The most plausible mechanism linking the reef-modules, drifting phytodetritus and reductions in redox is a baffling of water currents by the reef structure and the subsequent deposition of entrained material. This hypothesised mechanism is supported by hydrological modelling which has predicted a reduction in water currents in close proximity to the reef (Al-Bouraee, 2013). The depositionary environment at the reef edge, reported here, contrasts with that reported around other artificial structures, for example Davis et al., 1982 and Ambrose and
Anderson, 1990 and Barros et al. (2001) (collectively referred to as DAB Reefs from here) report a DNA Damage inhibitor coarsening of the sediment, and by inference, an increase in current speed, at the boundary of their study-reefs. The
impact-differences between the DAB Reefs and the LLR reef-modules may be attributed to the adjacent substratum: the DAB reefs were located on a fine sand contrasting markedly with the LLR site which consists of a cohesive, muddy-sand (Wilding, 2006 and Wilding and Sayer, 2002). In the case of the LLR, the piles of concrete blocks may offer a semi-permeable barrier to water thereby effectively acting to baffle, rather than deflect and accelerate, water flow around the perimeter. This baffling-effect is in-line with enough findings MAPK inhibitor of Fabi et al. (2002) and Guiral et al. (1995) who both report increased fine material associated with artificial structures. A simple reduction in current speed, over the sediment, will result in a decrease in the advective delivery of oxygenated water to the sediment surface (Diaz and Rosenberg, 1995 and Ziebis et al., 1996). This may explain the findings around Group D. Group D was exposed to relatively high water flow and phytodetritus was not seen to accumulate around it at any time. The minor reductions
in redox at the reef edge (Group D), which only occurred during the summer, may represent the consequences of hydrographic interactions that are independent of the deposition of phytodetritus. The lower sedimentary redox observed during the summer and autumn, compared with the rest of the year, were predicted as previous research had shown the accumulation of phytodetritus during that period (Wilding, 2006). The ∼80 mV reduction at the reef edge reported here is commensurate with that found at the edge of Loch Linnhe mussel farms, at 20 mm sediment depth, and which was associated with an increase, by between 1.8 and 8×, in macrofaunal abundance (Wilding, 2012 and Wilding and Nickell, 2013).