Volume 54, Issue 3

The invasive fucoid Sargassum muticum is currently consolidating its occupation of subtidal fringe habitat in Strangford Lough, Northern Ireland. The native laminiarian Saccharina latissima is the dominant species historically associated with the invaded habitat. The competitive interaction between Sargassum and Saccharina and its ultimate outcome is therefore of considerable consequence for the subtidal communities in Strangford Lough. To examine competition between adult macroalgae, a replacement series methodology was used to quantify intra - and inter -specific competition for light in the process of canopy over-growth. Competitive effects were not apparent for Saccharina , whereas Sargassum grew better mixed with Saccharina and at low densities, suggesting intra -specific competition is strong in this species. These results suggest increases in Sargassum will not affect adult stands of Saccharina .

To determine eco-physiological responses of three geographically separate strains of Phaeodactylum tricornutum , we exposed cultures of each strain to a combination of temperatures ranging from 12°C to 30°C and salinities from 5 to 130. Generally, the three strains were eurythermal and very euryhaline, especially when measured as maximum quantum yield of primary photochemistry. However, a decline in pigmentation under both hypo- and hyper-saline conditions tracked diminishing growth-rates. Under hyper-saline conditions, growth rates were further reduced as more proline was accumulated in each cell. In salinities >90 at 30°C, the physiological response was reduced to mere cell survival. Regulation of pigmentation and the time-course of both proline accumulation and growth were similar in the two cold-temperate strains from Vancouver and Plymouth, but different in the tropical strain from Guam, mirroring an epigenetic manifestation of environmental influences. In contrast, the tolerance ranges of all three strains seemed to be determined by phylogenetic background. Thus, the cold-temperate strain from Plymouth and the tropical strain from Guam, which are in the same phylogenetic group, had broader salinity and temperature tolerance ranges than the cold-temperate strain from Vancouver, which is in a neighbouring clade.

The section of the Liguro-Provençal basin north of the Balearic Islands is one of the most productive sites in the whole Mediterranean Sea, with intense phytoplankton bloom lasting about 2 months in late winter-early spring. The phytoplankton species composition of the area was investigated using light and electron microscopy to analyze bottle and net samples collected at several stations in spring 2000 and 2003. Serial dilution cultures established from bottle samples were also examined. A total of 168 phytoplankton taxa was identified, consisting of 73 Coscinodiscophyceae, 47 Dinophyceae, 25 Coccolithophyceae and 4 Prymnesiophyceae, 5 Prasinophyceae, 3 Chrysophyceae, 2 Cryptophyceae, 2 Dictyochophyceae, 1 Euglenophyceae, 1 Pelagophyceae, 1 Choanoflagellidea, 1 Filosea and 3 incertae sedis . We also provided a brief taxonomic description and original micrographs for 25 of the smallest and/or less known species identified in the study area, which may go undetected during routine microscopical analysis of fixed samples. Among these, 10 species were recorded for the first time in the Mediterranean Sea, confirming the need of detailed studies to reveal the biodiversity and biogeography of Mediterranean phytoplankton.

Molecular-assisted identification using plastid-encoded rbc L and mitochondrion-encoded COI loci identified five species of Polysiphonia sensu lato from 16 Florida and Caribbean Mexico samples. Morphological character states were examined and used to identify these species as Neosiphonia bajacali comb. nov., N. echinata comb. nov., N. sphaerocarpa , N. tepida , and Polysiphonia anomala . Descriptions are provided and the phylogenetic relationships of the five species were determined through maximum likelihood analyses of rbc L and nuclear-encoded SSU sequence data. Neosiphonia bajacali and N. echinata had a combination of character states described for Neosiphonia : rhizoids cut-off from pericentral cells, lateral branch or trichoblast initials on every segment in a spiral pattern, tetrasporangia in spiral series, and spermatangial stichidia developing as bifurcations of trichoblasts, and these new combinations are proposed. Examination of N. echinata , P. fracta and North Carolina specimens identified as P. breviarticulata revealed no significant morphological differences. Polysiphonia fracta is proposed as a synonym of N. echinata and the presence of P. breviarticulata within the western Atlantic is questioned. This is the first report of N. bajacali from the Caribbean and the first report of N. echinata from Caribbean Mexico.

One forma, Rhipocephalus phoenix f. longifolius , and 14 species of algae are newly reported from Puerto Rico. The latter include the rhodophytes Acrochaetium repens , Ceramium leptozonum, Callithamnion stuposum, Ceratodictyon intricatum, Hydrolithon chamaedoris, Kallymenia limminghei, Lithophyllum incrustans, Lithothamion ruptile, Mesophyllum ornatum, Polystrata fosliei, Ramicrusta textilis , the phaeophycean Dictyota stolonifera , plus the chlorophytes Halimeda pumila and Udotea unistratea . We also propose the new name Lithophyllum bathyporum, nom. nov. A. Athanasiadis et D.L. Ballantine to accommodate previous British and French records of Lithophyllum incrustans from northern Europe. The records of Lithophyllum incrustans and Dictyota stolonifera are the first confirmed reports for the western Atlantic. The report of Callithamnion stuposum is the first outside South Africa.

Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the first key enzyme in the photosynthesis pathway. This is the first study to obtain the full-length cDNA encoding Rubisco large subunit (RbsL) from Ulva linza . The partial rbc  L cDNA sequence of 1101 bp was first cloned by RT-PCR from the total RNA. Both sequences of the 3′ and 5′ ends were then amplified using 3′-RACE and 5′-RACE technologies, which yielded 605 bp and 371 bp DNA fragments, respectively. A full-length cDNA sequence of 1498 bp was deduced based on the overlapping sequences and was assigned to a new NCBI accession number: DQ813496. It contains a 1425-bp coding region (474 amino acids) for the Rubisco large subunit (RbsL), a leader sequence of 47 bp at 5′-UTR, and a polyA site at 3′-UTR. The leader sequence has no Shine-Dalgarno (SD) sequence and was similar to that of Euglena gracilis rbc  L with 76.60% A/T content. Bioinformatics analysis and a BLAST search result suggested that the cDNA sequence of U. linza was highly homologous with known full-length cDNAs of the same gene from other green algal species. Three catalytic sites and a CO 2 activator region were identified in the Rubisco large subunit of U. linza , and they were completely identical to those of Chlamydomonas reinhardtii and highly conserved with those of spinach and maize. Based on the cDNA sequence, the secondary and tertiary structures of the U. linza Rubisco large subunit were also predicted.

MicroRNAs (miRNA) are approximately 22 nt single stranded functional RNAs derived from long stem-loop precursors transcribed by RNA polymerase II. They regulate gene expression through post-transcriptional gene silencing and are important for the regulation of growth, development and stress responses in plants. Mature nucleotide sequences of many miRNA families are highly conserved across the plant kingdom and can be used to identify and annotate homologs and potential miRNA targets. In this study, mature miRNA sequences retrieved from the miRNA registry (miRBase) were used to identify precursor sequences of miRNA orthologs and their potential targets among Expressed Sequence Tags (ESTs) of the mangrove species Bruguiera cylindrica (L.) Blume, B. gymnorhiza (L.) Lam. and B. sexangula (Lour.) Poir. Candidate miRNA precursors, which potentially belong to the miR156/7, miR396 and miR529 families, had high sequence identity between Bruguiera cylindrica and Bruguiera gymnorhiza , and expression of RNA was confirmed in both species. A number of candidate targets for miR396 and miR529 were also identified among EST from B. gymnorhiza .

Phylogenetic relationships of the fungal symbiont of two brown algae were evaluated in the context of host diversity using ribosomal large subunit (nuLSU) sequences. Phylogenetic analysis indicates that Mycophycias ascophylli (phycobionts Ascophyllum nodosum, Pelvetia canaliculata ) is misclassified in Verrucariales (Eurotiomycetes). There was no evidence for speciation of M. ascophylli within its two hosts, nor evidence for geographic differentiation between the eastern and western Atlantic Ocean and the White Sea (Arctic Ocean). The placement of M. ascophylli in Capnodiales (Dothideomycetes) will require a reclassification of this species, and calls into question the current classification of the other species of Mycophycias, M. apophlaea .

Osmotic adjustment characteristics of mangrove leaves ( Avicennia marina ) were investigated over 45 days of growth under three NaCl concentrations (0, 200 and 600 m m NaCl). Maximum seedling growth occurred at 200 m m NaCl. Leaf water potential and osmotic potential were more negative under saltier conditions. The salinity treatments caused an increase in the leaf contents of Na + , Cl - , glycine betaine, total free amino acids and proline. However, inorganic ions (especially Na + and Cl - ) played a key role in osmotic adjustment in A. marina leaves, as they contributed 70% and 76% to these adjustments in 200 and 600 m m NaCl-treated plants, respectively. NaCl treatment induced a decrease in the organic solute contribution. Thus, growth of A. marina was stimulated by the 200 m m NaCl treatment due to effective osmotic adjustment, mainly by accumulation of inorganic ions. Reduction in growth when A. marina was subjected to high salinity stress (600 m m NaCl) appears to have been caused for the most part by the accumulation of excess NaCl (ionic effect), exacerbated by additional organic solute synthesis, rather than an osmotic effect.