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Macrofauna monitoring

Long term monitoring sites have been established along the Bay of Plenty Coast for benthic macrofauna (such as shellfish, worms, crabs and isopods) with annual data going back to 1991. The results below are for the low intertidal macrofauna at the Bay of Plenty Regional Council monitoring site at Pāpāmoa Beach. The last result in the time series was recorded on the 25th October 2011, following the first signs of oil on the beach on 10th October.

The first graph shows the average number of species recorded in each core sample and shows little change since the oil washed up on the beach (the last point is the 2011 result).

Macrofauna richness

The graph below show the average number of animals per core sample in broad groupings. The results show very good numbers for each group compared to previous years, even after the oil impacted the beach.

 Macrofauna abundance

Other important field observations made during the survey were that tua tua were very active and all reburying quickly after being dug up. Paddle crabs were very numerous, active and aggressive in the shallow subtidal area reaching densities up to around one per square metre. There were no obvious signs of excessive die off of any large macrofauna species such as the crabs or shellfish. Some dead tua tua were present but the numbers were low (<1 per 10 m of shoreline) and could be in the natural range.

In the core samples a number of very small tua tua (2.1 - 2.7mm) were present. The juvenile stages tend to be more sensitive to toxins than adults.

Overall there are no obvious signs of water borne acute/chronic (up to 2 weeks) toxicity effects. Biota such as crabs and isopods are showing the physical impacts of the oil through contact leading to death. Despite the positive signs it is possible that longer term chronic impacts from the oil could still be seen in macrofauna.