[Microbiology Research 2012; 3:e4] [page 13] Temporal variation in the phytoplankton community of Acapulco Bay, Mexico Agustín A. Rojas-Herrera, Juan Violante-González, Sergio García-Ibáñez, Víctor M. G. Sevilla-Torres, Jaime S. Gil-Guerrero, Pedro Flores-Rodríguez Unidad Académica de Ecología Marina, Universidad Autónoma de Guerrero, Acapulco, México Abstract Species composition and abundance of the phytoplankton community in Acapulco Bay, Mexico, were studied from May to December 2009. Samples were collected at 5 stations (4 coastal and one oceanic) at 3 depths (1, 5 and 10 m). Eighty-seven species were identified: 54 dinoflagellates, 32 diatoms and one sili- coflagellate. The community was structured mainly by adiaphoric species, that is species adapted to both neritic and oceanic environ- ments. Species abundance and composition varied significantly during the sampling period due to increased nutrient concentrations in the rainy season. Dinoflagellate species were more abundant during the dry season, and diatom species dominated numerically during the rainy season. Introduction Phytoplankton is one of the most complex communities in marine coastal environments. This community’s structure is dictated by two important groups of organisms: i) non-motile, fast-growing diatoms; and ii) motile flagellates and dinoflagellates which can migrate vertical- ly in the water column in response to light. All phytoplankton species are subject to water cur- rents and have developed strategies for rapid nutrient absorption and fast reactions to fluc- tuations in hydrographic conditions. 1 Thus, phytoplankton distribution and species compo- sition are affected by several processes, includ- ing high water temperature, and variations in thermal stability and nutrient circulation. Changes can occur in the taxonomic compo- sition of phytoplankton communities, the total cell abundance and species richness during annual seasonal cycles. These changes reflect the capacity of communities to respond to sea- sonal variations in light, nutrient and circula- tion patterns. 2 Under specific environmental conditions (e.g. high nutrient concentrations) these factors can cause some species to prolif- erate massively, causing harmful algal blooms (HAB) which can negatively affect marine communities. Of the more than 5,000 known marine phytoplankton species, approximately 40 species worldwide have been linked with the production of toxins. 3-5 Santa Lucia Bay, also known as Acapulco Bay, is located on the tropical Pacific coast of southern Mexico, in Guerrero State. The bay has a semi-circular (6.3 km diameter), amphitheater-like shape created by low hills (<500 m) surrounding the south-facing bay. It is considered to be very climatologically pro- tected (Agustín, unpublished data, 2011). Research on marine phytoplankton commu- nities abounds, 6-9 but to date there have been no studies assessing the phytoplankton species composition in Acapulco Bay, Mexico. The aim of the present study was to document current species composition and abundance in the phytoplankton community of Acapulco Bay, and quantify any temporal variation in these variables. Materials and Methods Phytoplankton samples were collected in Acapulco Bay between May and December 2009 at 5 stations: i) Club de Yates (16°50’N, 99°54’W); ii) Islote del Morro (16°51’N, 99°53’W); iii) Naval Base (16°51’N, 99°51’W); iv) Casa de Diaz Ordaz (16°50’N, 99°51’W); and v) Centro de la Bahia (16°49’N, 99°53’W). Van Dorn bottles were used to take samples of marine water (approximately 3 L in each sam- ple) at 3 depths (1 m, 5 m, and 10 m) at each station. Water temperature, pH and salinity were measured in situ with a YSI probe. Nutrient (nitrates, ammonium and phos- phates) concentrations were determined in each sample following a standard colorimetric method (Hanna equip). Phytoplankton sam- ples were fixed in concentrated Lugol’s solu- tion and cell quantification was made using the Utermöhl chamber sedimentation concen- tration method. 10 Phytoplankton species were identified according to a specialized bibliogra- phy. 11-16 Phytoplankton species distribution was established based on a review of published records for Mexico and other countries, and each species was classified as: (ES) estuarine, (NE) neritic, (AD) adiaphoric or (OC) oceanic. The Olmstead-Tukey association test 17 was applied to classify the phytoplankton species based on parameters of occurrence frequency and mean abundance: (D) dominant (abun- dant and frequent); (C) common (low abun- dance but frequent); (O) occasional (abundant but low frequency); and (R) rare (low abun- dance and low frequency). A one-way ANOVA was applied to identify significant differences in monthly parameters (temperature, pH and salinity) and nutrient concentrations. When significant deviations from normality were identified, parameters and concentration data were log-transformed (log ¥+1) to meet nor- mality and homoscedasticity requirements. Any differences in phytoplankton abundance at the 3 tested depths were identified with a one- way ANOVA. A χ 2 test was applied to identify significant differences in mean phytoplankton group abundance between months. Community parameters included total num- ber of species, total number of cells, the Shannon-Wiener (H) diversity index, species evenness (J) and the Berger-Parker Index (BPI) as a measure of numerical domi- nance. 18,19 The qualitative Jaccard similarity index was used to evaluate similarity or differ- ence in species composition between months. Student’s t-test was applied to identify differ- ences between community parameters, and correlations calculated using the Spearman’s range coefficient (r s ) were applied to identify the parameters that determined observed species distribution and composition patterns. Microbiology Research 2012; volume 3:e4 Correspondence: Juan Violante-González, Unidad Académica de Ecología Marina, Universidad Autónoma de Guerrero, Gran Vía Tropical No. 20, Fracc. Las Playas. C.P. 39390, Acapulco, Guerrero, México. E.mail: viojuang@yahoo.com.mx Key words: phytoplankton community, temporal variation, Acapulco bay, México. Acknowledgements: this research was partially financed by the Conacyt and the State of Guerrero through the project “Estudio ecológico de la Bahía de Acapulco” (FOMIX 2008-01). It was also partially financed through the PROMEP (Programa de Mejoramiento del Profesorado) as part of the collaborative project “Calidad Ambiental y Desarrollo Sustentable” of which all the authors are participants. The authors wish to thank Aristeo Martínez Ramírez, Cuauhtémoc V. Gutiérrez García, Cuauhtémoc Valle Rodríguez, Juan A. Meza García and Giovanni Moreno Díaz of the Marine Ecology Academic Unit (UAG) for their assistance with field and laboratory work Received for publication: 27 October 2011. Accepted for publication: 4 December 2011. This work is licensed under a Creative Commons Attribution NonCommercial 3.0 License (CC BY- NC 3.0). ©Copyright A.A. Rojas-Herrera et al., 2012 Licensee PAGEPress srl, Italy Microbiology Research 2012; 3:e4 doi:10.4081/mr.2012.e4 Non-commercial use only