Fish richness and species-habitat relationships in two coastal streams of French Guiana, South America

We examined the factors controlling fish species richness and taxa-habitat relationships in the Malmanoury and Karouabo coastal streams in French Guiana between the short and long rainy seasons. The aims were to evaluate the environmental factors that describe species richness on different scales and to define the ecological requirements of fish taxa in the two streams at that period of the year. We sampled ten regularly spaced freshwater sites in each stream with rotenone. We caught a total of 7725 individuals representing 52 taxa from 21 families and 6 orders. More taxa were caught in the Malmanoury (n=46) than in the Karouabo stream (n=37). These values augmented by the number of fish taxa caught only by gill nets in a parallel survey fitted very well to a log-log model of fish richness versus catchment area in Guianese rivers. Most of the fish taxa encountered in the Malmanoury and Karouabo streams were of freshwater origin and nearly all the fish species caught in these two small coastal streams were also found in the nearby Sinnamary River with the exceptions of the cichlid Heros severus and the characid Crenuchus spirulus. Moreover, no significant relationship was found between a size-independent estimate of fish richness and distance from the Ocean. Thus, despite their coastal position, the Malmanoury and Karouabo streams contained fish assemblages with strong continental affinities. At a local scale, independently of site size, those with relatively more habitat types harbored a relatively greater number of fish taxa. Canopy cover, water conductivity and bank length were the most important environmental variables for fish assemblage composition at that period of the year. Oxygen and vegetation participated also in defining fish habitat requirements but to a lesser extent. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Analysis of Fish Species Richness in Natural Lakes

There is a growing recognition of the need to conserve biodiversity that has been conceptualised in the Convention of Biological Diversity. Maintenance of fish species richness is particularly important, because habitat degradation in inland waters continues to accelerate on a global scale. Here we develop empirical models for predicting fish species richness in natural lakes in various geographical regions of the world. In tropical lakes where fish biodiversity is richer than in temperate lakes, fish species richness can be predicted by a few variables such as lake area and altitude. Low fish species richness in most temperate lakes might be due to the effect of glaciation on colonisation and speciation of fishes. In US, Canadian and northern European lakes, lake acidification is one of the important factors influencing fish species richness. Although limnological characteristics influence fish species richness in temperate lakes, lake area and altitude have greater predictive power. This is in contrast to fish species richness in rivers, which can be reliably predicted by basin area. In the power curves, which describe the relationship between fish species richness and habitat size in lakes and rivers, the exponent is always greater in tropical regions than in temperate regions. Because fish biodiversity is greater in the tropics threats to fish biodiversity through habitat degradation are greater than those in temperate inland waters.     

Early dry-season community structure and habitat use of young fish in tributaries of the River Sinnamary (French Guiana, South America) before and after hydrodam operation

We examined fish community structure and habitat use at the start of the dry seasons: (1) in 10 tributaries of the River Sinnamary (French Guiana) before and after the start of dam operation, and (2) in 10 upstream tributaries and at 10 littoral sites in the newly-created reservoir after the start of operation to assess the impact on fish juveniles of a hydroelectric dam built on the river's lower section. After the first year of dam operation, juvenile fish communities downstream of the dam showed an important decrease of the relative abundance of Characiformes, and Perciformes dominated. Principal components analysis revealed a distinct upstream-to-downstream progression in the juvenile fish communities with post-reservoir downstream and reservoir sites representing transitions between the upstream and pre-reservoir downstream sites. Canonical correspondence analysis and electivity indices of fish-habitat associations revealed three relatively distinct groups of sites, corresponding to the downstream, reservoir and upstream taxa. The proportion of juveniles presenting higher-than expected frequencies (Fisher's exact test) towards local environmental variables was higher for taxa more often caught in upstream sites. Inversely, juvenile taxa more frequently observed in downstream and reservoir sites appeared less selective towards local environmental characteristics. In the downstream reaches of the river, hydrodam operation is expected to drive the fish community towards a new biologically accommodated state where tolerant species will dominate and sensitive species will be lacking. This revised version was published online in July 2006 with corrections to the Cover Date.