The potential for coral reef establishment through free-living stabilization

Corals thrive in a variety of environments, from low wave and tidal energy lagoons, to high energy tidal reef flats, but remain dependent upon suitable substrate. Herein we reviewed the phenomenon of free-living corals (coralliths), examined whether they have the capacity to create their own stable habitat in otherwise uninhabitable, poor substrate environments through 'free-living stabilization', and explore their potential ecological role on coral reefs. This stabilization could be achieved by coral settlement and survival on mobile substrate, with subsequent growth into free-living coralliths until a critical mass is reached that prevents further movement. This allows for secondary reef colonization by other coral species. To preliminarily test this hypothesis we provide evidence that the potential to support secondary coral colonisation increases with corallith size. Due to the limited diversity of corallith species observed here and in the literature, and the lack of physiological differences exhibited by coralliths here to static controls, it seems likely that only a small selection of coral species have the ability to form coralliths, and the potential to create their own stable habitat

Future seagrass beds: can increased productivity lead to carbon storage?

While carbon capture and storage (CCS) is increasingly recognised as technologically possible, recent evidence from deep-sea CCS activities suggests that leakage from reservoirs may result in highly CO2 impacted biological communities. In contrast, shallow marine waters have higher primary productivity which may partially mitigate this leakage. We used natural CO2 seeps in shallow marine waters to assess if increased benthic primary productivity could capture and store CO2 leakage in areas targeted for CCS. We found that the productivity of seagrass communities (in situ, using natural CO2 seeps) and two individual species (ex situ, Cymodocea serrulata and Halophila ovalis) increased with CO2 concentration, but only species with dense belowground biomass increased in abundance (e.g. C. serrulata). Importantly, the ratio of below:above ground biomass of seagrass communities increased fivefold, making seagrass good candidates to partially mitigate CO2 leakage from sub-seabed reservoirs, since they form carbon sinks that can be buried for millennia.Bayden D. Russell, Sean D. Connell, Sven Uthicke, Nancy Muehllehner, Katharina E. Fabricius, Jason M. Hall-Spence