Gracilimonas tropica gen. nov., sp. nov., isolated from a Synechococcus culture.

An irregular, long, rod-shaped marine bacterium, designated CL-CB462(T), was isolated from a Synechococcus culture, which was established from surface water from the tropical Pacific Ocean. The physiological and biochemical features, fatty acid profile and phylogenetic position based on 16S rRNA gene sequences were investigated for the novel strain. Phylogenetic analysis of the 16S rRNA gene sequence showed that the closest relatives of strain CL-CB462(T) were Balneola vulgaris and Balneola alkaliphila. Strain CL-CB462(T) formed a robust clade with members of the genus Balneola in all phylogenetic trees constructed by three different methods. However, the 16S rRNA gene sequence similarity was very low (91.3-91.5 % similarity) and phenotypic and physiological features could clearly differentiate strain CL-CB462(T) from the genus Balneola. Cells of the novel strain were non-motile and spore-forming. The strain was able to grow at 1-20 % (w/v) (optimum of 3-6 %) sea salt concentration, at temperatures of 20-40 degrees C and between pH 6 and 10. The fatty acids were dominated by 15 : 0 iso (41.2 %) and 17 : 1omega9c iso (21.4 %). The DNA G+C content was 42.7 mol%. Based on polyphasic evidence, strain CL-CB462(T) was considered to represent a new genus. The name Gracilimonas tropica gen. nov., sp. nov. is proposed for the type strain of the type species (CL-CB462(T)=KCCM 90063(T)=DSM 19535(T)).

Latitudinal distribution of mesozooplankton in the off-equatorial northeastern Pacific before and after the 1998/99 La Niña event.

Factors affecting mesozooplankton distributions in the northeastern tropical Pacific Ocean were investigated using data obtained along a meridian line (5 degrees -12 degrees N, 131.5 degrees W) in the summers of 1998, 1999, and 2003. The survey periods corresponded to a sharp transition between the 1997-1998 El Niño and 1998-1999 La Niña events, the 1999 La Niña event, and near-normal conditions after the moderate 2002-2003 El Niño in the equatorial Pacific. A strong upwelling in the divergence zone from 10.5 degrees to 11 degrees N caused a shoaling of the thermocline depth (approximately 30 m), resulting in increases in nitrate and phytoplankton chlorophyll a (chl-a) concentrations, and, in turn, mesozooplankton abundance during the La Niña in 1999. In contrast, in 1998, remnants of El Niño characteristics, deeper thermocline depth (60-150 m) and warm surface water (>28 degrees C), led to low concentrations of nitrate, chl-a and low mesozooplankton abundance, except in the convergence zone around 7 degrees N. The thermocline depth and nitrate concentration obtained during the near-normal period in 2003 corresponded to intermediate values as compared to those obtained during El Niño and La Niña conditions. Interannual changes in the position and strength of ecotones, such as divergence and convergence zones, affected mesozooplankton community structure and cyclopoid-to-calanoid ratios along the 131.5 degrees W meridian line. The clustering pattern of the mesozooplankton community was mostly characterized by calanoid (mainly Clausocalanus sp.) and cyclopoid (mainly Oncaea sp.) copepods, accounting for most of the observed differences among groups during the study period. Cyclopoids and calanoids were more abundant in 1999 than in 1998 or 2003, with a sharp increase to the north, while they were less abundant to the north in 1998 and 2003. The cyclopoid-to-calanoid ratio peaked in the convergence zone in 1998 and the divergence zones in 1999 and 2003, apparently due to the strength and location of the ecotones. Principal component analysis (PCA) with environmental factors and dominant mesozooplankton groups showed that dominant groups were affected by nitrate and chl-a concentrations in 1998, by sigma-t (water density), nitrate and chl-a concentrations in 1999, and by sigma-t, salinity and chl-a concentration (except siphonophores) in 2003. Latitudinal distribution of thermocline depth before and after the 1998/99 La Niña event showed a distinct interannual difference. The abundance of mesozooplankton in the divergence zone in 1999 was distinctively higher than abundances found in the convergence and divergence zones in 1998 and 2003, which resulted from the shallow thermocline depth due to an intensified upwelling during the strong 1998-1999 La Niña event.

Why did the copepod Calanus sinicus increase during the 1990s in the Yellow Sea?

Recent field and retrospective data were combined to investigate variations from 1984 to 1998 in the spring abundance of dominant copepods in the Yellow Sea. A calanoid copepod, Calanus sinicus, was chosen to assess the long-term changes in abundance associated with temperature, salinity, chlorophyll-a and predator abundance. Average anomalies of sea surface temperature (SST), salinity, and the abundance of C. sinicus were positive in the 1990s and negative in the 1980s. The average abundances of C. sinicus in the study area in the 1990s were also significantly higher than those in the 1980s (p<0.01). Catches of the anchovy Engraulis japonicus, a predator of C. sinicus, showed a decreasing trend during the study period. The higher abundances of C. sinicus in the 1990s may have been affected by an increase in water temperature and a decrease in predators, without distinctive changes in chlorophyll-a concentrations during the study period.