Residents and visitors both revel in Kauai’s lush landscape, and beneath its seascape. However, it’s underwater where things don’t look so healthy. Scientists from the U.S. Geological Survey put together a detailed picture of the physical environment of the coral reefs at Makua Beach.
Circulation and Sediment, Nutrient, Contaminant, and Larval Dynamics on Reefs Completed
By Pacific Coastal and Marine Science Center
September 10, 2019
The overall objective of this research effort is to better understand how circulation and sediment processes impact coral reefs.
This study is part of the USGS Coral Reef Project.
The Problem
Sources/Usage: Public Domain. View Media Details
Terrigenous sediment run-off and deposition on coral reefs can significantly impact coral health by blocking light and inhibiting photosynthesis, directly smothering and abrading coral, and triggering increases in macro algae. The delivery of sediment and pollutants to reefs have increased globally as a response to human-induced changes to watersheds, as pointed out in the U.S. Commission on Ocean Policy. The Status of Coral Reefs of the World (2004) report states that sediment run-off is the major stressor to reefs in Hawaiʻi, Guam, and the Northern Mariana Islands, while the Coral Reefs of the USA (2008) and The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States (2008) reports recognize that sediment run-off is one of the most serious stressors affecting coral reefs not only in the Hawaiian and Mariana Islands, but also those off American Samoa, Puerto Rico, and in the U.S. Virgin Islands. Furthermore, it is the impact from local stressors such as terrestrial sediment, as compared to global climate change, that can be best rectified through local actions by Federal, State, and/or local land managers.
Sources/Usage: Public Domain. View Media Details
The dominant control on residence time of sediment, nutrient uptake, contaminant exposure, and larval dispersal in coral reef systems is the pattern of flow. Coral reefs are hydrodynamically rough, more than an order of magnitude greater than sandy sea floors. This roughness and the high geomorphic complexity of reefs cause currents to diverge around reef structures, resulting in high horizontal and vertical shear (flow going in different directions at different locations or depths). This can result in either the rapid transport of material in localized jets or the retention of material eddies that form in the lee of reefs; these zones of retention can either be beneficial (coral larval recruitment) or harmful (contaminants) to coral reef ecosystems. The high geomorphic and hydrodynamic complexity and diversity within and between reefs has limited our understanding of the nature of flow and the resulting magnitude and direction of transport of physical, chemical, and biologic material in these fragile ecosystems.
The Approach
The overall objective of this research effort is to better understand how circulation and sediment processes impact coral reefs. Achievement of this objective requires an understanding of the physical parameters driving flow, transport pathways and durations, and coral reef ecosystem processes. The goals of this effort are to:
- determine the patterns of flow over coral reefs that result from different forcing mechanisms such as waves, currents, surface tides, internal tides and those driven by wind, large-scale ocean currents, etc.;
- compare retention times of sediment, nutrients, and contaminants over complex coral reef morphologies with those along more linear coral reef systems;
- identify the circulation pathways by which separated reefs are linked through larval or pollutant transport, and at determine over what time and space scales these pathways occur; and
- evaluate how these processes and linkages will be affected by predicted changes in climate, such as sea-level rise and changes in the frequency and intensity of storms.
The approach to these interdisciplinary studies will rely on a combination of field measurements and physics-based numerical monitoring. We use a wide range of tools to try to answer these questions, including: oceanographic instruments (for example, acoustic Doppler current profilers, wave/tide gauges, temperature sensors, salinity sensors, turbidity sensors, chemical sensors) mounted on the seabed or on moorings, water-column profilers with similar suites of sensors, time-lapse camera systems deployed on land or underwater, GPS-equipped Lagrangian surface drifters, simple and rotary sediment traps, coral and sediment cores, geophysical sub-bottom surveys, and physics-based numerical models.
Below are multimedia items associated with this project.
What's Drifting Beneath Kauai's Ocean?
Residents and visitors both revel in Kauai’s lush landscape, and beneath its seascape. However, it’s underwater where things don’t look so healthy. Scientists from the U.S. Geological Survey put together a detailed picture of the physical environment of the coral reefs at Makua Beach.
Breaking Down Reefs, Building Up Beaches
On the remote western coast of Australia lies a UNESCO World Heritage Site above and below the sea. Researchers from the U.S. Geological Survey and University of Western Australia convened here at Ningaloo Reef and Jurabi Coastal Reserve to embark on the most extensive study EVER done into how coral reefs shape our coasts.
On the remote western coast of Australia lies a UNESCO World Heritage Site above and below the sea. Researchers from the U.S. Geological Survey and University of Western Australia convened here at Ningaloo Reef and Jurabi Coastal Reserve to embark on the most extensive study EVER done into how coral reefs shape our coasts.
The overall objective of this research effort is to better understand how circulation and sediment processes impact coral reefs.
This study is part of the USGS Coral Reef Project.
The Problem
Sources/Usage: Public Domain. View Media Details
Terrigenous sediment run-off and deposition on coral reefs can significantly impact coral health by blocking light and inhibiting photosynthesis, directly smothering and abrading coral, and triggering increases in macro algae. The delivery of sediment and pollutants to reefs have increased globally as a response to human-induced changes to watersheds, as pointed out in the U.S. Commission on Ocean Policy. The Status of Coral Reefs of the World (2004) report states that sediment run-off is the major stressor to reefs in Hawaiʻi, Guam, and the Northern Mariana Islands, while the Coral Reefs of the USA (2008) and The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States (2008) reports recognize that sediment run-off is one of the most serious stressors affecting coral reefs not only in the Hawaiian and Mariana Islands, but also those off American Samoa, Puerto Rico, and in the U.S. Virgin Islands. Furthermore, it is the impact from local stressors such as terrestrial sediment, as compared to global climate change, that can be best rectified through local actions by Federal, State, and/or local land managers.
Sources/Usage: Public Domain. View Media Details
The dominant control on residence time of sediment, nutrient uptake, contaminant exposure, and larval dispersal in coral reef systems is the pattern of flow. Coral reefs are hydrodynamically rough, more than an order of magnitude greater than sandy sea floors. This roughness and the high geomorphic complexity of reefs cause currents to diverge around reef structures, resulting in high horizontal and vertical shear (flow going in different directions at different locations or depths). This can result in either the rapid transport of material in localized jets or the retention of material eddies that form in the lee of reefs; these zones of retention can either be beneficial (coral larval recruitment) or harmful (contaminants) to coral reef ecosystems. The high geomorphic and hydrodynamic complexity and diversity within and between reefs has limited our understanding of the nature of flow and the resulting magnitude and direction of transport of physical, chemical, and biologic material in these fragile ecosystems.
The Approach
The overall objective of this research effort is to better understand how circulation and sediment processes impact coral reefs. Achievement of this objective requires an understanding of the physical parameters driving flow, transport pathways and durations, and coral reef ecosystem processes. The goals of this effort are to:
- determine the patterns of flow over coral reefs that result from different forcing mechanisms such as waves, currents, surface tides, internal tides and those driven by wind, large-scale ocean currents, etc.;
- compare retention times of sediment, nutrients, and contaminants over complex coral reef morphologies with those along more linear coral reef systems;
- identify the circulation pathways by which separated reefs are linked through larval or pollutant transport, and at determine over what time and space scales these pathways occur; and
- evaluate how these processes and linkages will be affected by predicted changes in climate, such as sea-level rise and changes in the frequency and intensity of storms.
The approach to these interdisciplinary studies will rely on a combination of field measurements and physics-based numerical monitoring. We use a wide range of tools to try to answer these questions, including: oceanographic instruments (for example, acoustic Doppler current profilers, wave/tide gauges, temperature sensors, salinity sensors, turbidity sensors, chemical sensors) mounted on the seabed or on moorings, water-column profilers with similar suites of sensors, time-lapse camera systems deployed on land or underwater, GPS-equipped Lagrangian surface drifters, simple and rotary sediment traps, coral and sediment cores, geophysical sub-bottom surveys, and physics-based numerical models.
Below are multimedia items associated with this project.
What's Drifting Beneath Kauai's Ocean?
Residents and visitors both revel in Kauai’s lush landscape, and beneath its seascape. However, it’s underwater where things don’t look so healthy. Scientists from the U.S. Geological Survey put together a detailed picture of the physical environment of the coral reefs at Makua Beach.
Residents and visitors both revel in Kauai’s lush landscape, and beneath its seascape. However, it’s underwater where things don’t look so healthy. Scientists from the U.S. Geological Survey put together a detailed picture of the physical environment of the coral reefs at Makua Beach.
Breaking Down Reefs, Building Up Beaches
On the remote western coast of Australia lies a UNESCO World Heritage Site above and below the sea. Researchers from the U.S. Geological Survey and University of Western Australia convened here at Ningaloo Reef and Jurabi Coastal Reserve to embark on the most extensive study EVER done into how coral reefs shape our coasts.
On the remote western coast of Australia lies a UNESCO World Heritage Site above and below the sea. Researchers from the U.S. Geological Survey and University of Western Australia convened here at Ningaloo Reef and Jurabi Coastal Reserve to embark on the most extensive study EVER done into how coral reefs shape our coasts.