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.

No abstract

Global warming effects on seaweed beds are already perceptible. Their geographical distributions greatly depend on water temperatures. To predict future geographical distributions of brown alga, Sargassum horneri, forming large beds in the northwestern Pacific, we referred to future monthly surface water temperatures at about 1.1° of longitude and 0.6° of latitude in February and August in 2050 and 2100 simulated by 12 organizations under an A2 scenario of global warming. The southern limit of S. horneri distribution is expected to keep moving northward such that it may broadly disappear from Honshu Island, the Chinese coast, and Korean Peninsula in 2100, when tropical Sargassum species such as Sargassum tenuifolium may not completely replace S. horneri. Thus, their forests in 2100 do not substitute those of S. horneri in 2000. Fishes using the beds and seaweed rafts consisting of S. horneri in East China Sea suffer these disappearances.

Abasic sites (AP sites) arise from hydrolysis of glycosidic bonds of DNA that is damaged by various external and internal processes; unrepaired AP sites give rise to genetic mutations. We have constructed highly reactive AP-site-detecting probes by introducing a hydrophobic and a hydrophilic residue in an aminooxy group. Synthesized probes containing either a naphthalene or a guanidine residue conjugate effectively with AP sites. In particular, a probe containing both functional groups shows the highest reaction rate, indicating that the hydrophobic and hydrophilic interactions act cooperatively in reaction with AP sites. The guanidine residue also contributes to the solubility of the molecules in aqueous media. The biotinylated probes provide much more sensitive detection of AP sites in genomic DNA than the conventional aldehyde-reactive probe.

No abstract