Manta Rays Feeding Under Light Off the Kona Coast

A manta ray feeds by swimming slow loops through a column of plankton, mouth open, filtering water through its gill plates. Off the Kona coast, a light held still in open water concentrates that plankton in one place, and a manta that finds it will keep returning to the same beam for as long as the food holds. That single mechanic, light, plankton, a filter feeder circling back, is the whole reason a manta encounter in Kona water can run far longer than a chance pass on a daytime reef dive.

What is a manta ray actually eating?

According to the National Oceanic and Atmospheric Administration, the giant manta ray feeds mainly on planktonic organisms such as euphausiids, copepods, mysids, decapod larvae and shrimp, with some studies noting it also takes small to moderately sized fish. It is a filter feeder, not a hunter in the usual sense: there is no chase, no strike, just volume moving through an open mouth.

How does a manta ray actually filter that much water?

The ray curls a pair of fins near its mouth, called cephalic fins, into an O shape and opens wide, turning its head into a funnel that pushes water and prey across its gill plates as it swims. NOAA notes that mantas also barrel roll, somersaulting over and over, and form feeding chains with other mantas to maximize the prey they take in. A diver who watches a manta long enough on a Kona dive will usually see at least one of these three patterns: the straight filtering pass, the barrel roll, or, when several animals are present, a short chain.

Which manta species actually show up on the Kona coast?

Hawaii's Division of Aquatic Resources lists two manta species in state waters: the giant oceanic manta ray, Mobula birostris, and the reef manta ray, Mobula alfredi. The division tells them apart mainly by their markings, and describes the oceanic species as one thought to spend most of its time in deep water, only occasionally coming close to shore. NOAA records the giant manta ray, the world's largest ray, at a disc width of up to twenty six feet and a weight of up to five thousand three hundred pounds.

Why does a light matter so much to how this dive works?

Plankton is drawn to light in open water, a basic response built into many of the small organisms a manta eats. A fixed light source at night holds a cloud of that plankton in one spot instead of letting it disperse across the water column the way it does under ambient moonlight or daylight. A manta that locates the light has little reason to leave it: the food keeps arriving in the beam faster than its filtering strips it out. Dive operations that run manta encounters along the Kona coast build the whole dive around this one behavior, positioning lights and divers so the rays have a reason to circle close and stay.

Why is touching a manta ray discouraged?

Hawaii's Division of Aquatic Resources asks anyone who sees an oceanic manta ray not to disturb its natural behavior by touching or chasing it. The practical version of the rule is simple: hold position, let the ray choose its distance, and keep hands out of its flight path rather than reaching toward it as it passes.

What does the giant manta ray's conservation status mean for a diver watching one?

NOAA Fisheries lists the giant manta ray as threatened under the Endangered Species Act, and the species also appears on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Neither listing bars a diver from watching a manta feed. Both reflect a species that recovers slowly from losses: NOAA describes giant mantas as slow growing, with among the lowest fecundity of all sharks and rays, typically a single pup every two to three years after a gestation thought to last around a year. That slow pace is a good reason to treat the no touching rule above as a working standard rather than a suggestion.

What should change about how a diver positions during a manta encounter?

Staying still does more than any swimming effort. A manta circling a light follows the food, not the diver, and a diver who holds one position, fins down, light aimed steady, gives the ray a predictable space to loop through. Chasing a manta that peels off toward darker water almost always ends the encounter faster than waiting would have, since the animal reads pursuit as a reason to leave the light rather than a reason to come closer.