ISSN 1063-0740, Russian Journal of Marine Biology, 2006, Vol. 32, No. 3, pp. 198–200. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.A. Filippov, 2006, published in Biologiya Morya.
The salinity of the Baltic Sea is markedly lower than
normal oceanic salinity; therefore, many freshwater
species form stable populations here. The amphipod
is a relic freshwater species, which
occurs widely in lakes of Northern Europe and estuar-
ies of rivers ﬂowing into the seas of the Arctic Ocean
. This amphipod is also a common inhabitant of the
Baltic Sea, where it occurs at salinities from 3.4 to
In brackish-water ecosystems, salinity often plays a
key role for the development of many species of aquatic
invertebrates. One of the major indices reﬂecting the
response of organisms to environmental factors is
potential salinity tolerance [3, 5, 6]. The assessment of
the potential tolerance range is important in theoretical
and practical aspects, particularly in solving problems
connected with the introduction of new species or the
evaluation of possible responses of populations to envi-
ronmental changes. To date, the ranges of potential tol-
erance to an environmental factor have been deter-
mined for very few species of aquatic invertebrates.
Many aspects of salinity adaptation and ionic regula-
tion in aquatic organisms [1, 2] have been studied fairly
adequately; however, how tolerance changes in relation
to environmental conditions has been investigated in a
limited number of widely distributed forms. Hence,
study of the tolerance of organisms in relation to habitat
conditions, as well as the assessment of potential toler-
ance, is very important.
The present study examines the change in the salin-
ity tolerance range of the amphipod
as a result
of acclimation of this species to different salinities.
MATERIALS AND METHODS
Experiments were carried out in May 1994 at the
Asko ﬁeld station of Stockholm University (Baltic Sea,
Asko Island). Amphipods (7–10 mm in body length)
were collected in the vicinity of the station from the
10 m depth with a bottom trawl. At sampling places,
salinity was 6.2‰. Prior to experiments, amphipods
were kept for 1 day at the initial salinity to remove
injured or impaired individuals and then placed in
aquaria with a salinity of 0.9, 1.3, 1.9, 2.6, 4.1, 6, 8.9,
13.6, 20.4, and 30‰ for subsequent acclimation
(300 specimens in each salinity).
Acclimation was carried out for 2.5 weeks in an iso-
thermal room (temperature 13
C) with constant light
and aeration. Each aquarium with amphipods contained
about 20 liters of water and a 1.5- to 2-cm layer of sand.
The water and special food of test animals was not
changed throughout the acclimation period.
After 2.5 weeks in water of different salinities, the
salinity tolerance range of amphipods was determined.
To this end, animals were removed from the acclima-
tion aquaria and placed in groups of 10 individuals in
vessels with water of the tested salinities (in two repli-
cas). Tests were conducted in 0.8-l vessels without a
substrate and aeration at a temperature of 20
2 days of exposure, the number of active animals (%) in
test vessels was calculated. The data were averaged for
each of the test salinities and formalized by means of a
sigmoid dose–response curve:
is the minimum value of the response function
(in our case 0%);
, the maximum value of the response
function (in our case 100%);
, the logarithm of a 50%
Adaptability of the Amphipod
(Crustacea: Amphipoda) to Salinity Changes
A. A. Filippov
ZAO Ekoproekt, Saint Petersburg, 192019 Russia
Received October 28, 2005
—Salinity tolerance of the amphipod
from the Baltic Sea was examined after
acclimation to increased and decreased salinity. There were adaptive shifts in tolerance related to ambient salin-
ity. A sharp change in salinity tolerance of amphipods occurred after acclimation to extremely low salinity.
Amphipods, salinity, tolerance, acclimation, Baltic Sea.