Distribution of phytoplankton abundance and physical properties on the southeastern shelf of the Bering Sea in summer

Oceanographic structure, nutrient concentration, and chlorophyll a concentration were surveyed from 55°N to 59°N along 166°W on the southeastern shelf of the Bering Sea during mid to late July of 1994,1995,and 1996. The present results show a consistent trend that, in every year, high chlorophyll a concentration occurred in the outer shelf domain around 55°00\u27N, as well as the coastal shelf domain, and that the concentrations were usually low in the central shelf domain although large yearly variation occurred. The high phytoplankton abundance in the southern outer shelf domain related to relatively high salinity water, which contained more nitrate than the central shelf domain water. It is suggested that the high abundance is maintained by a continuous supply of nutrients caused by interaction between the ocean current from the open water of the North Pacific and the bottom topography in the vicinity of Unimak Pass. On the other hand, alternative high chlorophyll a stock was observed in the coastal shelf domain, where the sea floor depth was about 40m and vertically homogenous water properties occurred. This suggests that the nutrient supply from the bottom maintains the high phytoplankton abundance. In the central shelf domain, chlorophyll a concentrations less than 1.0μg l^ were usually observed between 55°30\u27N and 58°30\u27N in 1995 and 1996. In 1994,however, chlorophyll a concentrations of 1.0 to 2.0 μg l^ were widely distributed. The slightly high concentrations coincided with a weak pycnocline and occurrence of cold bottom water, which contained high nitrate. It is suggested that phytoplankton abundance may be low when the pycnocline is well developed or the cold bottom water does not transport a large amount of nutrients in the central shelf domain of the southeastern Bering Sea

Structure, biomass distribution and trophodynamics of the pelagic ecosystem in the Oyashio region, western subarctic Pacific

Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton, mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m−2, among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria (15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned broadly into mean trophic level 3–4, and carbon flow through the grazing food chain was established based on the estimated annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds

Population structure and life cycle of Pseudocalanus minutus and Pseudocalanus newmani (Copepoda: Calanoida) in Toyama Bay, southern Japan Sea

Population structure and life cycle of Pseudocalanus minutus and P. newmani in Toyama Bay, southern Japan Sea, were investigated based on seasonal samples obtained by vertical hauls (0-500 m depth) of twin-type Norpac nets (0.33-mm and 0.10-mm mesh) over one full year from February 1990 through January 1991. Closing PCP nets (0.06-mm mesh) were also towed to evaluate vertical distribution patterns in September 1990, November 1991 and February 1997. P. minutus was present throughout the year. The population structure was characterized by numerous early copepodite stages in February-April, largely copepodite V (CV) in May-November, and a rapid increase of adults in November to January. As the exclusive component of the population, CVs were distributed below 300 m in September and November both day and night. These CVs were considered to be in diapause. In February most of the Cl to CIV stages were concentrated in the top 100 m. All copepodite stages of P. newmani were collected for only 7 months of the year, disappearing from the water column in Toyama Bay from mid-June onward and their very small population recovered in November. Vertical sampling in September failed to collect them down to 1000-m depth. The period of their absence corresponded to the period of seasonal warming of surface waters. Unlike P. minutus, P. newmani appears to lack the ability to sink to cooler water during the warm summer season in Toyama Bay. Vertical sampling in February revealed that all copepodite stages of P. newmani were distributed largely in the top 100 m. From these results, combined with the temperature-generation length relationship established by McLaren et al. (1989a), it is estimated that P. minutus and P. newmani have two and three generations, respectively, per year. Further, the present results for both Pseudocalanus species are compared with those reported from coastal waters in the northwestern Pacific and other regions

8. Interannual Variation and Vertical Distribution of Appendicularians in the South of St. Lawrence Island, Northern Bering Sea Shelf, in Summer

Ⅰ. Physical, Chemical Environment, Primary Production, Zooplankton and Their Coupling Model Studie

7. Succession of the Calanoid Copepod Community in Funka Bay during Spring Phytoplankton Bloom

Ⅰ. Physical, Chemical Environment, Primary Production, Zooplankton and Their Coupling Model Studie