DNA barcoding identifies a cosmopolitan diet in the ocean sunfish

Area of Science:

• Marine Biology
• Ichthyology
• Ecology

Background:

• The ocean sunfish (Mola mola) is the world's heaviest bony fish, reaching up to 2.3 tonnes.
• Its diet has been poorly understood, with previous assumptions of it being an obligate gelatinous plankton feeder.

Purpose of the Study:

• To characterize the diet of Mola mola in the north-east Atlantic Ocean.
• To investigate potential ontogenetic shifts in sunfish diet.

Main Methods:

• Molecular barcoding of diet content from 57 sunfish individuals.
• Analysis of DNA from stomach contents to identify prey items.

Main Results:

• 41 different prey items were identified, with crustaceans and teleosts forming the majority of the diet (84%).
• Cnidarians comprised only 16% of consumed prey, contradicting previous assumptions.
• Evidence of an ontogenetic diet shift was found: smaller sunfish consumed more benthic and coastal pelagic species, while larger sunfish consumed more pelagic prey.

Conclusions:

• Mola mola is a generalist predator with a diverse diet, including significant contributions from crustaceans and teleosts.
• The sunfish exhibits an ontogenetic shift in diet, with larger individuals consuming more pelagic prey.
• As a generalist predator, Mola mola's role in coastal food webs is more extensive than previously recognized, with potential ecological consequences if removed as bycatch.