Green gravel as a vector of dispersal for kelp restoration

Kelp forests are experiencing substantial declines due to climate change, particularly ocean warming and marine heatwaves, and active interventions are necessary to halt this decline. A new restoration approach termed “green gravel” has shown promise as a tool to combat kelp forest loss. In this approach, substrata (i.e. small gravel) are seeded with kelp propagules, reared in controlled conditions in the laboratory before out-planting to degraded reefs. Here, we tested the feasibility of cultivating Australia’s dominant kelp, Ecklonia radiata on green gravel with the aim of optimising the seeding conditions for E.radiata. We seeded substrata (i.e. gravel), that had different surface texture and size, with E. radiata gametophytes at two average seeding densities: high density of ~230 fragments mL-1 and low density of ~115 fragments mL-1. The tested substrata were small basalt, large basalt, crushed laterite and limestone. Gametophytes successfully adhered to all four tested substrata, however, gametophytes that adhered to the limestone gravel (the natural reef type off Western Australia) suffered extreme tissue bleaching likely due to dissolution and decrease in seawater pH. Gametophytes that adhered to the three other test substrata were healthy, fertilised following seeding and microscopic sporophytes were observed attaching to the gravel. Substrata and seeding density did not affect sporophyte growth (i.e. length) at the time of transferring into aquarium tanks (after three months of rearing in incubators) but over time substrata showed a significant effect on maximum lengths. After 12 months in aquarium tanks, sporophytes on both small and large basalt gravel were significantly larger than those on the crushed laterite. Gametophytes were also found to not only survive on the gravel itself but also detach from the gravel, settle successfully, fertilise and develop into healthy sporophytes ex situ on the surrounding substratum through lateral transfer. Substrata had a significant effect on density of detached gametophytes with rougher and larger gravel showing higher densities of detachment. Our results show the potential for green gravel to be a vector of dispersal for restoration in Western Australia where natural recovery of kelp forests has failed.publishedVersio

Warming enhances carbon dioxide and methane fluxes from Red Sea seagrass (Halophila stipulacea) sediments

Seagrass meadows are autotrophic ecosystems acting as carbon sinks, but they have also been shown to be sources of carbon dioxide (CO2) and methane (CH4). Seagrasses can be negatively affected by increasing seawater temperatures, but the effects of warming on CO2 and CH4 fluxes in seagrass meadows have not yet been reported. Here, we examine the effect of two disturbances on air–seawater fluxes of CO2 and CH4 in Red Sea Halophila stipulacea communities compared to adjacent unvegetated sediments using cavity ring-down spectroscopy. We first characterized CO2 and CH4 fluxes in vegetated and adjacent unvegetated sediments, and then experimentally examined their response, along with that of the carbon (C) isotopic signature of CO2 and CH4, to gradual warming from 25 ∘C (winter seawater temperature) to 37 ∘C, 2 ∘C above current maximum temperature. In addition, we assessed the response to prolonged darkness, thereby providing insights into the possible role of suppressing plant photosynthesis in supporting CO2 and CH4 fluxes. We detected 6-fold-higher CO2 fluxes in vegetated compared to bare sediments, as well as 10- to 100-fold-higher CH4 fluxes. Warming led to an increase in net CO2 and CH4 fluxes, reaching average fluxes of 10 422.18 ± 2570.12 µmol CO2 m−2 d−1 and 88.11±15.19 µmol CH4 m−2 d−1, while CO2 and CH4 fluxes decreased over time in sediments maintained at 25 ∘C. Prolonged darkness led to an increase in CO2 fluxes but a decrease in CH4 fluxes in vegetated sediments. These results add to previous research identifying Red Sea seagrass meadows as a significant source of CH4, while also indicating that sublethal warming may lead to increased emissions of greenhouse gases from seagrass meadows, providing a feedback mechanism that may contribute to further enhancing global warming.This research has been supported by the King Abdullah University of Science and Technology through baseline and CARF funding (grant nos. FCC/1/1973-32-01 and BAS/1/1071-01-01)

Carbon dioxide and methane fluxes from Red Sea seagrass sediments

Data of carbon dioxide and methane fluxes from vegetated and bare sediments exposed to warming and prolonged darkness

Green gravel as a vector of dispersal for kelp restoration

Kelp forests are experiencing substantial declines due to climate change, particularly ocean warming and marine heatwaves, and active interventions are necessary to halt this decline. A new restoration approach termed “green gravel” has shown promise as a tool to combat kelp forest loss. In this approach, substrata (i.e. small gravel) are seeded with kelp propagules, reared in controlled conditions in the laboratory before out-planting to degraded reefs. Here, we tested the feasibility of cultivating Australia’s dominant kelp, Ecklonia radiata on green gravel with the aim of optimising the seeding conditions for E.radiata. We seeded substrata (i.e. gravel), that had different surface texture and size, with E. radiata gametophytes at two average seeding densities: high density of ~230 fragments mL-1 and low density of ~115 fragments mL-1. The tested substrata were small basalt, large basalt, crushed laterite and limestone. Gametophytes successfully adhered to all four tested substrata, however, gametophytes that adhered to the limestone gravel (the natural reef type off Western Australia) suffered extreme tissue bleaching likely due to dissolution and decrease in seawater pH. Gametophytes that adhered to the three other test substrata were healthy, fertilised following seeding and microscopic sporophytes were observed attaching to the gravel. Substrata and seeding density did not affect sporophyte growth (i.e. length) at the time of transferring into aquarium tanks (after three months of rearing in incubators) but over time substrata showed a significant effect on maximum lengths. After 12 months in aquarium tanks, sporophytes on both small and large basalt gravel were significantly larger than those on the crushed laterite. Gametophytes were also found to not only survive on the gravel itself but also detach from the gravel, settle successfully, fertilise and develop into healthy sporophytes ex situ on the surrounding substratum through lateral transfer. Substrata had a significant effect on density of detached gametophytes with rougher and larger gravel showing higher densities of detachment. Our results show the potential for green gravel to be a vector of dispersal for restoration in Western Australia where natural recovery of kelp forests has failed