Variation in mesozooplankton community structure in the Japan/East Sea (1991–1999) with possible influence of the ENSO scale climatic variability

Seasonal and interannual change in mesozooplankton community structure in the offshore Tsushima Current area of the Japan/East Sea was studied in relation to climatic events and temporal variability of the upper water column environment from 1991 to 1999. We observed a clear seasonal succession in zooplankton community structure from a cold-water copepod-dominated community in winter and spring to a gelatinous, carnivorous and warm-water copepod-dominated community in summer and autumn. The mean abundance (inds. m⁻³) of the spring community was 3–4-fold higher than that of the other season. The spring community structure varied considerably between years: the community characterized by the summer–autumn type zooplankton assemblage appeared in 1991–1993 and 1998, while the community characterized by high abundance of cold-water copepods appeared in the mid 1990s. Time series profiles of water density and nutrients showed the thickness of the surface warm Tsushima Current and the cold subsurface water increased and decreased, respectively, limiting nutrient supply to the surface water in 1992 and 1998. These results suggest that a thick, warm surface layer might reduce the reproductive success and survival ratio of the cold-water copepods both directly and indirectly, by hindering their upward migration to the surface where food is available, and by limiting phytoplankton growth due to nutrient depletion, respectively. A Monsoon Index (MOI) showed weaker winter wind stress in 1992 and 1998, which might have attenuated formation of the cold subsurface layer in the northern Japan/East Sea and been responsible for surface warming of the study area. Since 1992 and 1998 were El Niño years, this study revealed that ENSO related climatic variability on an interannual time scale considerably influenced the lower trophic level ecosystem in the Japan/East Sea.     

Inter-decadal variability in zooplankton and phytoplankton abundance on the Newfoundland and Scotian shelves

Continuous Plankton Recorder (CPR) sampling on the Newfoundland and Scotian shelves covers three multi-year periods characterised by negative (1962–1971), positive (1992–2000) and negative/neutral (2001–2003) values of the NAO index. Water temperatures respond differently to changes in the NAO in different regions: a positive NAO index tends to lead to reduced temperatures on the Newfoundland shelf and to increased temperatures on the central/western Scotian shelf, and a negative NAO index to the reverse. Since the 1960s, the hydrographic changes due to the NAO have been superimposed on a freshening of the water column throughout the region, which is attributed to increased contribution of Arctic water outflow. Changes in plankton abundance measured by the CPR for the three time periods were generally, but not always, similar on the Newfoundland and eastern and western regions of the Scotian shelf, although Arctic species (e.g. Calanus glacialis, Calanus hyperboreus) were notably more abundant and warm water species (e.g. Metridia lucens, euphausiids) less abundant on the Newfoundland shelf than on the Scotian shelf. Three categories of phytoplankton (colour, diatoms, dinoflagellates) increased in abundance in the 1990s, and these increases generally persisted into 2001–2003. This is believed to be a response to the persistent freshening of the water column, probably due to increased stratification. The Arctic species C. glacialis and C. hyperboreus also showed persistent increases in abundance after 1992, perhaps due to increased transport from the Arctic, although the abundance of the Arctic slope water species Metridia longa decreased. Two groups, Calanus 1–4 and euphausiids, both thought to play important roles in the food chain, showed persistent decreases in abundance after 1992, especially on the Newfoundland shelf. In all regions, Calanus finmarchicus 5–6, Oithona spp. and Centropages hamatus abundance changed in association with variations in the NAO, although no common mechanism could be identified. C. finmarchicus 5–6 abundance decreased in the 1990s and increased after 2001, while the other two species showed the opposite pattern. Centropages typicus and M. lucens abundance on the Scotian shelf increased with rising temperature. This is attributed to increased production rates for the former and an increased influx of warm, M. lucens-rich, slope water on to the shelf for the latter. A comparison between ring net and CPR sampling on the Newfoundland shelf suggests that the Calanus 1–4 category is dominated by C. finmarchicus and that late stage C. glacialis and C. hyperboreus are grossly under-sampled compared to late stage C. finmarchicus.     

几种海洋浮游动物染色体初步研究

采用秋水仙素溶液浸泡，空气干燥，Ｇｉｅｍｓａ染色等方法对火腿许水蚤Ｓｃｈｍａｃｋｅｒｉａ ｐｏｐｌｅｓｉａ，太平洋纺锤水蚤Ａｃａｒｅｔｅａ ｐａｃｉｆｉｃａ（桡足类），百陶箭虫Ｓａｇｉｔｔａｂｅｄｏｔｉ（毛颚类）和厦门隔膜水母Ｌｅｕｃｋａｒｔｉａｒａ ｈｏｅｐｐｌｉｉ（水母类）等海洋游动物染色体的数目和形态作了初步分析。结果表明：火腿许火蚤染色体数目为２ｎ＝２４，太平洋纺锤水蚤２ｎ＝２０，百陶箭虫     

东海精致真刺水蚤(Euchaeta concinna)种群生态特征

根据1997—2000年东海23°30′—33°00′N、118°30′—128°00′E海域4个季节海洋调查资料,采用聚集强度等生态学方法和回归方差贡献等统计分析方法,对东海浮游桡足类精致真刺水蚤自然种群特征进行了研究,并与1979—1980年资料进行比较。结果表明,精致真刺水蚤在东海的优势性主要表现在秋季;其丰度和优势度有显著的季节变化,依次为秋季>冬季>夏季>春季;除夏季东海北部近海丛生指标I为1·34外,冬、春和夏3季I均为负值,秋季I值最高,有明显的聚集现象。与20年前结果相比,东海精致真刺水蚤优势度和占浮游桡足类总丰度的比例有所上升,这种现象可能与全球气候变暖相关。底层水环境的变化和暖流势力的强弱是影响东海精致真刺水蚤数量分布的主要因子。     

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities

The “Wind Events and Shelf Transport” (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000–03. WEST was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling-favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms. Observations of winds, ocean circulation, nutrients, phytoplankton and zooplankton off Bodega Bay and Point Reyes (38°N) were combined with model studies of winds, circulation and productivity. This overview of the WEST program provides an introduction to the WEST special issue of Deep-Sea Research, including the motivation for WEST, a summary of study components, an integrative synthesis of major research results to-date, and background on conditions during field studies in May–June 2001 (the upwelling period on which this special issue is focused).     

Mesozooplankton responses to iron-fertilization in the western subarctic Pacific (SEEDS2001)

A mesoscale iron-fertilization experiment was carried out in the western subarctic Pacific during summer 2001. The iron-patch was traced for 14 days after the fertilization, and the abundance and behavior of mesozooplankton were compared with those outside of the patch. The phytoplankton biomass in the patch rapidly increased to over 15 times the initial level by the later half of the observation period, and was composed of large-sized (>10 mm), centric diatoms. Dominant zooplankton species in the upper 200-m depth were large copepods: Neocalanus plumchrus, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica. Mesozoplankton biomass as well as species composition did not change significantly in the patch over the observation period. Furthermore, no changes of vertical distribution or diel vertical migration were observed for any species or stages of mesozooplankton throughout the observation period. However, the abundance of the first copepodite stages of N. plumchrus and E. bungii increased several fold in the patch after the diatom bloom formation compared to the densities outside the patch. The increases of both species are considered to be due to lowered mortality during the egg and nauplius stages. Spawning of N. plumchrus takes place at depth using lipid storage, while spawning of E. bungii takes place in the surface layer supported by grazing. These facts suggest that the relative importance of nauplii in the diets of the large copepods was decreased in the patch by the diatom bloom. Gut-pigment contents of dominant copepods in the patch increased 4–18 times, and the maximum values were observed during the bloom peak. However, the grazing impact on phytoplankton was low throughout the experiment, especially during the bloom period (<6% of the primary production).     

Short-term effects of changes in water management on the limnological characteristics and zooplankton of a eutrophic Mediterranean coastal lagoon (NE Iberian Peninsula)

The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community.     

Trophic structure of zooplankton in the Fram Strait in spring and autumn 2003

The trophic structure of zooplankton was investigated in Fram Strait (north western Svalbard) in spring and autumn of 2003. Depth-stratified zooplankton samples were collected at 12 stations on the shelf (200 m), across the shelf-slope (500 m) and over deep water (>750 m), using a Multiple Plankton Sampler equipped with 0.180-mm mesh size nets.Higher zooplankton abundance and estimated biomass were found in the shelf area. Abundance and biomass were two times higher in August, when sea-surface temperature was higher than in May. Herbivores dominated numerically in May, and omnivores in August, suggesting a seasonal sequence of domination by different trophic groups. Cirripedia nauplii and Fritillaria borealis prevailed in spring, whereas copepod nauplii and Calanus finmarchicus were numerically the most important herbivores in autumn. Small copepods, Oithona similis and Triconia borealis, were the most numerous omnivorous species in both seasons, but their abundances increased in autumn. Chaetognatha (mainly Eukrohnia hamata) accounted for the highest abundance and biomass among predatory taxa at all deep-water stations and during both seasons. Regarding vertical distribution, herbivores dominated numerically in the surface layer (0–20 m), and omnivores were concentrated somewhat deeper (20–50 m) during both seasons. Maximum abundance of predators was found in the surface layer (0–20 m) in spring, and generally in the 20–50 m layer in autumn. This paper presents the first comprehensive summary of the zooplankton trophic structure in the Fram Strait area. Our goals are to improve understanding of energy transfer through this ecosystem, and of potential climate-induced changes in Arctic marine food webs.     

Effects of pollution on zooplankton abundance and distribution in two estuaries of the Basque coast (Bay of Biscay)

The abundance and spatial distribution of mesozooplankton were compared in the euhaline region of the polluted Bilbao estuary and the unperturbed Urdaibai estuary. The environmental variables measured were salinity, temperature, dissolved oxygen saturation, chlorophyll a, particulate organic matter and Secchi disk depth. Differences in the environmental variables and zooplankton between the estuaries and within the estuaries were tested statistically. Differences in the patterns of mesozooplankton abundance with salinity in each estuary indicated that they were affected by pollution in the Bilbao. Total mesozooplankton, and several mesozooplankton categories were more abundant in the Bilbao at higher salinities but in the Urdaibai at lower salinities. Therefore, we deduced that, in the Bilbao, zooplankton abundance was enhanced by the moderate pollution at the outer euhaline zone and limited by the poorer conditions of the inner zone. The response of the various zooplankton categories to the pollution is discussed.