Seasonal variability of meio- and macrobenthic standing stocks and diversity in an Arctic fjord (Adventfjorden, Spitsbergen)

Strong environmental seasonality is a basic feature of the Arctic system, still there are few published records of the seasonal variability of the Arctic marine biota. This study examined the year-round seasonal changes of soft bottom macro- and meiobenthic standing stocks and diversity on a station located in an Arctic fjord (Adventfjorden, Spitsbergen). The seasonality observed in benthic biota was related to the pelagic processes, primarily the seasonal fluxes of organic and inorganic particles. The highest abundance, biomass and richness of benthic fauna occurred in the spring after the phytoplankton bloom. During the summer, when a high load of glacial mineral material was transported to the fiord, the number of both meio- and macrobenthic individuals decreased remarkably. The strong inorganic sedimentation in summer was accompanied by a decline in macrobenthic species richness, but had no effects on evenness. Redundancy analysis (RDA) pointed to granulometric composition of sediments (depended on mineral sedimentation) and organic fluxes as factors best related to meio- and macrobenthic taxonomic composition, but no clear seasonal trend could be observed on the nMDS plots based on meiobenthic higher taxa or macrobenthic species abundances in the samples. This study addresses the possible effects of changes in the winter ice cover on the fjordic benthic systems because it was performed in a year with no ice cover on the fjord.     

Seasonal Variability of Particulate Organic Matter in a Mountain Stream in Central Spain

The aim of this paper was to study the influence of environmental characteristics of the Mediterranean climate on seasonal variability of particulate organic matter abundance in a mountain stream. Coarse and fine fractions of both suspended and benthic particulate organic matter were determined on 14 occasions between February 1998 and November 1999 in a second‐order Mediterranean stream in Central Spain (Arroyo Mediano). Temporal variability of suspended organic matter followed a seasonal pattern, attributed to litter‐fall inputs, instream processing, and the hydrological regime. Suspended organic matter (SOM) and its seasonal variability fall well within the range reported for streams in temperate non‐Mediterranean deciduous forest. However, we found no seasonal trend in benthic organic matter (BOM) storage, and it seems that the amount of BOM remained fairly constant throughout the year. Reach retention (evaluated as the ratio between BOM and SOM per m²) was higher in summer during reduced stream flow, mainly due to coarse particulate organic matter storage. These observations do not differ from those reported for other headwater streams in temperate forested biomes, from which we conclude that there was no evidence of a Mediterranean influence on particulate organic matter dynamics in the Mediano stream, nor probably in other headwater Mediterranean streams. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Seasonal variation of pelagic invertebrate larvae in the shallow antarctic waters of Admiralty Bay (King George Island)

Recent studies have revealed increasing numbers of benthic invertebrate species producing pelagic larvae in Antarctic waters. This paper investigates temporal changes in larval abundance in shallow areas of Admiralty Bay. Plankton was collected from December to May of 2000/2001 and 2001/2002. Air and water temperature and solar radiation were significantly higher during the second year, characterising three seasonal periods early summer, late summer and early winter. Mean meroplankton abundance was 160 and 1,548 in d.100 m⁻³ for the first and second years, respectively. Mollusc veligers were dominant in both years. Analysis of variance showed that in 2001 veligers were present in the early winter and in 2002 they were synchronous with the late summer phytoplankton bloom; polychaetes and trochophors were concentrated in the early winter, while echinoderms and nemerteans were abundant in early summer. These results showed the importance of seasonality (i.e. a combination of air and water temperature, solar radiation and food supply) to the reproductive events of an Antarctic coastal nearshore environment.     

Depth profiles of plankton,particulate organic matter and microbial activity in the eastern Canadian Arctic during summer

Summary Deep profiles of particulate organic matter, microplankton (phytoplankton and bacteria), zooplankton and their metabolic activities were investigated during two summer voyages to the eastern Canadian Arctic. Magnitudes and depth distributions were similar in many respects to observations from temperate and tropical waters. Strong gradients in most properties were observed in the upper 50–100 m and subsurface maxima were generally associated with the upper mixed-layer (>50 m). In addition to the general vertical decreases in plankton biomass and metabolic activity there was evidence for both rapid transport (sinking) of organic matter and for enhanced (above background) levels of microbial metabolic activity in deep waters (>500 m). Zooplankton depth distributions differed from the pattern generally observed at lower latitudes; in the Arctic, zooplankton abundance decreased to a lesser degree with depth than particulate organics and microplankton. The overwintering behavior of high-latitude zooplankton appeared to be the best explanation for their relatively high abundance at depth. Despite this, however, zooplankton apparently contributed little to the total column community metabolism.     

The Seasonal Relationship Between Meroplankton and Megabenthos on Georges Bank,Gulf of Maine,Northwest Atlantic

A broad based environmental study of Georges Bank included samples of zooplankton and dredge samples of megabenthos for four seasons. The purpose of this account is to examine the seasonal relationship between meroplankton and megabenthos. Mean densities of meroplankton were relatively high at shallow near shore stations and the central Bank and low at deeper stations. Densities were highest in the summer and lowest in the winter for major taxa. For megabenthos the number of species, relative abundance and relative biomass was also highest in the summer and lowest in the winter. Dominant megabenthos provided year round occupants and seasonal pulses. Year round occupants and seasonal peaks of some megabenthos facilitate year round foraging by demersal finfish enhancing the general production of the Bank. It was concluded that Georges Bank megabenthos was part of a broad ranging continental shelf, sand bottom fauna extending at least from Gaspe Bay to the offing of Chesapeake Bay.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Storage and decomposition of particulate organic matter along the longitudinal gradient of an agriculturally-impacted stream

An agriculturally-impacted stream in northern Idaho was examined over a two-year period to determine seasonal and longitudinal patterns of the storage and decomposition of particulate organic matter. Biomass of benthic organic matter (BOM) was considerably less than values reported in the literature for comparable, undisturbed streams. Coarse, fine, and total benthic particulate organic matter were not correlated with parameters pertaining to stream size (e.g., stream order), but were correlated with sample site and amount of litterfall. The association of BOM with site and litterfall suggests that storage of particulate organic matter is a function of local characteristics rather than stream size. Low biomass of stored organic matter is a response to the low input of terrestrially-derived organic matter resulting from removal of climax vegetation.Leaf packs of alder, Alnus sp., were placed in the stream seasonally for 30 and 60 d. While there were significant differences for months, there was no significant difference among sites for leaf packs exposed for 30 d. Significant differences were observed among both sites and months for leaf packs exposed for 60 d; however, differences among sites accounted for only 5% of the variance. The absence of differences in decomposition of organic matter along the gradient of Lapwai Creek, despite heterogeneity of the drainage basin and availability of organic matter, may be in response to the overall low biomass of stored benthic organic matter. This study demonstrates that agricultural activity can substantially influence instream heterotrophic processes through reduced availability of organic matter and can shape community structure and ecosystem dynamics of streams flowing through agricultural drainage basins.     

Composition and sources of near reef zooplankton on a Jamaican forereef along with implications for coral feeding

Nocturnal near-reef zooplankton from the forereef of Discovery Bay, Jamaica, were sampled during winter and summer 1994 using a diver-operated plankton pump with an intake head positioned within centimeters of benthic zooplanktivores. The pump collected zooplankton not effectively sampled by conventional net tows or demersal traps. We found consistently greater densities of zooplankton than did earlier studies that used other sampling methods in similar locations. There was no significant difference between winter (3491±578 m^–3) and summer (2853±293 m^–3) zooplankton densities. Both oceanic- and reef-associated forms were found at temporal and spatial scales relevant to benthic suspension feeders. Copepods were always the most abundant group, averaging 89% of the total zooplankton, and most were not of demersal origin. The cyclopoids, Oithona spp., were the numerically dominant organisms, with an average density of 1684±260 m^–3. Other zooplankton (e.g., shrimp larvae, crab larvae, polychaetes, chaetognaths, amphipods, and isopods) were highly variable and much less abundant. Near-reef zooplankton abundances were high throughout the night sampling period, not just after sunset and before sunrise as previously described. Mean biomass was 4.5 mg C m^–3, with values ranging from 1.0 to 15.6 mg C m^–3. This work has important implications for evaluating which zooplankton types are available to benthic suspension feeders, including corals.     

DNA barcoding of Cirripedia larvae reveals new knowledge on their biology in Arctic coastal ecosystems

Hydrobiologia - Pelagic larvae of benthic organisms comprise a substantial part of the coastal Arctic zooplankton community in spring–summer. We studied the timing, growth, and pelagic...     

Zooplankton in Svalbard fjords on the Atlantic–Arctic boundary

Zooplankton abundance and community structures were studied in three west Spitsbergen fjords at the beginning of the warm phase, which seem to have entered in 2006. Sampling was conducted in summer 2007 at stations distributed along transects in Hornsund, Isfjorden and Kongsfjorden. Variations in zooplankton standing stocks and community structures (assessing taxonomic diversity and zoogeographical affiliations) were analysed in relation to the environmental variables using multivariate techniques. The hydrographic conditions in Hornsund were influenced by the cold Arctic Water, whereas those in Isfjorden and especially in Kongsfjorden were, to a greater extent, under the influence of the warm Atlantic Water. High abundances of both meroplankton and holoplankton organisms were observed in Kongsfjorden, with high contributions of boreal and ubiquitous species (Calanus finmarchicus and Oithona similis, respectively). In Hornsund at the same time, the zooplankton consisted mainly of boreo-Arctic and Arctic species, the abundances of which were comparable along the West Spitsbergen Shelf. Our results indicate that the difference in hydrography had measurable effects on the zooplankton community in the study area. Furthermore, by comparing regions of contrasting oceanographic conditions, we present evidence as to how the zooplankton structure will change in the Arctic ecosystems if the warming trends continue to operate with the same dynamics. The advection of Atlantic waters to the Arctic seas may lead to changes in zooplankton structure, with increased abundance and contributions of boreal and small ubiquitous species. The ‘warmer Arctic fjords’ scenarios may also induce more rapid development of both holoplankton and meroplankton populations and, consequently, modify the trophic interactions in plankton communities.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.     

Lipid‐rich zooplankton subsidise the winter diet of benthivorous Arctic charr (Salvelinus alpinus) in a subarctic lake

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Winter ecology of Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>) and brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis>) in a subarctic lake,Norway

We studied habitat choice, diet, food consumption and somatic growth of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) during the ice-covered winter period of a subarctic lake in northern Norway. Both Arctic charr and brown trout predominantly used the littoral zone during winter time. Despite very cold winter conditions (water temperature <1°C) and poor light conditions, both fish species fed continuously during the ice-covered period, although at a much lower rate than during the summer season. No somatic growth could be detected during the ice-covered winter period and the condition factor of both species significantly declined, suggesting that the winter feeding rates were similar to or below the maintenance requirements. Also, the species richness and diversity of ingested prey largely decreased from summer to winter for both fish species. The winter diet of Arctic charr <20 cm was dominated by benthic insect larvae, chironomids in particular, and Gammarus lacustris, but zooplankton was also important in December. G. lacustris was the dominant prey of charr >20 cm. The winter diet of brown trout <20 cm was dominated by insect larvae, whereas large-sized trout mainly was piscivorous, feeding on juvenile Arctic charr. Piscivorous feeding behaviour of trout was in contrast rarely seen during the summer months when their encounter with potential fish prey was rare as the small-sized charr mainly inhabited the profundal. The study demonstrated large differences in the ecology and interactions of Arctic charr and brown trout between the winter and summer seasons.     

Evolution saisonniere du zooplancton dans trois sites peu profonds de Thau,une lagune Nord-Mediterraneenne

A monthly zooplankton survey has been conducted from March 1982 to March 1983 at three shallow stations of Thau, a northern-mediterranean lagoon. These stations differ by their distance from the entry of sea-water in the lagoon. Parameters such as pH, temperature, dissolved oxygen, conductivity and turbidity have been measured simultaneously with the sampling in the same water layer. The zooplankton collected corresponds to species usually found in marine neritic communities. In the spring, species richness is maximum. During the summer, meroplankton forms dominant populations in the communities. Autumn is marked by a reduction of the number of species and of the abundance in both components, holoplankton and meroplankton. Few species are present in the winter holoplankton while meroplankton disappears practically from the samples. The sites under observation are subjected to unpredictable changes, in water movement as well as in the organization of the zooplankton communities. These modifications are strongly influenced by weather conditions.     

Seasonal Patterns of Abundance: Do Zooplankton in Small Ponds do the Same Thing Every Spring–Summer?

Small ponds ( ≤ 2 ha) are often a common landscape feature, but their ecology has been less well studied than that of lakes. Studies of some lakes and reservoirs show among-year repeatability in the seasonal abundance of different zooplankton (i.e., succession). For small ponds the seasonal dynamics of zooplankton community structure are relatively unstudied, as are any mechanisms underlying these dynamics. We took a community-level approach to studying the spring–summer abundance of zooplankton in two small Ohio ponds. In particular we wanted to know if repeatable patterns exist for zooplankton community structure in these ponds. We surveyed the spring–summer zooplankton communities in the ponds from 2001 to 2003 and used community-level ordination techniques (i.e., non-metric multidimensional scaling, NMDS) to characterize the assemblages. For both ponds the seasonal pattern of total zooplankton abundance differed significantly among years. We found that the proportional abundance of taxa across the season also varied among years. Elements of the zooplankton community, as described by the NMDS dimensions, showed among-year variation in the spring–summer trajectories that developed. Some of the variation in these zooplankton communities was associated with seasonal changes in water temperature. This among-year variation in the seasonal pattern of zooplankton community structure suggests that community dynamics in these small ponds may not be very repeatable. These complex dynamics of zooplankton thus challenges us to improve our characterization of zooplankton communities in small ponds such that we can better understand the factors that drive the patterns we observe.     

Evidence of spatial and temporal changes in sources of organic matter in estuarine sediments: stable isotope and fatty acid analyses

We investigated spatial and temporal changes in sources of organic matter in sediments within an estuarine environment in South Africa using fatty acids (FA) and stable isotopes (SI). Samples of sediments and sources of organic matter [i.e., particulate organic matter, microphytobenthos (MPB), macrophytes, salt marsh plants, and terrestrial leaves] were collected during spring and summer 2012, and autumn and winter 2013 from the upper, middle, and lower reaches. A Stable Isotope Analysis in R (SIAR) mixing model was used to identify the organic matter sources contributing to sediments in each estuarine reach and season. We found that diatom-associated fatty acids (20:5ω3; 16:1ω7) increased toward the upper reaches, while long-chained terrigenous fatty acids (24:0) tended to be more prevalent in lower reach sediments. In support of the FA results, the SI mixing model showed a substantial contribution from the marsh grass Spartina maritima in sediments of the lower estuary during periods of low-freshwater discharge (autumn and winter), while MPB was the main component in sediments from the upper and middle reaches during all seasons. Our results have implications for evaluating estuarine food webs since the spatial and seasonal variability in the organic matter deposited can influence estuarine community structure.     

Benthic algae support zooplankton growth during winter in a clear-water lake

We used stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ¹³C values of calanoid ( Eudiaptomus graciloides ) and cyclopoid ( Cyclops scutifer ) zooplankton in autumn suggest a food resource of pelagic origin during the ice-free period. The zooplankton δ¹³C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ¹³C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ¹³C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ¹⁵N of the C. scutifer food resource during winter was low compared to δ¹⁵N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via ¹⁵N-depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi-chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.     

中国近海浮游动物群落结构及季节变化

2006年7-8月、12月-2007年2月、2007年4-5月、2007年10-12月,对中国近海进行了4个航次生物、化学和水文等专业综合调查.根据采集的浮游动物样品分析鉴定结果,对中国近海浮游动物群落结构、种类组成及优势种的季节变化进行研究.结果表明,中国近海浮游动物有1330种,隶属于7门19大类群,浮游幼体47类,其中,节肢动物为最优势类群,有782种,占58.80％,其次为刺胞动物,有324种,占24.36％.在浮游动物群落结构中,4个海区均以桡足类和水母类的种类和数量占绝对优势.中国近海4个海区浮游动物种类数有明显季节变化,渤海和黄海,浮游动物种类数夏、秋季多于春、冬季;东海和南海,浮游动物种类数春、夏季多于秋、冬季.中国近海浮游动物群落大体可划分为6个主要生态类群:近岸低盐类群、低温高盐类群、高温高盐类群、低温广盐类群、高温广盐类群和广温广盐类群.结合同步调查的其它生物、水文、化学环境参数的分析结果,对中国近海浮游动物群落种类丰度与环境因子进行生物与环境变量关系分析,结果表明,浮游动物群落结构与水温、盐度、水深、溶解氧、硝酸盐和pH存在明显相关关系.水温和盐度是影响浮游动物群落结构最重要的两个环境因子.     

Oceanic habitat differences in The North Pacific

A pronounced faunal boundary and a gradient of Zooplankton biomass exist in the oceanic North Pacific. A summer and a winter set of observations were taken on transects normal to these latitudinal boundaries. The resulting data have been analysed both in terms of the measured variables from either side of the boundary area and of their interrelationships. Great differences between three major habitats in concentrations of nutrients, standing crops of phyto- and Zooplankton, average temperatures and average salinities have been demonstrated. Furthermore, the type of seasonal changes in these variables differed between habitats. In general, variations in Zooplankton abundance are related to plant abundance in the summer and phosphate-phosphorus in the winter. Horizontal and vertical temperature gradients are not strongly related to variations in Zooplankton abundance nor is the dissolved plus particulate organic carbon concentration; however, there is evidence that the dissolved plus particulate organic carbon does not behave as a conservative property either within or below the mixed layer. There appear to be some qualitative differences in fundamental ecological processes between these habitats.     

Mesocosm experiments: mimicking seasonal developments of microbial variables in North Sea sediments

This study investigated the suitability of mesocosms for studying the seasonal development of microbial variables in the benthic system of the North Sea. Undisturbed sediment cores were taken from two locations in the North Sea, one with sandy sediment (28 m depth) and the other with silty sediment (38 m depth) and installed in mesocosms in January–April 1989. Cores were kept as in situ temperature in the dark until December 1989. One set of sandy and silty sediments was starved and the other set received a supply of organic matter in May–June, simulating the settlement of the spring bloom of Phaeocystis pouchetii. Seasonal developments in bacterial production (methyl ³H-thymidine incorporation), abundance and biomass of bacteria and nanoflagellates and oxygen consumption were compared between the mesocosms and the field in surface sediments every 1.5 to 2.5 months. Effects of seasonal temperature variations (range 6–17.5 °C) on microbial variables in starved mesocosms were limited, which possibly indicates a subordinate role of temperature in microbial processes in North Sea sediments. Organic matter produced a direct response in bacterial production and oxygen consumption in mesocosms. Bacterial and protozoan abundance also increased. The effect of the organic input disappeared within 2 months and values of enhanced variables declined to initial levels. The organic matter enrichment in mesocosms apparently did not provide sufficient energy to keep the microbenthos active at field levels through summer.These results suggest that in the silty sediments in the field, organic matter is available for bacterial production throughout summer. In sandy sediments, the major organic matter input, which sets the seasonal pattern, appears to be in June. Apparently the seasonal development of microbial variables can be mimicked in mesocosms with organic matter supplies. Differences between the field and mesocosms are further illustrated by carbon budgets. Recycling of bacterial biomass was required to meet the bacterial carbon demand in the budget.Publication No. 22 of the project Applied Scientific Research Neth. Inst. for Sea Res. (BEWON).