Red tides in Masan Bay, Korea, in 2004–2005: III. Daily variations in the abundance of mesozooplankton and their grazing impacts on red-tide organisms Jae Seong Kim a , Hae Jin Jeong b, *, Yeong Du Yoo b , Nam Seon Kang b , Soo Kyeum Kim c , Jae Yoon Song d , Moo Joon Lee b , Seong Taek Kim e , Jung Hoon Kang f , Kyeong Ah Seong c , Won Ho Yih c a Water and Eco-Bio Corporation, Kunsan National University, Kunsan 573-701, Republic of Korea b School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea c Department of Oceanography, College of Ocean Science and Technology, Kunsan National University, Kunsan 573-701, Republic of Korea d Korea Engineering Consultants Corporation, 546-1, Guui-dong, Gwangjin-gu, Seoul 143-715, Republic of Korea e B&G Eco Tech, 140 Top-ri, Chukdong-myeon, Sacheon-si, Gyeonnam 664-811, Republic of Korea f South Sea Branch, Korea Ocean Research and Development Institute (KORDI), 391 Jangmok-ri, Jangmok-myon, Geoje, Gyungsangnam-do 656-830, Republic of Korea 1. Introduction Red tides have occurred in the coastal and offshore waters of many countries as well as in the mid-ocean (Holmes et al., 1967; Jeong, 1995; Imai et al., 2001; Sordo et al., 2001; Alonso-Rodriguez and Ochoa, 2004; Seong et al., 2006; Lee et al., 2013; J.Y. Park et al., 2013a). They can alter the balance of food webs and cause large- scale mortality of fish and shellfish (ECOHAB, 1995; T.G. Park et al., 2013b). Studies of red-tide formation and persistence suggest that grazing pressure may play an important role inbloom dynamics (Watras et al., 1985; Turner, 2006). Grazing by mesozooplankton is believed to sometimes contribute to the decline of red tides (Calbet et al., 2003; Tan et al., 2004). Many mesozooplankters such as copepods, cladocerans, and invertebrate larvae are known to feed on red-tide organisms (Houde and Roman, 1987; Turner et al., 1988, 2012; Carlsson et al., Harmful Algae 30S (2013) S102–S113 A R T I C L E I N F O Keywords: Cladocera Copepod Food web Grazing Harmful algal bloom Larvae A B S T R A C T To investigate the role of mesozooplankton in the dynamics of red tides in Masan Bay, Korea, we measured the abundance of mesozooplankton in daily samples collected from June 1, 2004 to May 31, 2005. Mesozooplankton were abundant in the winter, but rare in the summer, and had a range of abundance of 3–52,843 ind. m 3 . Similarly, both copepods and cladocerans were abundant in the winter, but rare in the summer, and had ranges of abundance of 0–48,817 ind. m 3 and 0–10,951 ind. m 3 , respectively. Invertebrate larvae were abundant in the fall but not in other seasons. The biomass of copepods was significantly positively correlated with salinity, dissolved oxygen, the biomass of the phototrophic dinoflagellates Heterocapsa triquetra and Prorocentrum minimum, and the biomass of the heterotrophic dinoflagellate Gyrodinium glaucum, but negatively correlated with water temperature and the biomass of heterotrophic bacteria and small algae. In addition, the biomass of cladocerans was significantly positively correlated with salinity and the biomass of euglenophytes and G. glaucum, but negatively correlated with water temperature. The biomass of invertebrate larvae was significantly positively correlated with water temperature, but negatively correlated with dissolved oxygen. These observations suggest that copepods and cladocerans may increase their populations by feeding on large phytoplankton in cold water, whereas invertebrate larvae may prefer warm water. The grazing coefficients for the copepods Acartia spp. on co-occurring Pfiesteria-like dinoflagellates (PLDs), P. minimum, Skeletonema costatum, H. triquetra, Heterosigma akashiwo, and Scrippsiella trochoidea were 0.104, 0.083, 0.042, 0.034, 0.033, and 0.030 d 1 , respectively. These results suggest that grazing by Acartia populations in Masan Bay can have a considerable impact on the populations of PLDs and P. minimum, but only a moderate impact on S. costatum, H. triquetra, S. trochoidea, and H. akashiwo. ß 2013 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: hjjeong@snu.ac.kr (H.J. Jeong). Contents lists available at ScienceDirect Harmful Algae jo u rn al h om epag e: ww w.els evier.c o m/lo cat e/hal 1568-9883/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hal.2013.10.010