CO₂ Enrichment Stimulates Dissolved Organic Carbon Release in Coral Reef Macroalgae

Abstract

This article provides a synthesis of the Middle Pleistocene hominin record of West Iberia, which comprises sites displaying abundant concentrations of large flake Acheulean (LFA) assemblages, as well as isolated examples of Early Middle Palaeolithic (EMP) technology. These sites typically have age ranges spanning Marine Isotopic Stages (MIS) 11-6, within the second half of the Middle Pleistocene, and are primarily located in fluvial environments related to the main regional river basins. The LFA sites display extensive occurrences of handaxes and cleavers on flake blanks (detached from large cores), with a large number of knapping remains, such as flakes or small-medium cores, showing elementary reduction patterns. Over the identified age range of these sites, especially during the MIS 9-6 interval, we observe constant technological stability, without strong variations over time, and independent of the functionality of individual sites. These fixed technological and behavioural patterns reinforce the African affinities of the southwestern European Acheulean, in contrast to Acheulean assemblages identified in the northernmost areas of Europe.

Rate and fate of dissolved organic carbon release by seaweeds: A missing link in the coastal ocean carbon cycle

“…Exudation of DOC by seaweeds may be a mechanism for maintaining cellular homeostasis to reduce the build‐up of photosynthetic products (“overflow hypothesis,” discussed below; Iñiguez et al. 2016a, Diaz‐Pulido and Barrón 2020). The exudation of DOC may also be a protective mechanism, thought to act as a feeding deterrent against herbivory (Abdullah and Fredriksen 2004), a competitive strategy for space competition with other seaweeds and corals (McCook et al.…”

“…Under this hypothesis, a greater proportion of DOC is actively exuded during the day when photosynthesis is occurring while at night only DOC leakage would occur (Barrón et al. 2014, Diaz‐Pulido and Barrón 2020), although the precise partitioning of active and passive release as influenced by light needs to be confirmed. Similar trends have been found in seaweed, with growth found to be inversely correlated with DOC release in the kelp, Laminaria hyperborea (Ochrophyta); hence, higher growth rates resulted in less DOC release (Abdullah and Fredriksen 2004).…”

“…It is hypothesized for macro‐ and microalgae that under elevated DIC concentrations, carbon fixation will increase and photosynthetic overflow will be enhanced if algae are limited by the availability of other nutrients and light (Riebesell 2004, Thornton 2014, Iñiguez et al. 2016a, Diaz‐Pulido and Barrón 2020). In response to elevated CO 2 concentrations under ocean acidification, seaweeds may show enhanced photosynthetic carbon overflow by which DOC is released as an effective mechanism maintaining the intracellular C:N balance (see above; Gordillo et al.…”

“…(Ochrophyta), Chlorodesmis fastigiata (Chlorophyta), and Lobophora cf. variegata (Ochrophyta) was examined at ambient and high CO 2 concentrations, during the day and at night (Diaz‐Pulido and Barrón 2020). During the day, DOC release by A. glomerata was 15 times higher under elevated CO 2 compared to ambient CO 2 , suggesting photosynthetic overflow (Diaz‐Pulido and Barrón 2020) but there was no difference between DOC release rates for the other species.…”

Scaling the effects of ocean acidification on coral growth and coral–coral competition on coral community recovery

“…While the lack of macroalgae in the model may still be representative of reefs where herbivores are abundant, the outcome of competition under OA may be different on reefs that lack adequate herbivory. Indeed, some macroalgae can benefit from increases in CO 2 and/or HCO -3 under OA (Koch et al, 2013;Diaz-Pulido & Barrón, 2020;Ho et al, 2021), enhancing the competitive ability of macroalgae versus corals, and possibly increasing macroalgal dominance on reefs under OA (Anthony et al, 2011;Diaz-Pulido et al, 2011;Johnson et al, 2012). As such, it is important for future studies to build on the present approach with more sophisticated models (i.e., that may include macroalgal dynamics where applicable) that can be developed as suitable empirical data become available.…”