© Science China Press and Springer-Verlag Berlin Heidelberg 2010 csb.scichina.com www.springerlink.com Article SPECIAL TOPICS: Ecology August 2010 Vol.55 No.23: 2522–2528 doi: 10.1007/s11434-010-4107-2 Dynamics of phytoplankton and picoplankton over a tidal cycle in a subtropical lagoon TEW Kwee Siong 1,2* , MENG Pei-Jie 1,2* , LEE Hung-Jen 3 , YE Yi-Xiu 2 , KUO Jimmy 1,4 , FANG Lee-Shing 5 & CHOU Wei-Rung 1 1 Museum of Marine Biology & Aquarium, Pingtung 94450, Taiwan, China; 2 Institute of Marine Biodiversity & Evolution, Dong Hwa University, Pingtung 94450, Taiwan, China; 3 Taiwan Ocean University, Keelung 202-24, Taiwan, China; 4 Institute of Marine Biotechnology, Dong-Hwa University, Pingtung 94450, Taiwan, China; 5 Cheng Shiu University, Kaohsiung County 833, Taiwan, China Received August 3, 2009; accepted January 28, 2010 The influences of a tidal cycle on the distribution of autotrophic plankton were investigated in a hyper-eutrophic lagoon desig- nated as a scenic area. Results showed that the highest concentrations of picoplankton and phytoplankton were found in the mid- dle and inner part of the lagoon, irrespective of the tides. The MDS result also revealed that phytoplankton communities, domi- nated by Ceratium furca, were similar among stations in the inner bay during both flood tides and ebb tides. The time series sam- pling results at the inlet-outlet channel revealed that almost the same amounts of phytoplankton and picoplankton were carried through the channel during flood and ebb tides, with no trend in nutrient fluctuations except for phosphate which had a net loss from the lagoon. The results showed that tidal cycles do not effectively flush away phytoplankton and picoplankton from the la- goon, and the blooming of phyto- and picoplankton is inevitable should the situation stay the same. Steps are needed to alleviate the eutrophication condition instead of depending on the natural process such as tidal cycle. phytoplankton, picoplankton, tidal cycles, nutrients, lagoon, Taiwan Citation: Tew K S, Meng P J, Lee H J, et al. Dynamics of phytoplankton and picoplankton over a tidal cycle in a subtropical lagoon. Chinese Sci Bull, 2010, 55: 2522−2528, doi: 10.1007/s11434-010-4107-2 Eutrophication, or the enrichment of a water body with nu- trients such as nitrogen and phosphorus, in the coastal area is a common problem faced by a lot of countries in the world [1,2]. An algal bloom resulting from eutrophication is not only aesthetically distracted, it also causes environ- mental problems such as anoxia, fish death, and sometimes human illness after consuming the contaminated shellfishes [3–5]. The abundance of phytoplankton and picoautotrophs in a water body depends on a number of factors: top-down effects, such as predation from zooplankton or bivalves [6,7], bottom-up effects such as the availability of nutrients [8] and physical factors such as temperature, salinity, pH, light and dissolved oxygen [9]. In a confined area such as a *Corresponding authors (email: tewks@nmmba.gov.tw; pjmeng@nmmba.gov.tw) bay or a lagoon, additional factors such as vertical mixing of water, and the efficiency of water exchange during tidal cycles also affect the phytoplankton abundance [10]. Exchange of water between lagoons and the ocean usu- ally depends on the tidal cycles [11–13] and wave actions [14]. Generally nutrient-rich water in a lagoon is diluted by coastal water during flood tides, and the nutrients in the mixed water are carried away to the open ocean during ebb tides. However, the efficiency of water exchange depends on several factors, including the volume and the shape of a lagoon, and the cross section of the inlet channel [15,16]. When the circulation is weak in a bay, the restricted regions could accumulate nutrients and phytoplankton biomass, which may lead to degradation of water quality and some- times blooming of algae [10].