5.3 Settlement and Dispersal of Macrofauna
141
water. Crustaceans belonging to the genus Gammarus (G. locusta, G. salinus) were
also found more closely to the bottom, while Urothoe poseidonis moved into
higher parts of the water column. There is still a need for more information concerning the vertical distribution of benthic macrofauna in the water column. Special attention of future research should be given to the question which life stages
may reach which height above ground and what this means in relation to the potential transport distance.
5.3.4
In situ Turnover Rates of Juvenile Macrofauna in Soft Sediments
A consequence of secondary dispersal of juvenile macrofauna, either by active
migration or passive resuspension, implies - at a given site at a given area - a turnover of organisms. Regular sampling of benthos documents the change of abundance over time. but does not give any information whether either input or output
of organisms or the relation between these factors had caused the change.
Beside benthos samples further methods have to be applied, such as emergence
or sediment traps, to analyse the turnover of organisms. Armonies (1994) was the
first to estimate the turnover rate by a combination of benthos and sediment trapsampling. A combination of driftfauna nets and benthos data was not suitable for
the quantitative evaluation of turnover rates, as the driftfauna catches only record
the occurrence of juveniles and adults in the higher water column but not close to
the bottom (Armonies, pers. com.; Jaklin unpublished data). Detailed questions on
population level, e.g. concerning the dependence of the turnover rate from (I) the
abundance, (2) size of the organisms or (3) abiotic conditions, could not be answered by applying the methods mentioned above.
For this reason an in situ staining technique was developed using neutral red as
marker (Jaklin unpublished data). Staining was carried out by pouring seawater
with dissolved neutral red onto fenced areas in the field. The fence was made of
plastic penetrating several cm into the sediment as well as protruding several cm
above the sediment surface. The stained seawater penetrated during the emergence
period into the sediment and stained the biota there. Surplus of neutral red was
washed away with the next flood period, after which the fence was removed. Sampling in the plots was done on a daily base, the technique is described in
Sect. 5.3.3. Juveniles of the bivalves M. balthica, E. americanus, C. edule and
Tellina sp. but also of the polychaetes Nereis spp., E. long a and P. elegans were
clearly visible stained. Thus, juveniles of several abundant species could be successfully stained, but this technique has its specific limitations similar to sediment
or emergence traps. Polychaetes such as S. armiger or Aphelochaeta marioni were
not stained sufficiently or the red colour was not visible due to the reddish colour
of the worms themselves. The same accounted for adult Hydrobia ulvae. According to laboratory experiments the staining did neither affect behaviour nor increased mortality of the macrofauna. In polychaetes the red colour persisted for a
period of 2-4 weeks, depending on the species stained and individual variability
(Jaklin, unpublished data).
First results obtained by staining experiments in 1995 implied that at the site
GP3 the local stock of the tube building polychaete P. elegans was completely
exchanged within 6 days. The turnover period of M. balthica at a site close to the
141
water. Crustaceans belonging to the genus Gammarus (G. locusta, G. salinus) were
also found more closely to the bottom, while Urothoe poseidonis moved into
higher parts of the water column. There is still a need for more information concerning the vertical distribution of benthic macrofauna in the water column. Special attention of future research should be given to the question which life stages
may reach which height above ground and what this means in relation to the potential transport distance.
5.3.4
In situ Turnover Rates of Juvenile Macrofauna in Soft Sediments
A consequence of secondary dispersal of juvenile macrofauna, either by active
migration or passive resuspension, implies - at a given site at a given area - a turnover of organisms. Regular sampling of benthos documents the change of abundance over time. but does not give any information whether either input or output
of organisms or the relation between these factors had caused the change.
Beside benthos samples further methods have to be applied, such as emergence
or sediment traps, to analyse the turnover of organisms. Armonies (1994) was the
first to estimate the turnover rate by a combination of benthos and sediment trapsampling. A combination of driftfauna nets and benthos data was not suitable for
the quantitative evaluation of turnover rates, as the driftfauna catches only record
the occurrence of juveniles and adults in the higher water column but not close to
the bottom (Armonies, pers. com.; Jaklin unpublished data). Detailed questions on
population level, e.g. concerning the dependence of the turnover rate from (I) the
abundance, (2) size of the organisms or (3) abiotic conditions, could not be answered by applying the methods mentioned above.
For this reason an in situ staining technique was developed using neutral red as
marker (Jaklin unpublished data). Staining was carried out by pouring seawater
with dissolved neutral red onto fenced areas in the field. The fence was made of
plastic penetrating several cm into the sediment as well as protruding several cm
above the sediment surface. The stained seawater penetrated during the emergence
period into the sediment and stained the biota there. Surplus of neutral red was
washed away with the next flood period, after which the fence was removed. Sampling in the plots was done on a daily base, the technique is described in
Sect. 5.3.3. Juveniles of the bivalves M. balthica, E. americanus, C. edule and
Tellina sp. but also of the polychaetes Nereis spp., E. long a and P. elegans were
clearly visible stained. Thus, juveniles of several abundant species could be successfully stained, but this technique has its specific limitations similar to sediment
or emergence traps. Polychaetes such as S. armiger or Aphelochaeta marioni were
not stained sufficiently or the red colour was not visible due to the reddish colour
of the worms themselves. The same accounted for adult Hydrobia ulvae. According to laboratory experiments the staining did neither affect behaviour nor increased mortality of the macrofauna. In polychaetes the red colour persisted for a
period of 2-4 weeks, depending on the species stained and individual variability
(Jaklin, unpublished data).
First results obtained by staining experiments in 1995 implied that at the site
GP3 the local stock of the tube building polychaete P. elegans was completely
exchanged within 6 days. The turnover period of M. balthica at a site close to the