The detection of vegetational change by multitemporal analysis of LANDSAT data: the effects of goose foraging

1 The North American mid-continent population of lesser snow geese now exceeds 3 million birds and the population is increasing in the order of 7% per annum. The foraging activities of the birds on Arctic breeding grounds are leading to loss of vegetation and habitat destruction, particularly in coastal areas bordering the Hudson and James Bays.
2 Multitemporal analysis of LANDSAT data has been carried out to detect vegetational change from 1973 to 1993 at La Pérouse Bay and its vicinity, the site of a breeding colony of snow geese.
3 Difference vegetation images (DVI) (difference between infra-red and red images) were prepared from images obtained in late summer in 1973, 1984 and 1993, in order to enhance vegetation density. Pair-wise differences were calculated between these DVI images, which resulted in three, secondary, classified images. Classification of the three secondary images (1973–84, 1984–93, 1973–93) yielded three well-defined classes: water, vegetation decline and no change in vegetation.
4 Histogram counts gave the following values for areas of vegetation decline: 1973–84, 1026 ha; 1984–93, 1428 ha; 1973–93, 2454 ha.
5 The loss of vegetation and the destruction of habitat are discussed in relation to the foraging activities of the expanding goose population.     

RESPONSE OF PACIFIC WALRUSES TO DISTURBANCES FROM CAPTURE AND HANDLING ACTIVITIES AT A HAUL-OUT IN BRISTOL BAY, ALASKA

Observations were made on herds of the Pacific walrus ( Odobenus rosmarus divergens ) to study their response during the capturing and handling of adult males in summer 1995 at a haul-out at Cape Peirce in southwestern Alaska. Three behaviors (alertness, displacement, and dispersal) were quantified from 16 capture sessions. Herd sizes ranged from 622 to 5,289 walruses. Handling of an immobilized walrus consisted of attempts to attach telemetry devices to the tusks and collect various biological samples. Handling activities resulted in an average of about 10-fold or greater levels of behavior in alertness, displacement, and dispersal than during precapture and darting periods. High levels of behavior usually occurred within the first 45 min of handling. In 8 of 10 capture sessions, walruses returned to predisturbance levels of behavior within 40 min of cessation of the handling disturbance. Alertness and displacement were moderately and negatively correlated with herd size during the handling period, which may reflect an effect of a threshold distance from the point of disturbance to responding individuals. Observations of walruses tagged with VHF radio transmitters indicated that the activities from a given capture session did not preclude tagged walruses from using the haul-out over a subsequent 11 -wk monitoring period. Moreover, non-tagged walruses continued to extensively use the haul-out during and after the period in which capture sessions were conducted.     

Lakes Hula and Agmon: destruction and creation of wetland ecosystems in northern Israel

A portion of the former Lake Hula wetland (northern Israel) was re-flooded in spring 1994 and the physical, chemical and biological developments within the resulting new lake and wetland complex (Agmon) was followed closely by a multi-disciplinary scientific team. The first three years of study relating to Lake Agmon are reported in this issue of Wetlands Ecology & Management. We provide in this paper a general background on the Lake Hula Draining Project in the 1950s and the recent re-flooding and creation of the Agmon wetland.     

大鹏湾反曲原甲藻种群变化率动态模型研究

大鹏湾反曲原甲藻种群变化率动态模型研究黄贯虹（广东民族学院计算机科学系,广州５１０６３３）郭远琼黄伟建（暨南大学华侨医院计算机室,广州５１０６３２）（暨南大学水生生物研究所,广州５１０６３２）ＳｔｕｄｙｏｆａＭｏｄｅｌｏｎＣｈａｎｇｅＲａｔｉｏｏｆｔ...     

大亚湾红树林研究1.澳头港的红树植物群落

本文报道了大亚湾澳头港附近的红树植物群落的种类组成、结构、外貌及演替。该地区红树群落的主要类型有７个,即白骨壤群落、白骨壤桐花树群落、白骨壤＋秋茄桐花树群落、海漆木榄群落、海漆桐花树群落、桐花树群落、老鼠勒群落。     

Distribution, biomass and primary production of an Ahnfeltia tobuchiensis (Ahnfeltiales, Rhodophyta) population in the Bay of Izmena, Kunashir Island

Regularities of distribution and primary production of an Ahnfeltia tobuchiensis (Kanno et Matsubara) Mak. population, an agar-containing red alga, were studied in the Bay ot Izmena. Experiments were conducted in a flow-through system under conditions similar to algal habitats. The population of A. tobuchiensis unattached to the ground may be from a few centimeters to as much as 1 m thick. It has been shown that only the upper part of a stratum 15–20 cm thick receives a sufficient amount ot light to realize its production potential. While 15–20% of photosynthetically active radiation (PAR) of that falling on the water surface reaches the stratum surface, only 0.1% of PAR from that falling on the water surface penetrates through stratum 15 cm thick. It has been shown for A. tobuchiensis that its photosynthetic rate curve during the daytime mainly follows the PAR intensity curve. The highest values of photosynthetic rate have been measured in the afternoon when PAR reaches its maximum. It is noted that a stratum 15–20 cm thick has peak values ot net primary production (NPP) which averages 3.2 g C m^?2 day^?1. The total area of A. tobuchiensis population was 23.4 km², and its biomass was 125 000 tons in this area. On average, the NPP of the A. tobuchiensis population made up in summer and in autumn was 46.8 and 25.0% of its biomass, respectively.     

Hysteresis in the temperature response of carbon dioxide and methane production in peat soils

The ability to predict the effects of climate change on trace gas fluxes requires a knowledge of microbial temperature responses. However, the response of a microbial community to temperature in a given substrate may be complicated by its thermal history. To examine the effect of sequentially changing temperature on methane and carbon dioxide production in different peat types, we incubated anaerobic peat samples from 3 types of northern peatlands, a bog, a sedge fen and a cedar swamp, in both rising and falling temperature regimes. Graphic and statistical comparisons of the different temperature regimes suggest hysteresis in microbial response to temperature, although the absolute rates at any given temperature often did not differ. Where regressions for temperature response (Arrhenius plots) were significant, they generally differed between temperature regimes. The greatest differences among treatments occurred during the first half of the 40-d incubation. Increases in carbon dioxide production were similar across all peat types, but methanogenesis varied widely: methane production was uniformly low in the bog peat but increased sharply with temperature in the other two peat types. The complicating effect of history or chronology on substrate responses to environmental stimuli may restrain our ability to model the responses of complex systems to changing conditions.     

Fish fauna as an indicator of environmental quality in an urbanised region of the Amazon estuary

This study describes the biological importance of Guajará Bay (Belém, Pará, Brazil) for fish fauna and presents a diagnosis of water quality in the main channel and creeks, using the icthyofauna as an ecological indicator. A total of 567 individuals from 40 species were identified. About 58% of these use Guajará Bay as a nursery ground, 49 and 81% use the bay as a breeding and feeding ground, respectively. There were no significant differences between environments as measured by the diversity index; however, fish relative abundance (catch per unit of effort) was greater in the creeks than in the main channel. A significant difference was detected in the fish fauna inhabiting the main channel compared with the creeks. In the main channel, icthyofauna significantly differed during December relative to other months.     

Selective predation by larval Agabus (Coleoptera: Dytiscidae) on mosquitoes: support for conservation-based mosquito suppression in constructed wetlands

1. Wetland insect predators can structure aquatic prey communities via selective predation, but receive considerably less attention than vertebrate predators. We conducted laboratory experiments to test selective predation by two species of larval dytiscid beetles ( Agabus ; Coleoptera: Dytiscidae) and the potential contribution of these beetles to suppression of mosquito populations in constructed wetlands.
2.  Agabus consumed copepods, ostracods and mosquito larvae in no-choice tests. When offered a choice, 76% of all prey consumed were mosquito larvae, indicating selective predation. Subsequent experiments revealed this preference was due to ease of capture of mosquito larvae over alternative prey.
3. Cannibalism and intraguild predation were common within and between species of Agabus , which may reduce the overall impact of the observed selective predation.
4.  Agabus larvae selectively preyed on mosquito larvae over alternative prey, which is not characteristic of some fish used as biological control agents for mosquitoes. Predator exclusion or similar experiments in the field could document how these results translate into a natural setting.
5. The findings of this study suggest developing mosquito suppression strategies focused on conservation of native wetland predators. These strategies are preferable to introducing non-native generalist predators, or applying pesticides.