The trophic structure of Spongosorites coralliophaga-coral rubble communities at two northeast Atlantic cold water coral reefs

Georgios Kazanidis,Ursula F M Witte

doi:10.1080/17451000.2016.1216569

Abstract

ABSTRACTWe examined the isotopic signatures (δ13C, δ15N) of fauna living in association with the sponge Spongosorites coralliophaga colonizing coral rubble on cold-water coral reefs in the northeast Atlantic – the shallow inshore (122–131 m collection depth) Mingulay 01 area and the deep offshore (683–800 m) Logachev 02 mound. The δ15N signatures of suspended particulate organic matter and three primary consumers, i.e. Spongosorites coralliophaga, Reteporella beaniana and Parazoanthus anguicomus were used as trophic baselines and the resulting trophic structure was compared. In both regions four trophic levels were distinguished. However, the use of S. coralliophaga or R. beaniana as baselines resulted in a skewed trophic structure due to the enriched δ15Ν signatures of these two species on the Logachev 02 mound. Using suspended particulate organic matter and P. anguicomus as baselines, the Mingulay 01 area communities were characterized by elevated relative biomass of lower trophic levels compared to the Logachev 02 mound. Relative biomass of suspension/filter feeders was also higher at the Mingulay 01 area. The two regions differed significantly with regard to the prevailing environmental conditions: apart from the difference in depth and distance from shore, the Mingulay 01 area was characterized by higher primary production in surface waters, tight pelagic–benthic coupling and higher velocity of bottom currents, and it is hypothesized that these characteristics were the main drivers of the observed differences. This study highlighted that multiple trophic baselines can provide a better interpretation of food-web structure and that the use of sponges or bryozoans as baselines across bathymetric gradients should be avoided.

Highlights

Heterotrophic ecosystems in the deep sea depend on the flux of organic matter from the upper layers of the ocean (Gage 2003 and references therein), and the quality, quantity and timing of this flux affect community composition and biomass (e.g. Billett et al 2001, 2010; Ruhl & Smith 2004; Wei et al 2010; Tecchio et al 2013)
We examined the isotopic signatures (δ13C, δ15N) of fauna living in association with the sponge Spongosorites coralliophaga colonizing coral rubble on cold-water coral reefs in the northeast Atlantic – the shallow inshore (122–131 m collection depth) Mingulay area and the deep offshore (683–800 m) Logachev mound
The δ15N signatures of suspended particulate organic matter and three primary consumers, i.e. Spongosorites coralliophaga, Reteporella beaniana and Parazoanthus anguicomus were used as trophic baselines and the resulting trophic structure was compared

Summary

Introduction

Heterotrophic ecosystems in the deep sea (defined here as regions below 200 m water depth) depend on the flux of organic matter from the upper layers of the ocean (Gage 2003 and references therein), and the quality, quantity and timing of this flux affect community composition and biomass (e.g. Billett et al 2001, 2010; Ruhl & Smith 2004; Wei et al 2010; Tecchio et al 2013). Heterotrophic ecosystems in the deep sea (defined here as regions below 200 m water depth) depend on the flux of organic matter from the upper layers of the ocean (Gage 2003 and references therein), and the quality, quantity and timing of this flux affect community composition and biomass Cold-water coral reefs are deep-sea heterotrophic ecosystems with high ecological and economical values (van Oevelen et al 2009; Henry et al 2013a, 2013b), but our knowledge of their trophic structure is limited even for reefs in the northeast Atlantic (Duineveld et al 2007; van Oevelen et al 2009), which are comparatively well studied (Roberts et al 2006). Reefforming cold-water coral species do not host symbiotic dinoflagellates (Roberts et al 2006), but rely on organic matter produced in the euphotic zone (Kiriakoulakis et al 2005; Dodds et al 2009; Duineveld et al 2012; Mueller et al 2014) and as a result often occur in regions where processes such as down-welling and advection increase the supply of food particles to the seafloor (Duineveld et al 2007; Davies et al 2009)

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Conclusion