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1.
Nutrients, chlorophyll-a, particulate organic carbon (POC), and environmental conditions were extensively investigated in the northern East China Sea (ECS) near Cheju Island during three seasonal cruises from 2003 to 2005. In spring and autumn, relatively high concentrations of nitrate (2.6~12.4 μmol kg-1) and phosphate (0.17~0.61 μmol kg-1) were observed in the surface waters in the western part of the study area because of the large supply of nutrients from deep waters by vertical mixing. The surface concentrations of nitrate and phosphate in summer were much lower than those in spring and autumn, which is ascribed to a reduced nutrient supply from the deep waters in summer because of surface layer stratification. While previous studies indicate that upwellings of the Kuroshio Current and the Changjiang (Yangtze River) are main sources of nutrients in the ECS, these two inputs seem not to have contributed significantly to the build-up of nutrients in the northern ECS during the time of this study. The lower nitrate:phosphate (N:P) ratio in the surface waters and the positive correlation between the surface N:P ratio and nitrate concentration indicate that nitrate acts as a main nutrient limiting phytoplankton growth in the northern ECS, contrary to previous reports of phosphate-limited phytoplankton growth in the ECS. This difference arises because most surface water nutrients are supplied by vertical mixing from deep waters with low N:P ratios and are not directly influenced by the Changjiang, which has a high N:P ratio. Surface chlorophyll-a levels showed large seasonal variation, with high concentrations (0.38~4.14 mg m-3) in spring and autumn and low concentrations (0.22~1.05 mg m-3) in summer. The surface distribution of chlorophyll-a coincided fairly well with that of nitrate in the northern ECS, implying that nitrate is an important nutrient controlling phytoplankton biomass. The POC:chlorophyll-a ratio was 4~6 times higher in summer than in spring and autumn, presumably because of the high summer phytoplankton death rate caused by nutrient depletion in the surface waters.  相似文献   

2.
南黄海和东海毛颚类生态特征的研究Ⅰ.数量分布的特征   总被引：2，自引：2，他引：0  
戴燕玉 《海洋学报》2006,28(6):106-111
根据国家海洋局1977年12月份至1978年11月份在黄海南部和东海(28°~34°N,120°30'~127°00'E)广大海域进行周年逐月份的12航次综合调查资料,对该海域毛颚类数量变动、时空分布及其与环境因子的关系进行了分析.结果表明,本调查区毛颚类的数量以6~9月份较高,7月份为年最高值.1~4月份为年低值期,尤以4月份为最低谷.其中在数量上取主导作用的种类是肥胖箭虫(Sagitta enflata)、强壮箭虫(S.crassa)拿卡箭虫(S.nagae)和百陶箭虫(S.bedoti)等种类.在平面分布上,长江口以北毛颚类数量一般高于长江口以南的海域,在南黄海,除夏季外,其他季节均有出现高值.在东海高密集区一般出现在不同水系交汇区,尤其在长江冲淡水、沿岸水和外海高温高盐水交汇的锋面最为密集.这对于不同水系在研究区内运动和消长有一定的指示意义.  相似文献   

3.
《Journal of Sea Research》2002,47(2):121-139
The hyperbenthos of the Frisian front, an enriched benthic area of the southern North Sea, and surrounding waters was investigated along two cross-frontal transects in August 1994 and April 1996. A total of 111 species was recorded, mainly peracarid crustaceans and decapods. On average, Calanus spp. (Copepoda), Schistomysis ornata (Mysidacea) and Scopelocheirus hopei (Amphipoda) represented more than 40% of the total density, while S. ornata constituted 30% of the biomass. Community structure differed strongly between the two months, as shown by the species composition and the much lower densities and biomasses in April.In August, the density of the holohyperbenthic fraction reached pronounced peaks in the Frisian front area: densities for chaetognaths, copepods, amphipods and mysids were one order of magnitude higher than in the surrounding waters. Diversity was also highest at the Frisian front. The high abundances may be explained by active migration and/or by passive transport to the food-enriched area. Merohyperbenthic species showed a less distinct increase in density in the front zone, but a clear south-to-north change in community structure was observed. These species are more heavily subjected to the prevailing tidal flow. The Frisian front fauna seems to be transitional between two merohyperbenthic communities established in late summer, one belonging to the environmentally different sandy Southern Bight to the south, the other to the silty Oyster Ground to the north.In spring, no such hyperbenthic enrichment over the Frisian front was observed. This is most probably due to the strong seasonality of the hyperbenthic fauna and the low water temperature, suggesting that production and subsequent recruitment had not started yet. Alternatively, winter storms could have resuspended particulate organic matter, followed by a rapid migration of the motile hyperbenthos to more northern depositional areas and thus leading to a temporal density decline. We conclude that the Frisian front is an enriched area for the hyperbenthos at the end of summer, as has already been reported for the benthic system.  相似文献   

4.
《Journal of Sea Research》2007,57(2-3):171-179
We examined the relationship between body size and maturation in male Japanese flounder Paralichthys olivaceus, and whether spatial variation in the occurrence of mature fish between southern (Fukushima and Miyagi prefectures, 38° N) and northern (Aomori Prefecture, 41° N) waters could be explained by variation in growth rates and somatic body condition. Male flounder in southern and northern waters matured sexually at two years of age; however, the probability of 2-y-old males being mature differed between the two waters. In southern waters, almost all 2-y-old males had mature testes during the spawning season (May–September), whereas the majority of 2-y-old males in northern waters remained immature during the same period. Males in southern waters had grown faster than those in northern waters by summer, two years after birth, but the length range of males in the two regions largely overlapped during the spawning season. The somatic condition of 2-y-old males in June was significantly higher in southern waters than in northern waters, but there was no significant difference in condition between immature and mature specimens in each region. The length-growth increments of 2-y-old males in southern waters during the growing season, just after the spawning season, were similar to those in northern waters. These discrepancies in fish between northern and southern waters did not appear to be explained by the theory of growth and energy allocation strategies. Our findings show that life-history traits of male Japanese flounder may vary on a small geographical scale off the Pacific coast of northern Japan.  相似文献   

5.
A tidal front is a unique structure in coastal waters where tidal mixing is dominant during the summer. Various indexes to define tidal fronts and their dynamics have been reviewed in coastal waters where tidal mixing is dominant. The classification of a front in coastal waters is determined by the freshwater inflow, heating/cooling, Ekman transport, and mixing intensity. The strength of mixing plays an important role, dynamically, in creating a tidal front. The hydrography and circulation around a tidal front are crucial in the biological processes leading to the cross-frontal transport of nutrients and phytoplankton blooms. Physical-biological cooperation is necessary to clearly assess the impact of a tidal front on the distribution of phytoplankton and chlorophyll a in the tidal front area.  相似文献   

6.
In the North West Mediterranean (NWM), mass mortality events (MME) of long-lived benthic species that have occurred over the last two decades have been related to regional warming trend. Gaining robust data sets on thermal regimes is critical to assess conditions to which species have adapted, detect extreme events and critically evaluate biological impacts. High resolution temperature (T) time series obtained during 1999–2006 from 5 to 40 m depth at four contrasted sites of the NWM were analyzed: Area Marina Protegida de les Illes Medes (NE Spain), Riou (Marseilles, France), Parc National de Port-Cros (France), and Réserve Naturelle de Scandola (Corsica, France). The seasonal pattern showed winter T around 11–13 °C, and summer T mainly around 22–24 °C near surface to 18–20 °C at depth. Stratification dynamics showed recurrent downwellings (>40 m) at Medes, frequent observation (1/3rd of the summer) of deep and cold upwelled waters at Riou, while Scandola exhibited stable summer stratification and highest suprathermoclinal T. Port-Cros showed an intermediate regime that oscillated between Riou and Scandola depending on the occurrence of northern winds. Data distribution study permitted to identify and to characterize 3 large scale positive anomalies concomitant with the mass mortality outbreaks of summers 1999, 2003 and 2006. The analysis of biological surveys on gorgonian populations showed significant impacts during the 3 years with temperature anomalies. Besides the degree of impact showed inter-annual differences which could be related to different T conditions concomitant to mortality events, from slight increase in T extreme of only 1–2 °C over short duration, to lengthened more classical summer conditions. Our results therefore support the hypothesis that shallow NWM populations of long-lived benthic species are living near their upper thermal thresholds. Given actual trends and projections in NWM, the repetition of new MMEs in the next decades is extremely likely. In such context, the acquisition of dedicated high resolution T series proves to be crucial for increasing our detection, understanding and forecasting abilities.  相似文献   

7.
The surface and sub-surface biological oceanography of tuna fishing grounds within the East Australian Current (EAC) was compared in 2004 with two other fishing areas further offshore. Our aim was to determine whether the biological oceanography of the region could explain the distribution and intensity of pelagic fishery catches inside and outside the EAC at that time. The EAC fishing area was noticeably warmer, less saline and lower in nutrients than waters in the other fishing areas. The EAC waters were dominated by large diatoms, the biomass of which was significantly higher than in the seamount and offshore areas, apparently the result of a cold core eddy beneath the EAC surface filament. Over the seamount and offshore more typical Tasman Sea waters prevailed, although the presence of a relatively deeper oxygen minimum layer over the seamount suggested topographically induced mixing in the area. Notably, sub-surface zooplankton and micronekton biomass was significantly higher around the seamount than in the two other areas. The offshore region was characterised by frontal activity associated with the Tasman front. Micronekton net biomass was generally highest in surface waters in this region. Examination of tuna catch records at that time showed yellowfin tuna (Thunnus albacares) dominated the catches of the EAC, whereas swordfish (Xiphias gladius) and bigeye tuna (Thunnus obesus) were the main species caught offshore. We suggest the yellowfin tuna concentrate in waters that are not only warmer but where prey species are concentrated near the surface. Offshore, deeper living species such as swordfish and bigeye tuna (T. obesus) can take advantage of prey species that are distributed deeper in the water column and along the flanks of the many seamounts in the region, or that are concentrated at fronts associated with the Tasman Front. Although only a snapshot of the region, relatively consistent catch data over time suggests the underlying biological oceanography may persist over longer time periods, particularly during the Austral spring.  相似文献   

8.
《Progress in Oceanography》2007,72(2-3):249-258
Centropages typicus and Centropages hamatus are two of the most abundant copepods on the continental shelf in the mid-Atlantic region of the western North Atlantic. Their range extends from the Scotian Shelf (C. typicus) and the Grand Banks (C. hamatus) in the north to Cape Hatteras in the south. South of Cape Hatteras they have only been observed in inshore waters of North and South Carolina and not offshore on the continental shelf or in coastal waters of eastern Florida. However, C. hamatus has been observed in western Florida. Abundances of both species are greatest in inshore regions in the mid-Atlantic Bight with C. hamatus tending to have a more coastal distribution. In this region seasonal variability is low with high abundances from late fall through mid-summer. In the north year-round presence of both species is confined to inshore areas and offshore banks such as Georges Bank, and Browns Bank, Emerald Bank and Western Bank on the Scotian Shelf. In this northern region there is a pronounced seasonal cycle in abundance with high abundances during late summer and fall. Periods of high reproductive rates are closely linked to blooms of large phytoplankton and food availability rather than temperature appears to be controlling population abundances.  相似文献   

9.
The distribution of pH and alkalinity has been used to calculate the distribution of total inorganic carbon (TC) and fugacity of carbon dioxide (fCO2) in the upper 200 m of the water column in coastal upwelling areas off northern Chile (23–24°S, near Antofagasta) and central Chile (30–31°S, near Coquimbo) during austral summer 1997. In these upwelling areas, colder surface waters were oxygen poor and strongly CO2 supersaturated (100% near Antofagasta and 200% near Coquimbo), although below the pycnocline the CO2 supersaturation invariably exceeded 200% in both areas. The larger surface CO2 supersaturation and outgassing at 30°S were associated with stronger winds that promoted the upwelling of denser water (richer in CO2) as well as a higher air–sea CO2 transfer velocity. The consistent decrease in intensity of the southerly winds (as derived from NSCAT scatterometer data) from 30–31°S to 23–24°S suggests a corresponding decline in the intensity of the CO2 outgassing due to upwelling. Additionally, we suggest here that the intensity of the local upwelling forcing (i.e. alongshore–equatorward winds) plays a role in determining the water mass composition and phytoplankton biomass of the coastal waters. Thus, while deep upwelling of salty and cold water resulted in high fCO2 (up to 1000 μatm) and very low phytoplankton biomass (chlorophyll a concentration lower than 0.5 mg m−3), the shallow upwelling of less salty (e.g. salinity <34.5) and less CO2-supersaturated water resulted in a higher phytoplankton biomass, which further reduced surface water fCO2 by photosynthesis.  相似文献   

10.
This study examines species composition and abundance of appendicularians in the northwestern coastal waters of South China Sea based on in situ data obtained by 169 μm planktonic nets during summer and winter, and discusses the influence of environmental factors on their distribution and assemblages. A total of 19 appendicularian species (including one unidentified species) was collected. Species richness is higher in summer than in winter, and it increases from inshore to offshore waters. Average abundance of appendicularians is 103.1 (±198.1) and 54.6 (±111.1) ind. m−3 in summer and winter, respectively. The abundance distribution of appendicularians is generally high around inshore waters during summer and winter, and with a higher abundance assemblage along the eastern coast from Leizhou Peninsula to Hainan Island, especially at the eastern mouth of Qiongzhou Strait in summer. Oikopleurids accounted for 97.5% and 99.6% of total appendicularians abundance in summer and winter, and the region of high values was the same to that of total appendicularians abundance. Oikopleura longicauda, Oikopleura rufescens, and Oikopleura fusiformis are dominant species during summer and winter. Results showed that spatial distribution of species richness of appendicularians is considered to be the result of physical factors such as temperature and salinity in summer and winter, while variations in abundance of appendicularians are affected by the combination of physical and biological factors. In particular, variations of appendicularians abundance are affected by food availability in summer.  相似文献   

11.
The location and seasonal variability of the tidal mixing front in the region of Shantar Islands are studied based on an analysis of satellite data. The Shantar tidal mixing front is related to the main features of the oceanographic structure of the northwestern shelf of the Sea of Okhotsk in summer. This front separates the coastal waters mixed by tidal currents and the stratified part of the shelf. The temperature tidal mixing front forms in July after the melting ice cover and disappears in the end of October when the stratification is broken. The mean position of the front changes insignificantly and is determined by the critical value of the Simpson-Hunter parameter (logh/u 3 = 2.5); the front is located over the isobath of 50 m. The temperature tidal mixing front corresponds to the front in the distribution of chlorophyll a determined from SeaWiFS and MODIS satellite imagery. High (when compared to the stratified part of the shelf) concentrations of chlorophyll a were observed within the zone of intense tidal mixing. Satellite images in the IR range of the spectrum (Landsat-5 TM) demonstrated that the front is dynamically unstable. Mixing effects connected with frontal submesoscale baroclinic eddies have an influence on the structure of the stratified part of the shelf.  相似文献   

12.
According to the results of the international expedition aboard the R/Vs Roger Revelle and Professor Khromov in the summer 1999, areas with low oxygen contents (below 210 μM/kg) and those with increased contents of dissolved inorganic carbon and phosphates were found that roughly coincided with one another. These areas are located near the bottom on the southwestern slope of the Tsushima Basin in the region of the Korea Strait and on the continental slope in the region of the Tatar Strait in the northern part of the sea at about 46° N. The set of hydrochemical data points to a high geochemical activity in the near-bottom layer of the areas noted. This activity is confirmed by direct observations of the composition of the interstitial water in the sediments collected in the northern part of the sea during the expedition of R/V Akademik M.A. Lavrent’ev in 2003. It was supposed that the main cause of the increased geochemical activity is the runoff of suspended and dissolved matter from the Korea and Tatar straits. In the areas mentioned, the near-bottom waters are characterized by low values of the nitrogen-phosphorus ratio (below 10), which is geochemical proof of the denitrification process occurring under the conditions of high oxygen concentrations characteristic of the Sea of Japan. Based on the value of the annual production in the Sea of Japan, a rate of denitrification equal to 3.4 × 1012 gN/year was calculated. Hence, it is confirmed that the geochemical processes in the near-bottom layer have a direct influence on the spatiotemporal characteristics of the hydrochemical properties of the waters of the Sea of Japan.  相似文献   

13.
This survey of the southernmost significant upwelling site in the Benguela Current showed that the oceanography is dominated by the seasonal wind cycle of predominant S-E winds in summer and N-W winds in winter. In the upwelling season, extending from September to March, a semi-permanent plume is isolated by a pronounced oceanic front whose position varies in the short-term and is related to wind direction. Surface waters change immediately and deeper waters more slowly to fluctuations in wind. The rate of upwelling was statistically related to wind data. A maximum rate of 32 m day?1 was found.In spring low temperature and salinity water flows northward on the shelf while between late summer and later winter oxygen-depleted water, rich in nutrients, flowed south at an estimated rate of 7–21 × 104 m3 s?1 in a counter current to the Good Hope Jet.Local depletion of oxygen occurs due to phytoplankton decomposition caused, in autumn, by falling light levels and, in summer in calm periods, by nitrate depletion (<1 μg-at N 1?1). Primary productions is estimated at 3.7 kg C m?2 yr?1 with a maximum growth rate (PImax) = 17.4–19.0 mg C mg chlorophyll a?1 hr?1 and half-saturation constant (KS) = 0.4–1.1 μg-at N 1?1. Nutrients were utilized and oxygen produced: ΔP:ΔN:ΔSi:ΔO=1:19.1 to 23.3:17.5 to 23.3:?227 to ?293. High N:Si ratios (maximum 4.28) were found in oxygen-depleted water produced locally while that coming from the north had low ratis, due to resolution of silica from the sediments and nitrate reduction. The mean zooplankton standing stock, 2.3 g dry weight m?2, was 12% of the phytoplankton crop. In summer stocks were maximal 40–100 km and minimal 20–50 km from the coast while in winter they were maximal inshore. Little vertical migration occurred and the waters above the thermocline contained the majority of the population.  相似文献   

14.
《Oceanologica Acta》1998,21(6):907-921
Phytoplankton distribution and primary productivity were investigated in the Bay of Seine (eastern English Channel, France) in spring and early summer of 1992 and 1994. In 1992, the horizontal distribution of phytoplankton species was determined over the whole Bay of Seine. In 1994, species distribution and primary productivity were studied along the salinity gradient of the Seine plume and in the neighbouring marine waters. Phytoplankton distribution was characterised by the permanent diatom dominance from early spring to early summer. The spring bloom did not occur uniformly over the bay, but was initiated in the marine waters, in the middle of the bay and progressed towards the coast where it developed, in June, in the diluted waters of the Seine plume. Phytoplankton distribution was also characterised by the dominance of large diatoms (Rhizosolenia) in marine waters and by the dominance of small species (Skeletonema costatum, Asterionella glacialis) in the plume waters. The greatest abundance of large diatoms was generally encountered below the euphotic zone. This accumulation seemed to be related to cell sedimentation and advection of marine waters below the diluted plume waters. The daily carbon productivity range was 1.4 to 3 g m−2 d−1. The highest values were measured in the plume waters (S > 28), suggesting the primary productivity in the plume was more controlled by light than by nutrients. The photic zone productivity/ chlorophyll a ratios (P/B; producted carbon per unit of Chla) were close to 40 mg mg−1 d−1 in the plume waters. P/B exceptionally reached 90 mg mg−1 d−1 in early summer. This value corresponded to a fast growing population of S. costatum. In marine waters, P/B varied from 22 mg mg−1 d−1, in spring, to 43 mg mg−1 d−1, in early summer.  相似文献   

15.
南海北部上层鱼类浮游生物多样性和丰度的季节变化   总被引：1，自引：0，他引：1  
The objective of this study was to investigate the seasonal variations of ichthyoplankton diversity and abun-dance in the northern South China Sea based on the data collected during summer, winter and spring. In total, 95 taxa of larval fishes were identified. The greatest number of species was recorded in spring, followed by summer and winter. The number of species was distributed mainly in the coastal waters from the east of Leizhou Peninsula to the southeast of Hainan Island during the surveyed periods of summer and spring, but in the offshore waters during winter. The abundance of larval fish was lowest in winter, increased in spring, and reached the maximum in summer. High abundance of larval fish was generally restricted to coastal waters with the isobaths less than 50 m. Seasonal variations of larval fish richness, abundance and diversity index were significant （P〈0.001）. Carangidae was the most common and abundant taxon in summer and winter, whileSardinella sp.,Thrissa mystax andLeiognathus sp. were dominant in spring. High diversity and abundance of larval fish might be attributed to increased temperature and coastal upwelling in spring and summer.  相似文献   

16.
No. 2 fuel oil-sea water dispersions were added to three large scale (13 m3) microcosms twice weekly for a period in 1977 and a 4 month period in 1978. Water column concentration of total hydrocarbons averaged 190 μg litre−1 in 1977 and 93 μg litre−1 in 1978. Several responses of t the phytoplankton community in the oiled microcosms, relative to control microcosms, were similar during both periods of oil addition: total phytoplankton abundance and chlorophyll concentration were elevated, species diversity was higher and diatoms represented a greater proportion of the total p phytoplankton abundance than flagellates during 4 months of oil addition in 1977 and the entire period of oil addition in 1978. Phytoplankton species composition in the oiled microcosms was similar to the source water, Narragansett Bay, but the microcosm assemblages were numerically dominated by populations of the diatom Chaetoceros spp. and nanoflagellates in 1977 and several Chaetoceros spp. in 1978. Reduced predation pressure and altered herbivore feeding behaviour combined with the low level, non-lethal (to the majority of phytoplankton populations), concentrations of No. 2 fuel oil in the water column are postulated as mechanisms that can account for the elevated phytoplankton abundance in the oiled microcosms relative to the controls.  相似文献   

17.
A spatial and temporal variation in physiochemical parameters in the southeastern Yellow Sea(YS) is investigated in the spring and summer of 2009 to 2011.Nutrient show a strong negative relationship with chlorophyll a(Chl a) concentration in spring,and the subsurface chlorophyll a maxima(SCM) layer was associated with the nitracline in summer.In summer,the SCM was usually found within or above the pycnocline and at the depths of shoals from the open sea to the coastal sea due to tidal and/or topographical fronts in the southernmost study area.High Chl a concentrations were found in the central southern YS,where the YS cold water layer expanded under the pycnocline and encountered water masses during spring and summer.After a typhoon in the summer of 2011,Chl a concentration increased,especially in the central southern YS,where cold waters occurred below the pycnocline.The results suggest that the development of thermohaline fronts may play an important role in the growth and accumulation of phytoplankton biomass in the upper layer of the southeastern YS during spring and summer.  相似文献   

18.
Traditionally, it was assumed that major spawning activity of Illex argentinus occurs in discrete pulses along the outer-shelf/slope off Argentina/southern Brazil during late-fall/winter and that early life stages develop near the Brazil–Malvinas Confluence (BMC). However, a novel hypothesis of the population structuring of the species was proposed that states that coastal waters may be important as spawning and feeding grounds. Here, we analyzed the spatial distribution of Illex argentinus inside San Matias Gulf based on the position of the CPUE of jiggers in order to improve the knowledge of the population structuring in coastal regions. Squids were mainly concentrated on the northern region of the gulf where favorable oceanographic conditions (e.g. water stratification, chlorophyll-a concentration peaks) to feeding and spawning are present. These results provided empirical evidences that individuals of I. argentinus use Argentinean coastal waters, particularly San Matias Gulf, as permanent feeding and spawning grounds which supports the new hypothesis.  相似文献   

19.
We studied the effect of four types of fronts, the coastal front, the middle front, the shelf partition front and the shelf break front on the quantitative distribution and the composition of plankton communities in the Pribilof area of the eastern Bering Sea shelf in late spring and summer of 1993 and 1994. The coastal fronts near St. Paul and St. George Islands and the coastal domains encircled by the fronts featured specific taxonomic composition of planktonic algae, high abundance and production of phytoplankton, as well as large numbers of heterotrophic nanoplankton. The coastal fronts also were characterized by high values of total mesozooplankton biomass, high concentrations of Calanus marshallae, as well as relatively high abundances of Parasagitta setosa and Euphausiacea compared to surrounding shelf waters. We hypothesize that wind-induced erosion of a weak thermocline in the inner part of the coastal front as well as transfrontal water exchange in subthermocline layers result in nutrient enrichment of the euphotic layer in the coastal fronts and coastal domains in summer time. This leads to prolonged high primary production and high phytoplankton biomass. In this paper a new type of front—the shelf partition front located 45–55 km to the north-east off St. Paul Island—is described, which is assumed to be formed by the flux of oceanic domain waters onto the shelf. This front features a high abundance of phytoplankton and a high level of primary production compared to the adjacent middle shelf. Near the southwestern periphery of the front a mesozooplankton peak occurred, composed of C. marshallae, with biomass in the subthermocline layer, reaching values typical for the shelf break front and the highest for the area. High abundance of phyto- and zooplankton as well as heterotrophic nanoplankton and elevated primary production were most often observed in the area adjacent to the shelf break front at its oceanic side. The phyto- and mesozooplankton peaks here were formed by oceanic community species. The summer levels of phytoplankton numbers, biomass and primary production in the shelf break frontal area were similar to those reported for the outer and middle shelf during the spring bloom and the coastal domains and coastal fronts in summer. In the environment with a narrow shelf to the south of St. George Island, the mesozooplankton peak was observed at the inner side of the shelf break front as close as 20 km from the island shore and was comprised of a “mixed” community of shelf and oceanic species. The biomass in the peak reached the highest values for the Pribilof area at 2.5 g mean wet weight m−3 in the 0–100 m layer. Details of the taxonomic composition and the numbers and production of phytoplankton hint at the similarity of processes that affect the phytoplankton summer community in the coastal domains of the islands, at the coastal fronts, and at the oceanic side of the shelf break front. The middle front was the only one that had no effect on plankton composition or its quantitative characteristics in June and July. Location of a variety of frontal productive areas within 100 km of the Pribilof Islands creates favorable foraging habitat for higher trophic level organisms, including sea birds and marine mammals, populating the islands.  相似文献   

20.
To better understand the development of the annually recurring late summer red water blooms of the phototrophic ciliate Myrionecta rubra in the Columbia River estuary we examined its standing stocks and measured its growth rates both in the estuary main channels and in Baker Bay, a peripheral embayment situated near the river mouth. Data collected during two summers show a biphasic development of M. rubra blooms, with an initial phase when the protist was only detected in Baker Bay, followed by an established phase when red waters were observed throughout the lower estuary. Ilwaco harbor (Baker Bay’s seaward-end) is at least one of the locations where the bloom starts since M. rubra was detected there at concentrations >100s cell L−1 before Chinook harbor (Baker Bay’s upriver-end) or the estuary main channels. In 2010, this initial phase lasted about 1.5 months, spanning the neap tide of early July to the beginning of the neap tide of mid-August. While high growth rates were measured in Ilwaco harbor during the initial phase (1.2–3.1 d−1) and in the estuary main channels in both surface red (0.7 d−1) and adjacent non-red (1.1 d−1) waters during the established period, growth of the ciliate was not detected in Ilwaco harbor during this second phase. Growth rate data obtained during the established bloom phase also suggest that M. rubra cells in the estuary mostly divide during the daytime and that red water patches might experience self-shading.  相似文献   

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