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In developing countries such as the Philippines, the inadequacy of even the most basic limnological datasets available has hindered planning and implementation of science-based management policies for inland waters. This situation is aggravated by overutilization of natural resources for ecosystem services such as water usage, aquaculture, fishing, and tourism. We reviewed published researches related to the Seven Maar Lakes (SMLs) in Luzon Is., Philippines to summarize information invaluable for the protection and sustainable use of these resources. Popular scientific search engines were utilized to gather peer-reviewed research articles and reports from both private institutions and government agencies. Literature and timeline from the 1930s to 2019 was classified into topics – namely socioeconomics, fisheries, biodiversity, and environment. Based on the literature survey, a variety of challenges, knowledge gaps, and promising research directions were identified, which are essential to the sustainable ecosystem management of the SMLs. Aquaculture practices impacting the lakes and its underestimated biodiversity were described. Measured vertical profiles of dissolved oxygen (DO), temperature, conductivity, pH, and salinity was supplemented by our preliminary limnological survey in the SMLs. Past and present monitoring data of selected physicochemical parameters were assessed from which the changing limnological status of the lakes was determined. We recommended measures motivated by strategic environmental assessments while still considering maintained economic yields. A sustained collaborative effort from different sectors is strongly suggested not only to manage the SMLs but also to address trade-offs among critical ecosystem services. Aside from the need for well-designed, long-term water quality monitoring, we also stress the synergistic interpretation of all available knowledge, which can contribute to the resolution of environmental issues at both local and global scales. [ABSTRACT FROM AUTHOR]

In this paper, we aimed to contribute to the conservation research of a heavily impacted tropical lake ecosystem by characterizing its previously undescribed fish diversity and also elucidating the trophic structure of its fish community. Our study area is Lake Sampaloc, a small crater lake in the southern region of Luzon Island, Philippines. This lake has been heavily used for economic resource functions, such as aquaculture, for decades. Hindrances to the effective implementation of regulatory provisions have produced detrimental ecological effects on the lake, which has recently been declared as "Threatened Lake of the Year 2014". We employed several sporadic fish surveys during a span of two years (2012 to 2014) to identify fishes in the lake. We also used stable isotope analysis to elucidate the trophic level and production reliance of important aquatic consumers. We discovered that the lake fish populations are heavily reliant on periphyton production and are mostly composed of non-native and potentially established invasive fish species. In addition, trophic niche overlaps are observed among non-native fish and native species. For the past three decades, Lake Sampaloc has been classified as eutrophic with high phytoplankton standing biomass. A possible direction for lake rehabilitation research is to investigate ways to change the present turbid state into a clear water system that is predominantly composed of submerged native vegetation. Such a macrophyte-based environment may help sustain the development and recruitment of native juvenile fish and also provide a more diverse functional habitat for fish assemblages that have overlapping trophic niches. [ABSTRACT FROM AUTHOR]