Groundwater that seeps into the coastal zone beneath the ocean's surface--termed submarine groundwater discharge (SGD)--is an important source of fresh water and nutrients to nearshore coral reefs throughout the globe. Although submarine groundwater is natural, it can act as a conduit for highly polluted water to shorelines. A recently published study, led by researchers at the University of Hawai'i at Mānoa's School of Ocean and Earth Science and Technology (SOEST), sheds light on the ways SGD affects coral reef growth.
"SGD is common on nearshore coral reefs, especially in Hawai'i, so we set out to test how SGD affects coral reef growth in Maunalua Bay, O'ahu." said Megan Donahue, associate researcher at the Hawai'i Institute of Marine Biology (HIMB) in SOEST and senior author of the study.
Two processes contribute to the overall growth of coral reefs: coral growth and bioerosion, the natural breakdown of coral reefs by reef organisms. To determine how SGD affects these processes, the research team outplanted small pieces of lobe coral on the reef flat in areas with a range of SGD and measured the changes in size over a six-month period.
They also put out blocks of dead coral skeleton across the same SGD gradients for one year to measure bioerosion rates. The blocks were scanned before and after the deployment with a micro-CT scanner, similar to a hospital CT scanner, to determine the amount of coral skeleton removed by bioeroding organisms in three dimensions.
In areas with high levels of SGD, it was a double whammy for coral reefs. Corals that were right next to SGD seeps performed poorly, likely due to the stress of too much fresh water.
"Additionally, we found that marine organisms responsible for bioerosion broke down the skeletal reef framework very quickly when exposed to high amounts of SGD," said lead author Katie Lubarsky, who completed this research as part of her graduate degree in Marine Biology at UH Mānoa. "Many bioeroding organisms are filter feeders that perform better in high nutrient environments, so the high nutrient groundwater likely enhanced bioeroder activity. This indicates that high inputs of nutrient polluted SGD could favor reef breakdown and substantially slow down overall reef growth."
To the researchers' surprise, SGD actually enhanced coral growth when the nutrient enrichment and freshwater from the groundwater was at low levels.
"Our results indicate that corals can thrive on SGD-impacted reefs if isolated from secondary stressors such as competition from seaweeds and sedimentation," said Donahue. "Maunalua Bay is situated in a highly urbanized area, and the coral reefs in the bay have become degraded as the population has boomed over the last 50 years. But active management to reduce invasive algae and limit fine sediments could allow coral recovery in Maunalua Bay."
"While the current study found that corals grow faster when exposed to low levels of SGD nutrient enrichment, coral cover remains extremely low on the Maunalua Bay reef flats," said Nyssa Silbiger, study co-author and assistant professor at California State University, Northridge. "Our next studies will focus on how SGD and herbivory from fishes impact coral-algal competition, coral recruitment rates, and bioerosion rates."
Marcie Grabowski | EurekAlert!
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Health and Medicine
20.04.2018 | Materials Sciences
20.04.2018 | Earth Sciences