Baseline Bloom of Scrippsiella trochoidea (Gonyaulacaceae) in a shrimp pond in the southwestern Gulf of California, Mexico Ismael Gárate-Lizárraga a, * , Christine J. Band-Schmidt a , David J. López-Cortés b , María del Socorro Muñetón-Gómez a,c a Laboratorio de Fitoplancton, Departamento de Plancton y Ecología Marina, CICIMAR-IPN, Apdo. Postal 592, La Paz, B.C.S. 23000, Mexico b Centro de Investigaciones Biológicas del Noroeste (CIBNOR), Mar Bermejo 195, Col. Playa Palo de Santa Rita, La Paz, B.C.S. 23090, Mexico c Centro de Estudios Tecnológicos del Mar No. 4, Avenida Instituto Politécnico Nacional y Calle Cetmar s/n, 23096 La Paz, B.C.S. 23000, Mexico In Mexico, shrimp are, by far, the most important aquaculture species, accounting for 70% of the live weight and 82% of the value of aquaculture production (Juárez, 2008). About 97% of shrimp ponds in Mexico are on the coasts of the Gulf of California (Páez- Osuna, 2001; Alonso-Rodríguez et al., 2004; Lyle-Fritch et al., 2006). Ponds are fertilized with organic or inorganic fertilizers or a combination. Each fertilizer has advantages or particular uses. Chemical elements used in aquaculture ponds are more precise than inorganic fertilizers, since they are applied by formula and produce results that are more consistent when algal blooms occur (Conte, 2000). Blooms of diatoms and chlorophytes are beneficial for cultivated shrimp, but dinoflagellates blooms (5 Â 10 5 cells l À1 ) are considered noxious (Clifford, 1994). Between 1990 and 1993, studies of three shrimp farms in northwestern Mexico mea- sured algae blooms in shrimp ponds (Cortc ´ s-Altamirano and Agraz-Hernández, 1994); Cortés-Altamirano and Licea-Durán, 1999). They found cyanobacteria (Anabaena elenkinii, A. aequalis, and Schizothrix calcicola) and dinoflagellates (Prorocentrum mini- mum, Gymnodinium incoloratum, Gyrodinium spirale, and Scrippsiel- la trochoidea) dominated the community. During those observations, blooms caused mortality of shrimp and fish on three occasions. The first bloom, caused by P. minimum, occurred in Sin- aloa shrimp ponds (Cortés-Altamirano and Agraz-Hernández, 1994). The second bloom, caused by S. calcicola, affected 900 per- sons after consuming shrimp (Ochoa et al., 2004). The third bloom, caused by Cochlodinium polykrikoides, killed captive fish (Gárate- Lizárraga et al., 2004). Along the southern Baja California coast, a few algae blooms have been reported in shrimp ponds. The most common responsible species, causing water discoloration in shrimp ponds, have been the prasinophyte Nephroselmis sp., dino- flagellates C. polykrikoides, P. rhathymum, P. minimum, and Hetero- capsa triquetra, and the diatom Nitzschia sigma (Gárate-Lizárraga et al., 1999; 2004; 2006; Sierra-Beltrán et al., 2005; Gárate- Lizárraga and Muñetón-Gómez, 2008). This study describes a short-term variation in a dinoflagellate bloom caused by S. trochoi- dea that occurred in a shrimp farm in the southwestern Gulf of California. From 12–27 November 1998, a phytoplankton bloom occurred in a commercial shrimp pond containing Litopenaeus vannamei (=Penaeus) located at Playa Eréndira, adjacent to Bahía de La Paz (Fig. 1). Sampling started on 17 November. Water samples were collected daily with a Van Dorn bottle to measure number of cells, chlorophyll a, inorganic nutrients, proteins, and carbohydrates. Seawater temperature was measured with a bucket thermometer. Phytoplankton samples were collected near the surface and were fixed with acid Lugol. Live and fixed cells were used for identifica- tion using specialized literature (Balech, 1988; Steidinger and Tan- gen, 1997). Cells were counted in 1-ml settling chambers under a phase contrast inverted microscope. Nutrients were measured according to Strickland and Parson (1972). N total was NO 2 + NO 3 ; ammonium was not determined. The N:P ratio was defined as mo- lar concentrations. For determining photosynthetic pigments, particulate organic biomass (proteins and carbohydrates), 250–500 ml seawater were passed through Whatman GF/F filters and then frozen at À20 °C until further analysis. Filters were thawed and ex- tracted in 10 ml of 90% acetone overnight in the dark at 4 °C. Chlorophyll a concentrations were calculated from spec- trophotometric absorbance measurements using the equations of Jeffrey and Humphrey (1975). Carbohydrates were quantified with the method of Dubois et al. (1956), which is based on the formation of furfurals in the presence of sulphuric acid. Proteins were determined by the method of Lowry et al. (1951), which consists of alkaline extraction in the presence of copper; this leads to formation of chromogenic bonds with the protein. The dinoflagellate S. trochoidea (Stein) Loeblich III was the responsible species for discoloring seawater from 12–27 November 1998 in a shrimp pond located in the southeastern corner of Bahía de La Paz. The bloom occurred when the seawater temperature was 26.5–27 °C, declining to 25 °C at the end of the bloom (Fig. 2A). Changes in other seawater factors (dissolved oxygen, ni- trates + nitrites, orthophosphates, and silicates) are shown in Fig. 2B. The N:P ratios were 4 ± 2, with the exception of the fourth and fifth day, when it exceeded the Redfield ratio (Fig. 2C). This was followed by a second increase in cells of S. trochoidea. The N:P molar ratio during the fourth and fifth day, in the pond was generally higher than the Redfield (1958) ratio of 16:1, which is re- quired for optimal phytoplankton growth (Fig. 2C). Burford (1997) suggests that phytoplankton growth might be limited by phos- phates rather than nitrates. 0025-326X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2008.09.016 * Corresponding author. Tel.: +52 612 123 0350x82434; fax: +52 612 122 5322. E-mail address: igarate@ipn.mx (I. Gárate-Lizárraga). Marine Pollution Bulletin 58 (2009) 145–149 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul