PHYLOGEOGRAPHIC STUDIES IN THE TROPICAL SEAWEED CLADOPHOROPSIS MEMBRANACEA (CHLOROPHYTA,ULVOPHYCEAE) REVEAL A CRYPTIC SPECIES COMPLEX1

The seaweed Cladophoropsis membranacea (Hofman Bang ex. C. Agardh) Børgesen is a widely distributed species on coral reefs and along rocky coastlines throughout the tropics and subtropics. In a recent population‐level survey openface>1600 individuals with eight microsatellite loci, a number of isolates from biogeographically disjunct locations could not be amplified for any of the loci. Nonamplifiable and amplifiable isolates co‐occurred within the Canary Islands, Cape Verde Islands, and in the Caribbean. These unexpected results led to question whether or not C. membranacea is a single species. Phylogenetic relationships were evaluated using rDNA ITS1 and ITS2 sequence comparisons from 42 isolates sampled from a subset of 30 of the 66 locations. Four well‐supported clades were identified. Sequence divergence within clades was <1%, whereas between‐clade divergence was 2%–3%. Intraindividual variation was extremely low with no effects on the analysis. A strong, but imperfect, correspondence was found between ITS clades and amplifiable microsatellite loci. It is concluded that C. membranacea consists of three cryptic species. Using Pacific isolates as an outgroup, the most basal clade included the Central Canary Islands, Cape Verde, and Bonaire (Caribbean) isolates and thus spanned the widest latitude. Two derived sister clades consisted of a southern transtropical group stretching across the SE Caribbean to the Cape Verde Islands and African coast (but not the Canary Islands) and a NE‐Canary Island‐Mediterranean clade that also included the Red Sea. The detection of overlapping biogeographic distributions highlights the importance of ecotypic differentiation with respect to temperature and the importance of shifting sea surface isotherms that have driven periodic extinctions and recolonizations of the Canary Islands—a crossroads of marine floral exchange—since the last glacial maximum.     

Seaweeds, latitudinal diversity patterns, and Rapoport's Rule

We analysed the geographic distribution of 645 species of marine benthic algae along the Atlantic coast of Europe and Pacific coast of temperate South America to test for the existence of an association between geographic range size and latitude (Rapoport's Rule) and for three key components of the explanations offered for it. We found that species in high diversity areas are characterized by small geographic ranges and by low specific growth rates as compared to species with large geographic ranges, thus supporting the Rapoport-rescue hypothesis. However, the pattern is not related to species' tolerances, to abiotic conditions or to climatic variability. Further, the inverse latitudinal diversity pattern shown by the marine algal flora of temperate Pacific South America, and the opposite patterns shown by tropical and subantarctic species within this flora, stressed that small geographic ranges are linked to high diversity areas in general, and not only in relation to the pole to tropic species diversity gradient.     

TWO SOLIERIACEAN ALGAE NEW TO THE MEDITERRANEAN: AGARDHIELLA SUBULATA AND SOLIERIA FILIFORMIS (RHODOPHYTA,GIGARTINALES)1

Two Atlantic species found in the Mediterranean Sea were ascribed to the family Solieriaceae on the basis of morphological features. In the extensive drifting beds of the Mar Piccolo basin (Taranto, Ionian Sea), Agardhiella subulata (C. Agardh) Kraft et Wynne and Solieria filiformis (Kützing) Gabrielson were the dominant species in summer. There were no attached populations, and perennation was ensured only by vegetative propagation. Characteristics of the outer cortex and chromatophores were useful for distinguishing the taxa at the species level and are recommended for recognition of sterile specimens.     

Biologically active oxylipins from seaweeds

Our previous research has shown that many red algae metabolize polyunsaturated fatty acids to oxidized products resembling the eicosanoid hormones from mammals. We have extended these studies to members of the Phaeophyceae and Chlorophyta and find they also possess similar biosynthetic pathways. From several we have identified novel prostaglandin-like substances. Studies of the molecular mechanisms by which some of these marine oxylipins are formed have revealed that novel oxidative reactions are utilized. Understanding of these biosynthetic pathways in detail has allowed their utilization to produce research biochemicals of high value, such as 12S-hydroperoxyeicosatetraenoic acid (12S-HPETE). Because of their biological properties, seaweed-derived oxylipins have potential utility as pharmaceuticals and research biochemicals.     

Changes in the population structure of Ascophyllum nodosum (L.) Le Jolis due to mechanical harvesting

The use of a Norwegian suction cutter to harvest populations of the brown alga Ascophyllum nodosum (L.) Le Jolis in southwestern Nova Scotia started in 1985. The impact of this type of mechanical harvest on the algal population structure was evaluated. Changes in the length and density of individual plants (clumps) within 0.25 m^–2 quadrats, as well as the length of individual shoots within clumps were monitored before and after an experimental harvest. The mechanical harvest cut mainly the longer plants, thus changed the initial bimodal size structure of the population to unimodal. There was a 20 to 36% plant mortality, reducing the plant density from 92.6 to 73.6 individuals m^–2. Pre-harvest size distribution of the tagged shoots was skewed to the right and became more normal after the harvest. Tagged shoots in the harvested quadrats suffered a 42% mortality as compared to 11% of those in the control quadrats. An understanding of the impact of the mechanical harvesting on the harvested population is essential in the design of a management strategy. Sources of variation in the impact of mechanical harvest include the tide level at time of harvest, length of time the machine operated in one site, skill of the machine operator, and sharpness of the machine cutting blades.     

A simple and rapid technique to PCR amplify plastid genes from spores of <Emphasis Type="Italic">Porphyra</Emphasis> C. Agardh (Bangiales,Rhodophyta)

A user-friendly and fast protocol using PCR was developed to amplify the plastid rbcL gene of Porphyra, the most economically valuable genus of Rhodophyta. The technique involved the use of monospores, providing the advantage of a small and genetically homogeneous set of cells and thus reducing the risk of biological or chemical contamination. An additional factor in the choice of the rbcL gene was the huge amount of sequence data deposited in molecular biology databases and their utility as molecular markers in taxonomic studies.     

Impacts of anthropogenic stresses on the early development stages of seaweeds

Seaweeds are important primary producers, and as such contributesignificantly to nearshore ecosystems. Studies on the effects ofanthropogenic stresses on these organisms have largely been concernedwith the vegetative adult stages of the life cycle. Here we review thelimited information on the sensitivity of early stages in the life cycleof seaweeds to global change (UV increase; global warming;increased storm frequencies) and pollution (eutrophication, trace metalsand oil). Impacts on fertility, substrate attachment, development,photosynthesis, growth and mortality are highlighted. In their naturalhabitats, early stages are shade-adapted, as they live shel tered underadult canopies and in pores of the substrata. Although some acclimationunder increased moderate irradiance is seen, higher solar irradiance,and especially ultraviolet-B, inhibits early development. Global warmingmay decrease the fertility and shorten the fertile period of somespecies. With the increasing likelihood of storms associated with globalwarming, gamete release may be inhibited while scouring by suspendedsediments may detach newly settled stages. Succession and localdistribution patterns are likely to be affected. Eutrophication canresult in accelerated development of the early stages of some algalspecies but sewage discharges have a negative impact on sperm motility,fertilisation and can cause increased mortality in germlings. Impacts ofother, indirect effects of eutrophication, including increased sedimentcover of substrata, scouring caused by wind-induced resuspension ofsediments, and grazing, are also expected to be negative. Toxic tracemetals affect gamete viability, inhibit fertilisation and development,and reduce growth rates. Gametes are particularly susceptible to oilpollution and interactions between hydrocarbons and the adhesive mucussurrounding the embryonic stages seem to inhibit settlement.Recommendations for future studies are provided that are aimed atgaining greater insight into the effects of anthropogenic stress on theweakest links in the development cycle of seaweeds.     

Unicells in soil extract in Scenedesmus strain 170

Scenedesmus strain 170 forms a completely colonial population in a dilute inorganic medium, but becomes unicellular upon the addition of soil extract. The nature of the soil extract factor is unknown.     

Temperature response of photosynthetic light‐ and carbon‐use characteristics in the red seaweed Gracilariopsis lemaneiformis (Gracilariales,Rhodophyta)

The red seaweed Gracilariopsis is an important crop extensively cultivated in China for high‐quality raw agar. In the cultivation site at Nanao Island, Shantou, China, G. lemaneiformis experiences high variability in environmental conditions like seawater temperature. In this study, G. lemaneiformis was cultured at 12, 19, or 26°C for 3 weeks, to examine its photosynthetic acclimation to changing temperature. Growth rates were highest in G. lemaneiformis thalli grown at 19°C, and were reduced with either decreased or increased temperature. The irradiance‐saturated rate of photosynthesis (P_max) decreased with decreasing temperature, but increased significantly with prolonged cultivation at lower temperatures, indicating the potential for photosynthesis acclimation to lower temperature. Moreover, P_max increased with increasing temperature (~30 μmol O₂ · g^?1FW · h^?1 at 12°C to 70 μmol O₂ · g^?1FW · h^?1 at 26°C). The irradiance compensation point for photosynthesis (I_c) decreased significantly with increasing temperature (28 μmol photons · m^?2 · s^?1 at high temperature vs. 38 μmol photons · m^?2 · s^?1 at low temperature). Both the photosynthetic light‐ and carbon‐use efficiencies increased with increasing growth or temperatures (from 12°C to 26°C). The results suggested that the thermal acclimation of photosynthetic performance of G. lemaneiformis would have important ecophysiological implications in sea cultivation for improving photosynthesis at low temperature and maintaining high standing biomass during summer. Ongoing climate change (increasing atmospheric CO₂ and global warming) may enhance biomass production in G. lemaneiformis mariculture through the improved photosynthetic performances in response to increasing temperature.     

Interaction of Mercuric Ions with Different Marine Algal Species

The use of different seaweeds such as Sargassum sp., Turbinaria conoides, and Ulva sp. in removing mercury(II) from aqueous solutions were investigated. The initial experimental runs, conducted at different equilibrium pH conditions, demonstrated that brown seaweeds outperformed green seaweed in Hg(II) biosorption at all pH conditions. In particular, at pH 5, maximum biosorption capacities of 170.3 and 145.8 mg/g were recorded for the brown seaweeds T. conoides and Sargassum sp., respectively, compared with 138.4 mg/g for the green seaweed Ulva sp. Isotherm data were modeled and interpreted using the Langmuir, Freundlich, Redlich-Peterson, and Toth models, with the latter described the Hg(II) isotherms with high correlation coefficients and low % error values. The kinetic data indicate the rapidity of the biosorption process, with the equilibrium achieved within 90 min. Several models, including the Elovich, pseudo-first-order, and pseudo-second-order models, were examined for their suitability with the present data; the correlation coefficient and % error values, along with better prediction of equilibrium uptake values, favored the pseudo-first-order model. The desorption experiments were highly successful for T. conoides biomass with 0.05 M HCl, whereas for the other two seaweeds, 0.05 M HCl resulted in high biomass weight loss. Reusing T. conoides biomass in three successive sorption-desorption cycles resulted in only 8.8% reduction in Hg(II) biosorption capacity compared with its original uptake.