Spatial and trophic niche overlap between Diplodus bellottii and Diplodus vulgaris in the Tagus estuary, Portugal

To evaluate the consequences of the coexistence of the Senegal sea bream Diplodus bellottii with one other species of Diplodus, Diplodus vulgaris'. in the Tagus estuary (Portugal), the distribution and feeding habits of juveniles and adults of both species were studied. Sampling took place between May 2001 and March 2002, in five zones, including the estuary and adjacent coastal area, using an otter trawl. Both species were abundant in the estuary and their distribution overlapped. The stomach contents analysis showed that the diet of both species was mainly composed of algae, bivalves and crustaceans. Diphodus bellottii and D. vulgaris showed a generalist feeding behaviour and were clearly omnivorous, being detected in a high trophic niche overlap between the two species. Competition for space and food may occur when densities are high and food became a limiting factor.