Science practice 63

Ecological indicators are used to assess the condition of the environment, to provide early warning signals of changes in the environment, or to diagnose the cause of environmental problems. Some important criteria for selecting an indicator include:

1. The indicator should provide an accurate picture of what it is supposed to indicate, such as “ecosystem health.”

2. The indicator should respond quickly to environmental changes.

3. The indicator should be easy to monitor.

4. The responses of the indicator in one or a few locations should indicate the state of the ecosystem in a larger area.

It has been suggested that seabirds are useful indicators. Two researchers discuss the effectiveness of using seabirds as indicators.

Researcher 1

Seabirds are valuable indicators because they are top predators in their ecosystem. Seabird populations and reproduction rates are regulated by prey abundance, and will therefore reflect environmentally induced changes in prey availability. The effects of reductions in prey resources, such as declining numbers of seabirds, are usually very rapid, due to the short food chain, which is another advantage.

A few species of small fishes are important species of the ecosystem, having a major effect on the ecosystem as a whole. Seabirds that eat mainly these key fish are good indicators of the ecosystem in general.

Additional demographic parameters that can easily be monitored in seabirds are population size, duration of foraging trips, and changes in body mass and offspring growth rate, all of which are useful environmental monitors.

Overall, seabirds are a cost-effective, useful, and meaningful indicator of environmental changes in ocean ecosystems.

Researcher 2

There are several reasons why seabirds may not be suitable as indicators of the impacts of environmental changes. First of all, not all marine ecosystems follow a top-down food chain. Some marine food webs are dynamic and can alternate between bottom-up and topdown. In addition, change in seabird numbers due to food scarcity usually has a lag of several months or even years. Because of this seabirds are not suitable as indicators of the food supply in all ecosystems.

In general, the effect of environmental change on seabird populations may take many years to become apparent. Its effect is complex and involves many physical and biological processes. This is a severe drawback to using seabirds as indicators. Another drawback is the handling effect. It is not fully understood what effect handling seabirds has on them. There is some evidence that bands placed on penguins to track them can reduce both breeding success and survival rates. With seabirds that are tagged and handled, it is difficult to be sure that observed effects are actually due to changes in the environment and not other factors.

The effect of environmental changes on seabirds is complex and it is not clear what the best way to monitor seabirds is. Therefore, seabirds are not a good choice for indicators.

Scientists used gas chromatography to analyze benzene concentrations in fuel vapors. The results of the analysis are displayed in Table 1.

Samples from four different brands of fuel were collected, with each brand offering both leaded and unleaded versions of fuel. A portion of each sample was analyzed for benzene concentration in the liquid, while the rest of the sample was placed in a vial and prepared for vapor analysis. Each vial was put into an oven, heated, and the gas chromatograph detected the concentrations of benzene in the vapor. Figure 1 displays the oven temperature during the experiment.

Figure 1

Table 1

A gasohol is a fuel blended with certain alcohols such as ethanol or methanol. Two of the fuels tested in this experiment (brands C and D) were gasohols. Figure 2 shows the average concentrations of benzene found in the liquid and vapor form of the leaded and unleaded fuels tested. Figure 3 compares the average concentrations of benzene found in gasohols and regular unleaded fuels.

Figure 2

Figure 3