Mnemiopsis Leidyi (Ctenophora, Lobata): Planktonic Or Benthic Methods?

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SHORT COMMUNICATION

Sampling ﬁeld distributions of Mnemiopsis leidyi (Ctenophora, Lobata): planktonic or benthic methods?

J. H. COSTELLO* AND H. W. MIANZAN1 BIOLOGY DEPARTMENT, PROVIDENCE COLLEGE, PROVIDENCE, RI -, USA AND 1CONICET-INIDEP, PO BOX ,  MAR DEL PLATA, ARGENTINA

*CORRESPONDING AUTHOR: [email protected]

SCUBA observations conﬁrm dense aggregations of the ctenophore Mnemiopsis leidyi in surface and bottom layers of waters off southern Argentina. These observations are consistent with results from prior studies indicating directed vertical migration of M. leidyi.

The lobate ctenophore Mnemiopsis leidyi occupies coastal bottom (Figure 2). During the time (13:00 h local time, waters over a wide latitudinal range: 40°N–46°S 10:00 h GMT, on 12 January 2002) of the most concen- (Harbison and Volovik, 1994; Mianzan, 1999). Although trated near-bottom ctenophore layers (average water endemic only to the eastern coasts of the Americas, M. temperature 20°C), few ctenophores were found near the leidyi has successfully invaded the Black Sea (Shushkina surface. and Musayeva, 1990; Shushkina and Vonogradov, 1991; Visual observations indicated that the location of the Studenikina et al., 1991; Zaitsev, 1992) and, more recently, bulk of ctenophores within the water column varied. On the Caspian Sea (Ivanov et al., 2000). Mnemiopsis leidyi is a several subsequent dives, the highest concentrations were highly versatile planktonic predator (Waggett and found within a meter of the surface (Figure 3). At other Costello, 1999; Costello et al., 1999) with potentially high times, the ctenophores appeared to be concentrated ingestion rates (Reeve et al., 1978; Kremer, 1979) that either near the bottom or at the surface, with relatively make it one of the most environmentally troublesome few individuals intermediate between the two depths. marine invaders (Harbison and Volovik, 1994). Local divers (R. Bebote Vera, personal communication) As with other planktonic predators, accurate quantita- noted that distributions of M. leidyi in these waters are tive estimates of abundance and distribution are essential often characterized by such layered aggregations. for understanding the trophic impacts of M. leidyi. Popu- Although environmental factors such as local tidal or lation estimates are typically based upon conventional net wind patterns may influence the formation of these sampling of the water column [e.g. (Burrell and Van ctenophore aggregations, no definitive evidence currently Engel, 1976; Mutlu, 1999)]. But how appropriate are exists to link aggregation formation with specific environ- these methods for quantification of M. leidyi distributions? mental variables. Direct visual observations throughout the water column This is the first report of direct visual observations of via SCUBA of M. leidyi from waters near Puerto Madryn, near-bottom aggregation formation by M. leidyi.However, Nuevo Gulf, Argentina (Figure 1), cast doubt on the suit- results of other studies provide evidence that the phenom- ability of conventional methodological approaches for enon we report was not a unique occurrence, but instead field sampling of ctenophores in that region. Dense aggre- may be an important and regular feature of M. leidyi gations of M. leidyi were observed to form a concentrated distribution patterns in some locales. Mnemiopsis leidyi layer within 1 m from the bottom (total water depth 5 m), dominated the zooplankton biomass at a tidal mixing with most ctenophores concentrated within 0.5 m from the front off Valdés Península, close to the sampling location

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Study area

Patagonia Valds Peninsula Nuevo Gulf Puerto an Madryn ce O tic lan At

66 65 64 63 W

Fig. 1. Location of the sample region at Puerto Madryn, Argentina ().

of the present work. There M. leidyi represented 60% of because conventional net sampling does not provide the total organic carbon and was more abundant at the sufficient information on ctenophoran vertical distri- stratified zone of the front (Mianzan and Guerrero, 2000). butions. If, as we observed at Puerto Madryn, the The population was able to perform vertical movements ctenophores are concentrated within a meter (often within of up to 70 m and, at times, the population was concen- 0.5 m) of the bottom, then conventional net tows would trated close to the bottom (H. W. Mianzan, unpublished miss the chief mass of ctenophores. Even oblique net tows data). Lobate stage M. leidyi can easily swim these would need to place the net mouth, not the cod end, distances on a daily or semidiurnal cycle. For example, an almost on the bottom in order to sample the near-bottom individual of 4 cm total length (lobes open) swimming at layer. Epibenthic sleds could be useful, but are not typi- 0.65 cm s–1 ( J. H. Costello, unpublished data) can traverse cally employed in ctenophore distribution studies. There- a 70 m vertical distance in 3 h. Wet biomass of M. leidyi fore, if near-bottom ctenophore layer formations are in near-bottom (<10 m from substrate) samples at the common, biases inherent in conventional net sampling tidal mixing front off Valdés Península were as high as could limit quantification and reporting of these patterns. 700 ml per 10 m3 (Alheit et al., 1991). These bottom layers Several alternative methodologies for sampling were dense enough to form a clear signal using a 38 kHz zooplankton distributions can quantify layers formed by acoustic system (Alvarez Colombo et al., 2000). The gelatinous zooplankton. Acoustic methods are not potential trophic importance of near-bottom layers of routinely used to record distribution patterns of most Mnemiopsis is indicated by the presence of these gelatinous zooplankton but rather low-frequency acoustic ctenophores in the gut contents of a variety of demersal systems have provided insight into gelatinous plankton fishes from the Argentine continental shelf (Mianzan et al., distributions in the field. Population distributions of the 1996). salp Iasis zonaria (Mianzan et al., 2001), the hydromedusa The generality of horizontal layer formation, particu- Aequorea victoria (Brierley et al., 2001) and the scypho- larly near-bottom layering, by M. leidyi remains un- medusa Aurelia aurita (Mutlu, 1996; Toyokawa et al., 1997) resolved. Since the formation of dense near-bottom have been documented using common low-frequency aggregations by M. leidyi has not been reported from other (38–50 kHz) acoustic systems. Even ctenophores (Pleuro- geographical regions, this pattern may represent a local- brachia bachei) have been recorded by acoustic methods ized, population-specific phenomenon. Alternatively, (Monger et al., 1998). Perhaps the most informative these patterns may be more widespread, but unnoticed, combination of quantitative methods involves directed

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Fig. 2. Top: M. leidyi ctenophores (individuals are 5–8.5 cm in total body length) aggregated in near-bottom waters at Puerto Madryn, Argentina, on January 8, 2002. Bottom: diver passing through the near-bottom ctenophore layer on same date. The diver’s arm is in contact with the bottom and no ctenophores are visible above the diver.

net sampling guided by acoustic data. It was this approach operated vehicles [e.g. (Davis et al., 1992)] can be used to that was used to assess dense near-bottom layers of M. locate and describe heterogeneous distributions of leidyi south of the Valdés Península tidal front (Alvarez gelatinous zooplankton. Colombo et al., 2000), and in the El Rincon area (Alvarez The choice of sampling methodology depends upon a Colombo et al., 2003) of Argentina. Alternatively, direct variety of factors affecting speciﬁc study situations. observation by either SCUBA, as in this report, However, vertical migration and the formation of near- submersibles [e.g. (Mackie and Mills, 1983)] or remotely bottom aggregations can affect abundance estimates as

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Fig. 3. Individual M. leidyi aggregated in surface waters at Puerto Madryn, Argentina, on January 9, 2002. Note the distribution of ctenophores relative to the meter stick held vertically from the surface by the diver.

well as our understanding of trophic interactions involv- Patagonia. IV° Jornadas Nacionales de Ciencias del Mar. Puerto ing ctenophores. Therefore, whatever the sampling Madryn, Argentina. 11–15 September, 29 (abstract). approach selected, studies of M. leidyi distribution and Alvarez Colombo, G., Mianzan, H. and Madirolas, A. O. (2003) abundance patterns should consider the potential for Acoustic characterization of gelatinous plankton aggregations: four study cases from the Argentine continental shelf. ICES J. Mar. Sci., in near-bottom aggregations and vertical migration. press. Brierley, A. S., Axelsen, B. E., Buecher, E., Sparks, C., Boyer, H. and ACKNOWLEDGEMENTS Gibbons, M. J. (2001) Acoustic observations of jellyfish in the Namibian Benguela. Mar. Ecol. Prog. Ser., 210, 55–66. We are indebted to B. Sullivan, C. Suchman and S. P. Burrell, V.G. and Van Engel, W. A. (1976) Predation by and distribution Colin for their critical reading and comments on the of a ctenophore, Mnemiopsis leidyi A. Agassiz, in the York River manuscript. Funding for this project was provided by the Estuary. Estuarine Coastal Mar. Sci., 4, 235–242. US NSF (OCE 9218507 and OCE-9820172) to J.H.C. Costello, J. H., Loftus, R. and Waggett, R. (1999) The influence of prey and UNMdP 15/E139 and Fundación Antorchas 13817- detection on capture success by the ctenophore Mnemiopsis leidyi 5 to H.W.M. We thank Dr M. Haller (CENPAT) for feeding upon adult Acartia tonsa and Oithona colcarva copepods. Mar. Ecol. Prog. Ser., 191, 207–216. support in using CONICET facilities at Puerto Madryn, Argentina. SCUBA and field support of R. ‘Bebote’ (Big Davis, D. L. and Pilskain, C. H. (1992) Measurements with underwater video: camera field width calibration and structured lighting. Mar. Baby) Vera and D. Galván were greatly appreciated. This Technol. Soc. J., 26, 13–19. is INIDEP contribution no. 1243. Harbison, G. R. and Volovik, S. P. (1994) The ctenophore, Mnemiopsis leidyi, in the Black Sea: a holoplanktonic organism transported in the ballast water of ships. In Nonindigenous Estuarine and Marine Organisms REFERENCES (NEMO). Proceedings of the Conference and Workshop, Seattle, WA, Alheit, J. et al. (1991) SARP studies on Southwest Atlantic anchovy, April 1993. US Department of Commerce, NOAA, Washington, Engraulis anchoita, off Argentina, Uruguay and Brazil. ICES IOC Rep. DC, pp. 25–36. Ser. C. M. 1991/L, 46, Session V, 32 pp., figures 1–10. Ivanov, V., Kamakin, A. M., Ushivtzev, V.B., Shiganova, T.A., Zhukova, Alvarez Colombo, G., Mianzan, H. and Madirolas, A. O. (2000) Carac- O., Aladin, N., Wilson, S. I., Harbison, G. R. and Dumont, H. J. terización acústica de la estructura espacial de las agregaciones del (2000) Invasion of the Caspian Sea by the comb jellyfish Mnemiopsis ctenóforo Mnemiopsis leidyi y de la hydromedusa Aequorea sp. en la leidyi (Ctenophora). Bio. Invasions, 2, 255–258.

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