Influence of temporal and spatial factors on abundance and richness of fish early stages in shallow tropical estuaries.

Accurate determination of abundance and richness of fish early stages in estuarine zones is critical to support management and protection plans; it is therefore necessary to consider all influential factors. Habitat diversity, seasonality, moon phase and diel variations, and their interactions are factors that can affect richness and abundance estimations. Appropriate spatial and temporal scales in sampling design are important to understand the assemblage dynamics of fish early stages. The objective of this research is to test how temporal and spatial scales influence the determination of abundance and richness of fish early stages based on a hierarchical sampling design considering season (dry and rainy), moon phase (new, crescent, full, and waning), day period (sunrise, midday, sunset, and night), habitat (coastal, riverine, mangrove, and Vallisneria americana beds), and their interactions. Samples were collected using a conical zooplankton net and towed horizontally for 5 min at a depth of 50 cm. A variance component analyses model showed that day period, season, and their interactions were the main factors determining variations in fish early stage abundances and richness (26.68, 10.78, and 12.82 %, respectively). The highest abundance and richness occurred at night, with significant seasonal variations related to the runoff from the Grijalva-Usumacinta basin. Abundance and richness were higher in the dry season, which were related to higher dissolved oxygen and water transparency. Presented findings can be generalized to tropical and subtropical estuaries with shallow waters. [ABSTRACT FROM AUTHOR]