Skar Kaldrananes Hvassahraun

1
Population structure and reproduction of the
beachflea (Orchestia gammarellus) at thermal and
non-thermal sites in Iceland Preliminary
investigations   Ólafur Patrick Ólafsson,
Þormóður Ingi Heimisson, Bergþóra
Kristjánsdóttir, Elva Ásgeirsdóttir, Freydís
Vigfúsdóttir, Rakel Júlía Sigursteinsdóttir, Jón
S. Ólafsson, Agnar Ingólfsson.   Institute of
Biology, University of Iceland Grensasvegur 12,
IS-108, Reykjavik, Iceland
Skarð
Kaldrananes
Hvassahraun
March 2002
Jan to May 2000 and 2001
Introduction   The beachflea Orchestia
gammarellus, a talitrid amphipod, is common in
southwestern Iceland, where its northward
extension appears limited by temperature
(Ingólfsson 1996). However, it also occurs at
widely spaced spots in northwestern Iceland,
where it is always associated with thermal
springs in the intertidal (Fig. 1). These
populations have probably been isolated for
thousands of years and are likely to differ
genetically (cf. Morritt and Ingólfsson 2000). It
is therefore of interest to compare life-history
attributes of these populations, which are known
to be influenced by temperature (Morritt and
Stevenson 1993).

May 2002
May 2002
Number in size class
August 2000
August 2000 and 2001
August 2000
August 2000
Fig. 1. Records of the beachflea Orchestia
gammarellus in Iceland, arranged in 10 x 10 km
squares (A. Ingólfsson, unpubl.). The three study
sites are indicated.
Width of pereon segment 1 (mm)
Fig. 2. Length distribution of juveniles
females (red) and adult males (blue) at the three
study localities at different periods. Ovigerous
females are indicated by solid red.
Methods   Here we report preliminary results from
three sites Hvassahraun, a non-thermal site in
southwestern Iceland, and Skarð and Kaldrananes,
thermal sites in the northwest (Fig. 1). The
Hvassahraun population was sampled bimonthly by
pit-fall traps for 20 months in 2000 and 2001 (A.
Ingólfsson unpubl.). Spot checks were made at
Skarð and Kaldrananes by hand-collecting in
July/August 2000, March 2002 (Skarð only), May
2002, and July 2002 (samples only partially
analysed). Animals were sexed, the width (length)
of the first thoracic segment (pereon 1) was
measured, and the reproductive state of females
was determined.
Table 1. Occurrence of ovigerous females at
Hvassahraun (SW-Iceland, non-thermal site), and
Skarð and Kaldrananes (NW-Iceland, thermal sites)
 
 
 
Results   The Hvassahraun population has a
limited breeding season with ovigerous females
occurring in June-August (occasionally September)
(Table 1). At Skarð ovigerous females were
already plentiful in March, and present in May at
both thermal sites (Fig. 2). The data set from
Hvassahraun clearly shows that females do not
breed until their second year. At the thermal
sites the life cycle appears to be completed
within one year. This is especially evident at
Skarð, where the female population in March
consisted almost entirely of large individuals,
many of which were ovigerous (Fig. 2). It is also
clear that reproduction at the two thermal sites
was not synchronized. The difference is best
seen in the May samples (Fig.2).
Discussion   The extended breeding season at the
thermal sites strongly indicates temperature as a
controlling factor, in agreement with the
conclusions of Morritt Stevenson (1993). The
two-year breeding cycle at Hvassahraun appears
unique among studied populations, where the life
cycle is completed within a year (e.g. Persson
1999), as appears to be the case with the thermal
populations (at least at Skarð). Also here,
temperature seems to be involved. The evident
difference between the two thermal populations
could possibly be genetic to some degree (cf.
Morritt and Ingólfsson 2000).
References   Ingólfsson, A. 1996. The
distribution of intertidal macrofauna on the
coasts of Iceland in relation to temperature.
Sarsia 8129-44. Morritt, D Ingólfsson, A.
2000. Upper thermal tolerances of the beachflea
Orchestia gammarellus (Pallas) (Crustacea
Amphipoda Talitridae) associated with hot
springs in Iceland. Journal of Experimental
Marine Biology and Ecology 255215-227. Morritt,
D Stevenson, T.D.I. 1993. Factors influencing
breeding initiation in the beachflea Orchestia
gammarellus (Pallas) (Crustacea Amphipoda).
Journal of Experimental Marine Biology and
Ecology 165191-208. Persson, L.-E. 1999. Growth
and reproduction in two brackish water
populations of Orchestia gammarellus (Amphipoda
Talitridae) in the Baltic Sea. Journal of
Crustacean Biology 1953-59.