46
J.A. Commito and N.M.J.A. Dankers
in assessing large areas of the bottom has already begun. Sugihara and May
(1990) have argued that the fractal dimension can be used to measure the
stability of space-occupying ecological systems. They suggest that a stable
system should exhibit large, uniform patches with low D values. As the patches
break up, they become more complex, resulting in higher D values. According
to this model, the fractal dimension varies inversely with persistence. Does
this model apply to mussel beds? The jury is still out on this question. Nobody
has explicitly tested the Sugihara and May model. The existing mussel-bed
data are equivocal at best. No mussel-bed studies have found the lowest D
values at the highest levels of density and percent cover, as predicted by the
model. Rather, D increased as density and cover rose to intermediate or high
levels (Snover and Commito 1998; Commito and Rusignuolo, 2000; see also
Kostylev et al. 1997 for a rocky shore example with Mytilus galloprovincialis in
Spain). This general result suggests that, with some modification, the
Sugihara and May model could be of benefit in the analysis of the spatial and
temporal dynamics of mussel beds.
2.4 Effects of Mussel Beds on Soft-Bottom
Community Structure
One reason to study the spatial and temporal dynamics of soft -bottom mussel
beds is because they cover large areas and may have an impact on benthic
community structure. Here we mean "structure" to be the species composition and relative abundances of the soft-bottom community members, not
to be confused with the physical architecture of mussel beds. Workers have
shown that mussel beds are an important regulating force on rocky shores
because they out-compete barnacles and other species for primary attachment space. Beds also provide habitat for species that are normally rare
because the complex matrix of byssal threads and trapped objects creates
space for animals to live. Patches of mussels serve as habitat islands in softbottom (Dittmann 1990; Dankers 1993) and hard-bottom systems, with
positive exponential and nonlinear power relationships between patch size
and species richness (Mytilus edulis - Asamuchi, northern Japan: Tsuchiya
and Nishihira 1986; Brachidontes rostratus - Victoria, southeastern Australia:
Peake and Quinn 1993).
Mussel beds also affect infaunal community structure. In her important
paper describing the types of adult -larval interactions that can occur in dense
infaunal assemblages, Woodin (l976) summarized the research of many
European and North American benthic ecologists. She created a series of testable hypotheses about the impacts that deposit feeders, tube builders, and
J.A. Commito and N.M.J.A. Dankers
in assessing large areas of the bottom has already begun. Sugihara and May
(1990) have argued that the fractal dimension can be used to measure the
stability of space-occupying ecological systems. They suggest that a stable
system should exhibit large, uniform patches with low D values. As the patches
break up, they become more complex, resulting in higher D values. According
to this model, the fractal dimension varies inversely with persistence. Does
this model apply to mussel beds? The jury is still out on this question. Nobody
has explicitly tested the Sugihara and May model. The existing mussel-bed
data are equivocal at best. No mussel-bed studies have found the lowest D
values at the highest levels of density and percent cover, as predicted by the
model. Rather, D increased as density and cover rose to intermediate or high
levels (Snover and Commito 1998; Commito and Rusignuolo, 2000; see also
Kostylev et al. 1997 for a rocky shore example with Mytilus galloprovincialis in
Spain). This general result suggests that, with some modification, the
Sugihara and May model could be of benefit in the analysis of the spatial and
temporal dynamics of mussel beds.
2.4 Effects of Mussel Beds on Soft-Bottom
Community Structure
One reason to study the spatial and temporal dynamics of soft -bottom mussel
beds is because they cover large areas and may have an impact on benthic
community structure. Here we mean "structure" to be the species composition and relative abundances of the soft-bottom community members, not
to be confused with the physical architecture of mussel beds. Workers have
shown that mussel beds are an important regulating force on rocky shores
because they out-compete barnacles and other species for primary attachment space. Beds also provide habitat for species that are normally rare
because the complex matrix of byssal threads and trapped objects creates
space for animals to live. Patches of mussels serve as habitat islands in softbottom (Dittmann 1990; Dankers 1993) and hard-bottom systems, with
positive exponential and nonlinear power relationships between patch size
and species richness (Mytilus edulis - Asamuchi, northern Japan: Tsuchiya
and Nishihira 1986; Brachidontes rostratus - Victoria, southeastern Australia:
Peake and Quinn 1993).
Mussel beds also affect infaunal community structure. In her important
paper describing the types of adult -larval interactions that can occur in dense
infaunal assemblages, Woodin (l976) summarized the research of many
European and North American benthic ecologists. She created a series of testable hypotheses about the impacts that deposit feeders, tube builders, and