Climate change and ocean acidification effects on seagrasses and marine macroalgae

Abstract

Although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO2 ], and lower carbonate [CO3 (2-) ] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO2 ]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (≥ 85%) with most species capable of utilizing HCO3 (-) ; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO2 -only users, lead us to conclude that photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated [CO2 ] similar to terrestrial C3 species. In the tropics, many species live close to their thermal limits and will have to up-regulate stress-response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO2 ] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO2 ] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO2 ] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H(+) and DIC. These fluxes control micro-environments that promote calcification over dissolution and may be more important than CaCO3 mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO2 ocean; therefore, it is critical to elucidate the research gaps identified in this review.

Biochemical and biophysical CO2 concentrating mechanisms in two species of freshwater macrophyte within the genus Ottelia (Hydrocharitaceae)

“…Within aquatic angiosperms, C 4 photosynthesis appears to be largely restricted to the Hydrocharitaceae, a monocotyledonous family of 18 genera and about 120 species that is believed to have an Oriental origin about 65 million years ago (Chen et al 2012 Halophila (Koch et al 2013); within Clade B in Egeria (Casati et al 2000) and Ottelia (this study).…”

“…Outwith the Hydrocharitaceae, although within the order Alismatales, the aquatic angiosperm (seagrass) Cymodocea (Cymodoceaceae) may also have some evidence for C 4 metabolism (Koch et al 2013) but this requires further investigation.…”

Calcareous green alga H alimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps

“…were absent at mean X ar 2.5 (HallSpencer et al 2008). Laboratory experiments revealed mixed responses of OA on Halimeda spp., with some species being negatively impacted, while others are not (Hofmann et al 2014;Koch et al 2013;Price et al 2011;Ries et al 2009;Sinutok et al 2011;N. Vogel et al pers.…”

Influence of Basin‐ and Local‐Scale Environmental Conditions on Nearshore Production in the Northeast Pacific Ocean

“…Still, caution must be exercised when applying these relationships to future scenarios, as unexpected patterns may arise given the nonstationary nature of biophysical relationships (Schmidt et al 2014). Moreover, the food webs considered here are likely to be altered due to a combination of (1) increasing frequency of storms that diminish kelp forest canopies (Byrnes et al 2011), (2) increasing kelp production driven by rising CO 2 concentrations (Koch et al 2013), (3) increasing mortality of benthic invertebrate larvae due to ocean acidification (Byrne 2011), and (4) changes in direct and indirect species interactions as the ranges of individual fish species shift (Ainsworth et al 2011), among other possibilities.…”