Bioavailability of macroalgal dissolved organic matter in seawater

Abstract

The bioavailability of macroalgal dissolved organic matter (DOM) was examined by decomposition experiments using released DOM from Ecklonia cava Kjellman (Phaeophyceae) living in Oura Bay, Shimoda, Izu Peninsula, Japan. The samples used for the decomposition experiments were obtained by enclosing the plants in bags. Based on the reduction rates of the concentrations of dissolved organic carbon (DOC), the turnover times of the macroalgal DOC were calculated to be between 24 and 172 d, with monthly-seasonal timescales. These values were mostly higher than those of phytoplanktonic DOC in previous studies (<1 mo). The relatively longer turnover time probably reflects the bio-refractory property of the macroalgal DOM. In most of the experiments (except for June), fucans and humic-like material were the major constituents of the released DOM. The fucans appeared to be partly decomposed during the experiments, but the compositional changes in the neutral carbohydrates in these seasons were less definite than those in June. The fluorescent intensity of the humic-like material did not decrease with time, suggesting a refractory character. Macroalgae are likely important DOM producers in Oura Bay, because the daily DOM production of E. cava accounts for 1.5 to 34% of DOM stock in Oura Bay per day. The concentration and the distribution of DOC inside and outside the bay strongly suggests that the released DOM was extensively exported out of the bay. These facts indicate that the macroalgal DOM contributes to marine DOM pools in a wider area including the adjacent coastal region.

Patterns and controls of reef‐scale production of dissolved organic carbon by giant kelp Macrocystis pyrifera

“…They hypothesized that Macrocystis may be an important source of DOC used to support BCD in many California near shore environments. Similar conclusions regarding the significance of kelp‐derived DOC to microbial production have been reached for coastal waters in other regions (Newell et al ; Newell and Lucas ; Wada et al ; Wada and Hama ).…”

Recycling versus export of bioavailable dissolved organic matter in the coastal ocean and efficiency of the continental shelf pump

“…The key role of dissolved organic matter (DOM) in the marine food web was already suggested in the early 20th century [e.g., Waksman and Carey , 1935], but this view was not broadly acknowledge by the scientific community until the 1970's [e.g., Pomeroy , 1974; Williams , 1981]. DOM in marine systems has many potential sources such as fish [ Dundas , 1985], macrophytes [ Søndergaard , 1981; Wada et al , 2008], particle hydrolysis [ Smith et al , 1992], plankton [ Lønborg et al , 2009b; Kawasaki and Benner , 2006], rain water [ Cornell et al , 1995], riverine sources [ Sobczak et al , 2005], and sediments [ Burdige et al , 2004], with the most important sources in coastal waters being riverine (terrestrial) and plankton (marine) sources [ Cauwet , 2002].…”

Comparison of marine macrophytes for their contributions to blue carbon sequestration

“…Most macroalgal species spend most of their life history attached to hard benthic substrata (Lu¨ning 1990) where they are unable to accumulate belowground C, thus limiting their capacity to act as C sinks that accumulate and maintain long-term C in their own right. However, once macroalgae become dislodged, they undergo a period of transport in surface waters by wind and water movement, until eventually sinking, decaying, or becoming cast upon depositional areas, including land (Thiel 2003, Thiel and Gutow 2005, McKenzie and Bellgrove 2009, Macreadie et al 2011, the deep sea (Wada et al 2008, Dierssen et al 2009), and coastal blue C habitats (Hyndes et al 2012, Macreadie et al 2012; Fig. 1e).…”