Roksana Majewska

Growth form analysis of epiphytic diatom communities of Terra Nova Bay (Ross Sea, Antarctica)

Diatoms have been long collected from the Southern Ocean but almost no data exist for epiphytic communities, despite their high ecological significance as an important food source in Antarctic coastal food chains. Here, we present a first growth form analysis of diatoms associated with rhodophyte hosts from Terra Nova Bay, Ross Sea, Antarctica. We performed this study to gather baseline information on the species composition of epiphytic diatom communities, determine the influence of some environmental variables on the diatom distribution patterns, and assess the caveats that must be taken into account in terms of sampling design. Macroalgal material was collected during the Italian Antarctic expeditions between 1990 and 2004. Epiphytic diatoms were studied by means of scanning electron microscopy. In terms of growth forms, there were no significant differences between the diatom communities on the different macroalgal host species. Motile (mainly small-celled Naviculaperminuta and other Navicula spp.) and adnate (Cocconeis spp.) diatoms dominated the community throughout the study period. Many of the macroalgal blades examined were also covered by epiphytic animals (calcareous bryozoans, hydroids) over most of their surface, with a significant effect on the associated diatom community structure. Our findings suggest that the bio-physicochemical characteristics of each sampling site affected the epiphytic diatom communities more than the substrate type provided by the macroalgal host or the sampling depth.

Epiphytic diatom communities of Terra Nova Bay, Ross Sea, Antarctica: structural analysis and relations to algal host

Abstract Epiphytic diatoms are important constituents of the Southern Ocean coastal water ecosystem, being a key element in many of the Antarctic trophic chains. However, only limited information exists relating to these microalgal communities. Here we describe our findings of a study on epiphytic diatoms from Terra Nova Bay (Ross Sea, Antarctica) based on material collected during the summer campaigns spanning from 1990–2004. Observations of diatoms associated with three rhodophyte species (Iridaea cordata (Turner) Bory, Phyllophora antarctica Gepp & Gepp, and Plocamium cartilagineum (L.) Dixon) were carried out with the use of a scanning electron microscope. A total of 73 diatom taxa (32 genera) were distinguished, of which 20 taxa exceeded 3% of total abundance. Cocconeis fasciolata (Ehrenberg) Brown, Navicula perminuta Grunow, and Fragilariopsis nana (Steemann Nielsen) Paasche appeared in every sample. The analysis of similarities (ANOSIM) test as well as non-metric multidimensional scaling analysis indicated the nature of host organism as a major factor influencing associated diatom community structure, whereas depth, site, and time of sampling seemed to be less important. The epizooic communities associated with sessile fauna epiphytic on macroalgae differed significantly from those associated with macroalgal surface. A pronounced difference between the communities epiphytic on various host macroalgae species was also observed, although most of the dissimilarities occurred between diatom taxa of the same growth form.

Diatoms and Other Epibionts Associated with Olive Ridley (Lepidochelys olivacea) Sea Turtles from the Pacific Coast of Costa Rica.

Although the sea turtles have long been familiar and even iconic to marine biologists, many aspects of their ecology remain unaddressed. The present study is the first of the epizoic diatom community covering the olive ridley turtle’s (Lepidochelys olivacea) carapace and the first describing diatoms living on sea turtles in general, with the primary objective of providing detailed information on turtle epibiotic associations. Samples of turtle carapace including the associated diatom biofilm and epizoic macro-fauna were collected from Ostional beach (9° 59´ 23.7´´ N 85° 41´ 52.6´´ W), Costa Rica, during the arribada event in October 2013. A complex diatom community was present in every sample. In total, 11 macro-faunal and 21 diatom taxa were recorded. Amongst diatoms, the most numerous were erect (Achnanthes spp., Tripterion spp.) and motile (Haslea sp., Navicula spp., Nitzschia spp., Proschkinia sp.) forms, followed by adnate Amphora spp., while the most common macro-faunal species was Stomatolepas elegans (Cirripedia). Diatom densities ranged from 8179 ± 750 to 27685 ± 4885 cells mm-2. Epizoic microalgae were either partly immersed or entirely encapsulated within an exopolymeric coat. The relatively low diatom species number, stable species composition and low inter-sample dissimilarities (14.4% on average) may indicate a mutualistic relationship between the epibiont and the basibiont. Dispersal of sea turtle diatoms is probably highly restricted and similar studies will help to understand both diatom diversity, evolution and biogeography, and sea turtle ecology and foraging strategies.

Benthic diatoms of the Vistula River estuary (Northern Poland): Seasonality, substrata preferences, and the influence of water chemistry

Seasonal studies of water bodies in separate branches of the Vistula River estuary in Northern Poland were conducted over 30 months from May 2005 to October 2007. Diatom samples were collected from different substrata from two sites located in the river mouth, which has physical characteristics as a result of a complex interplay of natural and human influences that have taken place over the last 100+ years. The diatom flora growing on hard surfaces near the river banks such as sand, muddy sand, rocks, macroscopic green algae and/or vascular aquatic plants was recorded. All diatom taxa collected were distinguished based on their morphological features using light (LM) and scanning electron microscopy (SEM). A total of 187 species belonging to 61 genera were identified. A canonical correspondence analysis indicated that the diatom assemblages were definitely associated with salinity as well as nutrient concentrations and substratum type. During the study, malformations of diatom valves were observed in 48% of the microphytobenthos samples. Abnormal outline morphology and ornamentation deformities in several individuals of nine different species were recorded, which were mainly in epilithic and epiphytic communities collected from spring to autumn.

Epibiotic Diatoms Are Universally Present on All Sea Turtle Species

The macro-epibiotic communities of sea turtles have been subject to growing interest in recent years, yet their micro-epibiotic counterparts are almost entirely unknown. Here, we provide the first evidence that diatoms are epibionts for all seven extant species of sea turtle. Using Scanning Electron Microscopy, we inspected superficial carapace or skin samples from a single representative of each turtle species. We distinguished 18 diatom taxa from these seven individuals, with each sea turtle species hosting at least two diatom taxa. We recommend that future research is undertaken to confirm whether diatom communities vary between sea turtle species and whether these diatom taxa are facultative or obligate commensals.

Summer Epiphytic Diatoms from Terra Nova Bay and Cape Evans (Ross Sea, Antarctica) - A Synthesis and Final Conclusions

Despite recent advances in polar marine biology and related fields, many aspects of the ecological interactions that are crucial for the functioning of Antarctic shallow water habitats remain poorly understood. Although epiphytic diatoms play an essential role in the Antarctic marine food web, basic information regarding their ecology, biodiversity and biogeography is largely unavailable. Here, we synthesise studies on Ross Sea epiphytic diatoms collected during 11 summer Antarctic expeditions between the years 1989/90 and 2011/12, presenting a full list of diatom taxa associated with three macroalgal species (Iridaea cordata, Phyllophora antarctica, and Plocamium cartilagineum) and their epiphytic sessile fauna. Diatom communities found during the three summer months at various depths and sampling stations differed significantly in terms of species composition, growth form structure and abundances. Densities ranged from 21 to >8000 cells mm-2, and were significantly higher on the surface of epiphytic micro-fauna than on any of the macroalgal species examined. Generally, host organisms characterized by higher morphological heterogeneity (sessile microfauna, ramified Plocamium) supported richer diatom communities than those with more uniform surfaces (Iridaea). Differences between epiphytic communities associated with different macroalgae were reflected better in species composition than in growth form structure. The latter changed significantly with season, which was related strongly to the changing ice conditions. A general trend towards an increasing number of erect forms in deeper waters and tube-dwelling diatoms in the shallowest sites (2–5 m) was also observed. This study explores further important and largely previously unknown aspects of relationships and interactions between Antarctic epiphytic diatoms and their micro- and macro-environments.

Shared Epizoic Taxa and Differences in Diatom Community Structure Between Green Turtles (Chelonia mydas) from Distant Habitats

The first reports of diatoms growing on marine mammals date back to the early 1900s. However, only recently has direct evidence been provided for similar associations between diatoms and sea turtles. We present a comparison of diatom communities inhabiting carapaces of green turtles Chelonia mydas sampled at two remote sites located within the Indian (Iran) and Atlantic (Costa Rica) Ocean basins. Diatom observations and counts were carried out using scanning electron microscopy. Techniques involving critical point drying enabled observations of diatoms and other microepibionts still attached to sea turtle carapace and revealed specific aspects of the epizoic community structure. Species-poor, well-developed diatom communities were found on all examined sea turtles. Significant differences between the two host sea turtle populations were observed in terms of diatom abundance and their community structure (including growth form structure). A total of 12 and 22 diatom taxa were found from sea turtles in Iran and Costa Rica, respectively, and eight of these species belonging to Amphora, Chelonicola, Cocconeis, Navicula, Nitzschia and Poulinea genera were observed in samples from both locations. Potential mechanisms of diatom dispersal and the influence of the external environment, sea turtle behaviour, its life stage, and foraging and breeding habitats, as well as epibiotic bacterial flora on epizoic communities, are discussed.

Epiphytic diatom communities on Phyllophora antarctica from the Ross Sea

Abstract Antarctic seaweeds play an important ecological role, but the vast macroalgal beds, typical of the shallow-water zone, are not efficiently grazed. However, macroalgal thalli are covered by epiphytic diatoms which represent a rich food source for higher trophic levels. We describe the abundances, growth form structure, species composition and distribution patterns in the diatom communities associated with Phyllophora antarctica from selected sites within the Ross Sea. The goal of this work was to learn more about the relationships between various components of the epiphytic community and its habitat. To examine diatoms at the microscale, four relatively well described sampling sites were chosen and analyses were performed on a large number of diatoms. All observations and counts were made with the scanning electron microscope. Samples collected in the same season but from different sites and under different sea and ice conditions differed significantly in terms of species composition, but all represented abundant and well-developed diatom communities. A list of species associated with P. antarctica from the investigated area is provided and the influence of the sampling effort on the observed diatom diversity is assessed.

Two new epizoic Achnanthes species (Bacillariophyta) living on marine turtles from Costa Rica

Abstract It has been known for a long time that marine mammals, such as whales and dolphins, host a very specific epizoic community on their skin. Whether or not a similar community exists on the carapaces of sea turtles is less studied. The present paper describes two new epizoic diatoms from the genus Achnanthes sensu stricto, Achnanthes elongata and Achnanthes squaliformis, found on the carapaces of nesting olive ridley sea turtles (Lepidochelys olivacea) in Ostional Beach on the Pacific coast of Costa Rica, based upon detailed scanning electron microscopy and comparison with the type material of Achnanthes groenlandica var. phinneyi and Achnanthes pseudogroenlandica. The two taxa appear to be closely related on the basis of their morphological features including long, slender valves, absence of terminal orbiculi, large cribrate areolae and absence of typical costae on the internal virgae of both valves. They can, however, be differentiated from each other by the number of areolae per stria, the position of the rapheless sternum and differences in their length/width ratio.

4th Polar Marine Diatom Taxonomy and Ecology Workshop, Cardiff University, UK, 4–9 August 2013

4th Polar Marine Diatom Taxonomy and Ecology Workshop, Cardiff University, UK, 4–9 August 2013 ZUZIA STROYNOWSKI1∗, REBECCA MINZONI2 & ROKSANA MAJEWSKA3 1Marine Geology Division, Portuguese Institute of Ocean and Atmospherics, Alfragide, Portugal 2Department of Earth Science, Rice University, Houston, USA 3Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, II University of Naples, Caserta, Italy