Prawn chemical “fingerprints” identify human influences in urban coastal habitats

By Samantha Munroe, PhD

Coastal habitats are diverse environments that provide critical services for a wide range of species, including humans. But coastal habitats also face a variety potential threats, such as habitat decline and pollution. Our new study used the chemical “fingerprints” of prawns to visualise the distribution of nutrients and pollutants in a busy urban bay. Our ultimate goal is to use these results to better understand the impact of humans on coastal ecosystems.

“Most of us enjoy having prawns for dinner, but the chemical ‘fingerprints’ of these tasty critters can also tell us a lot about the health about coastal habitats” says Dr Munroe.

Coastal bays are dynamic, ever-changing environments that receive a variety of inputs from both the land and sea. However, coastal areas also receive a lot of human inputs, such as urban and industrial pollution.

Managers need to be able to monitor these inputs to ensure sustainable coastal development and protect local species. Unfortunately, this is much easier said than done. Firstly, it can be difficult to access remote coastal ecosystems; after all, humans have yet to evolve fins or the ability to breathe underwater. Secondly, the equipment needed to monitor long-term environmental change is often extremely expensive, and may not be a financially viable option for researchers or managers.

Bioindicators are a highly effective alternative to monitor coastal habitat pollution. A bioindicator is any species that can accumulate unique molecular “fingerprints” that reflect local water chemistry. Although we most often think of prawns as a great addition to any meal, they are also excellent bioindicators that can tell us a lot about local habitat conditions.

Catching prawns
Prawns are collected at night on-board commercial fishing trawlers. The catch is sorted on deck and any non-target species (also known as by-catch) are returned to the ocean (Photo: Sam Munroe)

Our study created chemical maps of an urban, coastal embayment (Moreton Bay, Australia) by measuring the chemical concentrations of different elements in the muscle tissue of eastern king prawns (Melicertus plebejus). These maps allowed us to visualise the distribution of molecules of copper (Cu) and lead (Pb), but also of land and ocean-based nutrients. Such molecules are naturally occurring, but can be elevated in areas more affected by human activity.

Overall, we found that prawns collected closer to shore had higher concentrations of certain molecules. This suggests nearshore areas are more strongly affected by human activities, like run-off of nutrients from agriculture and waste plants.

Nutrients can enter coastal habitats through run-off and rivers, but also from more specific outputs. For example, we found that nearshore prawns had high levels of a chemical tracer known as δ15N (nitrogen isotope 15). This tracer may indicate nutrients that are derived from human activities. For instance, our sewage treatment plant clean the waste-water of bacteria, and emit nutrients like nitrogen into Moreton Bay.

Map
Distribution patterns of (A) δ15N, (B) copper (Cu) and (C) Lead (Pb) in Moreton Bay, Brisbane, Australia. In general, prawn concentrations were higher closer to shore. Land-based sources for these elements include a mix of natural sources (e.g. eroded soils) and human sources (e.g. urban pollution). (Image: Jack Coates-Marnane)

So what does all this mean for Moreton Bay? The good news is the concentrations of potential pollutants in prawns was low, so it does not appear to strongly effect prawn condition and they should be safe for human consumption. Our work also shows prawns are a great way to monitor the distribution of some pollutants and nutrients. Ideally, we should revaluate prawn “fingerprints” at regular intervals to detect any changes in ecosystem health.

This work recently appeared in PLOS ONE.

Twitter: @SEM_Munroe

Email: smunroe.com

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