Chaetoceros affinis blooms in Palauan meromictic marine lake S. Konno, N. Inoue, D. U. Hernández-Becerril, R.W. Jordan To cite this version: S. Konno, N. Inoue, D. U. Hernández-Becerril, R.W. Jordan. Chaetoceros affinis blooms in Palauan meromictic marine lake. Vie et Milieu / Life & Environment, Observatoire Océanologique - Laboratoire Arago, 2010, pp.257-264. hal-03262179 HAL Id: hal-03262179 https://hal.sorbonne-universite.fr/hal-03262179 Submitted on 16 Jun 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. VIE ET MILIEU - LIFE AND ENVIRONMENT, 2010, 60 (3): 257-264 CHAETOCEROS AFFINIS blooms IN palaUAN meromictic MARINE LAKES S. KONNO 1, N. INOUE 2, D. U. HERNÁNDEZ-BECERRIL 3 , R. W. JORDAN 4* 1 SCITA Center, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990 8560, Japan 2 Graduate School of Science & Engineering, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan 3 Lab. Diversidad y Ecología del Fitoplancton Marino, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México (UNAM), Apdo. postal 70-305, México, D.F. 04510, México 4 Department of Earth & Environmental Sciences, Faculty of Science, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan * Corresponding author: [email protected] CHAETOCEROS ABSTRACT. – Observations on net and water bottle samples obtained from marine lakes situated DIATOM BLOOM MARINE LAKE on Mecherchar Island in the Republic of Palau have revealed that Chaetoceros affinis commonly MEROMICTIC occurred in the meromictic lakes during 2001-2007, but was absent from the holomictic lakes and REPUBLIC OF PALAU lagoons. In Mecherchar Jellyfish Lake, C. affinis accounted for 42-93 % of the planktonic dia- toms during most of the sampled years, representing up to 3.4 x 105 cells/liter. High relative abun- dances of C. affinis were also recorded from several other meromictic lakes during one of the sampled years, with an absolute abundance of 5.7 x 105 cells/liter (79 %) recorded in L-shaped Lake. These observations are the first record of planktonic diatom assemblages in Palauan mero- mictic marine lakes. The characteristics of these meromictic marine lakes and hypotheses for the recurrence of C. affinis blooms in Mecherchar Jellyfish Lake are discussed herein. INTRODUCTION During the Pliocene and Pleistocene the uplift of Mio- cene carbonate platforms (coral reefs) resulted in a myriad The centric diatom genus Chaetoceros Ehrenberg con- of small ‘rock islands’ that now constitute the Palau archi- tains over 400 species (VanLandingham 1968, Kooistra pelago (Kelletat 1991). Subsequent erosion of the exposed et al. 2010), many of which live in coastal areas, produc- limestone, created a karst topography including a number ing high biomass blooms comprising long chains of cells of island basins. Today’s marine lakes were formed after and resting spores (Werner 1977). Although commonly the last glacial maximum (i.e. about 10,000 years ago), recorded from temperate and high latitude localities (e.g. when global sea level rose and the island basins became Rines & Hargraves 1987, Orlova & Selina 1993, Haecky filled with seawater, that had entered through cracks and et al. 1998, Sieracki et al. 1998, Booth et al. 2002, channels in the limestone. There are currently about 70 Shevchenko et al. 2006), high abundances have also been marine lakes in Palau, some of which are meromictic reported from subtropical and tropical regions, where (Hamner & Hauri 1981, Hamner & Hamner 1998). species such as C. amanita Cleve-Euler, C. ceratosporus Most of these Palauan lakes are surrounded by dense Ostenfeld, C. densus Cleve, C. elmorei Boyer, C. muel- forests of the red mangrove Rhizophora Linnaeus, but leri Lemmermann, C. salsugineus Takano, C. transisetus surprisingly few biological studies have been conduct- Johansen & Boyer and C. wighamii Brightwell may occur ed on the lake waters. In general, the meromictic lakes in estuarine waters or inland saline lakes (e.g. Brightwell have a three-layered water column; a productive epilim- 1856, Brunel 1962, Takano 1983, Rushforth & Johansen nion (mixolimnion) is separated from an unmixed anoxic 1986, Sanchez-Castillo et al. 1992, Johansen & Boyer hypolimnion (monimolimnion) by a thick layer of purple 1995, Trigueros et al. 2002, Oyama et al. 2005). photosynthetic sulphur bacteria (Chromatium Perty; There are thousands of saline lakes distributed around Venkateswaran et al. 1993) at the top of the chemocline the world (Mackenzie et al. 1995), many of which are (Fig. 1; see also the review by Lobban & Jordan 2010). non-marine. Most saline lakes are holomictic, monomic- The epilimnion is characterized by low diversity popula- tic or dimictic (well mixed or turning over once or twice tions of jellyfish (Hamner & Hauri 1981, Dawson 2005, a year, respectively), but true meromictic marine lakes Dawson & Hamner 2005), fish (Gotoh et al. 2009) and which incompletely or rarely turn over are relatively copepods (Saitoh et al. 2010), which differ from the scarce, possibly numbering less than 100 (Hamner & coastal and holomictic marine lake populations. Microal- Hamner 1998). At least 11 of these meromictic marine gal community studies in these lakes are almost non-exis- lakes are tropical, all of which are in the Republic of tent, with information solely from JFL, in which the phy- Palau, mostly located on Mecherchar Island – including toplankton was represented by chain-forming centric dia- the well known Mecherchar Jellyfish Lake (JFL). toms (e.g. Chaetoceros), large dinoflagellates (e.g. Cera- 258 S. KONNO, N. INOUE, D. U. HERNÁNDEZ-BECERRIL, R. W. JORDAN Fig. 1. – Schematic representation of a Palauan meromictic marine lake, with mangroves around the lakeside, a mixolimnion character- ized by jellyfish and planktonic diatoms, a thick bacterial layer of purple sulphur bacteria at the top of the chemocline, and an anoxic monimolimnion. Lake depth based on Mecherchar Jellyfish Lake. tium Schrank) and various microflagellates (Hamner et al. aluminium stub, coated with gold or platinum/palladium in an 1982). A more recent paper has recorded the presence of Eiko IB-3 ion sputter-coater and examined in a Hitachi S-2250N a new species of the diatom genus Paralia Heiberg in JFL scanning electron microscope. Photographs were taken with the (Konno & Jordan 2008). A few seaweed species inhabit camera attachment, using Fuji Neopan 120 SS black and white the shallower lakeside waters (Hara et al. 2002), while the film. In order to calculate absolute abundances, all of the dia- sediments from the shallower parts of JFL are known to tom frustules on the whole filter portion were counted. For those contain low diversity populations of benthic foraminifera filters with low abundances, counts of at least 300 diatom frus- (Lipps & Langer 1999, Kawagata et al. 2005a, b). tules were made on each water sample, however, the plankton In this study, we provide the first report on the plank- net samples were not quantified since the water volume passing tonic diatom communities of some of the meromictic through the net was unknown. All of the samples and negatives marine lakes of Mecherchar Island, and compare them used in this study are curated in the Department of Earth & Envi- with the communities in the island’s non-meromictic ronmental Sciences, Faculty of Science, Yamagata University. In general, the physico-chemical data were acquired using marine lakes and the surrounding lagoons. a multiple water-quality monitor (U-22, Horiba Co. Ltd.) at the same time as the water sample collection. However, on the three occasions when the monitor was broken, the water measurements MATERIALS AND METHODS were taken with a Hanna Instruments Piccolo Plus ATC Temp pH meter and a Shibuya Salinometer S-10 in July 2002, while con- Fieldwork in the Republic of Palau took place on eight occa- ductivity and salinity were measured with a Horiba Cond Meter sions between 2001-2007, with surface water samples taken ES-51, pH with a pH ep5 meter (Hanna Instruments), and tem- from a number of marine lakes on most trips, notably from perature and dissolved oxygen with a DO meter ID-100 (Iijima Mecherchar Island (see Fig. 2). Using a small boat, surface Electronics Corp.) in July 2005 and November 2006. No phys- water samples were also obtained from the lagoons surrounding ico-chemical data is available from 2004. The data for each of the larger islands, as well as from locations further offshore. In the lakes mentioned in this paper are documented in Hara et al. most cases the seawater was collected in plastic bottles (500 ml, (pers com). All the instruments were calibrated before the start of 1 l or 2 l), although during some of the earlier years the samples the fieldwork using commercially available standard solutions, were acquired with a Nytal-Swiss HD10 plankton net (mesh but due to logistical reasons (i.e. the difficulties associated with size 10 µm). Each water sample was filtered through a Milli- transporting equipment through the hot, dense jungle) they were pore® 47 mm, 0.45 µm porosity, HA-type polycarbonate filter not re-calibrated before taking measurements at each lake. using either a Nalgene® hand-operated vacuum pump or an Most of the informal names of Mecherchar Island lakes used A-3S Eyela Aspirator A-3S (Tokyo Rikakikai Co., Ltd.) filtra- in this paper are taken from Hamner & Hamner (1998), while tion apparatus. The filter was subsequently air dried and stored North Cassiopeia Lake and Cassiopeia Lake were named by in plastic petrislides for future SEM analysis.