Aim To analyse the relationship between fish species richness and salinity, and to provide a simple linear model for fish diversity trends across salinity gradients in a tropical coastal lagoon that can be compared with other similar ecosystems and other communities. To reinforce our conclusions, the salinity-fish richness relationship was investigated at different spatial scales (sampling station, set of stations and whole lagoon) and for two different periods, separated by 18 years.Location The Terminos coastal lagoon, a shallow tropical lagoon (mean maximum depths ranging between 3.5 and 4.5 m), is located in the southern Gulf of Mexico (18.5-18.8°N, 91.3-91.9°W). The lagoon is 70 km long and 30 km wide, with a surface area of 1700 km 2 .Methods Fish sampling, individual identification to the species level, and environmental variable measurements were carried out monthly at 17 sampling points. Multiple regression analysis with a backward selection procedure was used to relate fish species richness to environmental variables. Other statistical techniques, including cluster analysis and ancova, were applied to experimental data surveys.Results Among the different environmental variables, salinity was significantly and consistently related to fish species richness, whatever the period and the scale of observation. We found mainly significant negative correlations (P < 0.05) between fish species richness and salinity when sampling stations were analysed individually, and particularly for the river runoff zones with high variation in salinity throughout the year. For the entire lagoon, robust negative linear models were observed when fish species richness was organized into salinity ranges, with salinity explaining c. 8% of the variation in mean fish species richness (in a multiple regression analysis; 63-93% when considered in isolation). Main conclusionsIn the Terminos lagoon the relationship between fish species richness and salinity is mainly negative on any spatial scale. This result may be due partially to the penetration of freshwater fishes into estuarine areas following freshwater discharges, and partially to the dominance of estuarine taxa more able to tolerate low than high salinity values. Finally, we suggest that the 'realized' ecotone, where species from different origins really mix, is situated between 5 and 10&, corresponding to the highest fish richness.

This study describes the current state of the nektonic communities in Terminos Lagoon in relation to the main environmental factors, and documents variations in number of fish species, dominance and abundance, compared to studies performed in 1980. Information on several environmental factors (temperature, salinity, oxygen, pH and transparency) in the Terminos Lagoon between October 1997 and March 1999 allowed the classification of the lagoon into five zones or subsystems. The hydrological characteristics of these subsystems showed spatial differences compared with studies carried out during the 1980s. During the study period, the number of fish species was 105, compared with 154 species reported in the 1980s. Five fish assemblages were identified and appeared to be associated with the five zones or subsystems. Five fish species considered important based on their abundance in the lagoon during the 1980s declined in numbers: pig fish Orthopristis chrysoptera, Atlantic croaker Micropogonias undulates, striped burrfish Chilomycterus schoepfi, spotted seatrout Cynoscion nebulosus and Gulf toadfish Opsanus beta. Six fish species, previously of minor importance, however, were very abundant: star drum Stellifer lanceolatus, Atlantic anchoveta Cetengraulis edentulus, gafftopsail catfish Bagre marinus, sand seatrout Cynoscion arenarius, striped mojarra Eugerres plumieri and ground croaker Bairdiella ronchus. Among the dominant species, the silver croaker Bairdiella chrysoura and the sea bream Archosargus rhomboidalis experienced significant changes in average abundance and distribution patterns. These changes were probably related to the impact of human activities in the Terminos Lagoon and natural variability. # 2005 The Fisheries Society of the British Isles

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Accurate knowledge on fish trophic ecology and its modifications is crucial for understanding the impact of global change on ecosystems. In this context, we investigated the value of the δ 13 C and δ 15 N of otolith soluble organic matter (SOM) for identifying temporal diet shifts in American silver perch Bairdiella chrysoura over a 30-yr period characterized by strong changes in its population size and habitats within the Terminos Lagoon (Mexico). We first compared the otolith SOM isotopic signatures from present-day adults to those of muscle and the main local prey. Our results suggest that otolith SOM can be confidently extracted and analyzed for both present and past otoliths of this species. The mean otolith SOM signatures obtained (−15.92 ± 1.35 ‰ for δ 13 C and 9.38 ± 0.93 ‰ for δ 15 N) were consistent with those of the diet as 85% of the individual signatures were included within the prey isotopic niche area. Moreover, this study supports a trophic enrichment factor between diet and otolith (TEF diet-otolith ) close to 0 for δ 15 N, while for δ 13 C, the TEF otolith-muscle of + 0.02 ‰ warrants further investigation. Then, we compared past and contemporary otolith SOM signatures to investigate temporal diet shifts in B. chrysoura. This showed that δ 13 C and δ 15 N differed significantly between the past and present period even if the temporal shift remained relatively small (respectively +1.17 ‰ and -0.55 ‰). The present study substantiates the use of otolith SOM δ 13 C and δ 15 N as a proxy of fish present and past trophic position, opening the possibility for major progress in studies of temporal changes in food web ecology.

RESUMEN. La comunidad de peces en el sur del golfo de México es abundante y diversa y sus componentes se encuentran afectados por la captura incidental de la pesquería del camarón siete barbas. El presente trabajo describe y analiza los patrones de variación espacial y temporal de la abundancia y diversidad de la comunidad de peces, identificando las especies con dominio ecológico. Los muestreos se realizaron mensualmente entre febrero 2006 y enero 2007 en 37 sitios localizados desde la desembocadura del sistema Grijalva-Usumacinta hasta la desembocadura del sistema Chumpam-Balchacah al interior de la Laguna de Términos, en el estado de Campeche al sur del golfo de México. Se realizaron 444 arrastres experimentales con una red de prueba camaronera y se capturaron 26.386 peces con un peso conjunto de 407,1 kg. Se identificaron 94 especies agrupadas en 65 géneros y 38 familias. La abundancia y diversidad de la comunidad de peces se analizó en escalas espacial y temporal en términos de densidad (ind m ), índice de diversidad (H´n), riqueza de especies (DMg) e índice de equidad (J'). En cuanto a abundancia se distinguieron los altos valores registrados en agosto y septiembre, en sitios cercanos a las desembocaduras de los sistemas Grijalva-Usumacinta y Palizada-Del Este. La especie más importante en términos de abundancia fue el bagre Cathorops melanopus. Los intervalos de variación de los índices de diversidad en escala espacial fueron: H´n = 0,5-2,8 bits; Dmg = 2,6-5,3 sp. ind -1 y J´= 0,1-0,8 bits. En escala temporal los intervalos fueron H´n = 1,8-2,6 bits; Dmg = 5,1-6,7 sp. ind -1 y J´= 0,4-0,6 bits. Se identificaron nueve especies dominantes con 16.840 individuos y un peso conjunto de 278,5 kg, equivalente al 63,8% de la captura total. Palabras clave: abundancia, diversidad, peces, especies dominantes, Campeche, México. Spatial and temporal variability of fish community abundance and diversity off the coast of Campeche, MexicoABSTRACT. The fish community of the southern Gulf of Mexico is abundant and diverse, and its components are affected by the bycatch of the seabob shrimp fishery. The spatial and temporal abundance and diversity patterns of the fish community are described and analyzed in this paper, and the ecologically dominant species are identified. Monthly sampling was carried out from February 2006 to January 2007, at 37 sites located between the mouth of the Grijalva-Usumacinta system to the mouth of the Chumpan-Balchacah system inside the Terminos Lagoon, in the state of Campeche, southern Gulf of Mexico. Using an experimental trawl net, 444 experimental hauls were done, and 26,386 individuals were caught with a joint weight of 407.1 kg. In total, 94 species were identified, grouped in 65 genera and 38 families. The abundance and diversity of the fish community was analyzed on spatial and temporal scales in terms of density (ind m 2 ), biomass (g m 2 ), average weight (g ind -1 ), diversity index (H'n), species richness (Dmg), and evenness (J'). The abundance was high in August and September at sit...

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Growth, mortality, maturity, and recruitment of the star drum (Stellifer lanceolatus) in the southern Gulf of Mexico Crecimiento, mortalidad, madurez y reclutamiento de la corvinilla (Stellifer lanceolatus) en el sur del Golfo de México AbstractThe star drum Stellifer lanceolatus (Holbrook 1855) is a dominant species along the western part of the Campeche coastline, southern Gulf of Mexico, and it is regularly caught as bycatch in the seabob shrimp (Xiphopenaeus kroyeri) fishery. It is not commercially important but plays an important role in the transfer of energy through the ecosystem. The spatial and temporal abundance of the species allowed the identification of clear preferences in spatial size distribution. The von Bertalanffy growth model showed seasonal fluctuations and was defined by the following parameters: L ∞ = 18.5 cm, K = 0.4 yr -1 , t 0 = -0.083 yr -1 , C = 0.63, WP = 0.8, and Rn = 0.254. The parameters of the length-weight relationship were a = 0.52 × 10 -6 (condition factor) and b = 3.16, indicating isometric growth (t 0.05(2) , P > 0.05) with a correlation coefficient of 0.97. The monthly condition factor was lower from February to August and increased from September to November, associated with the maturity stage. Size and age at first maturity were 9.2 cm and 1.64 yr, respectively. Total mortality rate was 1.68 yr -1 . Recruitment was continuous with a main pulse from March to July. The life cycle of S. lanceolatus was determined, with reproduction occurring in the coastal zone, juveniles (<9.2 cm) then moving closer to shore until attaining maturity, and returning as adults to deeper areas to reproduce. Further studies are necessary to relate its life cycle to the environment. ResumenLa corvinilla Stellifer lanceolatus (Holbrook 1855) es una especie dominante en la porción occidental de la costa de Campeche, Golfo de México y es regularmente capturada como parte de la fauna acompañante en la pesca del camarón siete barbas (Xiphopenaeus kroyeri). No tiene importancia comercial pero desarrolla un papel importante en el sistema como vehículo de transferencia energética. La abundancia espacial y temporal de la especie permitió identificar claras preferencias de distribución por talla a nivel espacial. El modelo de crecimiento de von Bertalanffy mostró oscilaciones estacionales y está definido por los parámetros L ∞ = 18.5 cm, K = 0.4 año -1 , t 0 = -0.08304 año -1 , C = 0.63, WP = 0.8 y Rn = 0.254. Los parámetros del modelo de la relación longitud/peso fueron a = 0.52 × 10 -6 (factor de condición) y b = 3.16, y muestran un crecimiento isométrico (t 0.05(2) , P > 0.05) con un coeficiente de correlación de 0.97. El factor de condición mensual fue menor de febrero a agosto y se incrementó de septiembre a noviembre, asociado a la época de maduración. La talla de primera madurez se observó a los 9.2 cm y correspondió a una edad de 1.64 años. La tasa de mortalidad total fue de 1.68 año -1 . El reclutamiento fue continuo con un pulso principal entre marzo y julio. Se determinó el ciclo de vida de la ...