Stable-isotope analysis reveals sources of organic matter and ontogenic feeding shifts of a mangrove-dependent predator species, New Granada sea catfish, Ariopsis canteri.

To gain a better understanding on the trophic ecology of New Granada sea catfish, Ariopsis canteri, and their linkage to mangroves, nitrogen and stable carbon isotopes (δ15 N and δ13 C), as well as Bayesian mixing models, were used to explore trophic dynamics and potential ontogenic feeding shifts across different size classes: class I (8-20 cm), class II (21-32 cm) and class III (>32 cm). The study area was the estuary of the Atrato River Delta, where information about fish ecology is scarce. The δ13 C of size class I was lower (mean ± s.d. = -24.96 ± 0.69‰) than that of size classes II (-22.20 ± 0.90‰) and III (-22.00 ± 1.96‰). The δ15 N of size class I was lower (mean ± s.d. = 8.50 ± 0.67‰) than that of size classes II (9.77 ± 0.60‰) and III (10.00 ± 0.66‰). Body size was positively and significantly correlated to δ15 N and δ13 C. Individuals with LT > 32 cm presented the highest estimated trophic position (3.8). Five-source mixing models indicated that for class I, the mean estimated contribution of macroalgae was the highest (6%-57% c.i.), and for classes II and III, the mean estimated contribution of macrophytes was the highest (3%-53% c.i. and 4%-53% c.i., respectively). Ontogenetic feeding shifts of A. canteri were confirmed evidencing decreasing intraspecific competition between small and large individuals. Results suggest that mangroves are a nursery and feeding ground habitat for this species and that mangroves support A. canteri mainly due to the substrate/habitat that supports sources in the food webs. These results can be used in ecosystem-based fishery management focused on the protection of extensive mangrove areas in the southern Caribbean Sea.

Fish species from a micro-tidal delta in the Caribbean Sea.

A total of 66 fish species belonging to 32 families were recorded between November 2012 and April 2014 in the southern arm of the delta to the Atrato River. Total length (LT ; range: 1·7-48 cm), total mass (MT ), LT and MT relationships (b values ranged from 1·8 to 3·7, mostly with negative allometric growth), and LT frequency (for 25 species) were estimated for freshwater, estuarine and marine species. LT and MT of Porichthys pauciradiatus and Membras argentea are given for the first time and maximum LT records for 14 species exceed those in the literature.

Efecto de la conversión del manglar a potrero sobre la densidad y tallas de dos gasterópodos en el delta del río Turbo (golfo de Urabá, Caribe colombiano) / Effects mangrove conversion to pasture on density and shell size of two gastropods in the Turbo River Delta (Urabá Gulf, Caribbean coast of Colombia)

Mangrove deforestation is widespread in the Greater Caribbean but its impact on macrobenthos has not been evaluated to date. In order to assess the impact of mangrove conversion to pasture, densities and shell sizes of two dominant gastropods (Neritina virginea and Melampus coffeus) were compared among four mangrove types: 1) Rhizophora mangle-dominated fringing mangroves, 2) Avicennia germinans-dominated basin mangroves, 3) Mixed-species basin mangroves, and 4) A. germinansbasin mangroves converted to pastures, in the Turbo River Delta (Urabá Gulf, Colombia). Mangrove types were polygon-delimited with satellite images and color aerial photographs were taken in 2009. various (n<5) polygons per mangrove type were sampled in January, July and December 2009, and a total (n<20) 0.025m²-quadrats were randomly placed along each polygon. Forest structure variables, pore-water physico-chemical variables and sediment-grain metrics were measured in the four mangrove types. Mean density and size of both gastropod species were measured. The results showed that the mean density and size of both species were significantly greater in R. mangle-fringing mangroves. N. virginea density decreased gradually towards the A. germinans-basin mangroves seemly related to the diadromous life-history. This species nearly disappeared in the neighboring pastures because individuals were constrained to a few remaining flooded areas. In the pastures, M. coffeus individuals were clumped in the remaining A. germinans trees due to its climbing behavior as a pulmonate. We hypothesize that the decline of these two gastropods was related to physical microhabitat (e.g. trees, prop roots, and seedlings) degradation, and alteration of soil properties (e.g. temperature, pH, organic matter content). Finally, we also hypothesize that the local extinction of N. virginea due to clear-cutting may exert strong negative effects on the ecosystem function because it is a dominant omnivore.

El delta del río Turbo es una de las áreas del golfo de Urabá, Colombia donde la tala de manglar es más extensa y activa, por lo tanto, se evaluó el impacto de la conversión de manglar a potrero, comparando la densidad y talla promedio de dos gasterópodos (Neritina virginea y Melampus coffeus), variables dasonómicas, físico-químicas intersticiales y granulométricas del suelo entre varios parches de: 1) manglar de franja, 2) manglar de cuenca, 3) manglar de cuenca mixto y 4) manglar de cuenca convertido a potrero, en el delta del río Turbo de este golfo, entre enero y diciembre 2009. Las densidades y tallas de los gasterópodos fueron mayores en el manglar de franja. N. virginea fue muy abundante pero disminuyó hacia el manglar de cuenca (debido a sus hábitos diádromos), y desapareció casi completamente en los potreros, donde los individuos estuvieron agregados en las pocas áreas anegadas. En los potreros, los individuos de M. coffeus estuvieron agrupados en los árboles remanentes debido a su hábito arborícola y su condición de pulmonado. Se sugiere que la escasez de los gasterópodos está relacionada con la degradación del microhábitat físico, y la alteración de propiedades del suelo. Finalmente, también planteamos que la extinción local de N. virginea debida a la tala puede ejercer fuertes efectos negativos sobre la función ecosistémica debido a que es un omnívoro dominante.