Marc Eléaume1 1MNHN
Objectives
In a context of rapid global change, it is reasonable to think that the physical environment of benthic species will drastically change in a reduced time period.
Temperature, salinity, primary production and ice cover will probably undergo
substantial changes within the next decades. In turn, the composition and distribution of shelf benthic fauna will also be impacted. Cycles of glaciation/
deglaciation events in the past are known to have already heavily impacted on the shelf benthic biodiversity and shaped the structure and composition of existing communities.
Crinoids and starfish constitute a conspicuous component of the Antarctic shelf mega-epibenthos. A few species, like the emblematic Promachocrinus kerguelensis, are locally very abundant. About 40 species of crinoids and 250 starfish occur in the Southern Ocean. In the last few years, several new species of crinoids have been or are being described (Eléaume et al., 2011; 2012), increasing considerably the number of species known from the Southern Ocean. Genetic studies also have contributed to our knowledge of the diversity of crinoids in the Southern Ocean and suggest that cryptic species are still unrecognized within P. kerguelensis, Notocrinus virilis, Notocrinus mortenseni, Isometra graminea, and Isometra vivipara (Hemery et al., 2012). Our preliminary results on 18 species of common Southern Ocean starfish yielded the same results, revealing unexpected genetic diversity. Moreover, we found that populations of brooding species, because brooders don’t disperse much, are geographically structured and may be used as signatures of past glacial refugia. Both crinoids and starfish have brooding and broadcasting representatives in the Southern Ocean and may be used to test the existence all around the shelf of such refugia.
Our results suggest that the crinoid, and starfish biodiversity is only partially known and need to be further explored. The western Weddell Sea as well as the Bransfield Strait and the western coast of the Shetland Islands have never been properly investigated in terms of crinoid and asteroid diversity. One aim of the present project is to fill in these important biogeographic gaps.
In addition, because many taxa previously thought to be one species are now believed to be composed of complexes of cryptic species, the paradigm of their circumpolar distribution has to be revised. More generally, the study of genetic variation helps understand with some precision the geographic distribution and past history of benthic organisms.
Our goal is to better understand: (1) the circumpolar patterns of the benthic shelf fauna; (2) the genetic and geographic structure within species between population of target organisms; (3) the past history of crinoid and starfish in the Southern Ocean at different levels of integration, from gene to population and species.
Work at sea
Crinoid and starfish specimens were collected using the Agassiz trawl and a Rauschert dredge. Specimens or lots of specimens were given a unique field number and a picture was taken. Specimens were then preserved in 96 % pur ethanol. Not all the specimens were kept and preserved, due to the reduced storage space. Tube feet were collected from specimens in 2.5 ml eppendorf tubes with 96 % pur ethanol.
Preliminary results
A total of 32 trawling operations yielded asteroid or crinoid specimens (Tables 3.7.1 and 3.7.2), and 575 lots were collected and preserved. In addition 250 tissue samples were collected for DNA extraction.
Thirty five species of starfish were identified from the samples dredged (Table 3.7.1); some species were not recognised and will be further investigated. Among the identified material, 32 species were dredged from the Bransfield Strait, 23 from the Weddell Sea and 14 from the Drake Passage. In the Bransfield Strait, 30 species were dredged from the deeper stations, and 25 from the shallower stations.
In the Weddell Sea, only 4 species were collected from the deeper stations, and 23 from the shallow stations. In the Drake Passage, four species were dredged from the deeper and 13 species from the shallower stations.
Tab. 3.7.1: List of starfish species present and absent from the samples dredged from the three target areas and two depth ranges. 1 = presence ; 0 = absence.
BS WS DP
deep shallow deep shallow deep shallow
Acodontaster capitatus 1 1 0 1 0 0
Acodontaster elongatus 1 0 0 0 0 0
Acodontaster hodgsoni 1 1 0 1 0 1
Acodontaster sp. 0 1 0 1 0 0
Bathybiaster loripes 1 1 0 1 0 1
Cheiraster hirsutus 1 1 0 0 0 1
Cheiratser hirsutus 0 0 0 0 1 0
Cuenotaster involutus 1 1 0 1 0 0
Diplasterias brucei 1 1 1 1 0 1
Henricia sp. 1 1 0 1 0 0
Hippasteria sp. 1 1 0 0 1 1
Labidiaster annulatus 1 1 0 0 0 1
Leptychaster flexuosus 0 1 1 1 0 0
Lophaster gaini 1 0 0 0 0 0
Lysasterias armata 1 0 0 0 0 0
Lysasterias heteractis 1 1 0 1 0 0
Lysasterias perrieri 1 0 0 1 0 0
Lysasterias sp. 1 1 0 0 0 1
Morph 1 1 1 0 1 0 0
Morph 2 1 1 1 1 1 1
Morph 3 0 0 0 0 0 1
Notasterias armata 1 1 0 1 1 1
Odinella nutrix 1 0 0 0 0 0
Odontaster sp. 1 1 0 1 0 0
Paralophaster antarcticus 1 1 0 1 0 0
Paralophaster sp. 1 1 0 1 0 0
Pergamaster sp. 1 1 0 0 0 0
Perknaster sp. 1 0 0 1 0 0
Perknaster sp1 0 0 0 1 0 0
Perknaster sp2 1 1 0 1 0 0
Porania antarctica 1 1 0 1 0 1
Psilaster charcoti 1 0 1 1 0 1
Pteraster sp. 1 1 0 1 0 0
BS WS DP deep shallow deep shallow deep shallow
Rhopiella hirsuta 1 1 0 1 0 1
Solaster regularis 1 1 0 0 0 0
Ten species of crinoid were identified from the samples dredged (Table 3.7.2); it may be that the categories Eumorphometra sp., Isometra sp1, Notocrinus virilis and Notocrinus mortenseni represent several species each. This possibility will be further investigated. Among the identified material, 10 species were dredged from the Bransfield Strait, 6 from the Weddell Sea and 2 from the Drake Passage. In the Bransfield Strait, 9 species were dredged from the deeper stations, and 8 from the shallower stations. Anisomatra frigida and Kempometra grisea are thought to be rare species. Both occured in the deep canyon areas and K. grisea was regularly dredged from these environments. In the Weddell Sea, none was collected from the deeper stations, and six from the shallow stations. In the Drake Passage, one species were dredged from the deeper and one species from the shallower stations.
Tab. 3.7.2: List of crinoid species present and absent from the samples dredged from the three target areas and two depth ranges. 1 = presence ; 0 = absence.
BS WS DP
deep shallow deep shallow deep shallow
Anisometra frigida 1 0 0 0 0 0
Anthometrina adriani 1 1 0 1 0 0
Eumorphometra sp. 1 1 0 1 0 0
Florometra mawsoni 1 1 0 1 0 0
Isometra challengeri 0 1 0 0 0 0
Isometra sp1 1 1 0 1 0 0
Kempometra grisea 1 0 0 0 0 0
Notocrinus mortenseni 1 1 0 0 0 0
Notocrinus virilis 1 1 0 1 0 1
Promachocrinus kerguelensis 1 1 0 1 1 1
The preliminary results show that the species richness in the Bransfield Strait is higher as compared to the Drake Passage and Western Wedell Sea. There seem to be no difference in the Bransfield Strait between the deep and shallow stations.
However, the deep Western Weddell Sea shows a reduced diversity compared to the shallower shelf. The same trend seems to occur in the Drake Passage but with even lower levels of diversity.
Data managment
All species occurrences will be entered in the MNHN Marine Invertebrates database INVMAR and in the SCAR-MarBIN. DNA sequence data will be added in the barcode of life database BOLD and in GENBANK.
References
Eléaume M, Hemery LG, Bowden DA, Roux M (2011) A large new species of the genus Ptilocrinus (Echinodermata, Crinoidea, Hyocrinidae) from Antarctic seamounts. Polar Biology, 34, 1385‐1397.
Eléaume M, Bohn JM, Roux M, Améziane N (2012) Stalked crinoids (Echinodermata) collected by the R/V Polarstern and Meteor in the south Atlantic and in Antarctica.
Zootaxa, 3425, 1-22.
Hemery LG, Eléaume M, Roussel V, Améziane N, Gallut C, Steinke D, Cruaud C, Couloux A, Wilson NG (2012). Comprehensive sampling reveals circumpolarity and sympatry in seven mitochondrial lineages of the Southern Ocean crinoid Promachocrinus kerguelensis (Echinodermata). Molecular Ecology, 21(10), 2502-2518.