Responses of marine benthic microalgae to elevated CO2

Abstract

Increasing anthropogenic CO 2 emissions to the atmosphere are causing a rise in pCO 2 concentrations in the ocean surface and lowering pH. To predict the effects of these changes, we need to improve our understanding of the responses of marine primary producers since these drive biogeochemical cycles and profoundly affect the structure and function of benthic habitats. The effects of increasing CO 2 levels on the colonisation of artificial substrata by microalgal assemblages (periphyton) were examined across a CO 2 gradient off the volcanic island of Vulcano (NE Sicily). We show that periphyton communities altered significantly as CO 2 concentrations increased. CO 2 enrichment caused significant increases in chlorophyll a concentrations and in diatom abundance although we did not detect any changes in cyanobacteria. SEM analysis revealed major shifts in diatom assemblage composition as CO 2 levels increased. The responses of benthic microalgae to rising anthropogenic CO 2 emissions are likely to have significant ecological ramifications for coastal systems. Communicated by S. Dupont.

Consumers mediate the effects of experimental ocean acidification and warming on primary producers

“…For benthic microalgae, however, the effects of acidification and warming (in the absence of mesograzers) were weak-both in terms of biomass (which integrates effects over the whole experiment) and production (a short-term response). Similar weak responses of benthic microalgae to acidification and warming have recently been reported from a range of other systems (43)(44)(45)(46). Consequently, for shallow coastal sediments, benthic microalgae may be relatively resilient to the changes in pH and water temperature expected over the next century, regardless of mesograzer presence.…”

Decline in Coccolithophore Diversity and Impact on Coccolith Morphogenesis Along a Natural CO2 Gradient

“…Previous studies along pH gradients near Mediterranean volcanic seeps have demonstrated that although seawater acidification with CO 2 can benefit some organisms, such as heterokont algae, it is detrimental to most sessile calcified species and leads to a reduction in biodiversity (Porzio et al, 2011;Johnson et al, 2013;Kroeker et al, 2013b). Here we show that CO 2 seeps may also be useful for studying the effects of ocean acidification on plankton.…”

“…High CO 2 concentrations affect the metabolism, growth, calcification, and behavior of many marine organisms (Rodolfo-Metalpa et al, 2011;Kroeker et al, 2013a). Some photosynthetic organisms benefit from increased levels of CO 2 , although many calcified species are adversely affected by corrosion or competition from non-calcified forms (Porzio et al, 2011;Johnson et al, 2013;Kroeker et al, 2013b).…”

Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH

“…Volcanic CO 2 vents produce shallow-water gradients of pH across tens of meters, reaching values as low as 6.6-6.8 in the Mediterranean, for example around the most active vents in Ischia and Vulcano Islands, Italy (Hall-Spencer et al 2008;Johnson et al 2013) and pH values <7.7 (as low as 7.21) in volcanic seeps in Papua New Guinea (Fabricius et al 2011). Natural gradients in pH exists across a distance of <100 m from these volcanic CO 2 vents, where the pH increases to normal seawater values of 7.97-8.14 (Hall-Spencer et al 2008;Johnson et al 2013;Fabricius et al 2011). Volcanic eruptions may lead to extreme pH, such as the 6.2 values recorded in coastal waters following an underwater eruption giving rise to a novel shallow submarine volcano south of the island of El Hierro, Canary Islands, Spain (Fraile-Nuñez et al 2012).…”