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Methane-oxidizing bacteria (MOB) is a group of planktonic microorganisms that use methane as their primary source of cellular energy. For tropical lakes in monsoon Asia, there is currently a knowledge gap on MOB community diversity and the factors influencing their abundance. Herewith, we present a preliminary assessment of the MOB communities in three maar lakes in tropical monsoon Asia using Catalyzed Reporter Deposition, Fluorescence In-Situ Hybridization (CARD-FISH), 16S rRNA amplicon sequencing, and pmoA gene sequencing. Correlation analysis between MOB abundances and lakes' physicochemical parameters following seasonal monsoon events were performed to explain observed spatial and temporal patterns in MOB diversity. The CARD-FISH analyses detected the three MOB types (I, II, and NC10) which aligned with the results from 16S rRNA amplicons and pmoA gene sequencing. Among community members based on 16S rRNA genes, Proteobacterial Type I MOB (e.g., Methylococcaceae and Methylomonadaceae), Proteobacterial Type II (Methylocystaceae), Verrucomicrobial (Methylacidiphilaceae), Methylomirabilota/NC10 (Methylomirabilaceae), and archaeal ANME-1a were found to be the dominant methane-oxidizers in three maar lakes. Analysis of microbial diversity and distribution revealed that the community compositions in Lake Yambo vary with the seasons and are more distinct during the stratified period. Temperature, DO, and pH were significantly and inversely linked with type I MOB and Methylomirabilota during stratification. Only MOB type I was influenced by monsoon changes. This research sought to establish a baseline for the diversity and ecology of planktonic MOB in tropical monsoon Asia to better comprehend their contribution to the CH4 cycle in tropical freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Lake Taal is one of the most significant lake ecosystems in tropical East Asia. In 2011, a review paper consolidated all known biodiversity and limno-ecological studies conducted in Lake Taal from the beginning of the 20th century all the way to the late 2000s. It highlighted that insufficient funding, inadequate long-term monitoring data, and the publication culture of that time impeded having a comprehensive understanding of the lake. Since then, much research work has been done in Lake Taal, especially during the past decade. This review paper provides an analysis and summary of the research work conducted in Lake Taal over the past 10 years. The recent decade has seen a steady increase in scientific interest in Lake Taal made evident by more scientists and institutions working on topics involving the lake. Research grants, collaborations, and publications have also significantly increased during the past 10 years. This has led to an improved understanding of the lake's biodiversity, ecology, and impacts of intensive aquaculture and the introduction of non-native species. Taken together, this paper presents a better understanding of Lake Taal, which can be utilized for the design and improvement of conservation, preservation, and management programs for this multi-use freshwater system. [ABSTRACT FROM AUTHOR]

A floristic study of the diatoms (Bacillariophyceae) along the Marikina River in the eastern part of Metro Manila, Philippines, recorded at least 140 species belonging to 39 genera. Of these genera, one of the greatest number of species was observed in the genus Gomphonema (18 species). These species were identified and described under the bright field light microscope. Some species were further observed under the scanning electron microscope. A habitat description of the occurrence of the Gomphonema species is given. Twelve (12) out of the 18 species are new records for the country: G. brasiliense subsp. pacificum Moser, Lange-Bertalot & Metzeltin, G. chinense Liu & Kociolek, G. contraturris Lange-Bertalot & E.Reichardt, G. cuneolus E.Reichardt, G. exilissimum (Grunow) Lange-Bertalot & E.Reichardt, G. insigniforme E.Reichardt & Lange-Bertalot, G. javanicum Hustedt, G. kobayasii Kociolek & J.C.Kingston, G. pseudosphaerophorum H. Kobayasi, G. sundaense E.Reichardt, G. cf. qingyiensis L-X Zhang, P. Yu & Q-M You, and G. vibrio var. bohemicum (Reichelt & Fricke) R. Ross. Hence, this paper reports a total of 44 species of Gomphonema from the Philippines, including previous studies from 1937 to date. [ABSTRACT FROM AUTHOR]

We conducted a preliminary analysis on the effects of various physical and chemical parameters on the morphometry and reproductive capacity of the calanoid copepod Filipinodiaptomus insulanus (Wright, 1928), endemic to the Philippines, by proxying clutch size (CS). Specimens and water quality readings were obtained between October 2019 and February 2020 from four sites in northern Philippines. Only the sizes of adult males and non-ovigerous adult females showed significant differences (P < 0.05) among populations. Non-eutrophic, temporary shallow waters were the predominant habitat type of F. insulanus , corroborating earlier observations that it is mainly found in relatively pristine environments. Correlation analysis showed a significant indirect relationship (P < 0.001) between the size of individuals and temperature, a potential adaptive response to its environment. Such observations may be valuable in preventing the disappearance of this species from parts of its previously known range. [ABSTRACT FROM AUTHOR]

Sponge-microbe symbiosis is considered among the most primitive ecological relationships between metazoans and microorganisms. There is strong interest in understanding the occurrence of microbial communities in sponges due to their integral roles in host ecology, nutrient cycling, and production of potential bioactive secondary metabolites. However, most studies on sponges have been centered on marine species. In this study, the freshwater sponge Spongilla alba and its associated microorganisms were explored for the first time. Sponge samples collected from Lake Taal were taxonomically identified using gross morphology and spicules analysis. Both bacterial and fungal isolates were culturally characterized and molecularly identified using 16S rRNA gene for bacteria and ITS for fungi. Five bacterial species were identified as Pseudomonas sp., Enterococcus sp., Stenotrophomonas sp., Stenotrophomonas maltophilia, and Pseudomonas mosselii plus eight fungal species with spore sizes from 5-10 μm were identified as Colletotrichum truncatum, Trichosporon asahii, Rhizopus microsporus, Puccinia striiformis f. sp. tritici strain, Talaromyces columbinus, Phoma sp., Phomopsis sp., and Lichtheimia ramosa. Phylogenetic analysis revealed microbial sequences belonging to Proteobacteria (n = 4), Firmicutes (n = 1), Ascomycota (n = 4), Zygomycota (n = 2), and Basidiomycota (n = 2). The study reports infrequent occurrences of Enterococcus, Stenotrophomonas, Puccinia, and Lichtheimia species as freshwater sponge-associated microbes. This also presents the culturable microbial composition of freshwater sponges and rare occurrence of marine- and terrestrial-associated fungi T. asahii, R. microsporus, Phoma sp., Phomopsis sp., C. truncatum, and T. columbinus in a unique freshwater ecosystem such as Lake Taal. [ABSTRACT FROM AUTHOR]

The center-periphery hypothesis (CPH) predicts that peripheral populations will have lower genetic variation than those at the center of a species' distribution. However, ecological margins do not always coincide with geographical edges when topographies are diverse. Historical climate changes can also strongly affect genetic variation. Here, we examined genetic variation in Phyllodiaptomus tunguidus , a calanoid copepod endemic to the north-eastern Oriental. This species was predicted to exhibit a complex pattern of genetic variation across its range due to the diverse topographies and stable climate history of the north-eastern Oriental. To test this, we used geographic distance to the center of the distribution, current ecological suitability, and climate during the last glacial maximum as geographical, ecological, and historical factors, respectively, in our analyses. We measured genetic diversity and population differentiation using mitochondrial and nuclear markers. This showed that P. tunguidus had 3 refugia during the last glacial maximum (LGM). Such a pattern of multiple refugia complicates the determination of the center and periphery of spatial genetic diversity. Both regression models and redundancy analyses failed to support the CPH. Instead, they showed that geographical, ecological, and historical factors together shaped population genetic structure in this species. Ecological factors explained significantly more genetic variation than did geographical and historical factors—however, all three factors interacted significantly to affect the pattern of genetic variation. The results extend our understanding of the CPH and the extent to which it can explain genetic variation across populations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Relatively limited information exists on Lake Wood's limnology and ecology, an ancestral lake of the Subanens. Here, we provide a limnological characterization of the lake -- exploring its physical, chemical, and biological features. The data on lake morphometry were gathered using an echosounder; lower depth water samples were collected using a Niskin water sampler for physicochemical analyses while surface water samples were collected at five sampling sites for phosphate (PO4) analysis; and zooplankton samples were collected at several depths through vertical towing in March-April 2019. Lake Wood, located at 320 m above sea level, has an extensive surface area covering 7.38 km² with a maximum depth of 85 m. Lake water comes from rainfall, small rivers, and groundwater and empties into the Dumanquilas Bay via its only outlet -- the Biswangan River. Land use of the lake is predominantly cultivated land. Moreover, based on the trophic state index (TSI), the lake's current trophic status is eutrophic. During the study periods, thermocline and oxycline formed at 15 m below the surface of the lake. We recorded three cladocerans (Ceriodaphnia cornuta, Diaphanosoma cf. sarsi, and Moina micrura) and one copepod species (Thermocyclops crassus) in the lake, all of which are common limnetic species found in the Philippines. Based on our findings, we recommend more efforts to manage and rehabilitate the lake to control and manage eutrophication's negative impacts. Finally, our study contributes to understanding lakes in Mindanao that are less represented in Philippine freshwater research. [ABSTRACT FROM AUTHOR]

Zooplankton are key ecosystem components in the pelagic food web. These organisms move vertically to avoid visual predators (i.e. fish) that prey on them; such movement is known as diel vertical migration (DVM). This study aims to elucidate the dynamics of the daily vertical migration of zooplankton and to determine the factors that govern their migration behavior in an understudied Philippine Lake in Lake Wood (Mindanao Island) from March to April 2019. Zooplankton and several environmental parameters were sampled in the deepest part of the lake at specific depths (1 m, 15 m, 30 m, 50 m, and 70 m) during noon and midnight. Adult females of Thermocyclops crassus displayed typical diel vertical migration patterns accompanied by large migration amplitudes. The food-rich epilimnion supports the abundance of T. crassus during the night and rather dwells in the hypolimnion during the day to evade visual predators. The study underscores the intricate interplay among predation pressure, temperature, water transparency, and total dissolved solids, collectively shaping the observed vertical migration behavior of adult female T. crassus. These perspectives provide a deeper understanding of how these organisms navigate the intricate challenges posed by their environment, offering insights into their strategies for survival and thriving within the ecosystem. [ABSTRACT FROM AUTHOR]