Diet reveals links between morphology and foraging in a cryptic temperate reef fish

Area of Science:

• Marine Biology
• Ecology
• Evolutionary Morphology

Background:

• Predatory fish optimize foraging by selecting prey and microhabitats to maximize energy intake and minimize handling time.
• Morphological adaptations in fish populations often reflect local prey availability and foraging strategies.

Purpose of the Study:

• To investigate the relationship between diet variation, habitat type, and key morphological structures in the triplefin fish (Helcogrammoides cunninghami).
• To understand how habitat selection and prey usage influence the feeding morphology of this reef fish species.

Main Methods:

• A mensurative experiment was conducted at six kelp-dominated sites along the Chilean coast.
• Diet composition and prey distributions were analyzed in relation to habitat availability.
• Allometry-corrected morphological measurements (mouth gape, eye diameter, fin length, fin area, pectoral fin ratio) were correlated with prey types.

Main Results:

• Significant differences in triplefin diet were observed along the coast, correlating with habitat diversity and prey availability.
• Northern sites with low habitat diversity showed a preference for single prey types (bivalves or barnacles).
• Southern sites with heterogeneous habitats exhibited more diverse diets including amphipods, decapods, and cumaceans.
• Large mouth gape was linked to capturing mobile prey (decapods), while small mouth gape was associated with smaller prey (cumaceans, copepods).
• Larger eyes were observed in triplefins consuming sessile prey (hydroids).

Conclusions:

• Morphological structures in Helcogrammoides cunninghami co-vary with habitat selection and prey utilization.
• This abundant generalist reef fish displays variable feeding morphologies in response to environmental factors and prey distribution across its range.
• The findings highlight the adaptive plasticity of feeding structures in response to ecological pressures.