Fig 1.
Study area and sampling sites.
Table 1.
Description of sampling effort: number of samples, replicates and macroalgal surface examined in different months and at various sites within the Ross Sea.
In addition, a proportional value of macroalgal surface covered by epiphytic sessile fauna is given.
Table 2.
Epiphytic diatoms recorded on three macroalgal host species (Iridaea cordata, Phyllophora antarctica, Plocamium cartilagineum) at six sampling sites during 11 Antarctic expeditions.
Table 3.
Results of ANOSIM test performed on species and growth form abundance data.
Fig 2.
Nonmetric multidimensional scaling (nMDS) graph based on the species abundance data.
Ph—samples of epiphytic diatom communities associated with Phyllophora antarctica, Pl—samples of epiphytic diatom communities associated with Plocamium cartilagineum, Ir—samples of epiphytic diatom communities associated with Iridaea cordata.
Fig 3.
Extrapolation (plain lines) of rarefaction curves (lines with symbols) based on samples from locations where all three algal species were found (Cape Russell, Adélie Cove, Faraglione).
Fig 4.
Average abundances of diatom growth forms found on macroalgal surface in different months (based on all macroalgal replicates collected in Terra Nova Bay).
Fig 5.
Average abundances of diatom growth forms found on the surface of epiphytic sessile microfauna in different months (based on all replicates collected in Terra Nova Bay).
Fig 6.
Scanning electron micrographs of epiphytic diatoms from the Ross Sea.
a.-d. Iridaea cordata covered by dominating Cocconeis antiqua (Adélie Cove, Terra Nova Bay). e. surface of Phyllophora antarctica (Cape Evans, McMurdo Sound). Scale bars: a. & e. = 200 μm; b. = 10 μm; c. & d. = 100 μm.
Fig 7.
Average abundances of diatom growth forms found on macroalgal surface at selected sampling sites.
Fig 8.
Biplot diagram from RDA (redundancy analysis) visualizing the effect of depth on different diatom growth forms.
Supplemental environmental variables (sampling site, season), are added. Analyses is based on 166 subsamples. Due to the relatively low number of samples, results for Cape Evans and Cape Russell sampling sites are not shown. Score scaling is focused on growth form scores (standardized). Eigenvalues: 0.1225, 0.0309, 0.0092; p = 0.005. Adjusted explained variation = 10.3%. CR—Cape Russell, AD—Adélie Cove, F—Faraglione, M—Molo, TB—Tethys Bay.
Fig 9.
Phyllophora and Plocamium samples classified into two groups according to the host organisms: macroalga (epiphytic) or microfauna (epizooic).
The polygons are plotted in the space of the first RDA axes. Score scaling is focused on diatom taxa scores (standardized). Eigenvalues: 0.1967, 0.0994, 0.0706; p = 0.0002. Adjusted explained variation = 27.0%.
Fig 10.
Biplot diagram from a partial redundancy analysis (RDA) summarizing the variation in diatom species composition explained by the host organism (macroalga or microfauna), after removal of the effect of sampling site, season and depth of sampling.
Score scaling is focused on diatom taxa scores (standardized). Abundance data are log-transformed. Eigenvalues: 0.1967, 0.0994, 0.0706; p = 0.0002. Adjusted explained variation = 27.0%.
Fig 11.
Biplot diagram from a partial redundancy analysis (RDA) summarizing the variation in diatom growth form explained by the host organism effect (macroalga or microfauna), after removal of the effect of sampling site, season and depth of sampling.
Score scaling is focused on diatom growth form scores (standardized). Abundance data are log-transformed. Eigenvalues: 0.3084, 0.1085, 0.0969; p = 0.0002. Adjusted explained variation = 47.1%.
Fig 12.
Extrapolation (plain lines) of rarefaction curves (lines with symbols) based on samples of Phyllophora and its associated sessile fauna from locations where both were found (Cape Russell, Adelie Cove, Faraglione, Molo, Tethys Bay).
Fig 13.
Extrapolation (plain lines) of rarefaction curves (lines with symbols) based on samples of Plocamium and its associated sessile fauna.
Fig 14.
Scanning electron micrographs of epiphytic diatoms from Terra Nova Bay.
a. & b. examples of epiphytic sessile fauna. c.–e. diatoms on Plocamium cartilagineum. Scale bars: a. & b. = 200 μm; c.-e. = 100 μm.