Benthic macroalgae of the Arabian Sea 1 Benthic macroalgae of the ...

Benthic macroalgae of the Arabian SeaAlgal assemblages of Masirah Island (Oman) and the Socotra Archipelago (Yemen),a case studyTom SchilsResearch Group Phycology, Department of Biology, Ghent University, K. L. Ledeganckstraat35, 9000 Ghent, Belgiumtom.schils@rug.ac.beFig. 1. Stoechospermum polypodioides (Lamouroux) J. Agardh, a common brown alga ofthe coastal waters around Masirah Island. Scale bar = 1 cmSubsequent to the Oman 99 Mission (November 1999), a field trip to the Socotra Archipelago(Yemen; March - May 2000) was organised to compare the algal assemblages of Masirah Islandwith other upwelling areas in the Arabian Sea. During both campaigns, collection efforts werefocused on the diverse and species rich sublittoral algal vegetations. The biotic and abioticparameters of the sampling sites were documented, the observed seaweeds registered and themajority of the algae preserved on herbarium sheets (Fig. 1), as formalin specimens or silica gelsamples (molecular analysis). In addition to qualitative sampling, vegetation relevés (quadratsof 0.25 m 2 ) were used to determine the ecology of the algal vegetations around Socotra. Thevegetation parameters and the environmental variables were noted in situ (Schils 2000) andcompleted with biomass data in the field laboratory. The latter method (scraping-off phytomass)also showed its use for qualitative sampling, as it revealed the species richness of small algae inunderstory layers.Benthic macroalgae of the Arabian Sea 1

Databases (MS Access 2000) were designed to store the sample data of the different field trips.A first database, “Phycobase”, contains information on the (i) collected specimens; (ii) acompilation of all macroalgal genera classified by their latest systematic position; (iii) tablesand queries of all documented algal taxa of the northern Indian Ocean. This databaseautomatically detects new records of species and genera, executes exhaustive biogeographicalcomparisons, classifies specimens, etc. Additionally, the records (specimens) contain hyperlinksto html pages, which include descriptions and comparisons of the specimens with literaturereports of related taxa. The html documents are continuously updated and their structure issystematically arranged with links to (i) higher and lower taxonomic levels, (ii) macroscopicand microscopic images and (iii) personal comments of specialists. Currently 1721 specimensare stored in Phycobase, 587 from Masirah Island and 1134 from the Socotra Archipelago. Sofar, about 30% of the specimens are identified to species level and 50% to genus level.Preliminary checklists for both islands in the Arabian Sea were included in project reports(Schils 1999, 2000). At present, the research efforts aim at a systematic study of coherenttaxonomical groups, mainly belonging to the Rhodophyta.The second database, “SMM relevés”, contains the vegetation relevés. The database includesfor each sampling station the site description, the environmental variables and the relevés as subforms. This allows orderly and sound adjustments (refined identifications). All data arecombined in 2 tables, permitting analyses by means of cross tables (statistics, extraction ofmatrices for multivariate analyses, etc.).A prospective analysis of the vegetation relevés around the Socotra Archipelago (Tukey HSDtest; Schils 2000) shows that the sample sites of upwelling regions are characterised by asignificantly higher species richness (p < 0.5) compared to the other coastal areas. A similarpattern is observed for Masirah Island, where the algal communities of the east coast areanalogous to those of the south coast of Socotra Island. The sublittoral marine macroflora of theupwelling areas is characterised by the seasonal presence of gelatinous red algae(Dumontiaceae, Naccariaceae, Nemastomataceae and Schizymeniaceae). Similar vegetationsare found in distant regions in the Indian Ocean and the Pacific, which are subject to a coldwater regime with considerable current dynamics (e.g. Hawaii, Abbott pers. comm.). Millar &Kraft (1984) state that these rather “primitive” algae could persist over a long period in time inthese more or less constant sublittoral habitats. In this context, it is interesting to analyse theactual distribution patterns of these algae within the Indian Ocean and the Pacific.The first taxonomical topic covered the first observations of Naccariaceae taxa for the IndianOcean. Representatives of the genus Reticulocaulis (previously monospecific and endemic toHawaii) were collected in the coastal waters of Masirah and Socotra Island. Biogeographicaland taxonomical aspects of these algae were studied. The Omani specimens were compared indetail to formalin samples of the type species and the developmental stages (especially those ofthe female gametophytes) were discussed. The collection of R. mucosissimus off MasirahIsland, revealed a disjunct distribution pattern of the type species. The Socotran specimenspossessed the generic characteristics but differed from R. mucosissimus, resulting in thedescription of a new species, R. obpyriformis (Schils et al. submitted). R. obpyriformis showsadditional carposporophyte characteristics that confirm previously stated similarities (Abbott1985, 1999) with other “primitive” Florideophyceae, particularly Acrosymphyton. Thephylogenetic position of the genus and the family remain unclear. Pending molecular studies onReticulocaulis and additional Atractophora and Naccaria samples (the other Naccariaceaegenera) should clarify their phylogeny and biogeography.Benthic macroalgae of the Arabian Sea 2

The gelatinous red algae belonging to the families Dumontiaceae, Nemastomataceae andSchizymeniaceae were analysed in a subsequent study. The taxa of these families are relativelywell investigated in other parts of the world, but information on their presence and distributionin the Indian Ocean is lacking. The studied species assume a great affinity with the gelatinousred algal flora of Australia and the Great Barrier Reef in particular. However, the includednew records from other Indian Ocean localities show that many gelatinous red algae mighthave a wider distribution range. The observations of Hommersand (1986) support the latterpoint of view, he states that these rather “primitive” algae are widely distributed in the tropicsand in regions that bordered the original Tethyan Ocean. This implies that previouslymentioned biogeographical links (Børgesen 1934; Wynne 2000) with distant areas (Australia,Japan and South Africa) cannot be confirmed using representatives of these families incomparative studies. The floristic similarities would be mere results of comparing distant,well-investigated areas within regions of an inadequately known marine flora. In investigatingthese algae, we focused on the post-fertilization events that typify the families and species.New information concerning these critical characters, which have been scarcely observed inpast studies, is included in the manuscript (Schils & Coppejans submitted). Additionally, anewly described Platoma species (Fig. 2) constitutes the first record of this genus for theIndian Ocean.Fig. 2. A Platoma sp. nov. from Masirah Island, the first record of this genus for the IndianOcean. Scale bar = 1 cmAt present, a study on the Delesseriaceae (Rhodophyta) of the Arabian Sea is in process.Representatives of this family are relatively well documented for adjacent areas in the IndianOcean and these taxa are consequently a good tool for biogeographical analyses. Themorphology, anatomy and reproductive characteristics of ten species are being studied,including taxa with disjunct distribution patterns (e.g. Zellera sp.) and first records since theiroriginal description (e.g. Chauviniella jadinii). Another family of the Ceramiales, theRhodomelaceae, will be examined in the framework of an MSc thesis (2001-2002).Benthic macroalgae of the Arabian Sea 3

Other algal groups that require a thorough examination are the Chlorophyta, the Nemaliales andthe Rhodymeniales. This research will be executed in collaboration with the respectivelyspecialists: Frederik Leliaert (Chlorophyta; Ghent University, Belgium) and John Huisman(Nemaliales and Rhodymeniales; Murdoch University, Australia). As the phycologicalfieldwork was part of a multidisciplinary study, the coastal areas around the SocotraArchipelago will be analysed for ecological and seasonal patterns using the vegetation relevésand remote sensing data (Rebecca Klaus; Warwick University). The final goal is anextrapolation of these results to other upwelling areas in the Arabian Sea (e.g. Masirah Island).Previous biogeographical studies of the Arabian Sea showed floristic affinities with distantareas, e.g. Australia, Japan and South Africa (Børgesen 1934; Wynne 2000). Our preliminaryresults show floristic affinities with the East African Coast, the Indo-Malayan Region, westernand eastern Australia. These findings fit the hypothesis of Hommersand (1986), whichdemonstrates that ocean currents during the Miocene were determinant for the presentdistribution patterns of the marine macroflora. Prospective research using Phycobase shouldfacilitate an elaborate biogeographical analysis of this stepping stone region in the IndianOcean.ReferencesAbbott I. A. 1985. Vegetative and reproductive morphology in Reticulocaulis gen. nov. andNaccaria hawaiiana sp. nov. (Rhodophyta, Naccariaceae). Journal of Phycology 21: 554-561.Abbott I. A. 1999. Marine red algae of the Hawaiian Islands. Bishop Museum Press, Honolulu,Hawai’i. 477 pp.Børgesen F. 1934. Some marine algae from the northern part of the Arabian Sea with remarkson their geographical distribution. Kongelige Danske Videnskabernes Selskab, BiologiskeMeddelelser 11: 72 pp.Hommersand M. H. 1986. The biogeography of the South African marine red algae: a model.Botanica Marina 29: 257-270.Millar A. J. K. & Kraft G. T.. 1984. The red algal genus Acrosymphyton (Dumontiaceae,Cryptonemiales) in Australia. Phycologia 23: 135-145.Schils T. 1999. Macroalgae. In: (Planes S. & Galzin R. eds) Preliminary Report ScientificMission Oman 99, Sultanate of Oman, November - December 1999. Ardoukoba, Paris. 22-23, 64-69 pp.Schils T. 2000. Short Report: Macroalgal assemblages of the Socotra Archipelago, Yemen. In:(Hariri K. I. & Krupp F. eds) Conservation and Sustainable Use of Biodiversity of SocotraArchipelago. Marine Habitat, Biodiversity and Fisheries Surveys and management. Reportof Phase IV. Senckenberg Research Institute, Germany. 12 pp. accepted.Schils T. & Coppejans E. Gelatinous red algae of the Arabian Sea, including Platomabibendiforme sp. nov. (Gigartinales, Rhodophyta). submitted.Schils T., De Clerck O. & Coppejans E. Reticulocaulis mucosissimus and R. obpyriformis sp.nov., the first Naccariaceae (Rhodophyta) records for the Indian Ocean. submitted.Wynne M. J. 2000. Further connections between the benthic marine algal floras of the northernArabian Sea and Japan. Phycological Research 48: 211-220.Benthic macroalgae of the Arabian Sea 4