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Hull Biofouling
ID Guide

Quick reference for divers cleaning ship hulls in WA waters

Field Pocket Guide
⚠️ Found something dodgy? STOP & REPORT

Version 3.0 • January 2026

How to Use This Guide

The Job

You're cleaning hulls. You need to spot the bad stuff before you scrape it off. This guide shows you what to look for and what to report.

Why It Matters

Marine pests hitch rides on hulls. Some nasty ones have already turned up in WA — like carpet sea squirt at HMAS Stirling. Divers are our first line of defence.

NOXIOUS — Stop work. Report to DPIRD within 24hrs.
WATCH — Emerging threat. Document & report.
NATIVE — Normal WA fouling, no report needed
Note: This guide features key species from the WA noxious fish list. View the full list at fish.wa.gov.au or Schedule 5, Fish Resources Management Regulations 1995.

⚠️ Suspect a Noxious Fish?

  • STOP cleaning — cease work until DPIRD advises
  • Take photos — close-up + wide shot, use hand for scale
  • Note location (bow distance, depth, port/stbd)
  • DON'T scrape it off — leave specimen intact
  • Report to DPIRD within 24 hours (see back page)
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NOXIOUS — Report to DPIRD

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Carpet Sea Squirt NOXIOUS
Carpet Sea Squirt
Didemnum vexillum
Sea Squirt • WA Noxious Listed
  • Creamy/tan like old wax
  • Veiny look — like varicose veins
  • Leathery feel, NOT slimy
  • Drips down like candle wax
  • Detected: HMAS Stirling & Henderson
Don't confuse with: Native sea squirts — thinner, gelatinous, no veiny texture
Asian Green Mussel NOXIOUS
Asian Green Mussel
Perna viridis
Mussel • WA Noxious Listed
  • Young = bright emerald green
  • Older = brownish-green
  • Big — 80-165mm (hand-sized)
  • Blue-green inside when open
  • Not established in WA
Don't confuse with: Blue mussel — those are blue-black, not green
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NOXIOUS — Report to DPIRD

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European Fan Worm NOXIOUS
European Fan Worm
Sabella spallanzanii
Tube Worm • WA Noxious Listed
  • HUGE fan — 45-60mm across
  • Fan spirals in (not flat)
  • Stripy — orange/purple/white bands
  • Brown leathery tube
  • Established in WA — still report
Don't confuse with: Native serpulid worms — smaller fans, white hard tubes
Black-striped False Mussel NOXIOUS
Black-striped False Mussel
Mytilopsis sallei
Mussel • WA Noxious Listed
  • Small — only 25mm (thumbnail)
  • Dark stripes on shell
  • Packs in thick layers
  • Loves brackish water
  • Not established — check sea chests!
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NOXIOUS — Report to DPIRD

Crabs & Seastar
European Shore Crab NOXIOUS
European Shore Crab
Carcinus maenas
Crab • WA Noxious Listed
  • Green shell (can be orange under)
  • 5 spines each side behind eyes
  • Up to 90mm across
  • Hides in sea chests & rope guards
  • NOT established in WA — report!
Northern Pacific Seastar NOXIOUS
Northern Pacific Seastar
Asterias amurensis
Seastar • WA Noxious Listed
  • Large — up to 50cm diameter
  • 5 arms with upturned tips
  • Yellow-orange with purple/red marks
  • Underside completely yellow
  • Not in WA — devastating if arrives
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WATCH — Emerging Threats

Document & Report
Japanese Kelp WATCH
Japanese Kelp (Wakame)
Undaria pinnatifida
Kelp • WA Noxious Listed
  • Big brown fronds with midrib spine
  • Wavy ruffled edges
  • Can be up to 3m long
  • Frilly reproductive bit at base
  • In VIC/TAS/SA — NOT detected in WA
Killer Algae WATCH
Killer Algae
Caulerpa taxifolia
Algae • WA Noxious Listed
  • Bright green — stands out
  • Feather-shaped fronds
  • Spreads with creeping runners
  • Can grow to 65cm tall
  • In NSW estuaries — NOT in WA
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WATCH — Emerging Threats

Crabs & Oysters
Asian Paddle Crab WATCH
Asian Paddle Crab
Charybdis japonica
Crab • WA Noxious Listed
  • Back legs are flat paddles
  • 6 spines between the eyes
  • Up to 120mm across
  • Olive-brown to purple colour
  • In NZ — can spread disease
Large Oysters WATCH
Large Non-Native Oysters
Magallana spp.
Oyster • Hard to ID in-situ
  • Messy irregular shape
  • Rough frilly edges — SHARP!
  • Can get huge — up to 400mm
  • Glued flat to surface
  • Photo any large oysters for ID
Note: Includes Pacific, Black Scar & Suminoe oysters. Species ID requires lab analysis.
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WATCH — Emerging Threats

Mussels
NZ Green-lipped Mussel WATCH
NZ Green-lipped Mussel
Perna canaliculus
Mussel • Emerging Threat
  • Green "lip" on shell edge — key ID
  • Brown-green shell outside
  • MASSIVE — up to 240mm
  • Check vessels from NZ
Don't confuse with: Asian Green Mussel — smaller (165mm max), bright emerald, no green lip
Brown Mussel WATCH
Brown Mussel
Perna perna
Mussel • Emerging Threat
  • Dark brown to black shell
  • Up to 90mm (fist-sized)
  • Dense thick clumps
  • Thick shell, hard to break
  • From Africa/South America
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Niche Areas — Where Pests Hide

Key Inspection Points

Marine pests don't just attach to flat hull surfaces. Many hide in protected niche areas. Always check these locations carefully:

Sea Chests

Warm, protected water. Check for mussels, crabs, squirts

Rope Guards

Crabs shelter here. Check thoroughly

Gratings & Grilles

Accumulate sediment and organisms

Rudder & Prop

Cavities and gaps harbour pests

Bilge Keel Ends

Often missed. Accumulate growth

Anchor Wells

Algae, squirts, mussels common

🦀 Crabs to Watch For:

European Shore Crab — Green shell, 5 spines each side. NOT established in WA. NOXIOUS — report to DPIRD.

Asian Paddle Crab — Paddle-shaped back legs, 6 spines between eyes. Carries disease.

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Native — Normal WA Fouling

No Report Needed
Blue Mussel NATIVE
Blue Mussel ✓
Mytilus galloprovincialis
Mussel — Common
  • Blue-black to dark brown shell
  • Pointy triangle shape
  • Clumps together with threads
  • NOT green — that's Asian one
Native Tube Worms NATIVE
Native Serpulid Worms ✓
Serpulidae & Spirorbidae
Tube Worm — Common
  • Hard white calcium tubes
  • Small feathery fans
  • Spirorbids are tiny 3mm coils
  • NOT big spiral fans like European fan worm
Native Sea Squirts: Thin jelly-like mats, various colours, NOT veiny/waxy. If unsure between native and invasive — always report it.
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Quick Reference — WA Noxious Species

Species Status Quick ID
Carpet Sea Squirt NOXIOUS Creamy veiny mat, waxy, drips down
Asian Green Mussel NOXIOUS Bright green shell, 80-165mm
European Fan Worm NOXIOUS Big spiral fan 45-60mm, stripy
Black-striped Mussel NOXIOUS Small 25mm, dark stripes, sea chests
European Shore Crab NOXIOUS Green shell, 5 spines each side
N. Pacific Seastar NOXIOUS Large 5-arm, yellow-orange, 50cm
Japanese Kelp WATCH Brown fronds, spine, wavy. Not in WA
Killer Algae WATCH Bright green feathery fronds
Large Oysters WATCH Messy shell, sharp — photo for ID
Asian Paddle Crab WATCH Paddle legs, 6 spines between eyes
⚠️ This is not the complete WA noxious list. View full list: fish.wa.gov.au or Schedule 5, Fish Resources Management Regulations 1995.
Native Species Key Difference from Invasive
Blue Mussel Blue-black shell, NOT green
Native Tube Worms Small fans, white hard tubes
Native Sea Squirts Thin jelly mats, NOT veiny/waxy
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Report to DPIRD Within 24hrs

📞 FishWatch Hotline (24/7)

1800 815 507
For suspected noxious fish — call anytime

DPIRD WA

Email:
Aquatic.Biosecurity@dpird.wa.gov.au

MyPestGuide App:
Search "MyPestGuide Reporter"

MarineStream

Biofouling Manager:
Mat Harvey

Operations Manager:
Sam Diamond

✓ When Reporting, Include:

  • Photos — close-up + wide shot with hand for scale
  • Location on hull (bow distance, depth, port/stbd)
  • Vessel name and berth location
  • Date and time of sighting
  • Your contact details

⚠️ Important: Cease work until DPIRD advises how to proceed in a biosecure manner. Do not remove suspected noxious organisms.

Hull Biofouling ID Guide — WA • Version 3.0 • January 2026

© 2026 MarineStream • Species from WA Noxious Fish List (Schedule 5)

Image credits: CSIRO, DPIRD WA, Wikipedia Commons, DAFF

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Developed by Marine Scientist & Developer

Mat Harvey

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