Bar Reef Kalpitiya seasonal reef manta ray (Mobula alfredi) aggregation: oceanic upwelling?
What tidal currents and planktonic krill blooms attract aggregations of reef manta rays to the outer sandstone drop-off of Bar Reef in early morning?
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3 Answers from travellers
The outer barrier of Bar Reef Marine Sanctuary off Kalpitiya sits along the edge of the continental shelf drop-off. Between November and March (the calm northeast monsoon), strong oceanic bottom currents collide with submerged sandstone barrier ridges, driving cold, nutrient-rich deep water upward into the photic zone. This localized upwelling stimulates explosive blooms of sergestid shrimp and zooplankton. Reef Manta Rays (Mobula alfredi) congregate in schools of 10 to 30 individuals along the reef crest between 6:30 AM and 9:30 AM, executing synchronized barrel-roll feeding maneuvers through plankton slicks.
Snorkelers must maintain neutral buoyancy and avoid free-diving down into feeding rays; sudden vertical movements cause mantas to sound into deep water.
Clean-water cleaning stations on the reef slope feature dense colonies of cleaner wrasses (Labroides dimidiatus) that groom parasites from manta gills.
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