Regional variation in δ¹³C of coral reef macroalgae

Abstract

Macroalgae are important components on coral reefs that underpin food webs but are also indicators of declines in coral reef condition. The sensitivity of macroalgal communities to environmental factors, including climate and pollutants from the land, is important for the future state of coral reefs. We assessed regional variation in the photosynthetic physiology of macroalgae on the Great Barrier Reef and Moreton Bay, Queensland, Australia, using δ 13 C, tissue chemistry, and metabolic indicators over broad environmental gradients from six sites spanning 13 of latitude and varying distance from shore. Our data set included 568 samples from 54 genera and 19 macroalgal orders. The δ 13 C of tissues had a strong taxonomic basis (explaining 66% of the variation in δ 13 C), varying significantly among algal orders. Particularly low values of δ 13 C, indicating direct use of CO 2 (aq) in photosynthesis, were mainly associated with lineages within the Rhodophyta. We observed declines in δ 13 C with increasing depth (inshore only) and latitude, from offshore to inshore sites and with increasing tissue N and N : P ratio. Variation in δ 13 C of tissues among macroalgal lineages suggests evolution of a range of CO 2 acquisition pathways. Patterns in δ 13 C availability are most consistent with higher availability of CO 2(aq) in cooler water and inshore sites. δ 13 C in macroalgae could provide an important tool for monitoring changes in CO 2(aq) with increasing atmospheric CO 2 , with changes in ocean circulation and with changes to runoff from the land to the coastal oceans.

An analysis of the macroalgal δ<sup>13</sup>C variability in the Gulf of California

“…Our regression models showed that morphofunctional groups have a R 2 adjusted =0.34, and increase to genus (R 2 adjusted =0.41,) and to species (R 2 adjusted =0.46). This result is consistent with reported by Lovelock et al, (2020), which found that 66% of δ 13 C variability was explained by taxonomy. Although morphofunctional groups could explain less than genus or species, it is a great tool to increase the possibility of analyzes on a big spatial scale, especially when the species distribution could be limited.…”

“…The Gulf of California is a subtropical, semi-enclosed sea of the Pacific coast of Mexico, with exceptionally high productivity being the most important fishing regions for Mexico and one of the most biologically diverse worldwide marine areas (Zeitzschel, 1969;Espinosa-Carreón and Valdez-Holguín 2007;Lluch-Cota et al, 2007;Páez-Osuna et al, 2017). GC represents only https://doi.org/10.5194/bg-2021-50 Preprint.…”

“…Besides, GC presents complex hydrodynamic processes, including internal waves, fronts, upwelling, vortices, mixing of tides. The gulf's coastline is divided into three shores: extensive rocky shores, long sandy beaches, numerous scattered estuaries, coastal lagoons, and open muddy bays tidal flats and coastal wetlands (Lluch-Cota et al, 2007).…”

The requirement for external carbonic anhydrase in diatoms is influenced by the supply and demand for dissolved inorganic carbon

“…The combination of these factors may mean that large diatoms are better suited to lower irradiances. For example, a small number of non‐CCM macroalgal species exhibit exclusive CO 2 diffusive uptake (Raven et al., 1995) with a corresponding low light spatial distribution in deep habitats or beneath dense canopies where carbon demands of individuals are lower (Cornwall et al., 2015; Hepburn et al., 2011; Lovelock et al., 2020).…”

Stable Carbon and Oxygen Isotopes Indicate Photophysiology and Calcification Mechanisms of Macroalgae on Little Cayman Reefs

“…CCMs that allow marine macroalgae to utilize HCO 3 will likely still be favored under elevated atmospheric pCO 2 (~1,000 matm) predicted by 2100 due to HCO 3 remaining the dominant Ci species (>90%) of total DIC (~2,200 mmol kg -1 ) in seawater (Hartin et al, 2016), supported by the conservative CCM trait evolutionarily across marine macroalgae phyla (Stepien et al, 2016). Regardless of CCMs, higher seawater pCO 2 is likely to increase CO 2 as an Ci source for macroalgae as observed across latitudinal and coastal gradients of dissolved CO 2 (Lovelock et al, 2020, Stepien, 2015, Hofmann & Heesch, 2018.…”