Distribution and Abundance of Seagrasses in the Southwest Coast of Davao Oriental, Philippines
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Philippine Journal of Science 150 (S1): 383-394, Special Issue on Biodiversity ISSN 0031 - 7683 Date Received: 20 Aug 2020 Distribution and Abundance of Seagrasses in the Southwest Coast of Davao Oriental, Philippines Neil C. Capin, Brian L. Pototan, Aileen Grace D. Delima, and Annabelle U. Novero* Department of Biological Sciences and Environmental Studies College of Science and Mathematics, University of the Philippines Mindanao Mintal, Tugbok District, Davao City 8022 Philippines Seagrasses are an important coastal resource that serves as homes and breeding grounds of fishes and other marine organisms and are useful indicators for the detection of changes in the coastal environment since they are vulnerable to bio-physical stressors. This study assessed the seagrass resources in terms of composition, percent cover, community similarity, and diversity in four municipalities (Banaybanay, Governor Generoso, Lupon, and San Isidro) situated in the southwest coast of Davao Oriental province facing Davao Gulf. Thirty-six (36) transects, each with ten quadrats arranged in an alternate manner, were laid perpendicular to shore yielding a total of 360 plots. A total of eight seagrass species were observed: Cymodocea rotundata, Enhalus acoroides, Halodule pinifolia, Halophila minor, Halophila ovalis, Halophila spinulosa, Syringodium isoetifolium, and Thalassia hemprichii. Governor Generoso (33.77%) and San Isidro (26.01%) were classified to have fair seagrass bed conditions while Banaybanay (24.31%) and Lupon with the lowest coverage (15.90%) had poor status. T. hemprichii dominated the seagrass community in Banaybanay and Governor Generoso while C. rotundata were dominant in Lupon and San Isidro. The two most abundant species, T. hemprichii (41%) and C. rotundata (34.48%), had fair coverage comprising 75% of the entire seagrass while the remaining 25% cover was shared by Enhalus acoroides (19%) and other five species with very poor cover (0.30–2.43%). Diversity analysis using percent cover data revealed low diversity with overall Shannon index, H’= 1.2955, evenness J = 0.6657, and Simpson’s index of diversity, D = 0.3577. Dice community of coefficient grouped Banaybanay, Governor Generoso, and San Isidro together, indicating high similarities while separating Lupon, which had the poorest seagrass condition in terms of coverage. The status of seagrass diversity on the southwest coast of Davao Oriental calls for immediate attention and effective strategies to alleviate poor conditions and protect the seagrass beds. Keywords: Cymodocea rotundata, Davao Oriental, diversity, seagrass cover, seagrass management, Thalassia hemprichii INTRODUCTION an ecotone between a mangrove forest and coral reefs as well as a home of many marine organisms (Fortes 2013). Seagrasses are flowering plants that usually grow best Seagrasses serve as breeding and nursery grounds for in high-reducing sediments of shallow tropical and fishes and other marine organisms (Noel et al. 2012; subtropical locations in coastal communities, serving as Jumawan et al. 2015). They are also an important food *Corresponding Author: [email protected] source for sea cows (“dugong”) and sea turtles (Alcala 383 Philippine Journal of Science Capin et al.: Distribution and Abundance of Seagrasses Vol. 150 No. S1, Special Issue on Biodiversity in Southwest Coast of Davao Oriental et al. 2008; Vinson et al. 2016). Further, they aid in the and Campbell 2002). Lack of knowledge and information stabilization of sediments in the ocean floor (Vinson et al. about the importance of seagrasses leads to the destruction 2016) and play an important role in the carbon cycle and of the resource (McKenzie and Campbell 2002; Jumawan nutrient cycle in coastal habitats (Redondo et al. 2017). et al. 2015). This study determined the composition of seagrass, the extent of seagrass cover, distribution, The Philippines has been noted to have the second most diversity index, and community similarity to assess the numerous taxa of seagrasses with 16 species (Fortes 1990) condition of the seagrass beds in four municipalities next to Australia with 19 species (Carruthers et al. 2007). situated in the southwestern portion of Davao Oriental However, conditions of seagrasses in the country face a facing Davao Gulf. Results of the study could help the serious threat (Dedel et al. 2018). There are pieces of local policymakers and stakeholders to improve the evidence that seagrasses are also declining globally (Björk communities’ understanding of the status of their seagrass et al. 2008). This is because seagrasses are susceptible beds and help them better conserve and manage these to changes in water quality and environmental quality coastal resources. (Vinson et al. 2016). This characteristic turns seagrass communities into useful indicators of changes in the coastal environment since it is vulnerable to biological and physical inconstancy, which is not easily observable MATERIALS AND METHODS in either coral reef or mangrove forest (Fortes 2013). Because these ecosystems are linked with each other, the instability of one system affects the other; thus, the Study Area destruction of seagrass beds has a great impact on our This study was conducted in the southwest portion in the marine environment (Jumawan et al. 2015). province of Davao Oriental, Philippines located between 62°00’ and 71°00’N latitude and 125°00’ and 126°00’E In the Davao region, there is still a large area where the longitude. This portion of the province facing Davao existence of seagrasses remains unknown – particularly Gulf is composed of four coastal municipalities (https:// surrounding the Davao Gulf, which is one of the country’s davaooriental.gov.ph): Banaybanay, Lupon, San Isidro, marine key biodiversity areas (CI et al. 2009). According and Governor Generoso. Banaybanay has a marine reserve to Alcala et al. (2008), the Department of Environment in Burias Islet; Lupon has reported sightings of hawksbill-, and Natural Resources has established marine protected green-, and leatherback turtles (Alcala et al. 2008); San areas (MPAs) along the shore of Davao Gulf that is Isidro has fish sanctuaries (https://davaooriental.gov. mostly composed of seagrass beds. However, there are ph), and Governor Generoso had sightings of dugong limited published seagrass monitoring surveys available (Lucero 2010). These marine animals are dependent on the (Noel et al. 2012; Jumawan et al. 2015). One of the available source of seagrass species used as food (Alcala reasons for limited information on seagrasses is that et al. 2008). Three sampling sites each were selected in the research tends to focus mainly on coastal resources with municipalities of Governor Generoso, San Isidro, Lupon, immediate economic value (Fortes 2013). Nevertheless, and Banaybanay (Figure 1). the importance of seagrasses in the marine waters of the Davao Gulf is highly recognized in their roles as We relied on local knowledge and Landsat imagery to locate feeding and nursery grounds to various species of fishes, seagrass beds. Purposive sampling was used, a non-random macroinvertebrates, and marine animals. Lucero (2010) technique that did not need underlying theories or a set reported that dugongs (Dugong dugon) visiting Davao number of informants (Tongco 2007). In every municipality, Gulf feed mostly on Halophila species. Noel et al. (2012) the seagrass covers were categorized into three – dense (D), also identified 13 fish species and 20 macroinvertebrate semi-dense (SD), and sparse (S) – wherein three 100-m species in seagrass beds in three municipalities in Davao transects were established for every category (Figure 2). Gulf. Among five provinces sharing the waters of the The three categories were identified to select priority sites Davao Gulf, the province of Davao Oriental possessed to represent the study area. Through key informants from the longest coastline in the country of about 3% (Cabrera the local fisherfolks and “barangay” (hamlet) committee on and Lee 2020). With the observed coastal developments, agriculture, the three seagrass categories were identified. particularly in the southwestern portion of this coastline The site was visited only once. The following barangays facing the Davao Gulf, it is vital to assess the status of were sampled for each municipality: Maputi (D, SD) and seagrass beds. Kalubihan (S) in Banaybanay; Bagumbayan (S, SD, D) in Lupon; Baon (D), Bato-Bato (SD), and Cambaleon (S) Monitoring of seagrasses is very important to know the in San Isidro; and Lavigan (D, S) and Pundagitan (SD) in condition of the resource whether it is stable, declining, Governor Generoso. Each municipality consisted of nine or improving. Monitoring also is important in identifying transects, yielding a total of 36 transects. One hundred-meter areas that are in need of conservation measures (McKenzie (100-m) transect lines were established (nine transects per 384 Philippine Journal of Science Capin et al.: Distribution and Abundance of Seagrasses Vol. 150 No. S1, Special Issue on Biodiversity in Southwest Coast of Davao Oriental Figure 1. Location of the seagrass sampling areas in Davao Oriental, Philippines (Governor Generoso, San Isidro, Lupon, and Banaybanay) located at 62°00’ and 71°00’N latitude and 125°00’ and 126°00’E longitude. Figure 2. Categories of sampling for seagrass cover based on key informant interview in southwest coast of Davao Oriental, Philippines: A) dense, B) semi-dense, and, C) sparse. site) from the coastline where the seagrass occurred to the