Burrows of Pestarella tyrrhena (Decapoda: Thalassinidea):: hot spots for Nematoda, Foraminifera and bacterial densities

Burrow wall sediment (BWS) and chamber debris (CD) of Pestarella tyrrhena burrows were isolated and compared to surrounding sediments differentiated into surface sediment (SS), deep ambient sediment (DAS) and embedded ambient organic debris (EAD). The focus was on the meiofauna community along with granulometric characteristics including organic content (OC) and bacterial abundances. Clear trends were found for all parameters: the shrimp significantly increased OC within its burrow and affected grain size distributions. The oxidized burrow walls were highly consolidated, consisted of poorly sorted sediment enriched with silt and clay, and contained small particles of inacrophyte debris, while coarse inorganic and organic particles > 500 mu m were concentrated in the CD. Bacterial abundances (epifluorescence microscopy direct counts, SYBR Gold staining) were positively correlated with OC and were significantly higher in BWS than in SS or DAS. Nematode numbers were elevated three-fold and foraminiferal densities by two orders of magnitude in BWS versus non-burrow sediments. Among the anoxic sediments (DAS, EAD, CD) meiofauna densities in CD were highest. Nematode community analysis (PCA, CANOCO) revealed considerable differences between BWS and SS. The BWS harboured more taxa and was dominated by deposit feeders, while in SS epistrate feeders prevailed. These effects on different levels demonstrate the ability of R tyrrhena to create a specific microenvironment within the burrow. The burrow walls were most influenced by the shrimp's activity, which corresponds to their nutritional role.