Development and validation of the marine benthic copepod Robertsonia propinqua as a bioindicator to monitor estuarine environmental health

Abstract

Studies in the USA have reported that species of meiobenthic copepods can be used as bioindicators of sediment-associated contaminants. The main objective of this research project was to develop and validate methods to assess the effects of estuarine pollution, using the marine benthic copepod Robertsonia propinqua as a bioindicator of environmental health in New Zealand intertidal / estuarine areas. Cultures of R. propinqua were set up and maintained in the laboratory and individuals used in 96h acute and full life-cycle chronic bioassays using the pre-selected contaminants atrazine and zinc sulphate. From the 96h acute experiments it was found that the lethal doses at which 50% mortality occurred (LC50) for exposed nauplii and adult individuals were 7.5 mg/L and 31.8 mg/L, respectively for atrazine and 1.7 mg/L and 2.7 mg/L, respectively for zinc sulphate. This indicated that the nauplii life stage was more sensitive than were the adult life stages for exposure to both contaminants. Based on the 'trigger' values reported (atrazine = 0.013 mg/L, zinc = 0.015 mg/L) in the Australian and New Zealand guidelines for fresh and marine water quality, which provide values at which concentrations of contaminants can occur in the environment before they begin causing effects on aquatic fauna, it is unlikely that the calculated LC50s in the current research will induce biological effects in exposed copepods in the short-term. The calculated LC50 results were then used to further investigate the effects of chronic exposure of sediment-associated contaminants on the complete life-cycle (egg-reproductive adult) of R. propinqua. In a laboratory-based full life-cycle toxicity test, field-collected sediments from polluted sites in the Auckland and Bay of Plenty regions reduced reproductive output (nauplii and copepodite production) of R. propinqua individuals, but the number of males and females, gravid females, clutch size per female and the number of eggs produced were not affected by either the polluted or non-polluted (reference) sediment samples from both field regions. Field investigations of meiofauna community composition in polluted and non-polluted field sites were carried out in 2004 in the Auckland and Bay of Plenty field regions in New Zealand. Greater sediment organic content and a correspondingly deeper redox potential discontinuity layer occurred in all polluted field sites compared with the non-polluted sites. However, species composition could not be used to characterise polluted and non-polluted sites, as there were no dominant taxa which were representative of these sites. The results presented in this thesis indicate that R. propinqua has strong potential to be a good candidate species as a bioindicator of environmental contamination. Furthermore, the full life-cycle toxicity test could be used as a rapid test to detect immediate changes in individual reproduction and development as well as long-term population effects. The technologies developed as part of this research may eventually provide additional tools for commercial environmental consultancies and may compliment existing standard operating procedures for environmental assessments involving pollution of estuarine ecosystems.