🔍

Hull Biofouling
ID Guide

Quick reference for divers cleaning ship hulls in NSW waters

📍 NEW SOUTH WALES 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

Sydney Harbour and NSW ports see high vessel traffic. Carpet sea squirt was detected at Fleet Base East in May 2023. Caulerpa taxifolia is established in 14+ NSW estuaries. Divers are our first line of defence.

PROHIBITED — Prohibited matter under NSW Biosecurity Act. Report immediately.
WATCH — Emerging threat. Report within 24 hours
ESTABLISHED — In NSW. Prevent spread.
NATIVE — Normal NSW fouling, no report needed

⚠️ Found Something Dodgy?

  • STOP cleaning in that area
  • Take photos — close-up + wide shot, use hand for scale
  • Note location (bow distance, depth, port/stbd)
  • DON'T scrape it off until reported
  • Surface and tell your supervisor
2

PROHIBITED — Report Now

Page 1 of 4
Carpet Sea Squirt PROHIBITED
Carpet Sea Squirt
Didemnum vexillum
OUTBREAK - Sydney Harbour May 2023
  • Creamy/tan to yellow-grey
  • Waxy, veiny like varicose veins
  • Leathery feel, NOT slimy
  • Can thicken to 10cm, tendrils 1m
Don't confuse with: Native sea squirts — thinner, gelatinous, no veiny texture
Northern Pacific Seastar PROHIBITED
Northern Pacific Seastar
Asterias amurensis
Prohibited in NSW
  • Large — up to 50cm diameter
  • 5 arms with upturned tips
  • Yellow-orange with purple marks
  • Undersides completely yellow
  • $1B loss to Tas fisheries
3

PROHIBITED — Report Now

Page 2 of 4
Asian Green Mussel PROHIBITED
Asian Green Mussel
Perna viridis
APMPL Listed - Not in Australia
  • Young = bright emerald green
  • Older = brownish-green
  • Big — 80-165mm (hand-sized)
  • Blue-green iridescent inside
Don't confuse with: Blue mussel — those are blue-black, not green
Black-striped False Mussel PROHIBITED
Black-striped False Mussel
Mytilopsis sallei
APMPL Listed
  • Small — only 20-25mm (thumbnail)
  • Dark radiating stripes on shell
  • Prefers brackish water
  • Darwin eradication cost $2.2M
  • Check sea chests!
4

PROHIBITED — Report Now

Page 3 of 4
Asian Paddle Crab PROHIBITED
Asian Paddle Crab
Charybdis japonica
Prohibited in NSW
  • Paddle-shaped rear legs
  • 6 spines either side of eyes
  • 5 spines on each claw
  • Up to 120mm carapace
  • Carries White Spot Virus!
Asian Date Mussel PROHIBITED
Asian Date/Bag Mussel
Arcuatula senhousia
Prohibited - Est. in VIC/TAS/SA/WA
  • Small — up to 30mm
  • Thin, fragile, easily crushed
  • Greenish with zigzag markings
  • Iridescent radiating bands
  • Forms mats of 1000s per m²
5

PROHIBITED — Report Now

Page 4 of 4
Charru Mussel PROHIBITED
Charru Mussel
Mytella strigata
APMPL Listed 2020
  • Medium 22-50mm
  • Variable: black, brown, orange
  • Zigzags, spots, or bands
  • Blue-purple opalescent inside
  • Yellowish flesh
Chinese Mitten Crab PROHIBITED
Chinese Mitten Crab
Eriocheir sinensis
Prohibited
  • Dense hair "mittens" on claws
  • White-tipped claws
  • Up to 80mm carapace
  • Olive-brown, 4 spines per side
  • Can carry lung fluke parasite
6

WATCH — Watch Species

Page 1 of 2
NZ Green-lipped Mussel WATCH
NZ Green-lipped Mussel
Perna canaliculus
Watch Species
  • Green "lip" on shell edge — key ID
  • Dark brown to bright green shell
  • MASSIVE — up to 240mm
  • Check vessels from New Zealand
Japanese Kelp WATCH
Japanese Kelp (Wakame)
Undaria pinnatifida
APMPL - VIC/TAS only, Watch for NSW
  • Large 1-3m, golden-brown
  • Central midrib full length
  • Wavy ruffled edges
  • Frilly sporophyll at stalk base
7

WATCH — Watch Species

Page 2 of 2
Stalked Sea Squirt WATCH
Stalked Sea Squirt
Styela clava
Watch Species
  • Looks like brown pickle on stalk
  • Leathery, wrinkled like prune
  • 50-160mm tall, tough tunic
  • Stands alone, not in colonies
Vase Tunicate WATCH
Vase Tunicate
Ciona intestinalis
Watch Species
  • Translucent yellow-green
  • Tube/vase shaped, up to 150mm
  • Two siphons at top
  • Soft and squishy texture
Pleated Sea Squirt (Styela plicata) — Grey-brown, ridged like brain, up to 70mm. Already in some Aust. ports. Report if found on vessels.
8

ESTABLISHED in NSW — Prevent Spread

Page 1 of 2
Caulerpa CLASS 1
Caulerpa (Killer Algae)
Caulerpa taxifolia
NOXIOUS NSW - 14+ estuaries
  • Bright green feathery fronds
  • Up to 30cm in NSW
  • Creeping stolons/runners
  • Sydney Hbr, Pittwater, Lake Conjola
  • Illegal to possess in NSW
European Shore Crab EST
European Shore Crab
Carcinus maenas
Notifiable - 20+ southern NSW estuaries
  • Olive to dark green, 50-90mm
  • 3 blunt spines on rostrum
  • 5 spines each side of eyes
  • NO swimming paddles
  • Report to track spread
9

ESTABLISHED in NSW — Prevent Spread

Page 2 of 2
European Fan Worm EST
European Fan Worm
Sabella spallanzanii
Est. Eden 1996, Botany Bay
  • Spiral fan crown 45-150mm
  • Banded orange/purple/white
  • Brown leathery tube
  • Body up to 400mm in tube
Don't confuse with: Native serpulids — smaller fans (<20mm), white hard tubes
Pacific Oyster EST
Pacific Oyster
Magallana gigas
Movement Controls Apply
  • Large — up to 400mm
  • Irregular, sharp frilly edges
  • Grey-white to purple-brown
  • Competes with Sydney Rock Oyster
  • Can carry POMS disease
10

Native — Normal NSW Fouling

No Report Needed
Blue Mussel NATIVE
Blue Mussel ✓
Mytilus galloprovincialis
Mussel — Common
  • Blue-black shell, 50-100mm
  • Triangular/wedge shape
  • NOT green — that's Asian one
Sydney Rock Oyster NATIVE
Sydney Rock Oyster ✓
Saccostrea glomerata
Native NSW Oyster
  • Rounder and smaller (<80mm)
  • Less frilly than Pacific Oyster
  • Native to NSW waters
Native Tube Worms (Serpulidae): Small fans (<20mm), white hard calcareous tubes, often twin spiral fans. NOT the big brown leathery tube of European fan worm. If unsure — always report it.
11

Quick Reference Table

Species Priority Quick ID
Carpet Sea Squirt HIGH Creamy veiny mat, waxy, Sydney Hbr outbreak
Northern Pacific Seastar HIGH 50cm, 5 arms upturned tips, yellow-orange
Asian Green Mussel HIGH Bright green shell, 80-165mm
Black-striped Mussel HIGH Small 25mm, dark stripes, sea chests
Asian Paddle Crab HIGH Paddle rear legs, 6 spines, White Spot risk
NZ Green-lip Mussel MED Green lip on edge, massive 240mm
Japanese Kelp MED Brown fronds 1-3m, central midrib
Established NSW Status & Notes
Caulerpa CLASS 1 NOXIOUS - 14+ estuaries. Illegal to possess.
European Fan Worm Eden since 1996, Botany Bay. Prevent spread.
European Shore Crab Notifiable. 20+ southern NSW estuaries.
Pacific Oyster Movement controls. Competes with Sydney Rock.
12

Report It — NSW

🚨 NSW DPI Aquatic Biosecurity

1800 675 888
24-hour hotline
aquatic.biosecurity@dpird.nsw.gov.au

MarineStream

Biofouling Manager:
Mat Harvey

Operations Manager:
Sam Diamond

www.marinestream.com.au

National Resources

Marine Pests:
www.marinepests.gov.au

NIMPIS Database:
nimpis.marinepests.gov.au

✓ When Reporting, Include:

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

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

© 2026 MarineStream • Info from DAFF, NSW DPI, NIMPIS

13

Notes