Tropical Natural History 20(1): 104-110, April 2020 2020 by Chulalongkorn University
Short Note Has Halophila beccarii Ascherson (Alismatales, Hydrocharitaceae) Been Locally Extirpated in the Philippines?
LAWRENCE M. LIAO1* AND PAUL JOHN L. GERALDINO2
1Aquatic Botany Laboratory, Graduate School of Integrated Sciences for Life, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, 739-8528, JAPAN 2Department of Biology, University of San Carlos, 6000 Cebu City, PHILIPPINES * Corresponding Author: Lawrence M. Liao ([email protected]) Received: 29 July 2019; Accepted: 4 December 2019
The angiosperm genus Halophila the Bintula (=Bintulu?) River by Oeduardo Thouars is distributed in tropical and Beccari, the intrepid Italian botanical subtropical marine and estuarine habitats. collector and taxonomic authority on the Some species like H. decipiens Ostenfeld Palmae of the last century. A single are widely distributed, being the only collection was also reported from the member of the genus showing a pantropical southwestern coast of Taiwan3. range1, while other species like H. No documentation of H. beccarii from hawaiiana Doty & Stone and H. johnsonii the Philippines was included in the last Eiseman are rather restricted in distribution, global compendium2 although this has been confined only to the main Hawaiian islands reported by various authors4-9. All these and the southeastern coast of Florida, records, however, can be traced to a single respectively2. collection from Parañaque located on the Within the genus Halophila, H. beccarii southeastern shore of Manila Bay, collected Ascherson is recognized as a unique entity by the American botanist Elmer Drew owing to its lack of cross veins in the leaf Merrill in 1911 and distributed in several blades, among its most prominent features. herbaria. This habitat has since been Five sections within the genus have been reclaimed in the 1960s and became recognized and H. beccarii is the only urbanized for the most part and any species placed under Halophila section remaining populations of H. beccarii or any Microhalophila due to its diminutive and seagrasses would have been decimated in all delicate nature. It is primarily distributed on probability. This may have led some the shores of continental South and workers to hypothesize that H. beccarii has Southeast Asia, from western India in the been locally extirpated10. However there is farthest west of the range, on the Andaman disagreement on this point hinting that it Sea side of Thailand, Strait of Malacca, Gulf still occurs in a few areas around Manila of Thailand, going north along the coast of Bay and in the Lingayen Gulf on the Vietnam, to the region around Hong Kong northwestern coast of Luzon island without as its easternmost reach2. Outside of citing any herbarium voucher specimens11. continental Asia, a single site on Sarawak Both localities though have been heavily on the northwestern shore of Borneo was impacted and have been the site of documented2 where the type specimens of numerous incidents of fish kills due to H. beccarii were collected near the mouth of intensive aquaculture and other anthropogenic 105 LIAO AND GERALDINO – HALOPHILA BECCARII IN THE PHILIPPINES
activities in recent years12. Indeed, H. language means “place where bamboo fish beccarii has been listed as among the three corrals are found.” Today, Baclaran is a most vulnerable species of Halophila highly populated village of 28,385 people in around the world together with H. an area comprising only 63.72 ha, or a hawaiiana and H. baillonis Ascherson in population density of 445.46 ha-1 (http:// Hooker fil. (as H. baillonii)13. The shallower www.paranaquecity.com/statistics.html). The distribution of H. beccarii (max. 1 m deep) coastal areas off Parañaque and adjacent necessarily exposes it to greater risks points to the north and south have been compared to the other two which occur in subjected to large-scale land reclamation greater depths. projects in order to meet the demands for The objective of this paper is to ascertain more land as the metropolitan city of Manila the current status of H. beccarii in the expands. There are no longer mangroves in Philippines based on the examination of the area except for some strips of reforested extant herbarium specimens as well as field mangrove stands adjacent to dense human surveys during the past ten years. Based on settlements offshore. Artisanal fisheries the information on the biology of H. have long been replaced by commercial beccarii in neighboring countries as well as trawling. our own field observations, evidence is H. beccarii is usually restricted to the presented to assess the current status of this intertidal mudflats often with mangroves species. nearby14. The same habitat has been Herbarium specimens of H. beccarii described for H. beccarii in many parts of deposited in different Philippine herbaria India15 and other sites in continental were searched. Literature describing the Southeast Asia16. This narrow zone of ecology and conservation status of the occurrence close to sources of anthro- species as found throughout its distributional pogenic disturbance makes this species range was collated. Unfortunately, the search particularly vulnerable. While muddy for H. beccarii in different herbaria has substrates within mangrove forests are the failed to produce any single sample. The most preferred habitats similar to those three major Philippine herbaria searched are observed by the authors at the mangroves of the Philippine National Herbarium (PNH) of Sungei Buloh National Park in Singapore, the National Museum of Natural History in H. beccarii have been reported growing on Manila, the Silliman University Marine sandy substratum and down to a depth of Laboratory herbarium in Dumaguete City 1.7 m. Apparently the type of substrate and the University of San Carlos herbarium affects some growth parameters of H. (CEBU) in Cebu City. Numerous field beccarii. In a survey of seagrasses from surveys over the past ten years also yielded Bintan Island in the Riau Archipelago negative results. (Indonesia) only 2 h away from Singapore, H. beccarii was first reported from the no H. beccarii was documented owing to shores of Parañaque on the southeastern the predominantly sandy reef substrates fringes of Manila Bay at a time when there17, considering that this species has mangroves were abundant and low-impact been found in significant numbers of artisanal fishing activities were common4. A patches around the main island of Singapore prominent coastal village in Parañaque at such as in Chek Jawa and Sungei Buloh that time was Baclaran, which in Tagalog (unpublished data). These localities, while TROPICAL NATURAL HISTORY. 20(1), APRIL 2020 106 probably being impacted by anthropogenic them to colonize suitable substrates within a activities, are subjected to some degree of short time21. It is probably quite specialized freshwater influx from rivers draining into in its habitat choice growing in sites where the narrow Johore Straits from peninsular other species cannot survive. In fact, among Malaysia. the habitats in southern Thailand surveyed, The type of substrate apparently affects only H. beccarii and such hardy species as the distribution and density of seagrasses H. ovalis (R. Brown) Hooker fil. and especially for H. beccarii which has an Enhalus acoroides (L. fil.) Royle have been extremely narrow vertical distribution observed near river mouths where freshwater (depth range) of ca. 1 m for the most part13. influx and sedimentation are common22. The Comparing the shoot density of populations latter causes light penetration to decrease growing on muddy and sandy substrata, it affecting photosynthetic performance among was found that shoot density of H. beccarii phototrophs there. increased significantly in southeastern There have been many reports of Indian muddy habitats (6,152 shoots m-2) flowering periods of H. beccarii from compared to that in sandy substrates (3,632 throughout its known distributional range, shoots m-2), with corresponding total but these reports are often conflicting. biomass increases of more than quadrupled Clearly the flowering phenomenon in H. values in muddy substrates (25.5 g m-2) as beccarii is influenced by local conditions opposed to those in sandy bottoms (6.2 g m- more than genetic factors. One report found 2)15. The same highest shoot density and flower production under conditions of low biomass were documented during the dry salinity (5.38 ‰) coupled with low months of January to March in Bangladesh18. phosphate and high nitrate values23. In a An extreme situation reporting 9 ha of H. study determining the factors affecting beccarii off Donghai Island in western flowering and fruiting in H. beccarii from Guangdong province in China was Malaysia, it was found that air temperature documented19, although no biomass figures had the most profound effect24. Flowers were available. Farther west of Donghai were most abundant when air temperatures Island, a high shoot density of nearly 6,000 were low (25.5-26.0°C in January). The shoots m-2 for H. beccarii in Liusha Bay19. study, however, does not give a hint about Clearly, H. beccarii is a highly substrate- emersion time nor the extent of shade at the specific as well as a distinctly seasonal site. In the Sungei Buloh National Park in species. Perplexingly though, only a single Singapore, high biomass of H. beccarii was collection of H. beccarii was made during a observed by the authors under the canopy of multi-year survey conducted along the entire mangroves and in habitats subjected to 2,279 km coastline of Myanmar which may constant emersion and immersion. In this have estuarine habitats suitable for this habitat, populations were observed to grow species20. on small mud mounds each one surrounded It has been suggested that H. beccarii is by substrata usually without vegetation. a rather sensitive species as it disappears These mounds were apparently slightly quickly when unfavorable environmental elevated muddy substrates retained by the conditions occur, but which is compensated rhizome systems of the seagrass growing by a high fecundity rate and an ability to upon them when the surrounding space has grow their rhizomatous systems fast enabling been eroded by tidal action. 107 LIAO AND GERALDINO – HALOPHILA BECCARII IN THE PHILIPPINES
The seed coat morphology of several and southern coasts26. H. beccarii has only Halophila species from East Malaysia and been reported along the northern coasts Mauritius has been compared25. The testa which are under the influence of freshwater were found to have reticulations of distinct input from mainland Malay Peninsula while configurations ranging from rectangular to the same species was virtually absent along hexagonal, sometimes with small peg-like the southern coasts and offshore islands projections issued from the reticular space, farther south where conditions are marine. It features that may be useful taxonomic is noteworthy that within Southeast Asia, characters. These reticulations and projections specimens were encountered in greater are said to increase the surface area of the number along the estuarine coasts of seeds which would help them to become continental land mass compared to coastal buoyant by increasing their surface area to areas of insular countries (e.g., Indonesia, volume ratio. In addition, air bubbles might the Philippines). This is because there are also be trapped within these reticulations several larger river systems on the adding to their buoyancy. Interestingly, continental Southeast Asia draining however, despite the ornate reticulations southward creating large deltas and found on the seed coat of H. beccarii, seeds extensive swamp lands that provide ideal are negatively buoyant24. This negative growing conditions with reduced salinity. buoyancy may be an important constraint This is not the case with insular locations in towards long distance dispersal and may be Southeast Asia where river systems are one important factor to explain the localized often smaller, shorter and with a lesser river geographic distribution of this species. water output into the marine environment. Temperature plays an important role in The same could be said of the Indian the distribution of Halophila species just as Subcontinent wherein an extensive survey it regulates the geographic distribution of of H. beccarii reported healthy populations most marine organisms. However, no on the mainland27 except for a single record available data on the effect of temperature from the offshore Andaman Islands where it on H. beccarii can be found in the literature. was found on mudflats28. Salinity appears to have a profound In the Philippines, estuarine habitats such effect on the distribution of H. beccarii as mangroves and river mouths are under throughout its known distributional range. severe threat from human activities. Some The original type specimen of H. beccarii of these threats include the conversion of was found near a river mouth in Sarawak estuarine mangrove habitats into shrimp where freshwater influx was significant aquaculture farms29, upland deforestation causing a diluting effect on the seawater which contribute to the loss of forest top soil there. The same ideal estuarine habitats have causing massive soil erosion, mining been reported as hosting healthy populations activities that release toxic mine tailings of H. beccarii as in the case of southern without regard for existing regulations, Thailand22 and in mangroves with estuarine unsustainable agricultural practices that conditions in India14, 15. In the small island contribute to the nutrient load in natural nation of Singapore, there existed a north- waterways leading to eutrophication, coastal south dichotomy in the distribution of development and waste generation and seagrasses, which may be attributed to others13. These and other factors have salinity differences between the northern contributed to the degradation of many TROPICAL NATURAL HISTORY. 20(1), APRIL 2020 108 brackish water habitats in the Philippines, for verifying seagrass specimens deposited threatening many estuarine organisms in their respective collections. LML including H. beccarii. acknowledges the travel support granted by The survival of H. beccarii also hinges the Graduate School of Biosphere Science, on its genetic and reproductive Hiroshima University and the former characteristics. Populations of H. beccarii at Raffles Museum of Biodiversity Research at its northernmost range off southern China30 the National University of Singapore. The and in central Vietnam31 were found with authors are grateful for the comments of the low genetic diversity and high clonality anonymous reviewers which improved the further sounding alarm bells to its manuscript further. vulnerability to global climatic changes and human pressures. This is also exacerbated LITERATURE CITED by the poor protection afforded to seagrass habitats where H. beccarii may be an 1. Larkum, A.W.D. 1995. Halophila capricorni insignificant component. But all hope is not (Hydrocharitaceae): a new species of seagrass lost. Recruitment through sexual from the Coral Sea. Aquatic Botany 51: 319- reproduction, though less common than 328. https://doi.org/10.1016/0304-3770(95)0047 4-E. clonal growth, can potentially provide 2. Green, E.P. and F.T. Short, eds. 2003. World avenues for local, short-distance dispersal of Atlas of Seagrasses. Prepared by the UNEP seeds31 despite the fact that seeds are World Conservation Monitoring Centre. negatively buoyant24. 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