Volume 54, Issue 5

Natural biotic communities from Kalbadevi Bay were monitored in microcosms (1-l glass flasks) to test the hypothesis that iron released from ilmenite through microbial action contributes to proliferation of phytoplankton. Microcosms containing ilmenite had significantly higher phytoplankton growth compared with controls containing no ilmenite or those containing only ferrous sulfate. Phytoplankton cell numbers in the ilmenite-supplemented treatment were 20× higher than in controls. The later stages were marked by the dominance of bottom dwelling Nitzschia spp. and Navicula spp. Iron-preferring Eunotia spp. and Pinnularia spp. were also encountered. Hence, increased phytoplankton biomass may be attributable to the steady release of bio-available iron. We therefore infer that ilmenite mineral might sustain the phytoplankton community in ilmenite-dominated systems. Increases in density and diversity of phytoplankton over time and significant interrelationship between various parameters in the microcosm containing ilmenite indicate that stimulatory effect of iron released from this mineral could be beneficial to the biota in the system.

The brown macroalga Hizikia fusiformis was cultured in media with different copper (Cu) or cadmium (Cd) concentrations for 7 days; physiological indicators were measured to establish the toxic effects of Cu and Cd on this economically important seaweed. Relative growth rate of H. fusiformis was significantly reduced at Cu concentrations of ≥0.05 mg l -1 or Cd ≥4 mg l -1 . Chlorophyll a and carotenoid contents increased at low Cu or Cd concentrations, but significantly decreased at 0.25 and 0.50 mg l -1 Cu. Optimal quantum yield, maximum net photosynthetic rate and apparent photosynthetic efficiency were reduced with increasing Cu or Cd concentrations. Malondialdehyde content and the superoxide dismutase activity increased under Cu or Cd stress. Catalase activity also increased at low Cu or Cd concentrations, but significantly decreased at high concentrations. Nitrate reductase activity significantly increased at 0.05 mg l -1 Cu and 4 mg l -1 Cd, but was inhibited at high Cu or Cd concentrations. Thus, both Cu and Cd were physiological stressors for H. fusiformis , with Cu being more toxic than Cd.

Eisenia arborea is the kelp species that is distributed furthest south in the northern hemisphere. Although much is known about how the giant kelp, Macrocystis pyrifera , responds to nutrient-poor conditions, very little is known about Eisenia , even though these two kelps share much of their habitat. The response of E. arborea to environmental nitrogen shortage was explored by determining short-term nitrogen uptake in the laboratory, duration of internal nitrogen reserves in nutrient-poor tanks, and recovery of reserves during weekly pulse fertilization with nitrate. Nitrate uptake was linear for at least 3 h at all concentrations and did not exhaust nitrate in the media. In both experiments in nutrient-poor outdoor tank cultures, regardless of initial tissue nitrogen concentrations, tank nitrate fell to undetectable levels after 4 weeks, and internal tissue nitrogen reserves fell to 1.0% of dry weight within 5 weeks. Low internal reserves were replenished in fertilized treatments, which had significantly greater dry weight tissue nitrogen (up to 1.3%) than thalli in non-fertilized tanks, in which algae tissue nitrogen fell to and remained constant at 1%. We conclude that the nitrogen physiology of E. arborea is adapted to survive a maximum of 5 weeks in the field under nutrient-poor conditions, similar to the giant kelp M. pyrifera .

Thalli of Porphyra yezoensis growing in the intertidal region periodically experience diverse abiotic stresses induced by tidal cycles. To investigate the contribution of 70-kDa heat shock proteins (HSP70s) to abiotic stress tolerance in P. yezoensis thalli, we isolated the cDNAs of two HSP70 genes (designated as PyHSP70-1 and PyHSP70-2) from P. yezoensis by in silico cloning and RT-PCR amplification, and examined their relative mRNA expression levels in P. yezoensis thalli responding to various abiotic stresses using real-time quantitative PCR. The deduced amino acid sequences of the two PyHSP70s lacked signal peptides, but contained signature motifs and conserved domains of the HSP70 family. The two PyHSP70s shared high amino acid sequence similarities with cytosolic HSP70s from other algae and higher plants, and clustered together with all cytosolic HSP70s in the phylogenetic tree, indicating they belong to the cytosolic HSP70 family. Expression of the two PyHSP70 genes was induced by cold shock at 0°C and heat shocks at 20°C and 25°C, and was significantly upregulated in a dose-dependent manner. The expression patterns under heat shock, along with the absence of introns in the coding regions, demonstrate that the two PyHSP70s are inducible HSP70s. Expression of the two PyHSP70 genes was repressed by desiccation stress, suggesting that they do not play a role in tolerance to desiccation stress. The expression patterns in response to salinity stress were different between PyHSP70-1 and PyHSP70-2 genes. The expression of PyHsp70-1 was induced by a salinity of 5; however, the expression of PyHsp70-2 was induced by salinities of 35 and 45. The different expression patterns suggest that they have distinct biological tasks.

Numerous marine organisms, including macroalgae, produce bioactive compounds. As chemical extraction processes do not distinguish between compounds originating from the alga and its associated microflora, a key step immediately prior to isolation of molecules, is elimination of epibionts from the alga studied. In chemical, ecological and biotechnological contexts, a clear identification of the source organism, when symbiotic interactions occurs, is crucial. We aimed to improve understanding of specific secondary metabolite production by macroalgae through development of a metho-dology for removing microbial epibionts immediately prior to chemical extraction without damaging algal cell surfaces (to avoid extraction of endogenous macroalgal compounds at this stage). Various solutions were tested: non-polar solvents (dichloromethane and hexane), alcohols (methanol, ethanol and isopropanol), oxidants (sodium hypochlorite, hydrogen peroxide and iodine) and a natural product (tea tree oil) at various concentrations and contact times. Five macroalgal species were employed: Chondrus crispus , Fucus serratus , Palmaria palmata , Saccharina latissima and Ulva lactuca . Scanning electron microscopy was used to evaluate the surface integrity. The best epibiont removal rate without damaging tissue was obtained with mixtures of ethanol (40–50%) and sodium hypochlorite (1%). Interestingly, macroalgal moisture content influenced treatment efficacy.

We used response surface methodology to investigate the effect of time and temperature of hydrothermal processing (blanching) on the phytochemical content, texture and colour of a semi-dried brown seaweed ( Himanthalia elongata ). A central composite design was employed with a hydrothermal processing time of 10–30 min and temperature of 60–90°C. Predicted models were found to be significant for total phenolic content, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, total flavonoids, total condensed tannins, texture and colour. The predicted values for each of the responses were in good agreement with experimental values. Processing time had the most significant effect on phytochemical constituents of H. elongata . An acceptable edible texture and colour of seaweed was also achieved during the blanching procedure. Thus, central composite design and response surface methodology can be used to model phytochemical content, texture and colour of H. elongata while minimising the number of experiments required. Multiple response optimisation demonstrated that the phytochemical content of H. elongata may be maximised by blanching for 20.4 min at 80.5°C.

Sequence data from the nuclear large subunit ribosomal DNA (LSU), plastid large subunit of ribulose-l-5-bisphosphate carboxylase/oxygenase ( rbc L) and the DNA barcode region of the mitochondrial cytochrome c oxidase 1 gene (COI-5P) were analyzed separately and in combination to assess monophyly of the red algal genera Dilsea and Neodilsea in the northeastern Pacific. Except for the LSU, all analyses affiliated Neodilsea natashae with species of the genus Dilsea rather than species of Neodilsea . These results, as well as anatomical features of Neodilsea natashae , support its transfer to Dilsea , as Dilsea natashae .

Since the beginning of the 21st century, the Mediterranean shores of Israel have experienced invasions of several alien Indo-Pacific seaweed species. This phenomenon has been observed mainly on the northern Israeli Mediterranean shore, particularly near the port of Haifa. Here we report and discuss the first record of the common Indo-Pacific seaweed Codium arabicum from the Mediterranean Sea, namely, from the Levant coast of Israel. This macroalga was first identified morphologically, and the determination later confirmed by molecular techniques using two plastid DNA sequences: rbc L exon 1 and rps 3- rpl 16. High water temperatures for most of the year and free habitat space appear to facilitate the successful settlement and establishment of this species, as has been the case for hundreds of other invasive Indo-Pacific organisms along the Israeli Mediterranean shore.

Long-term annual monitoring of rocky intertidal and shallow subtidal shores of an Irish sea lough (1990–2010) documented major regime shifts in the past decade. When population densities of the purple urchin Paracentrotus lividus plummeted in Lough Hyne Marine Reserve in southwestern Ireland, the warm-water fucalean alga Cystoseira foeniculacea and ephemeral algae proliferated shortly after. We discuss the possible influences of release from herbivory and climate change on this algal proliferation, which blanketed the benthos. Smothering of the benthos led to high levels of shallow subtidal anoxia. Furthermore, the invasive fucalean alga Sargassum muticum has made repeated incursions into the reserve. Although being reduced by persistent eradication efforts (2003–2011), Sargassum is spreading within the lough. Limited seawater flushing and propagule dispersal within the lough and eutrophication in coastal waters may have contributed to community-level changes. Whether the regime change is cyclical (contingent on re-establishment of urchins within the lough and continued eradication of S. muticum ) or irreversible (the result of critical transitions) remains unclear.