The relative impact of incidental bioturbator disturbance will thus likely be larger in the short term for seeds without a dormancy period than for dormant seeds which may survive several disturbance events and for whom survival will be dictated over a longer period of time. Seeds with dormancy may, however, encounter additional predation pressure over the length of their dormancy period that also reduces the number of viable seeds in the seed bank and leads to lower seedling establishment rates. But these studied bioturbators are a small subset of the global and diverse bioturbating community that are capable of disturbing seeds and/or seedlings. Larger bioturbators may also disturb the sediment when they forage for infauna. The green crab (Carcinus disrupted maenas) and uprooted transplants in New England, USA (Davis et al. 1998). The portunid crab Z. marina is a known bioturbator of meadows in the Atlantic (Wilson Callinectes sapidus Zostera marina et al. 1990) and a relative, is a common bioturbator in Western Australia and Portunus armatus, was observed disturbing bare sediment during this study (Figure S4). Likewise, elasmobranches are known to dig into both bare and vegetated patches in search of food and generate large escarpments in the sediment (Orth 1975, Townsend & Fonseca 1998). Previous studies indicate these elasmobranch bioturbators may (Orth 1975, Backman 1984, Fonseca et al. 1994, Inglis 2000) or may not (Valentine et al. 1994) be able to disturb adult clones of seagrass species, but these studies have not incorporated seeds and seedlings which would be more susceptible to damage and loss from elasmobranch foraging. The widespread and diverse nature of bioturbators suggests these communities may play a more substantial role in seagrass seedling recruitment than currently acknowledged.
The relative impact of incidental bioturbator disturbance will thus likely be larger in the short term for seeds without a dormancy period than for dormant seeds which may survive several disturbance events and for whom survival will be dictated over a longer period of time. Seeds with dormancy may, however, encounter additional predation pressure over the length of their dormancy period that also reduces the number of viable seeds in the seed bank and leads to lower seedling establishment rates. But these studied bioturbators are a small subset of the global and diverse bioturbating community that are capable of disturbing seeds and/or seedlings. Larger bioturbators may also disturb the sediment when they forage for infauna. The green crab (Carcinus maenas) disrupted and uprooted Z. marina transplants in New England, USA (Davis et al. 1998). The portunid crab Callinectes sapidus is a known bioturbator of Zostera marina meadows in the Atlantic (Wilson et al. 1990) and a relative, Portunus armatus, is a common bioturbator in Western Australia and was observed disturbing bare sediment during this study (Figure S4). Likewise, elasmobranches are known to dig into both bare and vegetated patches in search of food and generate large escarpments in the sediment (Orth 1975, Townsend & Fonseca 1998). Previous studies indicate these elasmobranch bioturbators may (Orth 1975, Backman 1984, Fonseca et al. 1994, Inglis 2000) or may not (Valentine et al. 1994) be able to disturb adult clones of seagrass species, but these studies have not incorporated seeds and seedlings which would be more susceptible to damage and loss from elasmobranch foraging. The widespread and diverse nature of bioturbators suggests these communities may play a more substantial role in seagrass seedling recruitment than currently acknowledged.
AAM_a_sediment.docx