Seagrass (Zostera spp.) as food for brent geese (Branta bernicla): an overview

Brent geese (called brant in North America) are among the smallest and the most marine of all goose species, and they have very long migration routes between high Arctic breeding grounds and temperate wintering grounds. Like all other geese, brent geese are almost entirely herbivorous. Because of these ecological characteristics they have a high food demand and are strongly dependent on stopover sites to ”refuel” during the migration period. Three subspecies of brent geese are distributed around the Holarctic, forming seven populations with distinct migration routes. Most or all of these populations make heavy use of Zostera spp. during migratory stopovers on spring and/or autumn migration. Examples of Zostera stopover areas being used by large numbers of brent geese for several weeks each year are Izembek Lagoon (Alaska), lagoons in Baja California, the German/Danish Wadden Sea, the Golfe du Morbihan (France), British estuaries, and the White Sea (Western Russian Arctic). Brent geese feed on Zostera wherever they can, but they can only reach the plants at low tide or in shallow water. Changes in Zostera abundance affect brent goose distribution, and the ”wasting disease” affecting Atlantic Zostera stocks during the 1930s was at least partly responsible for a steep decline in brent goose population sizes on both sides of the Atlantic. While Zostera is of outstanding importance as food for brent geese, the impact of the geese on Zostera stocks seems to be less important – at many sites, the geese consume only a small amount of the available Zostera, or, if they consume more, the seagrass can regenerate fully until the following season. Received: 6 December 1998 / Received in revised form: 6 August 1999 / Accepted: 9 August 1999     

A review of research on the interactions between dugongs (<Emphasis Type="Italic">Dugong dugon</Emphasis> Müller 1776) and intertidal seagrass beds in Indonesia

Research on dugong–seagrass interactions in Indonesia was done during the period 1990 until 2005 in respectively East Aru, Maluku Province and East Kalimantan, Indonesia. This research investigated intensive rotational grazing by dugongs in intertidal inshore Halodule univervis seagrass meadows, dugong movements in relation to these grazing swards, and analyses of parameters explaining the temporal and spatial patterns of grazing in these meadows. In this paper, we report the findings of this long-term study. The patterns of movement and the results of snorkelling surveys confirmed a practice of regular recropping of restricted grazing swards by small feeding assemblages of dugongs. Dugong grazing showed a significant correlation with carbohydrate content of the below-ground biomass and no significant relation with total N. The timing of dugong grazing in these intertidal meadows coincides with high below-ground biomass and high carbohydrate content in the rhizomes of H. uninervis in the upper 0–4 cm sediment layer. Our findings support the hypothesis that temporal dugong grazing is ruled by carbohydrate content in below-ground biomass. The mechanisms of rotational grazing in restricted grazing swards are not yet well understood, and the maximisation of carbohydrates does not fully explain this phenomenon. Our research confirms that intertidal H. univervis seagrass meadows form a crucial resource for dugong survival. These relatively unknown biotopes need therefore more attention in research and conservation programmes.     

Interactions between hare and brent goose in a salt marsh system; evidence for food competition?

In this study we accumulate evidence that brown hare competes with brent goose for food resources in a temperate salt marsh. We show that both species overlap in habitat use and share food plants. The two herbivores mainly used the common habitat at different times of the day, with hares active in the dark and geese during the daylight. During the morning and evening, however, the habitat was exploited simultaneously. Food availability was manipulated by excluding brent geese on both small-scale (30 m²) and large-scale (0.96 ha) plots, while hares had free access everywhere. Exclusion of brent geese enhanced the level of utilisation by hares in both Festuca and Puccinellia dominated marshes, which are among the most intensively grazed parts of the salt marsh. The increase in hare grazing pressure following goose exclusion was stronger, when the adjacent control plots had attracted more goose visitation. When geese were excluded, the decrease in Festuca consumption by geese was completely matched by increased hare grazing, while for Puccinellia only part of the `surplus' was harvested. Enhanced levels of hare utilisation were not due to geese interfering directly with hare, nor due to hares avoiding goose droppings. Considering the interaction from the other perspective, hares were observed to disturb geese effectively in every spring. This might have reduced exploitation by geese of the shared resources. On the basis of our experimental results, we conclude that in this salt- marsh system competition for food with brent geese plays a role in the habitat use of hares, and that hares can reduce goose exploitation of shared habitats. Received: 30 March 1998 / Accepted: 6 July 1998     

Pattern and process in above-ground and below-ground components of grassland ecosystems

Abstract. This paper describes patterns of below-ground components in grassland ecosystems. It provides estimates of the contribution of below-ground organs to the total phytomass of the community and of different species to the below-ground phytomass; it describes the distribution of above- and below- ground organs of different species and the spatial and temporal correlation between above-ground and below-ground phyto-mass – both total standing crop and net primary production. 10 Siberian grasslands (meadows and steppes) were investigated during 15 yr. Ca. 70 % of the living phytomass is located in the soil and no less than 70 % of the net primary production is allocated in below-ground organs. Phytomass distribution in the soil layer is more homogeneous than above-ground. For some species the spatial distribution within 1-m² plots of the green and below-ground phytomass is similar, for others it is quantitatively or qualitatively different. According to the dominance-diversity curve, the above-ground size hierarchy is much stronger than the below-ground one. The active growth of above- and below-ground organs of a species may occur at different times of the season and it varies from year to year. Allocation of organic substances to rhizomes and roots occurs simultaneously and with proportional intensity.     

Decline of Canada geese (Branta canadensis) and common goldeneye (Bucephala clangula) associated with a collapse of eelgrass (Zostera marina) in a Nova Scotia estuary

Mean numbers of migrant Canada geese (Branta canadensis) in Antigonish Harbour in the southern Gulf of St. Lawrence (Canada) during October to December were similar (approx. 450–500 birds) for the period 1998–2000. Similarly, during this period, geese used two foraging sites. However, in 2001, the average number of birds decreased by half and the primary foraging sites were used only rarely. This coincided with a decline of about 95% in the biomass of roots and rhizomes of eelgrass (Zostera marina) that occurred between October 2000 and 2001. Eelgrass is the principal food of geese in this estuary. In addition, there was a reduction of around 50% in the numbers of common goldeneye (Bucephala clangula), which feed on invertebrates associated with eelgrass. Lower than usual weekly abundances of geese and goldeneye are probably the result of an unusually short residence time in the estuary, rather than a decline in the total number of visiting migrants. We attribute these changes in the distribution and abundance of geese and goldeneyes to the dramatic decline in eelgrass. Electronic Publication     

Dark-bellied brent geese Branta b. bernicla breeding near snowy owl Nyctea scandiaca nests lay more and larger eggs

Several studies have demonstrated that snowy owls Nyctea scandiaca defend an area around their nests against predators, hereby inadvertently creating safe havens for breeding dark-bellied brent geese Branta b. bernicla . However, studies investigating brent goose breeding ecology within the predator-exclusion zones of the snowy owls are absent. In 1999 and 2005, years of high lemming abundance Lemmus sibiricus and Dicrostonyx torquatus , brent geese were primarily breeding in association with snowy owls in the Medusa river catchment on western Taimyr, Russia. Goose nest failure, either as a result of nest abandonment by the adult birds or of nest depredation, increased with increasing distance from the owl nests. Within the brent goose colonies, clutch size as well as egg size increased with decreasing distance from the snowy owl nest, indicating an increasing adult quality closer to owl nests. However, as a result of the abandonment of eggs and goslings, the increasing clutch size did not result in a higher nest success during this study. Apparently brent geese compete for breeding sites close to owl nests, but details of this process remain unknown.     

Diurnal changes in pore water sulfide concentrations in the seagrass Thalassia testudinum beds: the effects of seagrasses on sulfide dynamics

The dynamics of the seagrass-sulfide interaction were examined in relation to diel changes in sediment pore water sulfide concentrations in Thalassia testudinum beds and adjacent bare areas in Corpus Christi Bay and lower Laguna Madre, Texas, USA, during July 1996. Pore water sulfide concentrations in seagrass beds were significantly higher than in adjacent bare areas and showed strong diurnal variations; levels significantly decreased during mid-day at shallow sediment depths (0-10 cm) containing high below-ground tissue biomass and surface area. In contrast, diurnal variations in sediment sulfide concentrations were absent in adjacent bare patches, and at deeper (>10 cm) sediment depths characterized by low below-ground plant biomass or when the grasses were experimentally shaded. These observations suggest that the mid-day depressions in sulfide levels are linked to the transport of photosynthetically produced oxygen to seagrass below-ground tissues that fuels sediment sulfide oxidation. Lower sulfide concentrations in bare areas are likely a result of low sulfate reduction rates due to low organic matter available for remineralization. Further, high reoxidation rates due to rapid exchange between anoxic pore water and oxic overlying water are probably stimulated in bare areas by higher current velocity on the sediment surface than in seagrass beds. The dynamics of pore water sulfides in seagrass beds suggest no toxic sulfide intrusion into below-ground tissues during photosynthetic periods and demonstrate that the sediment chemical environment is considerably modified by seagrasses. The reduced sediment sulfide levels in seagrass beds during photosynthetic periods will enhance seagrass production through reduced sulfide toxicity to seagrasses and sediment microorganisms related to the nutrient cycling.     

Effect of Planting Unit Size and Sediment Stabilization on Seagrass Transplants in Western Australia

Abstract The effect of increasing planting unit size and stabilizing sediment was examined for two seagrass planting methods at Carnac Island, Western Australia in 1993. The staple method (sprigs) was used to transplant Amphibolis griffithii (J. M. Black) den Hartog and the plug method was used to transplant A. griffithii and Posidonia sinuosa Cambridge and Kuo. Transplant size was varied by increasing the number of rhizomes incorporated into a staple and increasing the diameter of plugs. Planting units were transplanted into bare sand, back into the original donor seagrass bed, or into a meadow of Heterozostera tasmanica, which is an important colonizing species. Sprigs of A. griffithii were extracted from a monospecific meadow; tied into bundles of 1, 2, 5, and 10 rhizomes; and planted into unvegetated areas. Half the units were surrounded by plastic mesh and the remainder were unmeshed. All treatments were lost within 99 days after transplanting, and although larger bundles survived better than smaller ones, no significant differences could be attributed to the effects of mesh or sprig size. Plugs of P. sinuosa and A. griffithii were extracted from monospecific meadows using polyvinyl chloride pipe of three diameters, 5, 10, and 15 cm, and planted into unvegetated areas nearby. Half the units were surrounded by plastic mesh and the remainder were unmeshed. Posidonia sinuosa plugs were also placed within a meadow of H. tasmanica (Martens ex Aschers.) den Hartog. Only 60% of A. griffithii plug sizes survived 350 days after transplanting back into the donor bed; however, survival of transplants at unvegetated areas varied considerably, and analysis of variance indicated a significant two‐way interaction between treatment and plug size. Transplants survived better when meshed (90% survived) and survival improved with increasing plug size. Posidonia sinuosa transplants survived poorly (no plugs survived beyond 220 days in bare or meshed treatments) regardless of size. Survival of 10‐ and 15‐cm plugs was markedly better than the 5‐cm plugs in vegetated areas, including the H. tasmanica meadow. The use of large seagrass plugs may be appropriate for transplantation in high‐energy wave environments.     

Effects of changes in seagrass shoot density and leaf height on the abundance of juveniles of Acentrogobius pflaumii in a Zostera marina bed

The effects of changes in the structural complexity of a seagrass (Zostera marina) habitat on the density of juveniles of the streaked goby, Acentrogobius pflaumii, were investigated by field experimentation at Moroiso Bay, Miura Peninsula, Japan. The experimental design, which included seven treatments plus a control, included reduction of seagrass shoot densities and leaf heights as well as complete removal of seagrass. Throughout the study period, juvenile densities remained similar among the experimental quadrats, including the completely cleared quadrat. On the other hand, juveniles did not appear over the bare sandy substratum surrounding the experimental seagrass bed. Within the bed, prey densities were high, being similar among the experimental quadrats, whereas prey were relatively scarce over the surrounding bare substratum. This result suggested that streaked goby juveniles were not attracted to the structure of the Zostera bed per se and that their distribution patterns may be determined by other factors, such as prey availability. Received: September 25, 2000 / Revised: November 22, 2000 / Accepted: January 16, 2001     

Decomposition and nitrogen dynamics of turtle grass (<Emphasis Type="Italic">Thalassia testudinum</Emphasis>) in a subtropical estuarine system

Seagrass beds are pivotal in the functioning of coastal ecosystems in terms of productivity, organic matter turnover and nutrient cycling. Aiming to document decay and nitrogen (N) dynamics of turtle grass (Thalassia testudinum) in a subtropical estuarine system, decomposition patterns of leaves and rhizomes were characterized and compared. Nitrogen usage during decomposition of tissues, and of live tissues and epiphytes growing on live leaves, was also quantified and compared. Stable isotope ratios allowed tracing N within the seagrass bed, following N incorporation into seagrass tissues from the surrounding media (water, sediment). Leaves had a higher N content and decomposed at a faster rate (~6.4 times) compared to rhizomes. Leaching of soluble materials explain the rapid (0–3 days) initial mass loss of leaves (20%) and rhizomes (18%); with a loss of 85 and 56%, respectively, by the end of the study (77 days). Overall, leaves released N while rhizomes immobilized it. Nitrogen concentration was significantly different among live tissues. The main source of N for both seagrass tissues was the sediment, and water column for epiphytes. Differences in decomposition rates among seagrass tissues can be explained by the quality of the substrate and its susceptibility to microbial use. Seagrass leaves and rhizomes are equally important in taking up nutrients from either the water column or the sediments. This study provides a platform to study energy and matter transfers through detrital foodwebs linked to seagrass meadows.     

Above- and below-ground phytomass and net primary production in boreal mire ecosystems of Western Siberia

We measured phytomass stock and production in Western Siberian mire ecosystems (palsa, ridge, oligotrophic and mesotrophic hollows, fen). To determine the contribution of different phytomass fractions into total production, we developed a method to estimate below-ground production (BNP). Standing crop of living above-ground phytomass on treeless plots varied from 300 to 660 g m⁻², reaching maximum on palsa, where 81% of phytomass consisted of Sphagnum mosses and lichens. In the hollows and the fen, Sphagnum percentage varied from 70 to 95%. Standing crop of living below-ground phytomass varied from 325 to 1,210 g m⁻². It consisted of woody stems, stem bases, rhizomes and roots, with the latter contributing from 30 to 60%. Total production of mire ecosystems in northern taiga of Western Siberia ranged from 350 to 960 g m⁻² year⁻¹ and depended on microtopography of the ecosystem (the presence of permafrost and water table depth). Production of treeless plant communities located on the elevated sites depended on the presence of permafrost: in comparison with the ridge, palsa production was lower. Production on the low sites increased with increase pH and reached maximum (960 g m⁻² year⁻¹) in poor fens. Bryophytes were the major producers above ground. Their production varied from 100 to 272 g m⁻² year⁻¹ and reached maximum on ridges. BNP contributed 37–66%, increasing due to increased contribution of sedges.     

Ecosystem engineering by seagrasses interacts with grazing to shape an intertidal landscape

Self-facilitation through ecosystem engineering (i.e., organism modification of the abiotic environment) and consumer-resource interactions are both major determinants of spatial patchiness in ecosystems. However, interactive effects of these two mechanisms on spatial complexity have not been extensively studied. We investigated the mechanisms underlying a spatial mosaic of low-tide exposed hummocks and waterlogged hollows on an intertidal mudflat in the Wadden Sea dominated by the seagrass Zostera noltii. A combination of field measurements, an experiment and a spatially explicit model indicated that the mosaic resulted from localized sediment accretion by seagrass followed by selective waterfowl grazing. Hollows were bare in winter, but were rapidly colonized by seagrass during the growth season. Colonized hollows were heavily grazed by brent geese and widgeon in autumn, converting these patches to a bare state again and disrupting sediment accretion by seagrass. In contrast, hummocks were covered by seagrass throughout the year and were rarely grazed, most likely because the waterfowl were not able to employ their preferred but water requiring feeding strategy ('dabbling') here. Our study exemplifies that interactions between ecosystem engineering by a foundation species (seagrass) and consumption (waterfowl grazing) can increase spatial complexity at the landscape level.     

Seasonal patterns of partitioning and remobilization of 14C in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, ¹⁴C-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of ¹⁴C allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of ¹⁴C recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of ¹⁴C exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and ¹⁴C fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this ¹⁴C was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.     

Gap Dynamics in a Seagrass Landscape

We investigated gap dynamics within a shallow subtidal landscape characterized by seagrass vegetation and examined the relationship between gap formation and selected physical factors. The study was conducted over 2 y by using a biannual mapping of seagrass and water depth across an 48,800-m² area in Tampa Bay, Florida. In addition, monthly sediment deposition or erosion was recorded at 96 locations within the landscape. Gaps represented from 2.4% to 5.7% of the seagrass landscape, and all were within monospecific stands of Halodule wrightii. Gaps ranged in size from 10 to 305 m² and most frequently decreased in size over time. Most gaps were small and short lived (less than 6-mo duration), but the second age group most frequently recorded was at least 1.5 y old. No new species of seagrass invaded the gaps with Halodule replacing itself 100% of the time. Gaps were recorded over the entire range of water depths within the landscape. Neither gap area nor persistence of gaps was related to water depth. However gap area was associated positively with the number of extreme sedimentation events. Gaps originated not only from removal of interior vegetation (similar to classic gaps) but also from differential growth of the seagrass margin (similar to edaphic gaps). Distinct seasonal components to the mode of formation were detected with interior-produced gaps originating primarily in the winter and margin gaps most commonly during summer. These results combine to illustrate the importance of large-scale studies with fine-scale resolution for deciphering unique features of seagrass landscape dynamics. Our historical information suggests that a static enumeration of gaps may not provide an accurate assessment of disturbance intensity in this system, and the seagrass mosaic probably is explained best by a combination of disturbance regimes and edaphic factors, such as sediment stability. Moreover, we suggest that even in areas characterized by monospecific stands of vegetation and over short or moderate time periods, gaps indirectly may influence community structure and ecosystem function via modification of habitat arrangement. Received 17 September 1998; accepted 26 April 1999.     

Aggregative responses of brent geese on salt marsh and their impact on plant community dynamics

The aggregative responses and habitat preferences of a generalist herbivore, the dark-bellied brent goose Branta bernicla bernicla, feeding on salt marshes are examined in relation to vegetation community characteristics and the abundances of individual plant species. In the autumn, feeding was strongly concentrated on the low marsh, which had the highest biomass of the preferred food plant, Salicornia europaea. There was a strong aggregative response of the geese to the abundance of S. europaea. A decline in the availability of S. europaea led to an increase in the pattern of aggregation in relation to the two other major food plants on the low marsh, Aster tripolium and Puccinellia maritima. The availability of these food plants, however, reached critically low levels in mid-winter and the geese abandoned the low marsh for the high marsh. Within the high marsh, the plant communities selected tended to be dominated by the inedible species Limonium vulgare. The food plants selected were P. maritima in the winter and P. maritima and Triglochinmaritimum in the spring. On the high marsh, aggregative responses were shown to both P. maritima and T. maritimum, but in both cases, aggregation increased up to a critical level of biomass, and then declined. The prevention of grazing with exclosures for 3 years led to an increase in the abundance of P. maritima on both high and low marshes. This change was slight on high marsh but pronounced on low marsh, where S. europaea showed a decrease in abundance in the exclosures over this time. The implications of the aggregative responses for the population dynamics of P. maritima and S. europaea are discussed. Received: 11 September 1997 / Accepted: 12 December 1997     

Habitat switching by dark-bellied brent geese Branta b. bernicla (L.) in relation to food depletion

Seasonal changes in the distribution and feeding behaviour of dark-bellied brent geese Branta b. bernicla (L.) and the biomass of their food plants were studied in three successive winters on the Norfolk coast. The data was used, in conjunction with published information, to show how depletion, productivity and mortality of food plants drive the pattern of habitat switching in this species. It is then possible to explain the habitat shifts observed over the last 35 years and predict future changes. On arrival, geese fed first on algal beds and then on salt marsh, grass and arable fields before returning to feed entirely on the salt marsh in spring. The biomass of green algae, and subsequently the salt marsh vegetation, declined during the autumn and this could be attributed to depletion through goose grazing and natural mortality. As depletion occurred the geese fed more intensively, for a greater percentage of time and with an increasing pace rate, the net result, however, was a declining intake rate (as measured by defaecation rate). The algal biomass at which the geese switched from the algal beds to salt marsh was consistent between years, with heavy storm-induced loss of algae in one year resulting in an earlier switch. That the timing of habitat switches may be explained by depletion of food plants was further supported by historical data: the number of brent geese wintering at the site has increased dramatically over the last 30–35 years and the time of switching from algal beds to salt marsh and from salt marsh to salt marsh and fields has become progressively earlier, as expected from the increased depletion. The expected further increase in brent goose numbers will increase the rate of depletion of intertidal vegetation so that the switches between habitats will be more rapid and the geese will move inland earlier and remain inland longer. The expected increase in the brent goose population will thus result in a disproportionate increase in the levels of conflict between brent geese and agriculture.     

Boat-based videographic monitoring of an Adriatic lagoon indicates increase in seagrass cover associated with sediment deposition

Within the scope of a seagrass monitoring program in the Novigrad Sea, Central Croatian Adriatic, we predicted that the annual variability in coverage of seagrasses (Zostera marina, Zostera noltii, and Cymodocea nodosa) can be partially explained by the annual variability in sediment translocation. From 23 fixed DGPS-referenced monitoring video transects followed over three years (June 2007-2009), we calculated annual (i) changes in interior bed seagrass coverage, (ii) gain in seagrass at the lower edge of the bed and seagrass bed expansion, and (iii) accumulation of sediment, its depth dependence, and the associated changes in transect slope. We found that in 2007 to 2008, the year with net sediment accumulation, seagrass coverage increased and the bed expanded. In both years seagrass cover within the seagrass bed increased with increasing sediment accumulation, while seagrass bed expansion was highest under intermediate sedimentation rates. Boat-based videographic monitoring can document both natural sediment movement along the depth gradient, and species-specific responses necessary for informed management of submerged aquatic vegetation in the Adriatic Sea.     

Does intensive goose grazing affect breeding waders?

Increasing goose population sizes gives rise to conflicts with human socioeconomic interests and in some circumstances conservation interests. Grazing by high abundances of geese in grasslands is postulated to lead to a very short and homogeneous sward height negatively affecting cover for breeding meadow birds and impacting survival of nests and chicks. We studied the effects of spring grazing barnacle geese Branta leucopsis and brent geese Branta bernicla on occupancy of extensively farmed freshwater grasslands by nesting and brood‐rearing waders on the island Mandø in the Danish Wadden Sea. We hypothesized that goose grazing would lead to a shorter grass sward, negatively affecting the field occupancy by territorial/nesting and chick‐rearing waders, particularly species preferring taller vegetation. Goose grazing led to a short grass sward (<5 cm height) over most of the island. To achieve a variation in sward height, we kept geese off certain fields using laser light. We analyzed effects of field size, sward height, mosaic structure of the vegetation, proximity to shrub as cover for potential predators, and elevation above ground water level as a measure of wetness on field occupancy by nesting and chick‐rearing waders. The analysis indicated that the most important factor explaining field occupancy by nesting redshank Tringa totanus, black‐tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus and lapwing Vanellus vanellus as well as by chick‐rearing black‐tailed godwit and lapwing was short vegetation height. Distance to shrub cover and elevation were less important. Hence, despite very intensive goose grazing, we could not detect any negative effect on the field occupancy by nesting nor chick‐rearing waders, including redshank and black‐tailed godwit, which are known to favor longer vegetation to conceal their nests and hide their chicks. Possible negative effects may be buffered by mosaic structures in fields and proximity to taller vegetation along fences and ditches.     

Brent goose colonies near snowy owls: Internest distances in relation to abundance of lemmings and arctic foxes

Brent goose colonies around snowy owl nests have been studied near Medusa Bay (73°21′ N, 80°32′ E) and in the lower reaches of the Uboinaya River (73°37′N, 82°10′E), the northwestern Taimyr Peninsula, from 1999 to 2006. All brent nests within 680 m from an owl nest have been regarded as an individual colony. The results show that the area of the colony is always larger than the protected area around the owl nest. In years of low abundance of lemmings, brent geese nest generally closer to the owl nest than in years of high abundance. When arctic foxes are abundant, however, brent geese nest significantly closer to owls than when the foxes are scarce, irrespective of lemming abundance. The mechanism of brent colony formation around owl nests is based on a number of stimuli.     

微生物参与海草床元素循环及其生态修复功能

海草是分布在全球海岸带的沉水被子植物,与周围环境共同形成的海草床生态系统是三大典型海洋生态系统之一,具有十分重要的生态功能。20世纪以来,全球海草床衰退严重,研究海草床的生态修复迫在眉睫,现有修复方法未能足够重视微生物在海草床中的重要作用。本文综合阐述了微生物在海草床生态系统有机物矿化和营养流动过程中起到的作用,分析了微生物驱动下的海草床水体与沉积物之间的元素循环,提出了人类活动引起海草床退化的原因,总结了海草床微生物的系统研究方法,并在此基础上提出从微生物生态的角度修复海草床的新思路。