Development and validation of fish-based, multimetric indices for assessing the ecological health of Western Australian estuaries

Abstract

We describe the development of the first fish-based, multimetric indices for assessing and monitoring the health of Australian estuaries, and their application to the nearshore (< 2 m depth) and offshore (> 2 m depth) waters of the Swan Estuary, Western Australia. Suites of fish community metrics, including measures of species composition, diversity and abundance, trophic structure and life history function, were selected via a novel weight of evidence approach on the basis of their sensitivity to detect inter-annual change in estuarine condition. For each selected metric, seasonally-adjusted reference conditions were established for each spatial management zone of the Swan Estuary using 30 years of standardised historical fish assemblage data. This extensive data set provided a sound basis for determining the 'best available' standard of biotic integrity recorded over that time period and thus a reliable benchmark against which the current and future health of the estuary may be assessed and compared. The nearshore and offshore indices were robust to the effects of natural, intra-seasonal variability in environmental conditions, and so provide reliable tools for quantifying and classifying the ecological health of the Swan Estuary and its constituent management zones. The response of the nearshore index to an algal bloom confirmed that it is sufficiently sensitive to quantify ecological health responses to local-scale environmental perturbations and to track the subsequent recovery of the system following their removal. The indices provide managers with a reliable, quantitative method for assessing and communicating the health of the Swan Estuary and, similarly, of other estuaries across southwestern Australia.

The Fish Community Index: A Practical Management Tool for Monitoring and Reporting Estuarine Ecological Condition

“…Independent versions of the FCI were developed for assessing the condition of shallow (<2‐m depth) nearshore estuarine waters and for deeper (>2‐m depth) waters (Hallett, Valesini, Clarke, Hesp et al ), to account for the marked differences in their fish communities and the methods used to sample them. For detailed accounts of the processes by which component metrics were selected to comprise the indices, reference conditions were calculated, and scoring and grading thresholds established, the reader is referred to the primary literature (Hallett, Valesini, Clarke ; Hallett, Valesini, Clarke, Hesp et al ; Hallett and Hall ; Hallett ).…”

Quantifying uncertainty in environmental indices: an application to an estuarine health index

“…In the presence of intraannual temporal variation, seasonal water quality guidelines may help to capture some of the seasonal variability (within a year) and provide a more informative approach for assessing water quality compliance. Variations on this have been explored by others - Chainho et al (2007) examined how seasonal variation in benthic communities affected the ecological status of a Portuguese estuary, Coates et al (2007) took into account seasonal variation when establishing reference condition communities for assessing ecological status of estuaries using multi-metric fish indices, and Hallett et al (2012) adopted a seasonally adjusted reference condition approach in making an assessment of the health of West Australian estuaries using fish-based indices.…”

Quantile-based grading improves the effectiveness of a multimetric index as a tool for communicating estuarine condition

“…Under the provisional 52 condition classification system, the possible range of FCI scores (0-100) was subdivided 53 arbitrarily into four classes of equal breadth (good, fair, poor, very poor). Preliminary 54 validation demonstrated that these FCI classes were robust to natural and sampling-related 55 variability, and sensitive to the effects of relatively short-term, localised environmental 56 perturbations, exemplified by algal blooms (Hallett et al, 2012b). However, as the provisional 57 classification scheme was considered to be skewed towards producing fair to good grades, a 58 comparative evaluation was undertaken of the sensitivity and robustness of the provisional 59 condition classifications, against those from an alternative, alphanumeric grading system 60 whose grade boundaries were determined statistically from the distributions of observed, 61 historical FCI scores.…”

“…[2012b]), are broadly applicable to estuaries across WA and beyond. The nearshore and 48 offshore FCIs comprised respective suites of 11 and 7 fish community metrics, including 49 measures of species richness, diversity and abundance, trophic structure and life history 50 function (for a full account of metric selection, reference conditions and FCI calculation, and 51 the detailed rationale for these indices, see Hallett et al, 2012a;2012b). Under the provisional 52 condition classification system, the possible range of FCI scores (0-100) was subdivided 53 arbitrarily into four classes of equal breadth (good, fair, poor, very poor).…”

“…62 that the nearshore data set had previously been subjected to novel standardisation procedures 70 to minimise biases arising from multiple gear types over that period (Hallett and Hall, 2012). First, the sensitivities of the two approaches were evaluated for the nearshore FCI by 88 comparing the ecological condition assessments for samples collected prior to, during and 89 after a bloom of the dinoflagellate Karlodinium veneficum, which occurred in the Canning 90 Estuary (CE) zone during May 2011 (Hallett et al, 2012b). The sensitivity of the offshore 91 index could not also be assessed in this manner due to a lack of repeated sampling of the 92 offshore waters of this zone during and after the bloom.…”