Researchers looked at changes in ocean-surface temperature, salinity, and density in mangrove forests around the world in the twenty-first century. Their findings indicate that changes in surface-ocean density may have an impact on the dispersal patterns of widely distributed mangrove species, particularly in the Indo-West Pacific region, which is the primary hotspot of mangrove diversity.
Dr. Tom Van der Stocken of the VUB Biology Department led an international study that looked at changes in ocean-surface temperature, salinity, and density across mangrove forests around the world in the twenty-first century. According to the study, changes in surface-ocean density may have an impact on the dispersal patterns of widely distributed mangrove species, particularly in the Indo-West Pacific region, which is the primary hotspot of mangrove diversity. The study was published in the journal Nature Climate Change.
“Temperature and salinity changes caused by climate change influence sea-surface density. Because propagules of widely distributed mangrove species have densities similar to seawater, changes in ocean density have implications for mangrove oceanic dispersal. The density difference between the propagules and the surrounding water determines whether the propagules float or sink.” says Tom Van der Stocken, Marie Sk?odowska-Curie Postdoctoral Scholar at Vrije Universiteit Brussel and NASA Jet Propulsion Laboratory research affiliate.
Our research shows that the density of surface-ocean waters along mangrove forests will decrease by the end of the twenty-first century, and by a factor of two more in the Indo-West Pacific region than in the Atlantic East Pacific.
Nico Koedam
“It is expected that warming winter temperatures and sea level rise will impact the distribution of these carbon-rich forests, but changes in surface-ocean properties might also influence distributional patterns through dispersal.”
Mangroves are highly productive intertidal forests that occur along tropical, subtropical, and some temperate coasts. They support a broad variety of ecosystem goods and services and have an important place on the international climate mitigation and adaptation agenda. However, at the same time, these intertidal forests are strongly impacted by human activities and subjected to climate-driven changes in the marine, terrestrial and atmospheric processes to which they are tightly linked.
While previous research has focused on the potential impact of sea-level rise, altered precipitation regimes, rising temperatures, and increased storm frequency on mangrove ecosystems, the potential effects of climate-driven changes in seawater properties have not been considered.
“This is surprising, because the ocean is the primary dispersal medium of this’sea-faring’ coastal vegetation, and dispersal is a key process that governs a species’ response to climate change by changing its geographical range,” says Van der Stocken.
The paper, “Mangrove dispersal disrupted by projected changes in global seawater density,” is co-authored by VUB professors Bram Vanschoenwinkel and Nico Koedam, and in collaboration with the Moss Landing Marine Laboratories (MLML) and the University of California, Los Angeles (UCLA). The team made use of present and future sea-surface temperature and salinity data from the Bio-ORACLE database developed at Ghent University, and derived sea-surface density estimates from these data using the UNESCO EOS-80 equation of state polynomial for seawater.
“Our research shows that the density of surface-ocean waters along mangrove forests will decrease by the end of the twenty-first century, and by a factor of two more in the Indo-West Pacific region than in the Atlantic East Pacific,” says Koedam.
“It is important to note that our study uses current and future environmental conditions based on monthly averages, and that the actual variability in sea-surface density around these mean values may be higher than predicted in this study,” Vanschoenwinkel adds.
Van der Stocken says: “There is still uncertainty about how projected changes in seawater density will affect realized mangrove dispersal in different parts of the world, and more research on the biological response of mangroves to climate-driven changes in surface-water properties is needed. We used marine data layers to fill this gap in this study, and we hope that our findings will inspire future research that quantifies the effects of changes in ocean surface properties on propagule floating periods, dispersal, and connectivity.”
