An unseen invasion in Philippine lakes

Lakes are an important natural resource for our country. It provides communities with bountiful catches of fish and other aquatic animals such as crabs, prawns, snails and bivalves; its watersheds are home to highly diverse flora and fauna. Their natural beauty cannot be overlooked — with breathtaking views, and as venue for sports and other recreational activities (sailing, kayaking, sport fishing etc.), lakes have consistently been big natural tourist attractions. In the Philippines, lakes such as Taal, the seven lakes of San Pablo, the twin lakes of Danao and Balinsasayao and Paoay have continued to attract droves of tourists each year. In terms of geological origin, the Philippines is probably home to one of the greatest concentrations of volcanic lakes in the world. Ecologically, these serve a variety of functions, such as acting as heat and nutrient “sinks,” trapping excesses from the surrounding ecosystem, which has also been useful for scientists studying climate change and environmental degradation. Some have even dubbed lakes as “sentinels” of climate change. As is true with other lakes worldwide, human communities have sprung up in our lakeshores as testament to its role in shaping civilizations. The provinces of Laguna and Rizal, the city of Marawi and the communities of the T’boli all have lakes as the epicenter of their societies.

It is rather unfortunate that lakes are also one of the most sensitive and vulnerable aquatic ecosystems because they are enclosed systems. Decades of under-regulated building of factories without proper wastewater treatment facilities, the influx of informal settlers and poor monitoring of aquaculture activities have damaged some of our most prized lakes, including the Philippines’ largest — Laguna de Bay. Massive fish kills, murky waters, unsightly views and foul odors usually inflict damaged lakes. As large bodies of water with very narrow outlets to the sea (rivers), it takes decades for lakes to naturally flush out unwanted wastes and rehabilitate themselves. Furthermore, disease outbreaks in lakeshore communities can often be traced to their unsanitary practices that do not merely damage the lake, but also the health and wellness of the communities that live in it. Lakes are also extremely vulnerable to “alien invasions.” This was the case with the armored sailfin catfish, more popularly known as janitor fish, and the knife fish which are now established in Laguna de Bay. These fishes, along with many others from the aquarium and aquaculture trade, are not native to the Philippines. Their introduction poses a great threat to the local fish communities which may be outcompeted for space and resources. Invasion by non-indigenous fish has caught more attention because they are conspicuous and seen even among regular fish catch. Microscopic invasive species, meanwhile, have escaped attention in spite of their similar, if not more potent negative effects on lake ecosystems.

In our recent paper published in the journal Biological Invasions, we (a team of Filipino, Chinese and Belgian scientists) discuss the spread of an introduced species to 18 lakes in the whole archipelago. The calanoid copepod Arctodiaptomus dorsalis (< 1mm in size) is a Neotropical species (originally described from the US) that has spread beyond its natural range, usually to eutrophic (nutrient rich) aquatic ecosystems. Calanoid copepods are microscopic crustaceans that are normal inhabitants of lakes, but the distribution of different species is usually restricted based on geographical and latitudinal gradients. Our study was originally conducted to assess calanoid copepod diversity; to our surprise, however, we found out that instead of finding previously recorded species (and perhaps even new ones) we discovered how widespread this non-native species has become in the Philippines. Similar to the situation in North and Central America, we found that areas with newly established A. dorsalis populations are utilized heavily for aquaculture. We are afraid that the introduction of this species to our lakes may have displaced native and endemic calanoid copepods way before we got to properly document them. A. dorsalis may have come to the Philippines via drinking water reserves of transcontinental ships that dock in Manila Bay, an idea first suggested by the study of Tuyor and Baay (2001) when they recorded A. dorsalis from lakes Sebu, Mainit and Laguna de Bay. Its spread to other previously uninhabited lakes has been hastened by aquaculture. The presence of this invasive species has already caused a decline in the diversity of native calanoid copepods, and this may even spread further to mainland Asia. It is rather unfortunate that since it has now become so widespread, we cannot do much to stop its proliferation, especially since we depend heavily on cultured fish to satisfy the needs of our growing population. But hopefully this discovery can help make us more aware for the need to intensify efforts to study all aspects of Philippine biodiversity before they are further displaced by introduced species, habitat loss and climate change. Although calanoid copepods are microscopic and not as prominent as the Philippine Eagle, tarsier or tamaraw, a species lost is still a loss for all of us. 

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Based on the article Papa RDS, Li H, Tordesillas D, Han BP, and Dumont H. (2012). Massive Invasion of Arctodiaptomus dorsalis (Copepoda, Calanoida, Diaptomidae) in Philippine Lakes: A Threat to Asian Zooplankton Biodiversity? Biological Invasions10.1007/s10530-012-0250-9

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Dr. Rey Donne Papa (assistant professor of Biological Sciences at the University of Santo Tomas) is a limnologist who specializes in freshwater zooplankton ecology and systematics. He has conducted many researches in Lake Taal and has published in both national and international peer-reviewed journals. He was a recipient of the Tonolli Fund Postgraduate Fellowship in Limnology (International Society of Limnology) and was a DAAD Research Fellow at the Limnological Institute of the University of Konstanz, Germany. He finished his B.S., M.Sc. and Ph.D. degrees from the University of Santo Tomas. He can be reached at [email protected].

Dino T. Tordesillas (M.Sc. Biological Sciences candidate) is a faculty member at St. Paul’s University, Quezon City where he teaches biology. He has collected zooplankton from many lakes and freshwater ecosystems and is currently finishing his Master’s thesis on the species composition and distribution of Calanoid copepods in Philippine lakes.