Ecological Studies in the Antarctic Sea Ice Zone: Results of EASIZ Midterm Symposium

294 Pages·2002·23.06 MB·English

by  John S. Gray (auth.)

Wolf E. Arntz· Andrew Clarke (Ed .)
Springer
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Wolf E. Arntz· Andrew Clarke (Eds.)
Ecological Studies
in the Antarctic
Sea Ice Zone
Results of EASIZ Midterm Symposium
Springer
Professor WOLF E. ARNTZ
Alfred Wegener Institute for Polar and Marine Research
P. O. Box 120161
275515 Bremerhaven
Germany
Professor ANDREW CLARKE
British Antarctic Survey
High Cross, Madingley road
Cambridge CB3 OET
UK
ISBN-13: 978-3-642-63973-9 e-ISBN-13: 978-3-642-59419-9
DOl: 10.1007/978-3-642-59419-9
Library of Congress Cataloging-in-Publication Data
Eclogical studies in the Antarctic Sea ice zone: results of EASIZ midterm symposium/
Wolf E. Arntz, Andrew Clarke (eds.).
p. cm.
Includes bibliographic references (p. ).
TSBN-13: 978-3-642-63973-9
I. Marine ecology-Antarctica-Congresses. 2. Benthos-Antarctica-Congresses. I.
Arntz, Wolf. II. Clarke, A., 1949-
QH84.2. E25 2002
577. 7'7-dc21
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Foreword
Ten years ago Polar Biology published the book, Weddell Sea Ecology, containing the European
"Polarstern" study EPOS in the Weddell Sea and Peninsula waters 1988/89. In certain respects,
the present collection of papers, first published in Polar Biology in 2001, is a follow-up as it
combines papers partly based on three "Polarstern" expeditions to the same region. Further
articles relate to both land-based and shipborne studies, again primarily in the Atlantic sector
and around the Antarctic Peninsula. The SCAR programme, "Ecology of the Antarctic Sea Ice
Zone" (EASIZ), served as an umbrella for a truly international cooperation. Although funding
came exclusively from national sources, 40% of the scientists on board "Polarstern" were
foreigners. Out of the 35 papers of the present volume not less than 14 papers have multinational
authorship. The scope of EASIZ is wider ilian the Southern Ocean Studies in JGOFS and
GLOBEC. The Contents reflect emphasis on the study of benthos, which hitherto had not
received the necessary attention in the attempt to understand key questions of evolution and
zoogeography of fauna from the Southern Hemisphere. The information collected under EASIZ
enhanced greatly our recognition of the rather high biodiversity of ilie Antarctic shelf benthos.
In order to extend these studies to ilie deeper continental slopes and the deep sea, "Polarstern"
is presently on her way for ilie first international survey of deep-sea benthos in the Atlantic
sector of ilie Southern Ocean.
The volume also contains a wealth of ecological information on the coupling of the sea
ice, pelagic, and benthic subsystems. Furthermore, it deals with aspects of ecophysiology and
survival strategies in many taxa and communities, ranging from bacteria to mammals. Stu
dies in iceberg scourings have relevance to broad aspects of stability and resilience of benthic
systems. The epifaunal suspension feeders are the most conspicuous element of the Antarctic
benthos, but they have not been investigated exhaustively until EASIZ. Modern technology
was extensively employed, including video ROVs, underwater cameras, and telemetry.
It has been a long way from the oral presentations at the First EASIZ Symposium 1999
in Bremerhaven to the publication of the papers in Polar Biology and, subsequently, the
completion of this volume. Most contributions have been largely rewritten to include current
results. The conveners of the Symposium, Wolf Arntz and Andrew Clarke, became guest
editors. The usual game of "push and patience" resulted in a fine collection of manuscripts
which then underwent final scrutiny by the editorial office of Polar Biology. A great number of
referees were involved in the process. Their efforts and the patience and willingness of the
authors to revise their manuscripts, often more than once, are gratefully acknowledged.
The Scientific Committee on Antarctic Research (SCAR) is to be congratulated on the
outcome of the first part of EASIZ as documented in the present volume. Polar Biology will be
happy to receive further first-class manuscripts produced under EASIZ and its international
projects.
Bremen, April 2002 GOTTHILF HEMPEL
EASIZ so far
Some comments on the mid-term EASIZ Symposium
The midway point of the SCAR EASIZ (Ecology of the Antarctic Sea-Ice Zone) pro
gramme was marked by the first EASIZ Symposium, held at the Alfred-W egener
Institut, Bremerhaven, Germany, between 22 and 25 June 1999. The symposium was
attended by 130 scientists from 17 nations and, although the core of the meeting was
concerned with work undertaken during the second EASIZ cruise to the Antarctic on
RV Polarstern, the subjects presented covered the whole range of EASIZ science un
dertaken from both ships and shore stations in the past 4 years. A total of 140 talks
and posters was presented. The subject presented most extensively at the symposium
was biodiversity, but there were also a significant number of presentations in three
other areas of particular interest to EASIZ, namely the biological effects of ice, cryo
pelagic and pelago-benthic coupling, and the ecophysiology of polar marine organ
isms.
This mid-term symposium showed clearly that the EASIZ programme has devel
oped strongly and has already provided new insights into a number of the key eco
logical processes operating in the coastal and shelf ecosystem of Antarctica. In some
cases, recent work within the EASIZ programme has changed fundamentally our view
of the system, sometimes to an extent that will require the rewriting of textbook
paradigms that have been in existence for decades.
A major change in our view of polar marine systems has come from the re
cognition that many (though not all) groups of marine organisms in Antarctica are
taxonomically diverse. The previous paradigm of the bell-shaped curve determined by
high diversity in the tropics and depauperate faunas towards the poles will have to be
abandoned in favour of an asymmetric distribution of taxonomic richness in the two
hemispheres. The greater species richness of the Southern Ocean compared with the
Arctic Ocean may be the result of its greater age, the larger area and a higher level of
structural heterogeneity formed by living organisms. Topics for future studies will
include the role of spatial scale, e.g. local versus regional species richness, and the
factors determining latitudinal patterns where these exist O.S. Gray, keynote address).
The pycnogonids are a particularly rich and conspicuous group, with 31 genera
and 251 species in the Southern Ocean. T. Munilla summarizes results from over 40
expeditions and suggests that Antarctic waters have been a long-term centre of pyc
nogonid radiation and dispersion. For many other taxa, however, the species inventory
of the Southern Ocean is still far from complete, and recent finds are presented for
bathypelagic hydromedusae 0. Bouillon et al.), octopodid molluscs and sabellid
polychaetes. Both the number of octopodid species and their abundance increase with
latitude, and the endemic genus Pareledone seems to have undergone extensive ra
diation on the Antarctic seafloor (1. Allcock et al.). The polychaete families Polynoidae
and Sabellidae revealed a higher variability in reproductive features than hitherto
assumed, with, for example Harmothoe species brooding their eggs under the elytra
and Myxicola cf. sulcata incubating its embryos within the tentacle crown (M.e.
Gambi et al.). The first quantitative data on Weddell Sea deep-sea polychaetes are
provided by B. Hilbig. Species richness was found to be high compared to temperate
VIII
deep-sea areas in the Atlantic and Pacific Oceans, whereas population densities were
considerably lower. A striking difference in population density between Antarctic and
Arctic waters was also detected in peracarid crustaceans from epibenthic sledge
samples, with densities one order of magnitude higher in the Arctic (A. Brandt). This,
combined with a preliminary assessment that species richness is high, may reflect the
greater age and maturity of the Southern Ocean assemblages. The rate of speciation is
an important component of biodiversity, but no evidence for a slowing of molecular
substitution rates in serolid isopods under very low water temperatures could be
detected by C. Held; temperature does not seem to be the key determinant of nu
cleotide substitution rate. A cytogenetic study of the bathydraconid fish Gymnodraco
acuticeps (E. Pisano et al.) provides information on chromosomal diversification
during the cladogenesis of this notothenioid family whose intra-familiar relationships
are still very uncertain.
Using digestive tract analyses and relative species abundance data from three
summer cruises, P. Dauby et al. have assessed the impact of amphipod populations on
their prey in the Weddell Sea. Crustaceans, plankton particles and fish carcasses
contributed the bulk of the diet. Another facet of diversity, that of epibenthic habitats
occupied by gammaridean amphipods, was studied by C. De Broyer et al. The authors
distinguish three epibenthic strata and a variety of symbiotic microhabitats associated
with benthic suspension feeders. Studies such as these will be important in improving
trophic flow modelling in Antarctic waters. Based on a scanning electron microscopy
study of the mandibles and stomachs of three common Antarctic caridean shrimps
v.
whose diet was also studied using the experience of the various experts on board,
Storch et al. conclude that stomach contents do not correlate well with mouth and
stomach morphology, nor was there a clear relation with their observed life style or
habitat preferences.
The two final biodiversity contributions in this volume deal with benthic assem
blages. K. Jazdzewski et al. sampled a stony beach near Arctowski station during a
complete annual cycle and found an unexpectedly high abundance of amphipods at
the beginning of winter, possibly related to high autumn biomass of decaying algae on
the beach. Assemblages of necrophagous animals were studied using baited traps on
the continental shelf and in the deep sea of Enderby Land (Takeuchi et al.). Endemic
Antarctic amp hip ods and isopods prevailed at the shelf sites, which revealed a higher
diversity as compared with the deep-sea site, where the large cosmopolitan amphipod
Eurythenes gryllus was dominant. The biodiversity discussions of the symposium
benefitted considerably from the presence of biologists with first-hand experience of
both northern and southern polar regions; the field of bipolar comparisons is clearly
one which is potentially rich in insights and should be encouraged for the future.
The second major subject dealt with during the EASIZ Symposium were the in
teractions between the pelagial and the benthic ecosystem, and particularly benthic
suspension feeders. In a keynote address, J.-M. Gili et al. summarise recent results
from shallow and deep waters around Antarctica, emphasising that the traditional view
that the Antarctic benthos depends entirely on the short seasonal plankton blooms
with associated long periods of starvation during the major part of the year is ob
viously wrong. As in other oceans, many benthic suspension feeders in the Southern
Ocean continue feeding in winter and can make use of the food web based around
bacteria, nano- and picoplankton, unicellular organisms and organic detritus con
tained in the seston. In addition to this wide trophic range, they take advantage of the
processes of advection and resuspension. Their feeding strategy thus does not differ
much from that found in benthic suspension feeders elsewhere, and exchange pro
cesses between the pelagic and benthic realms may be of a similar order of magnitude
as in other oceans.
Quite a different look - from above - is cast on the shallow-water ecosystem of
Potter Cove (King George Island) by I. Schloss and G. Ferreyra. These authors mea
sured phytoplankton photosynthesis and wind-induced turbulent mixing as well as
light penetration in the inner and outer cove. They conclude that phytoplankton
development in the area is restricted by low irradiance caused by suspended glacial
flour and by wind-induced mixing, resulting in a low input to the benthos. Katabatic
IX
winds were also a key forcing factor for pelagobenthic coupling in Adelie Cove (Terra
Nova Bay, Ross Sea). Over short time scales, they altered water column stability,
vertical and lateral transport, nutrient evolution, primary production and degradation,
and enhanced carbon flux to the shallow sediments, which had a three to four times
higher organic matter content than sediments at the same depth offshore. This fa
voured the development of benthic detritus and large suspension feeders such as
Laternula elliptica (P. Povero et al.). The flow of matter at even shallower depths was
observed by Isla et al. at Johnson's Dock (Livingston Island). Erosion and transport of
ice from the glacier situated inside the dock influenced fluxes to the sediment sig
nificantly, contributing above all to a high lithogenic content. Organic input was
similar to that in deeper waters of Bransfield Strait, although in Johnson's Dock the
residence time of particles in the column was too short to allow for the biological
transformation found elsewhere.
Interesting evidence for opportunistic feeding was found by Orejas et al. in a study
of the diet of four Antarctic benthic cnidarians. The food differed strongly among
species and ranged from large zooplankters to the fine fraction of seston and re
suspended material. Finally, Plotz et al. in their investigation of Weddell seal foraging
showed that these seals feed predominantly on the abundant fish Pleuragramma
antarcticum, and this determined much of their diel diving behaviour. Both pelagic
and benthic diving occurred during daylight, but at night the seals foraged almost
exclusively in the upper pelagic zone. This study was the first to combine time-depth
recorder data and trawling, which turns out to be a promising approach for the future.
Sea ice is a special environment in the Antarctic, having many organisms asso
ciated with it and exerting a distinct influence (cryopelagic coupling) on the water
column. Furthermore, the impact of icebergs and anchor ice has a major influence on
the composition, stability and dynamics of the littoral and shelf marine ecosystems. Ice
biota and ice impacts were therefore the third major subject treated during the EASIZ
Symposium. In a keynote address, J. Gutt reviewed the effects of ice disturbance on
Arctic and Antarctic benthos assemblages. In this comparative study, he found sea ice
to be of greater relevance in the north and iceberg impact to be more common and
evenly distributed in Antarctic waters. Iceberg scouring enhances diversity because the
temporal pattern of disturbance allows for the co-existence of different successional
stages. By contrast, glaciers cause faunal impoverishment, though primarily only in
their close vicinity. Ice impact has also been important in the development of the
present-day benthic fauna.
Fluxes of particulate organic matter from the platelet ice layer and through the
water column were measured by D.N. Thomas et al. under the sea ice of the Drescher
Inlet during austral summer. As there was little evidence of algal activity within the
thick multi-year sea ice, algal growth must have taken place in the underlying platelet
ice layer. The magnitude of the diel POC flux was not very high, with diatoms, mainly
frustules of ice algae, sinking largely intact as faecal pellets to the benthos at about
400-m depth. This flux had important consequences for cryobenthic coupling. Fast-ice
bottom algae production was measured in McMurdo Sound in the 1999 summer at a
30-m-deep site without a platelet layer, and oxygen microelectrode measurements were
taken in situ by L.J. Trenerry et al. Their results complement former sea-ice pro
duction measurements in the area from the surface, the platelet layer and the bottom.
The role of Antarctic sea ice for meiofaunal organisms is demonstrated in a study by S.
Schnack-Schiel et al. Foraminifers dominated the sea-ice assemblages by number and
turbellarians by biomass. The greatest concentrations of meiofauna were found in the
lowest parts of sea ice in autumn and winter, but there may be high densities of these
organisms in upper and intermediate layers of porous sea ice in summer as well as on
the underside of flows and in the adjacent water.
Two further meiofauna studies by H.J. Lee et al. refer to the impact of iceberg
scour on these organisms at the seafloor. The first describes the response of a shallow
(8-9 m) meiofauna community off Signy Island to catastrophic iceberg scour. This
reduced meiofaunal abundance by over 95% and diversity was also reduced. However,
recovery was accomplished within 30 days, and over the longer term nematode
community structure was affected very little, pointing to a high degree of resilience of
x
this community to disturbance by ice. In a second study, three stations each at a
different stage of recolonisation following iceberg scour were studied between 255 and
298 m depth off Kapp Norvegia (Weddell Sea); these comprised a fresh scour, an older
scour and an undisturbed control site. Overall meiofaunal abundance and diversity
were significantly lower in the fresh scour and highest in the older scour. Nematode
abundance and diversity were also lowest in the fresh scour, however, whereas
abundance had recovered to the undisturbed level in the old scour, generic diversity
remained low, indicating that the continental shelf nematode community is sensitive
to iceberg disturbance.
The final two contributions in this section deal with iceberg impact on the mega
epibenthos and on demersal fish. Gutt and Starmans used video transects on the
eastern Weddell Sea shelf to classify the epibenthic megafauna into stages after iceberg
impact and unaffected fauna, taking into account bottom topography and con
centrations of grounded icebergs. Calculating impact factors from recently disturbed
areas and recovery time suggested that iceberg scouring is among the most significant
disturbances experienced by any large ecosystem on earth. Brenner et al. compared
areas affected by icebergs and undisturbed bottoms in the same area and conclude that
small-scale horizontal patterns caused by iceberg scour playa distinct role in niche
separation of the fish genus Trematomus. Different species preferred either disturbed
or undisturbed areas, as is indicated by total stomach contents and number of prey
taxa per fish.
Although the overwhelming part of the contributions offered at this symposium
was concerned with ecological questions and processes, physiology is also an im
portant facet of the programme, often providing causal explanations for the me
chanisms that underlie empirical ecological findings. In his keynote address, L.S. Peck
reviews recent advances in the understanding of adaptation to low temperatures in
marine organisms. He stresses the central role of energetics in this context. Polar
ectotherms have low resting metabolic rates, which may be related to mitochondrial
function at low temperature, slow growth and development rates, and low aerobic
scopes. Of particular interest is the suggestion that oxygen supply to the tissues may
determine thermal tolerance and also limit maximum size.
The question of how Antarctic macro algae acclimate to seasonal changes in light
was investigated by D.H. Liider et al. using the photosynthetic apparatus of the alga
Palmaria decipiens in culture experiments. Maximal quantum yield remained high
during autumn, winter and spring, whereas maximal photosynthetic activity and
pigment contents increased continuously in mid-autumn and winter, and were highest
in spring. In summer, all these variables decreased to their lowest values and
P. decipiens proved to be efficiently adapted to the short period of favourable light
conditions in Antarctica. The identification of repair and protective mechanisms that
allow Antarctic species to survive and reproduce under increased DVB flux is dealt
with in the contribution by M. Hernando et aI., who studied the role of mycosporine
like amino acids (MAAs) in the photo acclimation of Thalassiosira sp. using different
experimental irradiance treatments. This marine diatom accumulated high con
centrations of MAAs, which are important in protection against ultraviolet radiation,
on a time scale of hours to days. Whereas Antarctic algae seem to have been quite
successful in developing adaptive mechanisms to a changing environment, some
faunal taxa appear to have been less successful. Frederich et al. link the striking
absence of almost all reptant decapods from the waters south of the Polar Front to high
magnesium levels in the haemolymph and a consequent failure of cardiac and venti
latory performance in very cold water, with Mg2+ acting as an anaesthetic. These
authors investigated temperature-induced changes in oxygen consumption of two
brachyuran crabs from southern Chile and present a model to describe how Mg2 +
reduction in the haemolymph causes a change in the threshold temperature which
characterises the onset of cold-induced failure in oxygen supply to tissues. Bluhm et al.
address an old methodological problem related to the difficulty of age determination in
crustaceans by measuring an autofluorescent pigment, lipofuscin, in the brain of ten
polar species from various crustacean taxa. Lipofuscin granules occurred in easily
detectable amounts in five species. Pigment concentrations were correlated with
XI
individual size within the species but did not indicate absolute body size when
comparing different species. For those species that accumulate sufficiently high
quantities of lipofuscin, the pigment is a potential indicator of age.
Ascidians are another polar taxon where growth and age are not easily de
termined, although some Antarctic species are believed to be relatively fast-growing.
Combining results from colonisation panels and respiration measurements, Kowalke
et al. show ascidians from Potter Cove to have high growth rates, which were favoured
by a low basal metabolism and an extended longevity. These properties, together with
their capability of surviving under intense sedimentation, made them effective com
petitors among benthic suspension feeders. Finally, Bock et al. used NMR techniques
to compare temperature-dependent pH regulation in a stenothermal Antarctic and a
eurythermal temperate eelpout (Zoarcidae). They conclude that, in contrast to pre
vious reports in the literature, internal pH regulation in at least some Antarctic fish
occurred as predicted by the alphastat hypothesis of acid-base regulation.
It is clear from the results presented at the mid-term EASIZ Symposium (not all of
which could be included in this volume) that the EASIZ programme has been a
success. In common with all biology programmes sponsored by SCAR (the Scientific
Committee for Antarctic Research), support has been provided for developing the
programme and holding symposia, but not for fieldwork or other scientific costs. The
EASIZ programme has therefore had to rely on the National Programmes of SCAR
nations for the scientific aims to be realised. Half-way through the programme it is
clear that EASIZ work has been promoted particularly by work from a small number of
ship platforms, most notably RV Polarstern and RV Hesperides, and a range of shore
stations including (in no particular order) Arctowsky, Jubany/Dallmann, Signy, Ro
thera, Terra Nova and King Sejong Stations. One particular highlight of the EASIZ
work has been the development of taxonomic expertise in key taxa, notably in Russia,
Spain, Belgium and Germany. Whilst the wider programme of research proposed at
the start of the EASIZ programme has been taken up enthusiastically by many national
programmes, the core programme has been less successful. The core programme
proposal was that a number of shore stations, preferably from all parts of Antarctica,
should undertake a series of regular nearshore oceanographic and ecological mea
surements with the aim of documenting patterns of geographical and interannual
variability in key ecological processes in the seasonal ice zone. Whilst some work has
started, there is still room for better coverage and it is hoped that this will improve in
the second half of the programme.
The mid-term symposium was followed by a series of concurrent workshops, the
aims of which were to evaluate progress to date, and to determine those areas of EASIZ
science that should receive particular attention during the final stages of the pro
gramme. Five workshops were run, and attendance was very encouraging, revealing a
strong interest in the future progress of the EASIZ programme. The conclusion from
these review workshops was that certain fields had been covered fairly satisfactorily
(although not always exhaustively) to date. These included topics such as species
composition and distribution in most macroinvertebrate, fish and macro algal groups
on the Antarctic shelf, characterization of typical Antarctic species assemblages in the
benthos and plankton of some regions (Weddell Sea, Ross Sea, Antarctic Peninsula),
and the structure of the different forms of sea ice and ice biota. Good progress had also
been made in fields such as the impact of ice on benthic meiofauna and macrofauna
(including fish), life-history strategies related to sea ice and in the pelagic and benthic
subsystems, and the diving, foraging and migratory behaviour of pack ice seals. The
latter topic is an area where the EASIZ programme has a strong overlap with the SCAR
programme on Antarctic pack-ice seals (APIS). The wider programme proposed for
EASIZ had laid specific emphasis on the need to understand ecophysiological aspects
of organisms in the sea-ice zone, and the workshops recognised that significant pro
gress had been made in this area. Examples of such progress included studies of the
range of physiological tolerance related to mechanisms of molecular and physiological
adaptation, photoinhibition and UV effects on marine algae, the role of oxygen con
sumption for behaviour and activity and, lastly, secondary production, trophic rela
tions and energy flow in the benthos.