University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- ubP lished Research US Geological Survey 11-23-2007 Persistent near-bottom aggregations of mesopelagic animals along the North Carolina and Virginia continental slopes John V. Gartner Jr. Natural Science Department SP/G, [email protected] Kenneth J. Sulak Florida Integrated Science Center, US Geological Survey,, [email protected] Steve W. Ross Center for Marine Science, University of North Carolina, [email protected] Ann Marie Necaise Center for Marine Science, University of North Carolina Follow this and additional works at: http://digitalcommons.unl.edu/usgsstaffpub Part of the Geology Commons, Oceanography and Atmospheric Sciences and Meteorology Commons, Other Earth Sciences Commons, and the Other Environmental Sciences Commons Gartner, John V. Jr.; Sulak, Kenneth J.; Ross, Steve W.; and Necaise, Ann Marie, "Persistent near-bottom aggregations of mesopelagic animals along the North Carolina and Virginia continental slopes" (2007). USGS Staff -- Published Research. 1064. http://digitalcommons.unl.edu/usgsstaffpub/1064 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- ubP lished Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Mar Biol (2008) 153:825–841 DOI 10.1007/s00227-007-0855-1 RESEARCH ARTICLE Persistent near-bottom aggregations of mesopelagic animals along the North Carolina and Virginia continental slopes John V. Gartner Jr · Kenneth J. Sulak · Steve W. Ross · Ann Marie Necaise Received: 22 August 2006 / Accepted: 22 October 2007 / Published online: 23 November 2007 © Springer-Verlag 2007 Abstract Submersible observations during four missions widespread and persistent phenomenon along the continental over the North Carolina and Virginia continental slopes slope of the southeastern US Aggregations may exploit (184–900 m) documented the occurrence of large aggrega- areas of enhanced food resources at the bottom. tions of mesopelagic Wshes and macronektonic inverte- brates near or on the bottom. Aggregated mesopelagics formed a layer up to tens of meters deep positioned from Introduction a few centimeters to 20 m, usually <10 m, above the substrate. Aggregations were numerically dominated by The presence of mesopelagic animals in close proximity to microvores, notably the myctophid Wsh Ceratoscopelus the bottom is not unusual in waters where the seaXoor inter- maderensis and the penaeid shrimp Sergestes arcticus. sects the lower end of their migratory depth ranges along Consistently present but in relatively lower numbers, were continental slopes, seamounts and islands. The normal diel mesopelagic predators, including the paralepidids Notolepis vertical migration of mesopelagic fauna may be disrupted rissoi and Lestidium atlanticum, the eel Nemichthys scol- or truncated by proximity to land, abrupt changes in bottom opaceus, the stomiid Wshes Chauliodus sloani and Stomias topography (e.g., seamounts), and in upwelling areas boa ferox, and squids Illex spp. Near-bottom aggregations (Isaacs and Schwartzlose 1965; Kinzer 1977; Young and do not appear to be an artifact due to attraction to the sub- Blaber 1986; Genin 2004). For some mesopelagic species, mersible. Based on submersible observations in three areas larger, adult members may adopt a benthopelagic lifestyle. in 4 years spanning a decade, near-bottom aggregations These species discontinue or restrict vertical migrations, of midwater organisms appear to be a geographically remaining in deep waters, often near bottom (<5 m altitude) but not resting on the substrate, to feed or avoid predation (Marshall and Merrett 1977; Marshall 1980; Gartner 1991; Communicated by P.W. Sammarco. Stefanescu and Cartes 1992; McClain et al. 2001). These J. V. Gartner Jr (&) interactions of mesopelagic species with the bottom have Natural Science Department SP/G, St. Petersburg College, been considered temporary and incidental to vertical migra- 6605 5th Avenue N, St. Petersburg, FL 33711, USA tion (e.g., Isaacs and Schwartzlose 1965; Pereyra et al. e-mail: [email protected] 1969; Marshall and Merrett 1977; Marshall 1980), yet there K. J. Sulak is increasing evidence that they are important to benthic, Florida Integrated Science Center, benthopelagic and demersal trophodynamics (Gordon et al. US Geological Survey, 7920 NW 71st Street, 1995; Gartner et al. 1997; Merrett and Haedrich 1997; Gainesville, FL 32653, USA e-mail: [email protected] Cartes et al. 2001; Genin 2004; Madurell and Cartes 2005). Numerical estimations of mesopelagic animals observed S. W. Ross · A. M. Necaise from submersibles either in midwater or near the bottom Center for Marine Science, are rare and inconclusive. Visual counts during one daytime University of North Carolina at Wilmington, 5600 Marvin Moss Lane, Wilmington, NC 28409, USA dive (J. Craddock, personal communication cited by Mar- e-mail: [email protected] shall and Merrett 1977) of two species of myctophid Wshes 123 826 Mar Biol (2008) 153:825–841 near the bottom suggested low densities (one individual per and around the bases of these banks are rubble zones of m3 at 1,025 m), while Auster et al. (1992) observed dense dead coral branches, which extend up to hundreds of meters near-bottom aggregations of mixed mesopelagic species on away from the mounds. These ridges and reef mounds rise two dives, one made during the day from 390 to 610 m bot- as much as 100 m from the open substrate and accelerate tom depth and one at night at 510 m bottom depth. These bottom currents which favor attached Wlter-feeding corals, 1992 data may be the Wrst night observations of near-bot- sponges, and other biota. The deep coral banks and sur- tom aggregations (NBA), suggesting a lack of the expected rounding rubble zones concentrate biota in much the same upward migration. Other observers from submersibles have way as shallow coral reefs (Ross et al. unpublished data). reported high numerical densities of mesopelagic animals at midwater depths, as expected (Backus et al. 1968; Auster Submersible observations and sampling et al. 1992). As noted above, components of the mesopelagic fauna Visual and video camera observations from the DSRV occur frequently on various continental slopes, topographic Johnson-Sea-Link (JSL) submersible were conducted on highs, or upwelling areas during the day; however, the issue the upper to middle continental slopes (184–900 m bottom that we address here is the persistence of this phenomenon depth) oV North Carolina and Virginia during four cruises on a diel basis. In contrast to the diel vertical migration par- (1991, 1992, 2000, 2001; Table 1; Fig. 1). We made two adigm for mesopelagic fauna, i.e., rising en masse to form a 1.2–3.0 hr daytime JSL dives per day, one in the morning night-time layer in shallower water, we present evidence and one in the afternoon. In 1991 and 1992, we only used that certain migratory mesopelagic Wsh and crustacean spe- the externally mounted JSL video camera to record inter- cies regularly form dense (>10 individuals/m3) and persis- mittently during descent and continuously while on the bot- tent aggregations near the bottom over the continental slope tom on each dive. Because we increased our attention to of the western North Atlantic Ocean at depths of 300– water column phenomena, in 2000 and 2001, we supple- 900 m. Our Wndings further support the growing realization mented the external camera recordings with an internal that putative mesopelagic species may have a direct and hand held video camera, which we usually ran continuously signiWcant role in the trophodynamics of the benthic bound- from beginning to end of dive, except during ascent. For ary layer. most of the time on bottom, video observations were obtained with the both internal and external camera lenses set to wide angle and all JSL lights on. When specimens of Materials and methods particular interest were observed, the cameras were zoomed in to provide as much closeup detail as possible to assist Study sites with organism identiWcations. Each observer recorded audio observations onto both the videotapes and onto sepa- Data were collected from three general study areas on the rate audio recorders continuously during each dive. Speci- Virginia and North Carolina continental slopes (Fig. 1). All mens were collected as often as possible using the JSL three study areas were established as part of larger, ongoing suction sampler, often facilitated by dispensing a rotenone projects investigating the community structure and tropho- emulsion to narcotize mesopelagic species. A few mesope- dynamics of shelf edge and slope fauna. The Virginia mid- lagic Wshes were collected by 1.3 cm bar size Wne mesh dle slope (VMS) was sampled the least, and that area was frame mounted gill nets stacked into “sandwiches” on the described by Sulak and Ross (1996). The Hatteras middle lower bow platform of the JSL. Specimens collected by the slope (HMS) is an intensely studied area of complex bot- JSL were returned to the laboratory and treated in a manner tom topography (canyons) and complex oceanography (see similar to trawl captured specimens (see below). These col- Sulak and Ross 1996; Ross et al. 2001; Bauer et al. 2002). lections were made to both conWrm Weld identiWcations of The HMS is closest to land (»68 km) of all areas sampled organisms and for use in the collection