Changes In Algal Composition Research Articles

Changes in algal community structure via density‐ and trait‐mediated indirect interactions in a marine ecosystem

In various terrestrial and aquatic ecosystems, predators affect resources indirectly via intermediate prey. Such indirect interactions involve reducing the density of the prey (density-mediated indirect interactions, DMIIs) or changing the behavioral, morphological, or life history traits of the prey (trait-mediated indirect interactions, TMIIs). Although the importance of TMIIs has been highlighted recently, the strengths of both DMIIs and TMIIs under natural conditions have rarely been evaluated, especially in the context of resource community structure. We studied a three-level marine food chain involving the carnivorous snail Thais clavigera, its limpet prey Siphonaria sirius, and the limpet's food sources, the algae Lithoderma sp. and Ulva sp. We measured the strengths of DMIIs and TMIIs and observed how the algal community changes under the pressure of natural predation by T. clavigera on S. sirius. Neither DMIIs nor TMIIs affected the total algal cover or chlorophyll content per unit area. However, both types of indirect interactions caused similar changes in algal composition by increasing the cover of Ulva and decreasing the cover of Lithoderma. This change in the algal community was caused by a reduction in the limpet's preferential consumption of the competitively dominant Ulva over Lithoderma. These results suggest that both DMIIs and TMIIs have similar effects on the changes in resource community structure under natural conditions.

Long-term changes in the algal composition of the Vaal River, South Africa – did the Lesotho Highlands Water Project play a role?

The Vaal River has become so nutrient-enriched that algal blooms pose problems. A unique opportunity arose to determine if there were changes in the chemistry en algal composition of the Vaal River after oligomesotrophic Katse Dam (Lesotho) water was imported to augment supplies in the light of growing water demands in the Vaal River catchment area. Algal concentration and composition in the Vaal River during three periods (between 1992 and 1994, 1998 and 2000, as well as 2004 and 2006) were compared to those in the Katse Dam (1998–2006). Some algal species, initially absent from the Vaal River, appeared in the river during and after transfer. Mixed algal assemblages found in the Vaal River before transfer of Katse Dam water gradually changed after transfer to assemblages mainly composed of cyanobacteria. The total algal concentration in the Vaal River Barrage doubled from the period between 1992 and 1994 to that between 2004 and 2006, indicating that the transfer of clear, oligomesotrophic Katse Dam water did not dilute the eutrophic Vaal River water sufficiently in order to reduce algal concentrations. Results showed that continuous downstream pollution and eutrophication of the Vaal River system eliminated the diluting effect of Katse imports. This resulted in changes in algal composition and concentration in the Vaal, characteristic of those associated with increasing eutrophication.

Changes in Diatom Biodiversity in Lake Sinclair, Baldwin County, Georgia, USA

The effects of increased water temperature on algal community composition were investigated in Lake Sinclair, Baldwin County, Georgia, USA. The lake received waste cooling water from a coal burning power plant. Discharges of recycled lake water were, on average, 15°C ± 1.5°C (and up to 23°C) warmer than typical ambient temperatures. Seasonal changes in algal composition were observed, and the warmer sample site had a greater diversity of diatom species year round independent of changes in temperature. Thermal pollution created a high percent dissimilarity between diatoms at the warmer site and the remainder of the lake. Species turnover observed in natural samples was not detected for the warmer site. Anthropogenic thermal pollution was implicated as the factor inducing changes in the natural algal community composition, which may impact other trophic levels and ultimately the overall ecology of Lake Sinclair.

Effects of nutrients enrichment on algal communities: an experimental in mesocosms approach

AIM: The effect of different concentrations of nutrients on algal communities living at the bottom of mesocosms was examined; METHODS: The experiment was carried out in the tributary of Rosana reservoir (Corvo river) from November 22nd to December 16th of 2003. Mesocosms were set up in triplicate, with four treatments: nitrogen (N); phosphorus (P); nitrogen plus phosphorus (NP); plus a control treatment (C), consisting in addition of water from the reservoir; RESULTS: Results of the Principal Components Analysis applied on the abiotic variables have shown that two axes explained 93.6% of the total variability (69.6 and 23.9%, respectively). It was possible to identify a group of P (positive) and N (negative) treatments of axis 1. The addition of nutrients in the experiment resulted in changes in algal composition. Mean values of density ranged from 8.383 to 34.510 ind.mL-1. Higher densities occurred in the phosphorus and nitrogen plus phosphorus treatments. The most representative classes were Zygnemaphyceae, Chlorophyceae, Bacillariophyceae and Cyanobacteria, both in density and species richness; CONCLUSIONS: Phosphorus seems to be beneficial to green algae in general, since a marked increase in Zygnemaphyceae and Chlorophyceae was found in the treatments containing phosphorus and nitrogen plus phosphorus. In the nitrogen treatment, however, green algae decreased dramatically, while Cyanobacteria remained constant, indicating their capacity to live in changed environments and confirms the limiting role played by phosphorus on the algal groups.

Changes in algal composition and environmental variables in the high-altitude Mohale Dam — an important water supply reservoir to South Africa

Whereas limited knowledge exists on the ecology and algae present in Lesotho's high-altitude Katse Dam, nothing is published about these aspects in the linked Mohale Dam, completed in 2003. This study investigated the changes in algal composition and associated environmental variables since the construction of the Mohale Dam until the present. Monthly sampling in 2003 and 2006 indicated that dissolved inorganic nitrogen concentrations decreased, while dissolved inorganic phosphorus concentration increased 12-fold, resulting in increases in algal concentration and a shift from green algal dominance in 2003 to cyanobacterial dominance in 2006. Multivariate analyses indicated that cyanobacteria were favoured by high temperatures and low DIN:DIP ratios. Although currently non-problematic, the dominance of cyanobacteria may pose future potential problems, especially if further increases in nutrient concentrations occur. Strains of Microcystis aeruginosa, currently one of the dominant species, are toxic.

Relative strengths of benthic algal nutrient and grazer limitation along a lake productivity gradient

The relative effects of nutrients and herbivores on primary producers are rarely compared across ecosystems that vary in potential primary productivity. Furthermore, proposed mechanisms to explain such patterns remain understudied. Here, I examine the strength of nutrient and grazer (herbivore) limitation (i.e., the extent to which producers' growth is limited by insufficient nutrient supply or herbivory) of benthic algae across 13 southwest Michigan lakes that vary widely in productivity (i.e., resource supply). I compare the observed patterns of algal limitation and species composition to those predicted by two simple models: one that includes multiple species and species' traits (the food-web model) and one that includes no variation in species or traits (the food-chain model). Species in the food-web model are assumed to display a tradeoff between resource competitive ability and resistance to herbivory (the "keystone predator" tradeoff). Among these lakes, benthic algal nutrient limitation was positive (x=0.083 day-1) and declined significantly along a lake N:P gradient. In contrast, grazer limitation was negative (x=-0.019 day-1) and was not significantly related to any of the measured lake productivity variables. Negative grazer limitation indicated that the removal of grazers caused unexpected declines in algal biomass, which were potentially due to indirect, positive effects (e.g., nutrient recycling) of grazers. Nutrient limitation was significantly stronger than grazer limitation across lakes, which was more consistent with the food-web versus food-chain model. Changes in algal composition were also broadly consistent with predictions of the food-web model in that vulnerable, superior nutrient competitors dominated in low productivity lakes and more grazer-resistant species were observed in high productivity lakes. In general, these results point to the importance of examining limiting factors across systems and the consideration of key species' traits when predicting and interpreting patterns.

The survival of Sicyopterus stimpsoni, an endemic amphidromous Hawaiian gobiid fish, relies on the hydrological cycles of streams: evidence from changes in algal composition of diet through growth stages fish

Gut contents of larval, juvenile, and adult specimens of the Hawaiian gobiid fish Sicyopterus stimpsoni were examined to catalog the algal flora ingested by this species. The developmental stages of S. stimpsoni examined represented hallmark points in the fish’s life cycle corresponding with major migratory and metamorphic transitions. The algal flora was dominated by diatom species and shifted from taxa representative of a marine, planktonic community in larval fish to a freshwater, benthic community in juvenile and adult fish. This change in diet corresponds with the migration of larval fish to freshwater streams just prior to juvenile development in which rapid modification in mouth anatomy makes ingestion of planktonic algal species difficult. Benthic diatoms from juvenile and adult fish assemblages represented multiple genera that live in a narrow set of environmental conditions. These algae grow during a specific period in the development of the benthic algal community in Hawaiian streams. This suggests a highly specialized dietary behavior that depends heavily on continually restarting the benthic algal successional pattern, which appears to be regulated by the hydrological cycles of streams on the island.

MACROBENTHIC COLONIST GUILDS AND RENEGADES IN MONTEREY CANYON (USA) DRIFT ALGAE: PARTITIONING MULTIDIMENSIONS

Accumulations of sunken drift macrophytes are known to stimulate high secondary production in submarine canyon heads, but the details of macroinvertebrate colonization of these subsidies are poorly known. I conducted a series of algal and macrofanual sampling programs and manipulative algal-placement experiments in different Monterey Canyon head sub-habitats and seasons from 1988 to 1991 to elucidate the dynamics of macroinvertebrate associations with sunken drift macrophytes, severe annual sediment-flushing events, and the physical and chemical changes associated with these agents of subsidy and disturbance. Conducting these investigations in such a highly disturbed and subsidized setting, i.e., with multiple niche axes, would enable novel insights into how biological communities are structured. Up to 5.7 × 105 individual macrofauna/m2 inhabited naturally occurring patches of sunken drift algae in Monterey Canyon's s shallow head (Monterey Bay, California, USA), and the seasonally changing mosaics of macrophyte subsidies led to conspicuously converse responses of amphipods and polychaetes. Amphipods dominated natural patches of sunken algae during winter and spring, while polychaetes dominated during late summer and fall. This community shift corresponded with temporal changes in algal composition, dissolved oxygen (DO), and annual flushing disturbances. Repeated algal-colonization experiments in different habitats further highlighted the contrasting responses of amphipods and polychaetes to drift algae and other habitat characteristics. Mean abundances of motile amphipods increased between 8- and 148-fold within five days after placement of Enteromorpha patches (up to >4 × 105 individuals/m2) while abundances less than doubled in Macrocystis treatments. Amphipod species colonized Enteromorpha treatments in significantly greater numbers than any controls irrespective of date and sub-habitat. Polychaete species did not colonize algae treatments in significant numbers within five days, but experiments did reveal significant temporal and habitat differences in this group. Sampling of swimming macrobenthos in different canyon habitats and depths (including 30, 100, 300, and 500 m) revealed temporal and habitat patterns in crustaceans and provided explanations of guild functional contrasts. Attributes of two “evolutionary renegades,” the phytic polychaete Platynereis bicanaliculata and the hypoxia-tolerant crustacean Nebalia sp., indicated that adaptive constraints inherent in the phenologies and life histories of the two partitioned guilds help reinforce normal functional boundaries. Maximum species richness at intermediate DO and time since disturbance resulted from complementary responses of the two guilds to temporal and habitat characteristics that are shaped by an interacting regime of algal subsidy, hypoxia, and severe flushing disturbance. Corresponding Editor: R. V. Etter.

High Spirulina productivity under intensive light

Spirulina platensis * ) cultures were illuminated in a glass tube with light intensities of up to 394 klx (9.8 W of visible light per g of algae) using sun light concentrated by means of reflectors. No bleaching or photoinhibition was observed, but an increase in productivity of up to 270%, compared to parallel cultures under normal solar irradiance. The changes in algal composition under such intensive light are (the values depend on the light intensity): decrease in protein (by up to 40% and of phycocyanin (down to 18% of reference culture), increase in carbohydrates (up to more than 100%), chlorophyll (up to 167% of reference culture) and DNA (up to 40% above reference culture). Possible applications of these techniques are discussed.

Lipid metabolism of the Antarctic krill Euphausia superba and its ecological implications

Various developmental stages (early larvae to adults) of Euphausia superba have been collected in different seasons in the Weddell Sea, the Lazarev Sea and off the Antarctic Peninsula to investigate the role of lipids and fatty acids in the life cycle of the Antarctic krill. The total-lipid data for E. superba exhibited seasonal variations, with low lipid levels in late winter/early spring and the highest levels in autumn. Seasonal changes were most pronounced in the immature and adult specimens, increasing from about 10% lipid of dry mass to more than 40%. The fatty-acid compositions of the younger stages were dominated by 20:5(n-3), 22:6(n-3) and 16:0. These are typical phospholipid fatty acids, which are major biomembrane constituents. The phospholipid composition was similar in the older stages. With increasing storage of triacylglycerols in the lipid-rich immature and adult stages, the fatty acids 14:0, 16:0 and 18:1(n-9) prevailed, comprising about 70% of total triacylglycerol fatty acids. The trophic-marker fatty acids 16:1(n-7) and 18:4(n-3), indicating phytoplankton ingestion, were less abundant. They reflected, however, the dependence of the larvae on phytoplankton as well as the seasonal changes in algal composition. The generally close linear relationships between fatty acids and lipid suggest that the fatty-acid compositions of the collected specimens were largely independent of the respective developmental stage, season and region. The linear fit indicates that triacylglycerol accumulation started at a level of about 5% of total lipid. Considering the various overwintering scenarios under discussion, the life cycle and reproductive strategies of krill are discussed in the context of the lipid metabolism and fatty-acid composition of E. superba. Lipid production is effective enough to accumulate large energy reserves for the dark season, but E. superba does not exhibit the sophisticated biosynthetic pathways known from other Antarctic euphausiids and copepods. Although important, lipid utilisation appears to be just one of several strategies of E. superba to thrive under the extreme Antarctic conditions, and this pronounced versatility may explain the success of this species in the Southern Ocean.

The interactive effects of low pH, toxic metals, and DOC on a simulated temporary pond community

The effects of pH, potentially toxic metals, and dissolved organic carbon (DOC) on a freshwater, palustrine wetland assemblage (three amphibian species, one mosquito genus, and 18 genera of algae) were examined in 500 liter outdoor mesocosms. The design was fully factorial and exposure levels were set to represent concentrations that occur naturally in temporary ponds in central Pennsylvania, an acid-impacted region of the USA. Water chemistry was precisely regulated by use of an artificial pond water rather than using stream water or well water with partially unknown composition. Jefferson ( Ambystoma jeffersonianum) and spotted salamanders ( A. maculatum) were negatively impacted by low pH and high metal concentrations. Wood frogs ( Rana sylvatica) were negatively impacted by high DOC and low pH. These negative effects included increased time to metamorphosis and decreased survival and wet body mass at metamorphosis. Mosquito emergence was unaffected by pH, metals, or DOC. All three abiotic factors (metals, pH, and DOC) interacted to determine algal taxonomic composition. Hence, abiotic conditions may determine amphibian reproductive success both directly and indirectly, via effects on algae, since a primary food source of salamanders, zooplankton, are affected by changes in algal composition. These complex interactions should be considered in evaluating the possible toxicity of pond waters to fauna and flora. Until now, pH alone has been considered the primary limiting factor for amphibians breeding in temporary ponds.

Influence of season, ontogeny and tide on the diet of the temperate marine herbivorous fish Odax pullus (Odacidae)

The diet of the temperate marine herbivorous fish Odax pullus (Pisces: Odacidae) was examined using gut-content analysis followed by principal-component analysis and analysis of variance. Fish were collected near Leigh, on the northeast coast of New Zealand, from February 1983 to September 1984. The data were categorised by size of fish, season, and state of tide. A major ontogenetic shift in diet was observed. Juveniles fed on animal material (crustaceans and gastropods), epiphytic rhodophytes, and some phaeophyte material. Adults fed almost exclusively on two phaeophyte taxa, the laminarian Ecklonia radiata and the fucoid Carpophyllum spp. Dietary selection was evident at the level of particular plant components; the diet of larger fish in spring samples was dominated by fucoid reproductive receptacles. There was no direct evidence of a tidal influence on diet composition of O. pullus, although the relative proportions of E. radiata and Carpophyllum spp. ingested by adult fish appeared to vary with tidal state. The volume of gut contents varied seasonally for all size classes, although the timing of peak annual food intake varied among size classes. Tidal state did not influence the volume of the gut contents. The ontogenetic and seasonal trends evident in the diet of O. pullus appeared to be related to a number of factors including relative gut length, gonad development, ontogenetic changes in feeding anatomy and seasonal changes in algal composition.