Ocean Acidification and the Loss of Phenolic Substances in Marine Plants

Abstract

Rising atmospheric CO2 often triggers the production of plant phenolics, including many that serve as herbivore deterrents, digestion reducers, antimicrobials, or ultraviolet sunscreens. Such responses are predicted by popular models of plant defense, especially resource availability models which link carbon availability to phenolic biosynthesis. CO2 availability is also increasing in the oceans, where anthropogenic emissions cause ocean acidification, decreasing seawater pH and shifting the carbonate system towards further CO2 enrichment. Such conditions tend to increase seagrass productivity but may also increase rates of grazing on these marine plants. Here we show that high CO2 / low pH conditions of OA decrease, rather than increase, concentrations of phenolic protective substances in seagrasses and eurysaline marine plants. We observed a loss of simple and polymeric phenolics in the seagrass Cymodocea nodosa near a volcanic CO2 vent on the Island of Vulcano, Italy, where pH values decreased from 8.1 to 7.3 and pCO2 concentrations increased ten-fold. We observed similar responses in two estuarine species, Ruppia maritima and Potamogeton perfoliatus, in in situ Free-Ocean-Carbon-Enrichment experiments conducted in tributaries of the Chesapeake Bay, USA. These responses are strikingly different than those exhibited by terrestrial plants. The loss of phenolic substances may explain the higher-than-usual rates of grazing observed near undersea CO2 vents and suggests that ocean acidification may alter coastal carbon fluxes by affecting rates of decomposition, grazing, and disease. Our observations temper recent predictions that seagrasses would necessarily be “winners” in a high CO2 world.

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

“…We found that upper photic zone coccolithophore communities in southern Tyrrhenian Sea water and Levante Bay were very similar in areas unaffected by elevated CO 2 . Future studies could combine in situ mesocosm-type experiments to constrain the movement of plankton at the seeps or use Free Ocean Carbon Experiments to control the CO 2 dose (Arnold et al, 2012). Given the shallow nature of the seeps, such work could also incorporate investigations of the possible effects of ultraviolet radiation.…”

A novel in situ system to evaluate the effect of high CO2 on photosynthesis and biochemistry of seaweeds

“…To date, in situ responses of marine organism to dissolved CO 2 increase are based on observations made near volcanic vents (Hall-Spencer et al 2008, Martin et al 2008, Porzio et al 2011, Johnson et al 2012. Recently, different techniques of in situ CO 2 manipulation, such as the Coral−Proto Free Ocean Carbon Enrichment System (Kline et al 2012), the Free Ocean Carbon Enrichment System (Arnold et al 2012), and the Carbon-Enriched Open Chamber System (Campbell & Fourqurean 2011) have been proposed. The development of new CO 2 in situ experiments can provide new insights and give straightforward answers or at least provide a piece of the puzzle about the effect of OA on macroalgae.…”

Twenty-first century climate change and submerged aquatic vegetation in a temperate estuary: the case of Chesapeake Bay

“…High CO 2 /low pH conditions cause the loss of antimicrobial phenolics in many seagrass species (Arnold et al 2012;Arnold et al 2014; but see Martínez-Crego et al 2014; Figure 1 sites (i), (j)). Phenolic acids known to inhibit the growth of the seagrass wasting disease pathogen, Layrinthula spp., were reduced by as much as~95% under "acidified" conditions.…”