Species composition, abundance and distribution of seagrasses in the brackish waters of Balingoan, Misamis Oriental in relation to environmental parameters

80 Hamisain et al. Int. J. Biosci. 2020 RESEARCH PAPER OPEN ACCESS Species composition, abundance and distribution of seagrasses in the brackish waters of Balingoan, Misamis Oriental in relation to environmental parameters Rodzia D. Hamisain1, Yasmeen A. Sama1, Maria Lourdes Dorothy G. Lacuna1, Ronaldo R. Orbita2, Maria Luisa S. Orbita1* 1Department of Marine Science, Mindanao State University - Iligan Institute of Technology (MSUIIT), Iligan City, Philippines 2Department of Professional Education, Mindanao State University - Iligan Institute of Technology (MSU-IIT), Iligan City, Philippines Key words: Seagrass, brackish water, Gingoog Bay. http://dx.doi.org/10.12692/ijb/16.6.80-89 Article published on June 16, 2020 Abstract Seagrasses play an important role in marine and brackish waters both as primary producers and ecosystem engineers, thus sustaining biodiversity and ecosystem services. The ecology of seagrass was widely investigated in the marine region whereas their abundance and distribution in brackish waters is still limited. This study aimed to assess the composition, abundance and distribution of seagrasses in relation to some environmental parameters. Field sampling was conducted through transect-quadrat method and shoot density was determined along with water temperature, salinity, nutrients and water flow. The seagrass bed in Balingoan was a mixed community of H. pinifolia, T. hemprichii, C. rotundata, H. ovalis and E. acoroides. H. pinifolia dominated the area and its distribution extends from high to the lowest intertidal zone. Correlation analysis was significant between the seagrass species and the environmental parameters and it was species specific. * Corresponding Author: Maria Luisa S. Orbita  [email protected] International Journal of Biosciences | IJB | ISSN: 2220-6655 (Print), 2222-5234 (Online) http://www.innspub.net Vol. 16, No. 6, p. 80-89, 2020 81 Hamisain et al. Int. J. Biosci. 2020 Introduction Seagrasses are rhizomatous marine angiosperms widespread in both marine and brackish shallow waters from temperate to tropical regions (Short et al., 2007). In these regions, they often act as ecological engineers (Wright and Jones, 2006) forming extensive meadows that are among the most productive ecosystems on earth (McRoy and McMillan, 1997; Duarte and Chiscano, 1999). Seagrass meadows provide key ecosystem services, including organic carbon production and export, nutrient cycling, sediment stabilization, biodiversity, and trophic transfers to adjacent habitats (Duarte et al., 2005; Duffy, 2006; Orth et al., 2006; CullenUnsworth and Unsworth, 2013; Marco-Mendez et al., 2015). The abundance and distribution of seagrasses are controlled by the physical, chemical and biological properties of their environment (Greve and Binzer, 2004). In most tropical seas, which are usually characterized by clear waters and high incoming irradiance throughout the year, seagrass growth is often limited by the availability of nutrients (Powell et al., 1989; Short et al., 1990; Duarte, 1995). In addition, water temperature, salinity and water motion are also important variables affecting seagrass abundance and distribution in tropical regions (Lin and Shao, 1998; Erftemeijer and Herman, 1994). The ecology of seagrass was widely investigated in the marine domain whereas their abundance and distribution in brackish waters is still not exhaustive (Boscutti et al., 2015). Balingoan is a coastal municipality in the province of Misamis Oriental and its coastal water is part of the Gingoog Bay. The coastal area has underwater spring which causes the water to be less saline or brackish. This unique, unusual natural phenomenon provides viable platform for scientific exploration in the area because despite of its low salinity, the area encompasses a variety of tropical habitats including seagrasses. This study aimed to assess the abundance and distribution of seagrasses in relation to some environmental parameters in the area. This study provides additional data on the ecology of seagrasses and its trophic role in brackish waters especially in the tropical region. Materials and methods Study area The study was conducted in Barangay Mantangale, Balingoan, Misamis Oriental (9°00'26.6''N 124°51'34.4''E, Figure 1). Fig. 1. Location of the sampling site in Balingoan, Misamis Oriental (Sources: QGIS version 3). 82 Hamisain et al. Int. J. Biosci. 2020 The coastal area of Mantangale in Balingoan has an underwater spring that caused the water to be less saline or brackish. It had a salinity that ranged from 4-9‰ with a mean value of 6‰. The sampling site is known to encompass a variety of tropical habitats including mangroves, seagrass beds and coral reefs. Field sampling The study was carried out during low tide when seagrasses were exposed. The whole intertidal flat was divided into three regions: high, middle and low. For each region, a 50-meter transect line (with 3 replicates) was placed parallel to the shore, and for every 10 m-interval, a 0.5 m x 0.5 m quadrat was laid down at the right side of the transect line. All the seagrasses inside the quadrat were identified and recorded following the taxonomic keys of Calumpong and Meñez (1997) and Kuo and den Hartog (2001). Shoot density was measured by carefully counting the shoots per species for each quadrat and the shoot numbers were expressed as density (shoot/m-2). The density and relative density were calculated using the formula: Environmental Parameters Environmental parameters were measured randomly in the brackish waters surrounding the seagrass bed. Water temperature was measured in situ using an ordinary mercury thermometer while salinity was measured using a handheld refractometer. Water flow was estimated using clod cards (Doty, 1971) and the calculation of water flow (cm-2) was done based on the method of Anzai (2001). Nutrient analysis was carried out following the method of Grasshoff et al. (1983). Statistical analysis The difference in abundance represented by shoot density among species was analyzed through OneWay Analysis of Variance (One-Way ANOVA, level of significance, P of 0.05) in SPSS (version 8.0). Pearson’s correlation analysis was used to determine the correlation coefficients between environmental factors with seagrass abundance. Results and discussion A total of five (5) seagrass species were identified in the area: Cymodocea rotundata (Ehrenberg and Hemprich, ex Ascherson), Enhalus acoroides (L.f.) Royle, Halophila ovalis (R. Brown), Halodule pinifolia (Miki) den Hartog and Thalassia hemprichii (Ehrenberg) Ascherson (Table 1). Table 1. Identification of seagrasses in Balingoan, Misamis Oriental (Calumpong and Meñez, 1997; Kuo and den Hartog, 2011). Family Genus and Species Common Name Local Name Hydrocharitaceae Thalassia hemprichii Halophila ovalis Enhalus acoroides Sickle-grass Paddle weed Tape-grass Lusay Lusay Lusay Cymodoceaceae Cymodocea rotundata Halodule pinifolia Manatee-grass Needle-grass Lusay Lusay The total seagrass taxa of Balingoan represent 33.33% of the 15 reported taxa from the Philippines (Meñez et al., 1983; Short and Coles, 2001; Green and Short, 2003; Short et al., 2007). The five (5) seagrass species in this study are interesting information considering the total of fifteen (15) species for the entire Philippines. The seagrass bed of Mantangale, Balingoan was characterized as mixed meadow and the seagrasses that form this mixed bed encompass a considerable size range, from the smallest (Halophila ovalis) to the largest (Enhalus acoroides). According to the following authors (Brouns, 1987; Fortes, 1995; Terrados et al., 1998) most of the seagrass bed in SE is composed of mixed seagrass communities typically 83 Hamisain et al. Int. J. Biosci. 2020 comprise of up to 13 species, ranging broadly in size from small Halophila sp. to the large Enhalus acoroides. Likewise, Philippine seagrass beds are generally mixed (Meñez et al., 1983; Tomasko et al., 1993) in response to nutrient enrichment (Agawin et al., 1996), disturbance (Duarte et al., 1997), competition (Duarte, 2000) and water depth (Taplin et al., 2005). Table 2. Correlation coefficients (R) in relative density (%) with environmental parameters among seagrass species in Balingoan, Misamis Oriental. Species Coefficient of Correlations Temp Sal PO4 NO3 Water flow H. pinifolia -0.147 0.69 -0.748** 0.03 0.510 0.13 0.097 0.79 0.305 0.91 C. rotundata -0.073 0.83 -0.310 0.35 0.689** 0.02 0.307 0.16 0.075 0.21 H. ovalis -0.007 0.98 -0.693 0.51 0.234 0.15 0.052 0.97 0.725 0.48 T. hemprichii -0.999** 0.03 -0.284 0.37 0.303 0.14 0.374 0.23 0.207 0.52 E. acoroides -0.629 0.26 -0.029 0.94 0.433 0.27 0.500 0.39 0.843** 0.02 Legend: ** represents significant differences at p<0.05. The abundance of seagrass represented by shoot density varies among species (One-Way ANOVA, p < 0.05). H. pinifolia had the highest shoot density followed by C. rotundata and T. hemprichii (Figure 2). H. pinifolia is widely distributed throughout the Indo-west Pacific and is almost ubiquitous in tropical seagrass meadows often being dominant (Meñez et al., 1983; Waycott et al., 2004). This species is a rapid colonizer from seed and through vegetative growth; it plays an important role in maintaining seagrass habitat in areas of high disturbance and actively stabilizes sediments with an intertwining mat of rhizomes and fibrous roots. Likewise, this species was also dominant in the coastal lagoon of the east coast of Malaysia (Sidik et al., 2010), Valachchenai lagoon (Udagedara et al., 2017) and Negombo lagoon in Sri Lanka (Samarakoon and Van Zon, 1991). C. rotundata was second in rank in terms of abundance. This species is also an ecologically important tropical pioneer seagrass species distributed in the Indo-Pacific region. It is also found in Puttalam lagoon in Sri Lanka (Ranahewa et al., 2018) and one of the dominant seagrass species in Tongsha island in Taiwan (Lin et al., 2005). T. hemprichii was third in abundance and it is also one of the most widely distributed seagrass species dominating in many mixed meadows (den Hartog, 1970; Brouns, 1987; Vermaat et al., 1995; Gullström et al., 2002; Prathep, 2003). This species is known to be an important food source for dugongs and sea turtles and provides critical grazing habitat for fish (Phillips and Meñez, 1988). Two species, H. ovalis and E. acoroides have the lowest abundance. Halophila plants in mixed populations have low abundance due to high competition with other species in terms of light, space and nutrients (Japar Sidik, 2010). Moreover, the low abundance of E. acoroides was attributed to its slow growth rate because large seagrasses are slow growing with limited colonizing capacity (Duarte, 1991). Compared to other tropical seagrass species, E. acoroides is a very recognizable type of seagrass for it has long, wide and stiff leaves (Kuo and den Hartog, 2001) and known to have the widest tolerance and can live on muddy, sandy and sandy-muddy substrate (Dewi and Sukandar, 2017). 84 Hamisain et al. Int. J. Biosci. 2020 Fig. 2. The shoot density of seagrasses in Balingoan, Misamis Oriental. Different letters compared horizontally indicate statistically significant differences between the means at the level of 5% probability by Tukey test. The seagrass community was found 150 meters from the shoreline in a depth of 3 meters during high tide. The seagrasses were in patchy distribution and extends from high to the lowest intertidal zone but its species composition decreases which might be related to water depth and light availability (Duarte, 1991). The five species were present in the high intertidal region and dominated by H. pinifolia with 66% relative density (Figure 3). In mid region, all species were still present and C. rotundata dominated with 59% relative density. In the low intertidal region, only three species were found such as H. pinifolia, C. rotundata and T. hemprichii. H. pinifolia had the highest relative density (57%) followed by C. rotundata (38%). Fig. 3. The distribution of seagrasses in the intertidal flat of Balingoan, Misamis Oriental. 85 Hamisain et al. Int. J. Biosci. 2020 Significant correlation was detected in H. pinifolia, T. hemprichii, C. rotundata and E. acoroides with the environmental parameters measured in the area (Pearson’s Correlation, p<0.05, Table 2). Water temperature showed a significant negative correlation with T. hemprichii while H. pinifolia negatively correlated with salinity indicating that these species have low capability to produce high shoot density with changing temperature and salinity. Temperature is considered a major factor controlling seagrass growth because an increase in water temperature will affect the biochemical processes involved in photosynthesis and respiration (Tutin, 1942; Phillips et al., 1983; Lee and Dunton, 1996; Lee et al., 2005). Related study shows that high temperatures can reduce growth and productivity of T. testudinum (Barber and Behrens, 1985). Likewise, an increase in salinity would affect the morphology and physiology of seagrasses (Kuo and den Hartog, 2006; Taiz and Zeiger, 2009). A study done on H. wrightii shows that no increase in growth was seen and the leaf chloroplast was affected when the plant was exposed to salinity of 45ppt (Ferreira et al., 2017). On the other hand, phosphate was positively correlated with C. rotundata suggesting that an increase in phosphate would stimulate growth of this species, hence increases its shoot density and vice versa. Nutrient enrichment studies suggest that additions of inorganic nutrients can stimulate seagrass growth (Orth, 1977; Harlin and Thorne-Miller, 1981; Iizumi et al., 1982; Dennison et al., 1987; Short et al., 1990; Pérez et al., 1991; Murray et al., 1992; Williams and Ruckelshaus, 1993; Lee and Dunton, 2000) and this was observed in an experiment done on C. rotundata in Cape Bolinao, Pangasinan in response to nutrient addition (Agawin et al., 1996). Moreover, water flow was positively correlated with E. acoroides because strong water motion could increase the absorption of carbon dioxide and increase the nutrient uptake at the leaf surface of E. acoroides (Agawin et al., 2001; Hillman, 1989). Conclusion The recent research on seagrasses in the brackish waters of Balingoan has provided additional and important information on the composition, abundance and distribution of seagrasses in which data were still limited. Current findings suggest that the seagrass bed in Balingoan was a mixed stands comprised primarily of H. pinifolia, C. rotundata, T. hemprichii, H. ovalis and E. acoroides. It was dominated by H. pinifolia and its distribution extends from high to the lowest intertidal zone. Seagrass beds consisting of H. pinifolia contributed importantly to coastal ecosystems in Balingoan brackish waters because of its high density. Furthermore, the significant correlation between seagrasses and the environmental parameters in the area indicate the existence of a species specific relationship. Acknowledgment We would like to thank the Department of Marine Science, College of Science and Mathematics, MSU - Iligan Institute of Technology for all the support in the conduct of this research. References Agawin NSR, Duarte CM, Fortes MD. 1996. Nutrient limitation of Philippine seagrasses (Cape Bolinao, NW Philippines): in situ experimental evidence. 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