The prophylactic and therapeutic use of tetracyclines in aquaculture has been shown to contribute to the spread of tetracycline resistance in the environment. In this work, the prevalence of four different tetracycline-resistance genes, tetA, tetC, tetH, and tetM, in sediments from four aquaculture farms and their surroundings in the Baltic Sea was monitored by quantitative polymerase chain reaction (qPCR). The presence of three additional tetracycline-resistance genes (tetE, tetG, and tetW) was studied qualitatively by standard PCR, and the amount of bioavailable tetracyclines and total amounts of tetracycline and oxytetracycline in samples were also measured. None of the farms were using tetracycline at the time of the sampling and one of the farms had stopped all antibiotic use six years prior to the first sampling. Two of the farms were sampled over four successive summers and two were sampled once. Our results showed greater copy numbers of tetA, tetC, tetH, and tetM at the farms compared to pristine sites and demonstrated the presence of tetE, tetG, and tetW genes in the sediments under aquaculture farms at most sampling times. However, no resistance genes were found in samples collected 200 m from any of the farms. None of the samples contained therapeutically active concentrations of tetracyclines at any of the sampling times, suggesting that the increase in the prevalence of tetracycline resistance genes is caused by the persistence of these genes in the absence of selection pressure.

Rising atmospheric concentrations of carbon dioxide are causing surface seawater pH and carbonate ion concentrations to fall in a process known as ocean acidification. To assess the likely ecological effects of ocean acidification we compared intertidal and subtidal marine communities at increasing levels of pCO2 at recently discovered volcanic seeps off the Pacific coast of Japan (34° N). This study region is of particular interest for ocean acidification research as it has naturally low levels of surface seawater pCO2 (280–320 µatm) and is located at a transition zone between temperate and sub-tropical communities. We provide the first assessment of ocean acidification effects at a biogeographic boundary. Marine communities exposed to mean levels of pCO2 predicted by 2050 experienced periods of low aragonite saturation and high dissolved inorganic carbon. These two factors combined to cause marked community shifts and a major decline in biodiversity, including the loss of key habitat-forming species, with even more extreme community changes expected by 2100. Our results provide empirical evidence that near-future levels of pCO2 shift sub-tropical ecosystems from carbonate to fleshy algal dominated systems, accompanied by biodiversity loss and major simplification of the ecosystem.

No 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.