Diet composition influences the fitness of the herbivorous crab Grapsus albolineatus

The tropical rocky shore crab Grapsus albolineatus feeds primarily on filamentous algae but eats animal matter whenever it is available. During the summer the crab's diet switches to encrusting algae due to a die-off of filamentous algae. As a result of the switch the nutrients in the diet of the crab vary seasonally and may influence the fitness of the crab. Maintenance, growth, reproductive performance and nutrient storage of crabs were examined under four dietary regimes of increasing nutritional value ranging from low organic to high protein content. The nutritional quality of these diets significantly affected crab survival and moulting. Crabs fed on the nutritionally superior diet of algae and meat exhibited enhanced growth, higher levels of energy in the reproductive organs and stored more energy in the hepatopancreas than did individuals on the shore and crabs fed only on algal diets in the laboratory. Filamentous algae were a better food source than other algae, resulting in fewer deaths and superior levels of maintenance and growth. Growth and maintenance can occur on a pure algal diet, but reproductive performance and nutrient storage require some degree of added nutrients in the form of animal matter in the diet. Crabs fed coralline or foliose algae had higher mortality and fewer successful moults than crabs fed the other two diets. The fitness of G. albolineatus appears to be limited by the amount of extra nutrients obtained from animal matter. The opportunistic consumption of animal material in the form of carrion, or of animals associated with dietary algae, could be a key factor in the reproductive success of this crab.     

Diet,food preference,and algal availability for fishes and crabs on intertidal reef communities in southern California

Synopsis Herbivory by wide-ranging fishes is common over tropical reefs, but rare in temperate latitudes where the effects of herbivorous fishes are thought to be minimal. Along the west coast of North America, herbivory by fishes on nearshore reefs is largely restricted to a few members of the Kyphosidae, distributed south of Pt. Conception. This paper presents information on natural diets and results from feeding choice experiments for two abundant kyphosids from intertidal habitats in San Diego, California —Girella nigricans andHermosilla azurea, and similar data for the lined shore crab,Pachygrapsus crassipes, which also forages over intertidal reefs. These results are compared with the availability of algae in intertidal habitats measured during summer and winter, on both disturbed and undisturbed habitats. The diets of juveniles ofG. nigricans andH. azurea collected from nearshore habitats were dominated by animal prey (mainly amphipods), but adults of these fishes, andP. crassipes, consumed algae nearly exclusively, with 26, 10, and 14 taxa of algae identified fromG. nigricans, H. azurea, andP. crassipes, respectively. Algae with sheet-like morphologies (e.g.Ulva sp.,Enteromorpha sp., members of the Delesseriaceae) were the principal algae in the diets of the fishes, and calcareous algae (e.g.Corallina sp.,Lithothrix aspergillum) and sheet-like algae (Enteromorpha sp.) comprised the greatest identifiable portion of the shore crab's diet. Feeding choice experiments indicated that the fishes preferred filamentous algae (e.g.Centroceras clavulatum, Polysiphonia sp.,Chondria californica) and sheet-like algae (e.g.Enteromorpha sp.,Ulva sp.,Cryptopleura crispa) over other algal morphologies, whereas the shore crab chose jointed calcareous algae (e.g.Lithothrix aspergillum, Corallina vancouveriensis, Jania sp.) most frequently. The diets and preferences for algae by the fishes were generally most similar to the assemblage of algae available in early successional (disturbed) habitats during summer when sheet-like and filamentous algae are abundant. The shore crab exhibited the opposite trend with a diet more similar to late successional (undisturbed) habitats.     

The effects of grazing on the distribution and composition of low-shore algal communities on the central coast of Portugal and on the southern coast of Britain

A red algal turf is often found just below the barnacle/limpet zone of many European shores, especially on steep shores of moderate exposure. The hypothesis that grazing by limpets determines the upper limit of distribution of this red algal turf was tested on moderately exposed shores in Portugal and Britain. We also aimed to assess whether the grazing effect is modified at various spatial scales. Grazers were excluded by fences, with half-fenced and unfenced controls. Exclusion plots were rapidly colonised by green ephemeral algae in the months immediately after the beginning of the experiment (summer); these algae were later replaced by perennial algae. The percentage cover of turf-forming macroalgae showed a significant increase at both locations. The upper limit of distribution extended more than 50 cm on most of the shores studied. In contrast, control and half-fenced plots remained devoid of algae. After 2 years, ungrazed plots were mainly colonised by a red algal turf (e.g. Caulacanthus ustulatus, Gelidium spp., Laurencia pinnatifida) in Portugal, while canopy cover (Fucus serratus and Himanthalia elongata) dominated in Britain in marked contrast to the grazed plots. Physical factors acting at both local and geographical scales may explain these differences. However, although physical factors probably have an important influence on the identity, size and abundance of sublittoral fringe macroalgae, grazers play a major role in directly setting their upper limits. The effect of grazing by limpets was not consistent for all of the morphological algal groups and spatial scales considered in the present study. The effect of grazing on the cover of turf algae varied between Portugal and Britain (location scale), while effects on ephemeral and canopy algal cover varied at the shore scale within location.     

Diet and trophic plasticity of an herbivorous blenny Scartella cristata of subtropical rocky shores

The goals of the present study were to investigate the feeding rates of Scartella cristata, accounting for different water temperature regimes, and to analyse spatial and seasonal variations in its diet. The feeding rate of S. cristata was higher in warmer waters and was not correlated with season. A typical herbivorous diel feeding pattern was observed, with a steady increase in bite rate throughout the morning until a plateau in the early afternoon, followed by an abrupt decrease until the end of the daylight period. The gut contents of S. cristata included at least 41 different items. Detritus and algae (mainly filamentous) comprised most of the bulk of S. cristata's diet. Scartella cristata also exhibited significant seasonal and spatial variability in its diet. This study highlights the importance of detritus within the epilithic algal matrix in the diet of S. cristata and pinpoints that, as in coral reefs, the detrital pathway exerts an important role in the trophodynamics of subtropical rocky shores where these fish are abundant.     

The effects of tidal height,wave-exposure,seasonality and rock-pools on grazing and the distribution of intertidal macroalgae in New South Wales

The effects of grazers (mostly gastropods), height on the shore, wave-exposure, season of the year and the presence of shallow rock-pools on the abundance of intertidal macroalgae were examined on shores at Cape Banks (Botany Bay). At the beginning of each of the four seasons, experimental plots with and without grazers were cleared at four heights on three shores, of increasing exposure to waves, The colonization and growth of algae in these plots were monitored (by measurement of per cent cover and dry wt) for approximately the next 3 months in each season.In grazed plots, foliose algae only grew at the lowest levels on the shores. They were more abundant where wave-action was greater, and during the cooler periods of the year, when growth of the plants was enhanced. Higher on the shore, there was a positive correlation between algal cover in grazed plots and the amount of rainfall during the previous 10 days. In all seasons, there was much greater colonization of foliose algae where grazers were excluded. There was greater algal growth at lower levels on the shore, and where wave-action was stronger. Less algae grew in sheltered areas during warmer times of the year. The major seasonal difference found was the more rapid growth and occupancy of the rock by algae during the cooler seasons of the year.Experimental rock-pools were colonized more rapidly at lower levels on the shore, and during the winter. There was no difference between pools and control (non-pool) areas during winter. During summer, however, there was a greater per cent cover and biomass of algae in pools from which grazers had been excluded than in similar control areas.The results can be interpreted as being due to the greater survival and more rapid growth of algae under conditions of increased moisture, decreased emersion and decreased temperatures and light regimes during low tide (i.e. when physical stresses were reduced). These physical factors were, however, less important to the distribution of the algae than were the effects of grazers. Although few algae were present in any experimental plot, the number of species of algae per plot was considerably reduced in grazed areas.The results confirm that the patterns of vertical distribution and abundance of algae on rock-platforms in New South Wales are primarily the result of the activities of grazers. All algae in the present study were capable of living higher on the shore than they were normally found. Much of the variation along a gradient of wave-exposure, from season to season, and small-scale variation from place to place at any time can be explained by the complex interactions between the activities of grazers, and the effects of variations in the physical environment that influence the recruitment, survival and growth of the algae.     

Refuge function of marine algae complicates selection in an intertidal snail

Species with restricted gene flow often show trait-shifts from one type of environment to another. In those rock-dwelling marine gastropods that lack larval dispersal, size generally decreases in wave-exposed habitats reducing risk of dislodgement, while increases in less exposed habitats to resist crab-crushing. In Littorina fabalis, however, snails of moderately exposed shores are generally much larger (11–14 mm) than snails of sheltered shores (5–8 mm). Observations from the White Sea (where crabs are not present) indicate that in the absence of crabs snails are small (6–7 mm) in both habitats. We assumed that the optimal size for L. fabalis in the absence of crabs is less than 8 mm, and thus that increased size in moderately exposed habitats in areas with crabs might be a response to crab predation. In a crab-rich area (Sweden) we showed that crab predation is an important mortality factor for this snail species in both sheltered and moderately exposed habitats. In sheltered habitats, snails were relatively more protected from crab-predation when dwelling on their habitual substrate, fucoid algae, than if experimentally tethered to rocks below the algae. This showed that algae function as snail refuges. Snail dislodgement increased, however, with wave exposure but tethering snails in moderately exposed habitats showed that large snails survived equally well on rocks under the algae as in the canopy of the algae. Thus in sheltered habitats a small snail size is favored, probably due to life-history reasons, while increased risk of being dislodged from the algae refuges promotes a large size in moderately exposed habitats. This study shows an example of selection of a trait depends on complex interactions of different factors (life-history optimization, crab predation, wave induced dislodgement and algal refuges).     

Comparison of growth and lipid composition in the green abalone, Haliotis fulgens, provided specific macroalgal diets

Lipid composition of abalone was examined over a one-year interval. A feeding trial was designed to cover a full reproductive cycle in young adult green abalone, Haliotis fulgens, consisting of five diet treatments: the macrophytic algal phaeophyte Egregia menziesii, rhodophyte Chondracanthus canaliculatus, chlorophyte Ulva lobata, a composite of the three algae and a starvation control. The lipid class, fatty acid, sterol and 1-O-alkyl glyceryl ether profiles were determined for foot, hepatopancreas/gonad tissues and larvae. The major fatty acids were 16:0, 18:0, 18:1(n-7)c, 18:1(n-9)c, 20:4(n-6), 20:5(n-3) and 22:5(n-3), as well as 14:0 for abalone fed brown and red algae. 4,8,12-Trimethyltridecanoic acid, derived from algae, was detected for the first time in H. fulgens (hepatopancreas complex, 1.2–13.9%; larvae, 0.5% of total fatty acids). Diacylglyceryl ethers were present in larvae (0.6% of total lipid). The major 1-O-alkyl glycerols were 16:0, 16:1 and 18:0. Additionally, 18:1(n-9) was a major component in hepatopancreas/gonad and larvae. The major sterol was cholesterol (96–100% of total sterols). Highest growth rates were linked to temperature and occurred in abalone fed the phaeophyte E. menziesii (43 μm·day^–1, 56 mg·day^–1 yearly mean), an alga containing the highest levels of C₂₀ polyunsaturated fatty acids and the highest ratio of 20:4(n-6) to 20:5(n-3). This study provides evidence of the influence of diet and temperature on seasonal changes in abalone lipid profiles, where diet is most strongly related to body mass and temperature to shell length. The allocation of lipids to specific tissues in green abalone clarifies their lipid metabolism. These results provide a basis for improving nutrition of abalone in mariculture through formulation of artificial feeds.     

The effects of grazing by gastropods and physical factors on the upper limits of distribution of intertidal macroalgae

Summary The cover of foliose algae is sparse to non-existent above a low-level algal zone on many shores in N.S.W., except in rock-pools. Above this algal zone, encrusting algae, mostly Hildenbrandia prototypus, occupy most of the primary substratum on sheltered shores. Experimental manipulations at midtidal levels were used to test hypotheses about the effects of grazing by molluses and of physical factors during low tide on this pattern of algal community structure.Fences and cages were used to exclude grazers: molluscs grazed under roofs and in open areas. Cages and roofs provided shade, and decreased the harshness of the environment during low tide: fences and open areas had the normal environmental regime.In the absence of grazers, rapid colonization of Ulva and slower colonization by other foliose algae occurred in all experimental areas. The rate of colonization by Ulva sporelings was initially retarded on existing encrusting algae, but after a few months, cover of Ulva equalled that on cleared rock.Most species of algae only grew to maturity inside cages, and remained as a turf of sporelings inside fences. No foliose algae grew to a visible size in open, grazed areas. Grazing thus prevents the establishment of foliose algae above their normal upper limit on the shore, but the effects of physical factors during low tide prevent the growth of algae which become established when grazers are removed. Physical factors thus limit the abundance of foliose algae at mid-tidal levels.The recolonization of cleared areas by Hildenbrandia was not affected by the presence of a turf of sporelings, nor by the shade cast by roofs, but was retarded in cages where mature algae formed a canopy. Even under such a canopy, Hildenbrandia eventually covered as much primary substratum as in open, grazed areas. This encrusting alga is able to escape from the effects of grazing by having a tough thallus, and by its vegetative growth which allows individual plants to cover a lot of substratum, and by the tendency for new individuals to start growing from small cracks and pits in the rock, which are apparently inaccessible to the grazers.Mature foliose algae are removed from the substratum by waves, and many individual plants died during periods of hot weather. Sporelings in a turf were eliminated, after experimental fences were removed, by the combined effects of macroalgal grazers, which invaded the areas, and microalgal grarers which ate the turt from the edges inwards.The results obtained here are discussed with respect to other studies on limits to distribution of intertidal macroalgae, and the role of grazing in the diversity and structure of intertidal algal communities. Some problems of these experimental treatments are also discussed.     

A long-term comparison of the benthic algal flora of Clare Island, County Mayo, western Ireland

The marine benthic algal flora of Clare Island, off County Mayo, western shore of Ireland, was investigated; collections of intertidal and subtidal marine algae were made at 16 sites along the eastern and southern shores in the years 1990, 1993 and 2000–2002. The data and observations obtained were compared with the results of a similar survey conducted by Arthur Disbrowe Cotton in 1910–1911. Considering the results of the original survey and the new survey together, the marine algal flora of the island currently totals 293 species; 224 species were recorded by Cotton in the original survey, whereas 223 species were identified in the present study. Most species are common to the original and the new list and the main differences are easily explainable; the new survey used SCUBA diving, which allowed the collection of several subtidal species not collected in 1910, and Cotton reported several microscopic green and brown algae, usually difficult to recognise in the field, which were not rediscovered. The most remarkable differences consist in the current presence of some large intertidal brown algae (Bifurcaria bifurcata, Cystoseira foeniculacea and Cystoseira nodicaulis) that were not reported in the survey of 1910. Two algae, Codium fragile subsp. tomentosoides and Asparagopsis armata, were introduced in Europe after the original survey. At present, the benthic algal assemblages of Clare Island still have basically the same structure and distribution as in 1910 and, if compared with other coastal areas of Europe, the intertidal marine environment of Clare Island appears remarkably well conserved.     

Physical and biological conditions on a steep intertidal gradient at Rottnest Island,Western Australia

Seven species of grazing molluscs, two littorinids, one nerite, three limpets and one chiton, lived on the vertical intertidal rock wall at the landward edge of the coastal limestone platforms at Rottnest Island, Western Australia. On the average, the vertical ranges of these species overlapped broadly, although a consistent zonation pattern was conspicuous from the platform surface upwards for 2 m. On these vertical intertidal shores, physical and biological conditions were predicted quantitatively from easily made measurements of vertical height on the shore; the percentage of time any shore level was immersed in seawater, the percent weight loss of plaster clods, the standing crop of algae, and the growth rate of the limpet, Notoacmea onychitis, all decreased linearly or semi-logarithmically with increasing height on the shore. The standing crop of animals was greatest, largely due to the presence of the chiton, between 40 and 70 cm from the platform surface and decreased rapidly down the shore and more gradually towards higher shore levels. We interpret this information and the positive correlation between algal production rate, and egestion rate of the animal community at various levels of the shore as evidence supporting the idea that food may be in short supply on these shores.     

Effects of herbivory and the season of disturbance on algal succession in a tropical intertidal shore,Phuket, Thailand

The effects of herbivory and the season of disturbance on species composition and algal succession were experimentally tested at a tropical intertidal shore, Phuket Island, Thailand. Dead coral patches were cleared of all organisms during both the dry and rainy seasons in order to study the effects of season on algal succession and cages were set up to exclude fish herbivory. Algal succession in this intertidal habitat showed a simple pattern and took a year from the early Ulva paradoxa C. Agardh stage to the late Polysiphonia sphaerocarpa Børgesen stage. The abundance of algae during succession was under the influence of seasonal change. U. paradoxa reproduced and recruited throughout the year. Caging effects did not apparently influence algal abundance, perhaps because resident herbivorous damselfishes excluded other herbivores from their territories and maintained their algal “farms”. Unexpectedly, the percent cover of Ulva in the caged plots was lower than in uncaged plots. This pattern may indicate that caging excluded damselfishes only, but allowed small herbivores that consumed substantial amounts of soft filamentous algae in the cages.     

The role of nitrogen as a growth limiting factor in the eutrophic Lake Vesijärvi,southern Finland

The significance of nitrogen for algal growth was studied in Lake Vesijärvi in 1979 and 1980 by algal bioassay, using Selenastrum capricornutum and Anabaena cylindrica as test organisms. Nitrogen limited the growth of Selenastrum for the major part of the investigation period, while phosphorus seemed to be the most limiting factor for Anabaena. This difference was reflected in the in situ succession of phytoplankton. As the ratio of inorganic nitrogen to phosphate phosphorus became smaller, nitrogen-fixing blue-green algae became dominant. Nitrogen fixation was greatest at the beginning of July, coinciding with maximum heterocyst numbers.     

三峡水库神农溪2014年春季浮游藻类演替成因分析

摘要：【目的】研究三峡水库神农溪库湾春季水华期间浮游藻类演替及其成因分析。【方法】2014年3–5月在神农溪库湾布置了6个断面(SN01–SN06),在神农溪汇入长江干流河口附近水域设置1个断面CJBD,对浮游藻类、相关环境因子及水动力因子进行了同步监测,据此分析了水体层化结构及水动力特性。【结果】神农溪在监测时段内共检测到浮游藻类6门38种(属);库湾浮游藻类生物量时间上差异显著(ANOVA,P<0.05)。春季浮游藻类群落结构具有明显的演替规律,3月份暴发大面积的硅藻水华（藻密度>100×105 cells/L),小环藻(Cyclotella spp.)为优势藻种;4月在SN02–SN06暴发以小球藻(Chlorella spp.)为主要优势种、衣藻(Chlamydomonas spp.)为次优势种的绿藻水华(藻密度>100×105 cells/L),5月份受水位大幅消落影响,浮游藻类生物量降低且无明显优势藻种。【结论】在具备充足的营养盐的水体中,水体层化结构与水动力特性对浮游藻类演替影响重大。三峡水库水位处于快速消落阶段时,流速成为抑制神农溪库湾藻类生长的主要因素。     

Effects of interactions between algae and grazing gastropods on the structure of a low-shore intertidal algal community

Summary At low levels on shores in New South Wales, foliose algae are abundant and often occupy all substrata; microalgal grazing gastropods are rare or absent. At higher levels, foliose algae are sparse or absent and grazing gastropods are abundant. Hypotheses for the causes of the lower vertical limits of distribution of these grazers include the effects of increased predation or the deleterious physiological effects of increased period of submergence at lower levels on the shore. Alternatively, the presence of the algae, because they occupy space and deprive the grazers of substratum for feeding, may prevent the downward movement, or survival of the grazers at low levels. Under the first two of these hypotheses, algae are able to colonize and grow in low-shore areas as an indirect result of factors which remove grazers. Under the third hypothesis, the algae are directly responsible for the lack of grazers.Experimental clearings of the low-shore algae and introductions of the mid-shore limpets Cellana tramoserica and Siphonaria denticulata were used to test these hypotheses. C. tramoserica grazes microalgae and removes them from the substratum, preventing colonization. S. denticulata, in contrust, crops the algae, leaving a visible cover of algae on the substratum, which can grow rapidly. Because of its method of feeding, S. denticulata had no measurable impact on the rates of colonization, nor on the dry weights of algae, compared with those of ungrazed areas. C. tramoserica could keep cleared areas tree from foliose algae, but only when the limpets were mainfained in great density (10 per 900 cm²). They were less effective where wave-action was greater.Neither species of limpets could survive when placed onto beds of mature algae, because they had no substratum on which to cling and were swept away by the waves. C. tramoserica did not invade clearings below their lower limit of distribution where they had to move over a bed of foliose algae. Few C. tramoserica moved directly downshore into cleared areas. When placed on bare rock within low-shore beds of algae of different ages, S. denticulata remained amongst the algae and maintained their tissue-weights. Few C. tramoserica remained in areas with well-developed algae, compared with areas having sparse algal growth. Those Cellana which remained amongst well-developed algae lost weight, whereas limpets in areas with less algal growth mammtained their weights. In experimental cages in low-shore beds of algae, where the limpets were inaccessible to potential predators, C. tramoserica lost weight and died. On cleared areas they survived for many weeks, but lost weight and died as algae grew and covered the substratum. In the absence of predation, the micro-algal grazer C. tramoserica could not survive in lowshore areas because algae grew too fast and occupied the substratum, making it inaccessible for the limpets to graze; the algae, once grown beyond small sporelings, are not a suitable food-source for C. tramoserica, and the loss of weight and death of these limpets is attributable to starvation.The lower limit of distribution of C. tramoserica is not due to the direct effects of physical factors associated with prolonged submersion, nor to the impact of predators, but is apparently determined by the presence of rapidly growing, extensive beds of foliose algae at low levels on the shore. The cause of the limit of distribution of S. denticulata is not yet known and predation may prove to be important. Removal of S. denticulata from low-shore algal beds would not, however, affect the domination of substrata by algae. Grazing by S. denticulata at very great density had no effect on algal cover nor weight. In the intertidal community studied, the persistence of a low-shore algal zone, bounded above by abundant grazers is not influenced by the activities of predators, but is a direct result of interactions between the grazers and the algae.     

Reproduction and adult longevity of five species of planktonic cyclopoid copepods reared on different diets: a comparative study

1. The nutritional value of a pure algal food, the phytoflagellate Chlamydomonas reinhardtii, and a mixed diet was tested for five planktonic cyclopoid copepods (Acanthocyclops robustus, Cyclops vicinus, Cyclops abyssorum, Mesocyclops leuckarti and Thermocyclops crassus). The algae were offered at high density (4.5 × 10⁵ cells ml^–1; 22.5 mg C l^–1) in a flow-through system. The mixed diet consisted of concentrated natural plankton (rotifers, copepod nauplii, small copepodites and large phytoplankton forms) in the size range 50–150 μm and with a dry mass > 20 mg l^–1. Reproductive parameters (clutch size, interclutch periods, number of clutches produced) and adult longevity were monitored as indicators of nutritive value. 2. All species had a significantly lower reproductive output and a shorter or unchanged adult lifespan on the algal compared with the mixed diet. 3. The species differed considerably in their ability to use algae. Mesocyclops leuckarti produced no clutches with algae, and females died earlier than with the mixed food. Acanthocyclops robustus and C. vicinus produced smaller and fewer clutches, displayed a longer interclutch period and shorter (A. robustus) or similar (C. vicinus) lifespan on the algal food than on the mixed food. Thermocyclops crassus and C. abyssorum produced smaller clutches with the algal food, but interclutch period was shorter with the algal than with the mixed diet (T. crassus) or of the same length with both diets (C. abyssorum). Adult lifespan was the same under both food regimes. Unfed females produced no eggs. 4. The ability to utilize algae, the reproductive output and the reproductive allocation were not related to body size. Acanthocyclops robustus, a species of intermediate size, produced by far the largest clutches and the most eggs per lifetime under both food regimes and invested more in reproduction than the other species. 5. Reproduction was costly. Unfed and non-reproducing females of C. vicinus and C. abyssorum reached the same age or lived longer than fed and reproducing ones. 6. The adult cyclopoids tested are primarily omnivorous, but utilize algae which are frequently sufficient for egg production.     

Effect of pollution on phytoplankton in the Ashar Canal,a highly polluted canal of the Shatt al-Arab Estuary at Basrah,Iraq

The effect of pollution on the phytoplankton in the Ashar Canal was studied during March and June 1976. Higher temperatures were recorded in June. The canal water was more turbid than that of the adjoining Shatt al-Arab estuary due to high algal populations and sewage disposal. The chlorosity values were remarkably high in the canal, due to sewage disposal. The flood waters in June lowered the chlorosity in both estuary and canal. Sewage disposal into the canal decreased its dissolved oxygen content. The lower oxygen values in the estuary in June were accompanied with higher temperatures. The pH values were generally higher in the estuary and were also higher in June than in March.Eighty-six algal taxa were recorded, 45 of which were diatoms. The phytoplankton in the estuary was more abundant in March, due to the increase in currents and turbidity in June. The Chlorophyta, Conjugatophyta, Myxophyta and Bacillariophyta in the estuary showed reverse seasonal trends from those of the total phytoplankton. These algal seemed to flourish during periods of high temperatures. The dense blue-green algae recorded in June is attributed to the high temperature and dissolved organic matter. The Chrysophyta recorded high populations in the estuary in March and were totally absent in June. Lower temperatures and high transparency in March might have led to their relative abundance.The total phytoplankton in the Ashar Canal followed two different seasonal trends, one resembling and the other differing from those in the estuary. The disposal of domestic sewage and agricultural wastes in the canal seemed to lead to such adverse seasonal variations. The diatoms only dominated the phytoplankton at one station in both months. The sewage and agricultural wastes disposal seemed to favour the abundance of the other phyla than the diatoms. Increased organic load in the canal has led to a considerable increase in the Myxophyta in June. Blooms of Chlamydomonas sp. and Euglena acus increased the phytoplankton densities in March at stations II and IV, respectively. Benthic or periphytic algae were found in the phytoplankton populations. Raised salinity seemed to restrict the distribution of the planktonic diatom Bacillaria paradoxa. Among the noticeable widespread planktonic algae in the study area are Dinobryon sertularia, Pediastrum duplex and P. simplex.     

Food preference,food quality and diets of three herbivorous gastropods (Trochidae: Tegula) in a temperate kelp forest habitat

Summary The relationship between food preference and food quality (i.e. a food's contribution to growth and reproductive development) was examined in the laboratory for 3 species of herbivorous kelp forest gastropods (Tegula). The preference hierarchies of the 3 Tegula for 6 common algal species are the same: giant kelp (Macrocystis) is the most preferred food and brown algae are consumed at higher rates than red algae. Despite their strong preference for Macrocystis, the 3 species had significantly greater growth and/or reproductive development on a mixed-algae diet than on either brown or red algae alone. Laboratory preferences of the snails did not correspond closely with caloric content, estimated availability or quality of the algal species used in this study. However, the 3 Tegula are subject to strong benthic predation and Macrocystis provides an important spatial refuge in nature. The potential role of non-nutritional factors such as predator avoidance on the formation of food preferences is discussed.     

金沙江上段浮游藻类和着生藻类群落格局及其与环境因子的关系比较研究

比较河流浮游藻类和着生藻类群落的时空格局及其与环境因子关系的差异,有助于了解两类藻的区别与联系。然而,目前这方面的研究还不多。基于2019年秋季和2020年夏季金沙江上段干流17个样点藻类及水体理化指标的调查数据,分析了不同季节浮游藻类和着生藻类群落结构及其主要环境驱动因子,比较了两类藻的多样性格局及其与环境关系的异同。结果发现,调查河段的浮游藻类和着生藻类均以硅藻为主,其中浮游藻类以极小曲壳藻(Achnanthes minutissima)、钝脆杆藻(Fragilaria capucina)、适中舟形藻(Navicula accomoda)为主要优势种,着生藻类以极小曲壳藻(Achnanthes minutissima)、扁圆卵形藻(Cocconeis placentula)、橄榄绿色异极藻(Gomphonema olivaceum)为主要优势种。浮游藻类和着生藻类秋季平均密度分别为:2.41×10~5个/L、9.43×10~3个/cm~2,均明显高于夏季的平均密度(4.84×10~4个/L、4.84×10~3个/cm~2)。两类藻的群落格局表现出明显的季节变化,但只有着生藻分类单元...     

A preliminary study of temporal variation in the colonization of subtidal algae in an Ecklonia radiata community

Temporal changes in the colonization of settlement plates by algae were determined for an Ecklonia radiata (C. Ag.) J. Ac community. Relative covers of individual algal types were recorded on plates that were exposed for short periods (2 weeks) and then taken to the laboratory. Sets of plates were examined each month from April 1981 to March 1982.Marked seasonal changes were detected in the total cover of algae, the relative covers of individual algal types and the diversity of the colonizing community (as measured by the Shannon—Weaver diversity index and the number of algal types). Advantages and disadvantages of this method and other methods to determine the structure of the colonizing community are discussed.It is concluded that, in addition to examining subsequent biological processes, future studies on the dynamics of kelp communities should also estimate temporal variation in the settlement of algae.     

Biogeochemistry and microbial community composition in sea ice and underlying seawater off East Antarctica during early spring

Pack ice, brines and seawaters were sampled in October 2003 in the East Antarctic sector to investigate the structure of the microbial communities (algae, bacteria and protozoa) in relation to the associated physico-chemical conditions (ice structure, temperature, salinity, inorganic nutrients, chlorophyll a and organic matter). Ice cover ranged between 0.3 and 0.8 m, composed of granular and columnar ice. The brine volume fractions sharply increased above −4°C in the bottom ice, coinciding with an important increase of algal biomass (up to 3.9 mg C l⁻¹), suggesting a control of the algae growth by the space availability at that period of time. Large accumulation of NH₄ ⁺ and PO₄ ³⁻ was observed in the bottom ice. The high pool of organic matter, especially of transparent exopolymeric particles, likely led to nutrients retention and limitation of the protozoa grazing pressure, inducing therefore an algal accumulation. In contrast, the heterotrophs dominated in the underlying seawaters.