281 Philippine Seven Tropical Maar Lakes are Ideal Habitats for the Invasive Arctodiaptomus dorsalis Marsh, 1907 (Copepoda: Calanoida) Justine R. de Leon 1 *, Dino T. Tordesillas 1,2 , Irian J.L. Biag 3 , Sean H.L. Cusi 3 , John A.B. Tan 3 , Edna Marie Mijares 1 , Jaydan I. Aguilar 1 , and Rey Donne S. Papa 1,3,4 1 The Graduate School; 2 Senior High School 3 Department of Biological Sciences, College of Science 4 Research Center for the Natural and Applied Sciences University of Santo Tomas, Manila 1015 Philippines The presence of the invasive calanoid copepod Arctodiaptomus dorsalis in Philippine inland waters has been reported in numerous studies. Attempts to understand how it effectively proliferated in the country’s freshwaters have shown its preference towards shallow and productive waters – a feature shared by most lakes in the Philippines. In this study, we compared the body size and reproductive capacity – proxied by clutch size (CS) – of ovigerous female A. dorsalis obtained from established populations in the seven maar lakes (SML) of San Pablo, Laguna, Philippines. These measurements were also correlated with selected water quality parameters. Collection of ovigerous A. dorsalis and water quality parameters were conducted on a 3-mo sampling period during the southwest monsoon season in 2016. Statistical analysis shows that there exists a significant difference between the prosome length (PL) and CS of A. dorsalis from the seven lakes (p < 0.001), with the shallowest and most productive lake containing the most fecund population. Additionally, all water quality parameters showed a positive correlation with the PL and CS of ovigerous A. dorsalis from the SML (p < 0.01). This shows that the SML provides favorable conditions for the propagation of A. dorsalis, making it a model for in situ investigation of this invasive species’ ecology; the first step in incorporating zooplankton ecology as a tool for the development of lake management systems. Keywords: freshwater zooplankton, lake management, morphometrics, tropical lakes *Corresponding Author: justine.deleon.gs@ust.edu.ph INTRODUCTION Arctodiaptomus dorsalis (Marsh 1907) is a Neotropical calanoid copepod named after the dorsal projections on the posterior thorax of its adult females (Bruno 2005). First recorded in New Orleans, Louisiana, it has long since spread through the southwestern United States up to Haiti in the Antilles and northward to Colombia up to Venezuela (Reid 2007). Its entry into new habitats has been linked to the eutrophication of freshwaters due to the widespread use of aquaculture where this species has been found to thrive (Reid 2007; Havens and Beaver 2011). Intentional release of non-indigenous fish species for aquaculture has been shown to promote the introduction of related non-target species, copepods in particular Philippine Journal of Science 151 (1): 281-290, February 2022 ISSN 0031 - 7683 Date Received: 02 Aug 2021