Henschke et al. Marine Biodiversity Records (2016) 9:21 DOI 10.1186/s41200-016-0023-8 MARINE RECORD Open Access An observation of two oceanic salp swarms in the Tasman Sea: Thetys vagina and Cyclosalpa affinis Natasha Henschke1,2,3*, Jason D. Everett1,2,3 and Iain M. Suthers1,2,3 Abstract Background: Large oceanic salps are rarely encountered. The highest recorded biomasses of the salps Thetys vagina (852 g WW m−3)andCyclosalpa affinis (1149 g WW m−3) were observed in the Tasman Sea during January 2009. Results: Due to their fast sinking rates the carcasses and faecal pellets of these and other large salps play a significant role in carbon transport to the seafloor. We calculated that faecal pellets from these swarms could have contributed up to 67 % of the mean organic daily carbon flux in the area. This suggests that the flux of carbon from salp swarms are not accurately captured in current estimates. Conclusion: This study contributes information on salp abundance and biomass to a relatively understudied field, improving estimates for biogeochemical cycles. Background (Henschke et al., 2013) can increase the carbon flux in an The role of gelatinous zooplankton, such as salps, pyro- area up to ten-fold the daily average (Fischer et al., 1988) somes and cnidarians, in ocean food webs and biogeo- for a sustained period of time (Smith et al. 2014). chemical cycling has garnered increased attention in Due to their regular occurrence (Henschke et al., recent years (Lebrato et al., 2011; Henschke et al., 2013; 2014) and coastal dominance (Henschke et al 2011), Lebrato et al., 2013; Smith et al. 2014). Salps (Phylum: smaller salps such as Thalia democratica are studied Thaliacea, Order Salpidae) in particular, are significant with greater frequency. Although these smaller salps contributors to oceanic carbon flux. They have the highest contribute significantly to biogeochemical cycling with per-individual filtration rates of all marine zooplankton fil- fast growth rates (Heron, 1972a) and faecal pellets, car- ter feeders (Alldredge and Madin, 1982) consuming parti- casses of these smaller salps rarely sink as they are neu- cles across three orders of magnitude (1 μmupto1mm trally buoyant (Tsukamoto et al., 2009). The carcasses of in size; Vargas and Madin, 2004; Sutherland et al., 2010) larger salps however, sink rapidly and have the potential using a fine mucous net that is continuously secreted and to reach the sea floor in less than 2 days (Henschke et al., fed toward the oesophagus. This efficient feeding mechan- 2013; Lebrato et al., 2013). Due to the combined input ism and their alternating sexual and asexual life-cycle re- from both faecal pellets and carcasses, swarms of larger − sults in fast individual (up to 21 % in length h 1;Heron, salps are thought to play a greater role in carbon export − 1972a) and population (up to 2.5 d 1; Heron, 1972b; (Smith et al. 2014). Of significance however, is that very Henschke et al., 2015) growth rates. As a result, salps form little is known about the distribution and abundance of large swarms that often reach abundances greater than larger salps as they are oceanic and rarely encountered. − − 1000 individuals m 3 (~6 kg WW m 3; Henschke et al., The aim of this study is to document swarm observations 2014) and persist for up to 6 months (Smith et al. 2014). from the Tasman Sea of two large salps: Thetys vagina and When salps occur in high abundances, their fast-sinking Cyclosalpa affinis and compare these biomasses to previ- faecal pellets (Bruland and Silver, 1981) and carcasses ous observations. Thetys vagina is often observed opportunistically as a * Correspondence: [email protected] single individual and little is known about their ecology 1Evolution and Ecology Research Centre, University of New South Wales, (Nakamura and Yount, 1958; McAlice, 1986; Sims, 1996; Sydney, NSW 2052, Australia 2 Stone and Steinberg, 2014). Large biomasses (900 t WW Sydney Institute of Marine Science, Building 22, Chowder Bay Road, −3 Mosman, NSW 2088, Australia km )ofT. vagina have been observed in the Japan Sea Full list of author information is available at the end of the article (Iguchi and Kidokoro, 2006) and Tasman Sea (Thompson, © 2016 Henschke et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Henschke et al. Marine Biodiversity Records (2016) 9:21 Page 2 of 5 1948; Henschke et al., 2013). Although T. vagina has been Methods found across a wide temperature (7–20 °C) and salinity Salp samples were collected onboard the R.V. Southern (33.9–35.6) range (Thompson, 1948; Iguchi and Kidokoro, Surveyor in the austral summer (25–29 January 2009) in 2006; Henschke et al., 2013), there appears to be no sea- the western Tasman Sea (Fig. 1). Sampling stations were sonality to T. vagina swarms (Henschke et al 2013). located at Gascoyne Seamount (n = 5) and on the Chal- In the Japan Sea and Tasman Sea, higher T. vagina bio- lenger Plateau (n = 1). Gascoyne Seamount is part of the mass occurred in areas of higher chlorophyll a (Iguchi Tasmantid Seamount Chain in the Tasman Sea, and rises and Kidokoro, 2006; Henschke et al., 2013). As seamounts to 93 m below the surface from a bottom depth of have been found to promote localised upwelling (Boehlert 4000 m (Quilty, 1993). The Challenger Plateau is a large and Genin, 1987; Suthers, 1996), this is one factor that submarine plateau west of New Zealand, with depths may have encouraged the T. vagina population to aggre- varying from 500 to 1500 m, and is considered to be a gate around Gascoyne Seamount in this report. region of low pelagic productivity (Wood, 1991). Although the ecology of Cyclosalpa affinis is well stud- At each sampling station a Seabird SBE911-plus Con- ied (e.g. Madin, 1974; Madin et al., 1981; Vargas and ductivity–Temperature–Depth (CTD) recorder equipped Madin, 2004), their distribution is not well known. Unlike with an AquaTracker Mk3 fluorometer (Chelsea, UK) was T. vagina, the relationship between upwelling events and used to record salinity, temperature, and fluorescence, re- C. affinis populations is unknown. Long-term studies have spectively. Salps were sampled at the surface with a neu- found that C. affinis generally occurs in low numbers ston net (0.75 m × 0.75 m, 500 μmmesh;n = 2) and from − (<30 g WW m 3) and has been characterised as a cool- 0 to 40 m using a rectangular mid-water trawl (RMT; phase species, occurring after intrusions of cooler high 1 m × 1 m, 1 mm mesh, double-oblique tows; n =1).The latitude water (Lavaniegos and Ohman, 2003). However, neuston net was towed for 5 min, and the RMT for − C. affinis has also been found in the subtropical Tasman 30 min, both at 1.5 m s 1. All tows were undertaken at Sea (32.8°S and 32.57°S) and the warmer parts of the night (2100–0200 h). Immediately after sampling, zoo- Indian, Pacific and Atlantic oceans (Thompson, 1948) sug- plankton were preserved in 5 % formaldehye solution. gesting that its temperature tolerance may be quite broad. Salps were identified to species and total length and wet Fig. 1 Location plot showing sampling locations in the Tasman Sea. Overlaid is satellite derived a) sea surface temperature and b) chlorophyll a. Sampling stations on Gascoyne Seamount are represented by squares (n = 5) and Challenger Plateau is represented by triangles (n =1) Henschke et al. Marine Biodiversity Records (2016) 9:21 Page 3 of 5 − − weight was measured for each individual. Due to salps be- was 851.7 ± 280.6 g WW m 3 (12.7 mg C m 3;Fig.2d). ing damaged in the RMT net, total length of salps from These values are higher than biomasses previously sam- − the RMT samples could not be measured. Carbon calcula- pled in the Japan Sea (maximum of 0.9 g WW m 3;Iguchi tions were based on carbon-length relationships previ- and Kidokoro, 2006) and Tasman Sea (maximum of 0.7 g − ously established for T. vagina (Henschke et al., 2013) and WW m 3; Henschke et al., 2013). At one station during C. affinis (Madin et al., 1981). Pearson correlations were sampling, the weight of high abundances of T. vagina tore undertaken to determine if there were any relationships the RMT net. Higher biomasses in the oblique tows (vs. between salp biomass and location to the seamount. neuston tows) suggest that T. vagina were more abundant deeper in the water column (Fig. 2d). Aggregation of salp Results and discussion biomass in the top 40 m is consistent with previous re- The Gascoyne Seamount transect extended for 38 km search that has found that 98 % of T. vagina abundances crossing west-east over the seamount. At the time of sam- occurred in the top 200 m during both day and night pling, sea surface temperature at Gascoyne Seamount was (Henschke et al., 2013). There is no known data on verti- ~22 °C compared to Challenger Plateau which was cooler cal migration by T. vagina and all samples in this study (~19 °C) and had higher chlorophyll a concentrations were undertaken only at night, but anecdotal observations (Fig.