Figs 29-33 - uploaded by Tom Schils
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Reticulocaulis obpyriformis and Naccaria wiggii. bc = basal cell of carpogonial branch; cp = carpogonium; hy = hypogynous cell; sc = supporting cell of carpogonial branch; stc = sterile cell; tri = trichogyne. Scale bars = 10 µm (Fig. 29); 20 µm (Fig. 30); 50 µm (Figs 31, 32); 10 µm (Fig. 33). Figs 29-31. Reticulocaulis obpyriformis, SMM 446. Fig. 29. Discoid rhodoplasts (arrowheads) with thickened rims that give them an appearance similar to erythrocytes; the plastids densely fill an inner cortical cell and there are also surrounding reserve vacuoles (arrows). Fig. 30. Spermatangia (arrowheads) developing on terminal and intercalary cortical mother cells.
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Citations
... Tom Schils and Klaas Pauly of the Phycology Research Group, Ghent University, Belgium, carried out surveys mainly around Masirah Island and Barr Al Hikman on the Arabian Sea and the Sea of Oman coastlines over the period 1999 to 2006 e.g. [55][56][57] . Although the latter publication lists Ecklonia radiata in Dhofar this is presumed to be the record from 54 which is listed in their references. ...
Kelp forests are declining in many regions globally with climatic perturbations causing shifts to alternate communities and significant ecological and economic loss. Range edge populations are often at most risk and are often only sustained through localised areas of upwelling or on deeper reefs. Here we document the loss of kelp forests (Ecklonia radiata) from the Sultanate of Oman, the only confirmed northern hemisphere population of this species. Contemporary surveys failed to find any kelp in its only known historical northern hemisphere location, Sadah on the Dhofar coast. Genetic analyses of historical herbarium specimens from Oman confirmed the species to be E. radiata and revealed the lost population contained a common CO1 haplotype found across South Africa, Australia and New Zealand suggesting it once established through rapid colonisation throughout its range. However, the Omani population also contained a haplotype that is found nowhere else in the extant southern hemisphere distribution of E. radiata. The loss of the Oman population could be due to significant increases in the Arabian Sea temperature over the past 40 years punctuated by suppression of coastal upwelling. Climate-mediated warming is threatening the persistence of temperate species and precipitating loss of unique genetic diversity at lower latitudes.
... The genotypic cluster formed by Omanese specimens is highly divergent from the large haplotype cluster of tropical Indo-PaciWc specimens (Fig. 5). The Arabian Sea, which separates the Omanese population from the tropical ones is characterized by seasonal upwelling of cold, nutrient-rich water causing a pseudo-high-latitude eVect with associated cold-water seaweed community (Schils, 2002; Sheppard et al., 1992 ) from which H. discoidea appears to be absent. It is possible that the small Omanese population, which seems to be restricted to a stretch of coastline of a few hundreds of kilometers only mildly inXuenced by upwelling, represents a peripatric founder population which has diverged strongly from the tropical population by genetic drift. ...
... The subtropical regions of the Indian Ocean (Arabian Sea, SE Africa, SW Australia) foster rich seaweed Xoras and high endemism (Bolton et al., 2004; Phillips, 2001; Schils, 2002). Moreover, biogeographic links between these regions have been described on the basis of shared taxa (Joosten and van den Hoek, 1986; Norris and Aken, 1984; Schils and Coppejans, 2003). ...
Nuclear ribosomal and plastid DNA sequences of specimens belonging to section Halimeda of the pantropical green seaweed genus Halimeda show that the group under scrutiny contains many more genetically delineable species than those recognized by classical taxonomy. Discordances between phylograms inferred from nuclear and plastid DNA sequences suggest that reticulate evolution has been involved in speciation within the clade. Nonetheless, our data do not allow ruling out certain alternative explanations for the discordances. Several pseudo-cryptic species are restricted to the margins of the generic distribution range. In a clade of H. cuneata sibling species from widely separated subtropical localities in the Indian Ocean, the South African sibling branches off first, leaving the Arabian and West Australian species as closest relatives. We hypothesize that geographic isolation of the siblings may have taken place following Pleistocene or Pliocene periods of climatic cooling during which subtropical species occupied larger distribution ranges. A more basal separation of Atlantic, Indo-Pacific, and Mediterranean species indicates vicariance. The alternative events that could have caused this vicariance are discussed.
