The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

Abstract

Abstract. Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in pCO2 can have deleterious effects on calcifying animals, this change in carbonate 10 chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), bay scallops (Argopecten irradians), and blue mussels (Mytilus edulis) grown with and without North Atlantic populations of the green macroalgae, Ulva. In 6 of 7 experiments, exposure to elevated pCO2 levels (~1,700 µatm) resulted in depressed shell-and/or tissue-based growth rates of bivalves compared to control conditions (p<0.05) whereas rates were significantly higher in the presence of Ulva in all 15 experiments (p<0.05). In many cases, the co-exposure elevated pCO2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated pCO2 levels significantly improved their performance compared to the acidification only treatment (p<0.05). Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO2 delivery rates (p<0.05). Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable 20 for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated pCO2 levels and depressed Ω.

Hypoxia and Acidification, Individually and in Combination, Disrupt Herbivory and Reduce Survivorship of the Gastropod, Lacuna vincta

“…Resistance to acidification due to an abundance of food has been documented in other calcifying organisms (Pansch et al, 2014) and in forage fish (Gobler et al, 2018), bivalves (Melzner et al, 2011;Thomsen et al, 2013). Additionally, given that L. vincta utilizes macroalgae as both a habitat and a food source (Martel and Chia, 1991;Chavanich and Harris, 2002), the buffering capacity of macroalgae may minimize the harmful effects of exposure to acidification (Young and Gobler, 2018). In the present study, however, feeding did not provide a refuge from the negative effects of hypoxia, suggesting that the protection food offers against acidification may not occur in an ecosystem setting since hypoxia and acidification commonly coincide in space and time (Wallace et al, 2014;Baumann et al, 2015;Cai et al, 2017).…”

“…Initial and final water samples were taken at the beginning and conclusion of experiments to directly measure dissolved inorganic carbon (DIC) within experimental vessels. Samples were preserved using a saturated mercuric chloride solution and stored at ∼4 • C until analysis on a VINDTA 3D delivery system coupled with a UIC Inc. coulometer (model CM5017O) as per Young and Gobler (2018). CO 2 levels ( Table 1) were calculated from measured levels of DIC, pH, temperature, and salinity as well as the first and second dissociation constants of carbonic acid in seawater (Millero, 2010) using the program CO2SYS 1 .…”

Ocean acidification refugia in variable environments

“…Purposeful modification of seawater CO 2 chemistry will be most feasible in easily accessible coastal locations and for target economic purposes, such as aquaculture or small‐scale reef management (Mongin, Baird, Hadley, & Lenton, ). Phytoremediation, or modification of seawater CO 2 chemistry by seagrass, kelp, or algae cultivated alongside ocean acidification‐sensitive organisms, is an active area of research (Young & Gobler, ). However, its effectiveness in the field has significant limitations (Greiner et al, ; Mongin et al, ), and additional bubble stripping of high nighttime CO 2 levels in macrophyte beds may be necessary to ensure that the overall mean pH is significantly elevated when compared to that of surrounding waters (Koweek, Mucciarone, & Dunbar, ).…”

“…For example, daytime photosynthesis by seagrass meadows can radically elevate seawater pH across spatial scales of a few millimeters to hundreds of meters (Guilini et al, ; Hendriks et al, ; Manzello et al, ). For this reason, the idea of seagrass ecosystems, and phytoremediation in general, acting as OAR has garnered considerable attention within the scientific community (Hendriks et al, ; Manzello et al, ; Young & Gobler, ), governments (Nielsen et al, ; Washington State Blue Ribbon Panel on Ocean Acidification, ), and the media (OA‐ICC, ). One issue with the concept of seagrass ecosystems acting as OAR is that times of net photosynthesis are accompanied by periods of net respiration on daily and seasonal timescales (Duarte et al, ; Unsworth et al, ).…”

“…The presence of spatial and temporal variability in CO 2 chemistry across marine ecosystems has raised the idea that ocean acidification refugia (OAR), or locations where ocean acidification impacts could be less intense, exist naturally (Manzello, Enochs, Melo, Gledhill, & Johns, ). Proposed OAR include seagrass meadows and dense algal beds (Hendriks et al, ; Krause‐Jensen et al, ; Manzello et al, ; Unsworth, Collier, Henderson, & Mckenzie, ; Wahl et al, ; Young & Gobler, ), algal boundary layers (Cornwall et al, ; Hendriks, Duarte, Marbà, & Krause‐Jensen, ; Noisette & Hurd, ), mangroves (Sippo, Maher, Tait, Holloway, & Santos, ; Yates et al, ), slow‐flow habitats (Hurd, ), deep‐sea mounts (Tittensor, Baco, Hall‐Spencer, Orr, & Rogers, ), areas isolated from upwelling (Chan et al, ; Kapsenberg & Hofmann, ), and productive high‐latitude environments (Hendriks et al, ; Krause‐Jensen et al, ). These examples vary dramatically across spatial scales (e.g., a few millimeters in an algal boundary layer to a 100 m 2 seagrass bed), with no clear criteria as to what makes each area a potential OAR other than observed transient increases in seawater pH relative to surrounding waters.…”