Feeding Ecology and Stranding Mechanisms in Two Lanternfishes, Hygophum benoiti and Myctophum punctatum

Abstract

The feeding ecology of 2 vertically migrating midwater fishes -Hygophum benoiti and Myctophum punctaturnfound stranded along the shores of the Straits of Messina was studied in order to reconstruct the ecological mechanisms involved in their stranding processes. Diet analyses revealed that both fishes fed mostly on copepods and euphausiids but also on a variety of other food items. Ontogenetic changes in the diet indicated that size selection determined prey choice in all stages in the life cycle of H. benoiti. M. punctatum, on the other hand, became opportunistic with age, adding new components to the diet without excluding prey items eaten by smaller individuals. At the species level, prey choice involved selective feeding on more visible prey items such as bioluminescent copepods. The prey population primarily included surface and migrating sub-surface species. Knowledge of prey vertical distribution patterns in the Mediterranean Sea suggests active feeding by both predators in surface waters at night. The absence of deep water non-migrating elements in the diet implies that the current hypothesis of passive transport of species due to surfacing deep water masses in the Straits may not hold true for all stranded organisms. Alternative stranding mechanisms involving active trophic migrations are proposed for midwater species known to undergo strong diel vertical movements.