ArticlePDF Available

Abstract and Figures

Although the processes occurring at the front of an ice face in tidewater glacier bays still await thorough investigation, their importance to the rapidly changing polar environment is spurring a considerable research effort. Glacier melting, sediment delivery and the formation of seabird foraging hotspots are governed by subglacial discharges of meltwater. We have combined the results of tracking black-legged kittiwakes Rissa tridactyla equipped with GPS loggers, analyses of satellite images and in situ measurements of water temperature, salinity and turbidity in order to examine the magnitude and variability of such hotspots in the context of glacier bay hydrology. Small though these hotspots are in size, foraging in them appears to be highly intensive. They come into existence only if the subglacial discharge reaches the surface, if the entrainment velocity at a conduit is high and if there is sufficient macroplankton in the entrainment layer. The position and type of subglacial discharges may fluctuate in time and space, thereby influencing glacier bay hydrology and the occurrence of foraging hotspots.
Content may be subject to copyright.
1
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
www.nature.com/scientificreports
Subglacial discharges create
uctuating foraging hotspots for
sea birds in tidewater glacier bays
Jacek Andrzej Urbanski1, Lech Stempniewicz2, Jan Marcin Węsławski3,
Katarzyna Dragańska-Deja3, Agnieszka Wochna1, Michał Goc2 & Lech Iliszko2
Although the processes occurring at the front of an ice face in tidewater glacier bays still await thorough
investigation, their importance to the rapidly changing polar environment is spurring a considerable
research eort. Glacier melting, sediment delivery and the formation of seabird foraging hotspots
are governed by subglacial discharges of meltwater. We have combined the results of tracking black-
legged kittiwakes Rissa tridactyla equipped with GPS loggers, analyses of satellite images and in situ
measurements of water temperature, salinity and turbidity in order to examine the magnitude and
variability of such hotspots in the context of glacier bay hydrology. Small though these hotspots are
in size, foraging in them appears to be highly intensive. They come into existence only if the subglacial
discharge reaches the surface, if the entrainment velocity at a conduit is high and if there is sucient
macroplankton in the entrainment layer. The position and type of subglacial discharges may uctuate in
time and space, thereby inuencing glacier bay hydrology and the occurrence of foraging hotspots.
Tidewater glaciers and the waters of bays in front of ice faces are unique features of arctic ords. Recent years have
witnessed greater research eorts in these areas, as glacier retreat is one of the most spectacular, visible signs of
global warming1. Glacier bays play a signicant part in sedimentation, ice cover formation and iceberg calving,
thus bringing a substantial inuence to bear on the ecology of ord coastal waters2,3. Because glacier termini
are accessible only with great diculty, very few eld measurements have been carried out there, and then only
at some distance from the ice wall. Certain processes have therefore been investigated only in the laboratory or
using mathematical models. Several geophysical processes take place near or on the ice face of tidewater glaciers.
Ice-front melting due to contact with seawater creates constant upwelling along the ice face. Some authors sug-
gest that this process is negligible when compared with the terminus retreat rate4,5, but others have attempted to
demonstrate that it may play an important role6,7. e uvial discharge of meltwaters is another process generally
regarded as crucial to the hydrology and ecology of glacier bays. A discharge outlet may be situated beneath the
glacier (subglacial discharge), somewhere on the ice face itself (englacial discharge) or on the surface of the glacier
(supraglacial discharge). ere may be many outlets of dierent kinds on the glacier front, and the position and
volume of discharged water may dier in time as a consequence of varying weather conditions and changes in ice
face shape and movement5.
Subglacial freshwater discharge has been shown to be the primary process driving high rates of submarine
melting in tidewater glaciers8–10, which has the potential to control terminus morphology and calving style11. e
delivery to a ord system of uvial freshwaters, turbid as a result of the large concentrations of suspended matter
they carry, creates muddy plumes close to the glacier front and involves a huge ux of sediments2,5,12. e biolog-
ical importance of subglacial discharges is reected in the shallower euphotic zone, changes to water parameters
like salinity and temperature, and the entrainment of organisms and nutrients carried to the glacier front by the
rising plume13,14.
e signicance of submarine ice melting is most oen described using upwelling or buoyant convective
plume models6,10,12,15,16, whereas in research into sediment distribution, submarine discharges take the form of a
buoyant jet described as a forced plume whose behaviour depends on the density dierence between the plume
and seawater and on the jets momentum. e instant subglacial meltwater leaves a conduit at the glacier front,
intensive mixing of the plume with ambient marine waters takes place. e resulting buoyant plume rises until it
1GIS Centre, University of Gdansk, 80-952 Gdansk, Poland. 2Department of Vertebrate Ecology and Zoology,
University of Gdansk, 80-308 Gdansk, Poland. 3Institute of Oceanology, Polish Academy of Sciences, 81-712 Sopot,
Poland. Correspondence and requests for materials should be addressed to J.A.U. (email: cgisju@ug.edu.pl)
received: 06 July 2016
Accepted: 03 February 2017
Published: 07 March 2017
OPEN
www.nature.com/scientificreports/
2
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
reaches the surface or a layer of water with a density equal to that of the plume, aer which it begins to ow hori-
zontally. In stratied waters, therefore, a turbid subglacial plume may never reach the surface5,10. e plume grows
as a result of turbulent mixing with warmer ocean waters and drives locally intensied melting at the ice-ocean
interface15, which may lead to the formation of ice caves, reported to be tens of meters wide and deep5. Moreover,
if the jet’s momentum is the dominant force, superelevation of the jet may occur on the surface, a phenomenon
known as water “boiling”5 (Supplementary Video S2).
A number of specic ecological eects of meltwater discharge can be observed in the vicinity of the glacier
terminus. e water area around the subglacial discharge that is ice-free due to currents and muddy due to sus-
pended sediments is called the “brown zone17 and is considered an attractive foraging site for seabirds13, seals18
and white whales, which feed mainly on polar cod19. Large amounts of marine zooplankton, stunned or killed by
osmotic shock, may be found in such zones20–23. Meltwater discharges also aect the euphotic depth in glacier
bays, which has a direct impact on phytoplankton growth13. e type of microplankton near the glacier front
changes from autotrophic to heterotrophic, and bacteria increase in number, possibly because of the presence of
ne mineral particles acting as nuclei of microbial aggregates13. Large numbers of dead zooplankton are known
to sink to the seabed near glacier clis21, and several carrion-feeding benthic organisms take advantage of this
resource23. However, large concentrations of live macroplankton (euphausiids) have also been recorded on the
seabed near glaciers, apparently feeding there23. e presence of highly saline, winter-cooled water is typical of the
bottom layer of glacier bays in the Arctic, which produces the conditions preferred by the cold-water stenotherms
oen found there13. Altogether, the ecology of glacier bays is governed by the advection of biomass-rich waters
from the shelf and their interaction with the topography and hydraulic forces near the glacier.
Although the vast marine environment appears to be homogeneous, the macroinvertebrates and sh that
constitute the bulk of food taken by seabirds and marine mammals are patchily distributed. ey are concentrated
in certain specic areas like shelf slopes, ice edges, oceanographic fronts and upwelling sites, where physical gra-
dients enhance the abundance of prey and its availability to seabirds in several ways. ese areas are conspicuous
by their greater abundances of marine birds and mammals24. Glacier bays with intensive subglacial discharges are
just such areas and are well known as attractive foraging grounds for seabirds like black guillemots Cepphus grylle,
ivory gulls Pagophila eburnea and especially kittiwakes Rissa tridactyla. Large aggregations of these have been
observed in various parts of Svalbard in the previously mentioned “brown zones” of glacier meltwater outlets.
Marine mammals, such as ringed seals Pusa hispida, bearded seals Erignathus barbatus, belugas Delphinapterus
leucas and polar bears Ursus maritimus also occur there in much higher numbers than in other ord habitats13.
e large supply of easily available food is thought to be a reason for these concentrations of marine vertebrates
in the glacier bays, although the mechanism by which such foraging hotspots form is still a matter of intensive
discussion13. For foraging, however, seabirds use only a relatively small part of the “brown zone” close to the
glacier river discharge and along the border between the fresh and saline waters. As a result of wind and wave
activity, the “brown zone” is oen broken up into separate long strips moving over the water surface far away from
the glacier bay. Northern fulmars Fulmarus glacialis are oen observed foraging along them25.
is study was motivated by a series of observations of kittiwake aggregations foraging on the muddy, sub-
glacial waters discharged by glacier termini. In Kongsord in 2015 we noted huge numbers of kittiwakes, from
several hundred to a few thousand, foraging in front of the dierently sized ice caves at each glacier terminus
in the ord (Fig.1). Drone video of kittiwakes foraging in front of Storbreen in Hornsund can be found as
Supplementary Video S2. Present knowledge and understanding of the processes at tidewater glacier fronts is
still unsatisfactory, and a number of questions remain unanswered: Do measurements conrm the theory of
physical processes of subglacial water discharge? What is the mechanism of plankton ux to foraging hotspots?
How large are the bird aggregations and how important are these particular foraging areas for seabirds during
the chick-rearing season? What inuences the spatial and temporal distribution of such hotspots? Why do not all
water discharges in glacier bays inuence foraging aggregations? We set up three hypotheses in an attempt to nd
answers to these questions: 1) the muddy waters close to the glacier front occasionally create important foraging
areas for birds during the chick-rearing season; 2) discharges of subglacial water sometimes form relatively small
hotspots with large amounts of dead or stunned macroplankton on the surface of waters in front of the ice caves;
3) these hotspots are associated with turbid uvial discharge waters and come into being during the entrainment
of the seawaters surrounding the subglacial discharge where macroplankton occurs. We tested these hypotheses
experimentally by combining the results of tracking black-legged kittiwakes Rissa tridactyla (henceforth kitti-
wakes) equipped with GPS loggers with the results of coupling satellite images and in situ measurements of water
temperature, salinity, turbidity and macroplankton in glacier bays.
Study Area
We chose two ords – Kongsord and Hornsund – on the west coast of Spitsbergen, each with several glacier bays
having trunk tidewater glacier termini (Fig.2). e Kongsord is probably the best described ord in Svalbard,
and subglacial discharges of meltwater have been recorded there several times5,26. ere are large breeding col-
onies of kittiwakes in both ords13. Kittiwakes were also recorded at glacier ice faces in Hornsund during the
seabird and marine mammal surveys conducted by our team in Burgerbukta in 2014 and 201525. Two bays:
Burgerbukta and Raudvika were examined in closer detail. Burgerbukta splits into two narrow bays with tide-
water glaciers at their ends; these bays are up to 100 m deep, but the depth near the glacier terminus is unknown
because of its fast rate of retreat. Raudvika is a small glacier bay, formed in the last 20 years, and ends with the ice
face of the Kongsbreen glacier. is bay was chosen because the water was ice-free, the surface turbidity across
the bay was highly variable (which is important when calibrating satellite images) and aggregations of kittiwakes
were observed in front of the glacier terminus (Fig.1). e ice face is partly grounded in shallow water or on the
coast, but most of the bay is between 20 and 40 m deep, with similar depths near the ice face. Both Burgerbukta
www.nature.com/scientificreports/
3
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
and Raudvika have a sill at their mouths: this gives rise to the formation of a three-layered structure of the water
masses, with winter-cooled water at the bottom27.
Results
Distribution of subglacial water discharges. We used high resolution Landsat 8 satellite images taken
on 8 August 2015 to map the surface distribution of suspended particulate matter (SPM) in Raudvika. e main
challenge in such attempts is to make in situ measurements at the same time as the image is taken and to measure
the background readings of the whole range of values occurring at that time. As Raudvika is relatively small and
the SPM values there were highly variable (2–600 mg l1), we were able to create a best-tting regression model
describing the relation between the reectance ratio in bands 2 and 4 with measured SPM in that wide range,
with the time gap between taking an image and making measurements being < 3 h. e formula obtained was
used to convert the multispectral image to the SPM map (Fig.3); its universality with regard to other areas will
be discussed later. Surface SPM near the glacier ice face was spatially variable. e main subglacial discharge in
the middle of the glacier front had an SPM concentration > 300 mg l1 and a maximum width of about 300 m. A
foraging hotspot with about 1500 kittiwakes was observed near the ice front where this discharge occurred. e
waters along the ice face on both sides of the discharge were much less turbid, with SPM up to 15 mg l1. At both
ends of the glacier face, two melt water streams enter the bay, forming plumes with higher SPM levels. e trunk
glacier bays can be characterised as low-energy environments with limited mixing, where the main forcing factors
are tidal currents, gradient currents of meltwater discharge and stress due to katabatic winds. As a result, diverse
yet patchy structures rather than a uniform layer form at the water surface. With this method we were able to
remotely identify the meltwater discharges reaching the surface and to compare the subglacial discharges in two
branches of Burgerbukta in Hornsund by coupling satellite SPM mapping and T,S,SPM measurements at two
cross-sections: one about 200 m and the other about 3 km from Pajerlbreen (Fig.4). e SPM surface mapping
was carried out using a Landsat 8 image taken on 31 July, with SPM being calculated from bands 2 and 4 using the
procedure described above. Using the same image, an SPM map was also drawn for Brepollen, the eastern part of
Hornsund. e control measurements made at the same time in Vestre Burgerbukta were encumbered with a root
mean square error (RMS) of 11 mg l1. e surface SPM distributions in both Vestre and Istre Burgerbukta glacier
bays were very dierent. In Vestre Burgerbukta high SPMs were recorded only in two streams of glacier meltwater
at the ends of the glacier wall, whereas the SPM level in the water in front of Pajerlbreen was much lower. In Istre
Burgerbukta by contrast, in front of Mülbrachenbreen, SPM concentrations were very high, indicative of subgla-
cial discharge. Comparison of Istre Burgerbukta with Vestre Burgerbukta shows that the SPM concentration in
the whole bay much larger (Fig.4). e SPM cross-section in front of the Pajerlbreen glacier showed a plume of
Figure 1. Observations of seabird aggregations. Seabirds were observed near ice caves with subglacial
discharges at glacier termini in Kongsord in August 2015. e estimated number of kittiwakes in front of
Kongsbreen was 1500. e positions of the glaciers are shown on Fig.2.
www.nature.com/scientificreports/
4
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
water with high SPM (up to 180 mg l1) at a depth of about 14 m. is is indicative of a subglacial discharge in the
form of a buoyant plume, which ows horizontally aer having reached a density level of the water column equal
to the plume density. e density prole for this bay shows uniform stability in the water column down to 20 m.
e structure of the plume with a sharper upper edge is shown on the SPM prole. is plume was not observed
in the second cross-section in the mouth of Vestre Burgerbukta (Fig.4).
Macroplankton in glacier bays. ere is a constant dierence between the surface water macroplankton
sampled in the two parts of Burgerbukta, i.e. close to the glacier clis and away from them: near the glacier they
are more abundant and diverse than the controls (Fig.5). Detailed results can be found in SupplementaryTableS1.
ere was no taxon that was found only in the control samples but not near the glacier; on the other hand, there
were several that were recorded near the glacier but not in the controls. is shows that the plankton recorded
near the glacier is not a subsample of the ords specic near-surface (neuston) macroplankton community but
represents a selection of organisms living in the whole water column that were moved to the surface near the
glacier. e inuence of the glacier on surface plankton was especially strong in the case of large (10–30 mm
long), actively swimming crustaceans (three species of herbivorous euphausiids ysanoessa spp. and two species
of carnivorous hyperiids emisto spp.), which are represented much more abundantly in the near-glacier sam-
ples than in the controls. e dierence between the control and glacier front samples is less marked in the case of
poor swimmers like herbivorous copepods (0.2 to 2 mm long), and minimal in the case of passively mobile, car-
nivorous gelatinous plankton like Ctenophora and Hydromedusae. is shows that gelatinous plankton habitually
occurs near the surface in the ord and that the conditions close to the glacier have no eect on its occurrence
pattern. Analysis of 25 food samples collected from Kittiwakes in the colony at the same time shows the domi-
nance of Polar cod (84% samples), macroplanktonic euphausiids (44%) and hyperiids (24%).
Figure 2. Project location map. Kongsord and Hornsund (a,c) are situated on the west coast of Spitsbergen,
the largest island in Svalbard (d). In Kongsord (a) the area of interest was Raudvika bay, outlined by the red
rectangle. e contours in Raudvika (b) are drawn at 5 m intervals. In Hornsund (c) measurements were carried
out in Burgerbukta and its branches to Vestre Burgerbukta and Austre Burgerbukta. e depth contours on the
maps (a,c) are drawn for 50 and 100 m depths only. e maps were drawn in ArcGIS 10.3.1 for Desktop, Esri
Inc., http://www.esri.com.
www.nature.com/scientificreports/
5
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
Seabird foraging hotspots at glacier fronts. In the deep tidewater glacier bays seabirds usually con-
centrated in the vicinity of the ice caves with their subglacial discharges of muddy waters. ere are ice caves
of dierent sizes at the fronts of most glacier termini in both Hornsund and Kongsord (Fig.1). Some of them
attracted from several hundred to many thousands of foraging kittiwakes. e highest number observed in this
study was in July 2015, when around 10 000 individuals were foraging simultaneously along the c. 300 m frontline
of Storbreen (personal obs.).
e distribution of the kittiwake sites in Brepollen is illustrated on Fig.6. In 2015 several large aggregations
of kittiwakes were observed. e majority of birds equipped with GPS loggers (9 out of 12 birds; 75%) visited
this area during the study period and 36% of the 2 952 recorded body-water contacts took place in Brepollen.
e mean time of the birds’ foraging events at the main hotspot in Brepollen was 3.3 ± SE 0.31 hour. D etails
of the GPS tracking study of kittiwakes in Brepollen are listed in Table1. We measured the distribution of the
birds’ foraging aggregations at the biggest hotspot in front of Storbreen (more than 60% of water contact points
in Brepollen) using the overlap of minimum convex polygons (MCP)28 of foraging ranges. e mean foraging
range was 0.012 ± SE 0.003 km2 in area. e MCP overlap was more than 90% near the subglacial discharge of
Storbreen and formed a hotspot about 40 m in radius, while an overlap of over 50% covered an area with a radius
of about 100–120 m (Fig.6c). e area inside the 90% contour is 0.007 km2, while that inside the 50% contour is
0.034 km2. Both areas lie completely within the discharge plume. Figure6c also shows the concentration of water
contact points in this area as the distribution of the number of points in a 5 × 5 m cell grid. We used the MCP
method to compare the number of water contacts (which assume foraging) in Brepollen with other foraging areas.
In Brepollen the MCP was delineated around all points (n = 1068). We used the Kernel Density method for all
points outside Brepollen to choose the same number of points from the areas with the highest densities. en the
MCP was delineated around these 1068 points with the highest densities outside Brepollen and these continuous
surface areas were compared: 54.7 km2 in Brepollen compared with 4 800 km2 outside.
Discussion
Recent interest in bays with tidewater glacier termini has been generated mainly by the widely observed rapid
retreat of glaciers and calving ux resulting from global warming: rising sea temperature accelerate ice melting.
In this paper we describe the physical and biological features of the water in the vicinity of subglacial discharges
and the mechanism by which unique sites functioning as foraging hotspots for seabirds are formed. ey are
Figure 3. Mapping the surface distribution of suspended particulate matter in Raudvika. e composite
of Landsat 8 satellite image bands shows dierent colours of the water as a result of dierent SPM levels at
the surface. e sampling stations are shown by yellow circles (a). e correlation model was used to convert
reectance bands to SPM (b). e SPM map can be used to identify remote meltwater discharges reaching the
surface. e magenta circle shows the aggregation of birds (1500 birds) (c). e maps were drawn in ArcGIS
10.3.1 for Desktop, Esri Inc., http://www.esri.com. e Landsat image was provided by: U.S. Geological Survey,
Earth Resources Observation and Science (EROS) Center, 2016, Landsat products and services: EROS, Glovis
Web page, accessed 20 June 2016 at http://glovis.usgs.gov/.
www.nature.com/scientificreports/
6
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
very small in area and, as they attract thousands of birds feeding simultaneously, the foraging eciency in them
appears to be extremely high. at birds concentrate their foraging eorts in front of glaciers was known13, but
the scale of the phenomenon was not. e spots we investigated were less than 54.7 km2 in area: this is equivalent
to an area of 4800 km2 compared to the same amount of time the kittiwakes from one colony spend foraging on
other feeding grounds during one breeding season. e same number of body contacts with water were recorded
in both areas.
Figure 4. Subglacial discharges in Burgerbukta. e SPM distribution in Burgerbukta in Hornsund on 31
July 2015 (a) mapped from the Landsat 8 satellite image. Two SPM cross-sections were made using S, T, SPM
proles carried out at the same time (b). e T, S, SPM proles and water density measured at point P on the
cross-section closer to the glacier terminus are also presented; the density (dashed line) includes the inuence of
SPM (c). e maps were drawn in ArcGIS 10.3.1 for Desktop, Esri Inc., http://www.esri.com.
Figure 5. Macroplankton abundance in glacier bays. Macroplankton samples and near-surface
macrozooplankton density (individuals per sample) – “close” – stations near the glacier cli, 1 km – station away
from the glacier. e Landsat image was provided by: U.S. Geological Survey, Earth Resources Observation and
Science (EROS) Center, 2016, Landsat products and services: EROS, Glovis Web page, accessed 20 June 2016 at
http://glovis.usgs.gov/.
www.nature.com/scientificreports/
7
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
Tidewater glaciers can be classied as trunk or side-entry glaciers. It is worth mentioning that ever since
glacier retreat has become widespread, many glaciers that in the past were classied as side-entry are now trunk
glaciers. is has consequences for the local hydrology, as trunk glacier bays are a very low-energy environment5.
e most important process, making these bays unique, is glacier meltwater discharge. is may be of three
types – subglacial, englacial or supraglacial – to which we can add the subaerial rivers oen present on both
sides of glaciers. e meltwaters from all types are usually very turbid. ese subglacial discharges occasionally
create a mechanism by which zooplankton becomes concentrated (Fig.7). e mass of the glacier exerts a pres-
sure on the waters of a subglacial conduit that exceeds the hydrostatic pressure. Such pressures may give rise to
water velocities much higher than those in open channels. e mechanism by which a forced plume entrains
Figure 6. Kittiwake foraging hotspots. Foraging was recorded in 2015 in the Brepollen area, outlined as a red
rectangle (a), for a sample of kittiwakes from a colony in Hornsund – yellow dot (a). ree foraging hotspots
were recorded in Brepollen, where 36% of the kittiwakes’ foraging activity took place (b). e compactness
of kittiwake distribution at the Storbreen ice face - magenta arrow at (b) - shows that foraging overlap more
than 90% formed a hotspot about 40 m in radius (90% contour), while an overlap of over 50% covered an area
with radius of about 100–200 m (50% contour) (c). (c) also shows the concentration of water contact points of
Kittiwakes within the discharge plum. e maps were drawn in ArcGIS 10.3.1 for Desktop, Esri Inc., http://
www.esri.com.
Logger ID
All contacts with
water (cww)
cww in front
of Storbreen
% of cww in front
of Storbreen
cww in front
of Hornbreen
% of cww in front
of Horrnbreen
cww in front of
Storbreen&Hornbreen
% in front of
Storbreen&Hornbreen
1 221 0 0 0 0 0 0
2 109 9 8.2 3 2.8 12 11
3 268 7 2.6 0 0 7 2.6
4 271 103 38 90 33 193 71
5 121 38 31.4 28 23.1 66 54.5
6 166 94 56.7 16 9.6 110 66.3
7 109 0 0 0 0 0 0
8 289 0 0 0 0 0 0
9 420 161 38.3 53 12.6 214 50.9
10 366 103 28.1 0 0 103 28.1
11 173 24 13.9 0 0 24 13.9
12 439 339 77.2 0 0 339 77.2
Table 1. GPS tracking study of kittwakes in Brepollen in 2015. Mean = 31.29. std = 29.232.
www.nature.com/scientificreports/
8
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
ambient uid is described by the entrainment hypothesis29. According to this concept, which introduces the
idea of entrainment velocity, the volume of entrained water is proportional to the mean central velocity and
inversely proportional to the conduit radius. is creates a very ecient local mechanism of water mixing. One
can estimate that in Raudvika, assuming a subglacial discharge of about 40 m3 s1, the whole volume of water in
the bay will be aected by this mechanism in one or two weeks. e consequence of such an event is that all the
zooplankton are stunned or killed (the abrupt drop in salinity to < 24 PSU has been found fatal for most of the
local zooplankton21,23) and carried to one small area on the water surface. Since the entrainment velocity is much
larger close to a conduit, it will be mainly zooplankton from layers of a similar depth that are transported to the
surface. We observed, however, that not all subglacial discharges created foraging hotspots. In Burgerbukta, for
example, we found subglacial discharge plumes but no foraging hotspots. We regularly observed aggregations
of Kittiwakes during our bird surveys in July 2015, but the number of water contacts did not reach the level
assumed to indicate a hotspot. is could be due to the dierent eciency of a subglacial discharge in providing
readily available zooplankton at the surface: this can be explained by the part played by entrainment velocity that
depends on overburden pressure, which is a result of numerous factors of glacier origin. Our results show that
the intensity of entrainment uctuates in time and space. ere were probably no hotspots in Brepollen in 2014
but they were certainly in existence in 2015. We consider that such variability can be explained by the changes in
the presence and position of a subglacial discharge, entrainment velocity and the quantity of macroplankton in
the water column.
e potential ecological importance of meltwater discharges raises questions about their distribution and vari-
ability. Fluvial discharges and entrainment govern water structure and temperature, salinity and SPM distribution
in glacial bays. We derived a formula for converting satellite recorded reectance to SPM for a wide range of tur-
bidity values. We did this using Landsat 8 images, but our formula should also work well with Sentinel 2 images
because the matching bands are similar. ough mainly of inorganic origin, the SPM in the glacier bays may dier
in its mineralogical components, which inuence the colour of the water. We tested our formula in Burgerbukta,
where the colours of the turbid water are dierent from those in Raudvika, and obtained RMS = 11 mg l1. So the
formula may be useful and reliable for the high values of SPM common to glacier bays. Maps of surface SPM dis-
tribution show considerable variability of turbidity in front of the glacier. Turbid meltwater discharges reaching
Figure 7. Subglacial discharges and foraging macroplankton hotspots. e subglacial discharge is due
to the large entrainment velocity and creates an intensive mixing mechanism near the conduit, killing the
macroplankton (ac). e rising water - a buoyancy plume - delivers this plankton to the surface (a,b). When
the water ows close to the ice face, it increases the melting rate and helps to create ice caves (a). e rising
plume with plankton may also reach the surface at some distance from the ice front (b), or the plume does not
reach the surface at all when it meets a density of water equal to that of the plume (c) Occasionally the englacial
discharge may create a hotspot (d).
www.nature.com/scientificreports/
9
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
the surface form the main turbidity pattern. However, muddy waters are accompanied by patches of much clearer
water. As the Landsat 8 and Sentinel 2 images have respective spatial resolutions of 30 and 10 m, all the surface
meltwater discharges are identiable. e complex hydrology of glacier bays as dened by the forcing factor of
subglacial discharge may change in time and space, creating on occasion very attractive foraging grounds for
birds. is is possible, however, only if a subglacial discharge reaches the surface, the entrainment velocity at the
conduits is high, the depth at terminus is at least several tens of meters and there is sucient macroplankton in
the entrainment layer. Remote-sensing methods can be used to identify potential foraging hotspots at the water
surface. e question whether discharge plumes owing below the surface can give rise to foraging hotspots for
sh and marine mammals, as noted in Vestre Burgerbukta, remains speculative.
We found that tidewater glacier bays were important foraging areas for surface feeding seabirds, kittiwakes in
particular. Such sites, rich in easily available food and situated in the ord close to colonies, are used as supple-
mentary/contingency feeding grounds by seabirds that otherwise forage outside the ord30,31. For kittiwakes these
areas are of great signicance, at least temporarily. Such an opportunity for emergency feeding close to the colony
when weather conditions beyond the ord are bad may increase the breeding success of birds32–34 and buer the
adverse consequences of climatic and oceanographic changes35–37.
Depending on the stage of retreat, glacier bays have a different importance for marine birds and mam-
mals. e most attractive foraging grounds are formed in deep, tidewater glacier bays, with strong meltwater
discharges, which draw zooplankton from a large area, become denser and rise to the surface. Foraging con-
ditions for seabirds deteriorate when the glacier terminus reaches the coastline and the glacier bay becomes
shallow. A rapid decline in sea ice cover in the Arctic may have serious consequences for pagophilic species, and
changes in the cryosphere may have a drastic eect on Arctic biota, including seabirds and marine mammals38,39.
Climate-induced sea-ice shrinking and glacier retreat, considered in the context of the sea-ice contact zone used
by marine birds and mammals being reduced, may cause their numbers to decline. Tidewater glacier bays are thus
the last refuges for pagophilic arctic animals13,40–45.
Methods
We selected two bays – Burgerbukta in Hornsund (32 hydrological and 8 macroplankton stations) and Raudvika
in Kongsord (52 hydrological stations) – for the hydrological and macroplankton studies. In situ measurements
were made at the same time as the Landsat 8 satellite images were taken.
GPS tagging and tracking study of kittiwakes. e study took place in the Gnallberget colony in
Hornsund during the chick-rearing period in July 2015. e number of kittiwakes breeding in the colony is not
known but is believed to range from 1 000 to 10 000 pairs (Norwegian Polar Institute, unpubl. data). To investigate
the location of kittiwake foraging grounds, range of foraging ights and ight speed during the chick-rearing
period, miniature global positioning system (GPS) loggers (“Sterna”, Ecotone, Sopot, Poland; printed circuit
board size 35 × 16 × 10 mm) were used to record time, position and instantaneous speed. We used data from the
GPS loggers deployed on 12 birds. e birds were trapped on nests using a long pole with a loop of shing line at
the start of the chick rearing period (10–15 July). e GPS loggers were attached to the bird’s central tail feathers
using 2 mm wide strips of Tesa tape (code 4965 – Tesa Tape Inc., Charlotte, NC, USA). e birds were then
released aer no more than 10 min of handling. e foraging behaviour of kittiwakes observed in the tidewater
glacier bays revealed them to be swarming over the subglacial discharge, with rapid simultaneous nose-diving
and plunging into the surface water in pursuit of rising prey. Such behaviour usually resulted in the entire body
getting wet, including the tail, to which the logger was attached. Every attempt by the bird to catch a prey item
was registered by the logger’s conductivity sensor (wet-dry switch, 1 Hz sampling rate) as a record of contact with
water. e logger’s weight (including attachment = 7.5–8.5 g) was equivalent to 1.8–2.0% of the body mass of indi-
viduals from Spitsbergen (mean body mass ± SD of the 21 adults from Hornsund caught in the same period as the
GPS-logger equipped individuals: 408.0 ± 30.0 g). Sampling started aer the rst contact with salt water and the
sampling interval was set at 15 min. e eld-tested accuracy of the GPS receiver was ± 10 m for 95% of positions.
e GPS-loggers used a bidirectional radio link with the base stations installed in front of the colony, enabling
remote data download. To save battery power, the base station automatically switched o the loggers while they
were within the download range of the base station. e loggers started to collect GPS positions again when the
birds ew beyond that range. All registered point data relating to bird contacts with water were rst inspected in
GIS soware to identify potential hotspots in the glacier bays. We dened hotspots as areas with more than 50
points. As these occurred only in Brepollen, subsequent analyses were limited to this area. Subsets of points (as a
vector point layer) were created for two glacier bays with the termini of Storbreen and Hornbreen. e number
of points in each of the two main hotspots were determined for each logger and compared with the total number
of logger points with water contact. en, the ratio of hotspot use to all foraging sites could be calculated for each
bird equipped with a logger, and also the mean value of this ratio, which is an estimate of hotspot use by a colony.
All the results were entered in a Table1. To avoid autocorrelation of data, the time series of recorded locations of
each bird were divided into trips from and back to the colony. According to the mean ight speed, direction of
movement and occurrence of water contacts, the activity during each trip was divided into three parts: the ight
from the colony to the feeding grounds, foraging episodes and the return ight to the colony. is approach is jus-
tied by the birds’ activity during breeding. Each foraging episode was then treated as a separate sample. All the
foraging episodes in Brepollen (78 episodes of 9 birds) were identied and saved as a set of points with unique ID
number. For each foraging episode we delineated minimum convex polygons (MCP) to dene the foraging range.
e MCP is a commonly used method in telemetry analyses of animal movements28. Owing to the small number
of points in an event and its compactness, we used the 100% of points convention. e MCP size and time of each
foraging episode was also determined. To analyse the overlap of foraging ranges we converted MCPs to raster
grids with a 10 m spatial resolution. e raster value assigned to a rasterized MCP was determined by the time of
www.nature.com/scientificreports/
10
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
the foraging episode. en all rasters were added and normalized to the 0–1 range. Two contours 0.5 and 0.9
(50% and 90% of the weighted overlap) – were drawn. To analyse the density and distribution of body-water con-
tacts in a hotspot, we used quadrat analysis to measure the number of points in a cell grid46. e whole area was
covered by a grid with a regular mesh of square polygons (shnet) with a cell size of 10 m. e number of water
contact points falling inside was assigned to each cell.
All experiments with live kittiwakes were carried out in accordance with the guidelines of the Governor of
Svalbard and were granted under the provisions of the Regulations for the larger protected areas and bird reserves
in Svalbard #11d. The experimental protocol was approved by the Norwegian Animal Research Authority
(NARA) (ID 6467).
Macroplankton measurements. Macroplankton was sampled with a rectangular neuston net (30 × 50 cm
opening; 0.5 mm mesh). e net was used to collect samples from the surface to 30 cm depth and was hauled for
200 m at a speed of 2 knots from a zodiac rubber dinghy. Four samples were collected in the vicinity (about 200 m)
of a glacier clis, accompanied by control samples taken 0.5 km to 1 km away from the clis (Fig.5). Samples were
collected from the cod end and preserved in 4% formaldehyde solution, to be analysed a few months later in the
laboratory (SupplementaryTableS1).
Physical oceanographic measurements. All measurements were made from a zodiac rubber dinghy.
e STD proles were obtained using a SD204 self-contained instrument (SAIV A/S) that measures and records
water salinity, temperature, pressure and turbidity. e turbidity was measured using a backscatter sensor in FTU
(Formazin Turbidity Units). e sensor was calibrated to SPM using a conversion formula derived from the linear
relation between turbidity and SPM measured at the same spot (with R2 = 0.82). e density was calculated using
the standard salinity, temperature and pressure formula, modied to include the increase of density with high
SPMs. Field measurements of SPM were obtained from discrete water sampling at the surface. e concentration
of suspended particulate matter (SPM; mg l1), dened as the dry mass of particles per unit volume of seawater,
was determined using the standard gravimetric method. e concentration was estimated by vacuum-ltering
measured volumes of water samples onto pre-combusted (450 °C, 24 h), pre-weighed MN GF-5 lters (0.4 μ m
pore size). e amount of ltered water diered, depending on the SPM concentration, and generally ranged
between 150 and 2000 ml. is was enough for a distinct change in lter colour. Aer ltration of a sample, the
lter was rinsed with 30 ml of deionised distilled water to remove salt. Large organisms visible to the naked eye
were removed from the lters. ese were placed in Petri dishes and stored in a refrigerator until analysis in the
laboratory. Each lter was then air-dried at 60 °C for 24 h and weighed to determine the total dry mass of SPM.
e concentration was determined by dividing the total dry mass of SPM by the amount of ltered water. Some
samples were analysed in at least in two replicates, depending on the size of the sample, and the mean value cal-
culated. e bathymetry of Raudvika was measured using Valeport echosounder proling.
Satellite measurements. Two cloudless Landsat 8 satellite images covering the study area were acquired
for the days when eld measurements were carried out. Both Landsat 8 scenes were obtained from USGS Glovis
and processed in the same way. First, the DN was converted to TOA reectance with a correction for the suns
angle according to the USGS Landsat 8 product instructions. en, an atmospheric correction using dark object
subtraction (DOS1) was carried out, assuming 1% surface reectance from the dark objects. We used standard
methodology when seeking the best relation between satellite image information and SPM measured at the water
surface by testing the relations between dierent variables (a simple function of satellite image bands) and inde-
pendent variable (SPM) transformation using Ordinary Least Squares (OLS). e ratio of bands 4 and 2 (OLI4/
OLI2) in all the models tested represented the best signicance with excellent stability compared to the other
variables and was used to derive the formula for converting the satellite image to an SPM concentration map.
References
1. Oerlemans, J. Quantifying Global Warming from the etreat of Glaciers. Science 264, 243–245 (1994).
2. Svendsen, H. et al.e physical environment of ongsorden – rossorden, an Arctic ord system in Svalbard. Polar es. 21,
133–166 (2002).
3. Etherington, L. L., Hooge, P. N., Hooge, E. . & Hill, D. F. Oceanography of Glacier Bay, Alasa: Implications for biological patterns
in a glacial ord estuary. Estuaries and Coasts 30, 927–944 (2007).
4. Horne, E. P. W. Ice-induced vertical circulation in an Arctic ord. J. Geophys. es. Ocean. 90, 1078–1086 (1985).
5. Syvitsi, J. P. M. On the deposition of sediment within glacier-inuenced ords: Oceanographic Controls. Mar. Geol. 85, 301–329
(1989).
6. Bartholomaus, T. C., L arsen, C. F. & O’Neel, S. Does calving matter? Evidence for signicant submarine melt. Earth Planet. Sci. Lett.
380, 21–30 (2013).
7. Lucman, A. et al. Calving rates at tidewater glaciers vary strongly with ocean temperature. Nat. Commun. 6, 8566, doi: 10.1038/
ncomms9566 (2015).
8. Motya, . J., Hunter, L., Echelmeyer, . A. & Connor, C. Submarine melting at the terminus of a temperate tidewater glacier,
LeConte Glacier, Alasa, USA. Ann. Glaciol. 36, 57–65 (2003).
9. Fried, M. J. et al. Distributed subglacial discharge drives signicant submarine melt at a Greenland tidewater glacier. Geophys. es.
Lett. 42, 9328–9336, doi: 10.1002/2015GL065806 (2015).
10. imura, S., Holland, P. ., Jenins, A. & Piggott, M. e Eect of Meltwater Plumes on the Melting of a Ver tical Glacier Face. J. Phys.
Oceanogr. 44, 3099–3117 (2014).
11. Slater, D., Nienow, P. W., Cowton, T. ., Goldberg, D. N. & Sole, A. J. Eect of near-terminus subglacial hydrology on tidewater
glacier submarine melt rates. Geophys. es. Lett. 42, 2861–2868 (2015).
12. Mugford, . I. & Dowdeswell, J. A. Modeling glacial meltwater plume dynamics and sedimentation in high-latitude ords. J.
Geophys. es. Earth Surf. 116, F01023 (2011).
13. Lydersen, C. et al. e importance of tidewater glaciers for marine mammals and seabirds in Svalbard, Norway. J. Mar. Syst. 129,
452–471 (2014).
www.nature.com/scientificreports/
11
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
14. Armitsu, M. L., Piatt, J. F., Madison, E. N., Conaway, J. S. & Hillgruber, N. Oceanographic gradients and seabird prey community
dynamics in glacial ords. Fish. Oceanogr. 21, 148–169 (2012).
15. Jenins, A. Convection-driven melting near the grounding lines of ice shelves and tidewater glaciers. J. Phys. Oceanogr. 41,
2279–2294 (2011).
16. Salcedo-Castro, J., Bourgault, D., Bentley, S. J. & deYoung, B. Non-hydrostatic modeling of cohesive sediment transport associated
with a subglacial buoyant jet in glacial ords: A process-oriented approach. Ocean Model. 63, 30–39 (2013).
17. Hartley, C. H. & Fisher, J. e Marine Foods of Birds in an Inland Fjord egion in West Spitsbergen: Part 2. Birds. J. Anim. Ecol. 5,
370–389 (1936).
18. Freitas, C., ovacs, . M., Ims, . A., Feda, M. A. & Lydersen, C. inged seal post-moulting movement tactics and habitat selection.
Oecologia 155, 193–204 (2008).
19. Lydersen, C., Martin, A. ., ovacs, . M. & Gjertz, I. Summer and autumn movements of white whales Delphinapterus leucas in
Svalbard, Norway. Mar. Ecol. Prog. Ser. 219, 265–274 (2001).
20. Weslawsi, J. M., yg, M., Smith, T. G. & Oritsland, N. A. Diet of ringed seals (Phoca hispida) in a ord of west Svalbard. Arctic 47,
109–114 (1994).
21. Węsławsi, J. M. & Legeżyńsa, J. Glaciers caused zooplanton mortality? J. Planton es. 20, 1233–1240 (1998).
22. Węsławsi, J. M., Pedersen, G., Petersen, S. F. & Porazińsi, . Entrapment of macroplanton in an Arctic ord basin, ongsorden,
Svalbard. Oceanologia 42, 57–69 (2000).
23. Zajaczowsi, M. J. & Legezyńsa, J. Estimation of zooplanton mortality caused by an Arctic glacier outow. Oceanologia 43,
341–351 (2001).
24. Ballance, L. T., Ainley, D. G. & Hunt, G. L. Seabird Foraging Ecology. In: Encycl. Ocean Sci. Second Ed. 5 (eds Steele, J. H., orpe,
S. A. & Tureian, . .). Academic Press: London (2001).
25. Stempniewicz, L. et al. Marine birds and mammals foraging in the rapidly deglaciating Arctic ord - numbers, distribution and
habitat preferences. Clim. Change, doi: 10.1007/s10584-016-1853-4 (2016).
26. Cottier, F. . et al. Arctic ords: a review of the oceanographic environment and dominant physical processes. Geol. Soc. London,
Spec. Publ. 344, 35–50 (2010).
27. Sudgen, D. E. & John, B. S. Glaciers and Landscape: A Geomorphological Approach (Wiley, 1976).
28. Lent, P. C. & Fie, B. Home ranges, movements and spatial relationships in an expanding population of blac rhinoceros in the Great
Fish iver eserve. S. Afr. J. Wildl. es. 33(2), 109–118 (2003).
29. Turner, J. S. Turbulent entrainment: the development of the entrainment assumption, and its application to geophysical ows. J.
Fluid Mech. 173, 431–471 (1986).
30. otzera, J., Garthe, S. & Hatch, S. GPS tracing devices reveal foraging strategies of Blac-legged ittiwaes. J. Ornithol. 151,
459–467 (2010).
31. Jaubas, D., Iliszo, L., Wojczulanis-Jaubas, . & Stempniewicz, L. Foraging by little aus in the distant marginal sea ice zone
during the chic-rearing period. Polar Biol. 35, 73–81 (2012).
32. Jaubas, D. et al. Foraging closer to the colony leads to faster growth in little aus. Mar. Ecol. Prog. Ser. 489, 263–278 (2013).
33. Jaubas, D., Wojczulanis-Jaubas, ., Iliszo, L., Dareci, M. & Stempniewicz, L. Foraging strategy of the little au Alle alle
throughout breeding season - switch from unimodal to bimodal pattern. J. Avian Biol. 45, 551–560 (2014).
34. idawa, D. et al. Parental eorts of an Arctic seabird, the little au Alle alle, under variable foraging conditions. Mar. Biol. es. 11,
349–360 (2015).
35. Harding, A. M. A. et al. Flexibility in the parental eort of an Arctic-breeding seabird. Funct. Ecol. 23, 348–358 (2009).
36. Grémillet, D. et al. Little aus buer the impact of current Arctic climate change. Mar. Ecol. Prog. Ser. 454, 197–206 (2012).
37. Grémillet, D. et al. Arctic warming: nonlinear impacts of sea-ice and glacier melt on seabird foraging. Glob. Chang. Biol. 21, 1116–23
(2015).
38. Eamer, J. et al. Life lined to ice: A guide to sea-ice-associated biodiversity in this time of rapid change. CAFF Assess. Ser. No. 10 10
(2013).
39. Amélineau, F., Grémillet, D., Bonnet, D., Le Bot, T. & Fort, J. Where to Forage in the Absence of Sea Ice? Bathymetry As a ey Factor
for an Arctic Seabird. PLoS One 11, e0157764, doi: 10.1371/journal.pone.0157764 (2016).
40. uletz, . J., Stephensen, S. W., Irons, D. B., Labunsi, E. a. & Brenneman, . M. Changes in distribution and abundance of ittlitz’s
Murrelets Brachyramphus brevirostris relative to glacial recession in Prince William Sound, Alasa. Mar. Ornithol. 31, 133–140 (2003).
41. ovacs, . M., Lydersen, C., Overland, J. E. & Moore, S. E. Impacts of changing sea-ice conditions on Arctic marine mammals. Mar.
Biodivers. 41, 181–194 (2011).
42. Gilg, O. et al. Climate change and the ecology and evolution of Arctic vertebrates. Ann. NY Acad. Sci. 1249, 166–190 (2012).
43. Post, E. et al. Ecological Consequences of Sea-Ice Decline. Science 341, 519–524 (2013).
44. Prop, J. et al. Climate change and the increasing impact of polar bears on bird populations. Front. Ecol. Evol. 3, 1–12 (2015).
45. Descamps, S. et al. Climate change impacts on wildlife in a High Arctic archipelago - Svalbard, Norway. Glob. Chang. Biol. doi:
10.1111/gcb.13381 (2016).
46. Mitchell, A. e ESI Guide to GIS Analysis Vol. 2 (ESI Press, 2005).
Acknowledgements
e research leading to these results has received funding from the Polish-Norwegian Research Program operated
by the National Centre for Research and Development (under the Norwegian Financial Mechanism 2009–2014,
in the frame of Project Contract No. POL-NOR/199377/91/2014 [GLARE]).
Author Contributions
J.A.U. designed the study, performed the oceanographic eld measurements, analysed the satellite data and
was chiey responsible for writing the manuscript. L.S. ran the project to record all the GPS bird tagging data
and contributed signicantly to the writing of the manuscript. J.M.W. formulated the main research question,
performed oceanographic field measurements and all the macroplankton analyses, and contributed to the
writing of the manuscript. K.D. carried out oceanographic eld measurements and laboratory analyses, and also
contributed to the writing of the manuscript. A.W. performed oceanographic eld measurements and laboratory
analyses, and contributed to the writing of the manuscript. M.G. participated in the project to record all the GPS
bird tagging data and contributed to the writing of the manuscript. L.I. participated in the project to record all
the GPS bird tagging data.
Additional Information
Supplementary information accompanies this paper at http://www.nature.com/srep
Competing Interests: e authors declare no competing nancial interests.
www.nature.com/scientificreports/
12
Scientific RepoRts | 7:43999 | DOI: 10.1038/srep43999
How to cite this article: Urbanski, J. A. et al. Subglacial discharges create uctuating foraging hotspots for sea
birds in tidewater glacier bays. Sci. Rep. 7, 43999; doi: 10.1038/srep43999 (2017).
Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and
institutional aliations.
is work is licensed under a Creative Commons Attribution 4.0 International License. e images
or other third party material in this article are included in the article’s Creative Commons license,
unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license,
users will need to obtain permission from the license holder to reproduce the material. To view a copy of this
license, visit http://creativecommons.org/licenses/by/4.0/
© e Author(s) 2017
... Additionally, the vertical positioning of zooplankton may be influenced by upwelling, as meltwater at the fronts of marine-terminating glaciers enters the marine environment at depth and forms a buoyant plume that transports zooplankton to the surface. However, they may reach the surface at a distance from the glacier front depending on the density of the plume 34 . On the other hand, estuarine circulation, which is observed in Svalbard fjords, may entrap both advected and local zooplankton populations at specific depths of the inner bays 35 . ...
... Moreover, Calanus spp. stunned by freshwater might be upwelled to the surface at the front of marine-terminating glaciers, and this mechanism could form local foraging grounds for surface feeders such as seabirds 34 (not observed in this study), likely leading to a lower Calanus spp. abundance farther from the glacier (Deep regime). ...
Article
Full-text available
In polar regions, the release of glacial meltwater resulting in turbid plumes is expected to transform coastal waters with numerous consequences on the marine ecosystem. This study aimed to determine the influence of turbidity regimes on the vertical distribution of copepods together with their potential food (chlorophyll a fluorescence) and non-visual predators (gelatinous zooplankton). Hydrography, turbidity, suspended particulate matter and chlorophyll a were studied in July and August 2019 in West Spitsbergen waters (European Arctic). Fine-scale vertical distribution patterns of zooplankton were assessed by an optical counter (LOPC) and underwater camera (UVP) and verified by plankton nets. In waters with the shallow impact of dark plumes, Calanus spp. and gelatinous zooplankton were concentrated in the upper water layers, whereas in areas with a thick turbid layer, they were distributed evenly in the water column. However, chlorophyll a peaks were found to be restricted to the surface in the turbid waters and there were subsurface maxima in the shallow turbidity regime. Regardless of the region, the turbidity regime was a significant factor shaping the vertical distribution of Calanus spp. We speculate that similar trends might be observed in other rapidly emerging turbid ecosystems and urge that future plankton research should also include relatively simple turbidity measurements.
... Marine-derived nutrients deposited in and around the bird cliff represent a strong point source of nutrients to terrestrial and coastal ecosystems, and originate primarily from the pelagic zone where the surface-feeding Black-legged Kittiwakes and the diving Brünnich's Guillemots hunt. This difference in foraging behaviour impacts their choice of foraging grounds, e.g. with Kittiwakes tending to be more attracted to marine-terminating glacier fronts than Guillemots (Urbanski et al. 2017;Nishizawa et al. 2020). Both species will forage relatively nearby their colonies during the breeding season, commonly within a radius of 20 km from the colony and rarely leaving on foraging trips more than 50 km away from the colony (Mehlum et al. 2001;Falk et al. 2002;Bertrand et al. 2021). ...
... Several seabird species in Svalbard have experienced population decline in recent years (Anker-Nilssen et al. 2015CAFF 2017). Climate change in Svalbard, with longer and wetter summers, is likely to have important implications for both seabird-driven fluxes as well as other terrestrial impacts on marine systems (Bilt et al. 2019;McGovern et al. 2020). Increased terrestrial production has the potential to assimilate more of the nutrient input from seabird colonies, while increased microbial activity and runoff, including increased frequency of large rainfall events even during winter (Hansen et al. 2014), could enhance fluxes to the coast. ...
Article
Full-text available
Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes ( Rissa tridactyla ) and Brünnich’s Guillemots ( Uria lomvia ) on stream nutrient concentrations and fluxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ ¹³ C and δ ¹⁵ N) was used to assess whether seabird-derived nitrogen (N) could be traced into filamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO 3 ⁻ ) and nitrite (NO 2 ⁻ ) peaked in July at 9200 µg N L ⁻¹ in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO 4 ³⁻ ) in seabird-impacted streams were 21.9 µg P L ⁻¹ , tenfold higher than in controls. Areal fluxes from seabird-impacted study catchments of NO 3 ⁻ + NO 2 ⁻ and PO 4 ³⁻ had estimated ranges of 400–2100 kg N km ⁻² and 15–70 kg P km ⁻² , respectively. Higher δ ¹⁵ N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ ¹⁵ N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers.
... Arctic seabirds, particularly surface feeders, also aggregate near tidewater glaciers (also known as marine-terminating glaciers) in the melting season (McLaren & Renaud 1982;Lydersen et al. 2014;Stempniewicz et al. 2017;Nishizawa et al. 2020;Bertrand et al. 2021). Freshwater run-off from tidewater glaciers leads to upwelling and the entrapment of zooplankton, which results in predictable aggregations of prey (Węsławski et al. 2000;Lydersen et al. 2014;Urbanski et al. 2017). ...
Article
Full-text available
Seabirds in cold biomes sometimes aggregate near glacier fronts and at sea-ice edges to forage. In this note, we report on large aggregations of black guillemots (Cepphus grylle) at the edge of sea ice in front of the tidewater glacier Kongsbreen (Kongsfjorden, Svalbard). During several days in the second half of June 2011, we observed 49–155 individuals of black guillemots at this ice edge. They foraged actively, and many of the dives were directed underneath the sea ice. The outflow of glacial meltwater and resulting upwelling generated opportunities for the black guillemots to feed, likely on zooplankton or fish. The black guillemots used the sea ice as a resting platform between dives or diving sessions, and whilst on the ice, they interacted socially. On our last visit, the sea ice was gone, and the black guillemots had left the bay. At the neighbouring tidewater glacier Kronebreen, there was no sea ice connected to the glacier. Surface-feeding seabirds, particularly black-legged kittiwakes (Rissa tridactyla), were numerous at the plumes generated by meltwater from Kronebreen. Black guillemots were not seen at these plumes, but some individuals were seen scattered in the fjord system. Our observations add to the natural history of black guillemots and enhance our knowledge of ecological interactions and seabird habitat use shaped by tidewater glaciers.
... Indeed, the progressing "Atlantification" of the west Spitsbergen fjords is highly modifying the timing of phytoplankton bloom periods (Hodal et al., 2012;Hegseth and Tverberg, 2013), community compositions of protists (Kubiszyn et al., 2014;Smoła et al., 2017) and zooplankton Trudnowska et al., 2020b), influencing finally the overall food web interactions in the fjords Vihtakari et al., 2018;Csapóet al., 2021), leading in consequence to substantial burial of organic carbon (Avila et al., 2012;Smith et al., 2015;Zaborska et al., 2018). Moreover, those glacierimpacted fjord parts constitute important nurseries and feeding areas for fish, seabirds and marine mammals (Lydersen et al., 2014;Urbanski et al., 2017). ...
Article
Full-text available
As the environmental conditions are typically not homogenous, especially in coastal regions, they must provide a mosaic of distinct habitats that can be occupied by particles and plankton in a characteristic way. Here we analyze and map the spatio-temporal distribution patterns and the internal structure of 94 patches of various size fractions of particles and plankton studied by fine resolution measurements of two compatible laser counters performed in the upper epipelagial of two Arctic fjords over six summer seasons. Detected patches generally occupied only the minor part of the studied upper water column (on average 12%), and frequently occurred as multi-size-fraction forms. The observed concentrations within the patches were mostly 1.6 times higher than the background concentrations (max 4.1). The patches ranged in size horizontally from 1 to 92 km (median length 12 km) and vertically from 5 to 50 m (median 26 m). Because the designated patches varied in terms of their shapes and internal structure, a novel classification approach to of patches is proposed. Accordingly, seven types of patches were distinguished: Belt, Triangle, Diamond, Flare, Fingers, Flag, and Rosette. The particles and plankton exhibited all types of these distribution patterns, regardless of the size fraction and location. The observed steepening size spectra slopes over years implies that proliferating Atlantic water advection, triggering increasing role of the smallest size fractions, played the crucial role on compositional dynamics on temporal scale. The recurring high concentration patches of particles and plankton near glaciers suggest that their melting, together with biological production, were the strongest factors generating patchiness on the local scale. An observed under several occasions depth differentiation among size fractions building together vertically thin multi-size-fraction patches is an interesting feature for further studies. Even if distribution patterns of particles and plankton did not clearly reflect all patterns in the environmental water structuring, they happened to be related to the presence of glacier runoff, eddy, sea mountain and hot spots of chlorophyll fluorescence.
... These temperature and turbidity changes in turn affect nutrient concentrations and predator and prey abundances (Arimitsu and others, 2016); healthy predator-prey dynamics are important to ecotourism in the Kenai Fjords. Meltwater upwelling and iceberg calving from tidewater glaciers also help drive circulation patterns and the distribution of nutrients and planktonic food sources in fjords (Lydersen and others, 2014;O'Neel and others, 2015;Arimitsu and others, 2016;Urbanski and others, 2017), and tidewater glacier retreat from the marine environment could reduce or shut off the glacial contribution to fjord circulation. The ice-ocean interface also provides habitat for higher trophic-level species such as harbor seals who haul out on icebergs (Hoover-Miller and Armato, 2018;Womble and others, 2021) near Aialik, Northwestern and McCarty Glaciers and Kittlitz's murrelets that spend the summer breeding season near tidewater glaciers (Arimitsu and others, 2012). ...
Article
Full-text available
Glacier change in Kenai Fjords National Park in southcentral Alaska affects local terrestrial, fresh water and marine ecosystems and will likely impact ecotourism. We used Landsat 4–8 imagery from 1984 through 2021 to manually map lower glacier ice margins for 19 maritime glaciers in Kenai Fjords National Park. Of these glaciers, six are tidewater, three are lake-terminating, six are land-terminating and four terminated in more than one environment throughout the study period. We used the mapped ice margins to quantify seasonal terminus position and areal change, including distinguishing between ice loss at glacier termini and along glacier margins. Overall, 13 glaciers substantially retreated (more than 2 σ ), 14 lost substantial area and only two underwent both net advance and area gain. The glaciers that had insubstantial length and area changes were predominantly tidewater. Cumulatively, the lower reaches of these 19 glaciers lost 42 km ² of ice, which was nearly evenly distributed between the terminus and the lateral margins. The rapid rate of glacier change and subsequent land cover changes are highly visible to visitors and locals at Kenai Fjords National Park, and this study quantifies those changes in terms of glacier length and area.
... A study on subglacial discharge in Raudvika in Kongsfjorden, Svalbard, found C SPM ranging as high as 600 mg L −1 at the glacier front using Landsat-8 imagery and a band-ratio algorithm [84]. The direct discharge of turbid subglacial meltwater enriched with inorganic particles may, however, only compare to a certain degree to the retention potential of extensive river valleys that drain a comparably large area that is under various influences. ...
Article
Full-text available
Arctic coasts, which feature land-ocean transport of freshwater, sediments, and other terrestrial material, are impacted by climate change, including increased temperatures, melting glaciers, changes in precipitation and runoff. These trends are assumed to affect productivity in fjordic estuaries. However, the spatial extent and temporal variation of the freshwater-driven darkening of fjords remain unresolved. The present study illustrates the spatio-temporal variability of suspended particulate matter (SPM) in the Adventfjorden estuary, Svalbard, using in-situ field campaigns and ocean colour remote sensing (OCRS) via high-resolution Sentinel-2 imagery. To compute SPM concentration (CSPMsat), a semi-analytical algorithm was regionally calibrated using local in-situ data, which improved the accuracy of satellite-derived SPM concentration by ~20% (MRD). Analysis of SPM concentration for two consecutive years (2019, 2020) revealed strong seasonality of SPM in Adventfjorden. Highest estimated SPM concentrations and river plume extent (% of fjord with CSPMsat > 30 mg L−1) occurred during June, July, and August. Concurrently, we observed a strong relationship between river plume extent and average air temperature over the 24 h prior to the observation (R2 = 0.69). Considering predicted changes to environmental conditions in the Arctic region, this study highlights the importance of the rapidly changing environmental parameters and the significance of remote sensing in analysing fluxes in light attenuating particles, especially in the coastal Arctic Ocean.
... Much of the research to date on seabirds and climate change have focused on the impacts of increased ocean temperatures (e.g., Sandvik et al., 2005;Chambers et al., 2011;Descamps et al., 2017;Johnson and Colombelli-Neǵrel, 2020). Similar to other studies on Arctic systems showing the importance of glacial outflows on marine productivity as well as seabird foraging and populations (Greḿillet et al., 2015;Urbanski et al., 2017;Bertrand et al., 2021; see also Michel et al., 2015), our findings highlight that other factors need to be taken into consideration, such as the potential importance of river outflow for the health and resilience of the coastal ecosystem, and our results should be considered in future river management strategies. Given the wide distribution of seabirds, their key role in ecosystems, and the fact that droughts are becoming more and more frequent (Dai, 2013), future studies, both within Australia and elsewhere, are needed to identify which species may be affected by hydrological droughts to further enhance both seabird conservation and river management. ...
Article
Full-text available
Droughts in many regions of the world are increasing in frequency and severity which, coupled with effects from anthropogenic water extraction and diversion, are reducing river discharges. Yet to date, few studies have investigated the impacts of hydrological droughts (i.e., reduced river outflows to the ocean) on seabirds. Here, we examined the consequences of the “Millennium Drought” on the local decline of an iconic Australian seabird, the little penguin ( Eudyptula minor ). We analysed monthly and annual penguin numbers in relation to river outflow, rainfall, the characteristics of the coastal waters (sea surface temperatures and chlorophyll- a concentrations), and local abundance of key predators and prey species. We found a negative association between monthly penguin numbers and both sea surface temperatures and river outflow. Annual penguin numbers were positively associated with southern garfish numbers (our local indicator of food availability) but negatively associated with annual chlorophyll- a concentrations. Our findings emphasizing the need for further research into the effect of hydrological droughts on seabird populations and for improved river management that account for potential downstream impacts on the coastal environment receiving freshwater from rivers.
... The volume of water transported vertically may be 10-30 times the initial freshwater input Cape et al. 2019), and upwelling of deep, nutrient-rich waters into the photic zone stimulates production (Leu et al. 2015;Meire et al. 2017;Hopwood et al. 2018;Cape et al. 2019), even outside the fjords (Arrigo et al. 2017). The higher productivity and prey availability near glacier fronts resulting from these processes attract the prey of seals, such as polar cod (Arendt et al. 2013;Leu et al. 2015;Meire et al. 2017;Urbanski et al. 2017). ...
Chapter
Phocids (true seals) occur in oceans across the globe, from the tropics to polar oceans, and a few species have even colonized freshwater systems. As a group, they experience a wide range of local environmental conditions and oceanographic regimes that have shaped their behavior, allowing them to better take advantage of the specific patterns of prey distribution and abundance. Despite their suite of adaptations to life in the ocean, seals are still constrained to return to a solid substrate (land or ice) and haul out to reproduce, rest, and molt. This separation between their prey (ocean) and solid substrate (land/ice) shapes their life cycles and inextricably determines their at-sea movements and habitat preferences. In this chapter, we examine the biogeographic patterns of phocid seals in the context of past and current global oceanography, explore the use of animal-borne instruments (biologging) to study movements and the environments utilized. We review the relationships between phocid seal habitat utilization and behavior and the biophysical oceanographic characteristics that directly or indirectly influence the distribution of seals and their prey. The physical properties of the environment utilized by seals (water, sea bottom, and ice) are fundamental to understanding not only the behavior and ecology of true seals but also how they may be affected by annual and long-term changes in ocean climate.KeywordsPhocidsSealsOceanographyDistributionEnvironmentAnimal-borne instrumentsHabitat preferenceDivingSea ice
... In the northern Bering Sea, ice scouring may remove the entire biota from horizontal rock surfaces, leaving the only inhabitable space for adult perennial algae in crevices between ice scoured rocks (Heine, 1989). Gla2 was situated at the entrance to a glacial bay, with two large tidewater glaciers terminating at its end and retreating at a very fast rate (Urbański et al., 2017). Therefore, the effect of scouring the bottom by growlers and its force may be greater at Gla2 than at Gla1, where rocks and skjerras protect kelp stands against icebergs. ...
Article
Kelp forests supply many important ecosystem services that often are dependent on kelp morphological characteristics. Understanding the relationship between environmental factors and the morphological response of macroalgae is essential. The main aim of this study was to investigate the impact of factors associated with glacial activity and depth on the variability of dominant kelp species in the Arctic fjord, Hornsund. A total of 347 individuals of three kelp species (Alaria esculenta, cf. Laminaria digitata, Saccharina latissima) were collected in July 2003 at three sites located at different distances from glacier outflows (two sites under the influence of active tidewater glaciers and one site without any glacial impact) and at two depths (5 and 10 m). The length and wet weight of the thallus, blade and stipe were measured. The morphological response to environmental conditions was complex and species-specific. At one glacier-proximal site, light limitations due to seasonally increasing mineral particle flux did not affect kelp morphology, while iceberg scouring could have caused a reduction in kelp size and biomass at another site. Depth had a significant effect on the morphological traits of A. esculenta and S. latissima, which tended to have longer and heavier stipes at greater depths, most likely to improve light capture. No effect of depth on morphological traits of cf. L. digitata was noted. Regression models between thallus biomass and length, constructed for the kelp species that were studied, can be used in non-destructive kelp biomass estimations.
Article
Arctic lakes are an essential element of the environment. This study inventoried and classified lakes on three of the Svalbard Islands (Spitsbergen, Barentsøya, and Edgeøya) using Sentinel-2 images. The Forel-Ule color index (FUI) was employed to measure the lake's color, and a new equation to calculate the concentration of suspended sediment using satellite images was developed and tested using measurements from coastal waters. These two measures, plus the normalized difference vegetation index for vegetation on the lakeshore, and the lakes' location were used for clustering and classification. More than 1000 natural lakes were found on the three Svalbard islands. Nearly 80 % of these were smaller than 0.01 km² (1 ha), with the largest a few km² in area. Lake distribution analysis identified six zones of increased lake density, five of which were located along the western coast of Spitsbergen. The FUI was thus demonstrated to be useful for the monitoring of Arctic lakes. The K-means clustering results and analysis of the spectral signatures divided the lakes into seven classes: clear water, moderately clear water, tundra, coastal tundra, meltwater, extreme meltwater, and supraglacial lakes. Meltwater and clear water lakes were the two most common types, accounting for about 80 % of the total lake area.
Article
Full-text available
Climate-induced glacier retreat is considered in the context of its reducing the sea-ice contact zone used by marine birds and mammals as important foraging grounds and may cause declines in their numbers. To test this hypothesis, a survey was conducted in diversified habitats of a rapidly deglaciating Arctic fjord in Svalbard. Of the fifteen seabird and four mammal species found, coastal surface-feeders prevailed over benthic-feeders and pelagic pursuit-divers. Deep tidewater glacier bays were used by the most numerous but least heterogeneous foraging community, in contrast to the shallow lagoons of coastline-terminating glaciers and deglaciated shorelines. After the 15 years of glaciers retreat documented in Hornsund, the sea-ice contact zone used by birds and mammals has not declined. On the contrary, the increasing freshwater supply from underwater glacial rivers raising zooplankton up to the surface, thus making it available to seabirds, enhances the attractiveness of tidewater glacier bays. Along with the stage of retreat, the importance of glacier bays as feeding grounds changes. Foraging conditions deteriorate when the glacier terminus reaches the coastline and the glacier bay becomes shallower. However, glacier retreat enlarges the area of littoral habitats accessible to benthophages. Glacier-related habitats situated close to colony are used as alternative/emergency feeding grounds by seabirds that normally forage outside the fjord. This is especially important during the chick-rearing period and also during bad weather conditions in the open sea. Our study demonstrates that, so far, the abundance and species diversity of seabirds foraging in the rapidly deglaciating Hornsund are both high, suggesting that they benefit from the current intensive glacier melt. However, with further climate change an apparent biodiversity paradox may occur. Here, overall biodiversity will increase but local diversity of pagophilic species will decline. Such nonlinear responses complicate the prediction of future polar ecosystem dynamics.
Article
Full-text available
The earth is warming at an alarming rate, especially in the Arctic, where a marked decline in sea ice cover may have far-ranging consequences for endemic species. Little auks, endemic Arctic seabirds, are key bioindicators as they forage in the marginal ice zone and feed preferentially on lipid-rich Arctic copepods and ice-associated amphipods sensitive to the consequences of global warming. We tested how little auks cope with an ice-free foraging environment during the breeding season. To this end, we took advantage of natural variation in sea ice concentration along the east coast of Greenland. We compared foraging and diving behaviour, chick diet and growth and adult body condition between two years, in the presence versus nearby absence of sea ice in the vicinity of their breeding site. Moreover, we sampled zooplankton at sea when sea ice was absent to evaluate prey location and little auk dietary preferences. Little auks foraged in the same areas both years, irrespective of sea ice presence/concentration, and targeted the shelf break and the continental shelf. We confirmed that breeding little auks showed a clear preference for larger copepod species to feed their chick, but caught smaller copepods and nearly no ice-associated amphipod when sea ice was absent. Nevertheless, these dietary changes had no impact on chick growth and adult body condition. Our findings demonstrate the importance of bathymetry for profitable little auk foraging, whatever the sea-ice conditions. Our investigations, along with recent studies, also confirm more flexibility than previously predicted for this key species in a warming Arctic.
Article
Full-text available
Submarine melt can account for substantial mass loss at tidewater glacier termini. However, the processes controlling submarine melt are poorly understood due to limited observations of submarine termini. Here at a tidewater glacier in central West Greenland, we identify subglacial discharge outlets and infer submarine melt across the terminus using direct observations of the submarine terminus face. We find extensive melting associated with small discharge outlets. While the majority of discharge is routed to a single, large channel, outlets not fed by large tributaries drive submarine melt rates in excess of 3.0md-1 and account for 85% of total estimated melt across the terminus. Nearly the entire terminus is undercut, which may intersect surface crevasses and promote calving. Severe undercutting constricts buoyant outflow plumes and may amplify melt. The observed morphology and melt distribution motivate more realistic treatments of terminus shape and subglacial discharge in submarine melt models.
Article
Full-text available
Rates of ice mass loss at the calving margins of tidewater glaciers (frontal ablation rates) are a key uncertainty in sea level rise projections. Measurements are difficult because mass lost is replaced by ice flow at variable rates, and frontal ablation incorporates sub-aerial calving, and submarine melt and calving. Here we derive frontal ablation rates for three dynamically contrasting glaciers in Svalbard from an unusually dense series of satellite images. We combine ocean data, ice-front position and terminus velocity to investigate controls on frontal ablation. We find that frontal ablation is not dependent on ice dynamics, nor reduced by glacier surface freeze-up, but varies strongly with sub-surface water temperature. We conclude that calving proceeds by melt undercutting and ice-front collapse, a process that may dominate frontal ablation where submarine melt can outpace ice flow. Our findings illustrate the potential for deriving simple models of tidewater glacier response to oceanographic forcing.
Article
Full-text available
Freshwater produced by the surface melting of ice sheets is commonly discharged into ocean fjords from the bottom of deep fjord-terminating glaciers. The discharge of the freshwater forms upwelling plumes in front of the glacier calving face. This study simulates the meltwater plumes emanated into an unstratified environment using a nonhydrostatic ocean model with an unstructured mesh and subgrid-scale mixing calibrated by comparison to established plume theory. The presence of an ice face reduces the entrainment of seawater into the meltwater plumes, so the plumes remain attached to the ice front, in contrast to previous simple models. Ice melting increases with height above the discharge, also in contrast to some simple models, and the authors speculate that this "overcutting"may contribute to the tendency of icebergs to topple inwards toward the ice face upon calving. The overall melt rate is found to increase with discharge flux only up to a critical value, which depends on the channel size. Themelt rate is not a simple function of the subglacial discharge flux, as assumed by many previous studies. For a given discharge flux, the geometry of the plume source also significantly affects the melting, with higher melt rates obtained for a thinner, wider source. In a wider channel, two plumes are emanated near the source and these plumes eventually coalesce. Such merged meltwater plumes ascend faster and increase themaximummelt rate near the center of the channel. Themelt rate per unit discharge decreases as the subglacial system becomes more channelized.
Article
The Arctic is warming more rapidly than other region on the planet, and the northern Barents Sea, including the Svalbard Archipelago, is experiencing the fastest temperature increases within the circumpolar Arctic, along with the highest rate of sea ice loss. These physical changes are affecting a broad array of resident Arctic organisms as well as some migrants that occupy the region seasonally. Herein, evidence of climate change impacts on terrestrial and marine wildlife in Svalbard is reviewed, with a focus on bird and mammal species. In the terrestrial ecosystem, increased winter air temperatures and concomitant increases in the frequency of "rain-on-snow" events are one of the most important facets of climate change with respect to impacts on flora and fauna. Winter rain creates ice that blocks access to food for herbivores and synchronizes the population dynamics of the herbivore-predator guild. In the marine ecosystem, increases in sea temperature and reductions in sea ice are influencing the entire food web. These changes are affecting the foraging and breeding ecology of most marine birds and mammals, and are associated with an increase in abundance of several temperate fish, seabird and marine mammal species. Our review indicates that, even though a few species are benefiting from a warming climate, most Arctic endemic species in Svalbard are experiencing negative consequences induced by the warming environment. Our review emphasizes the tight relationships between the marine and terrestrial ecosystems in this High Arctic archipelago. Detecting changes in trophic relationships within and between these ecosystems requires long-term (multi-decadal) demographic, population- and ecosystem-based monitoring, the results of which are necessary to set appropriate conservation priorities in relation to climate warming. This article is protected by copyright. All rights reserved.
Article
Over 3000 sightings and fixes of individually identified black rhinoceros (Diceros bicornis minor) over a 14-year period provided information on the spatial organization and movements of these introduced animals and their offspring in the Great Fish River Reserve, South Africa. Core home ranges based on 50% adaptive kernel calculations proved useful for depicting spatial associations among individuals and shifts in areas of occupation. The mean home range size (minimum convex polygon) was 11.7 km2 and that of core adaptive kernel 6.8 km2. Annual and individual variations in home range size were great and social factors clearly affected size. For these and other reasons great caution is recommended in interpretation and Inter-population comparisons of home range sizes. Most individuals in this expanding population showed mobility, with home ranges shifting over time. Although clearly exhibiting individual home ranges, most females associated in clusters of three or more individuals. Calves generally moved away from their mothers at the time of her next calving, but some subsequently moved back into their mothers' core home range. In addition to mother-offspring pairs, some females also showed multiple-year associations in these clusters. Male home ranges overlapped, and individuals showed multiple-year associations until they reached approximately nine years of age. Males over age 8 were rarely sighted in the core home range of other similarly aged males.