Short-term effects of a large dam decommissioning on biofilm structure and functioning

Aging dams and the rising efforts to restore stream ecosystems are increasing the number of dam decommissioning programs. Although dam decommissioning aims at improving in-stream habitat, biodiversity, and ecosystem functioning in the long term, it might also cause ecological impacts in the short term due to the mobilization of the sediment accumulated in the reservoir. Benthic biofilm in particular can be impaired by episodes of high turbidity and scouring. We conducted a multiple before-after/control-impact experiment to assess the effects of the drawdown of a large dam (42 m tall), a first step to its decommissioning, on biofilm structure (biomass and chlorophyll-a) and functioning (metabolism, nutrient uptake, and organic matter breakdown). Our results show that the reservoir drawdown reduced the autotrophic biofilm biomass (chlorophyll-a) downstream from the dam, which in turn lowered metabolism. However, nitrogen and phosphorus uptake by the biofilm was not affected. Organic matter breakdown was slower below the dam than in nearby undammed reaches before and during drawdown. All drawdown effects quickly disappeared and reaches downstream from the dam approached values found in nearby undammed reaches. Thus, our results indicate that the effects of reservoir drawdown on stream biofilms exist but may be small and disappear rapidly.     

New branched Porolithon species (Corallinales,Rhodophyta) from the Great Barrier Reef,Coral Sea,and Lord Howe Island

Porolithon is one of the most ecologically important genera of tropical and subtropical crustose (non-geniculate) coralline algae growing abundantly along the shallow margins of coral reefs and functioning to cement reef frameworks. Thalli of branched, fruticose Porolithon specimens from the Indo-Pacific Ocean traditionally have been called P. gardineri, while massive, columnar forms have been called P. craspedium. Sequence comparisons of the rbcL gene both from type specimens of P. gardineri and P. craspedium and from field-collected specimens demonstrate that neither species is present in east Australia and instead resolve into four unique genetic lineages. Porolithon howensis sp. nov. forms columnar protuberances and loosely attached margins and occurs predominantly at Lord Howe Island; P. lobulatum sp. nov. has fruticose to clavate forms and free margins that are lobed and occurs in the Coral Sea and on the Great Barrier Reef (GBR); P. parvulum sp. nov. has short (<2 cm), unbranched protuberances and attached margins and is restricted to the central and southern GBR; and P. pinnaculum sp. nov. has a mountain-like, columnar morphology and occurs on oceanic Coral Sea reefs. A rbcL gene sequence of the isotype of P. castellum demonstrates it is a different species from other columnar species. In addition to the diagnostic rbcL and psbA marker sequences, the four new species may be distinguished by a combination of features including thallus growth form, margin shape (attached or unattached), and medullary system (coaxial or plumose). Porolithon species, because of their ecological importance and sensitivity to ocean acidification, need urgent documentation of their taxonomic diversity.     

Responses of the desert green algae,Chlorella sp. to drought stress

Desert algae are important components of the desert soil crust and play an essential role in desert soil ecosystem development. Owing to their special habitat, desert algae are often exposed to harsh environments, among which drought represents the most common stress. Green algae are considered to have drought tolerance potential; however, only a few studies have investigated this. In this study, we selected the green alga Chlorella sp., which was isolated from desert soil, and studied its physiological response to polyethylene glycol (PEG) 6000-induced drought stress. The results showed that drought stress can affect the photosynthetic efficiency of Chlorella sp., reduce its water retention ability, and destroy its ultrastructure. However, Chlorella sp. can cope with drought stress through a series of physiological regulatory strategies. Protective strategies include quick recovery of photosynthetic efficiency and increased chlorophyll content. In addition, induced synthesis of soluble proteins, lipids, and extracellular polysaccharide (EPS), and accumulation of osmotic regulatory substances, such as sucrose and trehalose, also contribute to improving drought tolerance in Chlorella sp. This study provides insights into the physiological responses of Chlorella sp. to drought stress, which may be valuable for understanding the underlying drought adaptation mechanisms of desert green algae.     

Occurrence of a novel group of hemagglutinins extractable by Pronase treatment in marine algae

Nine species of marine algae have been assessed for the presence of novel hemagglutinins not extractable with buffer, unless the algal tissue was pretreated with Pronase. All species examined contained hemagglutinins, indicating the existence of a novel group of hemagglutinins which differed from those reported previously in marine algae.     

CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN,A CYANOBACTERIAL SHEATH PIGMENT1

Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m^?2· S^?1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.     

BLUE-GREEN ALGAL MATS IN A SMALL STREAM1

Bedrock erosional features in a small stream (Little Schultz Creek, Bibb County, Alabama) created a variety of habitats for epilithic growth. One suck habitat was illustrated by the occurrence of small falls (<0.3 m) in the main channel of the stream and blue-green algal mats associated with them. The cohesive, laminar algal mats were found at 15 such sites along a 250-m reach of the stream. The primary mat matrix consisted of the blue-green alga Oscillatoria submembranacea Ardissone and Strafforella. The uppermost portion of each mat consisted of a thin (<1 mm thick) green layer of biologically active filaments. The lower layers were thicker (up to 2 cm thick) and consisted of brown laminae of Oscillatoria filaments, and associated sediments. In addition, numerous diatoms mere associated with the mat surface. Some were loosely attached (e.g. Achnanthes); others (Cymbella tumida (Bréb.) V. H.) were stalked. These mats were present throughout the year and showed a bimodal annual distribution with maxima hi February and July. In February, total mat coverage was higher than in July. This winter maximum may have been related to a mode of growth dependent upon sedimentation from storm events and subsequent upward growth of the alga. Mat primary productivity on an areal basis (432 mg C · m^?2· d^?1 in March and 907 mg C · M^?2· d^?1 in April) was 2–12 times the maxima measured on epizoic and cobbles surfaces and other bedrock surfaces in the same stream. The limited areal coverage of the mats, when compared to other surfaces available for algal colonization, made them less important than other epilithic and epizoic surfaces in terms of total primary production in this stream reach. However, we propose that the combination of their unique structure and high primary productivity may make these algal mats sites of high algal and bacterial metabolic activity, which may include anaerobic processes in midchannel, where such activity would not be expected to occur.     

NEW ENDOLITHIC CYANOBACTERIA FROM THE ARABIAN GULF. I. HYELLA IMMANIS SP. NOV.1

Hyella immanis, a new species of endolithic cyanobacterium that penetrates carbonate ooid sand grains in the Arabian/Persian Gulf, is formally described. Natural populations of the new taxon were sampled in moving ooid shoals at four locations along the east coast of Saudi Arabia, together with seven other endolithic taxa. The new species was isolated, and its properties were studied under experimental conditions. Small reproductive cells (baeocytes) exhibited positively phototactic gliding motility following release. In culture they grew into colonies forming isodiametric packages (prevalent on agar) and distinct pseudofilaments (prevalent in liquid culture). Carbonate penetration of the cultured strain in liquid culture proceeded at a rate of up to 10 μ· d^?1. Agitation of cultures with magnetic stirrers enhanced the frequency of borings and the initial boring rates, but it had no effect on the continuing boring activity. A fossil counterpart of the new species was identified in Upper Proterozoic (700–800 million years old) silicified oolitic and pisolitic rocks of East Greenland.     

LIFE HISTORY AND SYSTEMATIC POSITION OF PSEUDOCHORDA GRACILIS SP. NOV. (LAMINARIALES,PHAEOPHYCEAE)1

Pseudochorda gracilis sp. Nov. (Pseudochordacease, Laminariales) is described from the Japan Sea coast of Hokkaido/ the species is subtidal, epilithic and annual, appearing in spring and maturing in winter. Erect thalli grow solitary or in tufts on a small discoid holdfast. They are simple, cord-shaped and hollow, with inner hyphal filaments, cylindrical medullary cells and paraphyses consisting of 3–6 cells. Hair tufts are observed only in young thalli. Unilocular sporangia are sessile and narrowly ovate. In culture, P. gracilis shows a heteromorphic life history with oogamy, characteristic of the order Laminariales. Gametophytes are dioecious and dimorphic. Gametophytes mature under lower temperature conditions (usually below 10°C), and sporophytes mature under low temperature and short-day conditions (5°C, SD). The seasonal growth pattern of the species results from the photoperiod-temperature conditions controlling saprophyte maturation.     

MICROBIAL COLONIZATION ON NATURAL AND ARTIFICIAL MACROPHYTES IN A PHOSPHORUS-LIMITED,HARDWATER LAKE1

Epiphyte communities in a phosphorus-limited hard-water lake were compared over a 14-week period from Potamogeton illinoensis and structurally similar artificial plants of different leaf ages. Artificial plants were serially incubated in the lake to simulate the age of natural leaves. The physiognomy of loosely attached epiphytes appeared similar on the two substrata. Algal cell number and biovolume were 15-fold and 17-fold higher, respectively, on artificial leaves early in the growing season, but total algal density gradually became similar on natural and artificial plants. In contrast, the taxonomic composition of loosely attached algae became increasingly distinct, and mean cell biovolume on natural leaves was twice that on artificial leaves. Adnate epiphytes on both substrata developed from sparse populations of bacteria on new leaves to a community of diatoms, blue-green algae and numerous bacteria on mature and senescent leaves. Adnate community succession on natural leaves in late senescence/death differed from that on artificial leaves colonized for comparable periods in having (1) a marked increase in filamentous blue-green algae, (2) a subsequent decrease in all algae, and (3) a final fungi-dominated stage. The trends in colonization indicate that macrophytes in this oligotrophic lake provided a distinct habitat from that of artificial substrata for epiphytes throughout the growing season.     

SALINITY AND NUTRIENT LIMITATIONS ON GROWTH OF BENTHIC ALGAE FROM TWO ALKALINE SALT LAKES OF THE WESTERN GREAT BASIN (USA)1

Enrichment cultures of littoral benthic algae from Mono Lake, California, and Abert Lake, Oregon, were grown under conditions of varied salinity and nutrient content. Field-collected inocula were composed mainly of diatoms and filamentous blue-green and green algae. The yield of long-term cultures (30 days) showed tolerance over a broad salinity range (50–150 g·L^?1) for Mono Lake-derived algae. Algae from Abert Lake had a lower range of tolerance (25–100 g·L^?1) Organic content and pigment concentrations of algae from both lakes were also reduced above the tolerated salinity level. Within the range of salinity tolerance for Mono Lake algae, initial growth rates and organic content were reduced by increased salinity. The effects of macro- and micronutrient enrichment on algal growth in Mono Lake water were also tested. Only nitrogen enrichment (either as ammonium or nitrate) stimulated algal growth. Although the benthic algae cultured here had wide optima for salinity tolerance, the rates of growth and storage were limited by increased salinity within the optimum range. Although the lakes compared had similar species composition, the range and limits of tolerance of the algae were related to salinity of the lake of origin.