Marine Microphytobenthic Assemblage Shift along a Natural Shallow-Water CO2 Gradient Subjected to Multiple Environmental Stressors

Abstract

Predicting the effects of anthropogenic CO2 emissions on coastal ecosystems requires an understanding of the responses of algae, since these are a vital functional component of shallow-water habitats. We investigated microphytobenthic assemblages on rock and sandy habitats along a shallow subtidal pCO2 gradient near volcanic seeps in the Mediterranean Sea. Field studies of natural pCO2 gradients help us understand the likely effects of ocean acidification because entire communities are subjected to a realistic suite of environmental stressors such as over-fishing and coastal pollution. Temperature, total alkalinity, salinity, light levels and sediment properties were similar at our study sites. On sand and on rock, benthic diatom abundance and the photosynthetic standing crop of biofilms increased significantly with increasing pCO2. There were also marked shifts in diatom community composition as pCO2 levels increased. Cyanobacterial abundance was only elevated at extremely high levels of pCO2 (>1400 μatm). This is the first demonstration of the tolerance of natural marine benthic microalgae assemblages to elevated CO2 in an ecosystem subjected to multiple environmental stressors. Our observations indicate that

Effects of ocean acidification on the shells of four Mediterranean gastropod species near a CO2 seep

“…Ransome (2007) found that although the abundances of P. caerulea decreased with declining pH at a CO 2 seep off the island of Ischia, Italy, mean shell length increased significantly. The larger size of P. caerulea at low-pH sites at multiple CO 2 seep systems suggests that this species may be reaping the benefits of increased productivity of the microphytobenthos (Johnson et al, 2015). It has been previously demonstrated in mollusks that increased food availability offset decreases in calcification rates and growth due to ocean acidification (Melzner et al, 2011;Thomsen et al, 2013).…”

The stable microbiome of inter and sub-tidal anemone species under increasing pCO2

“…for further details in the carbonate chemistry within this area). Temperature, salinity, total alkalinity, sulfur concentrations, nitrate, phosphate, sediment texture, and total nitrogen and total organic carbon content within the sediment do not significantly differ along the north shore of Levante Bay14232425. However, nitrite and silicate have shown significant differences between site 3 and the reference site location25.…”

“…Temperature, salinity, total alkalinity, sulfur concentrations, nitrate, phosphate, sediment texture, and total nitrogen and total organic carbon content within the sediment do not significantly differ along the north shore of Levante Bay14232425. However, nitrite and silicate have shown significant differences between site 3 and the reference site location25. The vent site, in addition to having extremely low pH conditions (6.05), also contains elevated levels of trace elements, iron, and hydrogen sulfide compared with other sites further from the CO 2 vent2326.…”

“…Extremely low pH conditions of 6.05 consistently recorded within this site may have significantly altered the microbial communities. Variations in p CO 2 resulted in significantly different microbial communities of biofilms grown on glass slides52 as well as the microphytobenthic assemblage within Levante Bay25. Indeed, environmental influences shape microbial communities and drive spatial variation of microbial diversity53.…”

“…1). Although extensive physical parameters were not collected simultaneously with the anemone samples, thorough geochemical surveys have been conducted previously that characterize Levante Bay spatially and temporally232425. These surveys indicate that sites 1, 2, 3 and the reference site differ little except for within their carbonate chemistry composition (see Boatta et al 23.…”