Sheltered Sites Research Articles

Gonad development and fatty acid composition of Patella depressa Pennant (Gastropoda: Prosobranchia) populations with different patterns of spatial distribution, in exposed and sheltered sites

The present study examines the effect of shore exposure on the feeding performance (assessed by fatty acid analyses of the whole body) and gonad condition (stage of development and gonad somatic index, GSI) of Patella depressa populations. Male and female limpets were collected at exposed and sheltered sites, during winter and summer. The population at the exposed site was at a more advanced stage of gonad development, with a higher dispersion of gonad stages, both in winter and summer. Additionally, limpets from the exposed site, particularly the males, presented a higher GSI than the corresponding stage in the sheltered site. The quantitatively most important fatty acids were the saturated fatty acids (SFA) 16:0, 14:0, and 18:0, the monounsaturated fatty acids (MUFA) 18:1( n−7), 18:1( n−9), 16:1( n−7) and 20:1( n−9) and the polyunsaturated fatty acids (PUFA) 20:5( n−3) and 20:4( n−6). Females had a significantly higher fatty acid methyl esters (FAME) content (in summer and winter) and higher amounts of SFA and MUFA (in summer), which points to a higher degree of storage of neutral lipids in this sex. Male and female limpets at the exposed site had a significantly higher FAME, SFA, MUFA, PUFA and highly unsaturated fatty acids (HUFA) content than the corresponding sex in the sheltered site in summer. In addition, an inversion in the eicosapentaenoic acid (EPA)/arachidonic acid (ARA) and ( n−3)/( n−6) ratios was observed in the sheltered site, as a result of the significantly higher levels of ARA and ( n−6) fatty acids and lower amounts of EPA and ( n−3) fatty acids found in the sheltered limpets. A high variability among patches in the fatty acid composition in the exposed site was found in winter, possibly related to the aggregation of limpets at this time. The differences found between limpets from the exposed and sheltered sites suggest qualitative and quantitative differences in their diets. Additionally, the results show that the spatial aggregation strategy adopted by limpets in sites of great wave and wind exposure does not affect their feeding and reproductive success, at least in the site examined here. In fact, more developed gonads, a higher GSI and an elevated FAME content was found in the exposed population. Possible factors are suggested and discussed to explain these observations.

Seasonal variability in sediment distribution along an exposure gradient in a seagrass meadow in Shoalwater Bay, Western Australia

Seagrasses, by blocking water flow as it passes through the leafy canopy, are believed to have a significant impact on sediment dynamics, and the formation of sand and mud banks in some areas. The role of seagrasses in sedimentation processes is poorly understood in high-energy environments, such as those found in south-Western Australia. Studies of sediment size fraction distribution were conducted over a 14-month period within a Posidonia sinuosa meadow, at an exposed and a sheltered site, to investigate the role of seagrass canopies on sediment dynamics. Sediment size analyses, obtained by sieving sediment samples, showed a difference between exposed and sheltered sites, as well as seasonal influences on the data. A three-way ANOVA run on the data indicates a summer and winter pattern superimposed over the sheltered and exposed pattern. This suggests that during the calmer conditions experienced in summer there was an increased proportion of finer grain sizes at the sheltered site, while in winter the grain sizes tended to become coarser, more closely matching the pattern observed at the exposed site. These results suggest that reduced water motion at the sheltered site during summer permitted finer sediment grain sizes to settle out, while increased water motion during winter increased the proportion of coarse grain sizes. At the exposed site this seasonal difference was not observed. It therefore appears that the P. sinuosa canopy reduces flow through a dense meadow, but this effect appears to be modified by overall wave energy, observed to operate seasonally.

Environmental Factors Controlling the Distributions of Benthic Invertebrates on Rocky Shores of Lake Malawi, Africa

An airlift was used to collect 170 quantitative samples of benthic macroinvertebrates from the rocky nearshore zone of islands in southern Lake Malawi from August 1998 to Febuary 1999. Total invertebrate densities were very low (< 6,000 ind/m 2), and were dominated by Ostracoda, Hydracarina, and Chironomidae. Most of the insects were lotic forms, including hydropsychid caddisflies, heptageneid mayflies, and dryopoid beetles. Sampling sites differed in degree of exposure to wave-action, substratum texture, depth (1.5 to 5 m), and abundance of fish, and the density and diversity of the benthic fauna varied significantly with each of these factors. Both numbers of taxa and densities of invertebrates were greater at exposed than sheltered sites, and decreased with increasing depth. Gravel substratum harbored more taxa and higher densities of macroinvertebrates than did cobble or bedrock. The only seasonal change observed was a decrease in the abundance of animals during the rainy season at a sheltered site where sediment was deposited from a large river. There was a weak inverse relationship between the densities of fish and larger invertebrates on cobble and bedrock substrata. Bedrock surfaces covered by fish-exclusion cages supported five-fold more invertebrates than open surfaces after 2 months. Overall, the benthic fauna of rocky shores in southern Lake Malawi is a taxonomically rich community similar in composition and diversity to those reported from other Great Lakes worldwide. Continuous, intense fish predation appears to be responsible for low invertebrate densities and probably influences invertebrate species diversity.

Destructive grazing, epiphytism, and disease: the dynamics of sea urchin - kelp interactions in Nova Scotia

We measured the rate of advance of urchin (Strongylocentrotus droebachiensis) feeding aggregations (fronts) as they destructively grazed kelp beds (Laminaria longicruris) at both a wave-exposed site and a sheltered site in Nova Scotia over 3.5 years. The grazing fronts were composed of high densities of large adults (up to 98 and 70 per 0.25 m2at the exposed and sheltered sites, respectively). Urchins in the recently formed barrens, or in adjacent kelp beds, occurred at much lower densities and consisted mainly of juveniles. The fronts moved onshore into shallower water at each site, but their rate of advance varied markedly between sites and over time at each site, ranging from 0 to 4 m·month-1. The rate of advance of a front was related to the biomass of urchins; fronts did not advance below a threshold biomass of ~2 kg·m-2. Infestations of kelp by an epiphytic bryozoan (Membranipora membranacea) caused marked reductions in kelp canopy cover and biomass during winter, but the canopy regenerated through recruitment of juvenile sporophytes in spring. A localized outbreak of disease decimated S. droebachiensis at the exposed site in 1993, which enabled kelp to recolonize the barrens. Surviving urchins gradually reaggregated and resumed destructive grazing after ~1.5 years. A recurrence of disease in 1995 eliminated urchins at both sites and terminated the transition from kelp beds to barrens on a coastal scale. Our findings have important implications for the management of the urchin fishery, which targets grazing fronts for harvesting.

A comparison of two cartographic exposure methods using Fucus vesiculosus as an indicator

Morphological variation and vertical distribution of Fucus vesiculosus were quantified at several sites in the Finnish archipelago (Baltic Sea). F. vesiculosus samples were obtained from skerries at geographical distances of 1 km or more (large scale) and at intervals of ca 100 m around a single island (small scale). The results were examined in relation to wave exposure, calculated by Baardseth and effective fetch cartographic methods. Despite the fact that the exposure indices were calculated differently they correlated strongly. Vegetative morphological characteristics of F. vesiculosus illustrate the morphological differences both within and between exposure gradients. The tallest and widest F. vesiculosus plants were found at the sheltered end of the large-scale exposure gradient. Those from equally sheltered sites of the island were smaller in all respects. Thus, the trend from small narrow plants to large wide sheltered plants was expressed differently over the different geographical scales. Consequently localities with similar exposure indices may have morphologically different F. vesiculosus populations. Shores with similar cartographic exposure indices can be different in nature. Underwater topography and shore locations, either close to the mainland or at the outermost sites of the archipelago, affect the exposure. Although a sheltered shore is indicated, the sublittoral zone may be quite exposed to the movements of water. In contrast, in an open shore environment underwater rocks, boulders and shallow water areas can provide sheltered habitats. The depth range of the F. vesiculosus belt exhibited two distinctive patterns. At sheltered sites, around islands in the outermost reaches of the archipelago F. vesiculosus can grow to a maximum depth of 5 m. In exposed habitats the belt becomes narrower, reaching a maximum depth of 3 m. Closer to the mainland F. vesiculosus is found at exposed sites to a maximum depth of 5 m; the depth range at sheltered sites is narrower, only reaching depths of 2 m or less. In conclusion, the changes in plant morphology and in the vertical belt distribution are similar to each other along both gradients at the exposed ends of the wave action spectrum; however, the two gradients diverge at the sheltered ends of the spectrum.

Destructive grazing, epiphytism, and disease: the dynamics of sea urchin - kelp interactions in Nova Scotia

We measured the rate of advance of urchin (Strongylocentrotus droebachiensis) feeding aggregations (fronts) as they destructively grazed kelp beds (Laminaria longicruris) at both a wave-exposed site and a sheltered site in Nova Scotia over 3.5 years. The grazing fronts were composed of high densities of large adults (up to 98 and 70 per 0.25 m2 at the exposed and sheltered sites, respectively). Urchins in the recently formed barrens, or in adjacent kelp beds, occurred at much lower densities and consisted mainly of juveniles. The fronts moved onshore into shallower water at each site, but their rate of advance varied markedly between sites and over time at each site, ranging from 0 to 4 m·month-1. The rate of advance of a front was related to the biomass of urchins; fronts did not advance below a threshold biomass of ~2 kg·m-2. Infestations of kelp by an epiphytic bryozoan (Membranipora membranacea) caused marked reductions in kelp canopy cover and biomass during winter, but the canopy regenerated through recruitment of juvenile sporophytes in spring. A localized outbreak of disease decimated S. droebachiensis at the exposed site in 1993, which enabled kelp to recolonize the barrens. Surviving urchins gradually reaggregated and resumed destructive grazing after ~1.5 years. A recurrence of disease in 1995 eliminated urchins at both sites and terminated the transition from kelp beds to barrens on a coastal scale. Our findings have important implications for the management of the urchin fishery, which targets grazing fronts for harvesting.

Waterfowl Herbivory on Potamogeton pectinatus in the Baltic Sea

The impact of waterfowl herbivory on the macrophyte Potamogeton pectinatus was tested at six shallow sites adjacent to Asko island, in the northern Baltic proper. Protection by means of floating nets affected P. pectinatus at the three most sheltered sites but had no influence on the more wave-exposed sites. Ramet density in July of the first study year was 10-23 times higher in protected plots than in unprotected plots, at the sheltered sites. The density at two of the sites was constantly low in unprotected plots and remained much higher (10-80 times) in the protected plots throughout the 3-year study. At the third very sheltered site the impact of waterfowl was more variable. Additional studies of permanent plots and pot experiments revealed that waterfowl mainly suppressed P. pectinatus, not by grazing on shoots, but by eating subterranean tubers between late April and early June. This study suggests that waterfowl herbivory can constrain submerged macrophyte populations in shallow sheltered areas.

Deep‐water aquatic plant communities in an oligotrophic lake: physiological responses to variable light

SUMMARY1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer.2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level.3. There was evidence that the deep‐water community consisting of Chara corallina had adapted physiologically to low‐light conditions. Net light saturated photosynthesis (CO2 exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)−1 h−1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)−1 at 16 m vs. 4 mg Chl a (g dry wt)−1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (Ik) of the community at the lower boundary was only 78 μmol photons m−2 s−1. Photosynthetic parameters (Ik and α) as well as the Chl a content remained relatively constant throughout the seasonal and short‐term changes in radiation.4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep‐water community would be sensitive to any further changes in underwater light availability.

Population dynamics, productivity and biomass allocation of Zizania latifolia in an aquatic‐terrestrial ecotone

AbstractThe population and production ecology of a Zizania latifolia stand at a sheltered shore of the Hitachi‐Tone River were investigated. Shoot emergence was observed twice a year; the fist was a synchronized shoot emergence in April and the second was from August to October. Aboveground biomass was mostly occupied by leaves and peaked at 1500 g dry weight m−2 in August. The belowground biomass also reached its peak, 750 g dry weight m−2, in August. The secondary shoots were small in spite of their high density. Leaves were produced continuously throughout the season. The leaf life span was as short as 55.6 days for cohorts that emerged from May through to September. Total annual net production of Z. latifolia could be more than 3400 g dry weight m−2. Shoot clusters of several centimeters were observed in April. The following self‐thinning caused a regular distribution of the remaining shoots in August. Most shoots produced in August to October were found near a shoot persisting since April. They showed more concentrated distribution than shoots in April. A large biomass allocation to leaves and the ability to produce many clump shoots during the late growing period may facilitate dominance of Z. latifolia in relatively sheltered sites.

A comparison of two spectral wave models in the Southern California Bight

Two models, a spectral refraction model (Longuet-Higgins) and a parabolic equation method (PEM) refraction-diffraction model (Kirby), are used to simulate the propagation of surface gravity waves across the Southern California Bight. The Bight contains numerous offshore islands and shoals and is significantly larger (≈ 300 km by 300 km) than regions typically studied with these models. The effects of complex bathymetry on the transformation of incident wave directional spectra, S 0( f, θ 0), which are very narrow in both frequency and direction are difficult to model accurately. As S 0( f, θ 0) becomes broader in both dimensions, agreement between the models improves and the spectra predicted at coastal sites become less sensitive to errors in the bathymetry grid, to tidal changes in the mean water depth, and to uncertainty in S 0( f, θ 0) itself. The smoothing associated with even relatively narrow (0.01 Hz-5° bandwidth) S 0( f, θ 0) is usually sufficient to bring the model predictions of shallow water energy into at least qualitative agreement. However, neither model is accurate at highly sheltered sites. The importance of diffraction degrades the predictions of the refraction model, and a positive bias [O (10%) of the deep ocean energy] in the refraction-diffraction model estimates, believed to stem from numerical “noise” (Kirby), may be comparable to the low wave energy. The best agreement between the predicted spectra generally occurs at moderately exposed locations in deeper waters within the Bight, away from shallow water diffractive effects and in the far-field of the islands. In these cases, the differences between the models are small, comparable to the errors caused by tidal fluctuations in water depth as waves propagate across the Bight. The accuracy of predicted energies at these sites is likely to be limited by the uncertainty in specifying S 0( f, θ 0).

Factorial Analysis in the Ecology of Rocky Subtidal Areas Near Brest (West Brittany, France)

In order to investigate the characteristic species and the relative importance of selected environmental conditions of rocky bottom communities in coastal waters and to estimate their richness, 27 sites in the Brest area were surveyed by diving. The abundances of underwater species, from a check-list of 115, were plotted as number of individuals or colonies in m2 or in percentage cover of the rock, against the environmental conditions (depth, bedrock slope, substrate type and sediment nature of the nearest soft bottom). Raw data were converted to biovolume expressed as mm3 m–2 and expressed as log 10 (x + 1).Various correspondence analyses were applied to these data: the first included bedrock slope (lit/dark surfaces) and takes into account the four biological formations according to the depth. It shows zonation with depth and decreasing light as factor 1, hydrodynamic conditions (waves or current) as factor 2, mixing of estuarine and oceanic waters as factor 3 and turbidity as factor 4. Four species assemblages emerge from these four axes, for which the main species contributing to the four axes may be considered as characteristic species. These correspond well to four broad communities described in British waters: very exposed to wave-action, semi-exposed to wave-action, exposed to strong tidal current, very sheltered sites. The second analysis, in which lit and dark surfaces are distinguished, but some very close sites are fused together, shows in detail the photophilous or sciaphilous nature of the species. Values of hydrodynamic conditions and percentage of surface light plotted on the 'stations-points' of the graphs allow drawing of a factorial network which may be used as hydrodynamic and illumination scales.

Marbled Murrelet Chick and Eggshell Fragments from Inland Washington

A marbled murrelet (Brachyramphus marmoratus) chick and three small eggshell fragments (UWBM 43053) were found on the ground in the Helena Creek drainage 9.5 km south and 2.5 km east of Darrington in Snohomish County, Washington. The chick was found partially decomposed on 27 June 1989; the eggshell fragments were found on 14 July 1989, 1.5 m from where the chick was found. The site is 2.7 km up Helena Creek from its confluence with Clear Creek, or 6.3 km from its confluence with the River. The specimens were found 18 m north of a dry stream bed (about 4 m wide), and 240 m east of Helena Creek; elevation is 594 m. The mouth of the Snohomish River, 45-50 km to the southwest, is the closest salt water. The chick was identified by comparison with a color photograph and descriptions of chicks by Simons (1980) and Binford et al. (1975). The bird was maggoty when found; judging from the size of the larvae, it had been dead for perhaps 4 days. The chick nevertheless retained most of its plumage upon preparation. It was entirely downy, with a wing length (wrist to the end of the down) of less than 25 mm, suggesting that it was less than 3 days old (Simons 1980; Hirsch et al. 1981). Subtracting 30 days for the incubation period (Sealy 1974), we estimate a hatching date of 22-23 June and a laying date of 23-24 May. The three eggshell fragments, the largest of which is 6 mm across, were identified based on their similarity to Kiff's (1981) description of marbled murrelet egg specimens and a comparison with an egg (UWBM 43031) found on Long Island in Pacific County, Washington, in July 1989 (J. Atkinson, pers. comm.). Using Munsell color notation (Anon. 1976), the fragments had a ground color between 5GY 8/4 and 2.5GY 7/4; one had a 7.5Y 7/6 spot, and two were marked with blackish scrawls. These colors closely resemble those of UWBM 43031 and Kiff's descriptions. The chick and eggshell were found in unmanaged forest dominated by western hemlock (Tsuga heterophylla) and western red cedar (Thuja plicata) on a west-facing 30% slope. The overstory was western hemlock and western red cedar with some pacific silver fir (Abies amabilis). The hemlocks were primarily 40-45 cm dbh (diameter breast-height), with an understory of 10-20 cm dbh hemlocks. Canopy closure was 60-65%. The forest understory was comprised of sword fern (Polystichum munitum), devil's club (Oplopanax horridum), Oregon grape (Mahoma oregona), bunchberry (Cornus canadensis), deer fern (Blechnum spicant), huckleberry (Vaccinium sp.), western hemlock and vine maple (Acer circinatum). Tree size in the stand and the presence of scattered large remnant Douglasfirs support the assertion that the area was burned in the large Sauk Prairie fire which occurred around 1825 (Henderson and Peter 1984). The chick and eggshell fragments were found at the base of a western hemlock 23 m high and 41 cm dbh. There was no depression, scrape, droppings or other evidence of a ground nest; furthermore, ground vegetation would make access to a ground nest difficult. The hemlock was heavily infected with dwarf mistletoe (Arceuthobium tsugense), which results in multiple branches at infected sites along the tree limbs (known as witches' brooms). Witches' brooms collect organic material and are often covered with thick blankets of moss. The hemlocks in this part of the drainage were heavily infected with dwarf mistletoe, making witches' brooms common. The hemlock was 3 m from a large remnant Douglas-fir (Pseudotsuga menziesii) about 38 m high and 152 cm dbh. This tree had many large lateral branches covered with moss. The top of the Douglas-fir extended above most of the canopy and projected over the hemlock under which the chick was found. The proximity of the chick and eggshells to the trunk of the hemlock and to each other suggests that they fell from a nest in either the hemlock or the Douglas-fir. This habitat is consistent with that of other marbled murrelet tree nests (Marshall 1988), although the nest may possibly have been in a smaller tree than usual. The western hemlock with witches' brooms could have provided sheltered horizontal moss-covered nest sites like the large limbs on which other nests have been found.

Apparent Commensalism among Three Vaccinium Species on a Climatic Gradient

(1) Three Vaccinium species each in turn dominate a section of a gradient of light and temperature, with some overlap: V. uliginosum (ULI) dominates tundra sites, V. angustifolium (ANG) open but sheltered krummholz sites, and V. myrtilloides (MYR) shaded forest sites. This study examines congeneric interactions along that gradient. (2) Plant biomass, soil temperature and light intensity were used to characterize the gradient. The vertical distribution of biomass inside and outside congeneric interfaces (areas of direct interspecific contact) was determined to examine the nature of congeneric interactions. (3) Only 24-44% of the variation in biomass of ULI, ANG and MYR could be explained by light and temperature conditions alone, but adding the biomass of other vascular species to the analyses increased that range to 44-67%. (4) The biomass of each Vaccinium species was significantly reduced outside its own area of dominance, except in direct contact with the locally dominant congener. On the other hand, the biomass of the locally dominant Vaccinium species was either unchanged or somewhat larger in direct contact with a congener, compared to non-contact zones. (5) Several hypotheses are discussed to account for this apparent commensalism, including recent climatic changes, microsite effects, interspecific shelters against climate or pathogens, and innate or competition-induced growth patterns.

The relation between wave exposure and distribution of emergent vegetation in a eutrophic lake

SUMMARY 1. Maximum water depth penetration and changes in horizontal distribution during 39 years of the emergent vegetation in a eutrophic lake in southern Sweden were investigated.2. The capacity of the emergent vegetation to penetrate into deeper water areas was found to be higher at wave exposed than al sheltered sites.3. Differences in biomass and biomass allocation of the dominant speeies. Phragmites australis, between an exposed and a sheltered site suggest that horizontal expansion towards deeper water at sheltered sites is limited by unfavourable substrate conditions.

MARINE VEGETATION OF THE MUSERI AND ENTEDEBIR ISLANDS (DAHLAK ARCHIPELAGO, RED SEA)

The intertidal and shallow subtidal marine vegetation of two uninhabited islands in the Dahlak Archipelago, southern Red Sea, is described. The vegetation of these habitats is representative of the entire Archipelago, except for its seaward periphery. Under the highly sheltered conditions prevailing in most of this area, life in the intertidal and in the shallows is rather depauperated, the upper intertidal levels being mostly affected. On the rocky shores, the rarity of periwinkles is the most striking feature at these levels; a little lower down, barnacle belts are completely absent. Species diversity is rather low in the algal communities of the lower intertidal and the upper subtidal. Sciaphilic habitats at these levels harbor a more diverse vegetation, in which a number of species not previously reported from the Red Sea have been encountered. Mangal stands occur in the more sheltered sites. Avicennia marina belts are present in all mangal stands, Rhizophora mucronata belts occur in the highly sheltered sites on the leeward side of the Museri Island, while a single small stand of Ceriops tagal has been observed in a protected depression on the adjacent Desta Island. Bostrychietum, considered for a long time to be nonexistent in the Red Sea, has been found on A. marina aerial roots from an extremely sheltered location in the Melita Bay, Gulf of Zula, on the Ethiopian mainland coast. Caulerpetum serrulatae covers clayey bottoms in ca. 100 m deep troughs between the islands. It is exclusively composed of the low-light ecophene of Caulerpa serrulata , which differs from the normal, high-light form in bearing flat, ribbon-shaped assimilators.

SHORELINE EXPERIMENTS AND THE PERSISTENCE OF OIL ON ARCTIC BEACHES

ABSTRACT Experiments associated with the oiling of beaches in an arctic environment show that fetch and wave-energy conditions at the shoreline are primary factors in determining the persistence of stranded oil. Five intertidal sections of coast were oiled, each of which differed in terms of shoreline exposure and fetch. The oil loadings of the test beaches that were oiled artificially were in the same range as those from an adjacent nearshore spill, so that the experimental results can be assumed to replicate real-world oiling conditions. On the most exposed beach (fetch 90 kilometers) all oil was removed naturally after 80 days of exposure to open-water conditions. At a semi-exposed location, 85 to 95 percent of the oil was removed within 40 days, and at the most sheltered test sites (fetch less than 2 km) between 5 and 30 percent of the oil remained after an observation period of 160 open-water days. Data collection to determine fates of oil at the different sites over a four-year period is continuing. In this relatively low-energy wave climate environment, with an open-water season of about 60 days, most exposed beaches would be cleaned naturally to levels less than 500 milligrams/kilogram within 100 days, but where the fetch is less than 10 to 25 km the expected persistence of oil stranded in the intertidal zone could be greater than 10 years.

Composition and Succession of Lichen Communities in an Inner Coastal Dune Area in Southern Sweden

AbstractThe cryptogamic vegetation, dominated by lichens, in a secondary coastal dune area is described. The Coelocaulon aculeatum community colonizes large exposed sand patches. The Cladonia glauca–C. mitts community colonizes where litter has accumulated. The Cladonia mitis and C. portentosa communities occupy more sheltered sites than the Coelocaulon aculeatum community. The scattered Cladonia zopfii community colonizes both exposed and slightly more sheltered sand patches. The common Cladonia uncialis–C. mitis community usually colonizes smaller sand patches with some humus accumulation than those colonized by the Coelocaulon aculeatum community. The Cladonia mitis, the C. portentosa and the Cladonia uncialis–C. mitis communities and probably the Cladonia zopfii community are suggested to be final stages in the lichen succession.

Studies on the ecology of the vegetation at Mawson Statio Antarctica

The flora of Mawson Rock is fairly depauperate; the two commonest lichens are Buellia frigida and Caloplaca elegans and the only two mosses are Bryum algens and Grimmia lawiana. The lichens form open colonies on exposed rock, and closed patches on sheltered aspects. The mossfields are small and confined chiefly to gravels on northerly aspects receiving snow-bank melt waters. The moss colonies form cushions, turfs or hummocks and may be contorted by cryoturbic processes. Larger colonies thus contain greater cores of sand and gravel. Mature cushions of Bryum algens are up to 25 years old, but the deepest peats are certainly much older. The small biomass of green moss in the most sheltered sites at Mawson is similar to comparable mossfields on the exposed plateau of subantarctic Macquarie Island.

Accuracy of Canadian Snow Gage Measurements

Abstract Field investigation to assess the accuracy and comparability of precipitation gage measurements of snowfall in Canada was initiated in 1973. The MSC Nipher shielded snow gage (Canadian standard gage), the Universal (Belfort) precipitation gage, and the Fischer and Porter precipitation gage were tested at open and sheltered sites. Shielded and unshielded pairs of gages were compared at an open site. Gage catch was related to “ground true” snowfall water equivalent as measured on snow boards in a sheltered site. Each gage tested had unique performance characteristics. Curves of gage catch to ground true as a function of wind speed are given. The catch ratio of the Universal gage is higher than the Fischer and Porter for similar shielding and environmental conditions. The MSC Nipher shielded gage exhibits a superior catch efficiency. At lower wind speeds this gage can overcatch. For winds up to 5.5 m s−1 the catch of the Nipher gage is within 10% of true. A mean correction of 0.15 mm for retention l...

Aestivation Sites and Thermal Characteristics of an Aestival Microhabitat of Hypera brunneipennis1 , 2

In California, the Egyptian alfalfa weevil, Hypera brunneipennis (Boheman), aestivates in a variety of sheltered sites both near and far from, but not within, alfalfa fields. Within the microhabitat of one of these, hourly mean temperatures in the range optimum for survival and aestival development (20–25°C) prevailed during 46% of a 24-h period as opposed to only 25% of the period in an unsheltered site. Evidently the sheltered site offers the dormant weevils protection from direct exposure to lethal ambient temperatures and also provides them thermal conditions favorable for aestival development and survival through the summer.