Title Observations of organic falls from the abyssal Clarion-Clipperton Zone in the tropical eastern Pacific Ocean Authors Amon, Diva; Hilario, A; Arbizu, PM; Smith, CR Date Submitted 2020-09-11 Observations of organic falls in the abyssal Clarion-Clipperton Zone, tropical eastern Pacific Ocean Diva J. Amon a*, Ana Hilario b, Pedro Martinez Arbizu c, Craig R. Smith a a Department of Oceanography, University of Hawai’i at Mānoa, 1000 Pope Road, Honolulu, HI 96822 USA b Departamento de Biologia & CESAM, Universidade de Aveiro, 3810-125 Aveiro, Portugal c German Center for Marine Biodiversity Research, Senckenberg am Meer, Südstrand 44, D-26382 Wilhelmshaven, Germany *Corresponding author - D.J. Amon, [email protected] Acknowledgements The authors thank the National Research Foundation of Singapore, Ocean Mineral Singapore and the National University of Singapore for supporting this work done in partnership with the Keppel-NUS Corporate Laboratory, as well as UK Seabed Resources Ltd. Cruise SO239, EcoResponse was financed by the German Ministry of Education and Science BMBF as a contribution to the European project JPI-Oceans “Ecological Aspects of Deep-Sea Mining”. PMA acknowledges funding from the European Union Seventh Framework Programme (FP7/2007–2013) under the MIDAS project, grant agreement n° 603418 and funding from BMBF contract 03 F0707E. This work has also received funding from FCT (Apoios Especiais 2015 - Fundo de Apoio à Comunidade Científica) under the framework of JPI Oceans. Thanks to the Masters, crew and scientists of the RV Thompson (TN319, ABYSSLINE 02), the RV Sonne (SO239, EcoResponse) and the ROV Kiel 6000 (GEOMAR) for their support during fieldwork in the Clarion-Clipperton Zone. We are grateful to the AUV REMUS6000 team from Woods Hole Oceanographic Institution for the collection of the imagery during the UKSRL-funded AYBSSLINE 02 cruise. Further thanks to Dr. Jeffrey Drazen from the University of Hawai’i at Manoa for checking fish identifications, Christopher Mah from the Smithsonian Museum for identifying the asteroids, and Kai George from Senckenberg am Meer for help in identifying the laophontodid copepods. The conclusions put forward reflect the views of the authors alone. This is UH SOEST publication number XXXX. 1 1 Abstract 2 Organic falls can form nutrient-rich, ephemeral hotspots of productivity and biodiversity at the 3 deep-sea floor, especially in food-poor abyssal plains. We report here the first wood falls and 4 second carcass fall recorded from the Clarion-Clipperton Zone in the tropical eastern Pacific 5 Ocean, an area that could be mined for polymetallic nodules in the future. A small cetacean fall 6 in the mobile-scavenger stage likely recently arrived on the seafloor was observed, whereas most 7 of the wood falls were highly degraded. There were multiple species in attendance at the wood 8 falls including organic-fall specialists such as Xylophagaidae molluscs. Many of the taxa 9 attending the carcass fall were known mobile scavengers that regularly attend bait parcels in the 10 Pacific Ocean. These results further confirm that wood falls can occur at large distances (> 1450 11 km) from major land masses, providing an adequate supply of wood to the abyssal seafloor for 12 colonization by wood-boring molluscs and associated fauna. Organic falls may be regionally 13 abundant and are likely to influence species and habitat diversity in the abyssal areas of the 14 CCZ. 15 16 Keywords: whale fall, wood fall, scavenger, Clarion-Clipperton Zone, deep-sea mining, 17 Xylophagaidae 2 18 1. Introduction 19 Organic falls are ephemeral habitat islands, which include two important types: wood falls and 20 cetacean falls. These habitats are often nutrient-rich compared to the food-poor deep-sea floor, are 21 known to support a high diversity of both specialist and opportunistic species, are sources of 22 evolutionary novelty, and may also act as stepping stones between chemosynthetic deep-sea habitats 23 (Baco and Smith 2003; Distel et al. 2000; Smith et al. 2015). Whale falls, and to a lesser extent, wood 24 falls, pass through several decompositional stages on the deep-sea floor (Bienhold et al. 2013; Smith 25 and Baco 2003). Shortly after a cetacean carcass arrives on the seafloor, the mobile-scavenger stage 26 begins; during this stage, which may last weeks to years, the soft tissue is removed by large 27 scavenging organisms such as fish, galatheids and amphipods (Smith and Baco 2003; Smith et al. 28 2015). The enrichment-opportunist stage follows, supporting a different faunal assemblage that is 29 attracted to the detrital enrichment resulting from the previous stage, and can last for over 7 years 30 (Smith and Baco 2003; Smith et al. 2014a). This is followed by the sulfophilic stage, which occurs 31 when anaerobic microbial degradation of the lipid-rich skeleton creates reduced compounds that fuel a 32 chemosynthetic community that can last for decades (Amon et al. 2013; Schuller et al. 2004; Smith 33 and Baco 2003; Smith et al. 2015; Smith et al. 1998). Wood falls that are colonized by wood-boring 34 bivalves show a similar pattern to that of cetacean falls (Bienhold et al. 2013). The feeding activity of 35 wood-boring bivalves results in the deposition of detrital matter enriching the sediment surrounding 36 the wood fall (Bernardino et al. 2010; Bienhold et al. 2013). This enrichment stage can last for years 37 and leads to a sulfophilic stage as seen at most whale falls (Bernardino et al. 2010; Bienhold et al. 38 2013). 39 The Clarion-Clipperton Zone (CCZ) is a region of the tropical eastern Pacific Ocean where 40 deep-sea mining may take place in the near future (Ramirez-Llodra et al. 2011; Wedding et al. 2013). 41 High-grade polymetallic nodules, which could provide a commercial source of copper, cobalt, nickel, 42 and manganese (among other metals), are abundant in this six-million km2 region (Amon et al. 2016; 43 Clark et al. 2013). Thus far, there have been 16 leases (each up to 75,000 km2 in area) granted by the 44 International Seabed Authority for exploration in the CCZ with those for exploitation expected to soon 45 follow (https://www.isa.org.jm/). It is expected that nodule mining will drastically alter this unique 46 habitat and yet, very little is known about the ecology and biogeography of the fauna inhabiting the 47 region (Amon et al. 2016; Vanreusel et al. 2016). 48 Discoveries of organic-fall habitats have been serendipitous. It has been hypothesized that 49 cetacean falls are most abundant along cetacean migration routes, and wood falls in higher densities in 50 terrestrial conduits to the deep sea, e.g., estuarine areas, submarine canyons and on the continental 51 slope (Roman et al. 2014; Smith and Baco 2003; Vetter and Dayton 1998). Few organic falls have 52 been found in abyssal regions or even at great distances from land, likely not because they do not exist 53 but rather due to the low levels of deep-sea research in these remote areas. There has only been one 54 record of a natural modern organic fall in the CCZ: a large odontocete whale fall in the sulfophilic 3 55 stage, which was observed at 4850 m (Smith et al. 2015). Blackened areas of sediment and white 56 bacterial mats indicated the presence of sulfides resulting from the anaerobic decay of whale biomass 57 (Smith et al. 2015). The only recognizable fauna attending this whale fall were squat lobsters 58 (galatheids), likely from the genus Munidopsis (Smith et al. 2015). There have also been several 59 records of abyssal manganese-encrusted fossil whale falls in the CCZ (Heezen and Hollister 1971; 60 Smith et al. 2015)(Amon and Smith, unpublished data). However, no wood falls or wood-fall 61 associated fauna have been recorded from the vast region of the CCZ. Here, we present the first 62 records of wood falls, including one collected with associated fauna, and the second record of a likely 63 cetacean fall in the CCZ. We also discuss the ecology of these organic falls and the potential impacts 64 of polymetallic-nodule mining in the region on these unique habitats. 65 66 2. Methods and study sites 67 2.1. Locations of the organic falls 68 Seven organic falls were found serendipitously in the CCZ (Fig. 1). Four wood falls and a 69 cetacean fall were located during the second cruise of the ABYSSal baseLINE (ABYSSLINE) project, 70 AB02 (RV Thompson TN-319). This cruise conducted benthic baseline surveys in the exploration 71 contract area leased to UK Seabed Resources Ltd. (UK-1), the exploration contract area leased to 72 Ocean Minerals Singapore (OMS-1), and the International Seabed Authority’s Area of Particular 73 Environmental Interest 4 (APEI-4). Three wood falls (“A”, “B” and “C”) were observed during 74 megafaunal and geophysical surveys conducted by the AUV REMUS in the UK-1 exploration contract 75 area (Fig. 1 and Table 1). The cetacean fall and one wood fall “D” were observed during megafaunal 76 and geophysical surveys conducted by the AUV REMUS in the OMS-1 contract area (Fig. 1 and Table 77 1). Two more wood falls (“E” and “F”) were discovered during the SO239 EcoResponse cruise 78 onboard the RV Sonne, as part of the JPI Oceans (JPIO) “Ecological Aspects of Deep Sea Mining” 79 project. The falls were observed during two surveys using the ROV Kiel 6000. Wood fall “E” was 80 observed in an exploration contract area leased to IFREMER (IFREMER-East), and wood fall “F” was 81 observed in APEI-3, another of the areas targeted by the ISA for preservation (Fig. 1 and Table 1) 82 (Wedding et al.