Contrasting macrobenthic activities differentially affect nematode density and diversity in a shallow subtidal marine sediment

Abstract

By bioturbating and bio-irrigating the sea floor, macrobenthic organisms transport organic matter and oxygen from the surface to deeper layers, thereby extending the habitat suitable for smaller infauna. Next to these engineering activities, competition, disturbance and predation may also affect the spatial distribution of these smaller organisms. In a controlled laboratory experiment, we studied the effects of 3 functionally different macrobenthic species on the vertical distribution of nematodes. Abra alba, a suspension-deposit feeding bivalve reworking the sediment randomly, Lanice conchilega, a suspension-deposit feeding, tube-irrigating polychaete and Nephtys hombergii, a burrowing predatory polychaete, were added in single-species treatments to sediment from a coastal subtidal station in the Belgian part of the North Sea, sieved (1 mm) to remove macrofauna. After 14 d, the control treatment without macrobenthos was found to be detrimental to nematode density and diversity, which points to the importance of macrobenthic engineering to sustain the smaller components of the food web. Nematode densities were highest at the sediment surface in all treatments, but subsurface density peaks were observed in A. alba (to 3 cm depth) and L. conchilega (to 7 cm depth) microcosms. In the A. alba treatment, the dominant non-selective deposit feeders and the epistrate feeders shifted downwards probably to avoid disturbance and exploitative competition by the bivalve siphons at the surface, while they might have benefited from the faecal pellets deposited in the subsurface. In the L. conchilega treatment, the several dominant species were redistributed over depth layers, indicating polychaete-mediated habitat extension from surface into depth. Nematode communities seemed hardly affected by the presence of N. hombergii. These results reveal that functionally contrasting macrobenthic engineering effects shape nematode communities in different ways, which may maintain the role of nematodes in ecosystem functioning. The present study therefore highlights the need for conservation of macrobenthic functional diversity.KEY WORDS: Bioturbation · Macrobenthos · Ecosystem engineering · Nematodes · Vertical distribution · Diversity · Density Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 422: [179][180][181][182][183][184][185][186][187][188][189][190][191] 2011 organisms that inhabit marine soft sediments alter the distribution of high-quality organic matter (Graf 1989, Levin et al. 1997, oxygen and toxic metabolites in the sediment (Kristensen & Kostka 2005) through bioturbation and bio-irrigation activities (Aller 1988, Meysman et al. 2006) which, in turn, may influence the distribution of organisms that are too small to 'engineer' their own habitat, e.g. nematodes (Reise 1985) or bacteria (Mermillod-Blondin et al. 2004). The ecosystem-engineering concept is, however, controversial in that all organisms are affected by and change their abiotic environment to some exten...

Testing for nematode–granulometry relationships

“…There are a multitude of other environmental factors that may vary independently of granulometric properties and are known to structure marine nematodes. Examples of important structuring variables which might be also operating in the present dataset are quantity and quality of the organic matter (Danovaro and Gambi 2002), oxygen availability and the position of the redox layer (Steyaert et al 2007;Vieira and Fonseca 2013), abundance and composition of macrofauna species (Van Colen et al 2009, Braeckman et al 2011, and bacterial biomass and activity (Danovaro 1996), among others. We suggest that, at least for the present dataset, these variables are more important than granulometry in structuring local species richness.…”

Bottom–up and top–down mechanisms indirectly mediate interactions between benthic biotic ecosystem components

“…For example, macrobenthos is known to affect smaller-sized meiobenthos (32-500 μm) species populations through direct consumption (Coull, 1999) and indirect mechanisms that include mainly facilitation and competition interactions related to macrobenthos behavior that e.g. alter the distribution of food resources in the sediment (Braeckman et al, 2011), and species morphological traits such as the construction of physical structures that provide shelter from predation (Zühlke, 1998).…”

Is nematode colonisation in the presence of Scolelepis in tropical sandy-beach sediment similar to the colonisation process in temperate sandy beaches?

“…However, the three-dimensional sediment of sandy beaches is not exclusively inhabited by nematodes; diverse communities including species of different sizes of organisms, such as micro-, meio-(other than nematodes) and macrofauna are also found in sandy beach sediments. These organism group sizes generally interact with each other by means of trophic interactions (Schratzberger and Warwick, 1999;Tita et al, 2000;Aarnio et al, 2001) or non-trophic interactions (Van Colen et al, 2009;Braeckman et al, 2011;Maria et al, 2011) and, therefore, interactions between macrofauna and nematodes also influence the nematode composition of sandy beach sediments (Maria et al, 2011).…”