Abstract
Biological communities on the abyssal plain are largely dependent on detritus from the surface ocean as their main source of energy. Seasonal fluctuations in the deposition of that detritus cause temporal variations in the quantity and quality of food available to these communities, altering their structure and the activity of the taxa present. However, direct observations of energy acquisition in relation to detritus availability across megafaunal taxa in abyssal communities are few. We used time-lapse photography and coincident measurement of organic matter flux from water column sediment traps to examine the impact of seasonal detrital inputs on resource acquisition by the deposit feeding megafauna assemblages at two sites: Station M (Northeast Pacific, 4000 m water depth) and the Porcupine Abyssal Plain Sustained Observatory (PAP-SO, Northeast Atlantic 4850 m water depth). At Station M, studied over 18-months, the seasonal particle flux was followed by a salp deposition event. At that site, diversity in types of deposit feeding was related to seabed cover by detritus. At PAP-SO, studied over 30 months, the seasonal particle flux consisted of two peaks annually. While the two study sites were similar in mean flux (~8.0 mgC m−2 d−1), the seasonality in the flux was greater at PAP-SO. The mean overall tracking at PAP-SO was five times that of Station M (1.9 and 0.4 cm2 h−1, respectively); both are likely underestimated because tracking by some common taxa at both sites could not be quantified. At both sites, responses of deposit-feeding megafauna to the input of detritus were not consistent across the taxa studied. The numerically-dominant megafauna (e.g. echinoids, large holothurians and asteroids) did not alter their deposit feeding in relation to the seasonality in detrital supply. Taxa for which deposit feeding occurrence or rate were correlated to seasonality in particle flux were relatively uncommon (e.g. enteropneusta), known to cache food (e.g. echiurans), or to be highly selective for fresh detritus (e.g. the holothurian Oneirophanta mutabilis). Thus, the degree of seasonality in deposit feeding appeared to be taxon-specific and related to natural history characteristics such as feeding and foraging modes.
Highlights
Communities on the abyssal plain are largely dependent on detritus from the surface ocean as their main source of energy
At Station M, there is a seasonal signal in particulate organic carbon (POC) flux that was augmented by the deposition of salp carcasses to the abyssal sea floor in 2012 (Smith et al, 2014)
In the period covered by time-lapse photography, the POC flux recorded in the sediment trap peaked in June to August 2011, as described by Smith et al (2014), and the dominant flux in 2012 occurred between March and late May, with a peak in April, and another begin ning in mid-August
Summary
Communities on the abyssal plain are largely dependent on detritus from the surface ocean as their main source of energy. Seasonal variation in food supply has been linked to seasonality in the biological functions of individual megafauna, such as growth rates in some deep-sea echinoderms and fish (Gage, 1987; Tyler, 1988), and reproduction and recruitment in some echinoderms (Benitez-Villalobos and Diaz-Martinez, 2010; Booth et al, 2008; FitzGeorge-Balfour et al, 2010; Tyler, 1986; Tyler et al, 1982; Wigham et al, 2003) Such bio logical functions require energetic reserves above the basic energetic needs for survival, suggesting temporal variations in energy use. Different lifestyles result in different energy reserves, so the coupling of variations in energy avail ability, acquisition and use are not uniform across taxa; direct observations of energy acquisition in relation to availability across taxa in abyssal communities are few
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