César Flores-Coto

Relationship patterns between ichthyoplankton and zooplankton: a conceptual model

Selected cases of plankton studies were analyzed to illustrate the main types of relationships between the zooplankton and the ichthyoplankton abundance observed in the pelagic realm. Such relationships may exhibit a positive, a negative, or a random pattern. In the conceptual model here proposed, short-term oscillations among these patterns were attributed to small-scale biological processes, such as competition, predation, and intraguild predation, acting in conjunction with water turbulence. A negative relationship between zooplankton and ichthyoplankton abundance may be caused both by predation on fish eggs and larvae, and by detrimental competition and intraguild predation interactions for fish larvae. In contrast, positive relationships emerge from the absence or low abundance of major predators on the ichthyoplankton, and from food availability for fish larvae and competing species. The random pattern may appear as a gradual transitional stage between the negative and positive patterns, or be promoted by strong water turbulence – which generates random movements of individuals. The size of zooplankters greatly influences these small-scale phenomena. Hence, their role in the trophic web, the success in competition interactions and vulnerability to water turbulence depends on their size. Intra- and interspecific competition may be reduced by variability in body size within or among fish larvae populations. Owing to a strong interaction among phenomena at different scales, these small-scale processes are also influenced by larger scale features, such as seasonal changes in zooplankton biomass, water currents, or spawning periods of fish. At the space level, some theoretical studies have emphasized the role of water currents as a vector for fish larvae to reach the nursery grounds (migration triangle hypothesis), or to allow them to remain within their own population’s distributional area (member/vagrant hypothesis). At the temporal level, the match/mismatch theory insists in a synchrony between reproductive strategies of fish and cyclical changes in abundance and size spectrum of potential prey items for their larvae. In any case, a coincidence between favorable abiotic and biotic features during the whole life-cycle of fish would assure a success in survival of larvae and their subsequent recruitment to adult population.

Cross-shelf and vertical distribution of siphonophore assemblages under the influence of freshwater outflows in the southern Gulf of Mexico

Siphonophores are exclusively marine cnidaria and their predatory role in plankton food-webs is well recognised. In this study, we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of 149 samples were collected using a 505 μm multiple closing net at 1–6 levels (0–100 m) of the water column, depending on the bathymetry. Data on siphonophore species biovolumes (ml 100 m−3) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the ‘inner’ and the ‘outer’ assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially, the lowest diversity and mean siphonophore biovolumes values were registered in the ‘inner assemblage’, where the highest and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity, since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps, their prey. All the 23 species here registered were found in the ‘outer assemblage’; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the ‘outer’ group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the ‘inner assemblage’ during both seasons and, supporting previous observations, this species might be considered as an indicator of nearshore waters.

Larval distribution and abundance of pleuronectiformes from the southern gulf of Mexico

The larval material was collected with a bongo net during four oceanographic cruises, conducted on the southern Gulf of Mexico, between 1983 and 1984. A total number of 5163 larvae were captured; 11 species belonging to Bothidae, two to Cynoglossidae and two to Soleidae. Syacium gunteri (25·9%), Symphurus civitatus (24·0%), Etropus crossotus (9·5%) and Bothus ocellatus (8·1%) comprised more than 67% of total larvae. Except for Trichopsetta ventralis which has an oceanic distribution, all species occurred principally over the continental shelf. Relative high frequency of occurrence and great abundance of larvae of Engyophrys senta, Cyclopsetta fimbriata, Citharichthys gymnorhinus, Citharichthys abbotti, Citharichthys spilopterus and Citharichtys cornutus were recorded in the outer shelf and adjacent oceanic area. Larvae of S. gunteri, S. civitatus, B. ocellatus, E. crossotus, Cyclopsetta chittendeni and Symphurus plagiusa occurred mainly in areas less than 100 m deep and larvae of Trinectes maculatus and Achirus lineatus at the inner shelf (< 40 m deep). Most of the species occurred year-round; some of them showed some seasonality in occurrence, such as S. gunteri, E. crossotus and S civitatus which showed highest larval densities in the spring. Larvae of E. senta and C. fimbriata were most abundant in spring-summer and winter respectively.

Mesoscale distribution of Oikopleura and Fritillaria (Appendicularia) in the Southern Gulf of Mexico: spatial segregation

The mesoscale spatial distribution of Oikopleura and Fritillaria in the southern Gulf of Mexico was analyzed to know the existence of segregation between the...

Relationship between zooplankton biomass and continental water discharges in the southern Gulf of Mexico (1984-2001)

espanolLa biomasa zooplanctonica es reconocida como un importante indicador de la produccion secundaria; su variacion espacio-temporal en zonas neriticas es afectada particularmente por las descargas de los rios, por lo que se analiza el efecto espacio temporal de las descargas de aguas continentales en la distribucion de la biomasa zooplanctonica en el sur del Golfo de Mexico, en 5 areas frente a las costas de Veracruz, Tabasco y Campeche. El material analizado proviene de 534 muestras recolectadas en diferentes estaciones climaticas entre 1984 y 2001. Los volumenes de descargas de 5 regiones hidrologicas se obtuvieron de la base de datos gubernamentales. Los resultados muestran que las variaciones de la biomasa durante las estaciones del ano en las diferentes areas son muy similares al patron de las descargas. Los mayores valores de biomasa ocurren enfrente de las costas de Tabasco y los menores frente a Veracruz, donde se tienen las mayores y menores descargas de aguas continentales respectivamente. La variacion de la biomasa depende de las descargas, no solo en terminos de un ciclo anual, sino tambien directamente relacionada con el tamano del volumen vertido al oceano. El analisis de arbol permitio concluir que en el sur del Golfo de Mexico sobre la parte externa de la plataforma y zona oceanica, la biomasa siempre es baja, independiente de la estacion del ano o del area de que se trate. La mayor biomasa ocurre sobre la plataforma en profundidades bajas, pero su magnitud varia dependiendo del area y de la epoca. La biomasa frente a Campeche no depende de las descargas de aguas continentales sino se genera sobre la plataforma de Yucatan. EnglishZooplankton biomass is recognized as an important indicator of secondary production, its spatial and temporal variation in neritic zones is particularly affected by discharges of the rivers, and the spatial-temporal effect of continental water discharges on the distribution of zooplankton biomass in the southern Gulf of Mexico was analyzed for 5 areas off the coasts of Veracruz, Tabasco and Campeche. The analyzed material was obtained from 534 samples collected during different climatic seasons from 1984 to 2001. The discharge volumes of 5 hydrological regions were obtained from the governments data base. The results obtained indicated that biomass variation throughout the seasons in the different areas was very similar to the pattern of discharges. The greater biomass values were recorded off Tabasco and the lower values off Veracruz, where the greater and lower continental water discharges were recorded respectively. Biomass variation depended on the discharges, not only in terms of an annual cycle, but was also directly related to the volumes discharged into the ocean. A Tree analysis made it possible to conclude that biomass is always low on the outer shelf and oceanic region of the southern Gulf of Mexico, independently of the season of the year or of a particular area. A greater biomass was recorded on the shallow shelf, with a magnitude that varied in relation to the area and season. The biomass off Campeche did not depend on the continental water discharges, but was generated on the Yucatan shelf.

Environmental factors affecting structure and spatial patterns of larval fish assemblages in the southern Gulf of Mexico

Resumen en: The environmental factors that affect larval fish assemblages in the southern Gulf of Mexico were studied. Samples were collected with a Bongo net from t...

Vertical distribution of zooplankton biomass and ichthyoplankton density during an annual cycle on the continental shelf of the southern Gulf of Mexico

Se analizo estacionalmente la biomasa zooplanctonica (BZ) y la densidad ictioplanctonica (DI) en la columna de agua sobre la plataforma continental del sur del Golfo de Mexico, para determinar sus patrones de distribucion vertical y establecer si existe una relacion entre ambos componentes. Se muestrearon cinco niveles de profundidad: 0-6 m, 6-12 m, 12-18 m, 45-55 m y 95-105 m. El patron de distribucion vertical de la BZ y de la DI fue similar en todas las epocas de muestreo, con la mayor concentracion de organismos en los niveles superficiales y la mas baja en los niveles mas profundos. Estos resultados sugieren que la columna de agua en el area de estudio puede estar dividida en una capa superficial (0 a 18 m) y una capa profunda (45 a 100 m) y que las diferencias estacionales pueden ser atribuidas a los procesos de mezcla. Esta diferencia entre las capas superficiales y las profundas ocurre porque, en general, las capas superficiales de la columna de agua son las mas productivas. La relacion entre la BZ y la DI fue positiva y significativa (ANCOVA, P<0,05) a traves de las epocas de muestreo y en la mayoria de las profundidades probablemente porque el ciclo de produccion es continuo en el sur del Golfo de Mexico como sucede en areas tropicales y subtropicales, manteniendo la disponibilidad de alimento y consecuentemente, la relacion depredador-presa. La relacion BZ y DI en la columna de agua es afectada principalmente por la variacion estacional de las descargas de agua continental y el proceso de mezcla.

Larval abundance variation of Bregmaceros cantori Milliken & Houde, 1984, related to the El Niño events (1987-1996), southern Gulf of Mexico

Se analiza la influencia de El Nino Oscilacion del Sur (ENSO) sobre la variacion de la abundancia de las larvas del pez Bregmaceros cantori en el sur del Golfo de Mexico. El estudio se desarrollo entre 1987 y 1996, usando 20 cruceros oceanograficos. La abundancia de B. cantori fue relacionada con: (1) la anomalia de la temperatura superficial del mar (SSTA) del Oceano Pacifico central ecuatorial, (2) la temperatura promedio de la capa superficial de 30 m, de datos de las campanas, (3) las descargas de aguas continentales con datos provenientes de la estacion hidrologica mas cercana al area de estudio. Hubo una alta variabilidad de la abundancia de larvas de B. cantori a traves del tiempo, pero no se registro un patron estacional. Durante el periodo de estudio ocurrieron tres eventos de El Nino: 1987, 1992 y 1995. Los analisis estadisticos indicaron diferencias significativas en la abundancia de larvas entre los anos de El Nino y anos normales, sin el evento de El Nino. Se encontraron altas abundancias de B. cantori en los periodos de El Nino en comparacion con los anos normales. Es posible que las mayores abundancias de larvas de B. cantori durante anos de El Nino esten asociadas con relaciones depredador-presa

Immigration of Post Larvae of Penaeid Shrimp to Terminos Lagoon, Campeche, México: 2013 Annual Cycle

Immigration density magnitude and entry sizes of shrimp postlarvae to Terminos Lagoon were analyzed through sixteen fortnightly sampling from March to November in 2013, in three levels in the deepest channel of the Puerto Real inlet. Trapezium nets were used with 1.5 m length, 50 cm mouth diameter and 505 μm mesh, during each sampling 12 casts of 15 minutes/each were made. It was determined the presence of two species Litopenaeus setiferus and Farfantepenaeus duorarum, with total densities of 41.284 and 37.558 Pls 100 m-3 respectively. The annual cycle of immigration of postlarvae was very similar for both species, with a clear pattern of immigration throughout the year, linked to climatic variation, with the highest densities (88%) during rainy season. There were two periods of maximum density, related to the periods of greatest reproduction of these species. The density variation among cast reflects the presence of at least two and probably more postlarvae banks, located some closer than others to the mouth of the lagoon and with different densities in them. The average sizes of the two species were 7.9 mm total length of L. setiferus and 9.0 mm of F. duorarum. The differences in income sizes of both species seem to indicate the habitat preference of adult populations, L. setiferus occurring in more coastal areas than F. duorarum. Considering the variation in density and sizes throughout each sampling period, it is evident that the larvae on the banks belong to different cohorts and that have coincided in their location in front of the mouth.

Comparison of pteropod assemblages and their relationship with environmental variables in the southern Gulf of Mexico

A comparison of pteropod assemblages and their relationship with environmental factors in the southern coastal and oceanic zones of the Gulf of Mexico (GM) was performed during the springs (May–June) of 2006 and 2010. Zooplankton samples came from catches of 136 oblique tows with a Bongo net (0.61 m in mouth diameter; mesh 505 μm) and included 20 species of Euthecosomata, six of Pseudothecosomata, and three species and three genera of Gymnosomata. Four new records were found for the area (Diacavolinia strangulata, Cymbulia sibogae, Paraclione longicaudata and Thliptodon diaphanus). The most abundant species were Creseis conica, Limacina trochiformis and Creseis acicula, followed by Heliconoides inflatus. Pteropod abundance was higher in the neritic zone, particularly in the area of the epicontinental water discharge at the coastal front of the Veracruz-Tabasco zone, while higher diversity was observed in the oceanic zone. The cluster analyses and canonical correspondence analyses showed two assemblages (station groups) in each period: Oceanic and Coastal. The Oceanic assemblage was composed of species of oceanic origin with two indicator species (H. inflatus and Limacina lesueurii). This assemblage was correlated with increased sea surface temperature, at least during 2006, probably modulated by the influence of the Loop Current. The Coastal assemblage included both oceanic and neritic species and was subdivided into three, geographically distinct, station zones: (1) Veracruz-Tabasco zone characterized by Desmopterus papilio and L. trochiformis, their abundances inversely correlated with salinity and increased CO2, and influenced by river discharges and the narrow continental shelf; (2) Yucatan zone characterized by C. conica as an indicator species (2006); and (3) Confluence zone characterized by C. acicula (Laguna de Términos). Yucatan and Confluence zones were characterized by elevated pH, and reduced turbidity and temperature, at least during 2010.