Feeding ecology of dominant larval myctophids in an upwelling area of the Humboldt Current

Abstract

The feeding of 2 sympatric larval myctophids, Diogenichthys laternatus and Triphoturus mexicanus aff. oculeus, was analyzed in an upwelling area off northern Chile (23° S, 71° W). Diel feeding period, feeding incidence, feeding selectivity and diet overlap was estimated under different environmental conditions: coastal and oceanic areas and 2 depth strata in summer and winter 1997. Analyses were based on larval stomach contents and microplankton abundance estimates. Larval tooth morphology and relationships between larval length, mouth width and prey size were explored. Both species fed on the most abundant microplankton layer during daylight, and both preferred copepods and nauplii, although the diet of D. laternatus was more diverse. As expected, the diets of these species tended to overlap in periods and areas where food was more abundant, but diets dif- fered under conditions of low food availability. The 50 to 100 mm size range dominated the size spec- trum of ingested prey in both species. The smallest prey width was constant for the entire range of larval sizes. The largest prey width was variable both within and between species, and increased with larval size. Regression analyses of mouth size and body length showed a potential relationship in D. laternatus and a linear relationship in T. mexicanus aff. oculeus. Prey ingested by D. laternatus were wider than those ingested by T. mexicanus aff. oculeus at equal larval sizes. The species presented differences in dentition patterns (hook-like teeth and pharyngeal structures in D. laterna- tus, conical teeth in T. mexicanus aff. oculeus). Opportunistic feeding and the feeding characteristics of both species should favor persistence and high abundances in the upwelling area of the Humboldt Current.