A Quantitative Photographic Survey of ‘Spoke‐Burrow’ Type Lebensspuren on the Cape Verde Abyssal Plain

Abstract

A photographic survey of the seafloor was conducted during RRS Discover?, cruise 204 in SeptembedOctober 1993 at the oligotrophic site of the French EUMELI programme at c. 21" N : 31" W (4650 m) on the Cape Verde Abyssal Plain. Two systems were used, a wide angle system (WASP) obtaining usable photographs covering 10 to 30 m2, and an epibenthic sledge mounted system obtaining photographs of about 2 m2.A total of more than 3000 usable frames were obtained, covering about 64000 m2 of seafloor. The photographs indicated an epibenthic invertebrate megafaunal density of 5.2 hectare-' and a demersal fish density of I .8 hectare-'. In contrast, the photographs were dominated by lebensspuren, particularly of the 'spoke-burrow' type usually attributed to echiurans. Spoke-burrow density, where related burrows and other features such as sediment mounds are considered unitary, is estimated at 87 l hectare-'. We describe and quantify the five principal types of spoke burrow encountered in this study and. on the basis of these observations and some morphometric studies of the Iebensspwen, discuss the possible behaviour of their producers.We have no direct knowledge of the production rate of, or longevity of, lebensspuren in the study area. However, based on a number of assumptions and limited data from other areas we suggest that trace producer (mainly echiurans) density is on the order of tens of individuals per hectare. These trace producers probably greatly outnumber the rest of the invertebrate megabenthos, and we can only guess at the role this potential large population of hidden benthos might have in the overall structure and function of the deep-sea floor ecosystem.

The hemisessile lifestyle and feeding strategies of Iosactis vagabunda (Actiniaria, Iosactiidae), a dominant megafaunal species of the Porcupine Abyssal Plain

“…The second move occurred over 19 h, with a period of 13.3 h between disappearance and mound-building, 3.3 h of mound-building, and 2.3 h from emergence to establishment. The burrowing behaviour of I. vagabunda observed here suggests that the subsurface motion of the animal between burrows is similar to the consecutive 'U-shaped' burrowing behaviour described for echiurans (Bett, 2003;Bromley, 1996), as they produce a 'volcano-series' burrow system (Bett et al, 1995). Subsurface transit between burrow locations may reduce the risk of predation; alternative interpretations for episodic subsurface behaviour by deep-sea megabenthos (e.g.…”

“…This is the result of very limited in-situ observations. Deep-sea time-lapse photography has proved valuable in recording the feeding behavior and burrow creation of echiurans (Bett and Rice, 1993;Bett et al, 1995;Ohta, 1984), the foraging behavior of enteropneusts (Jones et al, 2013;Smith et al, 2005) and bathyal shrimp (Lampitt and Burnham, 1983), the activity and bioturbation of echinoderms (Bett et al, 2001;Vardaro et al, 2009), and the behaviour of anthozoans (Ansell and Peck, 2000;Lampitt and Paterson, 1987). Time-lapse imagery has previously been used to observe the movement of I. vagabunda between burrows, leading to the suggestion that it had a hemisessile lifestyle (Riemann-Zürneck, 1997b).…”

Time-lapse Photography in the Deep Sea

“…While these observations are valuable in themselves, they have also enabled improved estimates of the population density of echiurans. Bett et al [15] were able to combine data on the dynamics of spoke-burrow formation from Bathysnap observations ( Figure 4) with seabed survey photography estimates of spoke-burrow density to provide an estimate of the likely true density of echiurans.…”

The use of towed camera platforms in deep-water science

“…Towed camera platforms are used routinely in the investigation of deep-water biology (Machan and Fedra, 1975;Hashimoto and Hotta, 1985;Christiansen and Thiel, 1992;Hecker, 1994;Bett et al, 1995;Barker et al, 1999;Cailliet et al, 1999;Bett, 2001;Kollmann and Stachowitsch, 2001;Cranmer et al, 2003;Mortensen and Buhl-Mortensen, 2004) and geology (Hecker, 1990;Kleinrock et al, 1992;Leybourne and Vanwagoner, 1992;Barker et al, 1999;McHugh and Ryan, 2000;Masson, 2001;Wynn et al, 2002;Fornari, 2003), often for the initial assessment of the seabed character before more detailed investigations take place, such as in hydrothermal vent research or in the search for archaeological artefacts (Lonsdale, 1977a;Lonsdale, 1977b;McConachy et al, 1986;Ballard et al, 2000;Singh et al, 2000;Klinkhammer et al, 2001). …”