Volume 48, Issue 2

I would like to direct readers and contributors to the “Forum” section of this issue of Botanica Marina . It contains the first letters to the editor on a controversial issue. I hope that more of you will use this vehicle to express your opinions on difficult/interesting scientific matters in the field of marine botany. There are no special instructions for formatting letters to the editor, except that they must be prepared in MS Word for online submission at http://botmar.edmgr.com. When there is more than one author, each must sign accepting responsibility for the entire content of the letter. Letters may or may not be externally reviewed.

This study determined the effect of irradiance, temperature and photoperiod on the release of zygotospores and spermatia in Porphyra perforata from the Pacific coast of Baja California, Mexico. Reproductive blades were placed under controlled conditions of irradiance (5, 75, 150 and 300 μmol photons m −2  s −1 ), photoperiod [8:16; 12:12 and 16:8 light:dark (L:D)] and temperature (15, 18, 21 and 25°C). Peak zygotospore release occurred at 15–18°C and photoperiod of 16:8 L:D. Reproductive tissue released between 60% and 90% of zygotospores and spermatia during the first 10 days of incubation at 50 μmol photons m −2  s −1 , 18°C and photoperiod of 16:8 L:D. Maximum zygotospore and spermatium release occurred in tissue collected between June and November. The number of zygotospores released was approximately 40% greater than that of spermatia (2.7×10 6 vs. 1.6×10 6  g FW −1  d −1 ). The reproductive foliar phase was observed throughout the year, but only thalli collected from April to January released zygotospores and spermatia. Collectively, the results suggest that low temperature, as observed in upwelling events, may induce high zygotospore and spermatium release during summer months.

The algal assemblages of the northern Adriatic Sea have been studied intensively, but few quantitative data on their spatial and temporal dynamics are available. The intertidal assemblages of two coasts on the Gulf of Trieste were studied for a year, and the patterns of spatio-temporal variability were examined at several scales in space and time. Patterns for the whole assemblage and individual species were analysed by multivariate and univariate analyses. The assemblages of the two shores were relatively poor in species and characterised by different compositions. A moderate temporal variation was found, mostly related to differences between the periods winter-spring and summer-autumn. Patterns for individual species were mainly characterised by differences between the two shores ( Polysiphonia opaca ), interactions among shores and sampling dates ( Fucus virsoides , Ulva compressa , Gelidium pusillum , Lophosiphonia obscura ) and differences on the spatial scale of tens of metres ( Ceramium species in aggregate, Cladophora albida, Ectocarpus siliculosus, Ulva laetevirens ). The dissimilarity between the assemblages of the two shores was the emergent pattern, and differences in the texture and composition of the rocky substratum (marl and limestone, respectively) are considered perhaps the main causes of these differences. Future studies in this region should give more attention to this factor.

Sea urchin barrens occur commonly in temperate regions throughout the world and have significant implications for ecological processes on subtidal rocky reefs because they constitute areas of low productivity and diversity compared with habitats dominated by macroalgae. On the east coast of Tasmania, the occurrence of sea urchin ( Heliocidaris erythrogramma ) barrens in sheltered bays has additional implications in that they represent an important habitat of the introduced kelp Undaria pinnatifida . Identifying the factors responsible for ongoing maintenance of the barren habitat is essential in defining management options to promote recovery of native canopy-forming species. We used transplant experiments to investigate whether inhibition of recovery of native canopy-forming algae can occur in the absence of intense sea urchin grazing. High densities of native canopy-forming species successfully colonised paving blocks deployed in a dense algal bed adjacent to a sea urchin barren. Transplanting these paving blocks to plots on the barren from which sea urchins were removed resulted in >80% mortality of recruits after three months, and 100% mortality after seven months. The decline in macroalgal recruits on paving blocks transplanted to the urchin barren was associated with an increase in the cover and depth of sediment. A persistent cover of sediment also developed on paving blocks deployed on the urchin barren, where no native canopy-forming algal recruits were observed. While sea urchins are undoubtedly important in creating urchin barrens, our results suggest that other mechanisms can influence recovery of native canopy species. In sheltered and semi-exposed bays on the east coast of Tasmania, sedimentation appears to play a critical role in inhibiting early developmental stages of native macroalgae, thereby contributing to a positive feedback that acts to maintain the barren habitat.

The epilithic biofilms colonizing the intertidal and splash zones of a rocky shore in the southern Gulf of Mexico were studied by phase contrast and scanning electron microscopy (SEM), along with phytopigment analyses. These biofilm communities comprised a mixed assemblage of phototrophs, dominated by cyanobacteria, with occasional diatoms and other eukaryotic microalgae. Eight out of nine cyanobacterial genera identified were filamentous. A Stigonema species, a cyanobacterium that rarely occurs in marine habitats, was found in low intertidal samples. Microscopy analysis (phase contrast and SEM) showed that more diverse cyanobacterial populations (morphotypes) occurred on intertidal rocks than in splash zone biofilms, probably owing to the desiccation and thermal stress to which the latter are exposed. However, the phycobiliprotein content, as indicative of cyanobacterial biomass, was similar at both tidal levels. The numerical dominance of Pleurocapsa species and its wide distribution among intertidal and splash zone rocks may be related to its ability to withstand environmental stress by producing moisture-retaining external capsules.

Meadows of the seagrass Cymodocea nodosa (legislated as an endangered species) are the dominant vegetated communities in shallow soft bottoms throughout the Canary Islands (central east Atlantic Ocean). We provide baseline ecological information for this key species for the whole Canarian Archipelago by describing the spatial distribution patterns of structural parameters (percent coverage and shoot density) at different hierarchical spatial scales (from tens of meters to hundreds of kilometers). The coverage values varied between 42.5 and 100% (mean±SE=76.7±2.5%, N=80) and the mean shoot density per location ranged between 164 and 710 shoots m −2 (mean±SE=403.6±17.0 shoots m −2 , N=160). We observed a strong variability at small- to medium-spatial scales (locations within islands separated by tens of kilometres and sites hundreds of meters apart within locations) in contrast to a lack of inter-island variability. Additionally, the structural parameters respond differentially to different sets of ecological and physical processes operating at these scales.

Sulfated galactans were extracted from three samples of Champia novae-zealandiae from different environments, from Champia chatamensis and from Champia laingii , and their structural features were evaluated by 13 C NMR spectroscopy and by chemical analysis. The polysaccharides were similar, each containing diads with backbones of 3-linked D-galactose and 4-linked D- and 4-linked L-galactose, with the L-galactose predominating. The major component of each extract was the diad 3-linked D-galactose-2-sulfate and 4-linked L-galactose-2,3-disulfate, which was separable from other polymers that contained 3-linked 6- O -methyl-D-galactose, 3-linked pyruvylated D-galactose, 4-linked galactose-2,3,6-trisulfate and 3-linked D-galactose-2,4,6-trisulfate. The 13 C NMR spectra of the methylated, and methylated then desulfated derivatives of the predominant polymer were recorded and provisionally assigned. Accordingly, the extract is a mixture of polymers, and since it appears that every thallus produced some of each substitution pattern, it is likely that none of these substitution patterns will be of chemotaxonomic interest at the species level.

The structure of the polysaccharide extracted from Aeodes nitidissima was examined by 13 C NMR spectroscopy and by chemical means, and was found to consist of alternating 3-linked and 4-linked residues. The 3-linked residues comprised D-galactosyl-2-sulfate residues, some of which were substituted with sulfate ester or methyl ether at the 6-position or with pyruvate acetal linked at the 4,6-positions. The 4-linked residues comprised predominantly D-galactosyl with some 2- O -methyl-D-galactosyl and L-galactosyl together with small amounts of 3,6-anhydro-L-galactosyl residues. The composition of this polysaccharide is very similar to that of the polysaccharide from Pachymenia lusoria , which is in accord with the postulate that these algae are closely related within the order Halymeniales.

The structure of the polysaccharide extracted from a sample of Grateloupia intestinalis was examined by 13 C NMR spectroscopy, and was found to consist of two diads, one of which is that of β-carrageenan, and the other a precursor to α-carrageenan. No significant amounts of non-ionic polymer could be separated. There are also low levels of 4-linked L-galactose and 3,6-anhydro-L-galactose present (which confirms that the polysaccharide is not a carrageenan in the usual sense), and low levels of 6-sulfation on the 3-linked unit of the α-carrageenan precursor. This structure differs from that expected for Grateloupia species, possibly in accordance with other reports that the entity in New Zealand is in the genus Polyopes rather than in Grateloupia .

The polysaccharides extracted from Hymenena palmata , Hymenena palmata f. marginata, Hymenena variolosa and Acrosorium decumbens , all from the family Delesseriaceae, were examined by 13 C NMR spectroscopy and by linkage analyses. The backbones of all polysaccharides comprised mainly diads of 3-linked D-galactose and 4-linked L-galactose, and these were heavily substituted with sulfate ester. The polysaccharide from Hymenena palmata f. marginata has the same major component [3DG4S-4LG2S3S] as the polysaccharide from Myriogramme denticulata , also in the Delesseriaceae. The polysaccharides from the remaining samples appear to be very similar to each other and have greater sulfation. A predominant diad appears to be [3DG2S4S6S-4LG2S3S], while some persulfated polysaccharide appears to occur. A separate, sulfated xylan also appears to be present. Inadvertent desulfation appears to occur in dimethylsulfoxide solvent, possibly because of acute electron repulsion in the polysulfated material, and this gives uncertainty to the structural analysis.

The structure of the polysaccharides extracted from New Zealand samples of Grateloupia was examined by 13 C NMR spectroscopy and by chemical means, and was found to consist of alternating 3-linked and 4-linked residues. All Grateloupia polysaccharides had low levels of 2- O -methyl-3,6-anhydro-L-galactose, and variable levels of 6- O -methyl-D-galactose. The major diads of Grateloupia urvilleana polysaccharide were non-sulfated 3-linked galactose with 4-linked D-galactose-2-sulfate, and 3-linked galactose-2-sulfate with non-sulfated 3,6-anhydro-D-galactose. In Grateloupia stipitata and Grateloupia prolifera polysaccharides, approximately half the 4-linked units were in the L-form, and the diad comprising 3-linked D-galactose-2-sulfate and 4-linked L-galactose-2,3-disulfate, an entity previously found mainly in Champia species, was also present. The diads with 4-linked galactose in the D-form comprised 4-linked D-galactose or 3,6-anhydro-D-galactose, and these diads had the sulfation found in Grateloupia urvilleana , except that a large proportion of these diads had no sulfation at all. Although these polysaccharides contain the same sugars as Pachymenia polysaccharides, apart possibly from the diad comprising 3-linked galactose-2-sulfate and 3,6-anhydro-L-galactose, which is a minor component of the Grateloupia polysaccharides, the polysaccharides from the two genera have no diads in common.

The structural features of polysaccharides extracted from four New Zealand species of Lomentaria were examined. The polysaccharides retain the expected backbone structure of alternating 3-linked and 4-linked galactosyl units, with the 4-linked units containing some 3,6-anhydro-L-anhydrogalactose and galactose in the D- (40%) and L- (60%) configurations. Natural sulfation leads to twelve different units being found. Since none of the levels of 3-linked units matched those of 4-linked units, many units were in at least two different diads, and with such variation it is unlikely that there is a consistently repeating structure as such. An important diad combined 4-linked L-galactose-2,3-disulfate and L-galactose 2,3,6-trisulfate with 3-linked D-galactose-2,6-disulfate, a diad group equivalent to the principal diad in Champia polysaccharides with primary hydroxyl groups sulfated. A further important diad is 3-linked D-galactose-2,4-disulfate with 4-linked D-galactose-3-sulfate, a diad group also found in Hymenocladia sanguinea . Hence these results suggest that Lomentaria has an intermediate relationship with respect to Champia and Hymenocladia within the Rhodymeniales.

The seagrass Posidonia oceanica is able to reproduce by asexual formation of plantlets directly in the inflorescence. Pseudoviviparous plantlets were observed during May 2004 in 26% of the inflorescences in a P. oceanica meadow off the island of Formentera (Balearic Islands, Western Mediterranean Sea). We do not know how frequently pseudovivipary occurs in Posidonia oceanica , nor the mechanisms triggering it, but this strategy can contribute significantly to short-distance dispersal and meadow maintenance, which is especially relevant in a species whose meadows can persist for thousands of years and whose colonization of new space occurs very slowly.