The feeding rate can be estimated by using the leaf weight or surface area. The
equation that is most commonly adopted estimates the feeding rate by comparing
leaf dry weight before and after being provided to the Gammarids, divided by the
time (expressed in days) and the weight of the organisms. Usually the dry weight of
the leaf discs is adjusted with a constant. The authors recommend that the position of
the constant is dependent on when the leaves are conditioned and dried. If the leaves
are conditioned after being dried and weighed, the constant should multiply with the
initial dry weight, so that it takes into consideration that the leaf disc might have lost
more weight through being submerged in water during the experiment. However, if
the leaf discs are dried and weighed after being conditioned, the final dry weight
should be divided by the constant, because some of the leaf material might have been
lost through leaching and not through Gammarid feeding.
Another consideration is that the constant is not always calculated in the same
way, and this could ultimately alter the experimental results. Again, the authors
recommend that further research is required to understand the impact of the various
constant positions on the outcome of a study. Until then, the authors recommend that
the equation provided by Maltby et al. (2002) is adopted, as it is representative of
real-life environmental feeding.
When leaf area is used to calculate the feeding rate, the constant is not often
included in the equation. This means that the possible loss of leaf material due to the
leaching process is not taken into consideration. Leaf area is often used to calculate
the feeding rate for in situ experiments, so the authors recommend that if this method
is going to be used, a set of control leaves should also be established, in order to
calculate a leaching constant based on the difference in surface area.
It is clear that a standardised protocol is required, which would benefit the
scientific community and regulatory authorities and allow them to interpret and
compare published literature to understand the impact of various contaminants
(and mixtures) on the environment. This could be achieved by undertaking serial
experiments to clarify what impact these heterogeneities have on the final results.
There are methodologies such as Naylor et al. (1989) and Nilsson (1974) that have
been used many times, but unfortunately, there are still others that are the result of a
mixed methodology. The variability within feeding studies has already been
acknowledged, and the first steps towards standardisation have evolved (Agatz and
Brown 2014).
A standardised ex situ methodology would greatly benefit this field of research,
by not only allowing a more meaningful comparison between the peer-reviewed
literature, but also to better understand the impact that specific contaminants could
have on Gammarid populations and ecosystems. This could be enhanced further if ex
situ experiments are placed side by side with biomarker analysis and in situ studies.
In theory, in situ tests could provide a realistic and integrated understanding of real
environmental pollution. If standardised, in situ tests could be used by regulators to
critically evaluate the state of an ecosystem and the potential impact that a certain
contaminant or mixture could have on the environment. This is of particular interest
since the establishment of the Water Framework Directive (European Union 2000),
which outlines that all European water bodies should reach ‘good quality status’ by
36
G. Consolandi et al.
equation that is most commonly adopted estimates the feeding rate by comparing
leaf dry weight before and after being provided to the Gammarids, divided by the
time (expressed in days) and the weight of the organisms. Usually the dry weight of
the leaf discs is adjusted with a constant. The authors recommend that the position of
the constant is dependent on when the leaves are conditioned and dried. If the leaves
are conditioned after being dried and weighed, the constant should multiply with the
initial dry weight, so that it takes into consideration that the leaf disc might have lost
more weight through being submerged in water during the experiment. However, if
the leaf discs are dried and weighed after being conditioned, the final dry weight
should be divided by the constant, because some of the leaf material might have been
lost through leaching and not through Gammarid feeding.
Another consideration is that the constant is not always calculated in the same
way, and this could ultimately alter the experimental results. Again, the authors
recommend that further research is required to understand the impact of the various
constant positions on the outcome of a study. Until then, the authors recommend that
the equation provided by Maltby et al. (2002) is adopted, as it is representative of
real-life environmental feeding.
When leaf area is used to calculate the feeding rate, the constant is not often
included in the equation. This means that the possible loss of leaf material due to the
leaching process is not taken into consideration. Leaf area is often used to calculate
the feeding rate for in situ experiments, so the authors recommend that if this method
is going to be used, a set of control leaves should also be established, in order to
calculate a leaching constant based on the difference in surface area.
It is clear that a standardised protocol is required, which would benefit the
scientific community and regulatory authorities and allow them to interpret and
compare published literature to understand the impact of various contaminants
(and mixtures) on the environment. This could be achieved by undertaking serial
experiments to clarify what impact these heterogeneities have on the final results.
There are methodologies such as Naylor et al. (1989) and Nilsson (1974) that have
been used many times, but unfortunately, there are still others that are the result of a
mixed methodology. The variability within feeding studies has already been
acknowledged, and the first steps towards standardisation have evolved (Agatz and
Brown 2014).
A standardised ex situ methodology would greatly benefit this field of research,
by not only allowing a more meaningful comparison between the peer-reviewed
literature, but also to better understand the impact that specific contaminants could
have on Gammarid populations and ecosystems. This could be enhanced further if ex
situ experiments are placed side by side with biomarker analysis and in situ studies.
In theory, in situ tests could provide a realistic and integrated understanding of real
environmental pollution. If standardised, in situ tests could be used by regulators to
critically evaluate the state of an ecosystem and the potential impact that a certain
contaminant or mixture could have on the environment. This is of particular interest
since the establishment of the Water Framework Directive (European Union 2000),
which outlines that all European water bodies should reach ‘good quality status’ by
36
G. Consolandi et al.