The trophic biology of the holothurian <i>Molpadia musculus</i>: implications for organic matter cycling and ecosystem functioning in a deep submarine canyon

Abstract

Abstract. Megafaunal organisms play a key role in ecosystem functioning in the deep-sea through bioturbation, bioirrigation and organic matter cycling. At 3500 m water depth in the Nazaré Canyon, NE Atlantic, very high abundances of the infaunal holothurian Molpadia musculus were observed. To quantify the role of M. musculus in sediment cycling, sediment samples and holothurians were collected using an ROV and in situ experiments were conducted with incubation chambers. The biochemical composition of the sediment (in terms of proteins, carbohydrates and lipids), the holothurians' gut contents and holothurians' faecal material were analysed. In the sediments, proteins were the dominant organic compound, followed by carbohydrates and lipids. In the holothurian's gut contents, protein concentrations were higher than the other compounds, decreasing significantly as the material passed through the digestive tract. Approximately 33 ± 1% of the proteins were digested by the time sediment reached the mid gut, with a total digestion rate equal to 67 ± 1%. Carbohydrates and lipids were ingested in smaller amounts and digested with lower efficiencies (23 ± 11% and 50 ± 11%, respectively). As a result, the biopolymeric C digestion rate was on average 62 ± 3%. We estimated that the population of M. musculus could remove approximately 0.49 ± 0.13 g biopolymeric C and 0.13 ± 0.03 g N m −2 d −1 from the sediments. These results suggest that M. musculus plays a key role in the benthic tropho-dynamics and biogeochemical processes in the Nazaré Canyon.

Organic matter enrichment in the Whittard Channel; its origin and possible effects on benthic megafauna

“…de Stigter et al, 2011), or if effective transport processes like sediment gravity flows or dense shelf water cascading are present, may be transported down-canyon to greater depths (de Stigter et al, 2007;Canals et al, 2013). This capacity to focus organic matter flux is often reflected in enhanced abundance and biomass of benthic fauna within canyons (Maurer et al, 1994;Vetter and Dayton, 1998;Tyler et al, 2009;Ingels et al, 2009;De Leo et al, 2010;Amaro et al, 2010;Huvenne et al, 2011), as well as in more efficient burial of organic carbon in canyon sediments (e.g. Epping et al, 2002;Masson et al, 2010;Pusceddu et al, 2010).…”

Has Phytodetritus Processing by an Abyssal Soft-Sediment Community Recovered 26 Years after an Experimental Disturbance?

“…In both approaches, phytodetritus, e.g., diatoms or coccolithophores (Jeffreys et al, 2013), or zooplankton fecal pellets (Mayor et al, 2012) that have been enriched in 13 C and/ or 15 N are added to the benthic ecosystem (pulse) to track the uptake and processing of this material by microorganisms, meiofauna, metazoan macrofauna, and foraminifera (chase). Despite the high importance of deep-sea megafauna, dominated by holothurians, as e.g., grazers of labile phytodetritus (Miller et al, 2000;Gallucci et al, 2008;Amaro et al, 2010), logistic challenges of deepsea research have so far hampered the inclusion of megafauna in these stable isotope studies. This represents a major gap in our understanding of abyssal food webs (van Oevelen et al, 2012).…”

Exploring the Relationship between Macrofaunal Biodiversity and Ecosystem Functioning in the Deep Sea

“…Most deep-sea BEF investigations have used the meiofauna, particularly nematodes, as model taxa (Danovaro et al, 2008a;Leduc et al, 2013;Pape et al, 2013;Pusceddu et al, 2014b;Yasuhara et al, 2016;Zeppilli et al, 2016), whereas comparatively few studies have examined how microbial and viral components (Danovaro et al, 2008b), or of larger epifauna (Amaro et al, 2010), influence ecosystem functioning. In this study, BEF relationships were explored by focusing on the structural and functional diversity of the macrobenthic fauna.…”