Reproduction strategies and distribution of larvae and juveniles of benthic soft-bottom invertebrates in the Kara Sea (Russian Arctic) [Elektronische Ressource] : the influence of river discharge on the structure of benthic communities ; a larval approach / Ingo Fetzer

Ingo Fetzer

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2004
• Nombre de lectures: 62
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Reproduction strategies and distribution of larvae
and juveniles of benthic soft bottom invertebrates
in the Kara Sea (Russian Arctic)
The influence of river discharge on the structure of benthic
communities: a larval approach
Ingo Fetzer
Vorgelegt im Fachbereich 2 (Biologie/Chemie) der Universität Bremen
als Dissertation zur Erlangung des akademischen Grades
eines Doktors der Naturwissenschaften (Dr. rer. nat.)
Bremen 20041. Reviewer: Prof. Dr. Wolf Arntz
Alfred Wegener Institute/University of Bremen
2. Reviewer: Ass. Prof. Dr. Sigrid Schiel
Alfred Wegener Institute/University of KielContents
1 Introduction 11
1.1 Life history traits in marine invertebrates . . . . . . . . . . . . . . . . . . . . . . 11
1.2 Definition of ’larva’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.3 Historical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.4 ’Thorson’s rule’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.5 Ecological implications of reproduction modes . . . . . . . . . . . . . . . . . . 19
1.6 Aims of the study and hypotheses . . . . . . . . . . . . . . . . . . . . . . . . . 20
2 Material and Methods 23
2.1 Study area - environmental conditions . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Sampling areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.3 gear and treatment of samples . . . . . . . . . . . . . . . . . . . . . . 27
2.4 Data handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3 Results and Discussion 33
3.1 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2 Kara Sea ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.1 Zoobenthos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.2.2 Juveniles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2.3 Meroplankton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3 Influence of river discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.3.1 Influence of river discharge on plankton and benthos . . . . . . . . . . . 42
3.3.2 of hydrography on the distribution of larvae . . . . . . . . . . . 43
3.4 Reproduction modes and zoogeographic affiliation . . . . . . . . . . . . . . . . 49
4 Conclusion and future perspectives 55
5 Publications 57
5.1 Publication I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.2 II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.3 Publication III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.4 IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.5 Publication V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
6 Acknowledgements 217
7 Reference List 221SUMMARY
Summary
Reproduction strategies strongly influence distribution patterns and abundance of marine benthic
invertebrates. Most of them exhibit rather complex and diverse life cycles that are adapted to the
environment the species live in. The great diversity of life history patterns found has generated
intense debates among ecologists on classification of different development types and their rela
tionship to given biotic and abiotic environments. In the light of new findings from polar seas
much interest is given to the potential geographical shift in main life history traits of benthic in
vertebrates. However, until now little is known about the reproduction strategies of the majority
of Arctic invertebrates. Most species in temperate areas reproduce with pelagic larvae, which
often act as passive drifting particles in the water column. Their distribution is therefore mainly
determined by local hydrographic patterns, which can either transport them away or retain them
close to their spawning ground, the distribution of their adults (=place of release) and the du
ration of their stays in the water column. Direct development ensures that the offspring stays
on approved sites where adults already survived and guarantees sufficient recruitment within the
community since larvae are not endangered to be transported away by currents.
The main aims of this work are to determine the reproductive patterns of benthic invertebrates
in the Kara Sea and to analyse possible adaptations of reproduction strategies to polar conditions.
The structuring influence of river discharge and hydrography on the spatial distribution of larvae
and settled juveniles in relation to the distribution of their adults is investigated. Given the
specific characteristics of the Kara Sea, special emphasis is put on the role of the pycnocline
in separating meroplankton communities. The Kara Sea is a shallow shelf sea with an average
depth of 50 m located in the Russian Arctic. Besides strong fluctuations in light, temperature
and ice coverage, hydrography and ecosystems are strongly affected by the immense freshwater
input of the two adjacent rivers Ob and Yenisei. The outflow creates a pronounced bilayered
pelagic habitat with a confined pycnocline. Analyses of zooplankton samples from three years
revealed a strong structuring effect of river discharge on pelagic communities. River run off
varied significantly between years. Benthic communities are clearly shaped by the influence of
freshwater input but also by the deposition of imported organic material, which can be utilised
as a food source.
Pelagic larvae and juveniles of marine benthic invertebrates of the Kara Sea were sampled,
identified and their quantity and dispersal patterns in relation to the presence and distribution of
their adults analysed. At each sampling station, three plankton samples were taken: one below
the pycnocline, one across and one above it. Additionally, sediment samples were collected using
a large box corer and a multicorer to monitor adult and juvenile distribution, respectively.
During the investigation period in 2000 and 2001, 44 larval and 54 juvenile species were
identified. For 23 of the larval species adults were present in benthos samples. For the remaining
21 larval species, adults were reported from the adjacent Barents and Petchora Sea, indicating
a strong larval supply from the neighbouring seas. Most larvae were found in all water layers,
although highest abundances were present in the upper low salinity layer, revealing a high accli
matisation potential of most larvae to low salinities. Notably, the ophioplutei of the brittle star
Ophiocten sericeum, whose adults are very sensitive to lowered salinity, showed high concentra
VSUMMARY
tions within low salinity meltwater plumes. No differences in meroplankton densities were found
between the surface layer and the pycnocline, but surface and bottom layer differed significantly.
The pycnocline seems to act as a physical barrier for most larvae. Meroplankton densities of
3individual species were generally <1 ind. m , but ophioplutei of O. sericeum reached
3of 200 ind. m . The hydrographical regime strongly influences larval distribution both verti
cally and horizontally. Generally, lowest concentrations were found in the wake of the rivers,
although along a transect out of the Yenisei River local accumulation of larvae in the estuary
was found. Retention is most likely caused by circulation patterns created by the strong river run
off. Retention of larvae of benthic invertebrates within nursery grounds and/or the return to their
parental grounds is challenging for species in areas with strong riverine output. The importance
of retention in the study area was demonstrated for five exemplary species.
Most benthic species of the study area show an Arctic zoogeographic distribution, but a
considerable number of Arctic boreal, boreal and cosmopolitan species were also found. The
river run off may not only foster the survival of euryhaline species but through its thermal input
also creates favourable conditions for boreal species. Most invertebrate species in the Kara Sea
seem to reproduce directly. This large proportion can be explained in some parts by the high
share of peracarid crustaceans (Cumacea, Isopoda and Amphipoda) in the species composition.
While other taxa display a huge spectrum of reproduction modes, which vary strongly between
species and geographic regions, peracarids show a direct reproduction trait all over the world.
Their elimination from the dataset in this study reveals for the Kara Sea a larger share of species
reproducing with pelagic larvae. It is assumed that due to its variability in both biotic and abiotic
factors, the environment of the Kara Sea shelf often creates unfavourable conditions for benthic
species. Species with pelagic larvae or highly mobile species like most peracarid crustaceans
may have an advantage in reoccupying defaunated habitats.
The numerous larval types found in this study indicate that planktonic development is impor-
tant in the Kara Sea ecosystem. There is still a considerable lack of knowledge on reproductive
strategies of marine invertebrates, which especially holds true for organisms of the Arctic Ocean.
Better knowledge on reproduction traits and dynamics of polar benthic invertebrates is not only
a fundamental aspect for understanding Arctic ecosystems, but also a prerequisite for the inter-
pretation of their reaction