Amphipods as biomonitors of marine coastal environments: a Chatham Island case study

Abstract

New Zealand’s coastal marine environment has high economic, social and cultural importance. In order to manage, preserve and safely enjoy coastal environments and their resources, a good understanding of their biochemistry is required. Biomonitors provide a mechanism for monitoring changes in an environment especially in measuring metals entering the food chain. Trace metals are non-biodegradable, have the ability to become highly toxic to biota at relatively low concentrations, and bio-magnify up the food chain. Amphipods, a diverse order of crustacea, are widespread, abundant, relatively sedentary and important at the base of the food web. Furthermore, amphipods bioaccumulate pollutants through multiple sources, including seawater, sediment and their diet, and may thus provide a comprehensive insight into the chemistry of an environment.

This study investigates the trace metal chemistry of amphipods and associated algae, seawater and sediment, from coastal marine sites around Chatham Island. Samples were obtained from 11 coastal localities with the sampling sites located near potential point pollutants and on distinct basement lithologies, as well as a site identified by Te Aitanga o Ngā Uri o Wharekauri as relatively pristine. Three algal-dwelling amphipods (Aora sp. 1, Apohyale sp. 1, Eusiroides sp. 1) and one sand hopper species (Bellorchestia chathamensis (Hurley, 1956)) were found to be the most abundant and ubiquitous species collected. Sites were prioritised based on the abundances of these amphipod species and samples were analysed for >35 trace elements. Spatial and interspecific variations were observed for all amphipod species investigated. Eusiroides sp. 1 was the most sensitive algal-dwelling amphipod species analysed and consistently had highest concentrations of trace metals at a given site. No size effect was found for most trace element concentrations in two amphipod species. All three algal-dwelling amphipod species and associated seawater samples from Hanson Point South had elevated concentrations for > 19 trace metals, including potentially ecotoxic trace metals such as Ti, V, Cr, Co, Ni, Cu, and Fe. Arsenic was elevated in the algal-dwelling amphipod species at Owenga and Cd at Kaingaroa West and Cape Pattisson. Trace metal concentrations in the algal-dwelling amphipod specimens were broadly reflected in their associated seawater and/or algae. However there were variations in this, with the Hanson Point South amphipods more closely matching seawater than algae concentration patterns, and the algae at Owenga not showing As elevations noted in the amphipods. This suggests amphipods accumulate metals from a variety of sources, both directly from seawater and variably from algae. Sediments appeared to have little influence on the trace metals bioaccumulated in the amphipod specimens.

Results from this research demonstrate that species and size effects must be considered to rigorously use amphipods as biomonitors. Amphipods appear to provide a better insight to bio-available trace metal contamination compared to the other sample types analysed here. This thesis aids in the development and application of amphipods as biomonitors in New Zealand coastal waters and provides a baseline for sites located across Chatham Island for >30 trace elements. This baseline may be utilized by future studies to investigate temporal variations in trace metal concentrations on Chatham Island.