Adil Y. Al-Handal

Biodiversity, biogeography and zonation of marine benthic micro- and macroalgae in the Arctic and Antarctic

This paper reviews the composition, biogeography and zonation of benthic algae in Arctic and Antarctic polar regions. There is a marked contrast in the literature between the amount of information on microalgae vs. macroalgae. Perhaps not surprising in view of their size and conspicuous nature, the macroalgae are better known than the microalgae and they have been studied more intensively. Macroalgal biodiversity is greater in Antarctica than in the Arctic, as is the number of endemic species. Both these characteristics of the Antarctic marine macroalgal flora can be explained by the biogeographical histories of the regions. In contrast, endemism amongst Arctic and Antarctic benthic microalgae is generally considered to be low; however, there is very little evidence to support this and further molecular research is needed to document and clarify the biodiversity of marine benthic microalgae of both polar regions. The zonation or local distribution of polar macroalgae and microalgae is influenced by physiological, morphological, chemical and ecological characteristics that determine responses to a range of environmental factors, including the ability to resist and survive algal grazing. Typically, the lower depth distribution limit elevates with increasing latitude.

Marine epiphytic diatoms of the shallow littoral zone in Potter Cove, King George Island, Antarctica

Marine epiphytic diatoms of the shallow littoral zone in Potter Cove, King George Island, Antarctica

Marine benthic diatoms from Potter Cove, King George Island, Antarctica

Abstract Antarctic benthic marine diatoms from the Potter Cove region, King George Island were studied in samples collected during the austral summer 2003. A floristic list was made to add information on the Antarctic benthic diatom distribution. A total of 84 species was identified from four localities in Potter Cove, the majority of which are of cosmopolitan distribution. The most common taxa encountered were Cocconeis spp., Gyrosigma fasciola, Navicula cf. cancellata, N. cf. perminuta, Petroneis plagiostoma and Pleurosigma obscurum. Both G. fasciola and P. obscurum are recorded for the first time from Antarctica with such common occurrence. The overall diatom population in Potter Cove appeared rather different from other diatom populations observed in Antarctic marine habitats.

UV radiation : a threat to Antarctic benthic marine diatoms?

Abstract This investigation was motivated by the lack of ultraviolet radiation (UVR, 280–400 nm) studies on Antarctic benthic marine microalgae. The objective was to estimate the impact of UV-B (280–315 nm) and UV-A (315–400 nm), on photosynthetic efficiency, species composition, cell density and specific growth rate in a semi-natural soft-bottom diatom community. In both experiments, cell density increased over time. The most frequently observed species were Navicula cancellata, Cylindrotheca closterium, Nitzschia spp., and Petroneis plagiostoma. For both experiments, a shift in species composition and a decreased photosystem II (PSII) maximum efficiency (Fv/Fm) over time was observed, irrespective of treatment. UVR significantly reduced Fv/Fm on days 3 and 10 (Expt 1), disappearing on the last sampling date. A similar trend was found in Expt 2. A significant UV effect on cell density was observed in Expt 1 (day 10) but not in Expt 2. No treatment effects on species composition or specific growth rate were found. Thus, the UV effects were transient (photosynthetic efficiency and cell density) and the growth of the benthic diatoms was generally unaffected. Overall, according to our results, UVR does not seem to be a threat to benthic marine Antarctic diatoms.

COCCONEIS POTTERCOVEI SP. NOV. AND COCCONEIS PINNATA VAR. MATSII VAR. NOV., TWO NEW MARINE DIATOM TAXA FROM KING GEORGE ISLAND, ANTARCTICA

Details of two new small marine taxa of the genus Cocconeis Ehrenberg are described; C. pottercovei sp. nov. and C. pinnata var. matsii var. nov., which were observed as epipelic and epiphytic in Potter Cove, King George Island, Antarctica. Descriptions are based on both light and scanning electron microscope observations. C. pottercovei belongs to the group of Cocconeis taxa that bear very short and marginal striae on the rapheless valve while C. pinnata var. matsii belongs to the C. costata Gregory complex. They are mainly differentiated from the other similar taxa by stria number, stria arrangement and structure on both raphe and rapheless valves. A comparison with closely resembling taxa is given.

Two new marine species of the diatom genus Cocconeis Ehrenberg : C. melchioroides sp. nov. and C. dallmannii sp. nov., from King George Island, Antarctica

Two new marine diatom species, Cocconeis melchioroides and C. dallmannii are described from Potter Cove, King George Island, Antarctica. Detailed descriptions are given based on LM and SEM images for both species and compared with the only known morphologically related taxon, Cocconeis melchiori Frenguelli and Orlando. Both C. melchioroides and C. dallmannii belong to the Cocconeis group, in which the sternum valve has very short and marginal striae. They differ from each other in the number of striae, number of areolae, central raphe endings, crista marginalis and valvocopula. A comparison with the Cocconeis costata group is provided. Both species are common inhabitants of the marine surface sediment in the Potter Cove area.

Two new Cocconeis taxa (Bacillariophyceae) from coral sands off the Mascarenes (Western Indian Ocean) and some related unidentified taxa

Coral sands off Réunion Island and Rodrigues (Mascarene archipelago, Western Indian Ocean) support diverse diatom communities, particularly rich in Monoraphidineae. Recent surveys of reef environments (June 2005 and June 2007) permitted the recognition of several taxa belonging to the diatom genus Cocconeis, among which are two new, relatively small taxa, epipsammic on coral sand. Cocconeis coronata Riaux-Gobin et Romero sp. nov. is similar to C. scutellum but has its own distinctive features. In external view, the concave raphe valve possesses uniseriate striae and a subsident hyaline marginal rim, while the strongly convex sternum valve has a submarginal, generally continuous crest, a hexagonal pattern of areolation, short, rounded spines that are often regularly arranged around valve face areolae, a complex areola hymen and small marginal chambers. Some morphometric differences were noted between the populations of C. coronata at Réunion and Rodrigues. Cocconeis margaritata Riaux-Gobin et Al-Handal, sp. nov. is smaller, possesses a sternum valve like that of C. placentula and C. neothumensis, but has denser striation and small pearl-like concretions around the areola aperture on the sternum valve. Several other taxa that resemble, or may be varieties of, C. margaritata require further study before being formally described. Cocconeis margaritata and C. coronata are small and relatively rare, so their study requires scanning electron microscopy.

Species of the Cocconeis peltoides group with a marginal row of unusual processes (Mascarenes and Kerguelen Islands, Indian Ocean)

Two diatoms related to Cocconeis peltoides Hustedt (Bacillariophyceae), from coral reef environments (Mascarenes, Western Indian Ocean), are proposed as a new Cocconeis variety and a new C. species: Cocconeis peltoides var. archaeana Riaux-Gobin et Compère and Cocconeis sigillata Riaux-Gobin et Al-Handal. Cocconeis peltoides and the two new taxa possess an unusual marginal row of small processes on their sternum valve, internally opening as curb-like structures. Several other Cocconeis species, encountered during sampling campaigns in Kerguelen (Southern Ocean, Indian Ocean sector), also share such processes, including Cocconeis hauniensis Witkowski and Cocconeis germainii Riaux-Gobin, Witkowski et Romero. The shared characteristics of these taxa are examined and compared in detail.

COCCONEIS COSTATA VAR. SUBANTARCTICA VAR. NOV., A NEW MARINE DIATOM OFF KERGUELEN ARCHIPELAGO (SOUTHERN OCEAN, INDIAN SECTOR)

Cocconeis costata var. subantarctica var. no v., a rare taxon from the Kerguelen Archipelago (Southern Ocean, Indian sector), is described using light and scanning electron microscope observations and was compared to related taxa. Apart from the wide-elliptical central area devoid of striae, the raphe valve features highly resemble those of the C. costata complex: the open crista marginalis is similar to the one occurring in other varieties of C. costata, whereas the slightly dissymmetric and hook-like central raphe endings are a distinctive feature. This Subantarctic diatom has a two-layered sternum valve, with alveolate striae consisting of elongated chambers internally open through marginal elliptical wide and regular foramina. On the external side, striae of the sternum valve vary from biseriate to triseriate near the margin, and are not restricted to the foramina location. The resemblance of our new taxon with C. costata var. paciflca and C. barleyi, which also possess more or less extended SV chambers, is discussed. The epizoic diatom genera Bennettella and Epipellis, previously assigned to the genus Cocconeis Ehrenberg, also show such alveolate-chambered striae, but are associated with several other very specific features. Several small sized Cocconeis taxa from Antarctic and Subantarctic environments, such as C. costata var. antarctica and C. melchiori, show a certain morphological similarity to Cocconeis costata var. subantarctica var. nov., but they have marginal short striae on the sternum valve and lack a two-layered sternum valve or chambers.

New Amphicocconeis species off Mascarenes (Western Indian Ocean) and related taxa

Two new species were found on coral sediments of Mascarene archipelago: Amphicocconeis mascarenica sp. nov., relatively frequent in Réunion and rare in Rodrigues Islands, and A. rodriguensis sp. nov., relatively rare in Rodrigues and scarce in Réunion. Comparison was made with A. disculoides and A. debesii (Hustedt) De Stefano, and with species pertaining to Psammococconeis Garcia (P. brasiliensis and P. disculoides sensu Garcia). The Mascarenes taxa do not have simple raphe endings but terminal raphe fissures bent to the same side, which is a characteristic feature shared by Amphicocconeis taxa. Amphicocconeis rodriguensis has a raphe valve relatively similar to that of A. debesii (Hustedt) De Stefano, but with a denser striation; furthermore, the valvocopula of the sternum valve is narrow with simple to chiselled fimbriae. Amphicocconeis rodriguensis sternum valve is close to that of A. debesii (Hustedt) De Stefano. Amphicocconeis mascarenica shows a number of striae relatively low on both valves and both valvocopulae are generally extended and present rows of alternated small holes, which seems a unique feature for Amphicocconeis.