Volume 47, Issue 6

Four-season surveys of macroalgal assemblage structure on a coral reef in southern Taiwan were performed by transect investigation from October 1999 through August 2000. Species richness increased over time, and percentage cover and biomass peaked in April. Non-metric multidimensional scaling ordination analysis of species similarities between stations showed three distinct clusters corresponding to the upper reef flat, the lower reef flat and the reef slope. The macroalgal assemblage on the lower reef flat was further grouped into two clusters corresponding to the warmer months (October 1999 and August 2000) and the cooler months (January and April 2000), suggesting the macroalgal assemblage is structured primarily by zone and secondarily by season. Species richness, percentage cover, biomass, species diversity (H') and evenness (J') were highest on the lower reef flat, reflecting greater complexity in the macroalgal assemblage in this zone. However, species diversity and evenness on the lower reef flat and the reef slope did not show seasonal variations. Species diversity in the upper reef flat decreased in the warmer months due to the dominance of an unknown red alga in October 1999 and Enteromorpha linza in August 2000. The results of ANOSIM tests showed that species structure was different not only between zones but also between seasons, and the SIMPER analyses showed that, in the warmer months, Gracilaria coronopifolia , Enteromorpha linza , Laurencia spp. and Hypnea charoides were the species that separated the lower reef flat assemblage from other assemblages. In the same way, the unknown red alga (for October 1999), Enteromorpha linza (for August 2000), Halimeda spp., Mastrophora rosea and Portieria hornemannii were the species responsible for differences in structure between the upper reef flat and the reef slope. In the cooler months, the species responsible for differences in structures between the upper reef flat and the other two zones were Sargassum spp., Gracilaria coronopifolia , Enteromorpha linza and Padina australis , and those responsible for differences between the upper reef flat and the reef slope were Hypnea charoides , Halimeda spp., Mastophora rosea , Enteromorpha linza and Portieria hornemannii . The present investigation suggests that macroalgal abundance and structure on a coral reef in Nanwan Bay in southern Taiwan have marked spatial zonation and seasonal variations, and Sargassum on the lower reef flat has become the most abundant alga, as compared to 12 years ago.

Canopy removal by storms is a primary cause of mortality for the small kelp Ecklonia radiata in temperate Australasia. We simulated hydrodynamic drag from storms with in situ pull-tests to determine whether thallus size, life stage, aggregation, wave exposure and substratum affect the canopy removal process. A total of 466 individuals were pulled off 20 rocky reefs at 8–10 m depth in southwestern Australia. The majority (71%) of thalli dislodged at the rock implying that the canopy removal process in southwestern Australia is a substratum-controlled process. Dislodgment bared clean substratum where re-invasion by propagules or encroachment would be necessary to fill up the gaps. Maximum break forces (150–250 N) were found for large late stage kelps and kelp aggregates from wave exposed sandstone and granite reefs, and minimum values (25–100 N) for small juveniles and solitary kelps from protected limestone reefs. By applying size and break force data to the drag equation, water velocities required to break or dislodge E. radiata were calculated to 2–5 ms -1 for large kelps. These velocities are frequently encountered in wave-exposed shallow subtidal habitats, suggesting that thallus size is limited by the hydrodynamic environment.

A general description is provided for male and female gametes, their gametangia, and thalli of five species of the siphonaceous green macroalga Codium from Atlantic and Pacific shores. Both types of gametes were biflagellate, the flagella arising from a cap at the tip of the colorless extension of the hyaline apex, which also contained the nucleus. Male gametes were small (mean diameter for five species, 2.5 μm; length ranged from 5 to 10 μm) and had few chloroplasts; female gametes were considerably larger (mean diameter 11 μm; length ranged from 11 to 21 μm) with many chloroplasts. Monthly collections of C. isthmocladum indicated that female seasonality was broader than male seasonality and that hermaphroditic thalli were frequent. Comparison of these reproductive traits with reports for the invasive Codium, C. fragile ssp. tomentosoides, collected from the northwestern Atlantic coast suggested that 1) in localized areas, two subspecies or varieties may coexist, and 2) no functional male gametes were produced by C. fragile populations from this coastline. We speculate that Tokyo and Sagami Bays on the Pacific shores of Honshu, Japan, might contain the source populations for the invasive ssp. tomentosoides . Furthermore, we suggest that the extended presence of mature female thalli coupled with the apparent absence of mature male thalli might cause the prevalence of parthenogenesis in this genus.

A population of seaweeds from the Canary Islands successively reported as Sargassum diversifolium , S. vulgare f. diversifolium , or S. vulgare was examined monthly at the climax of vegetative and reproductive stage development to evaluate morphological taxonomic features. The primary and secondary blades are morphologically different (primary blades are spirally twisted and sinuous with serrate to nearly entire margins, whereas secondary blades are thinner with entire to slightly dentate-serrate margins); the vesicles are subspherical to slightly oblong, muticous or ending in a mucro or in a coronal blade; and the receptacles are furnished with spines. These characters are not applicable to Sargassum diversifolium, or to an infraspecific taxon of Sargassum vulgare or S. furcatum as previously suggested, and consequently, Sargassum orotavicum sp. nov. is described. Nomenclatural problems related to the name diversifolium and the affinities of the species involved are presented. According to their morphological characters, S. orotavicum , S. vulgare and S. furcatum belong to the subgenus Sargassum . However, S. vulgare and S. furcatum constitute genuine species of the subsection Cymosae of the section Malacocarpicae, whereas S. orotavicum appears related to species of the subsection Biserrulae of the section Acanthocarpicae.

Spyridia filamentosa is a commonly encountered species, especially in tropical and warm temperate locations. Molecular data, based on three genetic regions, plus morphological investigation of samples from the northeastern Atlantic reveal that samples identified as S. filamentosa from this area are distinct. Genetically these samples are more closely related to S. clavata than other S. filamentosa samples. Morphologically, the northeastern Atlantic Ocean samples are distinguishable by two (or occasionally one) small axial cells that lack cortication near the base of the determinate branches. Investigation of type material reveals that these samples should be recognized as Spyridia griffithsiana (J.E. Smith) Zuccarello, Prud'homme van Reine et Stegenga comb. nov. and that specimens of this new combination are found throughout the northeastern Atlantic Ocean and into the western Mediterranean Sea. Phylogeographic relationships within S. filamentosa show a complex distribution pattern. Samples from the same location can be in different evolutionary lineages (Cape Verde and Canary Islands). While some lineages seem to be confined to particular ocean basins, other lineages have a much wider distribution.

Solid-state 13 C nuclear magnetic resonance (NMR) and wide-angle X-ray scattering (WAXS) were used to characterise the cellulose in six species of Florideophycean algae. NMR identified cellulose I β as the dominant crystalline form in all species, and was used to estimate the widths of the sheets of cellulose chains. The mean value (±SD) was 3.9±0.4 nm. WAXS was used to estimate the thickness of microfibrils measured normal to the sheets of chains. The mean value (±SD) was 1.9±0.5 nm. Uniformity of these results across the six species supported a generalisation that Florideophycean algae biosynthesise cellulose chains in microfibrils that are narrower than those biosynthesised by Bangiophycean algae.

We examined factors that contribute to the structuring of lignicolous mangrove microfungal communities across ocean basins and plant families. In particular, we hypothesized that microfungal communities are more similar between locations in the same ocean basin as compared to locations in different ocean basins, and that trees that are more closely related phylogenetically share more similar microfungal communities than those less closely related. We assessed these hypotheses through a meta-analysis employing ordination analysis on published data of fungal hosts and fungal distribution. Based on these analyses, we conclude that microfungal communities are more similar within a single ocean basin than between ocean basins, but mangrove trees that are close phylogenetically do not necessarily harbor microfungal communities that are distinctly different from less closely related hosts.

Littoral surveys on Jersey shores in the Channel Islands (southern English Channel) revealed unexpected spatial variation in local-scale distributions of green macroalgae belonging to Codium species. Traditionally considered a low-shore alga, native C. vermilara inhabited high and/or mid-shore pools at nine of ten shores surveyed. This alga was frequent on semi-exposed shores. The introduced taxon C. fragile ssp. tomentosoides was patchily distributed with highest abundances in wave-sheltered areas. Zonation patterns of Codium spp. on Channel Island shores were more complex than those north of the English Channel.