title: Environmental and anthropogenic factors affecting the probability of occurrence of Oncomegas wageneri (Cestoda: Trypanorhyncha) in the southern Gulf of Mexico.
abstract: BACKGROUND
  Understanding the environmental and anthropogenic factors influencing the probability of occurrence of the marine parasitic species is fundamental for determining the circumstances under which they can act as bioindicators of environmental impact. The aim of this study was to determine whether physicochemical variables, polyaromatic hydrocarbons or sewage discharge affect the probability of occurrence of the larval cestode Oncomegas wageneri, which infects the shoal flounder, Syacium gunteri, in the southern Gulf of Mexico.
  
  
  METHODS
  The study area included 162 sampling sites in the southern Gulf of Mexico and covered 288,205 km(2), where the benthic sediments, water and the shoal flounder individuals were collected. We used the boosted generalised additive models (boosted GAM) and the MaxEnt to examine the potential statistical relationships between the environmental variables (nutrients, contaminants and physicochemical variables from the water and sediments) and the probability of the occurrence of this parasite. The models were calibrated using all of the sampling sites (full area) with and without parasite occurrences (n = 162) and a polygon area that included sampling sites with a depth of 1500 m or less (n = 134).
  
  
  RESULTS
  Oncomegas wageneri occurred at 29/162 sampling sites. The boosted GAM for the full area and the polygon area accurately predicted the probability of the occurrence of O. wageneri in the study area. By contrast, poor probabilities of occurrence were obtained with the MaxEnt models for the same areas. The variables with the highest frequencies of appearance in the models (proxies for the explained variability) were the polyaromatic hydrocarbons of high molecular weight (PAHH, 95 %), followed by a combination of nutrients, spatial variables and polyaromatic hydrocarbons of low molecular weight (PAHL, 5 %).
  
  
  CONCLUSIONS
  The contribution of the PAHH to the variability was explained by the fact that these compounds, together with N and P, are carried by rivers that discharge into the ocean, which enhances the growth of hydrocarbonoclastic bacteria and the productivity and number of the intermediate hosts. Our results suggest that sites with PAHL/PAHH ratio values up to 1.89 promote transmission based on the high values of the prevalence of O. wageneri in the study area. In contrast, PAHL/PAHH ratio values ≥ 1.90 can be considered harmful for the transmission stages of O. wageneri and its hosts (copepods, shrimps and shoal flounders). Overall, the results indicate that the PAHHs affect the probability of occurrence of this helminth parasite in the southern Gulf of Mexico.
authors.affiliation: Laboratorio de Parasitología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Km 6 Carretera Antigua a Progreso, Cordemex, Mérida, Yucatán, 97310, México. vvidal@mda.cinvestav.mx.
authors.forename: Víctor M
authors.initials: VM
authors.lastname: Vidal-Martínez
authors.affiliation: Laboratorio de Tecnologías Geoespaciales, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Km 6 Carretera Antigua a Progreso, Cordemex, Mérida, Yucatán, 97310, México. edgar.torres@mda.cinvestav.mx.
authors.forename: Edgar
authors.initials: E
authors.lastname: Torres-Irineo
authors.affiliation: Posgrado de Geografía. Facultad de Filosofía y Letras, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria, 04510, México DF, México. rodaromero@gmail.com.
authors.forename: David
authors.initials: D
authors.lastname: Romero
authors.affiliation: Oceanography Department and GERG, Texas A&M University, College Station, TX, USA. ggold@mda.cinvestav.mx.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gold-Bouchot
authors.affiliation: Laboratorio de Análisis Espaciales, Dpto. Zoología, Instituto de Biología, Universidad Nacional Autónoma de México, Apdo. Postal 70-153, 04510, México, DF, México. emm@ib.unam.mx.
authors.forename: Enrique
authors.initials: E
authors.lastname: Martínez-Meyer
authors.affiliation: Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Km 6 Carretera Antigua a Progreso, Cordemex, Mérida, Yucatán, 97310, México. dvaldes@mda.cinvestav.mx.
authors.forename: David
authors.initials: D
authors.lastname: Valdés-Lozano
authors.affiliation: Laboratorio de Parasitología, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Km 6 Carretera Antigua a Progreso, Cordemex, Mérida, Yucatán, 97310, México. leo@mda.cinvestav.mx.
authors.forename: M Leopoldina
authors.initials: ML
authors.lastname: Aguirre-Macedo
mesh_terms: D000818:Animals; D002589:Cestoda / Q000302:isolation & purification*; D004777:Environment; D004787:Environmental Pollution; D005393:Fish Diseases / Q000453:epidemiology / Q000469:parasitology*; D005432:Flounder; D019015:Geologic Sediments; D060851:Gulf of America / Q000453:epidemiology; D006841:Hydrocarbons, Aromatic / Q000032:analysis*; D015995:Prevalence; D011336:Probability; D045483:Rivers
chemical_list: D006841:Hydrocarbons, Aromatic