Multiple nets better explain the diversity of marine fish larvae in equatorial environments

Abstract

The quantitative assessment of fish larvae is a key issue in determining the composition of marine food webs. However, there is still a gap in this field regarding how to efficiently sample larvae, particularly in warm and nutrient-poor waters. We evaluated the differences found in larvae caught with two mesh size nets (330 and 500 μm) sampled in the open ocean: shelf break and slope (equatorial SW Atlantic). In total, 792 larvae were sampled, representing 14 orders and 55 families. Overall, larval density was low, and no difference in density was detected between the two net sizes (ind.100 m⁻³). However, a greater number of taxa (46 families) were found in the smaller net (300 μm) than in the larger (500 μm) (37). Moreover, 30.2% of families were found only in the 330 μm net, whereas 9.4% were found only in the 500 μm net. A total of 60.4% of taxa were common to both nets. Gonostomatidae, Paralepididae, Scombridae, Carangidae, Phosichthyidae, and the reef-associated families Scaridae and Gobiidae were the most abundant taxa in the smaller net. In contrast, Myctophidae, Gobiidae, Gonostomatidae, and Stomiidae were the most abundant in the larger net. We highlight mesophotic reefs and seamounts in the South Atlantic for adult spawning and larval growth, emphasizing the need for conservation actions and appropriate fisheries management. Finally, our results also indicate that the combination of different mesh net sizes provides a better baseline of fish larval diversity in warm and oligotrophic oceans.