Using amphipods as bioindicators of metal pollution in the marine environment

Abstract

<p>Heavy metals in the marine environment are a worldwide issue due to their toxicity, non-biodegradability and their ability to accumulate and magnify in organisms. Increased human activity has caused higher inputs of heavy metals, resulting in escalated pressures on delicate coastal ecosystems. A means of assessing the natural environment and how it is changing in response to pollution and other environmental degradation is through the use of biological indicator or biomonitor species. These organisms provide information on the bioavailability of metals present in the environment. In recent years amphipods, a diverse order of small crustaceans, have been increasingly used as bioindicators of disturbed aquatic communities. They are widespread and important components of many food webs, and likely to be frequently exposed to metal contamination through both sediment and seawater. The aim of this research was two-fold: 1) to use amphipods to examine variation across sites and species in concentration of 20+ trace elements and 2) to examine whether the uptake of two metals, copper (Cu) and neodymium (Nd), is mediated by the presence of the other metal or an elevated seawater temperature. To investigate variation of trace element concentrations across sites, the amphipod Eusiroides monoculoides was collected from three sites in the Wellington region, approximately 5 km apart: Oriental Bay, Evans Bay and Point Halswell. To investigate differences amongst species comparisons were made between Eusiroides monoculoides, Apohyale papanuiensis and Sunamphitoe mixtura when they occurred at the same site. Analysing the trace element concentrations of 36 metals was done using an Inductively Coupled Mass Spectrometer (ICPMS). Overall, although these sites were not greatly distant from each other, there were differences among sites. Evans Bay in general had the highest concentration of trace elements. Further, there were also species-specific differences and S. mixtura was the species with the highest concentration of trace elements. There was also a size effect, where the average dry weight of S. mixtura was negatively related to the concentration of trace elements in the body. To assess the effects of heavy metals Cu and Nd in both an ambient (14 °C) and elevated (20 °C) temperature, an experiment was run at Victoria University’s Coastal Ecology Lab (VUCEL). Sand hoppers, Bellorchestia quoyana, were collected from a single site in Wellington (Scorching Bay) and assigned to eight treatments: ambient and warm controls in raw seawater and ambient and warm seawater doped with Cu, Nd and Cu and Nd together. Amphipods from treatments with Cu and Nd added had significantly higher concentrations of these metals from the controls, however temperature had no effect, and neither was there an interaction between the metals. Similar to S. mixtura from the field study, dry weight of B. quoyana was negatively related to the concentration of trace elements in the body. Results from this work demonstrate that when using amphipods as bioindicator species it is important to consider species and size specific effects. This thesis also provides baseline data for 20+ elements from three Wellington sites and demonstrates that there can be unexpected variation across relatively small spatial scales. The laboratory experiment did not yield results that coincided with the consensus of the literature. The experiment showed that at least in this case, temperature did not mediate the uptake of metals and there was a negative relationship between size and metal uptake.</p>