Bloom of Noctiluca scintillans (Macartney) Kofoid & Swezy (Dinophyceae) in southern Brazil

Abstract

The dinoflagellate Noctiluca scintillans (Macartney) Kofoid & Swezy, commonly called sea sparkle, can aggregate into a bloom, and sometimes produces substances that are potentially toxic to marine life. Noctiluca scintillans is a large (up to 1200 µm), oblong, luminescent heterotrophic dinoflagellate, and is frequently associated with bloom events (ELBRACHTER; QI, 1998). The species is considered non-toxic, but is sometimes responsible for the mortality of fish and benthic fauna, associated with anoxia. More recently, it has been reported that N. scintillans may act as a vector of phycotoxins to higher trophic levels, by feeding on toxigenic microalgae (ESCALERA et al., 2007) . Noctiluca scintillans is widely distributed in temperate to tropical regions, where it commonly causes blooms (SRIWOON et al., 2008). The mechanism of bloom formation of N. scintillans has been examined in many parts of the world, e.g., in the German Bight (UHLIG; SAHLING, 1990), Dapeng Bay, South China Sea (HUANG; QI, 1997; WANG et al., 2008), Minnie Bay, Andaman Islands (EASHWAR et al., 2001; DHARANI et al., 2004), Sagami Bay, Japan (MIYAGUCHI et al., 2006), Thailand (SRIWOON et al., 2008), Gulf of Mannar, India (GOPAKUMAR et al., 2009) , Red Sea off Saudi Arabia (MOHAMED; MESAAD, 2007), northern Adriatic Sea (UMANI et al., 2004), and several parts of the Australian coast (AJANI et al., 2001, MURRAY; SUTHERS, 1999, DELA-CRUZ et al., 2002). Blooms by N. scintillans appear either pinkish-red or greenish. The former coloration has been reported in various temperate and subtropical waters, but the latter occurs only in tropical waters of the western Pacific and Indian oceans (ELBRACHTER; QI, 1998, SAITO; FURUYA, 2006). The majority of blooms are harmless water discolorations, predominantly caused by N. scintillans (AJANI et al., 2001). Hereafter, N. scintillans that lacks the symbiont is referred to as red Noctiluca (SRIWOON et al., 2008). On the coast of the state of Rio Grande do Sul (RS), most blooms are formed by diatoms (Asterionellopsis glacialis ). However, high concentrations of dinoflagellates are occasionally found, associated with low wave energy and high light intensity (ODEBRECHT et al., 1995). On the southern coast of Brazil, four mortality events have been recorded for the benthic fauna, associated with the presence of potentially toxic dinoflagellates (MACHADO, 1979; ROSA; BUSELATO, 1981; GARCIA et al., 1994, ODEBRECHT et al., 1995, MENDEZ, 1995). In this region, dinoflagellate blooms are irregular and seem to be more a response to the vagaries of unpredictable shifts in climatic factors, than to a deterministic mechanism. Nocturnal bioluminescence of Noctiluca scintillans was observed in northern RS in summer 2005, but was recorded only by a local newspaper (Zero Hora). The northern coast of Rio Grande do Sul extends for 120 km from Torres Beach at the border with the state of Santa Catarina, southward to Pinhal Beach. During three days in December 2008, a red color on the sea was visible from the beach [1] . On the first day (17 December), the bloom was visible at Capao da Canoa Beach (nearly 70 km from Torres Beach) and moved southward to Cidreira and Pinhal beaches by the third day (19 December), after which it vanished. The present report describes the first recorded reddish bloom of Noctiluca scintillans on the northern coast of Rio Grande do Sul, Brazil. The area off the RS continental margin is influenced by several water masses, including the Tropical Water (TW) of the Brazil Current; the South Atlantic Central Water (SACW), also called Subtropical Water (STW); and the coastal branch of the Falklands Current, which transports Sub-Antarctic Water (SAW). The thermohaline properties of water on the continental shelf vary as a result of the volume of fresh water discharged by the plume of the Plate River (RPP) and the Patos Lagoon, and the degree of influence of the TW and SAW. More locally, four water masses influence the northern coast: Subtropical Water of the continental shelf (STWP), Sub-Antarctic Water of the continental shelf (SAWP), Tropical Water (TW), and the South Atlantic Central Water (SACW). Only the TW ( ≥18.5°C; ≥36‰) and SACW