Processes That Affect Saltmarsh Erosion and Saltmarsh Restoration
181
particularly abundant, the polychaete Nereis diversicolor (hereafter Nereis),
the amphipod Corophium volutator (hereafter Corophium), the gastropod
Hydrobia ulvae (hereafter Hydrobia) and the bivalve Macoma balthica
(hereafter Macoma). Nereis may be predators of other invertebrates, they may
also filter-feed, but they are predominantly surface deposit feeders (see Smith
et aL 1996 for review). They excavate burrows to a depth of 10-40 cm (Davey
1994) from which they partially emerge to engulf sediment with epipelic
diatoms (Smith et aL 1996), filamentous algae, seeds, seedlings, and Zostera
leaves (Olivier et aL 1996; Hughes et aL 2000; Paramor and Hughes, in preparation). Exclusion of Nereis in experiments at Clementsgreen Creek allowed
colonisation by microphytobenthos and filamentous algae, and promoted
sediment accretion (Smith et aL 1996; Hughes 1999).
Corophium form V-shaped burrows to a depth of 5 cm and are predominantly surface deposit feeders too (Meadows and Reid 1966). They
partially emerge to scrape surface material into their burrows including
microphytobenthos, organic matter and detritus (Gerdol and Hughes 1994a).
Corophium reduce the shear strength of the sediment (Gerdol and Hughes
1994b) and may prevent the establishment of larger plants because their
bioturbation buries seeds and disturbs seedlings (Gerdol and Hughes 1993).
Hydrobia, which crawl on, or burrow just under, the sediment surface, are
deposit feeders consuming bacteria, small organic particles, and epipelic and
epipsammic diatoms (Fenchel et aL 1975; Austen et aL 1999). Austen et aL
(1999) concluded that Hydrobia increased the erodability of mud in the
Danish Wadden Sea by consuming microphytobenthos, and by the production of faecal pellets, which lack cohesive properties. Laboratory experiments
have demonstrated that Hydrobia prevent establishment of small seedlings,
by physical disturbance as the gastropods move over and through the surface
sediments (Hughes et aI., in preparation). In field experiments, Salicornia
seedlings that were protected from the effects of Hydrobia, by surrounding
them with pellets containing molluscicide, had a higher survivorship rate
than unprotected seedlings (Hughes et aI., in preparation).
Widdows et aL (1998) concluded that the erodability of the sediment in the
Humber Estuary was related to the activities of Macoma and the cockle
Cerastoderma edule. Macoma are facultative deposit feeders that feed by
directing their inhalent siphon onto the sediment surface, where, by sucking
up surface deposits, they may have a negative effect on sediment accretion
(Paterson and Black 1999). Sometimes Macoma are suspension feeders and
may aid deposition by incorporating inorganic particles, previously in suspension, into pseudofaeces. The pseudofaecal pellets and faecal pellets may
become incorporated into the sediment although they are easily transported
by currents and may contribute to the removal of surface sediments (Davey
and Partridge 1998). Kang et aL (1999) reported that suspension feeding
Cerastoderma consume microphytobenthos taken into suspension by wave
181
particularly abundant, the polychaete Nereis diversicolor (hereafter Nereis),
the amphipod Corophium volutator (hereafter Corophium), the gastropod
Hydrobia ulvae (hereafter Hydrobia) and the bivalve Macoma balthica
(hereafter Macoma). Nereis may be predators of other invertebrates, they may
also filter-feed, but they are predominantly surface deposit feeders (see Smith
et aL 1996 for review). They excavate burrows to a depth of 10-40 cm (Davey
1994) from which they partially emerge to engulf sediment with epipelic
diatoms (Smith et aL 1996), filamentous algae, seeds, seedlings, and Zostera
leaves (Olivier et aL 1996; Hughes et aL 2000; Paramor and Hughes, in preparation). Exclusion of Nereis in experiments at Clementsgreen Creek allowed
colonisation by microphytobenthos and filamentous algae, and promoted
sediment accretion (Smith et aL 1996; Hughes 1999).
Corophium form V-shaped burrows to a depth of 5 cm and are predominantly surface deposit feeders too (Meadows and Reid 1966). They
partially emerge to scrape surface material into their burrows including
microphytobenthos, organic matter and detritus (Gerdol and Hughes 1994a).
Corophium reduce the shear strength of the sediment (Gerdol and Hughes
1994b) and may prevent the establishment of larger plants because their
bioturbation buries seeds and disturbs seedlings (Gerdol and Hughes 1993).
Hydrobia, which crawl on, or burrow just under, the sediment surface, are
deposit feeders consuming bacteria, small organic particles, and epipelic and
epipsammic diatoms (Fenchel et aL 1975; Austen et aL 1999). Austen et aL
(1999) concluded that Hydrobia increased the erodability of mud in the
Danish Wadden Sea by consuming microphytobenthos, and by the production of faecal pellets, which lack cohesive properties. Laboratory experiments
have demonstrated that Hydrobia prevent establishment of small seedlings,
by physical disturbance as the gastropods move over and through the surface
sediments (Hughes et aI., in preparation). In field experiments, Salicornia
seedlings that were protected from the effects of Hydrobia, by surrounding
them with pellets containing molluscicide, had a higher survivorship rate
than unprotected seedlings (Hughes et aI., in preparation).
Widdows et aL (1998) concluded that the erodability of the sediment in the
Humber Estuary was related to the activities of Macoma and the cockle
Cerastoderma edule. Macoma are facultative deposit feeders that feed by
directing their inhalent siphon onto the sediment surface, where, by sucking
up surface deposits, they may have a negative effect on sediment accretion
(Paterson and Black 1999). Sometimes Macoma are suspension feeders and
may aid deposition by incorporating inorganic particles, previously in suspension, into pseudofaeces. The pseudofaecal pellets and faecal pellets may
become incorporated into the sediment although they are easily transported
by currents and may contribute to the removal of surface sediments (Davey
and Partridge 1998). Kang et aL (1999) reported that suspension feeding
Cerastoderma consume microphytobenthos taken into suspension by wave