Articles | Volume 14, issue 4
Biogeosciences, 14, 959–975, 2017
Biogeosciences, 14, 959–975, 2017

Research article 02 Mar 2017

Research article | 02 Mar 2017

Biogeochemical cycling and phyto- and bacterioplankton communities in a large and shallow tropical lagoon (Términos Lagoon, Mexico) under 2009–2010 El Niño Modoki drought conditions

Pascal Conan1, Mireille Pujo-Pay1, Marina Agab1, Laura Calva-Benítez2, Sandrine Chifflet3, Pascal Douillet3, Claire Dussud1, Renaud Fichez3, Christian Grenz3, Francisco Gutierrez Mendieta2, Montserrat Origel-Moreno2,3, Arturo Rodríguez-Blanco1, Caroline Sauret1, Tatiana Severin1, Marc Tedetti3, Rocío Torres Alvarado2, and Jean-François Ghiglione1 Pascal Conan et al.
  • 1Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire d'Océanographie Microbienne (LOMIC), Observatoire Océanologique, 66650, Banyuls/mer, France
  • 2Universidad Autónoma Metropolitana, Departamento de Hidrobiología, México D.F., Mexico
  • 3Aix-Marseille Université, CNRS–INSU, Université de Toulon, IRD, Mediterranean Institute of Oceanography (MIO) UM 110, 13288, Marseille, France

Abstract. The 2009–2010 period was marked by an episode of intense drought known as the El Niño Modoki event. Sampling of the Términos Lagoon (Mexico) was carried out in November 2009 in order to understand the influence of these particular environmental conditions on organic matter fluxes within the lagoon's pelagic ecosystem and, more specifically, on the relationship between phyto- and bacterioplankton communities. The measurements presented here concern biogeochemical parameters (nutrients, dissolved and particulate organic matter [POM], and dissolved polycyclic aromatic hydrocarbons [PAHs]), phytoplankton (biomass and photosynthesis), and bacteria (diversity and abundance, including PAH degradation bacteria and ectoenzymatic activities). During the studied period, the water column of the Términos Lagoon functioned globally as a sink and, more precisely, as a nitrogen assimilator. This was due to the high production of particulate and dissolved organic matter (DOM), even though exportation of autochthonous matter to the Gulf of Mexico was weak. We found that bottom-up control accounted for a large portion of the variability of phytoplankton productivity. Nitrogen and phosphorus stoichiometry mostly accounted for the heterogeneity in phytoplankton and free-living prokaryote distribution in the lagoon. In the eastern part, we found a clear decoupling between areas enriched in dissolved inorganic nitrogen near the Puerto Real coastal inlet and areas enriched in phosphate (PO4) near the Candelaria estuary. Such a decoupling limited the potential for primary production, resulting in an accumulation of dissolved organic carbon and nitrogen (DOC and DON, respectively) near the river mouths. In the western part of the lagoon, maximal phytoplankton development resulted from bacterial activity transforming particulate organic phosphorus (PP) and dissolved organic phosphorus (DOP) to available PO4 and the coupling between Palizada River inputs of nitrate (NO3) and PP. The Chumpan River contributed only marginally to PO4 inputs due to its very low contribution to overall river inputs. The highest dissolved total PAH concentrations were measured in the El Carmen Inlet, suggesting that the anthropogenic pollution of the zone is probably related to the oil-platform exploitation activities in the shallow waters of the southern of the Gulf of Mexico. We also found that a complex array of biogeochemical and phytoplanktonic parameters were the driving force behind the geographical distribution of bacterial community structure and activities. Finally, we showed that nutrients brought by the Palizada River supported an abundant bacterial community of PAH degraders, which are of significance in this important oil-production zone.

Short summary
Coastal lagoons are extremely rich, diverse, and dynamic but very fragile ecosystems subject to anthropogenic pressures. A joint France–Mexico biogeochemical study was conducted in the Términos Lagoon under severe drought related to an El Niño Modoki episode. In short, the water column of the Términos Lagoon functioned as a nitrogen sink, but variation in mineral stoichiometry across the lagoon mainly accounted for the heterogeneity in microbial distribution and activity.
Final-revised paper