Coulaud et al. (2011) reported a relationship between the surface and the dry mass of
their leaf discs, in order to facilitate possible comparisons between studies with
different methodologies. Consequently, it is recommended that a leaf change correction factor should be calculated based on leaf surface loss, to take leaf conditioning changes into consideration and to make data from these different techniques
more comparable.
5 Conclusions
Feeding behaviour has been used to investigate the sublethal effects of a wide range
of contaminants over the years. As well as providing information on an organism
level, feeding studies could also be adapted to understand the possible effects on
entire populations, and therefore potential threats to a population could be transposed, to understand the prospective repercussions on the ecosystem.
Throughout this review, it is noticeable that there are variations within the
adopted methodologies for the acclimation conditions, the leaf conditioning process
and the leaf species used. This review has also highlighted that several different
equations are used in the literature to quantify the feeding rate of Gammarids.
During the acclimation period, the organisms are kept at temperatures ranging
from 10 to 22
C, even though all of the species considered in this review are from
temperate countries. Temperature has been proven to have a significant impact on
Gammarids by affecting their physiological parameters and their immune system.
Temperature could ultimately have an impact on their feeding rate, which increases
when the temperature is raised. The authors recommend that a constant temperature
is maintained during the acclimation period and the experiment itself, in order to
have a reliable estimation of the feeding rate, independent of a temperature difference. Moreover, the acclimation and experimental temperature should reflect the
average conditions for the country where the experiment is being undertaken. In fact,
both Maltby et al. (2002) and Coulaud et al. (2011) demonstrated that temperature
has a major impact on feeding rate variability during in situ experiments. Consequently, when an in situ experiment includes several different deployments in
different geographical areas, temperature should be measured in each location, so
that the impact of temperature on the feeding rate can be estimated. Furthermore, the
media in which the organisms are acclimated should always be aerated.
Similarly, the authors recommend that light/dark cycles aiming to reproduce
seasonal conditions should be avoided, in order to allow the reproducibility of a
study regardless of the time of the year. However, this is not the case for in situ
studies. The temperature and light/dark cycles during acclimation for in situ experiments should best replicate the natural environment. Consequently natural light/
dark conditions and the air and water temperature should be measured, reported and
replicated.
Ex situ experiments should be standardised (e.g. using an artificial medium if
possible), meaning that the medium’s parameters (i.e. pH, conductivity, total
Feeding Behavioural Studies with Freshwater Gammarus spp.: The. . .
33
their leaf discs, in order to facilitate possible comparisons between studies with
different methodologies. Consequently, it is recommended that a leaf change correction factor should be calculated based on leaf surface loss, to take leaf conditioning changes into consideration and to make data from these different techniques
more comparable.
5 Conclusions
Feeding behaviour has been used to investigate the sublethal effects of a wide range
of contaminants over the years. As well as providing information on an organism
level, feeding studies could also be adapted to understand the possible effects on
entire populations, and therefore potential threats to a population could be transposed, to understand the prospective repercussions on the ecosystem.
Throughout this review, it is noticeable that there are variations within the
adopted methodologies for the acclimation conditions, the leaf conditioning process
and the leaf species used. This review has also highlighted that several different
equations are used in the literature to quantify the feeding rate of Gammarids.
During the acclimation period, the organisms are kept at temperatures ranging
from 10 to 22
C, even though all of the species considered in this review are from
temperate countries. Temperature has been proven to have a significant impact on
Gammarids by affecting their physiological parameters and their immune system.
Temperature could ultimately have an impact on their feeding rate, which increases
when the temperature is raised. The authors recommend that a constant temperature
is maintained during the acclimation period and the experiment itself, in order to
have a reliable estimation of the feeding rate, independent of a temperature difference. Moreover, the acclimation and experimental temperature should reflect the
average conditions for the country where the experiment is being undertaken. In fact,
both Maltby et al. (2002) and Coulaud et al. (2011) demonstrated that temperature
has a major impact on feeding rate variability during in situ experiments. Consequently, when an in situ experiment includes several different deployments in
different geographical areas, temperature should be measured in each location, so
that the impact of temperature on the feeding rate can be estimated. Furthermore, the
media in which the organisms are acclimated should always be aerated.
Similarly, the authors recommend that light/dark cycles aiming to reproduce
seasonal conditions should be avoided, in order to allow the reproducibility of a
study regardless of the time of the year. However, this is not the case for in situ
studies. The temperature and light/dark cycles during acclimation for in situ experiments should best replicate the natural environment. Consequently natural light/
dark conditions and the air and water temperature should be measured, reported and
replicated.
Ex situ experiments should be standardised (e.g. using an artificial medium if
possible), meaning that the medium’s parameters (i.e. pH, conductivity, total
Feeding Behavioural Studies with Freshwater Gammarus spp.: The. . .
33