Many of the regional differences in recorded species numbers can be attributed to differing sampling effort and methodologies between studies. The relative inaccessibility and lack of national research bases means that locations such as the South Sandwich Islands, the New Zealand sub-Antarctic, Bouvet and parts of East Antarctica are underrepresented in the database (Fig. 1). Other areas, such as Peter I Island, Elephant Island, Shag Rocks and many others, lack published intertidal community records.
The rarefaction analyses show that even when sampling is taken into account there are regional differences in species richness (Fig. 5). By far the most species-rich regions in this study were South Africa and southern New Zealand. This came as little surprise, given that their large geographical area, their known high marine species richness and high numbers of endemic species (Costello et al., 2010). The lower diversity observed from the Patagonian intertidal also reflects its comparatively low recorded overall marine species richness (Costello et al., 2010; Linse et al., 2006; Barnes & Griffiths, 2008). The little-studied intertidal fauna of the Falkland Islands showed similar diversity levels to that of Tierra del Fuego, which would be expected given its geographical location.
The islands of the sub-Antarctic with sufficient sampling effort for rarefaction analysis were Marion, Kerguelen and Macquarie. These islands represented three out of the four lowest species richnesses observed in this study. The island biogeography rule (MacArthur & Wilson, 1967) states that species richness typically increases with geographical area and decreases with isolation. This would go some way to explaining the pattern observed for these sub-Antarctic islands with the largest island, Kerguelen, being the richest and the smallest, Macquarie Island, being the least diverse (Fig. 5, Table 2). The geological ages of these islands vary between 0.45 and 30 million years; however, González-Wevar et al. (2014) showed that the youngest island, Marion, was colonized very shortly after its emergence. The islands also have similar glacial histories, with Kerguelen likely to have been most heavily glaciated and the last to begin deglaciation (Fraser et al., 2009). Given that Kerguelen has the highest species richness it appears that its glacial history has not significantly impacted its biodiversity compared to other sub-Antarctic islands. Extreme geographical isolation and a common glacial history appear to be the major factors determining the low intertidal biodiversity of these sub-Antarctic Islands.
|Tristan da Cunha||37.1 °S||12.25 °W||102||18||2820||4000||15.3||1||N/A|
|Gough||40.33 °S||9.54 °W||57||6||2670||3550||12.4||1||N/A|
|Antipodes||49.68 °S||178.77 °E||21||0.5||872||2580||7.9||1||N/A|
|Marion||46.9 °S||36.75 °E||290||0.45||1900||2500||5.5||6||17–2.3k|
|Crozet||46.42 °S||51.63 °E||280||8.1||2740||2350||4.8||2||11k|
|Kerguelen||49.37 °S||69.5 °E||7200||30||4110||2100||3.5||9||15k–present|
|Bouvet||54.43 °S||51.85 °W||49||1.39||2900||1700||−0.3||11||?|
|Macquarie||54.62 °S||158.9 °E||128||11.5||990||1600||5.1||2||17–8k|
|South Sandwich Is.||59.03 °S||26.52 °W||337||4||2600||1600||0.5||10||?|
|South Georgia||54.25 °S||37.0 °W||3755||120||2210||1500||1.5||11||19k–present|
|Heard||53.1 °S||73.5 °E||368||20||4570||1500||1.7||11||?–present|
|West Falkland||51.5 °S||60.5 °W||3500||3000||530||1250||7.7||2||N/A|
|South Orkney Is.||60.58 °S||45.5 °W||620||185||1400||600||−1.0||11||11.5k–present|
|King George Island||62.03 °S||58.35 °W||1150||106||900||120||0.5||11||15k–present|
The Antarctic Peninsula is one of the better studied regions with 185 species recorded from 30 localities and a species richness higher than that of the Patagonian regions and the sub-Antarctic. This is despite having some of the youngest deglaciation ages (Table 2) and high levels of winter and some summer sea ice. The sites furthest south (and therefore experiencing the highest disturbance due to ice encasement in winter and scour in summer) have a surprisingly high diversity, despite superficially appearing to be sparsely populated. Most species survive below the upper scoured surface of the cobble boulder matrix (Waller et al., 2006; Waller, 2013). It is likely that these cobble pavements are a relatively common feature where ice encasement occurs. Hansom (1983a,b) reported the presence of these structures at both the South Shetland Islands and various sites on the north-west coast of South Georgia. He estimated that they may have been present for at least 9000 years, providing a stable and protected environment for cryptic communities to become established.
King George Island shares 27% of its species with the Antarctic Peninsula and has higher biodiversity than Kerguelen, which is over six times larger. The intertidal species richness of King George Island is higher than that of any other Antarctic or sub-Antarctic island in this study. This could be attributed to its geographical closeness to the Antarctic Peninsula. Although it does not have as high overall biodiversity as the neighbouring Peninsula, it has 19 species of macroalgae compared with the 12 found around the Peninsula.
The intertidal biodiversity of the Antarctic island of South Georgia is lower than expected if the theory of island biogeography is applied. Given its geographical locality (relatively near to both South America and Antarctica), its large geographical size, significant age and relatively early deglaciation, it would be reasonable to expect South Georgia to be among the most diverse islands in the study. It is, in fact, the second least diverse area analysed, after Macquarie Island. Marion Island, for example, is 13 times smaller than South Georgia and 400 km further from any continent yet the intertidal biodiversity is ~20% higher. South Georgia's intertidal biodiversity is also far lower than that of the other well studied Antarctic regions. It has 37% of the richness of the Antarctic Peninsula for a given number of samples and 60% of that of the far smaller King George Island. Assuming that intertidal species richness is relative to overall marine species richness for an area, then South Georgia would be expected to have higher biodiversity than any of the other Antarctic or sub-Antarctic areas in this study (Linse et al., 2006).
The intertidal organisms of South Georgia may be suppressed by physical disturbance and nutrient input from some of the island's other inhabitants. Bonner (1985) attributed damage to vegetation on land and high levels of ‘manuring’ to fur seals. The current South Georgia population is estimated to be over 3 million breeding individuals. Along with the intense physical damage, this large seal population results in raised levels of nutrients from waste products. Increased nutrient levels from large colonies of animals have been shown to have a negative effect on intertidal biodiversity elsewhere (Wootton, 1991). Barnes et al. (2006) and Waller (2008) observed seals at every locality of their South Georgia studies and remarked upon the sparsity of intertidal life at Bird Island, which they attributed to trampling by fur seals. However, they also commented on the diversity of life on a boulder area of the same beach that was populated by 14 species representing nine classes, including gastropods present in their hundreds per metre square (Barnes et al., 2006). Given that the areas of South Georgia studied for intertidal organisms are in the north and west of the island, coincident with the main fur seal population (Boyd, 1993), then our levels of intertidal biodiversity for the island may be an underestimate. Another contributing factor to the low biodiversity may be that South Georgia has glaciers that calve into some bays leading to potential localized ice scour (Pugh & Davenport, 1997).
East Antarctica is probably the least studied intertidal area of any continent on Earth. With only three sampled intertidal locations with records of just six species of animal and four species of seaweed, it is difficult to judge whether the East Antarctic intertidal is virtually devoid of life as previous authors have stated (e.g. Knox, 1960) or if it is merely largely unsampled. Figure 1 shows that there are numerous localities in East Antarctica that have potential intertidal habitats, and shallow subtidal records from these regions confirm diverse life as shallow as 2 metres (Australasian Antarctic Expedition 1911-14, BANZARE Expedition 1931, Gruzov et al., 1967; Kirkwood & Burton, 1988). If there is an extensive intertidal fauna in East Antarctica it is likely to be isolated from that of West Antarctica by the extensive areas of rock free coast, deep shelf waters and floating ice shelves of the Ross and Weddell Sea regions and from the sub-Antarctic by large expanses of deep water and fast moving currents (Fig. 1).
The overall pattern of distinct Antarctic and sub-Antarctic intertidal biogeographical regions, both having a degree of species overlap with southern South America and each other, is similar to that found in the subtidal communities (Griffiths et al., 2009; Koubbi et al., 2014). The low subtidal connectivity observed between these regions and South Africa, Tasmania and New Zealand is also reflected in the intertidal records (Fig. 6). These patterns, given the glacial history of many of the geographical areas (Table 2), are more likely to reflect relatively recent oceanographic connections (González-Wevar et al., 2014) rather than the ancient Gondwanan break up signatures of deeper waters (Griffiths et al., 2009).
Given that the majority of species (51%) were only recorded intertidally at a single location and only 5% of species were recorded at ten or more locations, it is no surprise that a small number of well distributed species are driving the regional and larger scale biogeographical patterns. Although none of these species are obligate intertidal organisms, all have known distributions from coastal regions with none previously being reported from the deep sea (Figs 2, 3). Therefore, their distributions must be driven by shallow or surface currents either through larval transport, rafting or by swimming/walking shorter distances between suitable habitats.
Compared with the sub-Antarctic subtidal, intertidal areas shared a lower percentage of species. Griffiths et al. (2009) found up to 50% of sublittoral species were shared between sub-Antarctic islands but we found intertidal locations had a maximum of around 31%. Higher percentages of shared species were found between Antarctic intertidal regions but not as high as observed for the subtidal (Griffiths et al., 2009). The high number of species recorded only once implies that a wide range of species appear to be opportunistically exploiting the intertidal (potentially as nursery grounds, feeding grounds or to avoid predation) and is also probably a reflection of the generally low numbers of samples. Juvenile Pagothemia borchgevinki (Antarctic icefish) have been observed in shallow pools in the intertidal around Rothera Research Station (Adelaide Island) (pers ob.).
Nacella polaris is the most frequently reported species in this study and is the most significant species driving the Antarctic intertidal grouping, accounting for 38% of the observed similarity between locations. It has a wide distribution within the West Antarctic and Scotia Sea region. Other species of the genus Nacella have South American and sub-Antarctic distributions (González-Wevar et al., 2014) (Fig. 3a). The known distribution of N. polaris is restricted by availability of shallow/intertidal rocky substrata. The lack of records from the East Antarctic can be attributed to the distances between existing populations in West Antarctica and any suitable habitat in the East (Fig. 1). Although the distances to the islands of the Scotia Sea seem equally great, near-surface ocean drifters only take 4-8 months to cross Scotia Sea from Antarctic Peninsula to South Georgia (Thorpe et al., 2004). Although N. polaris has a long lived, ~2 month, planktonic larval phase (Bowden et al., 2006) this is not long enough to explain its current distributional pattern. For the species to have populations throughout the Scotia Sea would require a longer term transport mechanism such as rafting. The geological age of Marion Island (~0.45 Ma) was found by González-Wevar et al. (2014) to be consistent with that of the resident limpet species, Nacella delesserti. Nacella delesserti separated from its sister species, N. polaris, when it colonized Marion Island. Given the life history of N. polaris it is impossible for larval transport alone to explain this colonisation.
The most likely natural conduit for rafting organisms in the region is macroalgae. Smith (2002) estimated that over 70 million kelp rafts are afloat between 46 and 53 degrees south at any one time. All of the significant pattern-driving species of the Antarctic and sub-Antarctic were molluscs or macroalgae. Several of the key animal species distributions (Laevilitorina calignosa, Kerguelenella lateralis and the genera Nacella and Mytilus) reflect the distribution of kelp (Durvillaea antarctica and Macrocystis pyrifera). Although these two large kelp species are absent from the Antarctic, another species, Himantothallus grandifolius, is circumpolar and may play a role in transporting shallow water species around the continent.
Fraser et al.'s (2009) circum-sub-Antarctic analyses of DNA variation in Durvillaea antarctica support the hypothesis that this species only recently recolonized the sub-Antarctic. The species exhibits a striking degree of genetic homogeneity in this region compared with lower latitudes. Recolonization is likely to have involved a series of long-distance rafting events of the buoyant kelp from remote source populations. They also suggest that sub-Antarctic kelp was eliminated during the LGM. Similarly, the molecular results for Macrocystis pyrifera showed shared haplotypes among some of the sub-Antarctic islands and southern-central Chile, suggesting a recent colonization of the sub-Antarctic region (Macaya & Zuccarello, 2010).
Nikula et al. (2010) suggest that macroalgal rafting may explain similarities in the species composition of intertidal marine communities across the sub-Antarctic. They attributed the low genetic differentiation of kelp-dwelling crustaceans in the sub-Antarctic to rafting. Leese et al. (2010) examined gene flow in an isopod found around South Georgia, Bouvet, and Marion Islands. They concluded that rare long-distance dispersal via rafting, rather than vicariance or human-mediated transport, must be responsible for the observed molecular patterns. There is a distinct lack of knowledge as to how long species can survive while rafting in the open ocean but Fraser et al. (2011) documented 10 species of invertebrates rafting for several weeks between New Zealand and the neighbouring sub-Antarctic islands, covering a distance of at least 400 km. Helmuth et al. (1994) found large numbers of kelp rafts in the Scotia Sea and believed that rafting was responsible for the distribution of the bivalve Gaimardia trapesina. They estimated that kelp from South America would reach South Georgia by passive rafting after 100 days afloat travelling over 3700 km.
These proposed natural pathways both into and out of Antarctica and around the sub-Antarctic are dependent on the Antarctic Circumpolar Current and dispersal through West Wind Drift (Waters, 2008). There is a low probability that an individual raft will ever make landfall at localities with suitable conditions, given the vastness of the Southern Ocean and small size of the islands. However, once established, early colonizers face little competition for space and resources and may thrive (Waters et al
Ulva intestinalis, formerly referred to as Enteromorpha intestinalis (Linnaeus) Nees, is a green alga in the family Ulvaceae, of the genus Ulva (sea lettuce), also known by the common names gutweed and grass kelp. Until they were reclassified by genetic work completed in the early 2000s, the tubular members of the genus Ulva were in the genus Enteromorpha.
Generally world-wide. It can be found in Bering Sea near Alaska, Aleutian islands, Puget Sound, Japan, Korea, Mexico, Philippines,and Russia. Besides this, places it can be found in Israel, and in such European countries as Azores, Belgium, Denmark, Ireland, Norway, Poland, and in such seas as the Baltic, and Mediterranean Sea. It is also found in the shores of the Pacific Ocean.
The fronds have branches and are completely tubular expanding in width to mid-thallus. reaching 15 cm long or more. The cells are irregularly arranged and the chloroplast is hood-shaped and placed to one side, generally with only one pyrenoid. The species may be 10–30 centimetres (3.9–11.8 in) long and 6–18 millimetres (0.24–0.71 in) wide. They have rounded tips as well. The algae may be reproductive at all times of the year. The life-history shows an alteration of generations, isomorphic - gametophytic and sporophytic. In some references the species (Enteromorpha intestinalis) is treated as two subspecies: ssp. intestinalis (L.) Link and ssp. compressa (L.) Link.
In other languages
- ^ abGuiry, M.D., John, D.M., Rindi, F. and McCarthy, T.K. (Eds) 2007. New Survey of Clare Island. Volume 6: The Freshwater and Terrestrial Algae. p. 23. Royal Irish Academy. ISBN 978-1904890-31-7
- ^Gutweed - Enteromorpha intestinalis
- ^Grass-kelp, Gutweed
- ^ abcdBurrows, E.M. 1991. Seaweeds of the British Isles. Volume 2 Chlorophyta. British Museum (Natural History). ISBN 0-565-00981-8
- ^"Ulva intestinalis". Seaweeed of Alaska. Retrieved March 24, 2013.
- ^ abGuiry, M.D. (2012). "Ulva intestinalis Linnaeus, 1753". World Register of Marine Species. Retrieved March 24, 2013.
- ^"Gut weed - Ulva intestinalis". Retrieved March 24, 2013.
- ^Morton, O. 1994. Marine Algae of Northern Ireland. Ulster Museum ISBN 0 900761 28 8