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2 resultados encontrados para: AUTOR: Herzka, Sharon Z
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Background: We assessed metrics of the metazoan parasite infracommunities of the dusky founder (Syacium papillosum) as indicators of aquatic environmental health of the Yucatan Shelf (YS) prior to oil extraction. We sampled the dusky founder and its parasites along the YS, mostly during the 2015 north wind season (November–April). Our aims were: (i) to determine whether the parasite infracommunity metrics of S. papillosum exhibit signifcant diferences among YS subregions; (ii) to determine whether the probability of the occurrence of its parasite species and individu‑ als were afected by environmental variables, nutrients, heavy metals and hydrocarbons at the seascape level; and (iii) to determine whether there were statistical diferences between the parasite infracommunity metrics of S. papillosum from YS and those of Syacium gunteri from the Campeche Sound. Multivariate statistical analyses and generalised additive models (GAMs) were used to examine the potential statistical associations between the contaminants, environmental variables and parasite community metrics, and the maximum entropy algorithm (MaxEnt) was used to characterise the habitat’s suitability for the parasite’s probability of occurrence. Results: We recovered 48 metazoan parasite species from 127 S. papillosum, with larval cestodes and digeneans being the most numerically-dominant. Multivariate analyses showed signifcant diferences in parasite infracommu‑ nity metrics among Western YS, Mid YS and Caribbean subregions, with the latter being the richest in species but not in individuals. The GAM and MaxEnt results indicated a negative efect of top predators (e.g. sharks and rays) removal on parasite metrics. The parasite infracommunities of S. papillosum were twice as rich in the number of species and individuals as those reported for S. gunteri from the Campeche Sound.

Conclusions: The significant differences among subregions in parasite metrics were apparently due to the interruption of the Yucatan current during the north wind season. The fishing of top predators in combination with an influx of nutrients and hydrocarbons in low concentrations coincides with an increase in larval cestodes and digeneans in S. papillosum. The dusky founder inhabits a region (YS) with a larger number of metazoan parasite species compared with those available for S. gunteri in the Campeche Sound, suggesting better environmental conditions for transmis‑ sion in the YS.

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Variation in isotopic trophic structure and fish diversity in mangrove systems subject to different levels of habitat modification in the Gulf of California, Mexico
López Rasgado, Francisco Javier ; Lluch Cota, Salvador E. (coaut.) ; Balart, Eduardo F. (coaut.) ; Herzka, Sharon Z. (coaut.) ;
Contenido en: Bulletin of Marine Science Vol. 92, no. 4 (October 2016), p. 399-422 ISSN: 0007-4977
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Resumen en: Inglés |
Resumen en inglés

Anthropogenic modification of mangrove systems can lead to decreased habitat quality, potentially affecting food web structure and ecosystem function. Based on carbon and nitrogen stable isotopes, we evaluated the trophic structure of the fish communities from three mangrove systems in southern Baja California, Mexico, subject to varying levels of habitat modification. We hypothesized that anthropogenic habitat modification leads to differences in niche space (and hence trophic structure). We applied a Bayesian approach to the calculation of community level isotope-based metrics of functional trophic structure and compared the results to a structural (Shannon-Wiener) index of diversity. Frequency distributions of stable isotope ratios revealed differences between the highly modified mangrove system and those with limited or no habitat modification. Comparison of the isotopic composition of the dominant fish species sampled in summer and winter indicated limited seasonal differences in this arid region. However, isotope-derived metrics of niche space were evaluated in the most highly modified mangrove system, suggesting a greater complexity in nutrient and primary production sources, a higher level of dietary specialization, and low functional redundancy. Fishes from the most pristine mangrove system exhibited highest diversity, a more limited range of isotopic values, and smaller measures of isotopic niche space, indicative of higher trophic redundancy. Comparison of the standardized (baseline-controlled) species-specific isotope ratios indicated that in 37% of cases isotopic differences persisted, further supporting our interpretation of variations in trophic structure. This research highlights that mangrove habitat modification has a marked influence on functional trophic diversity, as well as the fish community structure.