Microdistribution of interstitial meiofauna, oxygen and sulfide gradients, and the tubes of macro-infauna

Abstract

Vertical and horizontal mlcro-scale gradients of oxygen and sulfide and meiofaunal distributions were examined concurrently in laboratory microcosms to assess the importance of tube/ burrow wall chemistry in generating microhabitat for subsurface meiofauna. These distributions were compared to field distributions at a subtidal site in Corpus Christi Bay, Texas (USA). Results reveal a continuum of microhabitats across oxygen and sulfide gradients in marine sands. The majority of taxa llved at [ 0 2 ] below 50 BM. These included microoxyphilic oxybiota living at [O,] >O and thiobiota at [O,] = 0. All classic thiobiota lived below the zero-oxygen line where sedirnents usually contained measurable sulfide. Most, but not all, subsurface taxa were attracted to burrows/tubes; however, only 1 taxon, Praeaphanostoma, lived in the microoxyphilic habitat of the burrow/tube wall's oxic halo. The remainder lived outside this zone where [ 0 2 ] = 0. No dominant species had substantially overlapping distributions. Each abundant species occupied its own unique microhabitat. Most microhabitat boundaries could be explained by changes in 0, and sulfide concentration; however, a few taxa were differentially distributed in microhabitats of similar chemistry, suggesting that other factors were important. Changing sediment chemistry may remove or create optimal microhabitat seasonally so that taxa must be able to exploit a range of suboptimal habitats to survive throughout the year. Most microhabitats, in shortest dimension, were no more than 2 to 3 times the animal's size, suggesting that traverses of no more than a few body lengths would be necessary to move from optimal to suboptimal habitat. Overall, the complex distributional patterns of meiofaunal species suggest that Fenchel & Riedl's (1970) simple 2-layered model of marine sand bottoms, comprising a surface oxic layer and a sulflde system, is inadequate. Even taxa living where [02] = 0 were distnbuted differentially along the sulfide gradient. Whether thiobiota and oxybiota are merely 2 ends of a continuum or really ecologically relevant subsets of subsurface meiofauna must b e reconsidered.

Leptonemella species (Desmodoridae, Stilbonematinae), benthic marine nematodes with ectosymbiotic bacteria, from littoral sand of the North Sea island of Sylt: taxonomy and ecological aspects

“…Our minicore examinations, however, give evidence that polychaete worm burrows are a preferred habitat of Leptonemella species, and the high population density reported by Jensen (1987a) adds to this suggestion. In general, there is a strong preference of the entire subsurface fauna for the vicinity of irrigated burrows (Reise 1981;Meyers et al 1987). In a comprehensive investigation of the oxygen/sulfide regime and nematodes associated with lugworm burrows in the intertidal, Wetzel et al (1995) conceived this habitat as permanently fluctuating, with drastic variations in the mm-range ideally meeting the requirements of 'sulfur bacteria'.…”

“…Accordingly, the nematodes living around the tail shaft region would be alternately exposed to irregular changes in concentrations of sulfide and oxygen. Subtidally, in the absence of tidal water movements episodic fluctuations of the redox conditions in the interstitial system of sediments may be of less importance, but steep gradients in the mm-range do exist also there (see Meyers et al 1987).…”

Biodiversity of benthic microbial communities in bioturbated coastal sediments is controlled by geochemical microniches

“…Microbial abundances and activities have been shown to increase due to the complex biogeochemical interactions induced by bioturbation activity (Hansen and Kristensen, 1998;Lohrer et al, 2004;Kogure and Wada, 2005). The construction of burrows increases the sediment-water interface, offering additional surfaces for microbial colonization and chemical reactions (Aller and Aller, 1986;Meyers et al, 1987;Reichardt, 1989;Grossman and Reichardt, 1991;Marinelli et al, 2002). The transport of particles (bioturbation) and the flushing of burrows (bioirrigation) create 3-dimensional geochemical zonation patterns with substantial changes of redox-conditions and the formation of temporally and spatially dynamic microenvironments.…”

Effect of the brittle star Amphiura filiformis (Amphiuridae, Echinodermata) on oxygen flux into the sediment

“…Many macroinfaunal species continuously rework the sediment and thus increase the oxygenation of the pore water (Marinelli 1992;Krager and Woodin 1993;Rosenberg et al 1997;Solan and Kennedy 2002). The meiofauna of the surficial sediment and the sediment around macrofaunal burrows apparently contribute to the interfacial flux as well by mixing the pore water through ''random walk'' within the interstitium of the sediment or by irrigating microcavities and microtubes (Meyers et al 1987;Aller and Aller 1992;Pike et al 2001).…”