Scienc e underpinning  the thresholds 
proposed in  the CRMS : Biofouling on 
vessels arriving to New Zealand  
  
 
MPI Technical Paper No: 2014 /22  
by Eugene Georgiades and Daniel Kluza  
 
 
 
ISBN No: 978- 0-478-43717 -1 (online ) 
ISSN  No: 2253- 3923 (online ) 
  
  
 
July 2014  
 
 
Scien ce Underpinning the Thresholds Proposed in  the CRMS:  
Biofouling on Vessels Arriving to New Zealand  
 
25 July 2014  
 
Approved for general release  
 
 
Christine Reed  
Manager, Biosecurity Risk Analysis  
Ministry for Primary Industries  
 
 
Disclaimer  
 
Every effort  has been made to ensure the information in this document is 
accur ate. The Ministry fo r Primary Industries (MPI) does n ot accept any 
responsibility or liability whatsoever for any error of fact, omission, interpretation or opinion that may be present, howe ver it may have occurred.  
  
Requests for further copies should be directed to:  
 Publications Logistics Officer  
Ministry for Primary Industries  
PO Box 2526  
WELLINGTON 6140  
 
Email: 
brand@mpi.govt.nz  
Telephone: 0800 00 83 33  
Facsimile: 04 -894 0300 
 This publication is also available on the Ministry for Primary Industries website at :  
http://www.mpi.govt.nz/news -resources/publications.aspx  
 
 © Crown Cop yright - Ministry for Primary Industries   
Contributors to this T echnical Paper  
 
1. Primary authors  
Dr Eugene Georgiades  Senior Adviser,  
Biosecurity Risk Analysis  Ministry for Primary Industries,  
New Zealand  
Dr Daniel Kluza  Senior Adviser,  
Biosecurity Ris k Analysis  Ministry for Primary Industries,  
New Zealand  
 
 
2. External Peer Review  
John Lewis  
Principal Marine Consultant  
ES Link Services Pty Ltd  
Melbourne, Victoria, Australia  
 
 
The contribution of MPI internal reviewers is also gratefully acknowledged.  
  
Contents  Page 
 
1 Summary of proposed biofouling thresholds  1 
2 Background  4 
3 Evaluation of thresholds  5 
3.1 Presence or absence of macrofouling on the hull  5 
3.2 Types of macrofouling that should be allowed  6 
3.3 Practical management of macrofouling  7 
3.4 Factors affecting macrofouling thresholds  8 
3.5 Intended vessel itinerary  13 
4 References  15 
 
i  
1 Summary of proposed biofouling thresholds  
 
This document presents  the scien ce that underpins  the thresholds proposed in the  Craft Risk 
Management Standard  (CRMS ): Biofouling  on Vessels Arriving to New Zealand .  
 
Biofouling is recognised as a significant pathway for introduction of non -indigenous marine 
species into New Zealand. The risk analysis of vessel biofouling notes that  the biosecurity 
risk can be mitigated by restricting the fouling on vessels entering New Zealand to the level of 
slime layer (microfouling) or less (Bell et al . 2011).  
 The setting of a level of clean at “slime layer” for the CRMS  is tractable when vessel s operate 
within the specifications of antifouling coatings. However, there are instances within “normal” vessel operation that may result in the establishment of macrofouling. For example, 
the waiting periods for the loading/unloading of cargo can be up t o 3 months in Australia. 
Because of such instances, the thresholds proposed in the CRMS  allow for the presence of 
some macrofouling species, albeit with restrictions to minimis e biosecurity risk. The 
thresholds proposed are designed to limit species richne ss, and to prevent successful 
reproduction and settlement of the allowed macrofouling species whilst considering the 
practicality/feasibility of implementation.  
 The proposed thresholds specifically focus on four taxonomic groups of organisms common 
to ear ly-stage macrofouling – macroalgae, barnacles, tubeworms and bryozoans. Macroalgae 
are found on hull surfaces of many otherwise clean vessels. They are usually found on the wind/water line area where antifouling systems are less effective and the light ava ilability is 
high. Barnacles, tubeworms and bryozoans are typically the first macro -organisms to colonise 
hull surfaces, thus they may provide habitat for other fouling species. The presence of early -
stage fouling by these species within the proposed thres holds serves as a warning to vessel 
owners that their biofouling management plan is failing. These vessels may pose a potential 
biosecurity risk to New Zealand on subsequent visits.  
 The practical difficulties in managing biofouling on different areas of t he hull are 
acknowledged within the thresholds proposed. For example, a greater tolerance of macrofouling species has been proposed for niche areas due to the specific difficulties in 
preventing biofouling on these areas. Further, tolerance for a green macroalgae on the 
wind/water line has also been proposed due to the challenge of preventing these organisms 
from fouling this area.  
 
The proposed thresholds are also governed by the intended duration of a vessel’s stay in New 
Zealand. For example, long -stay vessels must meet a higher standard of hull cleanliness due 
to the increased likelihood of release and establishment of non -indigenous species.  
 
Tables 1 and 2 summarise the recommendations  for the proposed thresholds in the CRMS:  
Biofouling on Vessels Arr iving to New Zealand.  
 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 1 Table 1 : Recommended b iofouling thresholds  for short -stay vessels.  
Vessel surface  Allowable biofouling  
All surfaces  Slime layer;  
Goose barnacles . 
Wind/water line  Green algal growth of no more than 50 mm in length;  
Brown and red a lgal growth of no more than 4 mm in length;  
Incidental (1%) coverage of one non- algal macrofouling 
organism type of either barnacles, tubeworms or bryozoans 
occurring as:  
 isolated individuals or small clusters; and  
 a single species, or an organism type that appears to 
be the same species.  
Hull area  Algal growth occurring as:  
 no more than 4 mm in length; and  
 continuous strips and/or patches of no more than 
50 mm in width.  
Incidental (1%) coverage of one non- algal macrofouling 
organism type of either barnacl es, tubeworms or bryozoans, 
occurring as:  
 isolated individuals or small clusters that have no algal overgrowth; and  
 a single species, or an organism type that appears to 
be the same species.  
Niche areas  Algal growth occurring as:  
 no more than 4 mm in leng th; and  
 continuous strips and/or patches of no more than 50 
mm in width.  
Scattered (5%) coverage of one non -algal macrofouling 
organism type of either barnacles, tubeworms or bryozoans, 
occurring as:  
 widely spaced individuals and/or infrequent, patchy clusters that have no algal overgrowth; and  
 a single species, or an organism type that appears to 
be the same species.  
Incidental (1%) coverage of a second non -algal macrofouling 
organism type of either barnacles, tubeworms or bryozoans, 
occurring as:  
 isolated  individuals or small clusters that have no 
algal overgrowth; and  
 a single species, or an organism type that appears to 
be the same species.  
 
 
2 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
Table 2 : Recommended b iofouling thresholds for long- stay vessels and/or vessels that 
intend to visit areas othe r those designated under the Act as Places of First Arrival . 
Vessel surface  Allowable biofouling  
All surfaces  Slime layer;  
Goose barnacles . 
 
Short -stay vessels  
For those vessels intending to remain in New Zealand for less than 3 weeks, the threshold for short -stay vessels applies.  
 Long -stay vessels  
For those vessels intending to remain in New Zealand for more than 3 weeks and/or visit areas other those designated under the Act as Places of First Arrival, the threshold for long -
stay vessels applies
. 
 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 3  
2 Background 
 
Biofouling is the process of accumulation of organisms on immersed surfaces. In the initial 
stages of the biofouling process, organic material sticks to a surface and is rapidly colonised 
by bacteria, microalgae and cyanobacteria forming a microf ouling layer (slime layer). The 
creation of a slime layer occurs rapidly on submerged surfaces. Aside from continuous cleaning, there is currently no effective technology to prevent slime layer formation, including 
biocidal or foul release coatings (Dobret sov et al. 2010).  
 Surface biofouling is a stochastic process based on the probability of biofouling organisms 
encountering a surface in a state that is suitable for attachment  (Aldred and Clare 2008) . 
Complex interactions take place between abiotic and bi otic factors. These interactions include 
the season of first submersion, length of submersion, surface type, presence of biofilm, 
biofilm type  and light availability ( Aldred and Clare 2008; Terlizzi and Faimali 2010). 
Despite the stochastic nature of the b iofouling process, ‘pioneering’ macrofoulers typically 
include green filamentous algae, barnacles, tubeworms and bryozoans (Hilliard et al. 2006; 
Lewis and Coutts 2010).  
 Where antifouling coatings are absent, worn, old, or damaged, Hilliard et al. (2006) suggested 
the following common successional pattern in port and coastal waters:  
• Primary slime layer with grey and green tinges that vary with diatom content and 
light;  
• Gossamer -like amphipod tubes (dependent on season and level of water movement);  
• Filament ous green algae that can develop into waterline or transom beards providing 
shelter to amphipods and other clinging biota;  
• Encrusting bryozoans;  
• Tubeworms, barnacles, turfing red algae, hydroids, erect bryozoans, ectocarpoid 
brown algae;  
• Mussels, oysters, encrusting sponges, sea anemones and sea squirts;  and 
• Larger mobile forms, including errant polychaetes, crabs, whelks, nudibranchs, 
crinoids and territorial fishes.  
 
The MPI risk analysis of vessel biofouling identified twelve taxonomic groups as posing n on-
negligible risks to New Zealand’s core values. The taxonomic groups identified were:  
• Amphipods and Isopods;  
• Barnacles;  
• Bivalves;  
• Bristleworms (including Tubeworms);  
• Bryozoans;  
• Crabs;  
• Echinoderms;  
• Flatworms;  
• Gastropods;  
• Hydroids;  
• Macroalgae;  and 
• Sea squi rts. 
 
Not all species within these groups will pose a biosecurity risk as they may be native, 
cosmopolitan, or already established. However, there are many non -indigenous species within 
4 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
these groups that demonstrate characteristics likely to pose biosecuri ty risks to New Zealand’s 
core values (Bell et al. 2011).  
 
It is noted that research is required to confirm the presence and translocation potential of 
potentially hazardous bacteria, viruses and microalgae before the development and 
implementation of bio film control measures can be justified. As already noted, preventing  the 
entry of non- indigenous bacteria, viruses and microalgae via vessel hull fouling cannot be 
practically achieved (Dobretsov et al. 2010) .   
 The most effective option to manage the bio security risks associated with vessel biofouling is 
prevention (Bax et al. 2003). Reactive measures, such as containment and eradication of species are labour intensive, time consuming, expensive, and often have limited success 
(Anderson 2005; Davidson et al. 2008). As a consequence , risk management should seek to 
prevent the establishment of macrofouling on the vessel hulls. However , it is noted that there 
are practical limitations to biofouling prevention requiring that thresholds be set that achieve a 
biosecurity outcome whilst facilitating trade.  
 
3 Evaluation of thresholds  
3.1 Presence or absence of macrofouling on the hull  
3.1.1 Allowance of slime layer only  
Other than continuous cleaning, there appears to be no effective antifouling technology available to preven t slime layer fouling (Dobretsov et al. 2010). Applying a slime layer 
threshold would manage the biosecurity risks presented by the groups of macrofouling taxa identified in the risk analysis of vessel biofouling (Bell et al. 2011).  
 The IMO has recently adopted guidelines for the control and management of biofouling of 
vessels to minimize the transfer of aquatic species (IMO 2011). The intent of these guidelines 
is to maintain the submerged surfaces and internal cooling systems of the vessels “as free of 
biofouling, as is practical.”  
 
3.1.2 Allowance of some macrofouling  
Best antifouling practice on a hull means no macrofouling species should be present (except 
for macroalgae on the wind/water line
1; Lewis pers. comm. ). However a review of the MPI 
commissioned r esearch on vessel biofouling has shown the presence of some macrofouling 
species on hull areas of newly antifouled/well -maintained vessels (Floerl et al. 2010; Inglis et 
al. 2010). The macrofouling found on these vessels were mainly located in niche areas that were not antifouled and/or were protected from hydrodynamic drag (Floerl et al. 2010; Inglis 
et al. 2010). Further, Mineur et al. (2007) showed no differences between new coatings (2 
months old) and those up to 30 months old in terms of macroalgae spe cies richness on 
merchant vessels. However, it is noted that antifouling age is not the only factor determining the likely presence of macrofouling species (Inglis et al. 2010; IMO 2011).  
 Although the slime layer threshold would manage the biosecurity ris ks identified from the 
vessel biofouling risk analysis (Bell et al. 2011), the amount of vessels with incidental macrofouling may require significant resource effort at each P lace of F irst Arrival (POFA) to 
make management decisions on vessels that pose an  acceptable biosecurity risk.  
 
Some of the practical difficulties identified with respect to vessel compliance with a threshold 
set at “slime layer” are:  
1 The terms “wind/water line” and “ boot-top” can be used synonymously, but for the pu rposes of this document the term “wind/water line” is 
preferred.  
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 5                                                 • How often is incidental fouling present?  
• What form does incidental fouling typically take?  
• Does inci dental fouling pose a biosecurity risk?  
• What action should be taken on non- compliant vessels with incidental fouling?   
 
To solve these problems the Risk Analysis Team identified macrofouling levels that occur as 
incidental fouling under best antifouling management practices. From this baseline, thresholds 
have been proposed taking into account organism biology, MPI commissioned research and 
international research findings, and comments received from public submissions.  
 
3.1.3 Recommendations  
The Risk Analysis Te am considers that some “early -stage” macrofouling species be allowed 
as biofouling without compromising the overall management of biosecurity risk. However, 
depending on their characteristics, such as mode of reproduction or ability to facilitate the 
intro duction of additional non -indigenous species, some restrictions on the amount of fouling 
allowed would be required.   
3.2 Types of macrofouling that should be allowed  
Analysis of the MPI commissioned research on vessel biofouling and international literature has allowed the Risk Analysis Team to identify species that are common as incidental fouling 
on well -maintained vessels.  
  
3.2.1 Goose barnacles  
Goose barnacles (lepadomorphs) are ubiquitous foulers of tropical, subtropical and temperate 
seas, with a pelagic lifecycle that includes attachment to drift wood, floating plant debris and 
hulls of slow moving vessels, as well as turtles and some whales (Barnes et al. 2004 ; Lewis 
2004). Densities of 20- 30 m
-2 are not uncommon in areas of low flow, including entrances of 
irregularly used seawater intakes or outlets (Hilliard et al. 2006). Stalked or goose barnacles, 
such as Lepas spp., often foul submerged surfaces in open oceans, including buoys, but are 
also sometimes found on vessel hulls (Lewis 2004).  
 
The presence of goose barnacles does not represent an unacceptable level of fouling risk 
(Hilliard et al. 2006), however, species of Lepas  may resemble bivalve molluscs to casual 
observers. Thus , goose barnacles can cause inspection concerns if misidentified as a potentia l 
bivalve pest resulting in wasted time and resource effort. A more serious biosecurity concern 
is the potential for small bivalves to be interpreted as goose barnacles (Hilliard et al. 2006). 
Goose barnacles were not considered a hazard species and not in cluded in the vessel 
biofouling risk analysis (Bell et al. 2011).  
 
3.2.2 Macroalgae  
Macroalgal fouling of hull surfaces of recreational, commercial and naval vessels is a 
common phenomena (Evans 1981; Hay 1990; Godwin et al. 2004; Floerl et al. 2005; URS 
2002, 2006 in Hilliard et al. 2006; Lewis and Gillham 2007; Mineur et al. 2007; Mineur et al. 
2008; Piola and Conwell 2010; Schultz et al. 2011; Inglis et al. in prep.; Lewis pers. comm. ). 
 A primary factor determining the proportion of photosynthetic algae withi n biofouling 
communities is light availability (Cowie 2010). Thus macroalgal species that require an appropriately lit environment are restricted in their potential zone of recruitment to 
conspicuous areas of the hull, such as just below the waterline ( Naval Sea Systems Command  
(NSSC ) 2006; Lewis and Gillham 2007; Mineur et al. 2007).  
 
6 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
The risk analysis of vessel biofouling (Bell et al. 2011) identified the macroalgal taxonomic 
group as a non- negligible biosecurity risk. However, the MPI commissioned research on 
vessel biofouling has shown a relatively high incidence (%) of macroalgae on all vessel types (Inglis et al. 2010; Table 3). Therefore, a threshold that manages the biosecurity risk but does 
not unnecessarily penali se low risk vessels is proposed (see section 3.4.1 Macroalgae).  
  
3.2.3 Barnacles, tubeworms and bryozoans   
The risk analysis o f vessel biofouling (Bell et al. 2011) identified the barnacle, tubeworm and 
bryozoan taxonomic groups as non -negligible biosecurity risks. However, it is recognised that 
macrofouling consisting of at least one of these organisms is common on all vessel types (Inglis et al. 2010; Table 3). Therefore, a threshold that manages the biosecurity risk bu t does 
not unnecessarily penalis e low risk vessels is proposed (see section  3.4.2 Barnacles, 
tubeworms and bryozoans).  
 Table 3: Fouling organism incidence by vessel type (percentage and number of vessels).  
 Macroalgae  Bryozoans  Barnacles  Tubeworms  
Commercial ( n = 270)  28% ( n = 76)  2% ( n = 5) 58% ( n = 157)  9% ( n = 24)  
Passeng er  (49)  51% (25)  6% (3)  55% (27)  6% (3)  
Fishing (3)  100% (3)  33% (1)  100% (3)  67% (2)  
Recreational (182)  29% (52)  72% (131)  70% (127)  47% (86)  
All vessels (504)  31% (156)  28% (140)  62% (314)  23% (115)  
 
3.2.4 Recommendations  
From the above findings it is r ecommended that the presence of:  
• Goose barnacles on vessel hulls are permitted without restrictions. The presence of goose barnacles may be used by Quarantine Inspectors as an indicator of the 
presence of restricted macrofouling;  
• Macroalgae on vessel hulls  are permitted – with restrictions (see section 3.4.1 
Macroalgae) ; and  
• Barnacles, tubeworms and bryozoans on vessel hulls are permitted - with restrictions 
(see section 3.4.2 Barnacles, tubeworms and bryozoans).  
 
3.3 Practical management of macrofouling  
Analys is of the MPI commissioned research on vessel biofouling and international literature 
has allowed the Risk Analysis Team to identify areas of well -maintained vessels that are 
prone to incidental fouling based on vessel and fouling organism traits.  
 3.3.1 Varied thresholds for specific areas of the hull surface  
There exist intrinsic differences in the ability to prevent biofouling on different areas of the 
vessel hull including wind/water line, hull areas and niche areas. Best antifouling practice on 
a hull means no macrofouling species should be present (except for macroalgae on the 
wind/water line; Lewis pers. comm. ). However , a review of the MPI commissioned research 
has shown the presence of some macrofouling species on hull areas of newly antifouled/well -
maint ained vessels (Floerl et al. 2010; Inglis et al. 2010). The macrofouling encountered on 
these vessels were mainly located in niche areas that were not antifouled and/or protected from hydrodynamic drag (Floerl et al. 2010; Inglis et al. 2010).  
 Niche area s are those areas on a vessel that may be more susceptible to biofouling due to 
different hydrodynamic forces, susceptibility to coating system wear or damage, or being inadequately, or not, painted, e.g., sea chests, bow thrusters, propeller shafts, inlet  gratings, 
dry-dock support strips, etc. Niche areas therefore pose a substantial biosecurity risk despite 
accounting for a relatively small proportion of the hull (James and Hayden 2000; AMOG 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 7 Consulting 2002; Coutts et al. 2003; Coutts and Taylor 2004; Fl oerl et al. 2010; Inglis et al. 
2010). In the MPI commissioned research on vessel biofouling,  a large proportion of species 
collected were present in niche areas (84% from the combined sample of passenger and 
fishing vessels and 89% from recreational vesse ls). Although 98% of species collected from 
merchant vessels were present in niche areas, it is noted that a greater sampling effort was applied to niche areas on the latter vessels (Inglis et al. 2010). Due to the susceptibility of 
niche areas to biofouli ng, a practical threshold is proposed that is above that allowed for 
wind/water line and hull areas.   
3.3.2 Uniform threshold for the whole of the hull surface  
Applying the proposed niche area threshold to the hull area would result in the potential for an 
increase in propagule pressure of non -indigenous species due to the relative surface area of 
the hull by comparison to niche areas. In the MPI commissioned research on the hull fouling of recreational vessels, hull area comprised approximately 93.2% of each recreational vessel’s 
submerged surface area, about 14 times more than the area comprised by niche areas (Floerl 
et al. 2008). Applying a higher niche area threshold to the wind/water line and hull areas also 
belies industry best practice and therefore canno t be justified. Applying the threshold 
proposed for the hull area to the niche areas may result in the non -compliance of a number of 
vessels that pose a minimal biosecurity risk causing unnecessary delays at the border and may 
negatively impact New Zealand ’s economic interests.   
 
3.3.3 Recommendation  
From the above findings it is recommended that the threshold for biofouling should be varied 
for specific areas of the hull surface.  
 
3.4 Factors affecting ma crofouling thresholds  
3.4.1 Macroalgae  
Allowing species within thi s taxonomic group to enter New Zealand without restrictions 
represents a non -negligible biosecurity risk (Bell et al. 2011).  
 The morphologies of macroalgal species associated with hull fouling are characterised as 
being small with flexible, filamentous o r sheet like vegetative structures and high growth rates 
(Ribera -Siguan 2003; Williams and Smith 2007; Lewis and Coutts 2010). T he cosmopolitan 
distribution of many well- known fouling taxa such as members of the Ceramiaceae, 
Ectocarpaceae, Ulvaceae and Cladophoraceae may be the result of biofouling and ballasting of wooden hulled ships of the past (Schaffelke et al. 2006). As a result of their now 
cosmopolitan distributions and incomplete records of origin, these taxa are now considered to 
be cryptogenic (i .e., of unknown origin). Macroalgae with cosmopolitan distributions are 
common on vessel hulls; for example, Mineur et al. (2008) found that the majority (58%) of the macroalgal species recorded on merchant vessels ( n = 22) had a cosmopolitan distribution.  
It is noted that the use of antifouling paint on modern vessels does not provide full protection from macroalgal fouling (Schaffelke et al. 2006; Lewis and Gillian 2007) . Resistance to 
antifouling biocides has been shown to influence macroalgae distributi ons in the past, 
whereby the dominant copper -resistant Enteromorpha (Ulva ) species were replaced by 
Ectocarpus  as the major cosmopolitan fouling alga on ships following the introduction of 
tributyl -tin containing antifouling paints (Callow 1986).  
 Wind/wat er line ( Boot -top) 
To manage the biosecurity risk posed by macroalgae, Hilliard et al. (2006) suggest that macroalgal fouling be restricted to “low levels of filamentous green macroalgae (i.e. small 
patches where the filament or blade growth is thin [i.e.,  < 4 mm beard]).”  
 
8 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
The rationale behind this limit is that thin patches with tufts less than 4 mm thick do not 
provide good nestling, flow -sheltering, feeding and hiding areas for amphipods or other 
mobile crustaceans in contrast to well developed algal beards. Note that brown and red algae were excluded from this allowance. Further, Hilliard (pers comm.) states that he has “yet to 
see any grasping crustacean using simple waterline ‘fur’ as a successful shelter from turbulent 
flow.”  
 However, application o f such a standard to the wind/water line may result in the exclusion of 
vessels likely to contain cosmopolitan species of green algae, such as Cladophorales and Ulvales (Minuer et al. 2007; Mineur et al. 2008; Lewis pers. comm. ).  Species within these 
taxa have an affinity for the wind/water line because of the high light/high turbulence 
conditions, coupled with high antifouling biocide tolerance. Compromise of the antifouling 
system in this region due to turbulent water movement, paint degradation from wet /dry cycles 
and/or UV degradation of the biocide may further facilitate establishment and growth of these 
species (Lewis pers. comm. ).  
 Considering the above, the Risk Analysis Team has reviewed images from the MPI 
commissioned research on vessel biofouli ng for merchant vessels, passenger vessels and 
recreational vessels and determined that a length of 50 mm for green macroalgae does not compromise the overall biosecurity risk of a vessel in terms of biofouling species present.  
Mineur et al. (2007) sugges ted that macroalgal fouling communities are short lived and have a 
high turnover on parts of the hull exposed to emersion, especially under high sun exposure.  
 The tolerances for red and brown macroalgae should remain at < 4 mm blade length as 
suggested by  Hilliard et al. (2006) as species within these taxa are not as ubiquitous as green 
macroalgae and thus present a different biosecurity risk. These restrictions should adequately protect New Zealand given that reproductive capacity of the algae should be l imited by the 
size and timing restrictions in place (Floerl et al. 2010; see section 3.5).  
 
Despite a suggested allowance of “small patches” of filamentous green algae (Hilliard et al. 
2006), the wind/water line provides these macroalgae with a suitable en vironment for 
settlement until light becomes a limiting factor. Because of the high prevalence of macroalgal fouling of the wind/water line , it is not practical to propose a limit on the extent of macroalgae 
occurring on this vessel surface.   
Preventing t he overgrowth of macrofouling species by macroalgae on the wind/water line 
may not be practically achievable due to the dynamic macroalgal growth conditions present on this section of the hull. Thus it is proposed that macroalgal overgrowth of permitted 
macrofouling be allowed on the wind/water line section of the hull.   
 Hull and niche areas  
To manage the biosecurity risk posed by macroalgae in hull and niche areas, it is proposed that MPI follows the advice of Hilliard et al. (2006). However, due to pract ical considerations 
at the border, such as the availability of taxonomic expertise, there should be no restrictions on algal morphology (e.g., coralline, bladed, foliose) or taxonomic group (e.g. , red, brown, 
green algae) in these areas. Restrictions shoul d be based solely on the length of the growth 
and the extent of its coverage. These restrictions should adequately protect New Zealand 
given that reproductive capacity of the algae should be limited by the size and timing 
restrictions in place (Floerl et al. 2010; see section 3.5).  
 Vessels coming into New Zealand with continuous algal turf on hull and niche areas represent 
a widespread failure of antifouling coating that is indicative of the presence of other 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 9 macrofouling species. A large turf (area) of m acroalgae increases the likelihood of the 
presence of blades > 4 mm long, i.e., the provision of habitat for other macrofouling species.  
 
Large algal turfs may impede the identification of macrofouling species on hull and niche 
areas, leading to the clear ance of non- compliant vessels through New Zealand’s border 
system. Further, the successional nature of hull biofouling means that the longer a macrofouling species has been present on a hull, the more likely it is to be covered by 
overgrowth.  Hence, it is  proposed that a restriction be put in place to limit the overgrowth of 
allowed macrofouling organisms to help mitigate the presence of sexually mature macrofouling individuals.  
  
Strips of algae are not uncommon in niche areas, particularly along their o uter edges.  A 
threshold for allowable macroalgal growth needs to balance between risk mitigation and vessel clearance. Following the advice of Hilliard et al. (2006) regarding the allowance of 
“small patches”, our review of the vessel biofouling hull imag es suggests that a 50 mm 
threshold allows for algal growth that is typically associated with well -maintained vessels.  
These findings are in agreement with those of Mineur et al. (2007) who found that small tufts 
(localised patches) of macroalgae (usually less than a few cm
2 in area) were a constant feature 
of the hulls of merchant vessels ( n = 22), even when most of the surface was free of fouling 
organisms.  
 
Recommendations  
For wind/water line , green algal growth should be no more than 50 mm in length;  red and 
brown algal growth should be no more than 4 mm in length.   
 
For hull areas and niche areas , any algal growth should be no more than 4 mm in length and 
in continuous strips and/or patches of no more than 50 mm in width;  no algal overgrowth 
should be permitted on the allowed macrofouling species (see section 3.4.2).  
 
3.4.2 Barnacles, tubeworms and bryozoans  
Allowing species within these taxonomic groups to enter New Zealand without restrictions 
represents a non -negligible biosecurity risk (Bell et al. 2011).  
 In terms of previous proposed thresholds for macrofouling, the following levels of fouling 
were deemed by Hilliard et al. (2006) as low risk:  
• Minor growth of green algae (as green slime, individual filaments or small patches < 4 
mm thick with no obvious projecting wads of thicker tufts);  
• Goose barnacles; and  
• Flat solitary calcareous discs, i.e., encrusting bryozoa or pink coralline algae.  
 
The following levels of fouling were deemed by Hilliard et al. (2006) as high risk:  
• Macroalgae beards (> 4 mm thick w ith numerous projecting tufts);  
• Balanomorph barnacles (i.e. , acorn, star and giant barnacles);  
• Tubeworm infestations;  
• Mussels and oysters;  and 
• Complex growths containing multiple spongy, filamentous, encrusting or foliose 
plants and animals.  
 Hilliard et a l. (2006) noted that one of the disadvantages of listing balanomorph barnacles as a 
high risk group is their common occurrence on most vessel types – particularly on anodes and 
where antifouling paint is absent, damaged or colonised by bryozoans. These fin dings were 
consistent with the MPI commissioned research on vessel biofouling (Inglis et al. 2010).  
10 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
 
The percentage cover and biomass of fouling organisms tend to be positively correlated with 
species abundance and richness, and increases in the extent and  amount of biofouling are 
therefore likely to increase biosecurity risk as well (Inglis et al. 2008).    MPI’s commissioned 
research attributed a higher level of biosecurity risk to vessels where any given hull or niche 
area had an level of fouling (LOF) rank of 4 or 5 (See Box 1) than to vessels where LOF was 
2 or 3.  Hull and niche areas with an LOF rank of 3 tend to have multi -species biofouling 
assemblages, whereas areas with an LOF rank of 2 typically have more limited biofouling species richness.  
 
 
 
Analysis of the results of the MPI commissioned research on biofouling of recreational 
vessels has shown that when combinations of the barnacle, tubeworm and/or bryozoan groups 
are present as hull biofouling, it is likely that add itional taxonomic groups will also be present 
(Table 4).  For the wind/water line and hull areas, it would appear prudent to allow only single species, or species that appears to be the same, rather than combinations of organisms 
from these broad taxonomic  groups.  
 
Table 4: Incidence of additional hull fouling groups occurring on recreational vessels in the presence of specific or combinations of macrofouling (percentage and number of 
vessels).  
Group combination  
(Total vessels n = 182)  Percentage  
Incidenc e Percentage incidence of 
additional groups present  
Bryozoans x Barnacles x Tubeworms  33.5% ( n = 61)  83.6% ( n = 51)  
Bryozoans x Barnacles  23.1% ( n = 42)  73.8% ( n = 31)  
Bryozoans x Tubeworms  9.3% ( n = 17)  76.5% ( n = 13)  
Barnacles x Tubeworms  3.3% ( n = 6) 50% ( n = 3) 
Bryozoans  6.0% ( n = 11)  64% ( n = 7) 
Barnacles  9.9% ( n = 18)  61% ( n = 11)  
Tubeworms  1.1% ( n = 2) 50% ( n = 1) 
 
 
 
 Box 1:  Level of fouling (LOF) ranks were developed to provide a measure of the amount and 
coverage of biofouling across a vessel hull (Floerl et al. 2005). The rank scale ranges from 0 (no 
fouling) to 5 (very heavy fouling).  
 
LOF 0: No visible fouling. Hull entirely clean, no biofilm (slime) on any visible submerged parts 
of the hull.  
 
LOF 1: Hull partially or completely covered in slime fouling. Absence of any macrofouling.  
 
LOF 2: Light fouling. 1 –  5 % of visible hull surface covered by macrofouling or filamentous 
algae. Usually remaining area covered in slime.  
 LOF 3: Considerable fouling. Macrofouling clearly visible but still patchy. 6 –  15 % of visible 
hull surface covered by macrofouling or filamentous algae. Usually remaining area covered in 
slime. Authorities need to decide whether this is locally acceptable.  
 
LOF 4: Extensive fouling. 16 –  40 % of visible hull surface covered by macrofouling or 
filamentous algae. Usually remaining area covered in slime.  
 LOF 5: Very heavy fouling. 41 –  100 % of visible hull surface covered by macrofouling or 
filamentous algae. Usually remaining area covered in slime.  
 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 11 Vessel niche areas tend to be more susceptible to biofouling accumulation (see 3.3.1).  MPI’s 
review of niche area images fro m well -maintained vessels found that when fouling was 
present, scattered individuals of a single species were often accompanied by incidental individuals of a second species.  Because of the difficulties of preventing the occurrence of 
biofouling in n iche areas,  a tolerance level allowing incidental coverage of a second non -algal 
macrofouling organism (restricted to barnacles, tubeworms or bryozoans) is proposed.  
 
Based on the information reviewed, it is recommended that biofouling on wind/water line and 
hull areas not exceed the low end of the LOF 2 coverage range (1%; Figure 1), and that 
biofouling in niche areas not exceed the maximum of this range (i.e., 5% of visible niche areas surface; see Box 1; Figure 2).  It is noted that for niche areas, this meas ure alone does 
not take into account the fouling complexity or species distribution.  
 
 Figure 1: Examples of incidental (1%) macrofouling.  
 
 
 
 
Low thresholds of fouling have been deliberately proposed  to limit opportunities for 
organisms to occur in proximity and/or accumulate in numbers to a level that could facilitate successful reproduction, i.e., reducing the propagule pressure by keeping the organisms too 
few in number and too far apart allow successful spawning, settling and establishment. It is 
noted that barnacles are restricted in their reproduction by physical constraints and that 
species such as tubeworms and bryozoans may be broadcast spawners (Ruppert and Barnes 
2004).  
 
Figure 2: Examples of scattered (5%) macrofouling.  
 
 
 
 
Further, the macrofouling thresholds proposed are based on preventing the potential for these 
organisms to facilitate the transport of other fouling species. Explic it consideration of ‘early 
stage’ macrofouling is a way of managing the risks posed by biofouling succession  and 
organism maturity. The thresholds proposed for organism spacing (i.e., incidental/scattered 
12 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
individuals) are characteristic of early stage foul ing assemblages —these tend to have low 
species richness, which helps to mitigate against the presence of other risk organisms. The 
longer a macrofouling species has been present on a hull the more likely it is to be 
reproductive.  
 Under best practice for hull maintenance, the presence of macrofouling species on a vessel 
hull represents a failure of the antifouling system (except for macroalgae on the wind/water 
line; Lewis pers. comm.). However, a review of the MPI commissioned research has shown 
the presence of some macrofouling species on hull areas of newly antifouled/well -maintained 
vessels (Floerl et al. 2010; Inglis et al. 2010). As a result, the thresholds for wind/water line and hull areas have been proposed at a level of an early stage of antifouli ng failure to be able 
to warn vessels regarding the prevention of unacceptable biosecurity risk on subsequent visits. Therefore, any vessel that arrives in New Zealand with any macrofouling on its hull should 
receive a warning regarding the consequences of  using an ineffective biofouling management 
plan.  
 Recommendations  
For wind/water line ( Boot -top) areas: the tolerance should be for incidental (1%) coverage of 
one non- algal macrofouling organism type of either barnacles, tubeworms or bryozoans, 
occurring  as isolated individuals or small clusters and as a single species or an organism type 
that appears to be the same species.  
 
For hull areas: the tolerance should be for incidental (1%) coverage of one non -algal 
macrofouling organism type of either barnacle s, tubeworms or bryozoans, occurring as 
isolated individuals or small clusters that have no algal overgrowth and as a single species or 
an organism type that appears to be the same species.  
 
For niche areas , the tolerance should be:  
• Scattered (5%) coverage of one non -algal macrofouling organism type of either 
barnacles, tubeworms or bryozoans, occurring as widely spaced individuals and/or infrequent, patchy clusters that have no algal overgrowth; and as a single species, or 
an organism type that appears to be the same species; and  
• Incidental (1%) coverage of a second non -algal macrofouling organism type of either 
barnacles, tubeworms or bryozoans, occurring as isolated individuals or small clusters that have no algal overgrowth and as a single species, or an  organism type that appears 
to be the same species.  
 
3.5 Intended vessel itinerary   
3.5.1 Varied threshold dependent on the intended vessel itinerary  
The majority of species likely to be encountered on vessel hulls do not reach sexual maturity 
within 4 weeks of set tlement (Floerl et al. 2010). The longer a vessel remains in New 
Zealand, the greater the risk that the species will spawn or escape from the biofouling and become established (Inglis et al. 2012). The magnitude of this risk is uncertain, as it will 
depend  on the season of arrival, the reproductive state of biofouling organisms, and their 
ability to spawn and produce viable offspring in New Zealand conditions. In general, the risk is likely to increase with the amount of biofouling present on the vessel (Sy lvester et al. 2011) 
and will vary with its geographic origin. Biofouling species from other temperate coastal environments are more likely to be able to establish self -sustaining populations in New 
Zealand waters than those with predominantly tropical dis tributions (Inglis et al. 2010; 
Sylvester et al. 2011 ). 
 
Ministry for Primary Indust ries  Science  Underpinning  the Thresholds Proposed in  the CRMS  • 13 Assuming that a vessel is deemed clean at the border according to the proposed thresholds, it 
should be able to remain in New Zealand for a period of 4 weeks, less the travelling time 
(from the last point of likely infestation), without posing a significant biosecurity risk. It is 
noted that the 4 -week period allowed is inclusive of travelling time to New Zealand, which is 
on average 11 days for international recreational vessels (Inglis et al. 2012). Takin g this into 
account, a vessel remaining in New Zealand a period of < 3 weeks will be deemed “short -
stay”. Exceeding the 3 week period would constitute a vessel being deemed “long -stay”.  
 Based on the data reviewed, the macrofouling thresholds recommended i n Section 3.4  are for 
short -stay vessels only (i.e., a vessel that remains in New Zealand for  a period of less than 3 
weeks). A s a result, the period available for maturation, reproduction and spawning is short 
enough to manage the likelihood of possible i ntroductions (Floerl et al. 2010).  
 
Long -stay vessels should be subject to more stringent thresholds than short -stay vessels 
because the longer a vessel remains in New Zealand , the greater the likelihood that any 
species present will spawn or escape from the biofouling and become established (Inglis et al. 
2012). Although there is evidence that wind/water line is often fouled by cosmopolitan 
species (Mineur et al. 2007), allowance of no macroalgae on the wind/water line of long -stay 
vessels or those vessel s that visit non -POFA areas is proposed because the CRMS  must cover 
all sea craft entering New Zealand, including those vessels that stay indefinitely and those that 
routinely visit for long periods, such as recreational vessels, fishing vessels and barges  (Inglis 
et al. 2012). Despite the ubiquity of some green macroalgae on the wind/water line, there is the potential for some species to be non -indigenous to New Zealand and thus would be 
allowed to mature and reproduce once through the New Zealand border. Further, it is possible that the presence of this macroalgae could shelter other macrofouling species or obstruct 
detection of these species by border staff. Also, from a risk perspective it would be inconsistent to disallow macroalgae fouling on hull and niche areas whilst allowing it on the 
wind and waterline.  
 
Recommendations  
As a result of the assessment conducted by the Risk Analysis Team , the threshold for long -
stay vessels is recommended to be set at “slime layer” fouling with allowance for goose 
barnacles. To ensure that the biosecurity risk is managed , long-stay vessels should ideally 
have an antifouling paint renewal or be cleaned within 4 weeks before entering New Zealand. Cleaning before departure reduces the abundance and density of biofouling o rganisms on a 
vessel’s hull, and if this is done within the 4 week timeframe that includes travelling time, it can help reduce the likelihood, frequency and success of spawning/dispersal events. Although 
the optimal approach would be to clean immediately b efore departure to New Zealand, this 
may not always be possible. While the 4 week window provides flexibility for vessel owners/operators and helps to mitigate against “spawning on arrival” events, a residual risk of 
post-border spawning remains. Border Cl earance Procedures will help MPI to flag vessels for 
further investigation where the approach to cleaning before arrival may not have been effective.  
 Vessels with itineraries that visit areas other those designated under the Act as Places of First 
Arrival  (POFA) should also be subject to more stringent thresholds i.e., the threshold for 
long-stay vessels. The higher threshold is recommended for the protection and maintenance of 
those areas that do not typically receive high vessel traffic. These areas can have national and 
international significanc e such as Fi ordland National Park, and the Kermadec Islands and sub -
Antarctic Islands. It is in the interests of both the regulator and vessel owner/operator to maintain these areas by preventing the introduction of non -indigenous species through vessel 
biofouling.  
14 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries   
  
3.5.2 Uniform thresholds regardless of the intended vessel itinerary  
Having all vessels meet the same threshold for entry into New Zealand represents an ideal 
situation from the regulatory perspective, howe ver:  
• The threshold proposed for short -stay vessels may not manage the biosecurity risk 
presented by long -stay vessels due to the period available for reproduction and 
spawning;  
• The threshold proposed for short -stay vessels may not manage the biosecurity r isk 
presented by vessels that visit non -POFA areas as it was not designed for the 
protection of high value pristine areas;  and 
• The higher threshold proposed for long -stay vessels and/or vessels that visit non -
POFA areas may cause delays to short -stay vesse ls that actually present an 
acceptable biosecurity risk. This will also result in the misallocation of MPI 
resources to make management decisions, albeit unnecessary, regarding these 
vessels.  
   
Recommendations  
From the above findings it is recommended tha t the threshold for biofouling should differ 
dependent on the intended vessel itinerary within New Zealand. Long -stay vessels should be 
required to meet a more stringent threshold than short -stay vessels.  
 
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18 • Science Underpinning the Thresholds Proposed in the CRMS  Ministry for Primary Industries