Antarctic bryozoans give hints of environmental changes in oceans

This is one of the conclusions of an article published in the journal Marine Ecology Progress Series and signed by Blanca Figuerola, researcher at the Department of Evolutionary Biology, Ecology and Environmental Sciences and Biodiversity Research Institute of the UB (IRBio), Piotr Kuklinski (Institute of Oceanology) and Paul D. Taylor (Natural History Museum, UK).

Ocean acidification: a threat to marine organisms

At a global level, the excess of atmospheric CO₂ is absorbed by ocean waters and it causes changes in water chemistry (pH decrease or ocean acidification). "The marine calcifiers that live in polar regions are particularly vulnerable to the effects of ocean acidification, a progress which is reducing their mineralization capacity and forming calcium carbonate (CaCO3) skeletons used as a protective and supporting structure against predators" says Blanca Figuerola, main author of the scientific study.

In these species, the mineralization capacity depends on the concentrations of calcium carbonate (CaCO3) dissolved in the water column, the temperature and pressure of these waters. In particular, cold waters of the Southern Ocean show higher concentrations of CO₂ and lower in CaCO3, and this reduces the availability of the carbonate required for the calcification process.

Studying bryozoan skeletal mineralogy

The scientific team has studied the global effects of ocean acidification in four Antarctic bryozoan species (Fasciculipora ramosa, Lageneschara lyrulata, Systenopora contracta and Melicerita obliqua), widely spread and abundant around the Antarctica in a wide range of depths. In addition, these species can incorporate significant amounts of magnesium (Mg) to the skeleton. According to Figuerola, "the skeletons with significant amounts of Mg are even more soluble and consequently, more susceptible to the ocean acidification than skeletons containing low Mg-levels."

The conclusions of the new project, which address depth-related changes in the levels of magnesium in Antarctic bryozoans for the first time, suggest that other environmental and biological factors (other than pH) could have a more important influence on the incorporation of Mg into the skeleton of these organisms. "Only Fasciculipora ramosa shows significant variability in Mg content in diverse depths, and this makes us think that other environmental and biological factors can have a variable influence depending on the species," says Blanca Figuerola.

"We now need to test this hypothesis in other species and in the same studied species too but in wider depth ranges and in other Antarctic areas because the minimum pH value can vary in depth depending on the area they are. With all this, we want to evaluate the bathymetric variability in the Mg content because factors related to depth have the potential to provide an analogue for future changes in the skeletal mineralogy of calcifying marine organisms. This is due to the ocean pH decreases in depth (with a minimum value of <7,7), which is related to the expected pH in surface ocean over the next 85 years).

Protecting marine reefs, protecting biodiversity

Bryozoan skeletons -like coral's- usually build the basic structure of isolated small reefs (known as patch reefs) and contribute to the formation of the known coral reefs, fragile ecosystems that are sensitive to the ocean acidification. These ecosystems have a great ecological and social value thanks to their biodiversity and the ecosystem services they provide: creation of habitats used as breeding, feeding and refuge areas for lots of species which have a commercial interest. "Therefore, the negative impact of ocean acidification on these organisms can also have negative consequences on other marine species of higher trophic levels" warns Blanca Figuerola.

The UB researcher will continue the study on marine bryozoans in different Arctic areas and the Antarctic Peninsula, one of the fastest warming places on Earth, within a new project, which Figuerola will lead at the Institute of Oceanology (Poland) with the support of the Centre for Polar Studies. Figuerola is one of the members of the Distantcom project, which is the continuation of the Ecoquim and Actiquim projects, led by Professor Conxita Àvila (Faculty of Biology- IRBio) to study chemical ecology, phylogeny, phylogeography and trophic ecology of marine invertebrate communities in the Antarctica. In the new project, which Dra. Conxita Àvila is a collaborator, it will study bryozoan samples collected during the last Antarctic campaign DISTANTCOM-1, launched in December, 2015.

It is worth remembering that the UB and IRBio team led by Conxita Àvila has contributed to the discovery of the first Osedax bone-eating worm in the Antarctic continent and the Mediterranean, the nemertean Antarctonemertes riesgoae, which has a bizarre reproductive behaviour, and the annelid Parougia diapason, a new species discovered in Deception Island, among others, in the South Shetland Islands in the Southern Ocean.