The truth behind common myths about marine pests

When it comes to marine pests, there are plenty of myths and misconceptions floating around (excuse the pun). Some of them sound convincing at first, but when you look closer, they don’t hold up against the science or the reality of how pests spread and establish. These misunderstandings can make it harder for all of us to take the right steps to protect our oceans, harbours and coastlines.

In this article, we unpack some of the most common myths about marine pests – from whether they’re “just a natural part of evolution” to whether cleaning your boat really makes a difference – and explain why the truth matters for the future health of our marine environment.

MYTH: Marine pest spread is a natural process that can’t be stopped

In one aspect you are right.  Marine pests can spread naturally in currents or the wind, but it takes longer and there are many natural barriers that stop them on the way. 

We know marine pests spread further and faster on boat hulls. Many of these, particularly those that travel  as biofouling on dirty hulls, are very resilient in a range of conditions, which means they are more likely to survive and thrive in their new location.

MYTH: It’s pointless cleaning my boat when the marina is infested
We hear you! It is disheartening to spend time and money cleaning and antifouling  your boat's hull and niche areas only to have to start the process again as the slime layer builds and a fouling species like Mediterranean fanworm makes its home in your prop shaft. 

But we know you don’t want to take that pest with you to wherever you go next - whether that’s the Abel Tasman or Poor Knights or somewhere closer to home. 

And that’s the key takeaway: Marinas and structures don’t move. It’s moving between places that presents the risk. 

The bad news is that to date there is no realistic way of removing Mediterranean fanworm from marinas once it’s established - but there are people working on it.


MYTH: There are no rules for International shipping

Protection of our borders is prescribed in the Biosecurity Act and it starts long before vessels get here:

All incoming vessels - and yes that’s cruising yachts and container ships - must prove they are free of marine pests on arrival by meeting the Craft Risk Management Standard  requirements including pre-border procedures, inspections and clearance standards. 

They will be turned away if they don’t meet the standard - four cruise ships were turned away in 2024, and they are not allowed to clean once in our waters.


MYTH: It’s a waste of time

As Tauranga, Gisborne, Tutukaka and the Marlborough Sounds prove, it’s possible to stay on top of marine pest spread - but you have to be on top of it all the time. 

In these places we’ve used a combo of strategies: 

  • Making sure that all vessels coming in are monitored and checked - often this is through the marinas 

  • Surveillance of high risk locations like ports, and popular anchorages 

  • Responding quickly to any incursion, before it establishes and gets out of control  

And when you think about it, it’s the marine pests that aren’t here yet, and the ones that haven’t spread to other locations, that are our success stories. 

Yes it’s challenging - and the cheapest and easiest way to stop incursions is to stop the spread on boats.


MYTH: Marine pests are a natural phenomena - it’s called evolution

Yes, change happens naturally all the time but when species are introduced that change happens faster and the surrounding environment doesn’t have time to adapt to the new incursion and rebalance. 

This means that native species can be smothered, starved or crowded out, resulting in a monoculture

We’ve seen it on land many times - think what happens when kikuyu grass gets into our lawn, possums into our forests, and even population explosions of goats and deer. 

This time, it's underwater, out of sight but not out of mind. 

Marine pests are real and they are threatening the ocean we love.



Image / ChatGPT

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Cawthron’s marine pest management research programme hits its stride