42
J.A. Commito and N.M.J.A. Dankers
abundant predators, the seas tar Asterias rubens, from eliminating mussel
patches. Mussels and seas tars were in dynamic equilibrium. Moreover, drift
fences demonstrated that Mytilus edulis clumps were lifted from the bottom
and carried by water currents to locations where they formed the nuclei of
new beds.
Other workers have shown that the dynamic nature of soft-bottom mussel
beds has a strong spatial scale component. Population performance depends
on location within an estuary (Mytilus edulis - Devon, England: McGrorty et
al. 1990; McGrorty and Goss-Custard 1991, 1993, 1995), proximity to the edge
of a saltmarsh (ribbed mussels, Geukensia demissa - Rhode Island, USA:
Bertness and Grosholz 1985), and position along a tidal height gradient in
saltmarshes (Bertness and Grosholz 1985; North Carolina, USA: Stiven and
Gardner 1992) and on soft-bottoms (McGrorty et al. 1990; McGrorty and
Goss-Custard 1991,1993,1995; Kiel Fjord: Reusch and Chapman 1997).
On a smaller spatial scale, researchers have argued that independent, nonclonal organisms like mussels live in dense aggregations because there are
benefits to living in close proximity to one's neighbors. Crab predation can be
lower on soft-bottom mussels in large, dense patches and the centers of small
patches than on solitary mussels and those living on the edges of patches
(Geukensia demissa - Rhode Island, USA: Bertness and Grosholz 1985; North
Carolina, USA: Lin 1991; Stiven and Gardner 1992; Mytilus edulis - northern
California, USA: Okamura 1986; Devon, England: McGrorty et al. 1990).
Presumably, crabs find it easier to attack soft-bottom mussels that are
exposed rather than protected by an impenetrable matrix of living mussels,
shell fragments, and byssal threads. One outcome is that differential predation
on the edges slows down patch growth and coalescence, as demonstrated by
the predator exclusion experiments of Reusch and Chapman (1997). Predation on mussel beds by bird predators such as oystercatchers, eiders, and
gulls has not been the object of much attention in North America (Guillemette and Himmelman 1996), but it has been intensively studied in Europe
(Meire and Ervynck 1986; Goss-Custard and Durell 1988; Bustnes and Erikstad 1990; Beukema 1993; Hilgerloh et al. 1997; McGrorty 1997; Nehls et al.
1997). In contrast to invertebrate predators, birds may not feed preferentially
on the edges of patches because their mobility and size give them access to a
greater spatial array of mussels, and their agonistic interactions force them to
spread out over large areas.
Mytilus edulis can defend against crab, seastar, and lobster predators (and
even respond to predator effluent) by growing thicker shells, producing more
byssal threads, and actively moving towards each other into larger clumps
with lower perimeter/area ratios, reducing their per mussel predation risk
(e.g., west coast of Sweden: Reimer and Tedengren 1997; Limfjorden, Denmark: Dolmer 1998; North Norfolk coast, United Kingdom: Cote and Jelnikar
1999; Maine coast, USA: Leonard et al. 1999). Movement into clumps could
J.A. Commito and N.M.J.A. Dankers
abundant predators, the seas tar Asterias rubens, from eliminating mussel
patches. Mussels and seas tars were in dynamic equilibrium. Moreover, drift
fences demonstrated that Mytilus edulis clumps were lifted from the bottom
and carried by water currents to locations where they formed the nuclei of
new beds.
Other workers have shown that the dynamic nature of soft-bottom mussel
beds has a strong spatial scale component. Population performance depends
on location within an estuary (Mytilus edulis - Devon, England: McGrorty et
al. 1990; McGrorty and Goss-Custard 1991, 1993, 1995), proximity to the edge
of a saltmarsh (ribbed mussels, Geukensia demissa - Rhode Island, USA:
Bertness and Grosholz 1985), and position along a tidal height gradient in
saltmarshes (Bertness and Grosholz 1985; North Carolina, USA: Stiven and
Gardner 1992) and on soft-bottoms (McGrorty et al. 1990; McGrorty and
Goss-Custard 1991,1993,1995; Kiel Fjord: Reusch and Chapman 1997).
On a smaller spatial scale, researchers have argued that independent, nonclonal organisms like mussels live in dense aggregations because there are
benefits to living in close proximity to one's neighbors. Crab predation can be
lower on soft-bottom mussels in large, dense patches and the centers of small
patches than on solitary mussels and those living on the edges of patches
(Geukensia demissa - Rhode Island, USA: Bertness and Grosholz 1985; North
Carolina, USA: Lin 1991; Stiven and Gardner 1992; Mytilus edulis - northern
California, USA: Okamura 1986; Devon, England: McGrorty et al. 1990).
Presumably, crabs find it easier to attack soft-bottom mussels that are
exposed rather than protected by an impenetrable matrix of living mussels,
shell fragments, and byssal threads. One outcome is that differential predation
on the edges slows down patch growth and coalescence, as demonstrated by
the predator exclusion experiments of Reusch and Chapman (1997). Predation on mussel beds by bird predators such as oystercatchers, eiders, and
gulls has not been the object of much attention in North America (Guillemette and Himmelman 1996), but it has been intensively studied in Europe
(Meire and Ervynck 1986; Goss-Custard and Durell 1988; Bustnes and Erikstad 1990; Beukema 1993; Hilgerloh et al. 1997; McGrorty 1997; Nehls et al.
1997). In contrast to invertebrate predators, birds may not feed preferentially
on the edges of patches because their mobility and size give them access to a
greater spatial array of mussels, and their agonistic interactions force them to
spread out over large areas.
Mytilus edulis can defend against crab, seastar, and lobster predators (and
even respond to predator effluent) by growing thicker shells, producing more
byssal threads, and actively moving towards each other into larger clumps
with lower perimeter/area ratios, reducing their per mussel predation risk
(e.g., west coast of Sweden: Reimer and Tedengren 1997; Limfjorden, Denmark: Dolmer 1998; North Norfolk coast, United Kingdom: Cote and Jelnikar
1999; Maine coast, USA: Leonard et al. 1999). Movement into clumps could