Fragmented kelp forest canopies retain their ability to alter local seawater chemistry

Abstract

Kelp forests support some of the most productive and diverse ecosystems on Earth, and their ability to uptake dissolved inorganic carbon (DIC) allows them to modify local seawater chemistry, creating gradients in carbon, pH, and oxygen in their vicinity. By taking up both bicarbonate and CO 2 as a carbon source for photosynthesis, kelp forests can act as carbon sinks, reducing nearby acidity and increasing dissolved oxygen; creating conditions conducive to calcification. Recent stressors, however, have reduced kelp forest canopies globally; converting once large and persistent forests to fragmented landscapes of small kelp patches. In a two-year study, we determined whether fragmented kelp patches retained the ability to alter local seawater chemistry. We found that diel fluctuations of multiple parameters of carbonate chemistry were greater in the kelp canopy than in the kelp benthos and in adjacent urchin barrens, consistent with metabolic activity by the kelp. Further, kelp fragments increased pH and aragonite saturation and decreased pco 2 during the day to a similar degree as large, intact kelp forests. We conclude that small kelp patches could mitigate oA stress and serve as spatial and temporal refugia for canopy-dwelling organisms, though this effect is temporary and confined to daylight hours during the growing season.

Antioxidative Properties of Baltic Sea Keystone Macroalgae (Fucus vesiculosus, Phaeophyceae) under Ocean Warming and Acidification in a Seasonally Varying Environment

“…Seaweeds modify local water chemistry due to their metabolic photosynthesis/respiration cycles [ 69 , 70 , 71 , 72 , 73 ], and they have the potential to increase H 2 O 2 concentrations in their habitat [ 24 ]. The thallus of the green seaweed Ulva rigida excretes H 2 O 2 , which can produce concentrations up to 4 µM in the experimental medium [ 74 , 75 ].…”

Characterizing Mean and Extreme Diurnal Variability of Ocean CO2 System Variables Across Marine Environments

“…Our approach to characterize extreme diurnal variability probabilistically at the local scale is consistent with the general approach used to characterize temperature extremes (e.g., Frölicher et al., 2018). However, the extreme diurnal variability will differ relatively more between stations in our case because CO 2 system variability is strongly influenced not only by ocean circulation and mixing but also by the productivity of local ecosystems, a factor that varies greatly between the open and coastal ocean, particularly near coral reefs (Drupp et al., 2013; Koweek et al., 2015; Yan et al., 2011), kelp forests (Murie & Bourdeau, 2020), and seagrasses (Berg et al., 2019).…”

Missing the forest for the trees: Do seaweed ecosystems mitigate atmospheric CO2 emissions?

“…Turbulence together with ocean acidification, more associated with a barren, can significantly increase the dissolution of calcium carbonate and conceivably increase the amount of bicarbonate outwelling (Eyre, Andersson, & Cyronak, 2014). In contrast, within a canopy system photosynthesis can significantly reduce acidification and turbulence (Morris, Graham, Kelvin, Ghisalberti, & Seaweed carbon mitigation services Swearer, 2019; Murie & Bourdeau, 2020). We now have a possible situation in which the replacement state NES may move closer or exceed its canopy counterpart.…”

“…Turbulence together with ocean acidification can significantly increase the dissolution of calcium carbonate and conceivably increase the amount of bicarbonate outwelling (Eyre et al, 2014). In contrast, photosynthesis within a seaweed canopy can significantly reduce acidification and turbulence (Morris et al, 2019;Murie and Bourdeau, 2020). In other words, the canopy is reducing the outwelling sequestration pool relative to a non-vegetated alternative or baseline system.…”