A New Observation of Microatolls in the Galapagos Isalnds, Ecuador
Abstract
Microatolls are shallow water coral colonies that develop their signature ring-like atoll shape from water depth limitations that prevent living tissue from growing any higher, encouraging outward growth instead. A secondary contributor to formation is the accumulation of sediment on the top of growing colonies, smothering upper surface polyps. Microatolls are described from numerous locations and form from several species in the Indo-West Pacific. However, microatolls occur at only three known regions in the tropical eastern Pacific and form from one species, Porites lobata. In the Galápagos Islands early researchers (1970s-1980s) observed microatolls at 2 sites, however they are no longer present at either location. In 2019 several microatolls were discovered in a small embayment on Champion Island. These Porites colonies exhibited typical microatoll morphology with depressed dead centers covered in sediment and a living outer ring. The upper portions of the shallowest colonies were at Mean Lower Low Water (MLLW), consistent with other reports of these formations. Colonies ranged from 0.5-1.0m diameter, some forming more elongated, scalloped structures without clearly defined central depressions. Additionally, sea lions (Zalophus wollebaeki) may be responsible for a novel contribution to microatoll formation. They were observed swimming close to living coral tissues and poking at them with their snouts, perhaps further limiting vertical coral growth through physical abrasion. The embayment at Champion Island provides the correct combination of shallow depth, sedimentation stress (and sea lion abrasion) to form these distinctive coral structures at one of only three known regions in the eastern tropical Pacific.
Faculty Sponsors
Dr. Joshua Feingold
Project Type
Event
Location
Alvin Sherman Library
Start Date
4-6-2021 12:00 PM
End Date
4-9-2021 12:00 PM
A New Observation of Microatolls in the Galapagos Isalnds, Ecuador
Alvin Sherman Library
Microatolls are shallow water coral colonies that develop their signature ring-like atoll shape from water depth limitations that prevent living tissue from growing any higher, encouraging outward growth instead. A secondary contributor to formation is the accumulation of sediment on the top of growing colonies, smothering upper surface polyps. Microatolls are described from numerous locations and form from several species in the Indo-West Pacific. However, microatolls occur at only three known regions in the tropical eastern Pacific and form from one species, Porites lobata. In the Galápagos Islands early researchers (1970s-1980s) observed microatolls at 2 sites, however they are no longer present at either location. In 2019 several microatolls were discovered in a small embayment on Champion Island. These Porites colonies exhibited typical microatoll morphology with depressed dead centers covered in sediment and a living outer ring. The upper portions of the shallowest colonies were at Mean Lower Low Water (MLLW), consistent with other reports of these formations. Colonies ranged from 0.5-1.0m diameter, some forming more elongated, scalloped structures without clearly defined central depressions. Additionally, sea lions (Zalophus wollebaeki) may be responsible for a novel contribution to microatoll formation. They were observed swimming close to living coral tissues and poking at them with their snouts, perhaps further limiting vertical coral growth through physical abrasion. The embayment at Champion Island provides the correct combination of shallow depth, sedimentation stress (and sea lion abrasion) to form these distinctive coral structures at one of only three known regions in the eastern tropical Pacific.
