Seasonal changes in zooplankton abundance, biomass, size structure and dominant copepods in the Oyashio region analysed by an optical plankton counter

To identify seasonal patterns of change in zooplankton communities, an optical plankton counter (OPC) and microscopic analysis were utilised to characterise zooplankton samples collected from 0 to 150 m and 0 to 500 m in the Oyashio region every one to three months from 2002 to 2007. Based on the OPC measurements, the abundance and biomass of zooplankton peaked in June (0–150 m) or August (150–500 m), depending on the depth stratum. The peak periods of the copepod species that were dominant in terms of abundance and biomass indicated species-specific patterns. Three Neocalanus species (Neocalanus cristatus, Neocalanus flemingeri and Neocalanus plumchrus) exhibited abundance peaks that occurred before their biomass peaks, whereas Eucalanus bungii and Metridia pacifica experienced biomass peaks before their abundance peaks. The abundance peaks corresponded to the recruitment periods of early copepodid stages, whereas the biomass peaks corresponded to the periods when the dominant populations reached the late copepodid stages (C5 or C6). Because the reproduction of Neocalanus spp. occurred in the deep layer (>500 m), their biomass peaks were observed when the major populations reached stage C5 after the abundance peaks of the early copepodid stages. The reproduction of E. bungii and M. pacifica occurred near the surface layer. These species first formed biomass peaks of C6 and later developed abundance peaks of newly recruited early copepodid stages. From the comparison between OPC measurements and microscopic analyses, seasonal changes in zooplankton biomass at depths of 0–150 m were governed primarily by E. bungii and M. pacifica, whereas those at depths of 150–500 m were primarily caused by the three Neocalanus species

Phenology in large grazing copepods in the Oyashio region, western subarctic Pacific

　Seasonal sequence of population structure (=copepodid stage composition) of large grazing copepods (Metridia pacifica, Eucalanus bungii and Neocalanus spp.) was analyzed based on seasonal samples collected with 100 μm mesh nets from 0-500 m stratum at Site H in the Oyashio region, western subarctic Pacific, during 1996-1997 and 2002-2007. On the premise that there are little year-to-year differences, the composite data were arranged to the date of samplings of each year to yield seasonal developmental patterns of each copepod. Seasonal developmental pattern estimated by tracing the sequence of mean copepodid stages of the population at each sampling date revealed that the recruitment season of the population was January for N. cristatus, March for N. flemingeri and May for N. plumchrus and E. bungii. In contrast to these copepods with single recruitment seasons in the year, M. pacifica exhibited two recruitment seasons (mid-May and August) in a year. Phenology in reproduction and development of these copepods reflects their species-specific differences in energy utilization pattern ; M. pacifica and E. bungii spawn in phytoplankton-rich surface layer in spring (females need to feed for spawning) while Neocalanus spp. spawn in deep layer in winter (females do not feed). Development from C1 to C5 of N. cristatus, N. flemingeri and N. plumchrus was in January to June, March to June and May to August, respectively, thus the three sympatric Neocalanus spp. showed a clear temporal separation in the developmental timing in the western subarctic Pacific. This temporal separation in utilizing the surface layer is considered to be a mechanism to reduce inter-specific food competition. Regional comparison of phenology in copepods within the entire subarctic Pacific and its adjacent waters revealed that reproduction timing of the surface spawning M. pacifica and E. bungii was highly variable, while this was not the case for deep spawning Neocalanus spp

The seagrass Zostera marina harbors growth-inhibiting bacteria against the toxic dinoflagellate Alexandrium tamarense

Seagrasses are known to have allelopathic activity to reduce growth of phytoplankton. We found growth-inhibiting bacteria (strains E8 and E9) from Zostera marina possessing strong activity against the toxic dinoflagellate Alexandrium tamarense. Strain E9 markedly inhibited growth of A. tamarense even with initial inoculum size as small as 2.9 cells ml(-1). This bacterium also had growth-inhibiting effects on the red-tide raphidophytes Chattonella antiqua and Heterosigma akashiwo, the dinoflagellate Heterocapsa circularisquama, and the diatom Chaetoceros mitra. Small subunit (SSU) ribosomal DNA (rDNA) sequencing analysis demonstrated that the most probable affiliation of these strains was Flavobacteriaceae, and proved that another inhibitory bacterial strain (E8) was the same species as strain E9. Two other bacterial strains (E4-2 and E10), showing different colony color and isolated from the same seagrass sample, revealed no growth-inhibiting activity. Interestingly, strain E4-2 showed the same sequences as E8 and E9 (100 %), and strain E10 matched E8 and E9 with 99.80 % similarity. Growth-inhibiting bacteria against the toxic dinoflagellate Alexandrium tamarense associated with seagrass, such as Flavobacterium spp. E8 and E9, are able to repress shellfish poisoning besides the allelopathic activity of seagrass itself

Seasonal changes in zooplankton abundance, biomass, size structure and dominant copepods in the Oyashio region analysed by an optical plankton counter

To identify seasonal patterns of change in zooplankton communities, an optical plankton counter (OPC) and microscopic analysis were utilised to characterise zooplankton samples collected from 0 to 150 m and 0 to 500 m in the Oyashio region every one to three months from 2002 to 2007. Based on the OPC measurements, the abundance and biomass of zooplankton peaked in June (0–150 m) or August (150–500 m), depending on the depth stratum. The peak periods of the copepod species that were dominant in terms of abundance and biomass indicated species-specific patterns. Three Neocalanus species (Neocalanus cristatus, Neocalanus flemingeri and Neocalanus plumchrus) exhibited abundance peaks that occurred before their biomass peaks, whereas Eucalanus bungii and Metridia pacifica experienced biomass peaks before their abundance peaks. The abundance peaks corresponded to the recruitment periods of early copepodid stages, whereas the biomass peaks corresponded to the periods when the dominant populations reached the late copepodid stages (C5 or C6). Because the reproduction of Neocalanus spp. occurred in the deep layer (>500 m), their biomass peaks were observed when the major populations reached stage C5 after the abundance peaks of the early copepodid stages. The reproduction of E. bungii and M. pacifica occurred near the surface layer. These species first formed biomass peaks of C6 and later developed abundance peaks of newly recruited early copepodid stages. From the comparison between OPC measurements and microscopic analyses, seasonal changes in zooplankton biomass at depths of 0–150 m were governed primarily by E. bungii and M. pacifica, whereas those at depths of 150–500 m were primarily caused by the three Neocalanus species

Wind damage at Ashoro Research Forest of Kyushu University caused by low pressure in October 2006

平成18年10月7日午後から8日午前中にかけて台風並みに発達し士低気圧により九州大学北海道演習林に大規模在風害が発生した。今後の資料とするため，ここではその被害概要についてまとめた。被害発生時，北海道演習林内では主に北ないし北北東方向から最大風速10m/s以上，瞬間最大風速20皿/.以上回風が吹いたと推定された。被害は北海道演習林のほぽ全域にわたり発生し，被害面積158ha，被害推定本数48,481本，被害推定材積21,284m^3に達した。今回の被害の特徴として，カラマツを中心とした針葉樹人工林，とくに40年生以上の壮齢林に大規模な風倒被害が発生したこと，被害が北東斜面の林分に集中し，風向とほぼ一致したこと，カラマツ林の被害形態は「根返り」が最も多く，次いで「傾斜・幹曲がり」で，「幹折れ」の被害はわずかであったこと等が挙げられた。This paper describes the investigation results of wind damage at Ashoro Research Forest, Kyushu University, Japan induced by heavy low pressure on October 7 and 8, 2006. When the low pressure was passing through Ashoro Research Forest, the estimated dominant wind direction was north or north-northeast, and the estimated maximum wind speed and the estimated maximum instantaneous wind speed were over 10 m/s and over 20m/s, respectively, based on the data from the four nearest AMeDAS (Automated Meteorological Data Acquisition System) observation points. The wind damage was scattered throughout Ashoro Research Forest. Total wind damage area, the estimated total number of damaged trees and their estimated total volume were 158 ha, 48,481 trees and 212,284m^3, respectively. The wind damage was observed in mainly artificial forests of Japanese larch. It was especially heacy in the matured forest stands (over 40 years old) and in the forest stands on the northeastern slope. Damage type of Japanese larch trees was mostly uprooting (75%), and the next largest type was leaning or bent (21%) and snapping was only 4%