Summer in Sydney means different things for different people, but if you consider food, chances are that many will think about seafood. With the recent opening of the new Sydney fish market adding fresh energy to the city’s food scene, seafood is firmly in the spotlight. And while taste and texture delight the palate of seafood fans, bivalves in particular do a lot more for all Sydneysiders than first meets the eye.
Oysters, mussels, scallops and clams are all bivalves. Sydney Harbour has hosted bivalve species for thousands of years, and Aboriginal populations have consumed the iconic Sydney rock oyster for at least 10,000 years. More recently, we have learnt to exploit the biology of these animals to monitor water quality, a practice referred to as biomonitoring.
Put simply, bivalves can be the aquatic equivalent of canaries in a coal mine, as their health status can act as powerful warning systems, alerting us to potential issues (for ourselves or the environment) in the water that they inhabit. Oysters and mussels are particularly important “sentinels” worldwide, as they live attached to rocks, filtering hundreds of litres of water per day, and are therefore exposed to the pollutants, bacteria and viruses present in the water.
Because they cannot move, bivalves constantly accumulate contaminants. In effect, we use them as passive “samplers” that can be analysed for the presence of dozens of environmental indicators. For example, metals such as zinc, copper, or lead are difficult to quantify directly in the water, as their concentrations are often too low for detection. But since bivalves can neither escape nor excrete them, concentrations in their tissues increase over time. In Sydney, oysters and mussels are used to assess the presence of these metals, among others, providing a means to detect pollutants otherwise untraceable.
Bivalves can also help us detect high levels of harmful bacteria such as Escherichia coli or Vibrio species, and to a certain extent, other pollutants such as pesticides and microplastics.
For those who consume seafood, this very word often rhymes with good times spent with family and friends around a platter. It is also nice to remind ourselves of the other benefits that nature provides us with, perhaps in a more discreet fashion, but with clear positive outcomes for all Sydneysiders.
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References
- Dove et al. (2025) ‘The ‘canary of the estuary’, the contribution of Sydney rock oyster aquaculture to understanding and protecting Australian estuarine health’ Marine and Freshwater Research.
- Jahan and Strezov (2019) ‘Assessment of trace elements pollution in the sea ports of New South Wales (NSW), Australia using oysters as bioindicators’ Scientific Reports.
- Markich and Jeffree (2019) ‘The euryhaline pygmy mussel, Xenostrobus securis, is a useful biomonitor of key metal contamination in the highly urbanised Sydney Estuary, Australia’ Environmental Pollution.
