6 Recolonization of Tidal Flats After Disturbance
Sabine Dittmann, Carmen-Pia Gunther & Ulrike Schleier
Abstract: The benthic recolonization of experimentally disturbed sandflat sites by
diatoms, nematodes and small macrofauna was studied with several treatments,
differing in intensity and timing of disturbance. Furthermore, recolonization following a natural disturbance, the ice winter 1995/96, was studied and compared
with the results of the experiments.
Diatoms were the fastest organisms recolonizing the disturbed sites. Within a
few days, their species number, species composition and individual abundances
were comparable to control situations. This colonization pattern depended on the
diatoms available in the ambient sediment at the time of disturbance. The mode of
recolonization was passive via sediment transport. The ice winter had little effect
on the diatoms and abundances were comparable to preceding years. Yet, three
species, which had not been recorded in the Wadden Sea before, occurred in the
tidal tlats in 1996.
Nematodes reached ambient densities in the experimentally disturbed plots
within a few weeks or months, with a slower recolonization the longer the disturbance had lasted. After the ice winter, nematode abundances increased steadily
and reached even higher values in summer 1996 than in the years before.
Smaller sized macrofauna recolonized disturbed experimental plots in spring
faster than plots disturbed in autumn. The recolonization was also faster, the
shorter the disturbance had lasted. The first stages of recolonization retlected the
ambient situation of the species composition and abundance of benthic organisms.
After several months, species numbers, abundance and community composition in
the disturbed plots could not be distinguished from the reference plots. The first
macrofaunal species colonizing the experimentally disturbed plots were the polychaete Pygospio elegans, Ostracoda and the amphipod Urothoe poseidonis. These
were also dominant in the benthic community in 1996 after the ice winter. Juvenile
polychaetes colonized the experimental sites to a higher degree than the ambient
sediment. The course of the recolonization was mainly dependent on the availability of settling organisms, i.e. larvae as well as postlarvae. The study period was not
long enough to record all successional stages.
6.1
Introduction
The analysis of recolonization after disturbances allows one to assess processes
that regulate and structure communities and to detect successional stages and their
underlying causes. Studies on the recolonization in soft sediment communities
Sabine Dittmann, Carmen-Pia Gunther & Ulrike Schleier
Abstract: The benthic recolonization of experimentally disturbed sandflat sites by
diatoms, nematodes and small macrofauna was studied with several treatments,
differing in intensity and timing of disturbance. Furthermore, recolonization following a natural disturbance, the ice winter 1995/96, was studied and compared
with the results of the experiments.
Diatoms were the fastest organisms recolonizing the disturbed sites. Within a
few days, their species number, species composition and individual abundances
were comparable to control situations. This colonization pattern depended on the
diatoms available in the ambient sediment at the time of disturbance. The mode of
recolonization was passive via sediment transport. The ice winter had little effect
on the diatoms and abundances were comparable to preceding years. Yet, three
species, which had not been recorded in the Wadden Sea before, occurred in the
tidal tlats in 1996.
Nematodes reached ambient densities in the experimentally disturbed plots
within a few weeks or months, with a slower recolonization the longer the disturbance had lasted. After the ice winter, nematode abundances increased steadily
and reached even higher values in summer 1996 than in the years before.
Smaller sized macrofauna recolonized disturbed experimental plots in spring
faster than plots disturbed in autumn. The recolonization was also faster, the
shorter the disturbance had lasted. The first stages of recolonization retlected the
ambient situation of the species composition and abundance of benthic organisms.
After several months, species numbers, abundance and community composition in
the disturbed plots could not be distinguished from the reference plots. The first
macrofaunal species colonizing the experimentally disturbed plots were the polychaete Pygospio elegans, Ostracoda and the amphipod Urothoe poseidonis. These
were also dominant in the benthic community in 1996 after the ice winter. Juvenile
polychaetes colonized the experimental sites to a higher degree than the ambient
sediment. The course of the recolonization was mainly dependent on the availability of settling organisms, i.e. larvae as well as postlarvae. The study period was not
long enough to record all successional stages.
6.1
Introduction
The analysis of recolonization after disturbances allows one to assess processes
that regulate and structure communities and to detect successional stages and their
underlying causes. Studies on the recolonization in soft sediment communities