De'ath and Fabricius:

"Due to the high correlation between PN, PP, SS and Secchi, it is not possible to resolve their individual effects on ecosystem status, and inclusion of all variables simultaneously leads to spurious conclusions about such effects. To obtain approximate trigger values, we therefore analysed the correlations of biota to each of the water quality variables SS, PN and PP separately, with relative distance across and along being included in all models (Fig. 30). Note that in contrast to the previous analyses, the effects of these analyses are not additive. Partial effects plots for biotic responses and predictive errors for biotic responses to Secchi and chlorophyll were similar when both variables were analysed separately compared to when both were included in the model simultaneously (not shown).

Macroalgal cover increased about four-fold with SS increasing from 1.2 to 2.0 mg L^-1, and remained high above 2.0 mg L^-1. Macroalgal cover also increased by >50 per cent (from 7 to 11 per cent) with PN increasing from 0.9 to 1.6 µmol L^-1 (12.6 – 16.8 µg L^-1), and by ~40 per cent (from 8 to 11 per cent) with PP increasing from 0.04 to 0.14 µmol L^-1 (1.24 – 4.34 µg L^-1).

Hard coral richness declined with increasing SS, with highest values at <0.8 mg L^-1 SS and low richness at >2.0 mg L^-1. It also declined with increasing PN and PP, with highest values at <1.0 µmol L^-1 PN (14 µg L^-1) and <0.06 µmol L^-1 PP (<1.86 µg L^-1) and low richness at >1.8 µmol L^-1 PN and >0.10 µmol L^-1 PP (25.2 and 3.1 µg L^-1)."

Figure 30: Partial effects of SS, PN and PP on the four measures of ecosystem status (only two shown). SS, PN and PP were analysed separately, with across and along included in each of these 3 models (not shown). As SS, PN and PP were analysed separately, their effects as displayed here are not additive. Dashed red lines show suggested trigger values (see text).

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Citation and/or URL

De'ath, G. & Fabricius, K.E. 2008, Water quality of the Great Barrier Reef: distributions, effects on biota and trigger values for the protection of ecosystem health: final report to the Great Barrier Reef Marine Park Authority. Research Publication 89, Australian Institute of Marine Science, Townsville, Australia

Spatial Coverage

Great Barrier Reef-wide 

Temporal Coverage

2006

Update Frequency

Annual

Other Information

None