Ecotoxicology of estuarine amphipod Paracorophium excavatum
Thesis DisciplineEnvironmental Sciences
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The estuarine tube dwelling amphipod Paracorophium excavatum was investigated for its suitability as a bio-indicator and bio-monitor. Distribution patterns of P. excavatum were determined at 13 sites in the Canterbury region that differed in particle size distribution ranging from sandy to muddy sediment, with overall low organic content. Low tide salinity ranged from 5 to 33 0/00 between sites and sediment moisture content ranged between 23 to 41% moisture. Amphipods were absent from most sites within the Avon-Heathcote Estuary. The availability, life history and fecundity of P. excavatum were compared from intertidal mudflat sites in Brooklands Lagoon and Kairaki over a period of thirteen months. Four sediment core samples were collected at monthly intervals and P. Excavatum’s population structure and life history pattern studied. The life history of P. excavatum can be characterised by fast-growing, annual, iteroporous, bivoltine, females ovigerous throughout the year and thelygenous (female biased) population. P. excavatum showed relative consistency in abundance throughout the year with monthly densities ranging from 875.79 per 0.1 m⁻² (July) to 1754.77 per 0.1 m⁻² (December) at Brooklands Lagoon and 1031.83 per 0.1 m² (November) to 1780.24 per 0.1 m² (December) at Kairaki. There was a linear relationship between numbers of eggs per female and female length. P. excavatum show no statistically significant difference in brood mortality between the early and later development stages. P. excavatum was investigated for its potential use in short-term (acute) sediment toxicity tests. In 10-days sediment tolerance tests using sediment from nine sites (8 + control) in the Avon-Heathcote Estuary, amphipod survival was overall high in most sites (above 70%). However, low survival was found for site 7 and 9, indicating that P. excavatum may be a good discriminator of sediment quality. However, P. Exc avatum mortality was not significantly correlated to sediment type (p = 0.99, ƒ = 0.06) nor copper content of sediment (p = 0.99, ƒ = 0.01). The effects of copper concentrations on the survival, emergence and reburial of P. excavatum were investigated. Amphipods were exposed to 10-days to 7 sub-lethal copper concentrations (2.7, 15.96, 20.45, 23.92, 32.02, 42.99 and 84.62 μg g-¹ wet weight sediment). The results show clear dose-dependent effects of copper on survival and behaviour on P. excavatum. Copper toxicity test indicates P. excavatum high sensitivity to the heavy metal copper. Median lethal concentration (LC₅₀) was 53.026 μg g⁻¹ Cu (wet weight) and edian effect concentration (EC₅₀) was 47.89 μg g⁻¹ Cu (wet weight). Emergence increased with increasing metal concentrations indicating that the ontaminants had a sublethal behavioural effect. Concentration of copper in P. excavatum tissues increased significantly with increasing metal sediment concentration. The ability of P. excavatum to accumulate heavy metals into their body tissues makes this species suitable for use used as a copper bio-indicator. Further work should concentrate on the response of P. excavatum to known contaminants and the influence of non-contaminant variables to better characterises P. excavatum's relative sensitivity. It is concluded that P. excavatum can be used as an effective tool for use in ecotoxicological studies. Natural behaviour, laboratory experiments, and sediment bioassays and its availability throughout the year has demonstrated that P. excavatum can be used as a bio-monitor.