Habitat characteristics and environmental parameters influencing fish assemblages of karstic pools in southern Mexico

Fish assemblage structure was evaluated and compared among 36 karstic pools located within protected areas of the Calakmul Biosphere Reserve (southern Mexico) and unprotected adjacent areas beyond the Reserve. Nonmetric multidimensional scaling (MDS), indicator species analysis (ISA), and canonical correspondence analysis (CCA) were used to identify which environmental factors reflected local influences and to evaluate the correlation of these variables with fish assemblages structure. Thirty-one species were encountered in these karstic pools, some for the first time within the Reserve. These aquatic environments were separated into three groups based on physico-chemical characteristics. Although CCA identified significant associations between several fish species (based on their relative abundance) and environmental variables (K, NH4, NO3, and conductivity), the most abundant species (Astyanax aeneus, Poecilia mexicana, and Gambusia sexradiata ) occur in most pools and under several environmental conditions. Baseline data on fish diversity along with a continued monitoring program are essential in order to evaluate the conservation status of fish assemblages and their habitats, as well as to measure the influence of anthropogenic impacts on pristine habitats such as the karstic pools of the Calakmul Biosphere Reserve.(AU)

A estrutura da assembleia de peixes foi avaliada e comparada entre 36 poços cársticos localizados dentro de áreas protegidas da Reserva da Biosfera Calakmul (sul do México) e nas áreas desprotegidas adjacentes à Reserva. A análise multidimensional não-métrica (MDS), a análise da espécies indicadora (ISA) e a análise de correspondência canônica (CCA) foram utilizadas para identificar as variáveis ambientais localmente mais importantes e para avaliar a correlação destas com a estrutura das assembleias de peixes. Trinta e uma espécies foram amostradas nos poços cársticos, algumas das quais representam o primeiro registro para a Reserva. Os poços foram separados em três grupos de acordo com as suas características físico-químicas. Embora a CCA tenha possibilitado a identificação de associações significativas entre várias espécies (baseado na abundância relativa das espécies) e as variáveis ambientais (K, NH4, NO3 e condutividade), as espécies mais abundantes (Astyanax aeneus, Poecilia mexicana e Gambusia sexradiata ) ocorreram na maioria dos poços em diferentes condições ambientais. A obtenção de dados de base sobre padrões de diversidade, associado a implantação de programas de monitoramento, são essenciais para a avaliação do estado de conservação das assembleias de peixes e seus habitats, assim como para proporcionar informações sobre a influência de impactos antropogênicos sobre habitats prístinos, tais como os poços cársticos da Reserva da Biosfera Calakmul.(AU)

Spatial patterns of diversity at local and regional scales in a tropical lagoon

The present study reports estimates of alpha (α), beta (β) and gamma (Γ) diversity for the fish community of Chacmochuch Lagoon (SE Mexico), a natural protected area located in the northern portion of the Mesoamerican Barrier Reef System. Fish specimens were sampled in 2004 and 2006. Field work was carried out at three climatic peaks: at 13 stations using a 70 m-long beach seine. The collected data were supplemented with information obtained from a previous work conducted in 2002 and were then analyzed with multivariate statistical methods. In addition, fish composition results from this study were compared to those reported for other similar ecosystems of the region. A total of 68 fish species were recorded, determined as peripheral (high-salinity species, usually marine affinity) most of them. Most of the fish species collected were determined as rare, and a few number of species were determined as common and dominant. Salinity, TSD, temperature, dissolved oxygen and other variables were measured to determine the influence over the fish communities, four groups of sites where determined. Results indicated a gradual decrease in the degree of species replacement towards the interior of the system (away from the coast). The estimated value of gamma diversity was high compared to that reported for other coastal systems of the region and, due to the high degree of habitat heterogeneity found in this system; beta diversity had a greater contribution to gamma diversity than alpha diversity. This lagoon acts as a nursing area for many of the fish species collected in this study as indicated by the presence of juvenile stages.(AU)

En el presente estudio, se midió y se determinó la biodiversidad alfa (α), beta (β) y gamma (Γ) de la comunidad de peces en el Sistema Lagunar Chacmochuch, un Área Natural Protegida (ANP) localizada en la zona norte del Sistema Arrecifal Mesoamericano. El trabajo de campo se realizó en 13 sitios de muestreo durante los ciclos anuales 2004 y 2006, considerando los tres picos climáticos representativos de la región. Para la captura se utilizo un chinchorro de 70 m de largo. La matriz de información utilizada para el análisis se complemento con datos obtenidos a partir de un trabajo realizado durante el periodo 2002. Análisis multivariados fueron utilizados para la generación de resultados. Los resultados de la composición de peces se compararon con los reportados para otros ecosistemas similares de la región. Un total de 68 especies fueron registradas siendo periféricas (especies de alta salinidad y afinidad marina) la mayoría de ellas. Del registro, la mayoría de las especies se determinaron como especies raras, un número menor fueron especies comunes y dominantes. La salinidad, SDT, temperatura, oxigeno disuelto y otras variables fueron medidas para determinar su efecto sobre la comunidad de peces, encontrando cuatro agrupaciones de sitios. Los resultados indican una disminución gradual de las especies hacia el interior del sistema (al alejarse de la costa). La diversidad gamma es alta comparada a otros sistemas costeros de la región; sin embargo la taza de recambio beta es la que determina su alta heterogeneidad. Especies en estadios juveniles y de importancia económica fueron dominantes en el sistema, lo que determinan la zona como un área de crianza.(AU)

Spatial and temporal structure of fish assemblages in a hyperhaline coastal system: Ría Lagartos, Mexico

The spatial and temporal fish species assemblages were analyzed throughout two annual cycles (2004-2005 and 2007-2008) in the Ría Lagartos Lagoon system, Mexico, via non-parametric multivariate analyses. We compared density and biomass of fish species among five habitat types defined by combinations of structure and environmental characteristics (hyperhaline, rocky, seagrass, channel, and marine), and three climatic seasons (dry, rainy, and northerlies). A total of 11,187 individuals distributed in 32 families and 63 species were collected. The most numerically abundant species were Floridichthys polyommus and Cyprinodon artifrons, while Sphoeroides testudineus contributed to the greatest biomass. Species composition consisted mainly of estuarine and euryhaline marine species. Spatially, a saline gradient was observed with marine conditions in the mouth, and increasing to over 100 in the inner zone of the system. Species richness, diversity and biomass declined from the mouth to the inner zone, while density showed an inverse tendency, with the highest values in the inner zone. Thus the salinity was the variable that best explained the spatial fish assemblages" structure. The ichthyofauna composition did not change over time, but the dominant species varied with the years. The abundance of juvenile specimens, suggest that the different habitats are used as feeding and breeding zones; hence it is proposed that protection strategies be pursued not only for the lagoon system but also for the northern zone of the Yucatan Peninsula.(AU)

Los ensamblajes espacio temporales de peces fueron analizados a través de dos ciclos anuales (2004-2005) y 2007-2008) en el sistema lagunar Ría Lagartos, México, vía análisis multivariados no paramétricos. Se comparó la densidad y biomasa de peces entre los cinco tipos de hábitats definidos por la combinación de características estructurales y ambientales (hiperhalino, rocoso, pastos, canal y marino) y tres temporadas climáticas (secas, lluvias y nortes). Un total de 11.187 individuos fueron recolectados, distribuidos en 32 familias y 63 especies. Las especies numéricamente más abundantes fueron Floridichthys poliommus y Cyprinodon artifrons, mientras que Sphoeroides testudineus contribuyó principalmente con la biomasa. La composición de especies consistió principalmente de especies marinas eurihalinas y estuarinas. Espacialmente, un gradiente de salinidad fue observado con condiciones marinas en la boca del sistema lagunar, incrementándose hacia la zona interna con valores superiores a 100. La riqueza de especies, diversidad y biomasa disminuyó desde la boca hacia la zona interna, mientras que la densidad mostró una tendencia inversa, con valores más altos en la zona interna. La salinidad fue la variable que mejor explicó la estructura espacial de los ensamblajes de peces. La composición de la ictiofauna no cambió en el tiempo, pero las especies dominantes varían con los años. La abundancia de especímenes juveniles sugiere que los diferentes hábitats son usados como zonas de alimentación y de crianza; por lo que se propone que la estrategia de protección continúe no sólo para el sistema lagunar sino para toda la zona norte de la Península de Yucatán.(AU)