Anthropogenically driven habitat formation by a tube dwelling diatom on the Northern Patagonian Atlantic coast

The tube dwelling diatom Berkeleya rutilans (Trentepohl) Grunow plays a key role as early colonizer and bloom former in coastal zones. Exuding large quantities of extracellular polymeric substances (EPS), it can form dense colonies in mucilaginous macroscopic branches, containing thousands of cells. Due to their pronounced three dimensional growths of its mucilaginous structures, it supports a variety of organisms and traps grains and detritus, which makes it an important habitat former and ecosystem engineer, contributing to sediment stabilization, which is a crucial issue in sedimentary areas. In the present study we investigated the identity and structural morphology of B. rutilans, blooming in a tidal channel in Northern Patagonia (S40° 43′ W64° 56′) and experimentally tested its potential physiological responses (e.g. growth rate) to nutrient elevation. The observed morphological plasticity and measured high growth rates under nutrient exposure make B. rutilans a likely indicator for eutrophication in sedimentary marine habitats. As to our knowledge the present study provides the first record of B. rutilans for Argentinean waters, we discussed the potential reasons for its occurrence and evaluated the ecological impacts of its presence. Due to the observed high colonization capability and rapid response to environmental alterations (e.g. eutrophication, substrate changes) it seems to benefit from human activities, which will consequently favor its further expansion within the disturbed area.     

Biogeography of bloom-forming microcystin producing and non-toxigenic populations of Dolichospermum lemmermannii (Cyanobacteria)

In the last decades, the cyanobacterium Dolichospermum lemmermannii showed an increasing spread to Southern Europe, raising serious concerns due to its ability to produce cyanotoxins. The widening of its geographic distribution and the observation of strains showing high optimum temperature underline its ecological heterogeneity, suggesting the existence of different ecotypes. To investigate its biogeography, new isolates from different European water bodies, together with strains maintained by the Norwegian Institute for Water Research Culture Collection of Algae, were genetically characterised for the 16S rRNA gene and compared with strains obtained from public repositories. Geographic distance highly influenced the differentiation of genotypes, further suggesting the concurrent role of geographic isolation, physical barriers and environmental factors in promoting the establishment of phylogenetic lineages adapted to specific habitats. Differences among populations were also examined by morphological analysis and evaluating the toxic potential of single strains, which revealed the exclusive ability of North European strains to produce microcystins, whereas the populations in Southern Europe tested negative for a wide range of cyanotoxins. The high dispersion ability and the existence of toxic genotypes indicate the possible spread of harmful blooms in other temperate regions.     

Insights into the harmful algal flora in northwestern Mediterranean coastal lagoons revealed by pyrosequencing metabarcodes of the 28S rRNA gene

This study investigated the genetic diversity of phytoplankton communities in six shallow lagoons located on the French coast of the northwestern Mediterranean Sea that represented a trophic gradient ranging from oligotrophic to hypereutrophic. The phytoplankton communities were sampled once a month from spring (May) to the beginning of autumn (September/early October) in 2012 and fractionated by size. Metabarcodes were generated from cDNAs by targeting the D1-D2 region of the 28S rRNA gene and pyrosequenced using Roche 454 technology. Examination of the annotated barcodes revealed harmful algal species not previously documented in these lagoons. Three ichthyotoxic species belonging to Pfiesteriaceae were detected: Luciella masanensis was relatively widespread and abundant in many samples, whereas Pfiesteria piscicida and Stoeckeria changwonensis were found as single barcode sequences. Furthermore, a phylogenetic analysis of barcodes annotated as belonging to Pfiesteriaceae suggested the existence of two previously undescribed clades. The other toxic or potentially harmful dinoflagellates detected through rare barcodes were Dinophysis acuminata, Vulcanodinium rugosum, Alexandrium andersonii and A. ostenfeldii. The two most abundant dinoflagellate taxa were Gymnodinium litoralis and Akashiwo sanguinea with respect to sequence numbers. Four diatom species from the genus Pseudo-nitzschia that potentially produce domoic acid were identified (P. galaxiae, P. delicatissima, P. brasiliana and P. calliantha). These observations are discussed in terms of the literature and monitoring records related to the identified taxa in this Mediterranean area.     

Alteration of plankton communities and biogeochemical cycles by harmful Cochlodinium polykrikoides (Dinophyceae) blooms

Cochlodinium polykrikoides is a globally distributed, ichthyotoxic, bloom-forming dinoflagellate. Blooms of C. polykrikoides manifest themselves as large (many km²) and distinct patches with cell densities exceeding 10³ ml⁻¹ while water adjacent to these patches can have low cell densities (<100 cells ml⁻¹). While the effect of these blooms on fish and shellfish is well-known, their impacts on microbial communities and biogeochemical cycles are poorly understood. Here, we investigated plankton communities and the cycling of carbon, nitrogen, and B-vitamins within blooms of C. polykrikoides and compared them to areas in close proximity (<100 m) with low C. polykrikoides densities. Within blooms, C. polykrikoides represented more than 90% of microplankton (>20 μm) cells, and there were significantly more heterotrophic bacteria and picoeukaryotic phytoplankton but fewer Synechococcus. Terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA genes revealed significant differences in community composition between bloom and non-bloom samples. Inside the bloom patches, concentrations of vitamin B₁₂ were significantly lower while concentrations of dissolved oxygen were significantly higher. Carbon fixation and nitrogen uptake rates were up to ten times higher within C. polykrikoides bloom patches. Ammonium was a more important source of nitrogen, relative to nitrate and urea, for microplankton within bloom patches compared to non-bloom communities. While uptake rates of vitamin B₁ were similar in bloom and non-bloom samples, vitamin B₁₂ was taken up at rates five-fold higher (>100 pmol⁻¹ L⁻¹ d⁻¹) in bloom samples, resulting in turn-over times of hours during blooms. This high vitamin demand likely led to the vitamin B₁₂ limitation of C. polykrikoides observed during nutrient amendment experiments conducted with bloom water. Collectively, this study revealed that C. polykrikoides blooms fundamentally change microbial communities and accelerate the cycling of carbon, some nutrients, and vitamin B₁₂.     

Green land: Multiple perspectives on green algal evolution and the earliest land plants

Green plants, broadly defined as green algae and the land plants (together, Viridiplantae), constitute the primary eukaryotic lineage that successfully colonized Earth's emergent landscape. Members of various clades of green plants have independently made the transition from fully aquatic to subaerial habitats many times throughout Earth's history. The transition, from unicells or simple filaments to complex multicellular plant bodies with functionally differentiated tissues and organs, was accompanied by innovations built upon a genetic and phenotypic toolkit that have served aquatic green phototrophs successfully for at least a billion years. These innovations opened an enormous array of new, drier places to live on the planet and resulted in a huge diversity of land plants that have dominated terrestrial ecosystems over the past 500 million years. This review examines the greening of the land from several perspectives, from paleontology to phylogenomics, to water stress responses and the genetic toolkit shared by green algae and plants, to the genomic evolution of the sporophyte generation. We summarize advances on disparate fronts in elucidating this important event in the evolution of the biosphere and the lacunae in our understanding of it. We present the process not as a step-by-step advancement from primitive green cells to an inevitable success of embryophytes, but rather as a process of adaptations and exaptations that allowed multiple clades of green plants, with various combinations of morphological and physiological terrestrialized traits, to become diverse and successful inhabitants of the land habitats of Earth.     

A spring poleward current and its influence on microplankton assemblages and harmful dinoflagellates on the western Iberian coast

Along-shore currents can propagate harmful algal blooms (HABs) over long distances in many coastal areas of the ocean. Harmful dinoflagellate blooms on the west coast of Iberia frequently occur when the Iberian poleward current (IPC) establishes on the continental slope. This has led to the suggestion that HABs could be transported northward by the IPC. To examine this possibility, the microplankton composition along the west coast of Iberia was studied in May 1993 coinciding with the presence of the IPC. The microplankton of the IPC was almost exclusively composed of small flagellates, with the notable absence of the harmful species usually associated with coastal waters. The primary influence of the IPC was to confine coastal microplankton populations to the shelf, where a downwelling convergence prevented their export from the coastal environment. Microplankton assemblages on the shelf revealed a north–south gradient related to different stages of succession. Earlier stages of succession in which diatoms were prominent were found on the northern shelf, whereas dinoflagellates were more abundant in the south. The toxic species Gymnodinium catenatum, which was only present in the southern shelf, did not show a northward transport associated with the IPC. It is suggested that the northward spreading of HABs along the west coast of Iberia must be related to the interaction between the IPC, which accumulates coastal populations on the shelf, and the latitudinal progress of microplankton succession that determines species composition. Thus, during the course of the season, HABs are likely to be observed in the south prior to their development in the north.     

Comparison of the functional and numerical responses of resistant versus non-resistant populations of the copepod Acartia hudsonica fed the toxic dinoflagellate Alexandrium tamarense

The functional and numerical responses of grazers are key pieces of information in predicting and modeling predator–prey interactions. It has been demonstrated that exposure to toxic algae can lead to evolved resistance in grazer populations. However, the influence of resistance on the functional and numerical response of grazers has not been studied to date. Here, we compared the functional and numerical responses of populations of the copepod Acartia hudsonica that vary in their degree of resistance to the toxic dinoflagellate Alexandrium tamarense. In common environment experiments carried out after populations had been grown under identical conditions for several generations, female copepods were offered solutions containing different concentrations of either toxic A. tamarense or the non-toxic green flagellate Tetraselmis sp. ranging from 25 to 500 μgC L⁻¹, and ingestion and egg production rates were measured. Throughout most of the range of concentrations of the toxic diet, copepod populations that had been historically exposed to toxic blooms of Alexandrium exhibited significantly higher ingestion and egg production rates than populations that had little or no exposure to these blooms. In contrast, there were no significant differences between populations in ingestion or egg production for the non-toxic diet. Hence, the between population differences in functional and numerical response to A. tamarense were indeed related to resistance. We suggest that the effect of grazer toxin resistance should be incorporated in models of predator and toxic prey interactions. The potential effects of grazer toxin resistance in the development and control of Alexandrium blooms are illustrated here with a simple simulation exercise.     

Culturing Selenastrum capricornutum (Chlorophyta) in a synthetic algal nutrient medium with defined mineral particulates

Algal nutrient studies in chemically-defined media typically employ a synthetic chelator to prevent iron hydroxide precipitation. Micronutrient-particulate interactions may, however, significantly affect chemical speciation and hence biovailability of these nutrients in natural waters. A technique is described by which Selenastrum capricornutum Printz (Chlorophyta) may be cultured in a medium where trace metal speciation (except iron) is controlled, not by organic chelation, but by sorption onto titanium dioxide. Application of this culturing protocol in conjunction with results from sorption studies of nutrient ions on mineral particles provides a means of studying biological impacts of sorptive processes in aquatic environments.     

Cyanobacteria and cyanotoxins in fishponds and their effects on fish tissue

Cyanobacteria can produce toxic metabolites known as cyanotoxins. Common and frequently investigated cyanotoxins include microcystins (MCs), nodularin (NOD) and saxitoxins (STXs). During the summer of 2011 extensive cyanobacterial growth was found in several fishponds in Serbia. Sampling of the water and fish (common carp, Cyprinus carpio) was performed. Water samples from 13 fishponds were found to contain saxitoxin, microcystin, and/or nodularin. LC–MS/MS showed that MC-RR was present in samples of fish muscle tissue. Histopathological analyses of fish grown in fishponds with cyanotoxin production showed histopathological damage to liver, kidney, gills, intestines and muscle tissues. This study is among the first so far to report severe hyperplasia of intestinal epithelium and severe degeneration of muscle tissue of fish after cyanobacterial exposure. These findings emphasize the importance of cyanobacterial and cyanotoxin monitoring in fishponds in order to recognize cyanotoxins and their potential effects on fish used for human consumption and, further, on human health.     

DEVELOPMENT OF PROTOPLASTS FROM HOLDFASTS AND VEGETATIVE THALLI OF MONOSTROMA LATISSIMUM (CHLOROPHYTA, MONOSTROMATACAE) FOR ALGAL SEED STOCK

The aim of this study was to isolate and cultivate the protoplasts of the green alga Monostroma latissimum Wittrock and subsequently induce them to form algal filaments to act as an algal "seed" stock. Protoplasts of the alga were isolated enzymatically with 4% cellulase Onozuka R-10 and 2% Macerozyme R-10. The highest number of protoplasts was obtained on a 50-rpm shaker with 1.2 M of sorbitol after 6 h of incubation, with a yield of 9 × 106 protoplasts·g−1 of fresh thallus (including holdfast). Protoplasts from both holdfasts and erect thalli usually began to form new cell walls within 5 h after isolation and began to divide from day 6 to day 9 in PES medium; cell clusters, filaments, and/or tubular thalli were formed from day 14 to day 18. For algae collected in March, about 60% of protoplasts isolated from vegetative thalli regenerated to form tubular thalli, and about 45% of protoplasts isolated from holdfasts regenerated to form filaments. However, for algae collected in May, about 1% of protoplasts isolated from vegetative thalli developed directly to form tubular thalli, and 59% of protoplasts regenerated to form cell clusters without the ability to differentiate, whereas protoplasts isolated from holdfasts failed to develop. Regenerated filaments were kept in an incubator for more than 3 years at 24° C under the low irradiance of 66μmol photons·m−2·s−1. After this time, they retained the ability to develop to form tubular thalli under irradiance of 166 and 300 μmol photons·m−2·s−1 at 18°–30° C. Subsequently, these tubular thalli can develop to form leafy thalli after being cultivated at high irradiance of 300 μmol photons·m−2·s−1 and at 18°–22° C. Therefore, the filaments could serve as"seed" stock for algal mass culture.