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Hull Biofouling
ID Guide

Quick reference for divers cleaning ship hulls in Tasmanian waters

📍 TASMANIA 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

Tasmania's pristine waters face major threats. The Northern Pacific Seastar has caused over $1 billion in damage to fisheries. Japanese kelp smothers native habitats. Divers are the front line against new introductions and further spread.

CRITICAL — Major established pest. Prevent spread!
DECLARED — Declared pest under TAS Biosecurity Act. Report to Biosecurity TAS.
ESTABLISHED — Present in TAS. Prevent further spread.
NATIVE — Normal TAS 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
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⚠️ CRITICAL — Major Established Pests

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Northern Pacific Seastar DECLARED
Northern Pacific Seastar
Asterias amurensis
CRITICAL - Established Derwent
  • HUGE — up to 50cm diameter
  • 5 arms with upturned tips
  • Yellow-orange with purple marks
  • Undersides completely yellow
  • $1B+ damage to Tas fisheries
  • Eats native shellfish, scallops
Population exploded: Millions in Derwent. Report any sightings outside known areas!
Japanese Kelp DECLARED
Japanese Kelp (Wakame)
Undaria pinnatifida
ESTABLISHED - Since 1988
  • Large 1-3m, golden-brown
  • Central midrib runs full length
  • Wavy ruffled edges
  • Frilly sporophyll at stalk base
  • Smothers native kelp forests
Don't confuse with: Native kelps — lack central midrib and frilly base. Giant kelp (native) has different structure.
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⚠️ CRITICAL — Major Established Pests

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European Fan Worm DECLARED
European Fan Worm
Sabella spallanzanii
ESTABLISHED - TAS Ports
  • HUGE fan — 45-150mm across
  • Fan spirals inward (not flat)
  • Stripy — orange/purple/white bands
  • Brown leathery tube up to 400mm
  • Competes with native filter feeders
Don't confuse with: Native serpulid worms — smaller fans (<20mm), white hard tubes
Asian Date Mussel DECLARED
Asian Date/Bag Mussel
Arcuatula senhousia
ESTABLISHED - TAS/VIC/SA/WA
  • Small — only up to 30mm
  • Thin, fragile, easily crushed
  • Greenish with zigzag markings
  • Iridescent radiating bands
  • Forms mats — smothers seagrass
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DECLARED — Report Immediately

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Carpet Sea Squirt DECLARED
Carpet Sea Squirt
Didemnum vexillum
DECLARED - Not in TAS
  • Creamy/tan to yellow-grey
  • Waxy, veiny like varicose veins
  • Leathery feel, NOT slimy
  • Can thicken to 10cm
  • Smothers EVERYTHING!
Don't confuse with: Native sea squirts — thinner, gelatinous, no veiny texture
Asian Green Mussel DECLARED
Asian Green Mussel
Perna viridis
DECLARED - Not in Australia
  • Young = bright emerald green
  • Older = brownish-green
  • Big — 80-165mm (hand-sized)
  • Blue-green iridescent inside
  • Check sea chests carefully
Don't confuse with: Blue mussel — blue-black, not green
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DECLARED — Report Immediately

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Black-striped False Mussel DECLARED
Black-striped False Mussel
Mytilopsis sallei
DECLARED - APMPL Listed
  • Small — only 20-25mm (thumbnail)
  • Dark radiating stripes on shell
  • Prefers brackish water
  • Darwin eradication cost $2.2M
  • Check sea chests!
Killer Algae DECLARED
Killer Algae
Caulerpa taxifolia
DECLARED - Not in TAS
  • Bright green - stands out
  • Feather-shaped fronds
  • Creeping runners
  • Up to 65cm tall
  • Smothers everything!
Also Watch: Charru Mussel (Mytella strigata) — 22-50mm, variable colors, blue-purple inside. Chinese Mitten Crab (Eriocheir sinensis) — hairy "mittens" on claws. Both DECLARED.
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ESTABLISHED in TAS — Prevent Spread

Monitor & Report Spread
European Shore Crab EST
European Shore Crab
Carcinus maenas
ESTABLISHED - Widespread TAS
  • Olive to dark green, 50-90mm
  • 3 blunt spines on rostrum
  • 5 spines each side of eyes
  • NO swimming paddles
  • Predates on shellfish
Pacific Oyster EST
Pacific Oyster
Magallana gigas
ESTABLISHED - Movement Controls
  • Large — up to 400mm
  • Irregular, sharp frilly edges
  • Grey-white to purple-brown
  • Can carry POMS disease
  • Watch your gloves — SHARP!
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WATCH — Watch Species

Report within 24 hours
NZ Green-lipped Mussel WATCH
NZ Green-lipped Mussel
Perna canaliculus
DECLARED - NZ Ferry Traffic
  • Green "lip" on shell edge — key ID
  • Dark brown to bright green shell
  • MASSIVE — up to 240mm
  • Check Spirit of Tasmania!
Vase Tunicate WATCH
Vase Tunicate
Ciona intestinalis
WATCH - Sea Squirt
  • Translucent yellow-green
  • Tube/vase shaped, up to 150mm
  • Two siphons at top
  • Soft and squishy texture
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Native — Normal TAS Fouling

No Report Needed
Blue Mussel NATIVE
Blue Mussel ✓
Mytilus galloprovincialis
Mussel — Common TAS
  • Blue-black shell, 50-100mm
  • Triangular/wedge shape
  • Clumps with byssal 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 (<20mm)
  • Spirorbids are tiny 3mm coils
  • NOT big brown leathery tube
Native Giant Kelp (Macrocystis): Very long (up to 30m+), gas-filled floats (pneumatocysts), no central midrib. Different from Japanese kelp. Tasmania's kelp forests are globally significant — protect them!
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Quick Reference Table

CRITICAL Species Status & Key ID
Northern Pacific Seastar $1B damage! 50cm, 5 upturned arms, yellow-orange
Japanese Kelp 1-3m brown, central midrib, frilly base
European Fan Worm Huge spiral fan 45-150mm, brown tube
Asian Date Mussel 30mm, fragile, zigzag, forms dense mats
HIGH Priority Quick ID
Carpet Sea Squirt Creamy veiny mat, waxy texture
Asian Green Mussel Bright green shell, 80-165mm
Black-striped Mussel Small 25mm, dark stripes, sea chests
Chinese Mitten Crab Hairy "mittens" on claws
Native Species Key Difference from Invasive
Blue Mussel Blue-black shell, NOT green
Giant Kelp Gas floats, no midrib (vs Japanese kelp)
Native Tube Worms Small fans (<20mm), white hard tubes
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Report It — Tasmania

🚨 Biosecurity Tasmania

03 6165 3777
Alt: 1300 368 550
invasivespecies@nre.tas.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 — Tasmania • Version 3.0 • January 2026

© 2026 MarineStream • Info from DAFF, Biosecurity TAS, NIMPIS

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Notes