Indicator summary

 Summary of indicator structure and function

Definition and/or background

The following is from Fulton et al 2004a -

Combined k-dominance plots for species biomass and numbers were developed as a method for assessing the status of polluted populations, without the need for reference to temporal or spatial series of control samples (Warwick 1986). These curves are known as Abundance-Biomass Comparison (ABC) curves and they plot cumulative dominance in biomass and numbers against a log species rank. The biological basis for ABC curve analysis is that in a stable marine benthic community, interspecific competition will lead to K-selected species being dominant in terms of biomass, and therefore the biomass curve is above the numbers curve. This is because smaller r-selected species such as annelid worms may be dominant numerically but do not represent a high proportion of the biomass. With fishing disturbance, the competitive equilibrium is prevented and K-selected species decline whilst smaller r-selected species become dominant, both numerically and in terms of biomass. The resulting plot sees the reversal of the biomass and number curves, relative to their “undisturbed” positions (Figure 1).

Figure 1: Conceptual diagram of ABC dominance curves (after Warwick 1986). (Figure provided by Fulton et al 2004a).

Attribute

Community structure

Purpose

Polluted populations, Fisheries

Taxa

Benthic taxa

Data required

The following is from Fulton et al 2004a -

• Biomass (weight) per species
• Numbers (counts) per species

Ecosystem applicability

The following is from Fulton et al 2004a -

So far this indicator has been tested for benthic communities in temperate, semi-enclosed coastal systems of the Northern hemisphere, but should have broad applicable for all marine systems.

Robustness

The following is from Fulton et al 2004a -

Potentially high: To date it has been empirically demonstrated for benthic faunal communities in Northern hemisphere habitats, but it would be useful to apply it to community assemblages that include fish and non-benthic invertebrates. In order to test the biological assumptions that underpin the change in the biomass/numbers curves for those communities, it would also be useful to apply it to data sets of fish and invertebrates from marine reserves that have recovered from fishing (e.g. data from temperate reef marine reserves in Tasmania, Edgar and Barrett 1999).  The limitation of this method is that it requires data collection of comparable thoroughness for all sites or times. Despite this, it has ABC curves (along with K-dominance curves, see above) are more useful than univariate measures and are as easily contrasted and interpreted (Rice 2000). For examining shifts in community structure across faunal groups, this indicator could also be used in conjunction with size-spectra slopes for fish assemblage analysis and the coefficient of variation of biomass variability for demersal fish communities (Blanchard and Boucher 2001).

Current status and trends

The following is from Fulton et al 2004a -

Whilst further empirical testing of this indicator is required, recent testing on trawling impacts of benthic invertebrate communities in fished areas and fished/unfished (marine reserve) reference areas of a Scottish Loch (Tuck et al. 1998) show it to be a promising indicator for gauging effects of community change after fishing. The indicator of this method is the W-statistic of the biomass/abundance curves, which is a measure of the difference between the abundance and biomass lines on an ABC plot (Clarke 1990). W can have values in the range (-1, 1) and the closer the statistic is to -1, when comparing disturbed with undisturbed communities, the more degraded the system. The statistical significance of the comparative W-statistics can be tested, for example by applying a two-way ANOVA (Tuck et al. 1998). In Tuck et al.’s (1998) study of benthic community response to trawling between fished and unfished habitats in Loch Gareloch, Scotland, the W-statistic was significantly different at the reference (marine reserve) site after 5 months of disturbance. In this case, the biomass curve fell below the numbers curve in the fished area, and remained in that state until after 18 months of recovery (Figure 2).

Figure 2: ABC curves comparing reference (unfished) with treatment (trawled) areas of Loch Gareloch in Scotland after 5 months (after Tuck et al. 1998). The W-statistic for the trawled site was 0.043, which under two-way ANOVA analysis was statistically significantly lower than the W-statistic for the reference site which was 0.119 indicating greater disturbance for the trawled site (after Tuck et al. 1998). (Figure provided by Fulton et al 2004a).

References

Fulton, E.A., Smith, A.D.M., Webb, H., and Slater, J. (2004a) Ecological indicators for the impacts of fishing on non-target species, communities and ecosystems: Review of potential indicators. AFMA Final Research Report, report Number R99/1546.

References that Fulton et al uses for this indicator:

Blanchard, F., and J. Boucher. 2001. Temporal variability of total biomass in harvested communities of demersal fishes. Fisheries Research 49: pp 283-93.

Clarke, K. R. 1990. Comparisons of dominance curves. Journal of Experimental Marine Biology and Ecology 138: pp 143-57.

Edgar, G. J., and N. S. Barrett. 1999. Effects of the declaration of marine reserves on Tasmanian reef fishes, invertebrates and plants. Journal of Experimental Marine Biology and Ecology 242: pp 107-44.

Rice, J.C. 2000. Evaluating fishery impacts using metrics of community structure. ICES Journal of Marine Science 57: pp 682-88.

Tuck, I. D., S. J. Hall, M. R. Roberston, E. Armstrong, and D. J. Basford. 1998. Effects of physical trawling disturbance in a previously unfished sheltered Scottish sea loch. Marine Ecology Progress Series 162: pp 227-42.

Warwick, R. M. 1986. A new method for detecting pollution effects on marine macrobenthic communities. Marine Biology 92: pp 557-62.

Background reading

Fulton, E.A., Fuller,M., Smith, A.D.M., and Punt, A. (2004) Ecological indicators of the ecosystem effects of fishing: Final report. AFMA Final Research Report, report Number R99/1546.

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