Re-discovery of Microatolls in the Galapagos Islands, Ecuador
Abstract
Microatolls are coral colonies with a signature ring-like shape. They form in shallow water where depth limits vertical growth, allowing them to be utilized as indicators of current and past sea level. Additional contributors to their formation include accumulation of sediment on the colonies which smothers corallites in the center of the structure, overgrowth by algae, and upper surface abrasion by bioeroding organisms. Microatolls occur at numerous locations in the Indo-West Pacific, however, they are reported at only two known locations in the tropical eastern Pacific: Caño Island, Costa Rica and the Galápagos Islands, Ecuador. More than 50 Porites lobata microatolls were observed in a small embayment on the northern coast of Champion Island. These colonies exhibited irregular microatoll morphology, with a more elongated, scallop-shaped boundary than the typical rounded form. Colony sizes ranged from 0.2m2 to more than 3.0m2 . Upper surface depressions were covered in sediment and filamentous algae, surrounded by an outer ring of living tissue. The shallowest living portions of colonies were centered at Mean Lower Low Water (MLLW), consistent with other reports of these formations. A resident colony of sea lions (Zalophus wollebaeki) in this embayment may be responsible for a novel contribution to microatoll formation. Abrasion by passing sea lions and the opportunistic placement of damselfish (Stegastes spp.) algal lawns may further limit vertical coral growth. Unlike other shorelines in the Archipelago, the embayment at Champion Island provides the critical combination of shallow depth, sedimentation stress, and biotic disturbances to form these distinctive coral structures.
Faculty Sponsors
Dr. Joshua Feingold
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-6-2022 12:00 PM
End Date
4-7-2022 5:00 PM
Re-discovery of Microatolls in the Galapagos Islands, Ecuador
Alvin Sherman Library
Microatolls are coral colonies with a signature ring-like shape. They form in shallow water where depth limits vertical growth, allowing them to be utilized as indicators of current and past sea level. Additional contributors to their formation include accumulation of sediment on the colonies which smothers corallites in the center of the structure, overgrowth by algae, and upper surface abrasion by bioeroding organisms. Microatolls occur at numerous locations in the Indo-West Pacific, however, they are reported at only two known locations in the tropical eastern Pacific: Caño Island, Costa Rica and the Galápagos Islands, Ecuador. More than 50 Porites lobata microatolls were observed in a small embayment on the northern coast of Champion Island. These colonies exhibited irregular microatoll morphology, with a more elongated, scallop-shaped boundary than the typical rounded form. Colony sizes ranged from 0.2m2 to more than 3.0m2 . Upper surface depressions were covered in sediment and filamentous algae, surrounded by an outer ring of living tissue. The shallowest living portions of colonies were centered at Mean Lower Low Water (MLLW), consistent with other reports of these formations. A resident colony of sea lions (Zalophus wollebaeki) in this embayment may be responsible for a novel contribution to microatoll formation. Abrasion by passing sea lions and the opportunistic placement of damselfish (Stegastes spp.) algal lawns may further limit vertical coral growth. Unlike other shorelines in the Archipelago, the embayment at Champion Island provides the critical combination of shallow depth, sedimentation stress, and biotic disturbances to form these distinctive coral structures.
