Predominance of picoplankton and nanoplankton in eutrophic Calder Lake

A study was conducted to examine factors regulating the biomass of algal picoplankton in Calder Lake, a small eutrophic lake in southern New York state. A particular focus was a current paradigm which suggests that larger cells may dominate in nutrient-rich waters, while smaller cells may predominate only in oligotrophic waters. Over two years, phytoplankton biomass consisted predominantly (74% on average) of very small organisms; nanoplankton (<20 to 2 µm: 39%) and picoplankton (<2 µm to 0.2 µm: 35%), despite the presence of surface blooms of colonial cyanobacteria (Microcystis aeruginosa, Anabaena limnetica), and dense metalimnetic populations of the dinoflagellate Ceratium hirundinella. This dimictic system is characterized by relatively high levels of total P (max = 85, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 9.7 µg P/L), inorganic P (max = 26, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 4.5 µg P/L), and total inorganic N (max = 285, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiEayaara% aaaa!3702!\[\bar x\] = 85 µg P/L), but larger forms were rarely the most abundant. Unlike some marine systems, greater abundance of algal picoplankton was not associated with deeper strata (low light), or warmer temperatures. Data suggest that midsummer nutrient limitation, especially P-limitation, favors the development of pico- and nanoplankton in the limnetic zone of eutrophic lakes.     

Optimization of algal photobioreactors using flashing lights

It has been reported that flashing light enhances microalgal biomass productivity and overall photosynthetic efficiency. The algal growth kinetics and oxygen production rates under flashing light with various flashing frequencies (5 Hz-37 kHz) were compared with those under equivalent continuous light in photobioreactors. A positive flashing light effect was observed with flashing frequencies over 1 kHz. The oxygen production rate under conditions of flashing light was slightly higher than that under continuous light. The cells under the high frequency flashing light were also observed to be healthier than those under continuous light, particularly at higher cell concentrations. When 37 kHz flashing light was applied to an LED-based photobioreactor, the cell concentration was higher than that obtained under continuous light by about 20%. Flashing light may be a reasonable solution to overcome mutual shading, particularly in high-density algal cultures.     

Marine macroalgae and their associated microbiomes as a source of antimicrobial chemical diversity

ABSTRACT

This article reviews the role of microbial biofilms in infection, and the antimicrobial chemical diversity of marine macroalgae and their associated microbiomes. Antimicrobial resistance (AMR) represents one of the major health threats faced by humanity over the next few years. To prevent a global epidemic of antimicrobial-resistant infections, the discovery of new antimicrobials and antibiotics, better anti-infection strategies and diagnostics, and changes to our current use of antibiotics have all become of paramount importance. Numerous studies investigating the bioactivities of seaweed extracts as well as their secondary and primary metabolites highlight the vast biochemical diversity of seaweeds, with new modes of action making them ideal sources for the discovery of novel antimicrobial bioactive compounds of pharmaceutical interest. In recent years, researchers have focused on characterizing the endophytic and epiphytic microbiomes of various algal species in an attempt to elucidate host-microbe interactions as well as to understand the function of microbial communities. Although environmental and host-associated factors crucially shape microbial composition, microbial mutualistic and obligate symbionts are often found to play a fundamental role in regulating many aspects of host fitness involving ecophysiology and metabolism. In particular, algal ‘core’ epiphytic bacterial communities play an important role in the protection of surfaces from biofouling, pathogens and grazers through the production of bioactive metabolites. Together, marine macroalgae and their associated microbiomes represent unique biological systems offering great potential for the isolation and identification of novel compounds and strategies to counteract the rise and dissemination of AMR.     

Animal associations with the dominant species of shallow water macrophytes along the coastline of the Vestfold Hills,Antarctica

Benthic grab samples, taken through core holes in sea-ice 1983, returned eight species of marine macrophytes which had associated fauna on at least one sample. A total of 24 animal taxa were found on these eight macrophytes. Phyllophora antarctica had a significantly greater biomass of attached fauna per unit of macrophyte biomass than any of the other seven species. It also had the greatest variety of epiphytic fauna (21 taxa). Phyllophora antarctica was the only macrophyte collected from comparatively protected Ellis Fjord, apart from filamentous algae, including Cladophora subsimplex and Geminocarpus austrogeorgiae, which were found in the most landward basin. It therefore played an important role in the ecology of the fjord. Palmaria decipiens was commonly collected at more exposed coastal sites and was dominant in Long Fjord, characterized here as intermediate in terms of water movement. Sixteen animal taxa were collected from this macrophyte with the greatest numbers being found in July and August. Only four animal taxa were collected from Iridaea cordata. The other five macrophyte species from which epiphytic animals were collected (Porphyra endiviifolium, Plocamium cartilagineum, Desmarestia menziesii, Himantothallus grandifolius and Cladophora subsimplex had animals associated with them on less than half the occasions when they were found.     

Effects of Phosphorus Removal on the Maximal Algal Growth in Bioassay Experiments with Water from Four Dutch Lakes

This paper reports the effects of phosphorus removal at three sewage wastewater treatment plants on the state of eutrophication of four shallow lakes in the south-eastern part of the Rijnland Waterboard area during the years 1980–1982. With chemical analyses and bioassay experiments using the natural phytoplankton population no significant lowering could be detected of respectively the phosphate concentration and the maximal algal growth potential. All lakes proved to be principally nitrogen limited except the Reeuwijk Lakes, which showed clearly, after a primary nitrogen limitation, a secondary phosphorus limitation. Therefore the main attention with respect to phosphorus reduction should be concentrated on the Reeuwijk Lakes in the first place. For the other lakes in the investigated area phosphorus removal will, when it is the only measure taken, presumably not lead at short notice to a decrease of the algal biomass.     

Coral mortality and interaction with algae in relation to sedimentation

The impact of sedimentation on coral–algal interactions was studied by monitoring tissue mortality and radial growth in two coral species, Colpophyllia natans and Siderastrea siderea, over a continuum of sediment input intensities. This study sets out to investigate (1) whether sedimentation can facilitate algal overgrowth of corals and (2) whether this was a significant cause of coral mortality. Over a 15-month period, 198 coral colonies were tagged and photographed at six sites along two replicate gradients of sediment input, spanning high inputs near river mouths to low inputs at exposed headlands. Photographs were taken so that they covered the interface between colonies and algae. Radial growth was measured along colony edges in contact with algae and unaffected by tissue loss from causes other than competition with algae. To establish whether algal overgrowth was a significant cause of coral mortality, tissue mortality on the colony surface area visible in the photographs was related to different causes, including sediment smothering, disease, and algal overgrowth. Radial growth became negative with increasing proximity to river mouths in C. natans and remained negative or close to zero throughout the gradients in S. siderea, overall suggesting that sedimentation can facilitate algal overgrowth on corals. However, the analysis of tissue mortality revealed that algal overgrowth was a relatively minor cause of tissue loss. In contrast, the most important cause of coral mortality in relation to sedimentation was from sediment smothering, probably during intense episodes of deposition associated with heavy rainfall. We conclude that sedimentation may lead to reef degradation by causing coral mortality through sediment smothering and burial, and then by suppressing the regrowth of surviving adult colonies through increased competition with algae.     

Competing phytoplankton undermines allelopathy of a bloom-forming dinoflagellate

Biotic interactions in the plankton can be both complex and dynamic. Competition among phytoplankton is often chemically mediated, but no studies have considered whether allelopathic compounds are modified by biotic interactions. Here, we show that compounds exuded during Karenia brevis blooms were allelopathic to the cosmopolitan diatom Skeletonema costatum, but that bloom allelopathy varied dramatically among collections and years. We investigated several possible causes of this variability and found that neither bloom density nor concentrations of water-borne brevetoxins correlated with allelopathic potency. However, when we directly tested whether the presence of competing phytoplankton influenced bloom allelopathy, we found that S. costatum reduced the growth-inhibiting effects of bloom exudates, suggesting that S. costatum has a mechanism for undermining K. brevis allelopathy. Additional laboratory experiments indicated that inducible changes to K. brevis allelopathy were restricted to two diatoms among five sensitive phytoplankton species, whereas five other species were constitutively resistant to K. brevis allelopathy. Our results suggest that competitors differ in their responses to phytoplankton allelopathy, with S. costatum exhibiting a previously undescribed method of resistance that may influence community structure and alter bloom dynamics.     

Ecophysiology in Relation to Exposure of Pendant Epiphytic Bryophytes in the Canopy of a Tropical Montane Oak Forest1

We investigated ecophysiological and morphological traits affecting light and water use of four commercially important pendant epiphytic bryophyte species in a montane oak‐bamboo forest in Costa Rica. Predictions based mostly on ecophysiological studies of temperate bryophytes and vascular plants were experimentally tested on tropical montane bryophyte species ranked on the basis of their distributions in the canopy from the most protected (1) to the most exposed sites (4): (1) Phyllogonium viscosum; (2) Pilotrichella flexilis; (3) Dendropogonella rufescens; and (4) Frullania convoluta. As predicted, highly exposed species tended to have higher light saturation and compensation points, higher dark respiration rates, more chlorophyll, higher chlorophyll a:b ratios, and higher nitrogen concentrations. Contrary to predicted trends, exposed‐site species had lower water contents at full saturation; there were no detectable differences among species in the rate of water loss. Rates of carbon gain in all species reached asymptotes with increasing water content, but the moisture compensation point for carbon uptake of the moss D. rufescens was substantially higher than in the other species. Observed patterns result from interactions among processes related to water storage and transport operating at different scales and are determined by various morphological traits including the density, size, and disposition of phylloids, as well as by whole‐clump architecture.     

Evidence for a role of protein phosphorylation in the maintenance of the cnidarian–algal symbiosis

The endosymbiotic relationship between cnidarians and photosynthetic dinoflagellate algae provides the foundation of coral reef ecosystems. This essential interaction is globally threatened by anthropogenic disturbance. As such, it is important to understand the molecular mechanisms underpinning the cnidarian–algal association. Here we investigated phosphorylation‐mediated protein signalling as a mechanism of regulation of the cnidarian–algal interaction, and we report on the generation of the first phosphoproteome for the coral model system Aiptasia. Mass spectrometry‐based phosphoproteomics using data‐independent acquisition allowed consistent quantification of over 3,000 phosphopeptides totalling more than 1,600 phosphoproteins across aposymbiotic (symbiont‐free) and symbiotic anemones. Comparison of the symbiotic states showed distinct phosphoproteomic profiles attributable to the differential phosphorylation of 539 proteins that cover a broad range of functions, from receptors to structural and signal transduction proteins. A subsequent pathway enrichment analysis identified the processes of “protein digestion and absorption,” “carbohydrate metabolism,” and “protein folding, sorting and degradation,” and highlighted differential phosphorylation of the “phospholipase D signalling pathway” and “protein processing in the endoplasmic reticulum.” Targeted phosphorylation of the phospholipase D signalling pathway suggests control of glutamate vesicle trafficking across symbiotic compartments, and phosphorylation of the endoplasmic reticulum machinery suggests recycling of symbiosome‐associated proteins. Our study shows for the first time that changes in the phosphorylation status of proteins between aposymbiotic and symbiotic Aiptasia anemones may play a role in the regulation of the cnidarian–algal symbiosis. This is the first phosphoproteomic study of a cnidarian–algal symbiotic association as well as the first application of quantification by data‐independent acquisition in the coral field.