER analysis can be appropriate for describing the dissimilarity of the mesozooplankton community in different environments such as oxygen gradients in the nearly hypoxic and hypoxic layers of the Gulf of Oman. The nine dominant species of zooplanktons in the coastal waters of the northern Bay of Bengal, Bangladesh accounted for the cumulative contribution of >80% within the whole community (Al-Mamun et al., Reference Al-Mamun, Akhtar, Rahman, AftabUddin and Modeo2020). The SIMPER results in Shi et al.'s (Reference Shi, Yuan, Zuo, Wang and Pakhomov2019) study revealed that in the two periods of June–July and September–November, the average similarities were higher than 70%, which indicated similar copepod assemblages.
Conclusion
The main objective of the current study was to investigate the spatial–temporal fluctuations of the community structure of surface copepods of Chabahar Bay in the Gulf of Oman. Five areas were investigated in four seasons (POM, NEM, PRM, and SWM) for the status of copepod communities and environmental parameters. The current study results indicated the diversity of copepod communities in different seasons of the Gulf of Oman. Among the 38 genera of copepods identified in the five stations, the most abundant belonged to the genus Oithona. Due to the different abundances of the copepods in different stations, the impact of human activities was visible in the studied stations. The results showed that environmental conditions determine the structure and distribution of zooplankton communities, especially copepods in Chabahar Bay. We recommend further survey on zooplankton communities, especially in relation to copepod biodiversity in different depths at the Gulf of Oman. This study provides essential baseline data for future large-scale research with regards to habitat and valuable information for ecological assessments and improved management of Chabahar Bay. Due to the increase of anthropogenic activities around this area, continuous monitoring of environmental parameters related to copepod communities will be necessary in the future.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S002531542400105X
Data
Data will be available on request.
Acknowledgements
The authors would like to express their gratitude to Aslam Rigi-Mirkazehi for his invaluable assistance with sample collection. We are also indebted to Dr Mehdi Ghodrati Shojaei for his expertise and guidance in statistical analysis. We are grateful to the University of Tehran and Chabahar Maritime University for providing research and laboratory facilities.
Author contributions
Z. D.: conceptualized the study, laboratory examination, data collection, analyses, and writing – manuscript draft. A. S.: conceptualized the study, project administration, collected samples, supervised the study, and writing – review and editing of manuscript. G. A.-F.: conceptualized the study and its design, collected data, and critically revised the manuscript. J. S.: conceptualized the study and revised the manuscript.
Financial support
This research was financially supported by the Department of Marine Biology, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor, Iran. This support is gratefully acknowledged as it facilitated the completion of the PhD thesis from which this work originated.
Competing interests
None.
