Electronic supplementary material 1 – Mysid Shrimp Behaviour Experiments
Introduction
The behavioural response of the prey, mysid shrimp (Tenagomysis spp.) used in the common
bully experiments to light and dark and perch odour could influence the feeding success and
behaviour of the common bullies. While no obvious differences in behaviour were noted,
research on mysid shrimp species does suggests the possibility of an effect of predator cues.
Lindén 2007 documented anti-predator behaviour of another species of mysid shrimp (Neomysis
integer) in response to the presence of European perch. Two other species of pelagic mysids
(Mysis mixta and Mysis relicta) have been shown to decrease feeding rates and alter prey
selection in response to a chemical cue of herring (Clupea harengus membras) (Lehtiniemi and
Lindén 2006). Observations of the mysid shrimp species in our research have also shown it to be
a predominantly nocturnal species (Sutherland and Closs 2001; Larkin 2005; Lill 2005)
suggesting a possible difference between activity levels in light and dark experimental periods.
To confirm the results of the common bully feeding experiment, a study of the location of mysid
shrimp in the water column in response to perch odour, as well as light and dark conditions was
completed.
Methods
The same experimental aquaria used with the common bully experiments detailed above with the
same aeration setups were used. A black line was drawn onto the sides of the aquaria prior to
experimental trials 10 cm above the bottom of the tank. After a minimum of one week in a
holding tank with 13 ppt saltwater and ‘Speight’s’ water solution 10 mysid shrimp were placed
into each of six aquaria filled to a depth of 20 cm with the 13 ppt saltwater and ‘Speight’s’ water
solution. The odour treatment consisted of the addition of 100 mL of perch odour water to each
aquarium and the control treatment consisted of the addition of 100 mL of ‘Speight’s’ spring
water to each aquarium immediately following the addition of the shrimp. Two experimental
periods were run for two hours in light and then an additional two hours of dark. Two more
experimental periods were run with the opposite light/dark cycle - starting in dark and then
ending in light. Spot observations of the presence of mysid shrimp above or below the 10cm line
were made at the start of the experimental period, 5 min, 10 min and every 20 min thereafter for
the 2 h period of the light period. This was repeated for the following alternate light/dark
condition. Two desk lamps with 60-watt red bulbs, placed approximately 2 m from the aquaria
were used to make observations in the dark. They were turned on only long enough to make spot
observations. For statistical analysis of the results we used generalized linear mixed model
(GLMMs), using the glmmPQL function in the R package MASS (Venable and Ripley 2002). Our
GLMM (logit-link with quasi-binomial family) had the shrimp positions (above or below) as the
response, the treatments (control or perch odour), the diel effect (light or dark) as fixed terms and
shrimp groups a random factor (this is to account for repeated observations of the same group of
shrimp).
Results
No statistically significant effects of light or dark, or perch odour on the location of mysid shrimp
within the water column were observed (Table AI).
Table AI Results of GLMM analysis on the location of mysid shrimp in the water column of the aquaria (above or
below 10cm) when exposed to perch odour or distilled water (treatment) during light and dark (time) replicates.
Response
Location in
water
column
Factor
Intercept
Treatment (odour)
Diel Period (dark)
Treatment x Diel Period
Value
-1.3795
0.2813
-0.0796
-0.1190
SE
0.1003
0.1374
0.1137
0.1535
d.f.
358
22
358
358
t
-13.7522
2.0470
-0.7006
-0.7756
P
<0.0001
0.0528
0.4840
0.4385
The treatment effect here is odour and the diel period effect is dark, giving the effect of odour on location in the water column, and the difference
in the location in the water column between light and dark periods.
A slightly insignificant effect of perch odour on the location of the shrimp in the water column
was observed (GLMM analysis; d.f. = 22, P = 0.0528). However, this is shown to be biologically
inconsequential by an average total difference of less than 1 shrimp observed above or below the
10cm line between light and dark, and treatment replicates (Fig. AI)
Bottom of Aquaria
9
8
7
6
5
4
3
2
1
0
10
Average number of
shrimp observed below
10cm in aquaria
Average number of shrimp
observed above 10cm in
aquaria
Top of Aquaria
10
9
8
7
6
5
4
3
2
1
0
Night Day
Night Day
Night Day
Night Day
Control
Odour
Control
Odour
Fig. AI Average ± S.E. number of shrimp observed in the bottom of the aquaria (below 10cm) and in the top of the
aquaria (above 10cm). (n = 96 for each replicate type – control, light; control, dark; perch odour, light; and perch
odour, dark)
Discussion
The results show no significant effect of the treatments (perch odour and control) or light and
dark on the location of mysid shrimp within the water column (above or below 10cm) in the
aquaria. This, therefore, does not suggest any influence of mysid shrimp behaviour on common
bully feeding behaviour or the use of cover in our experiments in the presence or absence of
perch odour, or light and dark conditions. This finding is supported by Sutherland and Closs
(2001) which found no significant difference in diel drift of this same genus of mysid shrimp.
While other research has shown changes in behaviour of various mysid shrimp species in
response to predatory cues, it is possible that mysid shrimp, or at least Tenagomysis spp. do not
change their position in the water column as a response. Other observations of behaviours were
not made as location in the water column was the key consideration for an effect on bully
behaviour. It may also be that they require a visual cue to trigger any significant behavioural
response to a predator. Lindén et al. (2003) documented a response of two littoral mysid species
(Neomysis integer and Praunus flexuosus) to European perch only when both chemical and visual
signals of perch were present. This study not only helps to confirm the findings of the common
bully feeding experiments, but also gives a better understanding of the behaviour of Tenagomysis
spp.
References
Larkin GJA (2005) Hypoxia in the Kaikorai Estuary: dynamics, causes and biological impacts:
Unpublished MSc thesis, University of Otago, Dunedin, New Zealand
Lehtiniemi M, Lindén E (2006) Cercopagis pengoi and Mysis spp. alter their feeding rate and
prey selection under predation risk of herring (Clupea harengus membras). Mar Biol 149:
845-854
Lill AWT (2005) The distribution, life history and production of mysid shrimp (Mysidacea
mysidae) in East Otago estuarine systems, in particular focusing on temporal open
estuaries. Unpublished MSc thesis, University of Otago, Dunedin, New Zealand
Lindén E (2007) The more the merrier: Swarming as and antipredator strategy in the Mysid
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Lindén E, Lehtiniemi M, Viitasalo M (2003) Predator avoidance behaviour of Baltic littoral
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