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Sedimentology of a wreck: The Rainbow Warrior revisited
Marine Pollution Bulletin 62 (2011) 2412–2419
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Sedimentology of a wreck: The Rainbow Warrior revisited Abigail M. Smith a,⇑, Louise Kregting a,1, Sophie Fern a,2, Ceridwen I. Fraser b a b
Department of Marine Science, University of Otago, P.O. Box 56, Dunedin, New Zealand Allan Wilson Centre for Molecular Ecology and Evolution, Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand
a r t i c l e
i n f o
Keywords: Carbonate sediments Rainbow Warrior Biocoenosis Thanatocoenosis Temperate carbonates
a b s t r a c t The wreck of the Rainbow Warrior, a 40-m ship sunk on 12 December 1987 in Matauri Bay (34° 590 S, 173° 560 E), Cavalli Islands, northeastern New Zealand, offers an opportunity to investigate the impact of artificial substrate on temperate carbonate sedimentation. Surface sediment samples showed no significant textural or compositional difference between sediments near the wreck and those far from it. The large and diverse carbonate-producing community resident on the wreck (dominated by bryozoans, corals and sponges) has not had a measurable influence on adjacent bottom sediments (dominated by bivalves and barnacles), even after 21 years. It is likely that carbonate production on the Rainbow Warrior is insufficient to leave any sedimentary record over the potential lifetime of the wreck on the seafloor, which informs our understanding of the long-term impacts of shipwrecks (and other artificial substrata) on the local benthic environment in shallow temperate ecosystems. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction On 10 July 1985, the 40-m Greenpeace vessel Rainbow Warrior was sunk by two French bombs at Marsden Wharf in Waitamata Harbour, Auckland, New Zealand. After refloating, she was declared irreparable and towed to Matauri Bay (34° 590 S, 173° 560 E) where she was sunk near the Cavalli Islands on 12 December 1987 to serve as a recreational diving resource and fish sanctuary (Hooker et al., 1988). The wreck sits on unvegetated sand in 26 m of water with a 15° list to starboard (Fig. 1); it is marked with a buoy and visited by several commercial dive trips a week in summer. Lying in the path of the subtropical East Auckland Current (Gordon et al., 2010), the water around the Cavalli Islands typically reaches minimum sea surface temperatures of 14–16 °C in winter (August) to maximum temperatures of 20–22 °C in summer (February) (Brook, 2002). It is an area of moderate biodiversity (Gordon et al., 2010), supporting over 70 species of fish (Nicholson, 1979) and at least 140 species of marine macrobenthic invertebrates (Grace and Hayward, 1980). Sediments near the wreck site in the northwest Cavalli Islands are dominated by coarse shelly sand, mainly formed of molluscs and barnacles (Grace and Hayward, 1980; Hooker et al., 1988; Smith, 1992). The nearest rocky reef is
⇑ Corresponding author. Tel.: +64 3 479 7470; fax: +64 3 479 8336. E-mail address: [email protected] (A.M. Smith). Present address: Queens University Belfast, Marine Laboratory, The Strand, Portaferry, County Down BT22 1PF, United Kingdom. 2 Present address: School of English, Journalism and European Languages, University of Tasmania, Hobart, Australia. 1
0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2011.08.028
approximately 500 m away (Hooker et al., 1988), on the port side of the wreck. After sinking, the Rainbow Warrior was rapidly covered with encrusting organisms, both soft (algae, anemones) and calcified (bryozoans, molluscs) (Table 1). In less than a year most available surfaces were covered by over fifty species of invertebrates and algae (Hooker et al., 1988). In 1991, 4 years after sinking, divers visiting the wreck estimated coverage by bryozoans alone to be about 20% (Smith, 1992). A brief report in 1993 commented on the diversity of fish and listed among the attached organisms calcareous sponges and a wide variety of gastropods (Enderby, 1993). By 1994 the wreck’s superstructure had mostly collapsed; the remains were covered in sessile organisms, with the exception of silt-covered horizontal surfaces (Szabo and Grace, 1994). Diver and biologist R.V. Grace, who has photographed the wreck often since 1988, argued that a ‘climax community’ of corals, bryozoans and sponges had been reached on the wreck surfaces in about 7 years (Szabo and Grace, 1994; Grace, 2005). Sunken vessels have traditionally been considered to be ecological assets as they provide new habitat and a refuge for marine organisms (Pickering et al., 1999; Baine, 2001; Svane and Petersen, 2001). Generally, therefore, artificial reefs have been investigated in relation to their effects on near-shore fish populations (Baine, 2001) and benthic communities (e.g., Baynes and Szmant, 1989; Walker et al., 2007). Several studies have looked at biogeochemical processes near artificial reefs (Falcão et al., 2007, 2009), as well as the effects of sediments on surrounding infaunal communities (e.g., Fricke et al., 1986; Ambrose and Anderson, 1990) and sediment texture. To our knowledge, however, research on how wrecks
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173°58’12”E
b
N
34°58’12”S
Motukawanui Island Cav all iP as sa ge Matauri Bay
c Motutapere Hamaruru Panaki Islands Island Island Horonui Island 10
175°E
N
400 m
d
E
N Is orth la nd
W
S
40°S
N
20 m
170°E
a
m
wreck
15
2 km
m
N
B
Port Bow
Stern
45°S
So
ut
h
Is
la
nd
Tasman Sea
A
F
South Pacific Ocean
Starboard
E 300 km
C 10 m
D
Fig. 1. Location of the Rainbow Warrior wreck, sunk in 1987, and transects sampled in 2008: (a) Map of New Zealand showing the location of the Cavalli Islands; (b) Matauri Bay/Cavalli Islands region with the location of the wreck indicated by a red cross; (c) the location of the Rainbow Warrior wreck in relation to nearby islands; (d) about 40 m long, the wreck sits at a water depth of 26 m and the bow faces southeast. For each of six transects, sediment samples were taken at distances of 0, 2, 5, 10, 15 and 20 m from the wreck.
or artificial reefs may alter nearby sediment composition is nonexistent. The well-documented Rainbow Warrior allows us to use the difference between the carbonate-producing fauna on the ship surfaces and those in the ambient sediment to examine the effect of an artificial reef on marine coastal sediments. In particular, here we investigate whether carbonate skeletal material originating from the wreck makes a significant contribution to the composition of local bottom sediment after 21 years.
2. Methods Over two days (30 September 2008–1 October 2008) in the austral spring, surface (top 3 cm) sediment samples were collected
manually by divers on six transects, each with six sites (Fig. 1). Sediment samples were numbered according to transect letter and distance from the wreck in m (e.g., RW-D15) and split into three subsamples. An archive of about 100 ml was labelled, photographed, and kept in fresh water. A dried bulk sample of about 100 ml was retained for dry-sieving and carbonate content analysis. The remainder of the sample was washed through a 1 mm sieve and the coarse sand to gravel fraction (where most carbonate skeletal fragments can be identified to taxa) dried for compositional analysis. About 50 ml of each bulk sample was dry-sieved to half-phi intervals in order to calculate mean grain size and sorting coefficient. About 50 ml of each bulk sample was weighed, immersed in 90% HCl and allowed to bubble, stirred frequently, and when all carbonate was dissolved, rinsed, dried, and reweighed to
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Table 1 Benthic organisms listed as having been found attached to or resident on the sunken Rainbow Warrior, Cavalli Islands, New Zealand (as reported in Hooker et al., 1988; Smith, 1992; Enderby, 1993; Szabo and Grace, 1994). While spelling errors have been fixed and common names added when possible, the taxonomy has not been updated. Taxon
Species
Common name
Source
Phaeophyceae (brown algae)
Ecklonia radiata Sargassum sp. Champia laingii Stenogramme interrupta Corallina officinalis Laurencia distichophylla Schizoseris sp. Griffithsia traversii Arthrocardia corymbasa Ceramium sp. Lomentaria caespitosa Cladhymenia sp. Polysiphonia spp. Ulva sp. Caulerpa flexilis
Kelp Sargassum
Enderby (1993) and Szabo and Grace (1994) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988)
Rhodophyceae (red algae)
Chlorophyceae (green algae) Porifera (sponges)
Ancorina sp. Aplysilla rosea Stelleta sp. Anthozoa (anemones and corals)
Hydrozoa (hydroids)
Platyhelminthes (flatworms) Annelida (segmented worms)
Alcyonium aurantiacum Culicea rubeola Corynactis haddoni Actinothoe albocincta Solanderia sp. Symplectoscyphus johnstoni Pennaria sp.
Coralline turf
Sea lettuce Sea rimu Calcareous sponges Horny sponges Encrusting sponges Staghorn sponge Ancorina sponge Pink sponge
Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Szabo and Grace (1994) Hooker et al. (1988)
Soft coral Encrusting coral Jewel anemone White-striped anemone
Szabo and Grace (1994) Szabo and Grace (1994) Enderby (1993) and Szabo and Grace (1994) Hooker et al. (1988) and Enderby (1993) Enderby (1993) Hooker et al. (1988) Hooker et al. (1988)
Stylochoplana sp. Hydroides norvegica Filograna sp. Nereid sp. Polynoid sp.
Hooker Hooker Hooker Hooker Hooker
et et et et et
al. al. al. al. al.
(1988) (1988) (1988) (1988) (1988)
Mollusca Gastropoda (snails and slug)
Maurea tigris Maurea puctulata Astraea sp. Charonia capax Cabestana spengleri Mayena australasiae Jason mirabilis Dendrodoris gemmacea Tritonia incerta Sigapatella novaezelandiae Cookia sulcata
Tiger shell Tiger shell Circular saw shell Trumpet shell Trumpet shell Trumpet shell Nudibranch Jewel nudibranch Apricot-coloured nudibranch Slipper limpet Cook’s turban
Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Hooker et al. (1988) and Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Hooker et al. (1988) Hooker et al. (1988)
Molluscs Bivalvia (clams) Arthropoda Insecta (insects) Arthropoda Amphipoda (amphipods)
Teredo sp. Philanisus plebejus Apherusa translucens Ceina egregia Tetradeion crassa Hyale grenfelli Astacilla sp. Plagusia capensis Notomithrax minor Halicarcinus cookii Elminius modestus
Shipworm Marine caddisfly
Szabo and Grace (1994) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Szabo and Grace (1994)
Arthropoda Isopoda (isopods) Arthropoda Decapods (crabs)
Arthropoda Crustacea (barnacles) Bryozoa (lace corals)
Waterispora sp. Bugula flabellata Lichenopora novaezelandiae Galeopsis grandipora Steginoporella magnifica Disporella fibriata Hornera sp. Celleporaria sp. Celleporaria agglutinans Hemipustulopora harmeri Disporella gordoni Cellaria tenuirostris Galeopsis porcellanicus
Ascidia (sea squirts)
Cnemidocarpa bicornuta Corella eumyta Aplidium spp
Red rock crab Decorator crab Acorn barnacle
Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Smith (1992) Smith (1992) Smith (1992) Smith (1992) Smith (1992) Orange ascidian
Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988)
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Table 2 Texture and composition of 36 sediment samples from six transects around the Rainbow Warrior, Cavalli Islands, New Zealand. Supplementary material available online (Online Resource 1). Sample number
Transect Distance Collection from RW date (m)
Wt.% Wt.% Gravel Sand
Modal grain Mean grain size size (phi) (mm)
Percent Bivalves Barnacles Echinoids Bryozoans Gastropods carbonate
RW-A-00 RW-A-02 RW-A-05 RW-A-10 RW-A-15 RW-A-20 RW-B-00 RW-B-02 RW-B-05 RW-B-10 RW-B-15 RW-B-20 RW-C-00 RW-C-02 RW-C-05 RW-C-10 RW-C-15 RW-C-20 RW-D-00 RW-D-02 RW-D-05 RW-D-10 RW-D-15 RW-D-20 RW-E-00 RW-E-02 RW-E-05 RW-E-10 RW-E-15 RW-E-20 RW-F-00 RW-F-02 RW-F-05 RW-F-10 RW-F-15 RW-F-20
A A A A A A B B B B B B C C C C C C D D D D D D E E E E E E F F F F F F
56.0% 79.9% 90.2% 27.1% 76.0% 61.7% 54.0% 68.3% 64.2% 23.1% 35.3% 50.8% 43.2% 87.9% 54.9% 56.8% 48.9% 45.1% 24.7% 65.9% 37.5% 63.2% 30.4% 54.3% 16.2% 11.9% 25.9% 12.5% 9.4% 19.5% 67.7% 90.6% 25.5% 0.7% 9.3% 47.2% 0.7% 45.4% 90.6% 0.25 36
1.51 2.03 2.19 1.34 1.57 1.52 1.58 1.88 1.79 1.18 1.68 1.40 1.21 2.09 1.52 1.59 1.35 1.26 1.19 1.77 1.19 1.62 1.36 1.53 0.89 0.89 1.19 0.69 0.67 0.97 1.90 2.13 1.21 0.55 0.65 1.09 0.55 1.39 2.19 0.42 36
60.7% 53.0% 21.5% 83.2% 39.1% 61.6% 71.0% 52.2% 62.4% 87.6% 92.7% 67.6% 87.5% 72.3% 91.1% 64.6% 75.6% 70.1% 92.3% 56.6% 80.6% 70.0% 76.3% 84.6% 93.7% 94.7% 92.3% 93.7% 91.8% 93.9% 85.0% 93.9% 93.9% 95.5% 90.0% 87.1% 21.5% 77.2% 95.5% 0.18 36
0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20
30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 Minimum Mean Maximum Standard deviation N
44.0% 20.1% 9.8% 72.9% 24.0% 38.3% 46.0% 31.7% 35.8% 76.9% 64.7% 49.2% 56.8% 12.1% 45.1% 43.2% 51.1% 54.9% 75.3% 34.1% 62.5% 36.8% 69.6% 45.7% 83.8% 88.1% 74.1% 87.5% 90.6% 80.5% 32.3% 9.4% 74.5% 99.3% 90.7% 52.8% 9.4% 54.6% 99.3% 0.25 36
2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 0 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 1 phi coarse sand 0.5 phi coarse sand 0.5 phi coarse sand 1 phi coarse sand 1 phi coarse sand 1 phi coarse sand 2 phi gravel 2 phi gravel 0.5 phi coarse sand 1 phi coarse sand 1 phi coarse sand 2 phi gravel 2 phi gravel 1 phi coarse sand 36
determine the insoluble residue (and thus wt.% CaCO3) in each size fraction. 5 g of each >1 mm fraction was sorted into skeletal components by taxon; while some grains were non-carbonate, they are not included in the weight percentages calculated.Pair-wise correlations between all measured sediment parameters were carried out using JMP 7.0 (SAS, 2007). 3. Results Thirty-six sediment samples collected in 2008 on six transects were all coarse shelly sands or gravels (Table 2, Fig. 2). Modal grain sizes ranged from coarse sand (0.5 mm; 0.5 phi) to gravel (2 mm; 1.0 phi). No sample had more than 5% grains smaller than 0.25 mm (2 phi) with mean grain size ranging from 0.55 to 2.19 mm (mean = 1.39, stdev = 0.42, N = 36). 34 samples were more than half carbonate: the mean carbonate content was 77% (stdev 0.18, N = 36). The carbonate was formed mainly from bivalves (mean = 67%, stdev 0.22, N = 34) with significant contributions from barnacles (mean = 30%, stdev = 0.21, N = 34). Bryozoans, gastropods and echinoids formed only small proportions of those samples in which they occurred. There is a strong relationship between carbonate content and grain size: as the mean grain size increases, the wt.% carbonate decreases (R = 0.6300, N = 36, p < 0.0001). Wt.% gravel, too, is inversely correlated with carbonate (R = 0.7072, N = 36, p < 0.0001),
49.5% 59.7% 87.6% 42.2% 71.0% 81.0% 72.0% 65.1% 65.1% 6.9% 71.6% 87.2% 92.7% 100.0% 89.4%
46.7% 38.9% 3.3% 55.2% 26.0% 18.7% 25.7% 34.9% 34.5% 89.7% 27.0% 7.7% 7.0% 0.0% 6.2%
0.5% 0.0% 0.0% 1.7% 1.5% 0.0% 0.0% 0.0% 0.0% 3.4% 1.1% 0.0% 0.2% 0.0% 0.2%
0.0% 0.9% 0.0% 0.0% 0.8% 0.0% 0.0% 0.0% 0.0% 0.0% 0.4% 2.0% 0.0% 0.0% 1.8%
3.3% 0.4% 9.1% 0.9% 0.8% 0.4% 2.2% 0.0% 0.4% 0.0% 0.0% 3.1% 0.0% 0.0% 2.4%
41.8% 75.5% 53.6% 87.4% 30.2% 92.4% 45.0% 93.5% 46.4% 54.1% 77.5% 80.6% 28.6% 94.6% 64.8% 88.8% 58.6% 37.8% 74.4%
56.8% 24.5% 39.6% 12.3% 59.9% 5.7% 48.5% 6.3% 49.5% 40.2% 20.2% 15.7% 68.6% 3.7% 31.1% 11.2% 30.3% 43.2% 16.7%
0.0% 0.0% 2.4% 0.0% 4.2% 0.0% 0.6% 0.0% 2.1% 3.3% 1.6% 0.9% 2.9% 0.0% 1.6% 0.0% 2.0% 10.8% 5.1%
0.0% 0.0% 3.9% 0.3% 3.6% 1.9% 5.8% 0.2% 0.0% 0.8% 0.0% 0.9% 0.0% 1.7% 2.5% 0.0% 8.1% 5.4% 0.0%
1.5% 0.0% 0.5% 0.0% 2.1% 0.0% 0.0% 0.0% 2.1% 1.6% 0.8% 1.9% 0.0% 0.0% 0.0% 0.0% 1.0% 2.7% 3.8%
6.9% 66.7% 100.0% 0.22 34
0.0% 29.6% 89.7% 0.21 34
0.0% 1.4% 10.8% 0.02 34
0.0% 1.2% 8.1% 0.02 34
0.0% 1.2% 9.1% 0.02 34
suggesting that non-carbonate minerals, when present, occur in the coarsest fraction (as gravel and pebbles). There is no apparent correlation between distance along a transect and any of the textural sedimentary parameters reported here. There is, however, a difference among transects – all of the samples on transect E and most on transect F are different from the other four, due to the lower gravel fraction, higher sand fraction, and higher carbonate values than the other transects. Essentially, the non-carbonate pebbles did not appear in those samples. The relationship between barnacles and bivalves is strongly negative (R = 0.9845, N = 34, p < 0.0001), indicating that the sedimentary carbonate is essentially a two-element mixture, with other components being minor. Among those minor components, echinoids are weakly inversely correlated with bivalves (R = 0.5439, N = 34, p = 0.009), and positively correlated with barnacles (R = 0.128, N = 34, p = 0.0128) and bryozoans (R = 0.3954, N = 34, p = 0.0206). None of the carbonate components are correlated with distance from the wreck, nor are there significant faunal differences among transects. 4. Discussion The character of local sediment near the Cavalli Islands prior to the sinking of the wreck is perhaps best described by Grace and Hayward (1980); their dredge (numbered 6) was taken near the
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Transect code (A-F) 100
A BCD E F
A BCD E F
A BCD E F
A BCD E F
A BCD E F
A BCD E F Size classes (phi)
Weight (percent)
80
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0
60
40
20
0 0
2
5
10
15
20
A BCD E F
A BCD E F
Distance from wreck (metres) Transect code (A-F) 100
A BCD E F
A BCD E F
A BCD E F
A BCD E F
Size classes (phi)
Weight (percent)
80
pan 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0
60
40
20
0
0
2
5
10
15
20
Distance from wreck (metres) Transect code (A-F) 100
A BCDE F
A BCDE F
A BCDE F
ABDE F
A BCDE F
A BCDE Sediment carbonate components
Weight (percent)
80
Bivalves Echinoids Bryozoans Barnacles Gastropods
60
40
20
0
0
2
5
10
15
20
Distance from wreck (metres) Fig. 2. Texture and composition of 36 surface sediment samples from six transects around the Rainbow Warrior, Cavalli Islands, New Zealand. Top: sediment texture; Middle: texture of insoluble residue (i.e., non-carbonate sediment); Bottom: carbonate components making up the sediment size fraction greater than 2 mm.
wreck site in 25 m water depth. It was described as a very coarse shelly sand dominated by molluscs and barnacles, with associated polychaetes, various echinoids and a few bryozoans. Essentially the same type of sediment was found immediately under the wreck in 1991, four years after the ship was sunk there. Smith (1992) concentrated on the bryozoans on the wreck and in the sediments. Six sediment samples collected in 1991 on one tran-
sect were all coarse shelly gravel dominated by barnacle plates, with some bivalves, echinoid fragments, and algae-encrusted pebbles. While bryozoans covered some 20% of the wreck at that time, they made up less than 5% of the sediments. The species found in the sediment were not the species common on the wreck. It was concluded that four years was not long enough for wreck-derived sediment to appear in the carbonate sedimentary record (Smith, 1992).
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Fig. 3. Bryozoans, corals, algae and sponges dominate the surfaces of the sunken Rainbow Warrior, October 2008 (Austral springtime): (a–c) sponges, soft coral, hydroid (Solanderia sp.) and anemones; (d) macroalgae; (e) algae, hydroids and anemones; (f) sponges, soft coral, bryozoans and anemones; (g) macroalgae growing on ship deck; and (h) orange finger bryozoan Steginoporella neozelandica among algae, hydroids and anemones. White scale bars represent approximately 0.06 m, and black scale bar approximately 1.0 m.
Over two decades the wreck has acquired a considerable attached fauna and flora (Table 1). Bryozoans, sponges, serpulid worms and corals are the main carbonate producers on board (Fig. 3). In 2008, there was still little sign of this wreck-fauna carbonate in the sediments. Coarse sediment fragments were dominated by bivalves and barnacles, almost none of which have been noted or photographed on the wreck. The sediment therefore shows no effect of the wreck, even after 21 years (Fig. 4). Perhaps this result should not be surprising. Carbonate sediment production on temperate shelves is on the order of 1–3 cm/ 1000 years (e.g., Nelson, 1988); 21 years of production would thus produce less than 1 mm of accumulated sediment. Near a biodiverse wreck and in a subtropical environment we might expect carbonate production to be somewhat higher, but even if it were as high as on some tropical coral reefs, e.g., 10–30 cm/1000 years (e.g., Kukal, 1990), we would only expect to find 0.2–0.6 cm of carbonate accumulation in 21 years. Given the high-energy nature of the environment, mixing could dilute the wreck contribution con-
siderably (see, e.g., Ward et al., 1999; McNinch et al., 2001) and render it undetectable. A significant disjunction between a living community (or biocoenosis) and its related death assemblage (thanatocoenosis) is not unusual – but commonly found on a greater timescale. The unrepresentative nature of the fossil record is axiomatic. In some modern environments, the biocoenosis and adjacent, recently-produced thanatocoenosis are broadly similar (e.g., Bernárdez et al., 2010), whereas in others they are drastically different, with the difference attributed to taphonomic processes such as dissolution (Takahashi, 1983), bioerosion and abrasion (Boucot, 1953). It seems somewhat less intuitive, however, that a thanatocoenosis which has undergone almost no taphonomic change would so poorly represent the living carbonate-producing community immediately adjacent. At the Rainbow Warrior wreck site, the disjunction appears to be due to a lag in carbonate sedimentation. The sediments simply have not yet had time to record the new productive environment above.
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programme in the USA, for example, has generated considerable debate as to the ecological usefulness of such reefs (e.g., Schroeder and Love, 2004). Even if some temporary enhancement of biodiversity among organisms that require hard substrate does occur, the lifetime of most wrecks on the seafloor is less than that necessary to make any kind of record in the sediment. In a sedimentological sense, a wreck such as the Rainbow Warrior will leave no trace behind. Acknowledgements We acknowledge the support of the Department of Earth Science, University of Waikato and the Department of Marine Science, University of Otago. Dr. Roger Grace, Dr. Hugh Grenfell, Michael Dravitzki, Dr. Katrin Berkenbusch and April Brown assisted in collecting samples. Useful conversations with Prof. Hamish Spencer and Dr. Roger Grace improved the manuscript. Fig. 4. Surface sediments near the sunken wreck Rainbow Warrior show little difference with distance from the wreck or over time (1991 photos from Smith, 1992). Each photo represents 30 mm2 of sediment sample.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.marpolbul.2011.08.028.
Some wrecks or artificial reefs have been found to exert no influence on adjacent sediment texture (Davis et al., 1982; Danovaro et al., 2002; Wilding, 2006), whereas others are ringed by a ‘halo’ of relatively more coarse sediments than the surrounding norm (Turner et al., 1969; Ambrose and Anderson, 1990). For those studies that showed a significant difference in grain size, authors suggest that the introduced structure alters the hydrodynamic environment, thus promoting deposition of coarser sediments (Baynes and Szmant, 1989; Ambrose and Anderson, 1990), which may or may not originate at the wreck itself. Given that the Rainbow Warrior is already losing its superstructure (Szabo and Grace, 1994), it may be such an ephemeral (geologically speaking) carbonate source that no evidence for its passing will be retained in the sedimentary record. A sediment record of 3 cm thickness would, after all, require the wreck to persist as a carbonate source until 2987 – an unlikely prospect. An instructive comparison could be drawn with the wreck of the Minato Maru 102, wrecked on 6 September 1983 at Shearers Rock in the Hauraki Gulf (36° 410 S, 174° 550 E, 30 m water depth) (Leahy and McDougall, 1984). Divers noted 28 years later that the wreck is ‘‘completely’’ intact (Obern, 2011) and nearly upright on a quite muddy bottom (Obern, 2010). A better record of carbonate production by attached organisms could perhaps be found around this wreck. The justification for submerging a wreck on the seafloor is usually to increase biodiversity by increasing habitat availability. The improvement in biodiversity is seen as ecologically useful in seeding local habitats and perhaps providing nursery grounds for economically valuable fish stocks, as well as in terms of developing SCUBA-based ecotourism (Hooker et al., 1988). One can argue that the attached flora and fauna, and possibly some crevice-dwelling motile species, in and on the Rainbow Warrior wreck itself add to local biodiversity, albeit temporarily. There is, however, as yet very little evidence of increase in diversity either on the seafloor or in the water column. Brook’s (2002) extensive survey found 71 species of fish around the Cavalli Islands, very similar to the 74 species known before the wreck was sunk there (Nicholson, 1979). Deploying unwanted ships or oil rigs on the seafloor, so-called artificial reefs, is understandably attractive to those who would otherwise have to pay disposal costs. Although there is evidence of improvement in biodiversity at least in some artificial reef environments, there is also evidence of considerable harm caused, particularly by tyre-reefs (Morley et al., 2008). The ‘‘Rigs to Reefs’’
References Ambrose, R.F., Anderson, T.W., 1990. Influence of an artificial reef on the surrounding infaunal community. Mar. Biol. 107, 41–52. Baine, M., 2001. Artificial reefs: a review of their design, application, management and performance. Ocean Coast. Manag. 44, 241–259. Baynes, T.W., Szmant, A.M., 1989. Effect of current on the sessile benthic community structure of an artificial reef. B. Mar. Sci. 44, 545–566. Bernárdez, P., Varela, M., Pazos, Y., Prego, R., Francés, G., 2010. Biocoenosis and thantocoenosis of diatoms in a western Galiacian ría. J. Plankton Res. 32, 857– 883. Boucot, A.J., 1953. Life and death assemblages among fossils. Am. J. Sci. 251, 25–40. Brook, F.J., 2002. Biogeography of near-shore reef fishes in northern New Zealand. J. Roy. Soc. N. Z. 32, 243–274. Danovaro, R., Gambi, C., Mazzola, A., Mirto, S., 2002. Influence of artificial reefs on the surrounding infauna: analysis of meiofauna. J. Mar. Sci. 59, S356–S362. Davis, N., VanBlaricom, G.R., Dayton, P.K., 1982. Man-made structures on marine sediments: effects on adjacent benthic communities. Mar. Biol. 70, 295–303. Enderby, T., 1993. Life on the Rainbow Warrior. Poirieria 16, 2p. Falcão, M., Santos, M.N., Vicente, M., Monteiro, C.C., 2007. Biogeochemical processes and nutrient cycling within an artificial reef off Southern Portugal. Mar. Environ. Res. 63, 429–444. Falcão, M., Santos, M.N., Drago, T., Serpa, D., Monteiro, C., 2009. Effect of artificial reefs (Southern Portugal) on sediment-water transport of nutrients: importance of the hydrodynamic regime. Estuar. Coast. Shelf Sci. 83, 451–459. Fricke, A.H., Koop, K., Cliff, G., 1986. Modification of sediment texture and enhancement of interstitial meiofauna by an artificial reef. Trans. Roy. Soc. S. Afr. 46, 27–34. Gordon, D.P., Beaumont, J., MacDiarmid, A., Robertson, D.A., Ahyong, S.T., 2010. Marine biodiversity of Aotearoa New Zealand. PLoS ONE 5 (8), e10905. Grace, R.V., 2005. Rainbow Warrior – Twenty years after the big bang. (accessed 21.09.10). Grace, R.V., Hayward, B.W., 1980. The macrobenthos of the Cavalli Islands, northern New Zealand. Tane 26, 189–209. Hooker, S.H., Ackley, J.C., Creese, R.G., 1988. Baseline survey of the Rainbow Warrior. Report commissioned by the New Zealand Underwater Association, 36p. Kukal, Z., 1990. The rate of geological processes. Earth Sci. Rev. 28, 7–258. Leahy, P.J., McDougall, R.J., 1984. For the record: Minato Maru No. 102. N. Z. Mar. News 34, 62–63. McNinch, J.E., Wells, J.T., Drake, T.G., 2001. The fate of artifacts in an energetic, shallow-water environment: scour and burial at the wreck site of Queen Anne’s Revenge. Southeast. Geol. 40, 19–27. Morley, D.M., Sherman, R.L., Jordan, L.K.B., Banks, K.W., Quinn, T.P., Spieler, R.E., 2008. Environmental enhancement gone awry: characterization of an artificial reef constructed from waste vehicle tires. Environ. Prob. Coastal Reg. VII 99, 73– 87. Nelson, C.S., 1988. An introductory perspective on non-tropical shelf carbonates. Sed. Geol. 60, 3–12. Nicholson, J., 1979. A checklist of fishes from the Cavalli Islands, Northland, New Zealand. Tane 25, 133–139. Obern, J., 2010. Minato Maru: trip report 26 December 2010. TechDive New Zealand Trip Reports, 2p. (downloaded 15.08.11).
A.M. Smith et al. / Marine Pollution Bulletin 62 (2011) 2412–2419 Obern, J., 2011. Return to the Minato Maru: trip report 22 May 2011. TechDive New Zealand Trip Reports, 2p. (downloaded 15.08.11). Pickering, H., Whitmarsh, D., Jensen, A., 1999. Artificial reefs as a tool to aid rehabilitation of coastal ecosystems: investigating the potential. Mar. Pollut. Bull. 37, 505–514. Schroeder, D.M., Love, M.S., 2004. Ecological and political issues surrounding decommissioning of offshore oil facilities in the Southern California Bight. Ocean Coast. Manag. 47, 21–48. Smith, A.M., 1992. Aspects of the sedimentology of New Zealand bryozoans and mixed carbonate-clastic deposits: a contribution to the temperate shelf carbonate model. Ph.D. Dissertation, University of Waikato, New Zealand. Svane, I., Petersen, J.K., 2001. On the problems of epibioses, fouling and artificial reefs, a review. Mar. Ecol. 22, 169–188.
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Szabo, M., Grace, R., 1994. Wreck to reef: the transfiguration of the Rainbow Warrior. N. Z. Geog. 23, 82–94. Takahashi, K., 1983. Radiolaria biocoenosis-thanatocoenosis relationship in pelagic oceans. AAPG Bull. 67, 556–557. Turner, C.H., Ebert, E.E., Given, R.R., 1969. Man-made reef ecology. Calif. Dep. Fish Game Fish Bull. 146, 1–221. Walker, S.J., Schlacher, T.A., Schlacher-Hoenlinger, M.A., 2007. Spatial heterogeneity of epibenthos on artificial reefs: fouling communities in the early stages of colonization on an East Australian shipwreck. Mar. Ecol. 28, 435–445. Ward, I.A.K., Larcombe, P., Veth, P., 1999. A new process-based model for wreck site formation. J. Archaeol. Sci. 26, 561–570. Wilding, T.A., 2006. The benthic impacts of the Loch Linnhe artificial reef. Hydrobiologia 555, 345–353.
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Sedimentology of a wreck: The Rainbow Warrior revisited Abigail M. Smith a,⇑, Louise Kregting a,1, Sophie Fern a,2, Ceridwen I. Fraser b a b
Department of Marine Science, University of Otago, P.O. Box 56, Dunedin, New Zealand Allan Wilson Centre for Molecular Ecology and Evolution, Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand
a r t i c l e
i n f o
Keywords: Carbonate sediments Rainbow Warrior Biocoenosis Thanatocoenosis Temperate carbonates
a b s t r a c t The wreck of the Rainbow Warrior, a 40-m ship sunk on 12 December 1987 in Matauri Bay (34° 590 S, 173° 560 E), Cavalli Islands, northeastern New Zealand, offers an opportunity to investigate the impact of artificial substrate on temperate carbonate sedimentation. Surface sediment samples showed no significant textural or compositional difference between sediments near the wreck and those far from it. The large and diverse carbonate-producing community resident on the wreck (dominated by bryozoans, corals and sponges) has not had a measurable influence on adjacent bottom sediments (dominated by bivalves and barnacles), even after 21 years. It is likely that carbonate production on the Rainbow Warrior is insufficient to leave any sedimentary record over the potential lifetime of the wreck on the seafloor, which informs our understanding of the long-term impacts of shipwrecks (and other artificial substrata) on the local benthic environment in shallow temperate ecosystems. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction On 10 July 1985, the 40-m Greenpeace vessel Rainbow Warrior was sunk by two French bombs at Marsden Wharf in Waitamata Harbour, Auckland, New Zealand. After refloating, she was declared irreparable and towed to Matauri Bay (34° 590 S, 173° 560 E) where she was sunk near the Cavalli Islands on 12 December 1987 to serve as a recreational diving resource and fish sanctuary (Hooker et al., 1988). The wreck sits on unvegetated sand in 26 m of water with a 15° list to starboard (Fig. 1); it is marked with a buoy and visited by several commercial dive trips a week in summer. Lying in the path of the subtropical East Auckland Current (Gordon et al., 2010), the water around the Cavalli Islands typically reaches minimum sea surface temperatures of 14–16 °C in winter (August) to maximum temperatures of 20–22 °C in summer (February) (Brook, 2002). It is an area of moderate biodiversity (Gordon et al., 2010), supporting over 70 species of fish (Nicholson, 1979) and at least 140 species of marine macrobenthic invertebrates (Grace and Hayward, 1980). Sediments near the wreck site in the northwest Cavalli Islands are dominated by coarse shelly sand, mainly formed of molluscs and barnacles (Grace and Hayward, 1980; Hooker et al., 1988; Smith, 1992). The nearest rocky reef is
⇑ Corresponding author. Tel.: +64 3 479 7470; fax: +64 3 479 8336. E-mail address: [email protected] (A.M. Smith). Present address: Queens University Belfast, Marine Laboratory, The Strand, Portaferry, County Down BT22 1PF, United Kingdom. 2 Present address: School of English, Journalism and European Languages, University of Tasmania, Hobart, Australia. 1
0025-326X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2011.08.028
approximately 500 m away (Hooker et al., 1988), on the port side of the wreck. After sinking, the Rainbow Warrior was rapidly covered with encrusting organisms, both soft (algae, anemones) and calcified (bryozoans, molluscs) (Table 1). In less than a year most available surfaces were covered by over fifty species of invertebrates and algae (Hooker et al., 1988). In 1991, 4 years after sinking, divers visiting the wreck estimated coverage by bryozoans alone to be about 20% (Smith, 1992). A brief report in 1993 commented on the diversity of fish and listed among the attached organisms calcareous sponges and a wide variety of gastropods (Enderby, 1993). By 1994 the wreck’s superstructure had mostly collapsed; the remains were covered in sessile organisms, with the exception of silt-covered horizontal surfaces (Szabo and Grace, 1994). Diver and biologist R.V. Grace, who has photographed the wreck often since 1988, argued that a ‘climax community’ of corals, bryozoans and sponges had been reached on the wreck surfaces in about 7 years (Szabo and Grace, 1994; Grace, 2005). Sunken vessels have traditionally been considered to be ecological assets as they provide new habitat and a refuge for marine organisms (Pickering et al., 1999; Baine, 2001; Svane and Petersen, 2001). Generally, therefore, artificial reefs have been investigated in relation to their effects on near-shore fish populations (Baine, 2001) and benthic communities (e.g., Baynes and Szmant, 1989; Walker et al., 2007). Several studies have looked at biogeochemical processes near artificial reefs (Falcão et al., 2007, 2009), as well as the effects of sediments on surrounding infaunal communities (e.g., Fricke et al., 1986; Ambrose and Anderson, 1990) and sediment texture. To our knowledge, however, research on how wrecks
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173°58’12”E
b
N
34°58’12”S
Motukawanui Island Cav all iP as sa ge Matauri Bay
c Motutapere Hamaruru Panaki Islands Island Island Horonui Island 10
175°E
N
400 m
d
E
N Is orth la nd
W
S
40°S
N
20 m
170°E
a
m
wreck
15
2 km
m
N
B
Port Bow
Stern
45°S
So
ut
h
Is
la
nd
Tasman Sea
A
F
South Pacific Ocean
Starboard
E 300 km
C 10 m
D
Fig. 1. Location of the Rainbow Warrior wreck, sunk in 1987, and transects sampled in 2008: (a) Map of New Zealand showing the location of the Cavalli Islands; (b) Matauri Bay/Cavalli Islands region with the location of the wreck indicated by a red cross; (c) the location of the Rainbow Warrior wreck in relation to nearby islands; (d) about 40 m long, the wreck sits at a water depth of 26 m and the bow faces southeast. For each of six transects, sediment samples were taken at distances of 0, 2, 5, 10, 15 and 20 m from the wreck.
or artificial reefs may alter nearby sediment composition is nonexistent. The well-documented Rainbow Warrior allows us to use the difference between the carbonate-producing fauna on the ship surfaces and those in the ambient sediment to examine the effect of an artificial reef on marine coastal sediments. In particular, here we investigate whether carbonate skeletal material originating from the wreck makes a significant contribution to the composition of local bottom sediment after 21 years.
2. Methods Over two days (30 September 2008–1 October 2008) in the austral spring, surface (top 3 cm) sediment samples were collected
manually by divers on six transects, each with six sites (Fig. 1). Sediment samples were numbered according to transect letter and distance from the wreck in m (e.g., RW-D15) and split into three subsamples. An archive of about 100 ml was labelled, photographed, and kept in fresh water. A dried bulk sample of about 100 ml was retained for dry-sieving and carbonate content analysis. The remainder of the sample was washed through a 1 mm sieve and the coarse sand to gravel fraction (where most carbonate skeletal fragments can be identified to taxa) dried for compositional analysis. About 50 ml of each bulk sample was dry-sieved to half-phi intervals in order to calculate mean grain size and sorting coefficient. About 50 ml of each bulk sample was weighed, immersed in 90% HCl and allowed to bubble, stirred frequently, and when all carbonate was dissolved, rinsed, dried, and reweighed to
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Table 1 Benthic organisms listed as having been found attached to or resident on the sunken Rainbow Warrior, Cavalli Islands, New Zealand (as reported in Hooker et al., 1988; Smith, 1992; Enderby, 1993; Szabo and Grace, 1994). While spelling errors have been fixed and common names added when possible, the taxonomy has not been updated. Taxon
Species
Common name
Source
Phaeophyceae (brown algae)
Ecklonia radiata Sargassum sp. Champia laingii Stenogramme interrupta Corallina officinalis Laurencia distichophylla Schizoseris sp. Griffithsia traversii Arthrocardia corymbasa Ceramium sp. Lomentaria caespitosa Cladhymenia sp. Polysiphonia spp. Ulva sp. Caulerpa flexilis
Kelp Sargassum
Enderby (1993) and Szabo and Grace (1994) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988)
Rhodophyceae (red algae)
Chlorophyceae (green algae) Porifera (sponges)
Ancorina sp. Aplysilla rosea Stelleta sp. Anthozoa (anemones and corals)
Hydrozoa (hydroids)
Platyhelminthes (flatworms) Annelida (segmented worms)
Alcyonium aurantiacum Culicea rubeola Corynactis haddoni Actinothoe albocincta Solanderia sp. Symplectoscyphus johnstoni Pennaria sp.
Coralline turf
Sea lettuce Sea rimu Calcareous sponges Horny sponges Encrusting sponges Staghorn sponge Ancorina sponge Pink sponge
Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Szabo and Grace (1994) Hooker et al. (1988)
Soft coral Encrusting coral Jewel anemone White-striped anemone
Szabo and Grace (1994) Szabo and Grace (1994) Enderby (1993) and Szabo and Grace (1994) Hooker et al. (1988) and Enderby (1993) Enderby (1993) Hooker et al. (1988) Hooker et al. (1988)
Stylochoplana sp. Hydroides norvegica Filograna sp. Nereid sp. Polynoid sp.
Hooker Hooker Hooker Hooker Hooker
et et et et et
al. al. al. al. al.
(1988) (1988) (1988) (1988) (1988)
Mollusca Gastropoda (snails and slug)
Maurea tigris Maurea puctulata Astraea sp. Charonia capax Cabestana spengleri Mayena australasiae Jason mirabilis Dendrodoris gemmacea Tritonia incerta Sigapatella novaezelandiae Cookia sulcata
Tiger shell Tiger shell Circular saw shell Trumpet shell Trumpet shell Trumpet shell Nudibranch Jewel nudibranch Apricot-coloured nudibranch Slipper limpet Cook’s turban
Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Hooker et al. (1988) and Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Enderby (1993) Hooker et al. (1988) Hooker et al. (1988)
Molluscs Bivalvia (clams) Arthropoda Insecta (insects) Arthropoda Amphipoda (amphipods)
Teredo sp. Philanisus plebejus Apherusa translucens Ceina egregia Tetradeion crassa Hyale grenfelli Astacilla sp. Plagusia capensis Notomithrax minor Halicarcinus cookii Elminius modestus
Shipworm Marine caddisfly
Szabo and Grace (1994) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Szabo and Grace (1994)
Arthropoda Isopoda (isopods) Arthropoda Decapods (crabs)
Arthropoda Crustacea (barnacles) Bryozoa (lace corals)
Waterispora sp. Bugula flabellata Lichenopora novaezelandiae Galeopsis grandipora Steginoporella magnifica Disporella fibriata Hornera sp. Celleporaria sp. Celleporaria agglutinans Hemipustulopora harmeri Disporella gordoni Cellaria tenuirostris Galeopsis porcellanicus
Ascidia (sea squirts)
Cnemidocarpa bicornuta Corella eumyta Aplidium spp
Red rock crab Decorator crab Acorn barnacle
Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988) Smith (1992) Smith (1992) Smith (1992) Smith (1992) Smith (1992) Orange ascidian
Hooker et al. (1988) Hooker et al. (1988) Hooker et al. (1988)
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Table 2 Texture and composition of 36 sediment samples from six transects around the Rainbow Warrior, Cavalli Islands, New Zealand. Supplementary material available online (Online Resource 1). Sample number
Transect Distance Collection from RW date (m)
Wt.% Wt.% Gravel Sand
Modal grain Mean grain size size (phi) (mm)
Percent Bivalves Barnacles Echinoids Bryozoans Gastropods carbonate
RW-A-00 RW-A-02 RW-A-05 RW-A-10 RW-A-15 RW-A-20 RW-B-00 RW-B-02 RW-B-05 RW-B-10 RW-B-15 RW-B-20 RW-C-00 RW-C-02 RW-C-05 RW-C-10 RW-C-15 RW-C-20 RW-D-00 RW-D-02 RW-D-05 RW-D-10 RW-D-15 RW-D-20 RW-E-00 RW-E-02 RW-E-05 RW-E-10 RW-E-15 RW-E-20 RW-F-00 RW-F-02 RW-F-05 RW-F-10 RW-F-15 RW-F-20
A A A A A A B B B B B B C C C C C C D D D D D D E E E E E E F F F F F F
56.0% 79.9% 90.2% 27.1% 76.0% 61.7% 54.0% 68.3% 64.2% 23.1% 35.3% 50.8% 43.2% 87.9% 54.9% 56.8% 48.9% 45.1% 24.7% 65.9% 37.5% 63.2% 30.4% 54.3% 16.2% 11.9% 25.9% 12.5% 9.4% 19.5% 67.7% 90.6% 25.5% 0.7% 9.3% 47.2% 0.7% 45.4% 90.6% 0.25 36
1.51 2.03 2.19 1.34 1.57 1.52 1.58 1.88 1.79 1.18 1.68 1.40 1.21 2.09 1.52 1.59 1.35 1.26 1.19 1.77 1.19 1.62 1.36 1.53 0.89 0.89 1.19 0.69 0.67 0.97 1.90 2.13 1.21 0.55 0.65 1.09 0.55 1.39 2.19 0.42 36
60.7% 53.0% 21.5% 83.2% 39.1% 61.6% 71.0% 52.2% 62.4% 87.6% 92.7% 67.6% 87.5% 72.3% 91.1% 64.6% 75.6% 70.1% 92.3% 56.6% 80.6% 70.0% 76.3% 84.6% 93.7% 94.7% 92.3% 93.7% 91.8% 93.9% 85.0% 93.9% 93.9% 95.5% 90.0% 87.1% 21.5% 77.2% 95.5% 0.18 36
0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20 0 2 5 10 15 20
30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 30-September-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 1-October-08 Minimum Mean Maximum Standard deviation N
44.0% 20.1% 9.8% 72.9% 24.0% 38.3% 46.0% 31.7% 35.8% 76.9% 64.7% 49.2% 56.8% 12.1% 45.1% 43.2% 51.1% 54.9% 75.3% 34.1% 62.5% 36.8% 69.6% 45.7% 83.8% 88.1% 74.1% 87.5% 90.6% 80.5% 32.3% 9.4% 74.5% 99.3% 90.7% 52.8% 9.4% 54.6% 99.3% 0.25 36
2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 0 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 2 phi gravel 2 phi gravel 0.5 phi coarse sand 2 phi gravel 1 phi coarse sand 0.5 phi coarse sand 0.5 phi coarse sand 1 phi coarse sand 1 phi coarse sand 1 phi coarse sand 2 phi gravel 2 phi gravel 0.5 phi coarse sand 1 phi coarse sand 1 phi coarse sand 2 phi gravel 2 phi gravel 1 phi coarse sand 36
determine the insoluble residue (and thus wt.% CaCO3) in each size fraction. 5 g of each >1 mm fraction was sorted into skeletal components by taxon; while some grains were non-carbonate, they are not included in the weight percentages calculated.Pair-wise correlations between all measured sediment parameters were carried out using JMP 7.0 (SAS, 2007). 3. Results Thirty-six sediment samples collected in 2008 on six transects were all coarse shelly sands or gravels (Table 2, Fig. 2). Modal grain sizes ranged from coarse sand (0.5 mm; 0.5 phi) to gravel (2 mm; 1.0 phi). No sample had more than 5% grains smaller than 0.25 mm (2 phi) with mean grain size ranging from 0.55 to 2.19 mm (mean = 1.39, stdev = 0.42, N = 36). 34 samples were more than half carbonate: the mean carbonate content was 77% (stdev 0.18, N = 36). The carbonate was formed mainly from bivalves (mean = 67%, stdev 0.22, N = 34) with significant contributions from barnacles (mean = 30%, stdev = 0.21, N = 34). Bryozoans, gastropods and echinoids formed only small proportions of those samples in which they occurred. There is a strong relationship between carbonate content and grain size: as the mean grain size increases, the wt.% carbonate decreases (R = 0.6300, N = 36, p < 0.0001). Wt.% gravel, too, is inversely correlated with carbonate (R = 0.7072, N = 36, p < 0.0001),
49.5% 59.7% 87.6% 42.2% 71.0% 81.0% 72.0% 65.1% 65.1% 6.9% 71.6% 87.2% 92.7% 100.0% 89.4%
46.7% 38.9% 3.3% 55.2% 26.0% 18.7% 25.7% 34.9% 34.5% 89.7% 27.0% 7.7% 7.0% 0.0% 6.2%
0.5% 0.0% 0.0% 1.7% 1.5% 0.0% 0.0% 0.0% 0.0% 3.4% 1.1% 0.0% 0.2% 0.0% 0.2%
0.0% 0.9% 0.0% 0.0% 0.8% 0.0% 0.0% 0.0% 0.0% 0.0% 0.4% 2.0% 0.0% 0.0% 1.8%
3.3% 0.4% 9.1% 0.9% 0.8% 0.4% 2.2% 0.0% 0.4% 0.0% 0.0% 3.1% 0.0% 0.0% 2.4%
41.8% 75.5% 53.6% 87.4% 30.2% 92.4% 45.0% 93.5% 46.4% 54.1% 77.5% 80.6% 28.6% 94.6% 64.8% 88.8% 58.6% 37.8% 74.4%
56.8% 24.5% 39.6% 12.3% 59.9% 5.7% 48.5% 6.3% 49.5% 40.2% 20.2% 15.7% 68.6% 3.7% 31.1% 11.2% 30.3% 43.2% 16.7%
0.0% 0.0% 2.4% 0.0% 4.2% 0.0% 0.6% 0.0% 2.1% 3.3% 1.6% 0.9% 2.9% 0.0% 1.6% 0.0% 2.0% 10.8% 5.1%
0.0% 0.0% 3.9% 0.3% 3.6% 1.9% 5.8% 0.2% 0.0% 0.8% 0.0% 0.9% 0.0% 1.7% 2.5% 0.0% 8.1% 5.4% 0.0%
1.5% 0.0% 0.5% 0.0% 2.1% 0.0% 0.0% 0.0% 2.1% 1.6% 0.8% 1.9% 0.0% 0.0% 0.0% 0.0% 1.0% 2.7% 3.8%
6.9% 66.7% 100.0% 0.22 34
0.0% 29.6% 89.7% 0.21 34
0.0% 1.4% 10.8% 0.02 34
0.0% 1.2% 8.1% 0.02 34
0.0% 1.2% 9.1% 0.02 34
suggesting that non-carbonate minerals, when present, occur in the coarsest fraction (as gravel and pebbles). There is no apparent correlation between distance along a transect and any of the textural sedimentary parameters reported here. There is, however, a difference among transects – all of the samples on transect E and most on transect F are different from the other four, due to the lower gravel fraction, higher sand fraction, and higher carbonate values than the other transects. Essentially, the non-carbonate pebbles did not appear in those samples. The relationship between barnacles and bivalves is strongly negative (R = 0.9845, N = 34, p < 0.0001), indicating that the sedimentary carbonate is essentially a two-element mixture, with other components being minor. Among those minor components, echinoids are weakly inversely correlated with bivalves (R = 0.5439, N = 34, p = 0.009), and positively correlated with barnacles (R = 0.128, N = 34, p = 0.0128) and bryozoans (R = 0.3954, N = 34, p = 0.0206). None of the carbonate components are correlated with distance from the wreck, nor are there significant faunal differences among transects. 4. Discussion The character of local sediment near the Cavalli Islands prior to the sinking of the wreck is perhaps best described by Grace and Hayward (1980); their dredge (numbered 6) was taken near the
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Transect code (A-F) 100
A BCD E F
A BCD E F
A BCD E F
A BCD E F
A BCD E F
A BCD E F Size classes (phi)
Weight (percent)
80
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0
60
40
20
0 0
2
5
10
15
20
A BCD E F
A BCD E F
Distance from wreck (metres) Transect code (A-F) 100
A BCD E F
A BCD E F
A BCD E F
A BCD E F
Size classes (phi)
Weight (percent)
80
pan 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0
60
40
20
0
0
2
5
10
15
20
Distance from wreck (metres) Transect code (A-F) 100
A BCDE F
A BCDE F
A BCDE F
ABDE F
A BCDE F
A BCDE Sediment carbonate components
Weight (percent)
80
Bivalves Echinoids Bryozoans Barnacles Gastropods
60
40
20
0
0
2
5
10
15
20
Distance from wreck (metres) Fig. 2. Texture and composition of 36 surface sediment samples from six transects around the Rainbow Warrior, Cavalli Islands, New Zealand. Top: sediment texture; Middle: texture of insoluble residue (i.e., non-carbonate sediment); Bottom: carbonate components making up the sediment size fraction greater than 2 mm.
wreck site in 25 m water depth. It was described as a very coarse shelly sand dominated by molluscs and barnacles, with associated polychaetes, various echinoids and a few bryozoans. Essentially the same type of sediment was found immediately under the wreck in 1991, four years after the ship was sunk there. Smith (1992) concentrated on the bryozoans on the wreck and in the sediments. Six sediment samples collected in 1991 on one tran-
sect were all coarse shelly gravel dominated by barnacle plates, with some bivalves, echinoid fragments, and algae-encrusted pebbles. While bryozoans covered some 20% of the wreck at that time, they made up less than 5% of the sediments. The species found in the sediment were not the species common on the wreck. It was concluded that four years was not long enough for wreck-derived sediment to appear in the carbonate sedimentary record (Smith, 1992).
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Fig. 3. Bryozoans, corals, algae and sponges dominate the surfaces of the sunken Rainbow Warrior, October 2008 (Austral springtime): (a–c) sponges, soft coral, hydroid (Solanderia sp.) and anemones; (d) macroalgae; (e) algae, hydroids and anemones; (f) sponges, soft coral, bryozoans and anemones; (g) macroalgae growing on ship deck; and (h) orange finger bryozoan Steginoporella neozelandica among algae, hydroids and anemones. White scale bars represent approximately 0.06 m, and black scale bar approximately 1.0 m.
Over two decades the wreck has acquired a considerable attached fauna and flora (Table 1). Bryozoans, sponges, serpulid worms and corals are the main carbonate producers on board (Fig. 3). In 2008, there was still little sign of this wreck-fauna carbonate in the sediments. Coarse sediment fragments were dominated by bivalves and barnacles, almost none of which have been noted or photographed on the wreck. The sediment therefore shows no effect of the wreck, even after 21 years (Fig. 4). Perhaps this result should not be surprising. Carbonate sediment production on temperate shelves is on the order of 1–3 cm/ 1000 years (e.g., Nelson, 1988); 21 years of production would thus produce less than 1 mm of accumulated sediment. Near a biodiverse wreck and in a subtropical environment we might expect carbonate production to be somewhat higher, but even if it were as high as on some tropical coral reefs, e.g., 10–30 cm/1000 years (e.g., Kukal, 1990), we would only expect to find 0.2–0.6 cm of carbonate accumulation in 21 years. Given the high-energy nature of the environment, mixing could dilute the wreck contribution con-
siderably (see, e.g., Ward et al., 1999; McNinch et al., 2001) and render it undetectable. A significant disjunction between a living community (or biocoenosis) and its related death assemblage (thanatocoenosis) is not unusual – but commonly found on a greater timescale. The unrepresentative nature of the fossil record is axiomatic. In some modern environments, the biocoenosis and adjacent, recently-produced thanatocoenosis are broadly similar (e.g., Bernárdez et al., 2010), whereas in others they are drastically different, with the difference attributed to taphonomic processes such as dissolution (Takahashi, 1983), bioerosion and abrasion (Boucot, 1953). It seems somewhat less intuitive, however, that a thanatocoenosis which has undergone almost no taphonomic change would so poorly represent the living carbonate-producing community immediately adjacent. At the Rainbow Warrior wreck site, the disjunction appears to be due to a lag in carbonate sedimentation. The sediments simply have not yet had time to record the new productive environment above.
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programme in the USA, for example, has generated considerable debate as to the ecological usefulness of such reefs (e.g., Schroeder and Love, 2004). Even if some temporary enhancement of biodiversity among organisms that require hard substrate does occur, the lifetime of most wrecks on the seafloor is less than that necessary to make any kind of record in the sediment. In a sedimentological sense, a wreck such as the Rainbow Warrior will leave no trace behind. Acknowledgements We acknowledge the support of the Department of Earth Science, University of Waikato and the Department of Marine Science, University of Otago. Dr. Roger Grace, Dr. Hugh Grenfell, Michael Dravitzki, Dr. Katrin Berkenbusch and April Brown assisted in collecting samples. Useful conversations with Prof. Hamish Spencer and Dr. Roger Grace improved the manuscript. Fig. 4. Surface sediments near the sunken wreck Rainbow Warrior show little difference with distance from the wreck or over time (1991 photos from Smith, 1992). Each photo represents 30 mm2 of sediment sample.
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.marpolbul.2011.08.028.
Some wrecks or artificial reefs have been found to exert no influence on adjacent sediment texture (Davis et al., 1982; Danovaro et al., 2002; Wilding, 2006), whereas others are ringed by a ‘halo’ of relatively more coarse sediments than the surrounding norm (Turner et al., 1969; Ambrose and Anderson, 1990). For those studies that showed a significant difference in grain size, authors suggest that the introduced structure alters the hydrodynamic environment, thus promoting deposition of coarser sediments (Baynes and Szmant, 1989; Ambrose and Anderson, 1990), which may or may not originate at the wreck itself. Given that the Rainbow Warrior is already losing its superstructure (Szabo and Grace, 1994), it may be such an ephemeral (geologically speaking) carbonate source that no evidence for its passing will be retained in the sedimentary record. A sediment record of 3 cm thickness would, after all, require the wreck to persist as a carbonate source until 2987 – an unlikely prospect. An instructive comparison could be drawn with the wreck of the Minato Maru 102, wrecked on 6 September 1983 at Shearers Rock in the Hauraki Gulf (36° 410 S, 174° 550 E, 30 m water depth) (Leahy and McDougall, 1984). Divers noted 28 years later that the wreck is ‘‘completely’’ intact (Obern, 2011) and nearly upright on a quite muddy bottom (Obern, 2010). A better record of carbonate production by attached organisms could perhaps be found around this wreck. The justification for submerging a wreck on the seafloor is usually to increase biodiversity by increasing habitat availability. The improvement in biodiversity is seen as ecologically useful in seeding local habitats and perhaps providing nursery grounds for economically valuable fish stocks, as well as in terms of developing SCUBA-based ecotourism (Hooker et al., 1988). One can argue that the attached flora and fauna, and possibly some crevice-dwelling motile species, in and on the Rainbow Warrior wreck itself add to local biodiversity, albeit temporarily. There is, however, as yet very little evidence of increase in diversity either on the seafloor or in the water column. Brook’s (2002) extensive survey found 71 species of fish around the Cavalli Islands, very similar to the 74 species known before the wreck was sunk there (Nicholson, 1979). Deploying unwanted ships or oil rigs on the seafloor, so-called artificial reefs, is understandably attractive to those who would otherwise have to pay disposal costs. Although there is evidence of improvement in biodiversity at least in some artificial reef environments, there is also evidence of considerable harm caused, particularly by tyre-reefs (Morley et al., 2008). The ‘‘Rigs to Reefs’’
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