The Importance of Early Life History Characteristics: A Novel Approach for Evaluating Impacts of Habitat Modification and Sediment Contamination on Estuarine Fish Larvae

Ecological characteristics related to the life cycle and reproductive practices of different fish guilds may play an important role in determining their sensitivity to environmental modification. Relationships between life history characteristics, habitat modification, and contaminants have rarely been assessed for marine fish larvae. We investigated the large-scale distribution of stressors and relative sensitivity of larval fish guilds in estuarine environments. Larval fish communities were sampled along the surface and bottom using a plankton tow/benthic sled within the inner and outer zones of three heavily modified and three relatively unmodified estuaries. Larval community composition differed significantly between heavily modified and relatively unmodified estuaries. Species were classified into distinct guilds according to estuarine usage and egg laying characteristics. Estuarine species and demersal egg layers were significantly more abundant in modified estuaries while estuarine opportunist species and pelagic egg layers trended towards higher abundance in relatively unmodified systems. Differences in larval community composition were strongly related to sediment metal contamination and reduced seagrass cover in modified areas. These findings suggest that contamination and habitat alteration have substantially different effects on larvae of various guilds. Early life history characteristics represent a valuable tool for identifying and assessing sensitive fish taxa.