Effects of temperature and phytoplankton community composition on subitaneous and resting egg production rates of Acartia omorii in Tokyo Bay.

To clarify the effects of temperature and phytoplankton community composition on Acartia omorii (Copepoda: Calanoida) egg production, its abundance and egg production rates were investigated from 2016 to 2018 in Tokyo Bay, Japan. Abundance was high from March to May (> 3.0 × 104 individuals m-3) and low or undetected from late June to December (≤ 0.4 × 104 individuals m-3). In 2018, most eggs were subitaneous until April; diapause eggs appeared in May when the water temperature exceeded 20 °C. The weight-specific egg production rate (SEPR, Cegg Cfemale-1 day-1) had two peaks. In the first peak in January, > 90% of eggs were subitaneous; in contrast, in the second peak in May, 60% of eggs were unhatched, including diapause eggs. The first peak of subitaneous eggs may contribute to planktonic population development from March to May. In contrast the second peak of diapause eggs probably enhances their recurrence in the next winter. Multiple regression analysis revealed that subitaneous SEPR showed a negative response, whereas diapause SEPR showed a positive response to temperature. Subitaneous SEPR positively correlated with the proportion of small diatoms in phytoplankton carbon biomass, whereas unhatched SEPR positively correlated with the proportion of inedible preys in large diatoms and dinoflagellates. Edible diatoms may induce subitaneous egg production, whereas low-food availability may induce diapause egg production. These results suggest that phytoplankton composition and water temperature have strong impacts on the dynamics of A. omorii via egg production.

What natural and social scientists need from each other for effective marine environmental assessment: Insights from collaborative research on the Tomakomai CCS Demonstration Project.

We propose actions to guide collaboration between 'natural' and 'social' science disciplines in marine environmental issues. Despite enthusiasm for interdisciplinarity on environmental issues, institutional and disciplinary barriers remain for interdisciplinary working in practice. This paper explores what natural and social scientists need from each other for more effective impact assessment in the marine environment. We reflect on collaboration between natural- (especially marine biology) and social scientists (especially environmental sociology) researching the Tomakomai CCS Demonstration Project in Japan; including subsequent expansion of the research team and wider evaluation of project outcomes. We identify two areas of mutual support: community and stakeholder engagement on marine monitoring; and identification of points in regulatory/policy processes where qualitative findings may gain traction alongside quantitative results. We suggest interdisciplinary collaboration for marine environmental research could be helped by making time to learn from each other within projects; and by working together more closely in the field.

Effect of cell size on growth rates of two Skeletonema species and their competitve interactions.

We investigated shifts in growth rates and cell size reduction-restoration processes in two species of diatoms, Skeletonema japonicum and Skeletonema dohrnii. Growth rates greatly fluctuated from 1.0 to 2.1 per day, even under the same conditions. Rates increased from 1.1 to 2.1 per day with decreasing valve diameter; however, rates quickly decreased to 1.0 per day when cell size reached the threshold for initiating auxosporulation. We also conducted co-culture experiments using different size combinations of the two species. The experiment was started using the same cell densities (75 cells · mL-1 ) of both species, and when batch cultures reached late exponential phase, the cultures were reinoculated twice into new medium. When large (valve diameter of 17 µm) S. japonicum cells and small (6 µm) S. dohrnii cells were co-cultured, the S. dohrnii contributed 99% of the total cell density on day 16 (S. dohrnii: 263,900 cells · mL-1 ; S. japonicum: 2,000 cells · mL-1 ). In contrast, when small (9 µm) S. japonicum cells and large (15 µm) S. dohrnii cells were co-cultured, small S. japonicum cells accounted for 97% of the total cell density after only 13 d (S. dohrnii: 1,900 cells · mL-1 ; S. japonicum: 62,500 cells · mL-1 ). This study demonstrated that diatom growth rates covary with cell size, and this phenomenon potentially determines the outcome of competition between species.

Morphological and Molecular Phylogenetic Position of Prorocentrum micans sensu stricto and Description of Prorocentrum koreanum sp. nov. from Southern Coastal Waters in Korea and Japan.

Prorocentrum micans is an extremely variable dinoflagellate species, with many different local forms reported worldwide. Because of this morphological diversity, it is important to establish whether these various forms belong to P. micans sensu stricto. For this study, P. micans-like specimens were isolated from several localities in the southern coastal waters of Korea and Japan. The morphological characteristics and the molecular signatures of P. micans were re-examined. Moreover, a new Prorocentrum species, Prorocentrum koreanum sp. nov. was established through detailed light microscopy and scanning electron microscopy observations. Examination of the periflagellar platelets revealed that P. koreanum sp. nov. differs from P. micans. Furthermore, P. koreanum and P. micans exhibited different distribution patterns of trichocyst pores. Through molecular phylogeny analysis of small subunit (SSU) rRNA, internal transcribed spacer (ITS), and large subunit (LSU) rRNA sequence, we found P. koreanum to be more closely related to P. mexicanum and P. rhathymum than to P. micans. Additionally, ITS2 compensatory base changes also provide strong evidence to support P. koreanum and P. micans being separate species.

Seasonal variations of water column nutrients in the inner area of Ariake Bay, Japan: the role of muddy sediments.

To investigate seasonal variations of nutrient distribution in the mudflat-shallow water system, we conducted field surveys once a month from August 2007 to July 2008 in the inner area of Ariake Bay (IAB), Japan. The NH4 (+)-N concentration of the water column increased in autumn because of the high NH4 (+) release from the sediments, ranging from 850 to 3,001 µmol m(-2) day(-1). The NO3 (-)-N concentration was maximal in January, which was thought to be caused by NO3 (-) release from the oxic sediments and by NO3 (-) regeneration due to water column nitrification. The PO4 (3-)-P concentration of the water column was high in summer-autumn due to the high PO4 (3-) release from the reduced sediments, ranging from 22 to 164 µmol m(-2) day(-1). We estimated the total amounts of DIN and PO4 (3-)-P release (R DIN and [Formula: see text], respectively) from the muddy sediment area of the IAB. In summer-autumn, R DIN and [Formula: see text] corresponded to about 47.7 % of DIN input and about 116.6 % of PO4 (3-)-P input from the river, respectively. Thus, we concluded that the muddy sediments were an important source of nutrients for the water column of the IAB during summer-autumn. In addition, we found that phosphorus necessary for the growth of Porphyra (Porphyra yezoensis, Rhodophyceae) would be insufficient in the water column when phosphorus during the Porphyra aquaculture period is supplied only from the river. Therefore, the phosphorus release from the muddy sediments was thought to play an important role in the sustainable production of Porphyra in Ariake Bay.

Monitoring of algicidal bacterium, Alteromonas sp. strain A14 in its application to natural Cochlodinium polykrikoides blooming seawater using fluorescence in situ hybridization.

The red tide of dinoflagellate, Cochlodinium polykrikoides has frequently occurred in coastal waters, causing severe damage to fisheries. In the present study, the algicidal bacterium Alteromonas sp. A14 isolated from the southern coast of Korea was applied to a red tide of C. polykrikoides in a laboratory experiment. In the experiment, the abundance of the strain A14 was monitored using fluorescence in situ hybridization. Inoculation of the A14 at a final cell density of 9.0 x 10(5) cells/ml caused a significant decrease in C. polykrikoides abundance from 1,830 to 700 cells/ml during 2 days, while abundances of harmless diatoms rapidly increased from 3 days. Abundances of both A14 and other bacteria increased to 1 day. After 1 day, with flagellate abundance increased, bacterial abundance decreased. Finally, algicidal bacterial abundance decreased to 3.5 x 10(4) cells/ml. In the biological control of harmful algal blooms, in addition to decrease in target algal abundance and not occurrence of other harmful blooms, decrease in abundance of utilized organism is also important. This study emphasizes the importance of monitoring the inoculated bacterium when applying bacterium to natural seawater.

Assessing primary and bacterial production rates in biofilms on pebbles in Ishite stream, Japan.

Various measurements of microbial productivity in streambed pebble biofilms were analyzed almost monthly for 1 year to quantify the importance of primary production as an autochthonous source of organic matter utilized to support heterotrophic bacterial production in the dynamic food web within this natural microbial habitat. Bacterial density varied from 0.3x10(8) to 1.4x10(8) cells cm-2, and chlorophyll a concentration ranged from 0.7 to 25.9 microg cm-2, with no coupled oscillation between seasonal changes in these two parameters. In bottle incubation experiments, the instantaneous bacterial growth rate of bacteria was significantly correlated with their production rate [measured by frequency of dividing cells (FDC)] as follows: ln mu=0.138FDC-3.003 (n=15, r2=0.445, p<0.001). FDC values in the pebble biofilms increased with fluctuations during the study period, ranging from 3.6% to 9.2%. Bacterial production rates largely fluctuated between 0.15 to 0.92 microg C cm-2 h-1, and its seasonal pattern was similar to that of bacterial density. Net primary production measured between May 2002 to November 2002 attained minimum level (0.5 microg C cm-2 h-1) in June and maximum level (1.9 microg C cm-2 h-1) in August. Percentages of bacterial production to net primary production ranged between 21% and 120%. Because this ratio extends both below and above 100% for these parameters, it is likely that both autochthonous and allochthonous supplies of organic matter are important for production of bacteria in the pebble biofilms that develop in rapidly flowing fresh water streams.