CONDICIONES GENERALES DE LOS CONTRATOS DE EJECUCIÓN DE OBRAS

As stated in the methodology, we have directly compared the numbers of fauna colonising the packages even though the packages were calculated to have slightly different volumes. As a result of this assumption, results will only be considered significant if p <0.001. The number of individuals (classified into classes and phyla) recovered from the deployments were compared between sites and also between substrates. The total numbers of individuals found on the two substrates on Coral Seamount were significantly different (χ² = 1706.14, df = 1, p <0.001) as well as on each substrate on Atlantis Bank (χ² = 4723.53.18, df = 1, p <0.001). The total number of individuals on bone differed significantly between Coral Seamount and Atlantis Seamount (χ² = 2090.26, df = 1, p <0.001) and also on wood (χ² = 4211.76, df = 1, p <0.001). Total faunal

numbers differed between substrates with wood having more fauna than bone (χ² = 721.85, df = 1, p <0.001), and also between sites with Atlantis Bank having more fauna than Coral Seamount (χ² = 510.61, df = 1, p <0.001).

All arthropod, bivalve, malacostracan and molluscan numbers were significantly different between sites and substrate types (p <0.001). All numbers of copepods differed significantly except the total numbers on wood and bone substrate. The numbers of polychaetes were all significantly different except between bone and wood at Atlantis Bank, and between wood on Coral Seamount and Atlantis Bank. For gastropods numbers, all were significantly different except between substrates on Coral Seamount, and between the bone deployments on the two seamounts. All the numbers of asteroids, cnidarians (anthozoans), crinoids, echinoderms, echinoids, nemerteans, ophiuroids, pycnogonids and scaphopods were not significantly different between the two sites and on both substrate types.

The numbers of individuals assigned to each functional group were significantly different (p <0.001)between sites and substrate types. This however excluded the numbers of ‘Deposit Feeders’, ‘Suspension Feeders’ and ‘Grazers’ on bone and wood at Atlantis Bank, and also the number of ‘Deposit Feeders’ and ‘Grazers’ on wood between the Atlantis Bank and Coral Seamount. The number of individuals in the ‘Other’ functional group was also not significantly different between wood and bone at both sites surveyed and both substrates at each site

surveyed.

Sorenson’s coefficient was used to compare the similarity at species level between

presence/absence data of the faunal assemblages of the four deployments, bone from Coral Seamount, wood from Coral Seamount, bone from Atlantis Bank and wood from Atlantis Bank. This test showed that the faunal assemblages at the bone and wood deployments from Coral Seamount had the least difference with 59% Sorensen’s similarity followed by the wood and bone from Atlantis Bank, which had 30% similarity. The assemblages colonising bone samples from the two sites had 21% similarity and the two wood assemblages had 13%. The bone from Coral Seamount and the wood from Atlantis Bank had 23% similarity and the wood from Coral Seamount and the bone from Atlantis Bank had 6% similarity. A cluster analysis using the group average of these results was plotted into a dendrogram, which can be seen in Figure 4.8.

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Figure

‎

4.8 Similarity between the faunal assemblages at the four deployments. A cluster dendrogram using the group averages of results from Sorenson’s similarity tests performed on the species presence/absence data from the four deployment assemblages: bone from Coral Seamount (Coral Bone), wood from Coral Seamount (Coral Wood), bone from Atlantis Bank (Atlantis Bone) and wood from Atlantis Bank (Atlantis Wood).

Table 4.1. Fauna colonising bone and wood deployments on two seamounts in the Southwest Indian Ridge. Fauna were identified to the lowest taxonomic level, counted and assigned a functional group related to diet from information found in the literature indicated. The numbers for each species may be underestimates as some individuals may have been lost during collection from the seafloor.

Coral Seamount Atlantis Bank

Phylum Class Order Family

Genus and

Species/Morphotype Bone Wood Bone Wood Functional group Reference

Annelida Polychaeta Amphinomida Amphinomidae sp. A - - - 5 Predators/Scavengers

(Fauchald and Jumars, 1979; Ward et al., 2003)

sp. B - - - 1 Predators/Scavengers

(Fauchald and Jumars, 1979; Ward et al., 2003)

Capitellida Capitellidae Capitella sp. A 56 1 - 7 Deposit feeders (Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Capitella sp. B 53 1 - - Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Capitella sp. C 69 4 - - Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Capitella sp. D 40 2 - - Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992) Eunicida Dorvilleidae sp. A 5 - 2 1 Other

(Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Ophryotrocha sp. AA 269 6 - - Grazers (Wiklund et al., 2009b)

Ophryotrocha sp. AB 17 - - - Grazers (Wiklund et al., 2009b)

Ophryotrocha sp. AC 7 2 - - Grazers (Wiklund et al., 2009b)

Ophryotrocha sp. AE 3 - - - Grazers (Wiklund et al., 2009b)

Phyllodocida Glyceridae Glycera sp. A - - - 1 Predators/Scavengers (Fauchald and Jumars, 1979; Boggemann et al., 2012) Hesionidae sp. A - - - 1 Predators/Scavengers

(Fauchald and Jumars, 1979; Desbruyeres et al., 1985) sp. B 7 1 - - Predators/Scavengers

(Fauchald and Jumars, 1979; Desbruyeres et al., 1985) sp. C 4 - - - Predators/Scavengers

(Fauchald and Jumars, 1979; Desbruyeres et al., 1985) Lacydoniidae sp. A - 1 - - Deposit feeders (Fauchald and Jumars, 1979) Phyllodocidae sp. A 1 - - - Predators/Scavengers

(Fauchald and Jumars, 1979; Blake, 1985)

Pilargidae sp. A 1 - - - Predators/Scavengers (Fauchald and Jumars, 1979) Polynoidae Austrolaenilla sp. A 5 1 - - Predators/Scavengers

(Fauchald and Jumars, 1979; Pettibone, 1993)

Austrolaenilla sp. B - - - 2 Predators/Scavengers

(Fauchald and Jumars, 1979; Pettibone, 1993)

Austrolaenilla sp. C - - 7 2 Predators/Scavengers

(Fauchald and Jumars, 1979; Pettibone, 1993)

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Syllidae sp. A 6 - - - Predators/Scavengers (Fauchald and Jumars, 1979) Sabellida Sabellidae sp. A - 1 - - Suspension feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Jasmineira sp. A 6 17 - - Suspension feeders (Fauchald and Jumars, 1979; Kukert and Smith, 1992) Terebellida Acrocirridae Flabelligella sp. A 1 4 - - Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992)

Flabelligella sp. B 1 1 - - Deposit feeders (Fauchald and Jumars, 1979; Kukert and Smith, 1992) Trichobranchidae Octobranchus sp. A - 1 - - Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992) Cirratulidae sp. A - - - 1 Deposit feeders

(Fauchald and Jumars, 1979; Kukert and Smith, 1992) Arthropoda Copepoda Harpacticoida sp. A 69 - 23 74 Grazers

(Geptner and Ivanenko, 2002; Galkin and Goroslavskaya, 2008)

Malacostraca Amphipoda sp. A - - 15 - Other (Ruppert and Barnes, 1996) Calliopiidae sp. A 42 22 - - Predators/Scavengers (Shoemaker, 1930) Podoceridae Podocerus sp. A 85 17 - - Suspension feeders (Barnard et al., 1988) Sebidae Seba sp. A 3344 227 120 - Predators/Scavengers (Kunzmann, 1996) Decapoda Hippolytidae Eualus oreios 1 - - - Predators/Scavengers

(Squires et al., 2000; Birkely and Gulliksen, 2003)

Lebbeus ketophilus 1 - - - Predators/Scavengers (Butler, 1980; Jensen, 2006)

Inachidae Dorhynchus sp. A - - - 1 Predators/Scavengers (Duineveld et al., 2007) Mathildellidae Neopilumnoplax heterochir - - - 3 Predators/Scavengers

Munidopsidae Munidopsis mandelai - - - 7 Other

(Turner, 1977; Hoyoux et al., 2009; Hoyoux et al., 2012) Palinuridae Projasus parkeri - - - 3 Predators/Scavengers

(Personal observation; Parin et

al., 1997)

Isopoda sp. A 2 2 - - Other (Ruppert and Barnes, 1996) Arcturidae sp. A 1 1 - - Suspension feeders (Barnes and Conlan, 2012) Munnopsidae sp. A 18 - - - Predators/Scavengers (Svavarsson et al., 1993; Gudmundsson et al., 2000) Pycnogonida Pantopoda Ammotheidae Sericosura mitrata 1 1 - - Predators/Scavengers

(Arnaud and Bamber, 1987; Sweeting et al., 2013) Austrodecidae Austrodecus valdiviens - 7 - 2 Predators/Scavengers

(Fry, 1965; Arnaud and Bamber, 1987)

Austrodecus sp. B 1 - - 3 Predators/Scavengers

(Fry, 1965; Arnaud and Bamber, 1987)

Colossendeidae Hedgpethia sp. A 2 - 9 1 Predators/Scavengers (Arnaud and Bamber, 1987) Nymphonidae Nymphon sp. A 1 - - - Predators/Scavengers

(Stock, 1978; Arnaud and Bamber, 1987)

Nymphon sp. B - 1 - - Predators/Scavengers

(Stock, 1978; Arnaud and Bamber, 1987)

Nymphon sp. E - 2 - - Predators/Scavengers

(Stock, 1978; Arnaud and Bamber, 1987)

Nymphon sp. F - 1 - - Predators/Scavengers

(Stock, 1978; Arnaud and Bamber, 1987)

Rhynchothoracidae Rhynchothorax sp. A 2 6 - 1 Predators/Scavengers

(Fry, 1965; Arnaud and Bamber, 1987)

Cnidaria Anthozoa Antipatharia sp. A 1 - - - Suspension feeders (Wagner et al., 2012) Echinodermata Asteroidea Forcipulatacea Asteriidae cf. Perissasterias sp. A - 1 - - Predators/Scavengers (Jangoux, 1982; Ruppert and Barnes, 1996)

Crinoidea Comatulida Antedonidae Thysanometra sp. A - - - 1 Suspension feeders

(Turner, 1977; Ruppert and Barnes, 1996)

Echinoidea sp. A - - - 1 Other

(De Ridder and Lawrence, 1982; Ruppert and Barnes, 1996) Camarodonta Echinidae Polyechinus agulhensis - - 1 - Deposit feeders (De Ridder and Lawrence, 1982) Cidaroida Cidaridae sp. A - - 4 - Predators/Scavengers

(De Ridder and Lawrence, 1982; Jacob et al., 2003)

Echinothurioid

a sp. A - - 3 - Predators/Scavengers

(Personal observation; De Ridder and Lawrence, 1982) Ophiuroidea Ophiurida Ophiacanthidae sp. A - - - 1 Predators/Scavengers

(Warner, 1982; Smith, 1985; Stohr and Segonzac, 2006) Ophiomyxidae Ophioscolex sp. A - 1 - - Predators/Scavengers (Warner, 1982)

Mollusca Bivalvia Myoida Pholadidae Xylophaga murrayi - 870 - - Xylophagous (Personal observation; Knudsen, 1961; Turner, 1973, 1977)

Xylophaga cf. indica - - - 6850 Xylophagous

(Personal observation; Knudsen, 1961; Turner, 1973, 1977) Mytiloida Mytilidae Idas sp. A 148 - 468 22 Mixotrophs

(Smith et al., 1989; Smith and Baco, 2003)

Idas sp. B - - 41 126 Mixotrophs

(Smith et al., 1989; Smith and Baco, 2003)

Idas sp. C - - 260 - Mixotrophs

(Smith et al., 1989; Smith and Baco, 2003)

Pectinoida Pectinidae sp. A - 5 - - Suspension feeders (Le Pennec et al., 2003) Gastropoda Littorinimorpha Ranellidae Sassia nassariformis - - 4 17 Predators/Scavengers (Morton, 1990)

Nudibranchia Aeolidiidae sp. A - - - 2 Predators/Scavengers

(Todd, 1981; Ruppert and Barnes, 1996)

Phasianelloidea Colloniidae Colloninae sp. A - - 4 19 Grazers (Zuschin et al., 2009) Trochoidea Calliostomatidae Venustatrochus georgianus - 1 - - Predators/Scavengers (Williams et al., 2010) Scaphopoda sp. A - - 1 - Deposit feeders (Kukert and Smith, 1992) Nemertea sp. A - 1 - - Predators/Scavengers (Ruppert and Barnes, 1996)

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4.4

Discussion

Organic falls are known to host distinct assemblages in the deep sea, usually attracting a variety of specialist and opportunistic fauna, which utilise the wood and bone for different purposes such as nutrition and shelter. For the first time, we have characterised the faunal assemblages at Indian-Ocean organic falls, which are remarkable for the diversity and abundance of both opportunists and specialists on what are relatively small 'targets' on the seafloor for larval settlement. In addition, it is notable that the faunal assemblages from the two sites are so different in both diversity and composition, to the extent that the geographical location was a more important determinant of species composition than substrate type, despite bone and wood being quite different in their organic structure and nature of degradation by specialist organisms. At the more southerly Coral Seamount, the organic falls were characterised by generally higher diversity but much lower colonisation by specialist organic-fall molluscs (Idas molluscs in the case of bones, and Xylophaga molluscs for the wood). In contrast, the warmer waters of the Atlantis Bank hosted a lower diversity organic fall but with much higher abundances of both Idas and Xylophaga molluscs. It was also notable that the species of Xylophaga was different at each seamount, despite being found at similar depths and not separated by any great geographic distance for a species thought to have impressive dispersal capabilities (Voight and Segonzac, 2012). Here we discuss in further detail the two main structuring variables (site and substrate type) and compare our results with other recent studies of organic falls from global locations.

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