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CITATION Phillips, B.T., M. Dunbabin, B. Henning, C. Howell, A. DeCiccio, A. Flinders, K.A. Kelley, J.J. Scott, S. Albert, S. Carey, R. Tsadok, and A. Grinham. 2016. Exploring the “Sharkcano”: Biogeochemical observations of the Kavachi submarine volcano (Solomon Islands). Oceanography 29(4):160–169, https://doi.org/10.5670/ oceanog.2016.85.

DOI https://doi.org/10.5670/oceanog.2016.85

COPYRIGHT This article has been published in Oceanography, Volume 29, Number 4, a quarterly journal of The Oceanography Society. Copyright 2016 by The Oceanography Society. All rights reserved.

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EXPLORING THE “SHARKCANO” Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands)

By Brennan T. Phillips, Matthew Dunbabin, Brad Henning, Corey Howell, Alex DeCiccio, Ashton Flinders, Katherine A. Kelley, Jarrod J. Scott, Simon Albert, Steven Carey, Rami Tsadok, and Alistair Grinham

160 Oceanography | Vol.29, No.4 ABSTRACT. An expedition to the Kavachi submarine volcano (Solomon Islands) Tuni, 1987). The most detailed investiga- in January 2015 was serendipitously timed with a rare lull in volcanic activity that tion prior to this study, which took place EXPLORING THE “SHARKCANO” permitted access to the inside of Kavachi’s active crater and its flanks. The isolated during a single day in May 2000, was con- Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands) location of Kavachi and its explosive behavior normally restrict scientific access to ducted from an approximate 1 km perim- the volcano’s summit, limiting previous observational efforts to surface imagery and eter surrounding the actively erupting peripheral water-column data. This article presents medium-resolution bathymetry of main peak. That study provided insights the main peak along with benthic imagery, biological observations of multiple trophic into the eruptive processes of Kavachi levels living inside the active crater, petrological and geochemical analysis of samples based on conductivity-​temperature-​ from the crater rim, measurements of water temperature and gas flux over the summit, depth (CTD) casts and surface imagery and descriptions of the hydrothermal plume structure. A second peak was identified (see Baker et al., 2002). A magnitude 8.1 to the southwest of the main summit and displayed evidence of diffuse-flow venting. earthquake that shook the entire region Microbial samples collected from the summit indicate chemosynthetic populations in April 2007 prompted the reconnais- dominated by sulfur-reducing ε-proteobacteria. Populations of gelatinous animals, sance of a conspicuous surface plume fol- small fish, and sharks were observed inside the active crater, raising new questions lowing a subaerial eruption visible from about the ecology of active submarine volcanoes and the extreme environments in a nearby island (Wunderman, 2007). which large marine animals can exist. The latest published evidence of activ- ity was obtained by NASA’s EO-1 sat- INTRODUCTION eruptions has prevented scientists from ellite on January 29, 2014 (NASA Earth The New Georgia Island Group is the observing the proximal area of Kavachi’s Observatory, 2014), and it appears simi- result of a complex tectonic configu- summit crater. lar in behavior to the 2007 eruption. ration, characterized by subduction of Of the roughly 30 active submarine vol- This study was conducted during a the active Woodlark Spreading Center canoes known worldwide, only a few have quiescent phase, which allowed for the (WSC) beneath the Solomon Islands been observed during or closely following first closeup look inside and around the intra-oceanic arc. This triple junction is an active eruption, for example, Northwest shallow summit of Kavachi. Our research the site of active volcanism, crustal uplift Rota-1 (W.W. Chadwick et al., 2010), team took advantage of this rare lull in that closely matches subducted bathy- West Mata (Resing et al., 2011), El Hierro volcanic activity to gather geological, metric features from the WSC, and a pro- (Santana-Casiano et al., 2013), Kick’em biological, and oceanographic observa- posed “slab window” that leaves astheno- Jenny (Devine and Sigurdssson, 1995), tions using relatively simple equipment spheric mantle in direct contact with a and Axial Seamount (W.W. Chadwick and methodologies. We report here on thin overlying crust (Mann et al., 1998; et al., 2012, and references therein). our initial results, which include evi- J. Chadwick et al., 2009). The Kavachi Despite these limited studies, active sub- dence of diffuse-flow venting on a con- submarine volcano (8°59'S, 157°58'E) is marine volcanoes are considered import- firmed second peak, a megafaunal com- situated ~30 km northeast of the sub- ant natural laboratories for observing the munity living inside the active crater, duction zone and rises abruptly to the effects of ocean acidification on marine and insights into the eruptive processes surface from more than 1,000 m water animals (e.g., Hall-Spencer et al., 2008), and magma source characteristics of depth (Figure 1). By far the most active with Kavachi being an extreme example Kavachi’s active volcanism. volcano in the region, Kavachi is known of such an environment. for frequent phreatomagmatic (denoting Kavachi erupts nearly continuously. METHODS explosive water-magma interaction) and Reports of airborne steam and ash visible This work was conducted in January 2015 subaerial eruptions leading to occasional from shore are common, and the forma- with operations based out of Gatokae ephemeral island emergence (Johnson tion and erosion of multiple islands over Island, Western Province, Solomon and Tuni, 1987). The remote geographic the past century indicate the summit is Islands. Approaches to the summit crater location and inherent danger of frequent in a constant state of flux (Johnson and were made after several days of observing inactivity from a safe perimeter—normal eruptive activity for Kavachi is audible FACING PAGE. Article co-authors Alistair Grinham and Matthew Dunbabin prepare an autonomous on the surface, and no such sounds were surface drifter for deployment over Kavachi’s summit crater. Photo is taken looking north toward Vangunu Island, with the volcano’s surface plume visible in the middleground where the water heard during the course of this expedi- changes color from dark blue to light blue-green.” tion. All equipment used was lightweight,

Oceanography | December 2016 161 relatively low cost, and deployed using transmission, and atmospheric pCO2 general trend depicting the volcano, sim- small boats. Down-looking images of the were deployed as described by Dunbabin ilar to swath editing in multibeam sonar seafloor paired with water-column mea- (2016). Total CO2 flux was calculated processing. This “cleaned” point-cloud surements were made using a GoPro using the drifter’s measurements of flux (~85,000 soundings; see online supple- camera in a deep-rated housing, battery- per unit area, which was extrapolated mental Figure S1) was then used to create powered lights, and a National Oceanic to represent the total size of the bubble three individual continuous curvature and Atmospheric Administration/Pacific zone. A downward-looking camera was spline surfaces, each with unique spatial Marine Environmental Laboratory mounted on the drifter, which logged its extent and resolution. This multisurface (NOAA/PMEL) Miniature Autonomous position, and after multiple runs through approach was necessary in order to accu- Plume Recorder (Walker et al., 2007) the bubble zone it was possible to esti- rately represent varying degrees of data mounted on an instrument frame that mate the total surface area by noting the density over the study area, with the most was raised and lowered with an electric appearance and disappearance of bubbles soundings concentrated at the summit fishing reel. Baited drop-camera record- on camera footage. caldera, and the least at the foot of the vol- ings were achieved using an autonomous We measured bathymetry with cano (Flinders et al., 2014). The three sur- National Geographic Remote Imaging a Lowrance HDS-5 echosounder faces (100 m study-wide, 35 m volcano-​ DropCam following methods described (50/200 kHz). IVS Fledermaus software focused, and 7 m summit-focused) were by Friedlander et al. (2014). Surface drift- was used to manually remove sound- then blended to create a single individual ers measuring water temperature, light ings that qualitatively deviated from a surface for visualization. Blending con- straints ensured that within each specific area, only the highest resolution surface 157°E 158°E 159°E 160°E would be used. Santa Scuba divers collected rock and bac- Isabel Vangunu terial samples by hand. Major and trace 8°S New element analyses were conducted using Georgia a Perkin Elmer Optima 3100 XL induc- 8.98°S

Kavachi 9°S tively coupled plasma atomic emission spectrometer (ICP-AES) and a Thermo X-Series 2 quadrapole inductively cou- pled plasma mass spectrometer (ICP-MS; Kelley et al., 2003). The Marine Geological Sample Laboratory at the University of Rhode Island prepared the sample slides. Bacterial DNA was extracted using PowerSoil® DNA Isolation Kit (MO BIO Laboratories, Carlsbad, California), poly-

9.00°S merase chain reaction (PCR)-amplified using universal 16S rRNA gene primers (27F: AGR GTT YGA TYM TGG CTC AG, 1100R: GGG TTN CGN TCG TTG) and cloned with pGEM-T Easy (Promega, Madison, Wisconsin). After removal of 157.96°E 157.98°E vector and primer sequences, all clones 1 km were imported into the software pack- 0.1 km age mothur (http://www.mothur.org) to –1,000 –800 –600 –400 –200 Depth (m) –60 –45 –30 screen for putative chimeras and generate FIGURE 1. Bathymetry of Kavachi and the summit crater (inset, lower right). Red circles indicate an initial alignment against a SILVA-based locations of water column profiles and benthic imagery. White diamonds locate baited drop cam- reference set (SEED version 119). Quality eras deployments. The blue line delineates the path of a surface drifter that measured tempera- screened and aligned 16S rRNA clones ture and atmospheric CO2. The contour map and the inset at lower right were created from approx- imately 85,000 depth soundings visualized and edited as a three-dimensional​ point-cloud using were then imported into the ARB environ- IVS Fledermaus. The inset map at upper right was created with Generic Mapping Tools (v 4.5) using ment (http://www.arb-home.de), manu- data available from Marine Geoscience Data System’s Global Multi-Resolution Topography Data Synthesis (v 3.1). A map with ship tracklines used to create this plot is provided in online supplemen- ally curated, and added to the master ARB tal Figure S1. tree (tree_SSURefNR99_1200_slv_123).

162 Oceanography | Vol.29, No.4 Based on the location of Kavachi clones The deepest soundings on the peak are been observed are enriched in suspended within the tree, we chose an additional ~70 m water depth and indicate asym- particulate matter, 3He, and sulfur, and 32 related sequences from the ARB metrical terrain surrounded by almost exhibit depressed pH values (Walker database for further phylogenetic anal- uniform flanks with 18° slopes that et al., 2008). Video recorded by a scuba ysis, including representatives from descend to depths greater than 1,000 m. diver around the outside of the crater Campylobacter (Campylobacteraceae) We confirm the existence of a “southwest rim reveals widespread, vigorous gas and Sulfuricurvum (Helicobacteraceae) as extension,” or secondary summit, located bubbling originating from the shallow- outgroups. Where possible, 16S sequences 1.3 km southwest of the main summit; it est regions surrounding orange, cloudy from pure cultures were included. rises to 260 m, and there is a narrow col hydrothermal plume water inside the Phylogenetic analysis was conducted between the peaks (Figure 1). Previously crater that almost completely obscures using rapid bootstrapping (1,000 infer- published bathymetric maps suggested visibility (Figure 2A). The diver who ences) and subsequent maximum like- the existence of this feature, but lacked recorded this footage reported physical lihood search within RAxML (v. 8.2.4) the resolution to define it (Exon and discomfort from caustic water contacting under a GAMMA model of rate hetero- Johnson, 1986; Johnson and Tuni, 1987; his skin when he approached the outer geneity and general time reversible (GTR) Baker et al., 2002). Bottom imagery was line of bubbles. Optical backscatter and substitution matrix. Sequence data are collected at five sites on the Southwest oxidation-​reduction-​potential (ORP) deposited in GenBank under the acces- Extension, with one image presenting signals were observed directly over the sion numbers KU761314-KU761325. evidence of chemolithoautotrophic bac- summit crater, and a minor ORP signal teria commonly associated with hydro- was seen to the north of the Southwest RESULTS thermal venting (Figure 2B). Extension summit at a depth of approx- Edifice Morphology imately 220 m. Minor ORP signals can The summit of Kavachi has an oblong, Hydrothermal Plumes indicate diffuse venting sources on the pockmarked crater measuring approx- Opportunities to sample hydrothermal seafloor (Baker et al., 2016), and given imately 120 m × 75 m with a length- plumes associated with actively erupt- our visual confirmation of bacterial wise strike of 115° and a rim rising to ing submarine volcanoes are often lim- mats on the summit of the Southwest an average of 24 m depth (Figure 1). ited by safety concerns. Those that have Extension, it is reasonable to assume that

FIGURE 2. (A) Oblique view of a line of bubbling gas along the outer edge of Kavachi’s crater with orange, cloudy plume fluids in the background. (B) Downward-looking view of a microbial mat on the summit of the Southwest Extension. (C) Bluefin trevally, (D) snapper, (E) hammerhead shark, and (F) a silky shark observed using a baited drop camera deployed inside the crater.

Oceanography | December 2016 163 this minor anomaly may be associated disperses and/or escapes to the atmo- communities to exploit. Non-vent- with this source. sphere almost immediately upon reaching specific benthic scavengers, deposit feed- A surface drifter measuring atmo- the surface. We were unable to constrain ers, and filter feeders can utilize chemo- spheric CO2 and water temperature at the pH of vented fluids directly inside synthetic biomass to support up to 100% 0, 2, and 5 m depths measured ΔT val- Kavachi’s crater, but a pH of 6.1 was mea- of their nutritional input (MacAvoy et al., ues of >13°C above ambient (approxi- sured in a single water sample collected 2002). Plumes originating from hydro- mately 29°C) over the crater, which per- within the surface plume. This compares thermal vent fields are known to support sisted down-current from the main to pH values ≤5 measured within the cra- increased microbial biomass, which may summit (Figure 3). A >300% step ters of other active submarine volcanoes sustain higher trophic levels in the water increase in atmospheric CO2 concentra- (Staudigel et al., 2006; Kilias et al., 2013), column (Bennett et al., 2013; Dick et al., tion occurred in the surface water over and aligns with observations of acidic 2013; Burd and Thomson, 2015). the bubble zone, indicating bubbling gas (possibly pH <1.0) hydrothermal fluids Extensive microbial mats in and from the summit contained large con- driven by high concentrations of CO2 and around the active crater were visually centrations of CO2 (other gases were not SO2 at the NW Rota-1 submarine volcano distinct, with dense orange- and white-​ measured). The measured unit area flux (Resing et al., 2007). We therefore charac- colored regions observed on the exter- rate was 19.5 kg m–2 d–1, and assuming a terize the plume inside of Kavachi’s crater nal flanks down to approximately 100 m similar rate across the whole surface bub- as a discrete “extreme” environment: hot, water depth. Orange-colored bacterial ble zone, the total flux rate was 153 t d–1. caustic, and particulate-laden. samples colonizing scoriaceous tephra This estimate lies within the lower range collected from the summit at ~24 m of previously reported studies (Burton Biology of the Active Crater depth on the outside of the crater rim et al., 2013). The increased availabil- Seamounts serve as unique and important were used for 16s rRNA clone library ity of dissolved CO2 within the bubble biological habitats that support increased analysis. In total, 12 clones were retrieved zone provides a labile carbon source for biomass and biodiversity of benthic and with an average length of 1,050 base chemolithoautotrophic communities sur- pelagic species (Rogers, 1993; Stocks pairs. Phylogenetic analysis (Figure 4) rounding the venting site. and Hart, 2007). Volcanically active sea- revealed that all clones were related Our observations align with those mounts, defined as those exhibiting fluid/ to Sulfurimonas (Epsilonproteobacteria, made in 2000 by Baker et al. (2002), who gas venting or active eruption, are of par- Campylobacterales, Helicobacteraceae), concluded from their perimeter survey ticular interest as they offer chemosyn- a genus known for growing chemolitho- that Kavachi’s hydrothermal discharge thetic energy pathways for microbial autotrophically using sulfur and CO2 in low-pH hydrothermal systems (Yanagawa 45 AB C et al., 2013). In general, Kavachi clones FIGURE 3. Autonomous drifter were related to sequences found in other

) data collected over Kavachi’s 40 0.2 m active crater. (top) Water tem- iron/sulfur-rich hydrothermal systems, 2 m perature at three depth inter- including the East Pacific Rise and Lau 5 m vals. (bottom) Atmospheric Basin. Kavachi clones fell into one of three 35 CO2 measured at the surface

emperature (°C over roughly the same tran- distinct groups within the Sulfurimonas. T sect as the temperature drifter.

ter Group 1 was related to several pure culture 30 Sections delineated by (A) are Wa upcurrent of the crater, (B) are isolates, although the only highly similar directly over the crater, and sequence (99% identity) was an uncul- 25 00:00 00:30 01:00 01:30 02:00 02:30 (C) are downcurrent. tured environmental clone retrieved from Elapsed Drift Time (hh:mm) the Arctic Ocean in 2002. The closest rel- 0.12 AB C ative of group 2 (95% identity) was a sin- gle clone retrieved from particulate detri- (%)

2 0.10 tus associated with the tubeworm Ridgeia CO 0.08 piscesae, while the closest relative of

0.06 group 3 was from iron-rich hydrothermal sediments. These Sulfurimonas clones 0.04 may represent unique diversity within

face Astmospheric 0.02 the genus, possibly restricted to Kavachi

Sur and similar submarine volcano systems. 0.00 00:00 02:00 04:00 06:00 08:00 Given the presence of Sulfurimonas in Elapsed Drift Time (mm:ss) clone libraries, it is possible that the

164 Oceanography | Vol.29, No.4 orange-colored microbial mats seen on needed to elucidate the role of microbes Caranx melampygus, and a Lutjanus sp. the peak of the Southwest Extension indi- in geochemical cycling at Kavachi. snapper were also seen; notably, these cate the presence of diffuse-flow sulfur- Baited drop-camera deployments groups of fish were impacted the least on and CO2-enriched hydrothermal fluids inside Kavachi’s crater at 50 m depth reefs following a subaerial volcanic erup- on this external feature. However, it is revealed multiple species of fish and zoo- tion in the Mariana Archipelago (Vroom curious that no Zetaproteobacteria were plankton, apparently associated with and Zglicynski, 2011). Appendicularians recovered during clone library analy- active venting processes (Figure 2C–F; (pelagic tunicates) drift in abundance sis. Typically, these bacteria are associ- online supplemental Video S1). Two spe- throughout recordings from inside ated with orange-colored mat material in cies of shark, the scalloped hammer- the crater, similar to an Oikopleura sp. marine hydrothermal systems and indi- head Sphyrna lewini and the silky shark observed in great densities inside a cate active iron oxidation. Organisms Carcharhinus falciformis, approached hydrothermal plume at Okinawa Trough such as Sulfurimonas are typically asso- the baited camera multiple times in an (Lindsay et al., 2015). In two other active ciated with white-colored mats indicative aggressive pattern; in some cases, sharks submarine volcanoes, Vailulu’u Seamount of sulfur oxidation. More thorough geo- appeared to be swimming from greater (American Samoa) and Kolumbo chemical and microbiological analyses are depths inside the crater. Bluefin trevally, (Greece), the craters are dominated by

8 5 Sulfurimonas sp. AST-10 genome (AUPZ01000025) 5 0 Sulfurimonas denitrificans DSM 1251 genome (CP000153) 7 9 Sulfurimonas sp. HDNS4 isolate (LC029408) 100 East Pacific Rise clone 9M32_078 (JQ287031) Lau Basin inactive sulfide clone ABEsIN_D2 (KC682699) East Pacific Rise TrapR2 clone RESET_28B05 (JN874235) Rio Tinto clone RT07B_BI_38 (EF441901) Loihi Seamount clone PVB_63 (U15102) Kavachi clone 3 Kavachi clone 7 group 1 FIGURE 4. Phylogenetic tree of Kavachi clone 6 Kavachi clone 1 16S rRNA clones retrieved from 100 orange-colored microbial mats col- Arctic Ocean clone Arctic96B-13 (AF355050) lected from scoriaceous tephra Kavachi clone 10 5 5 at the crater rim. All 12 clones fell Juan de Fuca hydrothermal clone AV08-BC-37 (JQ712432) into three distinct clades within the Lau Basin inactive sulfide clone TuiMs_LR3F4 (KC682636) genus Sulfurimonas. 7 2 Aespoe hard rock iron-ixodizing biofilm clone 070125-BRIC7-7 (FJ037619) Sulfurimonas gotlandica GD1 genome (AFRZ01000001) 6 5 100 East Pacific Rise hydrothermal vent clone L50-WB7 (DQ071286) East Pacific Rise hydrothermal vent clone L50-WB11 (DQ071281) 7 6 9 9 Mid-Atlantic Ridge iron-rich substrate clone AT-cs10 (AY225615) Sulfurimonas Rio Tinto basin clone RT07B_BI_100 (EF441903) 8 4 Sulfurimonas paralvinellae isolate (AB252048) East Pacific Rise hydrothermal vent clone CH1_22 (AY672505) Logatchev hydrothermal vent field clone 263-66 (FN554146) 5 2 Kavachi clone 5 Kavachi clone 2 9 6 group 2 Kavachi clone 11 100 Kavachi clone 9 Ridgeia piscesae clone HF8GH2b88 (JN662179) 6 5 7 6 Kavachi clone 4 9 9 Kavachi clone 12 group 3 6 4 Kavachi clone 8

5 6 9 9 South Tonga iron-rich hydrothermal sediments clone V1F94b (FJ905733) 9 7 5 9 Kueishan Island white vent clone KSTwh-C1-7-B-006 (JQ611133) Campylobacterales bacterium Ho30-mm isolate (AB301716) 100 East Pacific Rise hydrothermal clone BR2 (EF218991) 8 3 Juan de Fuca Ridge hydrothermal chimney clone Q1-b23 (FR853046) Dudley hydrothermal vent clone 4132B27 (EU555128) 100 Sulfuricurvum sp. EW1 isolate (KF494428) Sulfuricurvum Sulfuricurvum kujiense DSM 16994 genome (CP002355) 5 7 Campylobacter insulaenigrae NCTC 12927 isolate (DQ174183) 100 Campylobacter coli isolate (GQ167676) Campylobacter Campylobacter lari isolate ATCC 35221 (AY621114) 0.05

Oceanography | December 2016 165 microbial mats and “kill zones” where Petrology/Geologic Samples as mid-November 2014 (author Simon carcasses of larger animals such as fish are Three volcaniclastic samples collected Albert, November 16, 2014). Visual anal- found on the seafloor (Sigurdsson et al., from the shallow rim of Kavachi’s crater ysis of thin sections of samples indi- 2006; Staudigel et al., 2006). It is likely that (~25 m depth) during this recent study cates that Kavachi’s explosive eruptions the high crater walls at these sites cause encompass a broad range of eruptive tex- are driven by a combination of pri- physical entrainment and concentration tures, including vesicular scoria, dense mary volatile degassing and phreato- of vent fluids (e.g., Christopoulou et al., lavas, and scoriaceous tephra. While magmatic interactions (Figure 5A,B). 2016), while Kavachi’s crater is relatively the last reported eruption of Kavachi Major element analysis of bulk sam- shallow and subjected to high surface cur- was in 2007, aerial steam columns were ples indicates they are basaltic and rela- rents that allow rapid mixing to occur. reported by shore observers as recently tively mafic at ~6 wt.% MgO. Trace ele- ments (Figure 5C) show patterns typical of arc lavas, although Kavachi Ba/La and Ba/Nb ratios are among the highest of the A entire Solomon Island arc, suggesting an extreme composition for the subducted slab-derived fluid (Niu and Batiza, 1997; Schuth et al., 2004; König et al., 2007; Schuth et al., 2009). Ratios of moder- ately to highly incompatible field strength elements, which are thought to reflect the mantle source composition inde- pendent of slab-derived influences, are B also among the highest in the Solomon Islands (e.g., Zr/Nb = 93–95), suggest- ing that the mantle source of Kavachi is highly depleted. Given Kavachi’s posi- tion between the trench and the main Solomon volcanic front, the volcano likely taps a forearc mantle that is highly depleted due to prior melting beneath the 100 main arc front volcanoes. C Kavachi Lavas (This Study) Solomon Islands (Schuth et al. [2004, 2009]; König et al. [2007]) DISCUSSION Depleted MORB (Niu & Batiza, 1997) Our observations of secondary and ter- 10 tiary consumers inside Kavachi’s hydro- thermal plume contribute to ongoing research into the physiological and behavioral resiliency of marine animals Sample/NMORB 1 to increased temperature, acidity, and turbidity. This is most relevant in the con- text of climate change, as well as increased water turbidity and sediment resuspen- 0.1 sion from deep-sea mining activities. Rb Ba U Nb La Pb Nd Sm Zr Eu Tb Ho Er Yb Cs Th Ta K Ce Pr Sr Hf Ti Gd Dy Y Tm Lu The ecosystem that is supported by the FIGURE 5. (A) Photomicrographs of basaltic lava from Kavachi summit crater with phenocrysts extreme environment of Kavachi’s crater of plag-cpx-ol set in a groundmass of microlite-rich glass. The left image is transmitted light, may offer clues to the types of animals the right image is crossed polars, and each image is 2.5 mm wide. (B) Photomicrograph of that have survived past major changes basaltic scoria from Kavachi summit crater with phenocrysts of plag-cpx-ol and abundant vesicles (left image is transmitted light, right image is crossed polars). (C) Normal mid-ocean in ocean chemistry, and those that will ridge basalt (NMORB)-normalized trace element diagram after Hofmann (1988). Thick, solid thrive in future ocean conditions. lines are three whole-rock Kavachi lava/tephra samples from this study, and the thin solid Appendicularians demonstrate a pos- line is a highly depleted NMORB for reference. Compositions are normalized to the NMORB of Sun and McDonough (1989). Raw data for the Kavachi Lavas are provided in the online itive response to decreased pH val- supplemental Table S1. ues (Troedsson et al., 2013), which may

166 Oceanography | Vol.29, No.4 explain the apparent plume-associa- be representative of ocean basin-scale of marine animals to rapid changes in tive behavior seen among Oikopleura sp. megaplume events caused by periods of their environments, as well as the abil- Glass tunicates (gelatinous chordates in increased volcanism in Earth’s geologic ity of the ecosystem to recover from an the same subphylum as appendicularians) history (e.g., Sinton and Duncan, 1997). eruptive event. If gelatinous zooplankton, were the only observed metazoan living A further understanding of the physiol- sharks, and other fish species have a par- inside the Kolumbo submarine caldera kill zone (Sigurdsson et al., 2006; Carey et al., 2013). Given their apparent resil- ience to hydrothermal fluids and their unique ability to filter-feed on picoplank- ton (Bedo et al., 1993; Gorsky et al., 1999; The ecosystem that is supported by the Ribes et al., 2003; Lesser and Slattery, extreme environment of Kavachi’s crater may offer 2015), animals such as Oikopleura sp. and glass tunicates could mediate an energy clues to the types of animals that have survived pathway for suspended chemolithoauto- past major“ changes in ocean chemistry, and those troph production into higher trophic lev- els. While no study has directly investi- that will thrive in future ocean conditions. . gated oceanic climate change effects on bluefin trevally or snapper, cardinalfish and damselfish exhibit decreased meta- bolic performance and significant mortal- ity when exposed to temperatures above ” 32°C (Munday et al., 2009; Johansen and ogy and behavior of organisms that thrive ticular tolerance for hot and acidic water, Jones, 2011) and depressed antipreda- in these environments could offer new do these groups have a greater chance tor responses when exposed to increased insights into the evolutionary history of of surviving human-induced changes to

CO2 concentrations (Ferrari et al., 2011; marine animals. ocean chemistry and periods of increased Munday et al., 2014). Elevations in water This study offers rare observations of submarine volcanism on a global scale? turbidity are a well-established stressor one of the most active submarine volca- What happens to the crater community to reef fish (Wenger et al., 2011, 2013; noes in the world. Kavachi’s ephemerally before, during, and after an eruption, and Hess et al., 2015). Sharks and other elas- active summit area consists of a shallow how often do these cycles occur? Kavachi mobranchs demonstrate behavioral ther- oblong crater and a small secondary peak represents a fascinating natural labora- moregulation with an affinity for warmer to the southwest that exhibits signs of tory for investigating these questions and temperatures (Schlaff et al., 2014), and diffuse-flow hydrothermal venting. Mafic remains full of mysteries to explore. while there is evidence suggesting that basaltic lavas collected from the sum- SUPPLEMENTAL MATERIAL ocean acidification may have a negative mit are among the most extreme compo- Supplemental Figure S1, Table S1, and Video V1 are effect on odor tracking in sharks (Dixson sitions in the Solomon Island arc, likely available at https://doi.org/10.5670/oceanog.2016.85. et al., 2015), there are also indications of reflecting an unusual tectonic position REFERENCES physiological and behavioral resiliency between the trench and the main line of Baker, E.T., G.J. Massoth, C.E. de Ronde, J.E. Lupton, (Heinrich et al., 2014, 2015). arc volcanoes. Inside the crater, vigor- and B.I. McInnes. 2002. Observations and sam- pling of an ongoing subsurface eruption of Importantly, Kavachi’s hydrothermal ously vented CO2-rich gas and warm Kavachi volcano, Solomon Islands, May 2000. plume, seen during the quiescent volca- turbid water convect toward the surface Geology 30(11):975–978, https://doi.org/10.1130/​ 0091-7613(2002)030<0975:OASOAO>2.0.CO;2. nic phase when these observations were and are dispersed by the prevailing cur- Baker, E.T., A.J. Resing, R.M. Haymon, V. Tunnicliffe, made, is comparatively extreme relative rents. Bacteria collected from Kavachi’s J.W. Lavelle, F. Martinez, V. Ferrini, S.L. Walker, and K. Nakamura. 2016. How many vent fields? to climate change-driven ocean tempera- summit indicate these fluids are enriched New estimates of vent field populations on ocean ture and acidification effects. Projections in sulfur, and high-temperature and ridges from precise mapping of hydrothermal dis- charge locations. Earth and Planetary Science to the year 2100 agree on a maximum low-pH measurements were made inside Letters 449:186–196, https://doi.org/10.1016/​ ∆−0.4 pH and ∆+4°C for surface seawa- the surface plume. Surprisingly, this hos- j.epsl.2016.05.031. Bedo, A.W., J.L. Acuna, D. Robins, and R.P. Harris. ter on a global scale (Field et al., 2014), tile environment hosts a vibrant ecosys- 1993. Grazing in the micron and the sub-​micron compared to our estimated ∆−1.9 pH tem, including gelatinous zooplankton, particle size range: The case of Oikopleura dioica (Appendicularia). Bulletin of Marine and ∆+13°C between Kavachi’s plume reef fish, and sharks. The presence of these Science 53(1):2–14. and the surrounding surface waters. animals in such extreme conditions poses These extreme conditions, however, may new questions centered on the resiliency

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tions and subduction zone geometry. Journal of marine sediment under high-CO2 and low-pH Petrology 50(5):781–811, https://doi.org/10.1093/ extremes. The ISME Journal 7(3):555–567, petrology/egp019. https://doi.org/10.1038/ismej.2012.124. Sigurdsson, H., S. Carey, M. Alexandri, G. Vougioukalakis, K. Croff, C. Roman, ACKNOWLEDGMENTS D. Sakellariou, C. Anagnostou, G. Rousakis, The authors wish to thank the Solomon Islands gov- C. Loakim, and A. Gogou. 2006. Marine inves- ernment and the Peava Village community for per- tigations of Greece’s Santorini volcanic field. mitting and assisting in our research activities. We Eos, Transactions American Geophysical thank Fabio Estaban Amador, Eric Berkenpas, and the Union 87(34):337–339, https://doi.org/​ National Geographic Society/Waitt Grants Program 10.1029/2006EO340001. for making this project possible. Sharon Walker pro- Sinton, C.W., and R.A. Duncan. 1997. Potential links vided valuable reviews and discussion that greatly between ocean plateau volcanism and global improved this manuscript, and the authors also wish ocean anoxia at the Cenomanian-Turonian to thank two anonymous reviewers for their support- boundary. Economic Geology 92:836–842, ive and constructive criticism. The NOAA/PMEL Vents https://doi.org/10.2113/gsecongeo.92.7-8.836. program provided plume-sensing instrumentation. Staudigel, H., S.R. Hart, A. Pile, B.E. Bailey, E.T. Baker, This work was supported by National Geographic S. Brooke, D.P. Connelly, L. Haucke, C.R. German, Society grants #W324-14 and W364-14 to B.T. Phillips, I. Hudson, and others. 2006. Vailulu’u Seamount, and additional funding was provided by the University Samoa: Life and death on an active sub- of Rhode Island’s Graduate School of Oceanography marine volcano. Proceedings of the National Alumni Association. Academy of Sciences of the United States of America 103(17):6,448–6,453, https://doi.org/​ 10.1073/pnas.0600830103. AUTHORS Stocks, K.I., and P.J. Hart. 2007. Biogeography Brennan T. Phillips ([email protected]) and biodiversity of seamounts. Pp. 255–281 in is Postdoctoral Fellow, Harvard University, John Seamounts: Ecology, Fisheries, and Conservation. A. Paulson School of Engineering and Applied Blackwell Fisheries and Aquatic Resources Series, Sciences, Cambridge, MA, USA, and formerly a stu- Blackwell, Oxford, UK. dent at the Graduate School of Oceanography, Sun, S.S., and W.F. McDonough. 1989. Chemical University of Rhode Island (URI), Narragansett, RI, and isotopic systematics of oceanic basalts: USA. Matthew Dunbabin is Principal Research Implications for mantle composition and pro- Fellow, Queensland University of Technology, cesses. Geological Society, London, Special Brisbane, Queensland, Australia. Brad Henning is Publications 42(1):313–345, https://doi.org/​ Remote Imaging Engineer, National Geographic 10.1144/GSL.SP.1989.042.01.19. Remote Imaging Team, Washington, DC, USA. Troedsson, C., J.M. Bouquet, C.M. Lobon, Corey Howell operates the Wilderness Lodge, A. Novac, J.C. Nejstgaard, S. Dupont, S. Bosak, Gatokae Island, Solomon Islands. Alex DeCiccio H.H. Jakobsen, N. Romanova, L.M. Pankoke, and is a photographer for the Graduate School of others. 2013. Effects of ocean acidification, tem- Oceanography, URI, Narragansett, RI, USA. perature and nutrient regimes on the appendicular- Ashton Flinders is a student at the Graduate School ian Oikopleura dioica: A mesocosm study. Marine of Oceanography, URI, Narragansett, RI, USA. Biology 160(8):2,175–2,187, https://doi.org/10.1007/ Katherine A. Kelley is Associate Professor, Graduate s00227-012-2137-9. School of Oceanography, URI, Narragansett, RI, USA. Jarrod J. Scott is Postdoctoral Research Associate, Bigelow Laboratory for Ocean Sciences,

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