Community Grazing Research Articles

Propagule supply controls grazer community structure and primary production in a benthic marine ecosystem

Propagule supply controls grazer community structure and primary production in a benthic marine ecosystem

Plankton community structure during an ecosystem disruptive algal bloom of Prymnesium parvum

The purpose of this paper was to study the plankton food web structure in Lake Koronia during an extremely dense bloom of Prymnesium parvum. The Prymnesium bloom fulfilled the main criteria of an ecosystem disruptive algal bloom, since it was a massive persistent, monospecific bloom which disrupted the dynamics of the plankton community. It appeared after an N-fixing cyanobacterial bloom, when a decrease in temperature and low nitrogen conditions may have caused a positive feedback, which allowed the replacement of cyanobacteria by the invasive Prymnesium. The initiation of the bloom was further facilitated by the disruption of zooplankton grazing, with the biomass of the primary grazers, rotifers and cladocerans, dropping to undetectable levels. Furthermore, the rest of the phytoplankton responded to the onset of the bloom by an 82% decrease. Cyanobacteria and diatoms exhibited the highest decrease in biomass (95 and 99%, respectively) followed by chlorophytes (55% decrease). This enabled the uncontrolled increase of the P. parvum population to numbers close to the highest abundance ever recorded. At that point, the grazing community was reinstated and the system became replete with nutrients with an N:P ratio of 10:1. This coincided with the beginning of the bloom termination, which was followed by an increase in the biomass of competing phytoplankton.

Modelling ungulate dependence on higher quality forage under large trees in African savannahs

In African savannahs, large trees improve grass quality, particularly in dry and nutrient poor areas. Enhanced below-canopy grass nutrients, such as nitrogen and phosphorus contents should therefore attract and benefit grazers. To predict whether ungulates really need these forage quality islands we focused on four grazer species, i.e., zebra, buffalo, wildebeest, and warthog, differing in body size and digestive system. We confronted literature estimations of their feeding requirements with forage availability and quality, observed in three South African savannah systems, through linear modelling. The model predicted the proportion of below-canopy grass that grazers should include in their diet to meet their nutritional requirements. During the wet season, the model predicted that all animals could satisfy their daily nutrient requirements when feeding on a combination of below- and outside-canopy grasses. However, wildebeest, having relatively high nutrient demands, could meet their nutrient requirements only by feeding almost exclusively below canopies. During the dry season, all animals could gain almost twice as much digestible protein when feeding on below – compared to outside-canopy forage. Nonetheless, only warthogs could satisfy their nutrient requirements – when feeding almost exclusively on below-canopy grasses. The other ungulate species could not meet their phosphorus demands by feeding at either site without exceeding their maximum fibre intake, indicating the unfavourable conditions during the dry season. We conclude that grazing ungulates, particularly warthog, zebra, and buffalo, actually depend on the available below-canopy grass resources. Our model therefore helps to quantify the importance of higher quality forage patches beneath savannah trees. The composition of grazer communities depending on below-canopy grasses can be anticipated if grazer food requirements and the abundance of large trees in savannahs are known. The model suggests that the conservation of large single-standing trees in savannahs is crucial for maintenance of locally grazing herbivores. Grosse Bäume in afrikanischen Savannen können, vor allem in trockenen und nährstoffarmen Gebieten, die Grasqualität signifikant verbessern. Eine erhöhte Grasqualität unterhalb des Baumkronenbereichs, wie sie in drei südafrikanischen Savannenlandschaften gemessen wurde, kann demzufolge grasfressende Tierarten anziehen und für diese von großem Nutzen sein. Wir untersuchten als Beispiel vier grasfressende Paarhuferarten, Zebra, Büffel, Gnu und Warzenschwein, die sich durch ihre Körpergröße und ihr Verdauungssystem unterscheiden. Mit Hilfe eines linearen Programm-Modells konnten wir voraus sagen, ob diese grasfressenden Tierarten ihren Nährstoffbedarf während verschiedener Jahreszeiten erfüllen können, wenn sie unterhalb der Baumkronen fressen. Während der Regenzeit konnten alle Tierarten ihren täglichen Nährstoffbedarf decken und profitierten vom nährstoffreichen Gras, das unter Bäumen wuchs. Gnus schienen Schwierigkeiten zu haben, ihren hohen Qualitätsansprüchen zu genügen, aber sie konnten ihren Nährstoffeintrag effektiv erhöhen, wenn sie sich fast gänzlich vom Gras unter Bäumen ernährten. In der Trockenperiode konnten alle Tierarten beinahe zweimal so viel verdaubares Protein zu sich nehmen, wenn sie statt ausserhalb der Baumkronen unter Bäumen frassen. Allerdings waren die Warzenschweine als einzige Spezies in der Lage, ihren Nährstoffbedarf gänzlich zu decken, und dies nur, wenn sie zu 100% unter Bäumen frassen. Demgegenüber konnten die anderen Tierarten ihren Phosphorbedarf nicht decken, ohne den maximal durch ihr Verdauungssystem abbaubaren Fasergehalt zu überschreiten. Wir schließen daraus, dass grasfressende Tierarten, insbesondere Warzenschwein, Zebra und Büffel, effektiver fressen können, wenn sie die vorhandenen Grasressourcen unterhalb der Baumkronen nutzen. Unser Modell kann dazu beitragen, Futterpräferenzen und Grasfresser-Bewegungen vorauszusagen, wenn Futter-Ressourcen räumlich uneinheitlich verteilt sind. In Savannen kann somit die Zusammensetzung der Gemeinschaft der Grasfresser, die in von der Grasqualität unterhalb der Bäume abhängt, vorausgesagt werden, wenn deren Nährstoffbedarf einerseits und der Baumbewuchs andererseits bekannt ist. Unsere Ergebnisse heben die Wichtigkeit der Bäume für den Erhalt von Grasfressern hervor, und wir empfehlen, große Savannenbäume und damit auch die grasfressenden Tierarten zu schützen.

Rural needs: free (range) grazing

SUMMARY India carries a huge livestock population. Small ruminants, namely, goats and sheep, play a vital role in securing the livelihood of small and marginal farmers and landless labourers. Such animals should not be blamed for the ecological degradation, soil erosion and desertification caused by human activities. There is an acute shortage of livestock feeds and fodders in India, and also a large gap between needs and availability, even more so in arid and semi-arid regions. The feeds and fodders available on community grazing land, on the roadside and in forests during the rainy season should be harvested and utilised during the scarcity period. The extensive system of livestock rearing should be replaced with semi-intensive and intensive systems for commercial milk and meat production. Locally available crop residues and agroindustrial by-products should be enriched and utilised for compounding cheaper, complete feeds for livestock as feed pallets and blocks.

Resource utilization by large migratory herbivores of the Athi‐Kapiti ecosystem

AbstractThe goal of the study was to establish whether the changes in land use affect resource utilization by large migratory herbivores in the Athi‐Kapiti ecosystem. Athi‐Kapiti ecosystem comprises Nairobi National Park and the Athi‐Kapiti plains (community livestock grazing grounds). Land use information was obtained from existing literature. Pin frame technique and harvest method were used for plant biomass sampling, while road and foot counts were conducted for migratory large herbivores and livestock within the ecosystem, from November 2003 to May 2004. Emphasis was given to the wildebeest (Connechaetes taurinus), zebra (Equus burchelli) and cattle. Results show that green plant biomass available in the park was significantly different from that on Athi‐Kapiti plains [Wilcoxon (two‐tailed), P < 0.05]. Further analysis showed significant seasonal differences in the park [T test (two‐tailed), P < 0.05]. In the community grazing area, significant monthly and seasonal variations in plant biomass were evident (one way ANOVA, P < 0.05). In summary, more wildebeest were observed on Athi‐Kapiti plains than in the park. The zebra showed monthly variations within the whole ecosystem, resulting in a distinct movement pattern. Plant biomass varied depending on the rainfall, which in turn influenced the movement of migratory herbivores within the ecosystem.

Grazing and nutrients reduce recruitment success of Fucus vesiculosus L. (Fucales: Phaeophyceae)

Coastal eutrophication has resulted in the reduced abundance of the perennial macroalga Fucus vesiculosus L. due to negative effects of increased turbidity, spatial competition, and grazing. We conducted a factorial field experiment to explore the main and interactive effects of three factors on the recruitment success of F. vesiculosus. We manipulated (1) substrate occupancy by offering unoccupied substrates and substrates occupied by a natural assembly of macroalgal spores, periphyton and loose material, (2) nutrient availability by exposing substrates to ambient and enriched nutrient conditions, and (3) herbivory by exclosing the natural herbivore community and enclosing either small ( Hydrobia spp.) or large ( Theodoxus fluviatilis L.) snails. Microrecruit density of F. vesiculosus depended on the density of parent algae in ambient nutrient availability, whereas, under enriched conditions, such dependency disappeared. Microrecruit density was lower on previously occupied than on unoccupied substrates and at enriched rather than ambient nutrient levels. The lowest recruitment success resulted from a combination of these two treatment levels. The microrecruit density of F. vesiculosus decreased sharply with the density of filamentous algae indicating that competition with opportunistic species contributed to poor recruitment success. Microrecruit density did not differ between the grazer exclosure and the natural grazer community treatment level reflecting locally low grazer densities and consequent weak grazing pressure in the study site. However, the enclosure of snails at higher densities that still naturally occur in the nearby areas affected the recruitment success of F. vesiculosus. This effect was dependent on nutrient availability; at ambient levels, snail grazers had only a minor negative effect on microrecruit density whereas under enriched conditions, both snail species negatively affected recruitment success. Thus, instead of reducing competition and thereby benefiting the perennial slow-growing F. vesiculosus, negative grazing effects by both snail species increased under nutrient-enriched conditions.

Interactions between phytoplankton and zooplankton in the hypertrophic Swarzedzkie Lake in western Poland

The hypertrophic Swarzedzkie Lake, Poland, is characterized by high species diversity, abundance and biomass of both phytoplankton and zooplankton (up to 99.5 mg WW L −1 and 817.75 μg DW L −1 , respectively). The community grazing rate calculated with the use of two empirical models, and based on herbivorous crustaceans, peaked in spring and early autumn up to 150.6% of water filtered per day, and was the lowest during winter. Simple statistics revealed a positive correlation between zooplankton biomass and chlorophyll a concentration (r = 0.404, P = 0.033) and between zooplankton abundance and phytoplankton biomass (r = 0.42, P = 0.028). Canonical statistics indicated, however, that the relationship exists only with size groups and/or living forms of a few taxonomical groups of phytoplankton. Redundancy analysis (RDA) confirmed a positive influence of the community grazing rate on micro- and nanoplanktonic Cryptophyceae, but not on the microplanktonic Cyanobacteria, as was suggested by canonical correlation analysis. RDA also indicated a weak negative influence on nanoplanktonic Euglenophyceae and Chlorophyceae exerted by filtering crustaceans. Some taxonomically diverse flagellated nanoplanktonic algae were grazing sensitive, whereas microplanktonic cryptophytes and coenobial green algae were significantly grazing resistant.

Community structure and grazing impact of mesozooplankton during late spring/early summer 2004/2005 in the vicinity of the Crozet Islands (Southern Ocean)

Net sampling within the vicinity of the Crozet archipelago, in the Indian Ocean sector of the Southern Ocean, was conducted during late spring/summer (November 2004-January 2005) to describe the composition, distribution and grazing impact of mesozooplankton, and to investigate their relationships with the prevailing oceanographic regime in the area. The mesozooplankton community was intimately linked with the large-scale physical circulation in the region. To the west and north of the Islands, the sub-Antarctic Front (SAF) presented a strong biogeographic boundary between subtropical and sub-Antarctic species. South and east of the SAF, the mesozooplankton community was dominated by Polar Frontal Zone (PFZ) copepod species. Cluster analysis of mesozooplankton abundance data identified two main communities in the PFZ, termed here Island and Oceanic. Island stations, representing the proposed iron-fertilised productive region north of the archipelago, contained an abundance (mean of 2269 ind m(-3)) of the neritic copepod Drepanopus pectinatus, whose presence indicated that the water had interacted with the Crozet Island shelf at some point. D. pectinatus was present in samples north of Crozet up to the SAF, confirming that water passing the Crozet Islands could be transported, throughout the region to the north. The Oceanic stations, south of the Islands and within the SAF, contained similar mesozooplankton abundances and biovolume to the Island stations suggesting little enhanced impact of the iron-fertilised phytoplankton bloom through the mesozooplankton food web. Copepod community grazing pressure, in both Island and Oceanic stations, during November and December was small ( < 7% of chlorophyll-a standing stock per day, < 35% primary production per day). By January, a phytoplankton bloom had developed at some of the Island stations (up to similar to 3000 mg C m(-2) d(-1)) and grazing pressure was < 1% of chlorophyll-a standing stock per day. At the oceanic stations, primary productivity had reduced from similar to 460 to similar to 200 mg C m(-2) d(-1), typical values for high-nutrient low-chlorophyll (HNLC) waters, and the copepod community grazing pressure had increased to similar to 90% of daily primary productivity. This suggests that a combination of grazing and micronutrient availability controls phytoplankton biomass in HNLC waters to the south of Crozet, while grazing had little impact on the iron- fertilised bloom north of the Crozet Islands. The intense seasonal phytoplankton bloom around Crozet may therefore be exported to the sea floor rather than fuelling the higher trophic levels. (C) 2007 Elsevier Ltd. All rights reserved.

Combating Land Degradation through Participatory Means: The Case of Swaziland

This paper examines a community grazing project to rehabilitate degraded land in Swaziland. Using data from interviews, questionnaires, and focus groups, we show that the ways in which participatory, decentralized approaches to natural resource management play out at the local level are closely linked to national-level power structures. The successes and issues that emerge at different stages of the grazing project reflect local socioeconomic priorities and show how people manage their time and labor according to household livelihood goals. However, the project favored the interests of cattle owners who were already the more socially and politically powerful members of the community. We argue that for participatory natural resource management to be more meaningful to communities, projects should focus on local ecological priorities, rather than addressing the environmental concerns that are rooted within existing dominant power structures. This requires change to social and political relationships across levels and the building of new institutions.

Microzooplankton composition, biomass and grazing rates along the WOCE SR3 line between Tasmania and Antarctica

Microzooplankton species composition and grazing rates on phytoplankton were investigated along a transect between ∼46 and 67°S, and between 140 and 145°E. Experiments were conducted in summer between November 2nd and December 14th in 2001. The structure of the microbial food web changed considerably along the transect and was associated with marked differences in the physical and chemical environment encountered in the different water masses and frontal regions. On average microzooplankton grazing experiments indicated that 91%, 102%, and 157%, (see results) of the phytoplankton production would be grazed in the <200, <20 and <2 μm size fractions, respectively, indicating microzooplankton grazing was potentially constraining phytoplankton populations (<200 μm) along most of the transect. Small ciliates in general and especially oligotrich species declined in importance from the relatively warm, Southern Subtropical Front waters (6.8 μg C/L) to the colder waters of the southern branch of the Polar Front (S-PF), (∼0.5 μg C/L) before increasing again near the Antarctic landmass. Large changes in microzooplankton dominance were observed, with heterotrophic nanoflagellates (HNF), ciliates and larger dinoflagellates having significant biomass in different water masses. HNF were the dominant grazers when chlorophyll a was low in areas such as the Inter-Polar Frontal Zone (IPFZ), while in areas of elevated biomass such as the S-PF and Southern Antarctic Circumpolar Current (SACC), a mix of copepod nauplii and large heterotrophic and mixotrophic dinoflagellates tended to dominate the grazing community. In the S-PF and SACC water masses the tight coupling observed between the microzooplankton grazers and phytoplankton populations over most of the rest of the transect was relaxed. In these regions grazing was low on the >20 μm size fraction of chlorophyll a, which dominated the biomass, while smaller diatoms and nanoplankton in the <20 μm size fraction were still heavily grazed. The lack of grazing pressure on large phytoplankton contributes to this region's potential to export carbon with larger cells known to have higher sinking rates.

Structure and function of the pelagic ecosystem in Young Sound, NE Greenland

An annual carbon budget of the pelagic food web is constructed for a 36 m deep station in Young Sound. Data were collected during a 2-week mid-summer sea-ice covered period in 1999, during the open-water period of 1996, 2003, 2004, 2005 and during winters of 1997 and 2003. The measurements revealed that during sea-ice cover the water column of outer Young Sound was strongly heterotrophic and sustained by organic material advected into the fjord from the open sea. The pelagic community thus originated from the marginal ice zone at the entrance to the fjord. No succession was observed in the plankton community during this period, and the grazing pressure of the dominating zooplankton groups (ciliates, heterotrophic dinoflagellates, meroplankton and copepods) was 10 times higher than primary production, while the bacterial carbon demand was three times higher than primary production.&#x0D; During the open-water period, the grazing community was completely dominated by copepods, which were capable of grazing down the entire primary production. This contrasts with several other investigated Arctic marine pelagic ecosystems further south, where the protozooplankton community is quantitatively more important than copepods. In Young Sound, both zooplankton groups are present simultaneously, and copepods thus act both as competitors for food and as predators in relation to the protozooplankton. On an annual basis, the carbon budget was unbalanced; the total carbon need of the grazers equaled primary production, leaving no room for the estimated bacterial carbon demand, which was of the same size as the carbon demand of the grazers. Thus, Young Sound is a net heterotrophic system relying on import of organic material from the open sea or possibly from land.

Carbon cycling and climate change: Predictions for a High Arctic marine ecosystem (Young Sound, NE Greenland)

This chapter reviews current predictions of future changes in the High Arctic marine ecosystem Young Sound, NE Greenland. A high-resolution regional atmosphere-ocean model predicts an increase in atmospheric temperature of 6–8°C and in precipitation of 20–30% by the end of this century (2071–2100), leading to increased freshwater runoff, thinning of sea ice, and an increase in open-water period from 2.5 months to 4.7–5.3 months. Evaluation of the consequences of enhanced freshwater runoff to the fjord revealed that the mixed layer thickness of the water column will change only marginally, whereas the transport of saltwater from the Greenland Sea to Young Sound below the halocline is predicted to increase considerably due to stimulated estuarine circulation.&#x0D; The thinning of sea ice and the increase in the open-water period is expected to enhance primary productivity in the area due to a c. 50% increase in light availability. The phytoplankton bloom will continue to occur in a sub-surface layer, but as the exchange between the fjord and the Greenland Sea increases, production will benefit from increased import of nutrients. We estimate that primary productivity in the area will have tripled by the end of the century compared with present-day levels. The longer ice-free period will induce a shift in the pelagic food web structure, from a copepod-dominated grazer community to a situation with growing influence of protozooplankton.&#x0D; The increased pelagic production will enhance sedimentation and thus intensify bacterial mineralization at the sea floor along with carbon burial. This will reduce oxygen availability in the sediment and the relative importance of anaerobic degradation will increase. The rise in sedimentation will also improve food availability for the benthic animals and thus stimulate growth and production until a certain threshold, where sulphide released from anaerobic sulphate reduction may become inhibitory. Finally, an increase in the ice-free period will prolong the period in which birds and marine mammals – e.g. walruses – have access to the food-rich coastal area, and thus improve their foraging conditions. All in all, conditions in Young Sound in 2071–2100 are predicted to resemble present-day conditions c. 450 km further south, e.g. Scoresby Sound.

The annual organic carbon budget of Young Sound, NE Greenland

On the basis of data presented in the previous chapters a carbon budget for the respective compartments of the outer region of Young Sound (76 km2) was established. The average and maximum water depth of the region was 76 m and 177 m, respectively. Primary production was mainly related to the activity of phytoplankton (65%), benthic macrophytes (21%) and benthic microphytes (13%), while the contribution sea-ice algae and corallines was negligible (&lt;1%). The pelagic grazing community was completely dominated by copepods, which were capable of consuming 87% of the pelagic primary production.&#x0D; The benthic carbon demand was almost balanced by the measured sedimentation of POC and the benthic primary production. The organic carbon collected in the sediment traps was estimated to consist of 40% terrestrial carbon, 20% fecal pellets, while the rest was poorly defined marine detritus. The benthic sink for settling organic material was dominated by microbial respiration (59%) and only to a minor extent related to macrofauna respiration (15%) and carbon preservation (26%).&#x0D; The total primary production in the region (1119 t C yr-1) only sustained c. 40% the estimated organic carbon demand (2850 t C yr-1). Thus, the independently determined input of TOC (990 t C yr-1) imported to Region 1 from land via freshwater runoff and the TOC import of 1446 t C yr-1 from the Greenland Sea are required to balance the carbon sinks of the net heterotrophic region. A complete balance between the respective compartments cannot be expected, as the various components of the carbon budget are determined independently. The microbial and viral loops remain poorly constrained, as does the carbon demand of the top predators. Only the importance of walrus was quantitatively assessed.

Methodological issues in forestry mitigation projects: a case study of Kolar district

There is a need to assess climate change mitigation opportunities in forest sector in India in the context of methodological issues such as additionality, permanence, leakage and baseline development in formulating forestry mitigation projects. A case study of forestry mitigation project in semi-arid community grazing lands and farmlands in Kolar district of Karnataka, was undertaken with regard to baseline and project scenario development, estimation of carbon stock change in the project, leakage estimation and assessment of cost-effectiveness of mitigation projects. Further, the transaction costs to develop project, and environmental and socio-economic impact of mitigation project was assessed.

Resource partitioning in a grazer guild feeding on a multilayer diatom mat

The gut contents of a guild of invertebrate grazers inhabiting the moss Fontinalis and feeding on epiphytic diatoms in a small Québec stream were analyzed to characterize resource partitioning and food selection. A multivariate approach (RLQ analysis coupled with a revised version of 4th-corner analysis) identified distinct diet patterns among co-occurring grazers. These patterns were mainly explained by differential ingestion of diatoms that differed in their spatial positions within the multilayered periphyton mat. When the size range of available diatoms was large, diet differences were partly explained by diatom size. Comparison of diatoms in grazer guts with diatoms available in the environment indicated selective feeding in different levels of the periphyton mat by grazers. Some grazers (scrapers) fed preferentially on tightly attached diatoms, whereas others (surfers) favored overstory diatoms. Spatial segregation of feeding within the periphyton mat by members of the grazer guild was more evident in a period of potential resource limitation (July) than when food was abundant (May). Our results suggest that all layers/growth forms in the diatom mat are used, resulting in spatial partitioning of the resource when considering the entire grazer community. Therefore, foraging theories already established for other ecosystems are confirmed in the unique context of stream benthos.

Euphausiid population structure and grazing in the Antarctic Polar Frontal Zone — austral autumn 2004

The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region (<25mg Chl a m−2), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 m−3 to 3.1 m−3 and from 0.1mg dry weight m−3 to 8.1mg dry weight m−3 respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). A multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, and (2) restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. Euphausia triacantha had the highest daily ingestion rate, ranging from 1 226.1ng pigment (pigm) ind−1 day−1 to 6 029.1ng pigm ind−1 day−1, whereas the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4–943.0ng pigm ind−1 day−1). The total grazing impact of selected euphausiids ranged from <0.1μg pigm m−2 day−1 to 20.1μg pigm m−2 day−1, corresponding to <0.15% of the areal Chl a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggest that phytoplankton represent a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements.

Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of ∼1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m −2) is similar to phytoplankton production (6–10 g C m −2). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m −2 yr −1. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem. In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m −2 yr −1 is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m −2 yr −1 of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m −2 yr −1 was determined. A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves ( Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.

Recurrent Seasonal Variations in Abundance and Composition of Filamentous SOL Cluster Bacteria ( Saprospiraceae , Bacteroidetes ) in Oligomesotrophic Lake Mondsee (Austria)

The spatial and temporal variation of SOL cluster bacteria was assessed in oligomesotrophic Lake Mondsee and adjacent lakes by fluorescence in situ hybridization over two annual cycles. The filamentous SOL bacteria were present in Lake Mondsee throughout the study period, and the seasonal dynamics of the SOL community were remarkably similar with respect to both abundance and composition in the two consecutive years. Only two of the three SOL subclusters were detected in Lake Mondsee and four connected lakes. These two populations significantly differed in size distribution and demonstrated pronounced but recurrent differences in seasonality and length of period of appearance in Lake Mondsee. Extensive sampling of the lakes in September 2003 revealed low horizontal variation in the composition of the SOL community within Lake Mondsee but marked variations with depth. Between connected habitats pronounced differences in the composition and abundance of the SOL community were detected. The interaction of SOL bacteria with bacterivorous protists, mesozooplankton, and phytoplankton was investigated in order to reveal variables controlling the structure and dynamics of SOL communities. No strong indication for a bottom-up influence of phytoplankton was found, while the estimated community grazing rates of mesozooplankton on SOL bacteria indicated a top-down control of SOL abundance during mesozooplankton peaks in spring and early autumn. Furthermore, species-specific differences in grazing of mesozooplankton on SOL bacteria were observed. In general, the overall composition of SOL communities was controlled by abiotic factors (water chemistry), while their dynamics seemed to be controlled by abiotic and biotic interactions.

A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale

Odontogriphus omalus was originally described as a problematic non-biomineralized lophophorate organism. Here we re-interpret Odontogriphus based on 189 new specimens including numerous exceptionally well preserved individuals from the Burgess Shale collections of the Royal Ontario Museum. This additional material provides compelling evidence that the feeding apparatus in Odontogriphus is a radula of molluscan architecture comprising two primary bipartite tooth rows attached to a radular membrane and showing replacement by posterior addition. Further characters supporting molluscan affinity include a broad foot bordered by numerous ctenidia located in a mantle groove and a stiffened cuticular dorsum. Odontogriphus has a radula similar to Wiwaxia corrugata but lacks a scleritome. We interpret these animals to be members of an early stem-group mollusc lineage that probably originated in the Neoproterozoic Ediacaran Period, providing support for the retention of a biomat-based grazing community from the late Precambrian Period until at least the Middle Cambrian.

Effect of dissolved domoic acid on the grazing rate of krill Euphasia pacifica

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 312:169-175 (2006) - doi:10.3354/meps312169 Effect of dissolved domoic acid on the grazing rate of krill Euphausia pacifica Sibel Bargu1,*, Kathi Lefebvre2, Mary W. Silver1 1Department of Ocean Sciences, University of California at Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA 2NOAA Fisheries/NWFSC, 2725 Montlake Boulevard East, Seattle, Washington 98112, USA *Email: sibelbargu@hotmail.com ABSTRACT: Some amino acids released from phytoplankton into the water are known to be feeding stimulants to zooplankton. However, domoic acid (DA), a neuroexcitatory amino acid released by some species of the diatom genus Pseudo-nitzschia, has the potential to be a feeding deterrent due to its neurotoxicity. Euphausiids (krill) are important members of the zooplankton grazer community and key prey items for many high level carnivores in the world’s oceans. Although it is known that krill do consume toxic Pseudo-nitzschia spp. during blooms, there is currently no information concerning the effect of dissolved DA on the rate of feeding or the grazing behavior of krill. Therefore, we conducted experiments in which Euphausia pacifica were fed non-toxic P. pungens along with different added levels of either dissolved DA or glutamic acid (GA), an amino acid with a similar structure to DA. Krill grazing rates did not change significantly with added GA, but decreased significantly in the presence of DA. The rapid response of krill to dissolved DA suggests that either direct toxic action on the filtering apparatus or a chemoreceptor-like mechanism may suppress grazing in the krill. We suggest that these dissolved DA concentrations are relevant, given the DA concentrations found in Pseudo-nitzschia spp. populations in Monterey Bay and the feeding biology of krill. In either case, the suppression of feeding by dissolved DA suggests that high dissolved DA concentrations, should they occur in the field, may be a mechanism whereby blooms are perpetuated due to reduced losses to grazers such as krill. KEY WORDS: Dissolved amino acid · Domoic acid · Glutamic acid · Pseudo-nitzschia · Krill · Euphausia pacifica · Feeding response Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 312. Online publication date: April 24, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.