Spatio-temporal variation of the zooplankton community in a tropical caldera lake with intensive aquaculture (Lake Taal, Philippines)
Rey Donne s. Papa· Macrina T. Zafaralla . Reiner Eckmann
Abstract Zooplankton were collected from Lake such as the Brachionus Trichocerca quotient (QBrr) Taal between January and December 2008 in order to and the ratio. of calanoids to c1adocerans and cyclo test for differences in species composition and poids, clearly demonstrate the eutrophic state of the abundance between a lake basin with intensive fish lake. A comparison with previous studies suggests cage (FC) aquaculture and an open water area that the lake was already eutrophic prior to the without FCs. Most species showed similar patterns introduction of aquaculture in the 1970s. The trophic of occurrence in both basins while having differences conditions in Lake Taal may be attributed to the in abundance. Several rotifer species were more lakes' tropical and volcanic nature, with productivity abundant in FC sites most of the year, while for further enhanced by increased nutrient input from microcrustaceans higher abundances in FC sites only aquaculture. happened during the first 2 months. Their distribution is attributed to the presence of higher nutrient levels Keywords Atelomixis· Sardinella tawilis . in FC sites as well as wind-induced basin-wide water Monsoon seasons· Brachionus Trichocerca quotient movements during the different monsoon seasons which disperse plankton and nutrients from FC sites to other parts of the lake. Zooplanktonic indicators, Introduction
The Iimnological features of tropical lakes are strongly affected by rain and wind during the Handling editor: Karl E. Havens monsoon seasons, both of which influence mixing and stratification. Strong winds and intense rainfall R. D. S. Papa (18]) Department of Biological Sciences, Graduate School following episodes of hot weather can lead to the and Research Center for the Natural Sciences, formation of multiple thermoclines, while heavy University of Santo Tomas, Manila, Philippines precipitation also promotes nutrient runoff from the email: [email protected]; [email protected] watershed. Together with high average temperatures M. T. Zafaralla and intense solar radiation, these factors support high In stitute of Biological Sciences, University productivity in tropical lakes (Tailing & Lemoalle, of the Philippines Los Banos College, Laguna, Philippines 1998). Volcanic lakes are a product of previous or R. Eckmann Limnological In stitute, University of Konstanz, persisting volcanic activity. The rocks and sediments Con stance, Germany in such lakes are natural sources of phosphorous, thus providing nutrients to boost phytoplankton growth. a new Taal Volcano Protected Landscape Manage Active volcano lakes may have thermal vents that ment Plan has been organized in order to monitor the serve as benthic heat sources and thereby enhance the lake and its watershed (Tvpl-Pamb, 2009). mixing of layers (Golterman, 1973; Tailing & Zooplankton community structure, population Lemoalle, 1998; Amarasinghe et aI., 2008). About dynamics, and production are strongly influenced by 10% of the total number of lakes worldwide occur in lake productivity (Sousa et aI., 2008; Zhou et aI., the tropics and of these, 10% are of volcanic origin 2009). The response of zooplankton to changes in (Lewis Jr., 1996). The unique combination of char nutrient content is a useful means of monitoring the acteristics found in tropical volcanic lakes makes anthropogenic eutrophication of lakes. We employed them particularly prone to eutrophication (Lewis Jr., this approach to assess the current state of Lake Taal 2000; Amarasinghe et aI., 2008). Lake Taal, the site and to compare it with previous data on the lake's of this study, is an active tropical volcanic lake trophic condition. located in Luzon, the largest island of the Philippine We hypothesized that aquaculture was the main archipelago. The lake occupies the remains of a cause of eutrophication in Lake Taal, and that its collapsed caldera and has a volcanic island at its effects would be manifest in the structure of the center. The island separates the lake into two zooplankton community. We further hypothesized basins a shallower northern zone in which fish cage that spatial patterns of zooplankton abundance and (FC) culture is practiced intensively and a deeper composition would reflect patterns of nutrient input, southern area, from which aquaculture cages are i.e., we expected to find differences between culture absent. areas and Fe free OW. Aquaculture, the branch of agriculture concerned with the farming of aquatic life, has increased at an average annual rate of 9.2% since 1970, compared Materials and methods with only 1.4% for capture fisheries and 2.8% for terrestrial farmed meat production (www.FAO.org). Study area This impressive growth rate is closely linked with the ever increasing world population and the concomitant Lake Taal (13°55' 14°05'N, 120°55' 121°105'E) is rise in demand for food. However, mismanagement the third largest lake in the Philippines. It is a caldera and a lack of proper scientific guidance have often lake with a surface area of 268 km 2 with mean and meant the ecosystem health has been sacrificed in maximum depths of 90.4 and 198 m, respectively. attempts to maximize profit and yield. The excessive Lake volume is 21,426 x 106 m3 with a 682.8-km2 use of commercial feeds increases nutrient input into catchment area and drains via the Pansipit River to aquatic ecosystems (Borges et aI., 2010), enhancing Balayan Bay in the southwest (Papa et aI., 2008; Perez phytoplankton growth, decreasing water transpar et aI., 2008). It is home to the worlds' lowest active ency, and increasing microbial activity in the sedi volcano (Taal volcano island), which has erupted 33 ments. In Lake Taal, aquaculture in net cages started times since 1572 (Zlotnicki et aI., 2009). Taal in 1975 and by the year 2000 was contributing Volcano Island partially separates the north (max. 15,268 mt or 52% of the country's total annual Fe depth 100 m) and south (max. depth 198 m) culture production (Vista et aI., 2006). At present, basins of the lake (Ramos, 2002; Perez et aI., 2008). Nile tilapia (Oreochromis spp.) and milkfish (Chanos Lake water is neutral to slightly alkaline (7.2 8.9 pH) chanos) are the most commonly reared fish (Aypa with high conductivity (1,600 1,700 J.!S/cm) (Perez et aI., 2008) in the lake. In 2006, the Lake Taal et aI., 2008). milkfish and tilapia were supplied with an average of 144 and 60.5 kg of feed per day, respectively (White Sampling et aI., 2007). Past under-regulation of stocking den sities and feed inputs into Lake Taal has led to a A total of six sites representing OW (south basin) and decline in water quality (Mamaril Sr., 200 I) which Fe areas (north basin) were sampled monthly from has threatened open water (OW) fisheries and January to December 2008 (Fig. I). Temperature, depreciated the esthetic value of the lake. In response, dissolved oxygen (DO), and transparency were Unger & Lewis (1991), and Amarasinghe et al. ..N (2008). 8 Data analysis
Data were analyzed using PAST Software Version 1.81 . Normal distribution was tested using the Shapiro Wilk test. Differences in spatio-temporal abundance, biomass, and physico-chemical variables were determined after values were log(x + 1) trans formed and compared across sampling periods using Kruskal Wall is ANOVA with a Bonferroni corrected pairwise Mann Whitney as a post hoc test. Principal component analysis was used to ordinate 72 sample Fig. 1 Map showing the six sampling sites in the north (NB) units and 4 factorial axes, which were grouped and south (SB) basins of Lake Taal. Arrows indicate wind according to monsoon season. The relationship of direction during the northeast (NE), southeast (SE), and southwest (SW) monsoons zooplankton biomass to physico-chemical data and FC number was analyzed using canonical correspon dence analysis (CCA) with Type II Scaling, while measured using a Radioshack infrared thermometer, Cluster Analyses with Bray Curtis similarity matrices the Winkler iodometric method, and a Secchi disc, were used to determine similarities in taxon occur respectively. Plankton samples were obtained with rence. The Brachionus Trichocerca quotient (Qsrr) two replicate vertical tows per site from 40 m to the (Silidecek, 1983) and the calanoid to cladocera + surface using a conical 80-flm mesh plankton net cyclopoid ratio were computed to quantify zooplank (diameter = 30 cm) and fixed in 5% formalin. ton community characteristics in relation to trophic Mean daily total rainfall, prevailing wind direction status. and details of tropical storms, depressions, and typhoons during the 2 weeks prior to each sampling were obtained from the government-run weather Results station. The number of FCs was obtained from the Provincial Government Environment and Natural Physico-chemical and meteorological variables Resources Office (PGENRO) of Batangas Province. Secchi disc transparency (SOT) ranged between 1.5 Specimen processing and 6.9 m with the highest values recorded in OW sites in January and February and the lowest values Zooplankton identification was performed to species seen in March and May in the FC sites (Fig. 2). SOT level for rotifers and cladocerans, while copepods in OW sites was higher than in FC sites for the first were grouped into adult male or female cyclopoids or 5 months of the sampling year. The succeeding calanoids, and copepodite or nauplius stages accord months saw similar SOT for OW and FC sites, ing to Fernando (2002), Mamaril (1986), Mamaril & except July and November, when OW sites had Fernando (1978), Dussart & Defaye (2001) and higher values than FC sites. Surface water tempera Petersen (2007). The number of egg-bearing females tures were similar for both basins, ranging between was also tallied. Density was determined by counting 25.9 and 31 .3°C. The lowest temperatures were zooplankton in three l-ml Sedgewick-Rafter sub observed in January and February, while highest samples per replicate (Wetzel & Likens, 1991). temperatures were recorded in July. Surface DO Individual lengths were measured to the nearest values ranged between 6.8 and 12.3 mg/l, and though 0.025 mm (Amarasinghe et aI., 2008). Total biomass similar for both basins were generally higher in OW (in flg/l) was determined for each taxon using length sites except in the months of May, June, September, weight regressions from Lewis (1979), Urabe (1992), and November. Fig. 2 Secchi disc 32 transparency, surface water 30 temperature, and surface U dissolved oxygen (DO) of 28 <> Lake Taal in 2008. 14 c. 26 E Kruskal Wallis ANOVA E 12 P values for SOT: 0.002, for c. 24 ~ 10 Temp: 0.79, for DO: 0.42. .9: 0 22 Significance was accepted C 8 at P < 0.016 6 8 --+- OW (Sout h Basin) ]: 6 -0- Fe (North Basin) I- 4 C Cl) 2
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Oec 2008
Seven typhoons/tropical storms/tropical depres Rotifers sions occurred within the 2-week periods prior to each sampling. May saw three typhoons, while June, July, Keratella tropica, Brachionus forficula, and Hexar August and September had one each. Total rainfall thra intermedia were the most abundant and com ranged from 3 to 431 mm per day, with the lowest monly occurring rotifers (Table I) followed by precipitation in February and the highest in July. B. havanaensis and Polyarthra vulgaris. A further High SDT and low DO contributed most variation 10 species either had low abundances or were rarely between sites during the northeasterly (December encountered in samples. Abundance was higher at FC March) and intermediate (October November) mon sites for Filinia longiseta, H. intermedia, K. tropica soon, while low SDT and high DO contributed much (P = 0.009), and P. vulgaris (P = 0.002) (Fig. 4). variability during the southeasterly (March April) Temporal variations were also observed in the monsoon. Typhoon occurrence and low SDT as well abundances of the other rotifer species. Percentages as high rainfall and wind direction were influential of ovigerous individuals were low for all rotifer during the southwesterly (May September) monsoon. species, with more recorded in FC areas than in OW PCA showed that the number of typhoons and low sites. B. falcatus had the highest percentage of egg SDT dominated the first principal component (51 .6% bearing individuals in both OW and FC sites. The variance), while the second principal component Brachionus Trichocerca quotient (Qsrd for the year (17.2% variance) was dominated by high SDT and 2008 was seven. low DO (Fig. 3). Microcrustaceans Spatio-temporal analysis of zooplankton Microcrustacean abundance and biomass was initially A total of 15 rotifer, 6 c1adoceran, and 3 copepod higher in FC compared to OW sites which became species were identified. One copepod (Pseudodiapto more similar in the succeeding months. Nauplii were mus brehmi) was not included in the subseq uent the most abundant forms among all taxa, followed by analyses due to its rarity. Overall, copepods made up cyclopoid copepodites. Among the c1adocerans, Cer 64% of average zooplankton abundance, followed by iodaphnia cornuta and Bosminafatalis had the highest the rotifers (27%) and c1adocerans (9%). In terms of abundance and biomass, respectively (Table 2). biomass, the copepods contributed 84% of the total, Calanoid copepods (males, females, and copepo while the c1adocerans made up 14% and the rotifers dites), nauplii, B. fatalis, c. cornuta, and Diaphano 2%. soma sarsi exhibited peak abundance in January Fig. 3 peA plot of 4 environmental variables: SDT, DO, temp., ave. wind dir. (Wind), typhoon 3 .2 * occurrence (T) and rainfall SDT (RF) in 2008. Plus northeast 2.4 monsoon, asterisk southwest monsoon, open square southeast monsoon, 1.6 open circle intermedi ate N Wind season .....c Cl) c 0.8 a.0 E 0 0 U
.0.8 Temp**** -1 .6 * o -2.4
-2.4 -1 .6 .0.8 0 0 .8 1.6 2.4 3 .2 4 Component 1
Table I Mean abundance, biomass, and frequency of occurrence of rotifer species from the open water (OW) and fish cage areas (FC) of Lake Taal
Average abundance (ind.ll) Average biomass (~gll) Frequency occurrence P value
OW Fe OW Fe OW Fe Abundance Biomass
Keratel/a tropica 30.9 57.4 4.0 7.5 lOO 100 0.009* 0.009* Brachionus fOfjicula 24.7 30.0 5.4 6.6 lOO 100 0.916 0.91 6 Hexarthra intermedia 30.0 66.8 6.9 15.4 lOO 100 0.011 0.011 Polyarthra vulgaris 0.3 9.3 0.1 2.7 58 92 0.001 * 0.001 * Brachionus havanaensis 2.9 9.9 1.7 5.9 33 50 0.945 0.945 Brachionus falcalus' 1.9 3.2 66 75 0.335 Brachionus quadridenfatus 0.0 0.0 0 8 Brachionus angularis' 0.1 0.5 17 25 0.5 61 Brachionus diversicomis' 0.2 0.8 25 25 0.548 Brachiol1us calycij/orus' 0.1 0.6 25 25 1.0 Filinia opoliensis 1.0 1.6 75 67 Filinia IOl1gise/a 0.1 0.9 42 83 Lecane bulla 0.1 0.0 17 0 Anuraeopsis navicula 1.0 1.5 67 67 Trichocerca capucina' 0.1 2.2 33 33 0.118 Total 94.3 184.7 18.2 38 .1
(') Denotes species whose abundance peaks were selected prior to stat isti cal analysis. Significance was accepted at P < 0.01 , indicated by an asterisk
(Fig. 5). C. cornuta, B. Jatalis, M. micrura, Diaphan Male and female calanoid copepods exhibited similar osoma spp. , and copepods had higher densities in Fe occurrence and abundance peaks, whereas in cyclo sites in January and February compared to OW sites. poids, females were more abundant than males. Peak K. tropica B. havanaensis H. intermedia 200.------. 200 .------, 200 ..,.------.,
150 150 150
100 100 100
50 50 50
O ...l..------=.--I 0-'------"'''---0-----' B. forficula P. vulgaris B. calyciflorus 200,----,------. 200 /0"'~------".----7
150 100 11 50
O -'-<:x.-.---'---=O::J'----'
B. diversicornis A. navicula B. falcatus ~ 10.------, 10 ,------.,.------. 20 ..,.------,
8 'ti 8 15 ~ ~ 6 6 'Cij 10 a; 4 4 C 5 2 2
B. angularis T. capucina L. bulla 10 ,------, 10 .------'------,-.----.
8 8
6 6
4 4
2 2
F. opoliensis F.longiseta B. quadridentatus 10
8 .'!l o- 2
- OW (South Basin) --0-- Fe (North Basin)
Fig. 4 Rotifer densities from open water (OW) and fish cage (Fe) areas of Lake Taal in 2008. Note differences in y axis values used Table 2 Monthly averages of abundance, biomass, frequency of occurrence, and P values of microcrustaceans from the open water (OW) and fish cage areas (FC) of Lake Taal, collected in 2008
Average abundance (ind.ll) Average biomass (J.lgll) Frequency of occurrence P value
OW FC OW FC OW FC Abundance Biomass
Nauplii 95.6 199.5 103.7 216.5 100 100 0.577 0.577 Calanoid Copepodile 35. 1 43.0 366.8 450.1 100 100 0.95 0.95 CycJopoid Copepodite 87.0 83.0 263 .2 251.2 100 100 0.579 0.579 Calanoid female 4.3 6.4 187 .5 280.9 75 83 0.42 0.42 Calanoid male 3.0 5.4 65.0 116.0 58 83 0.21 0.21 Cyclopoid female 29.4 26.5 185.5 167.3 100 100 0.849 0.849 CycJopoid male 13.7 11.8 46.7 40.4 100 100 0.419 0.419 Ceriodaphnia cornU/a 36.7 54.8 23.5 35.0 100 100 0.207 0.207 Moina micrura 7.3 15.8 44.0 94.8 100 100 0.015 0.015 Bmmina fatalis 19.8 32.2 47.2 77.4 100 100 0.893 0.893 Diaphanosoma excisum 3.9 5.1 6.0 7.9 67 100 0.31 0.31 Diaphanosoma sarsi 3.6 5.0 14.5 20.2 92 100 0.941 0.94 1 Diaphanosoma tropicwn 2.2 2.1 9.0 8.4 67 92 0.984 0.984 Total 341.4 490.7 1362.6 1766.0
Average abundances of M. miaum and B. fatalis were higher in FC sites due 10 high densities in January (B. faIC/lis) and January to March (M. micrura) abundance for cyclopoids was observed in July for different zooplankton taxa included clustered near the females and in August for males. Calanoid copepodites center of the bi-plot. Bray Curtis Cluster Analysis were generally less abundant than cyclopoids. Cala confirmed the results of CCAs and the spatio noid copepodite abundance peaked in April in OW temporal analyses of zooplankton distribution. The sites, while cyclopoids were most abundant in March. taxa which had more variable abundances between Naupliar abundance peaked in January at 1,300 ind./I OW and FC sites grouped together (Fig. 8). The in FC sites but then remained below 300 ind./I for the nauplii, cyclopoid copepods, copepodites, C. cornuta, rest of the year. B. jatalis, K. tropica, and H. intermedia formed Bosmina jatalis, Moina micrura, and Ceriodaph one group, while the calanoid copepods, D. sarsi, nia cornuta recorded the highest percentage of egg D. excisum, D. tropicum, and B. havanaensis formed bearing individuals, while Diaphanosoma spp. had another. the lowest (Fig. 6). Of all female copepods recorded throughout the entire year, fewer than 5% were egg bearers (Table 3). The calanoid to c1adocera + Discussion cyclopoid ratio was low for all sampling months, reaching a maximum of 0.5 in May, while no It was hypothesized that FC sites may exhibit calanoids were observed in October. different zooplankton abundance and community composition compared to OW sites. Nutrient inputs from uneaten fish feed, increased microbial activity in Multivariate analysis the lake bottom, and a decrease in water quality have been noted in the vicinity of FCs in Lake Taal The CCA bi-plot showed how the sites grouped (Alcanices et aI., 200 I; Vista et aI., 2006; Perez et aI., together based on the presence of FCs as well as 2008; Hall are et aI., 2009). The density of FCs in the physico-chemical variables such as DO, temperature, north basin has already exceeded the lake's carrying and SDT (Fig. 7). There was a clear distinction capacity (White et a I. , 2007). We observed hi gher between sites I and 3 (OW) and 4 and 6 (FC). The SDT and DO in the OW compared to the FC areas, C. cornuta B. fatalis M. micrura D. excisum 300,------, 300 ,------, 100 .,.------,
250 250 80 200 200 60 150 150 40 100 100 20 50 50
D. tropicum D. sarsi Cy. Male Cy. Female 50.,.------~ 300y 250 40 150
-0 30 ~ 100 ~ .iij 10 20 c: eLl 50 o 10
o ..l.-__-=-...il!!joi;"--.J
Cal. Male Cal. Female Cy. Copepodite Cal. Copepodite 50,------~ 50,,------, 300 .,.------~ 300 ,------.
250 250 40 40 200 200 30 30 150 150 20 20 100 100
10 10 50 50
2000 .,-,r-__N_ a_u...!.p_li_i --~
1500
1000 ____ OW (South Basin) 500 -0- Fe (North Basin)
Fig. 5 Microcrustacean densities from open water (OW) and fish cage (Fe) areas of Lake Taal in 2008. Note differences in y axis values used Fig. 6 The monthly Calanoid Cope pod Cyclopoid Copepod percentage of ovigerous 50,------, 50,------, microcrustacean females recorded during 2008. Note 40 40 different y ax is used for D. exciswn 30 30
20 20
10 10
C. cornuta M. micrura 100 ,------, 100 .------.
80 80
60 60
40 40
:!l 20 20 iii E .f O -'------~ VI B. fatalis D. excisum 5... 100 ,------. Q) Cl .s; 80 o 'Q'!. 60
40
20
0 -'------' D. sarsi D. tropicum 50 ,------, 50 ,------'------,
40 40
30 30
20 20
10
--e-- OW (South Basin) -0- Fe (North Basin) Table 3 Average percentage of ovigerous rotifer and micro suggesting higher turbidity due to uneaten feed and crustacean females in monthly samples collected from Lake fish feces and/or higher primary production due to Taal in 2008 from open water (OW) and fish cage (FC) sites high-nutrient input. Overall, the zooplankton com Percentage munity showed similar species composition for an OW FC entire year in both parts of the lake (Tables 1, 2). However, higher abundances were found in FC sites K. tropica 3.7 4.0 either during the first few months (microcrustaceans) B.Joificula 2.7 6.8 or throughout most of the year (rotifers). B. havanaensis 1.9 3.3 The higher nutrient levels in FC sites may have H. intermedia 1.9 0.4 promoted increased primary productivity which in P. vulgaris 0.0 2.4 turn led to higher zooplankton densities; however, the Calanoid Copepod 3.8 2.5 lack of spatial differences in the distribution of Cyclopoid Copepod 1.3 2.4 zooplankton may be attributable to the influence of C. cornuta 17.9 18.3 wind and rainfall in dispersing plankton and nutri M. micrum 30.6 \9.7 ents. Limnological characteristics unique to tropical B. Jatalis 42.8 34.2 regions such as the formation and dissipation of D. excisum 0.0 0.1 thermoclines in tropical lakes (atelomixis) are D. sarsi 0.3 1.8 strongly influenced by wind-induced water move D. tropicum 6.0 6.0 ments and temperature inversions caused by rainfall (Lewis Jr., 1996). Lake Taal lies only 2.5 m above
Fig. 7 Canonical correspondence analysis of the six sampling sites in Lake Taal (I 3 OW, 4 6 2.5 FC). Each point represents one zooplankton taxa that 5 have been included in the 2 analysis. Secchi disk transparency (SDT), dissolved oxygen (DO), 1.5 temperature (TEMP), and number of fish cages (FC) were used as environmental variables • Fe
o
2 6
-1
-1.5
~+---~----.----.----~---.----~----.---~----.------2 -1.6 -1.2 .0.8 .oA 0 OA 0.8 1.2 1.6 Axis 1 Fig. 8 Cluster analysis ...------1 CIF based on Bray Curtis similarity matrices of CIM zooplankton biomass in the Brh sampling sites of Lake Taa!. De Keratella tropica Kt, Brachionus fQ/ficula Brf, Ds Hexarthra intermedia Hi, Dt Polyarthra vulgaris Pv, Hi Brachionus havanaensis Brh, Nauplii n, Calanoid Kt Copepodite ClC, Cc Cyclopoid Copepodite CyC, Calanoid female CIC CIF, Calanoid male ClM, CyF Cyclopoid female CyM, Bri Cyclopoid male CyM, Ceriodaplmia comu/a Cc, Bf Moina micrura Mm, CyC Bosmina fatalis Bf, n Diaphanosoma excisum De, Diaphanosoma sarsi CyM Os, Diaphanosoma Mm tropicum Dt Pv
o 0.12 0.24 0.36 0.48 0.60 0.72 0.84 0.96 Slmllarity
sea level, and the uneven height of the caldera ridges the comparable densities of the microcrustaceans in makes it prone to strong winds. Wind-induced the OW and FC sites. currents are important in determining the distribution Lake mixing, wind currents, and increased rainfall of epilimnetic larval fish, phyto- and zooplankton may not have played a prominent role in determining (Rinke et aI., 2009), and in Lake Taal, their influence the abundance and distribution of rotifers as they is likely to be even greater due to the smaller size of were found in higher densities in FC sites even after tropical zooplankton (Fernando, 1980). Lake mixing, lake mixing. Results of the Kruskal Wallis ANOVA which coincides with the northeast monsoon (December revealed higher abundances in FC sites compared to to February), may have been the reason why the OW sites for K. tropica and P. vulgaris, while F. higher abundances of microcrustaceans in FC sites longiseta and H. intermedia occurred in higher only happened during the earlier part of the year as it numbers in FC sites in most months albeit the can aid the dispersal of both plankton and nutrients differences were not significant for abundance values. from areas with higher concentrations. The onset of Canonical correspondence analysis showed that the southwesterly monsoon where there is higher abundance did not vary significantly between OW rainfall and stronger wind from typhoons further and FC sites except for five taxa which were more supported this. Nutrient run-offs from the sediments associated with FC sites (copepod nauplii and four during periods of heavy rainfall also increase the rotifer species B. havanaensis, H. intermedia, P. amount of nutrients entering the lake (White & San vulgaris, and K. tropica). They either had high Diego-Mcglone, 2008). The principal component abundances in FC sites in I month (copepod nauplii analysis shows how the physical and chemical and B. havanaensis) or in several months (H. variables in the lake were influenced by the monsoon intermedia, P. vulgaris, and K. tropica). Cluster seasons (Fig. 3). This may have further supported analysis then confirmed that taxa with similar distri phytoplankton populations in OW sites which led to butions formed distinct groupings. Those with higher densities in FC sites were more closely related with areas, though some had higher abundances in FC sites one another, while those that had similar densities similar to the abundances of dominant rotifer species. between OW and FC sites were found in the other Predation by Sardinella tawilis may have an group. The abundance of dominant rotifers in FC influence on zooplankton abundance and distribution. sites may be due their tolerance for more eutrophic S. tawilis is the dominant pelagic fish species in Lake environments. Previous studies have used rotifer Taal and is an efficient size-selective zooplanktivore abundance and occurrence as efficient bioindicators (Papa et aI., 2008). Their largest available prey would of higher trophic levels (Si