65196 Appendix Seven The Northland Regional Council Report on the exotic caulerpa Perimeter Management at Omakiwi Cove Bay of Islands.pdf

Perimeter Management
Omākiwi Cove, Bay of Islands


Perimeter Management Report
1

Acknowledgements
Northland  Regional  Council  would  like  to  acknowledge  the  ongoing  support,  leadership,  and
involvement of Ngāti Kuta and Patukeha hapū throughout the Caulerpa response in Te Rāwhiti, Bay of
Islands, in addition to the following partners.

-
Bay of Plenty Regional Council Dive Team
-
Commercial Dive Specialists
-
Marine and Environmental Field Services
-
Ministry of Primary Industries
-
National Institute of Water and Atmospheric Research


Executive summary
Exotic Caulerpa (C. brachypus and C. parvifolia) was identified in Te Rāwhiti Inlet, Bay of Islands, in
May 2023. Considering the ability of these species to spread rapidly, form dense monocultures, and
smother  and  displace  native  species,  the  Ministry  for  Primary  Industries  and  Northland  Regional
Council instigated a response to address the incursion. This document reports on one element of that
response; to understand the spatial extent of exotic Caulerpa in Te Rāwhiti, and to reduce that spatial
extent via the removal of infestations found in the outer regions of a Controlled Area Notice zone.

Over a 12-month period (May 2023 to April 2024), 568 delimitation survey transects were conducted.
Exotic Caulerpa was found on less than 12% of these, and in one instance it was found outside the
boundaries  of  the  Controlled  Area  Notice  zone.  Infestations  found  close  to,  and  beyond,  the
boundaries of this zone were treated with benthic mats and / or chlorine. Benthic mats that were
recovered indicated this treatment method was successful in ensuring mortality of exotic Caulerpa.
Methodological  adjustments  are  discussed  that  would  assist  in  improving  the  efficacy  and
recoverability of benthic mats in future.

Perimeter Management Report
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List of figures and tables

Figure 1. The Controlled Area Notice (CAN) in Te Rāwhiti Inlet, Bay of Islands. No anchoring or fishing
is permitted within this zone. Source: Ministry of Primary Industries (MPI). …………………………………….. 6

Figure 2. Modelling particle dispersal via surface currents. The black arrow indicates dispersion point.
The green dots indicate likely location after 30 days. Source: Cawthron Institute. …………………………… 7

Figure 3. (A) A Northland Regional Council diver undertaking a timed-swim survey dive to search for
exotic Caulerpa. (B) An example of information recorded for each transect in the Caulerpa Infestation
GIS platform via ArcGIS Fieldmaps. …………………………………………………………………………………………………… 8

Figure 4. Use of benthic matting and chlorine tablets to address exotic Caulerpa infestations. (A) A
benthic mat placed over an infestation of exotic Caulerpa. (B) A chlorine tablet underneath a benthic
mat.  (C) Benthic mats held in place by metal stakes and chain. (D) A Northland Regional Council diver
conducts water testing for residual chlorine. ………………………………………………………………………………….… 9

Figure 5. Exotic Caulerpa delimitation surveys conducted in the Bay of Islands from May 2023 to April
2024.  Orange  transects  indicate  presence  of  exotic  Caulerpa.  Green  transects  indicate  no  exotic
Caulerpa found. ……………………………………………………………………………………………………………………………… 11

Figure 6. Monthly exotic Caulerpa delimitation surveys conducted in the Bay of Islands from May 2023
(A) to April 2024 (K). Orange transects indicate presence of exotic Caulerpa. Green transects indicate
no  exotic  Caulerpa  found.  September  2023  is  not  included  in  this  figure  as  no  transects  were
conducted during that month. ……………………………………………………………………………………………………….. 12

Figure  7.  Mortality  of  exotic  Caulerpa,  indicated  by  bleaching  of  Caulerpa  fragments,  following
treatment with benthic matting and chlorine tablets. …………………………………………………………………… 13

Figure 8. Sites in which exotic Caulerpa was treated in July and August 2023 in Te Rāwhiti Inlet, Bay of
Islands. …………………………………………………………………………………………………………………………………………… 14

Table  1.  The  number  and  length  of  delimitation  survey  transects  conducted  per  month  over  a  12
period, between May 2023 and April 2024, and the presence of exotic Caulerpa found during these
surveys. ……………………………………………………………………………………………………………………………………….… 10

Table 2. Summary of benthic treatments undertaken for exotic Caulerpa infestations in Te Rāwhiti,
Bay of Islands. Site labels correspond to Figure 8. …………………………………………………………………………… 14

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Perimeter Management Report

1.Introduction
Invasion by non-native Caulerpa sp. has resulted in a range of negative impacts to marine species and
ecosystems globally (Holmer et al. 2009; McKinnon et al. 2009; Felline et al. 2012). Caulerpa sp. can
grow across intertidal and subtidal zones, down to a depth of 40m, and can establish on a diverse
range  of  natural  substrates  including  sand,  mud,  and  reef,  in  addition  to  manmade  structures.  In
favourable conditions it spreads quickly, forming dense monospecific beds that cover the sea floor,
smother benthic marine life, and displace mobile species through alteration of key habitats. Invasion
by non-native Caulerpa sp. therefore poses a significant risk to local marine species and ecosystems
and subsequently to associated cultural, commercial, and recreational values and activities. As such,
some non-native Caulerpa sp. are listed as unwanted organisms by Biosecurity New Zealand.

Two non-native species of Caulerpa (Caulerpa brachypus and C. parvifolia, herein collectively ‘exotic
Caulerpa’) have been discovered in Aotearoa (Biosecurity New Zealand 2024). First identified in July
2021 at Aotea / Great Barrier Island (Blind Bay, Tryphena Harbour, and Whangaparapara Harbour;
Middleton 2023), these  infestations  have  since  been subject  to  removal trials  via  various methods
(suction dredging, benthic mats, and chlorine;  Tait et al.  2024).  Further surveys in 2022 led to the
discovery of infestations at Ahuahu / Great Mercury Island, and in May 2023 it was identified in several
locations  in  the  Bay  of  Islands  including  Omākiwi  Cove,  Te  Rāwhiti  inlet,  and  into  Albert  Channel
(Botting 2023). It has since also been discovered at Waiheke Island, Kawau Island, Mokohinau Islands,
and Rākino Island (Biosecurity New Zealand 2024).

The most likely human-mediated vector for exotic Caulerpa into, and around, Aotearoa is recreational
vessels anchoring with fragments entangled in anchoring equipment, as exotic Caulerpa is capable of
proliferating  quickly  from very small fragments.  Subsequently,  Controlled Area Notice (CAN) zones
have been introduced in several locations in the upper North Island to prevent activities such as fishing
and anchoring, and subsequently reduce the risk of further spread (Biosecurity New Zealand 2024;
Fig. 1).

1.1. Objectives

Considering  the  potential  threat  posed  by  the  incursion  of  exotic  Caulerpa  in  Te  Rāwhiti  Inlet,  an
agreement between the Ministry for Primary Industries (MPI) and Northland Regional Council (NRC)
was  instigated  in  August  2023  (Caulerpa  Response  Te  Rāwhiti  Treatment  Trials  &  Perimeter
Management C0035933). The intent of this agreement was to assess the feasibility of suction dredging
as  a  method  to  achieve  local  eradication  (Objective  4.1),  and  to  conduct  surveillance  to  better
understand and reduce the spatial extent of the infestation within the bounds of the Te Rāwhiti CAN
(Objective 4.2; Fig. 1). The latter objective was to be approached by removal or in-situ treatment of
infestations found in the outer extent of the CAN.

This document reports on Objective 4.2. Perimeter Management of the above agreement:

(a)  To  complete  surveillance  that  improves  the  understanding  of  the  spatial  extent  of  the
exotic Caulerpa infestation in the Te Rāwhiti Inlet Controlled Area Notice area.

(b)  To  reduce  the  spatial  extent  of  the  exotic  Caulerpa  infestation  in  the  Te  Rāwhiti  Inlet
Controlled Area Notice area by prioritizing the removal of exotic Caulerpa located in the outer
region of the Te Rāwhiti Controlled Area Notice.
Perimeter Management Report
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Figure 1. The Controlled Area Notice (CAN) in Te Rāwhiti Inlet, Bay of Islands. No anchoring or fishing is permitted within this
zone. Source: Ministry of Primary Industries (MPI).
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Perimeter Management Report

2.Methods
2.1. Site selection

The  selection  of  sites  at  which  to  focus  perimeter  management  survey  efforts  was  strategically
informed by several information sources:

•  NRC  vessel  hull  surveillance  data,  collected  over  six  years  from  more  than  10,000  vessels
across Northlands' harbours, documenting anchoring behaviour in Northland.
•  Active collaboration between NRC and local kaitiaki, hapū, and iwi to incorporate the vast
repository of knowledge they possess regarding their rohe.
•  An  Envirolink-funded  report,  produced  in  partnership  between  NRC  and  the  Cawthron
Institute,  that  used  network  and  particle  tracking  modelling  to  determine  likely  vessel
movements  from  areas  with  known  exotic  Caulerpa  infestations  to  within  the  Northland
region, and dispersal patterns of exotic Caulerpa via surface currents (Floerl et al. 2023).

Analyses conducted by Floerl et al. (2023) indicated that Te Rāwhiti Inlet, Omākiwi Cove, and the inner
Bay  of  Islands  received  51%  of  potential  anchoring  events  within  the  survey  network.  Modelling
particle tracks similarly indicated Te Rāwhiti Inlet and Albert Channel were at greatest risk of receiving
fragmented exotic Caulerpa via surface currents (Fig. 2). Initial survey locations were subsequently
centred within the Te Rāwhiti Inlet and Albert Channel, including on the mainland and nearby islands.

The above information sources also informed priority survey sites beyond the Te Rāwhiti CAN. These
locations formed the basis of a wider surveillance project conducted in April and May 2024, which
covered mainland sites and islands between Whangaroa Harbour in the north and Whangārei Harbour
in the south.

Figure 2. Modelling particle dispersal via surface currents. The black arrow indicates dispersion point. The green dots indicate
likely location after 30 days. Source: Cawthron Institute.

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2.2. Diver transects

To delimit the presence, and manage the spread, of exotic Caulerpa in the Te Rāwhiti CAN, diver-based
delimitation surveys were conducted throughout Te Rāwhiti Inlet and Albert Channel from the time it
was  first  detected  at  Omākiwi  Cove  in  early  May  2023.  Surveys  were  conducted  by  various
organisations, including divers from Northland Regional Council (NRC), the National Institute of Water
and  Atmospheric  Research  (NIWA),  the  Department of  Conservation  (DOC),  Marine  Environmental
Field Services (MEFS), Bay of Plenty Regional Council dive team, and Commercial Dive Specialists (CDS).

A  15-minute  bearing  search  technique  was  used  to  search  for  exotic  Caulerpa.  Divers  followed  a
predetermined bearing for 15 minutes and systematically searched the substrate for exotic Caulerpa
(Fig.  3A).  If  detected,  the  GPS  location  was  recorded  on  the  Caulerpa  Infestation  GIS  platform  via
ArcGIS Fieldmaps (Fig. 3B). This was done by the diver conducting a series of pulls on a surface marker
buoy  to  indicate  to  the  vessel  crew  to  record  a  GPS  position,  or  with  the  use  of  underwater
communications. The relatively shallow depth of anchorages in the Bay of Islands (<10m) allowed for
multiple sites to be searched daily without depth limited restrictions.

Additional information recorded in the ArcGIS Caulerpa Infestation platform included start and end
location of the transect, start and end depth of the transect, presence / absence of exotic Caulerpa
along  the  transect,  density  of  exotic  Caulerpa  (if  present),  primary  and  secondary  substrates,  and
visibility (Fig. 3B). From this information the total length and search area of each transect could be
calculated.

(A)
(B)

Figure 3. (A) A Northland Regional Council diver undertaking a timed-swim survey dive to search for exotic Caulerpa. (B) An
example of information recorded for each transect in the Caulerpa Infestation GIS platform via ArcGIS Fieldmaps.

2.3. Benthic treatment

In locations that exotic Caulerpa was encountered during the delimitation surveys, and the size of the
patch was less than 36 m2, benthic mats constructed from sheets of plastic wrap were placed over the
infestation  (Fig.  4A).  Benthic  matting  could  not  be  used  for  patches  greater  than  36  m2  due  to
consenting  limitations,  however  no  patches  greater  than  this  size  were  found  outside  of  Omākiwi
Cove.

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Perimeter Management Report

Each mat was tailored onsite according to the size of the infestation found, with additional material
extending beyond the perimeter of the patch to ensure it was fully contained and treated. The mats
were secured to the substrate using a combination of 400mm metal stakes with a 100mm head and
weighted chain or rocks. The location of the mat was recorded in the Caulerpa Infestation GIS platform
via ArcGIS Fieldmaps.

In  several  instances  chlorine  tablets  were  also  placed  under  the  benthic  mat  (Fig.  4B)  and,  when
available, weight was placed on top of the matting to reduce water flow, thereby concentrating the
effects  of  the  chlorine  (Fig.  4C).  Each  chlorine  tablet  was  200g  and,  depending  on  the  size  of  the
infestation, multiple chlorine tablets were used to ensure the necessary concentration requirements
were  achieved.  Concentration  requirements  were  based  on  ~200  mg/L  of  free  available  chlorine
required to successfully eliminate 99% of a Sabella spallanzanii infestation (Morrisey et al. 2016). For
sites at which chlorine was used, water samples were collected from underneath the mats prior to
their removal to ensure residual chlorine levels were no greater than 0.2mg/L (Fig. 4D).

Chlorine  was  not  used  for  infestations  found  in  sites  of  significant  ecological  importance,  such  as
kaimoana beds. In these locations only benthic matting was used. In these scenarios it was necessary
to leave the benthic mats in place for a duration of approximately one month to ensure mortality of
exotic Caulerpa via lack of sunlight.

(A)
(B)

(C)
(D)

Figure 4. Use of benthic matting and chlorine tablets to address exotic Caulerpa infestations. (A) A benthic mat placed over
an infestation of exotic Caulerpa. (B) A chlorine tablet underneath a benthic mat. (C) Benthic mats held in place by metal
stakes and chain. (D) A Northland Regional Council diver conducts water testing for residual chlorine.

Perimeter Management Report
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2.4. Biosecurity

All dive operations were conducted in a manner that ensured minimum contamination between dive
sites  to  prevent  the  spread  of  exotic  Caulerpa.  Diving  was  not  undertaken  in  areas  where  exotic
Caulerpa was not known to be present directly after diving in known infestation areas. Additionally,
after  each  dive  day  that  exotic  Caulerpa  was  detected,  NIWA’s  decontamination  protocols  were
followed for all dive and survey gear (soaked in a detergent and freshwater solution).

3.Results
3.1. Diver transects

From 1st May 2023 to 30th April 2024, 568 delimitation survey transects were conducted, covering a
total of 122.8 km (Table 1). Of these transects, 109 were conducted under this perimeter management
contract (C0035933), with the remainder being conducted under a range of additional surveillance
contracts. Survey effort was concentrated in the initial months post-detection (May – August 2023;
Fig. 6A-5D) in Bay of Islands, and in April 2024 (Fig. 6K) for wider surveillance.

Of the  total 568 transects conducted, exotic Caulerpa was  present on 11.8 %  (67),  the majority of
which  were  in  the  vicinity  of  Omākiwi  Cove  where  a  large  infestation  is  known  to  exist  (Fig.  5).
Infestations  were  also  found  near  the  boundaries  of  the  CAN,  including  on  the  eastern  side  of
Waipohutukawa Bay (surveyed in June 2023; Fig. 6B), Pareanui Bay (surveyed in June 2023; Fig. 6B),
and on the southern side of Poroporo Island (surveyed in April 2024; Fig. 6K). One infestation was
found outside the boundaries of the CAN (south of Mahenotiti Island; surveyed in June 2023; Fig. 6B).
The primary substrates in which exotic Caulerpa was found were sand (54.6%), in addition to muddy
sand and sandy gravel (12.5% and 10.94%, respectively).

Table 1. The number and length of delimitation survey transects conducted per month over a 12 period, between May 2023
and April 2024, and the presence of exotic Caulerpa found during these surveys.
Total
Transect
Transects with
Transects with exotic
Transects conducted
Month
transect
count
exotic Caulerpa (#)
Caulerpa (%)
under C0035933
length (km)
May 2023
94
16.3
18
19.35
42
June 2023
70
14.2
14
20
15
July 2023
50
12.3
3
6
27
August 2023
52
12.6
4
7.84
25
September 2023
0
0
0
0

October 2023
5
1
2
40

November 2023
7
1.5
0
0

December 2023
9
0.8
0
0

January 2024
18
3
2
12.5

February 2024
14
1.8
10
71.43

March 2024
19
1.8
10
58.82

April 2024
230
57.5
4
1.76

568
122.8
67
11.8
109
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Perimeter Management Report

Figure 5. Exotic Caulerpa delimitation surveys conducted in the Bay of Islands from May 2023 to April 2024. Orange transects indicate presence of exotic Caulerpa. Green transects indicate no
exotic Caulerpa found. CAN indicated by red outline.

(A) May 2023

(B) June 2023

(C) July 2023

(D) August 2023

(E) October 2023
(F) November 2023

(G) December 2023

(H) January 2024

(I) February 2024
(J) March 2024

(K) April 2024

Figure 6. Monthly exotic Caulerpa delimitation surveys

conducted in the Bay of Islands from May 2023 (A) to April

2024 (K). Orange transects indicate presence of exotic
Caulerpa. Green transects indicate no exotic Caulerpa
found. September 2023 is not included in this figure as no

transects were conducted during that month.

3.2. Benthic treatment

In July and August 2023, eight infestation sites were treated (Table 2). The infestations ranged in size
from 50 cm2 to 4 m2. In all instances benthic matting was used, and in five instances chlorine was also
used. Chlorine was not used when exotic Caulerpa was found near important kaimoana sites and / or
octopus. On one occasion hand removal methods were used in response to discovery of a distinct,
detached ball of exotic Caulerpa. No treatments were applied to infestations found in the vicinity of
Omākiwi Cove, as this site is the focus of the suction dredging trials. Infestations found on the south
side of Poroporo Island in April 2024 during the wider surveillance contract (Fig. 6K) were similarly
treated with benthic mats and chlorine, the results of which are reported in the wider surveillance
report.

Inspection of exotic Caulerpa underneath three benthic matts was conducted approximately one week
after mat placement. Mortality of exotic Caulerpa was evidenced by the bleached colouration of the
fragments (Fig. 7), and water sampling indicated residual chlorine levels were at 0 ppm. The benthic
mats and any residual chlorine tablets were then removed.

Several  benthic  mats  were  not  recovered  due  to  difficulties  presented  by  low  visibility  and  soft
sediment hindering search operations. Opportunities for refining the treatment protocols to ensure
recoverability of benthic mats are discussed below.

Figure 7. Mortality of exotic Caulerpa, indicated by bleaching of Caulerpa fragments, following treatment with benthic
matting and chlorine tablets.

Perimeter Management Report
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Table 2. Summary of benthic treatments undertaken for exotic Caulerpa infestations in Te Rāwhiti, Bay of Islands. Site labels
correspond to Figure 8.
Treatment  Caulerpa
Treatment
Treatment
Site
Outcome
Comments
date
patch size
type
quantity
A
13/06/23
Ø 100 cm
Benthic mat
4 x 3 m
Exotic Caulerpa
Placed by MEFS.

Ø 20 cm
1 x 1 m
eliminated. Mat

Chlorine
7 x 200 g
removed.

B
30/07/23
900 cm2
Benthic mat
2 x 2 m

Placed by BOP.

Chlorine
2 x 200 g

C
31/07/23

Benthic mat

Placed by BOP.

Chlorine

D
01/08/23
2,500 cm2
Benthic mat
4 x 2 m

Placed by BOP.

50 cm2
Chlorine
3 x 200 g

E
01/08/23

Benthic mat
2 x 2 m
Mat not recovered.   Placed by BOP. No chlorine was

used as an octopus’ hole was

observed nearby.

F
02/08/23
Ø 50 cm
Benthic mat
2 x 2 m

Placed by BOP.

Chlorine
1 x 200 g

G
09/08/23

Benthic mat
4 x 4 m
Mat not recovered
Placed by MEFS & NRC. No chlorine

used due to proximity to significant

kaimoana site.

H
09/08/23
Ø 100 cm
Benthic mat

Mat not recovered
Placed by MEFS & NRC. Hand
removal of ball of Caulerpa (<1m
diameter), followed with benthic
mat. No chlorine used as close
proximity to kaimoana site.

A

D

B

F

C

E  G

H

Figure 8. Sites in which exotic Caulerpa was treated in July and August 2023 in Te Rāwhiti Inlet, Bay of Islands.

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Perimeter Management Report

4.Discussion
4.1. Surveillance of spatial extent of exotic Caulerpa

The primary objective of the perimeter management project was to conduct surveillance to improve
understanding of the spatial extent of the exotic Caulerpa infestation in Te Rāwhiti Inlet. Delimitation
surveys  conducted  over  a  12  month  period  demonstrated  that  exotic  Caulerpa  was  found
predominantly  in  the  vicinity  of  the  large  infestation  in  Omākiwi  Cove,  although  smaller,  distinct
infestations were found in other locations close to, and in one instance beyond, the boundaries of the
CAN (Fig. 5).

Considering the ease and speed with which exotic Caulerpa is able to spread, it is possible that these
infestations, if not successfully treated, could spread beyond the boundaries of the CAN and further
into  Te  Rāwhiti  Inlet  and  the  Albert  Channel.  However,  benthic  treatments  undertaken  here  and
discussed  below,  in  conjunction  with  completion  of  the  wider  surveillance  contract,  associated
treatments, and continued adherence to strict biosecurity procedures in the delivery of these projects,
may assist in mitigating this risk.

4.2. Reduction of spatial extent of exotic Caulerpa

The secondary objective of the perimeter management project was to reduce the spatial extent of the
exotic Caulerpa infestation in the Te Rāwhiti CAN by prioritizing the removal of exotic Caulerpa located
in  the  outer  region  of  the  CAN. Eight  infestations  (including  the  one  found  outside  the  CAN
boundaries) were treated, using a combination of benthic matting, chlorine tablets, and hand removal
(Table 2; Fig. 8).

For the benthic mats that were recovered, mortality of exotic Caulerpa was evident via the bleached
colouration of fragments, and thus this method proved beneficial in reducing spatial extent. It may be
assumed that the additional mats not located had a similar impact upon exotic Caulerpa, however this
was  not  able  to  be  confirmed.  Minor  methodological  adjustments  would  assist  in  ensuring  mat
recovery and thus assisting with confirmation of the reduction of spatial extent.

4.3. Efficacy of benthic mats

Several  variables  were  identified  that  influenced  the  efficacy  of  benthic  mats  in  treating  exotic
Caulerpa infestations, including substrate type, depth, swell, visibility, and the patch size and dynamics
of  the  exotic  Caulerpa  infestations.  These  are  discussed  in  conjunction  with  methodological
adjustments that could improve this approach in future.

Substrate  type.  In  locations  where  only  a  narrow  band  of  soft  sediment  was  present  over  harder
substrates, securing the mats in place using metal stakes was challenging, and the availability of rocks
to help anchor the mats could not be relied upon. This could be addressed by placing chain along the
edges of the mats to better secure them.

Depth and swell. In shallow water (<6m) the mats were often affected by large swells, which could
both move the mat if not fully secured and reduce the effect of chlorine by flushing the water under
the  mat.  The  latter  also  occurred  in  sites  with  strong  currents.  This  could  also  be  addressed  by
placement of chain along the edges of the mat to ensure the edges do not lift so substantially.
Off gassing of chlorine. The application of chlorine to the benthic community, and the subsequent
biological activity, can cause large amounts of gas to concentrate underneath the benthic mat. This
has the potential to lift the mat. However this could be addressed with the installation of vents to
allow the built-up gas to escape (e.g. duckbill vent).
Visibility.  In  areas  of  fine  sediment,  placement  of  mats  quickly  disturbed  the  visibility  and  made
conditions  challenging  to  complete  the  placement  of  the  mat.  Further,  swell  and  current  often
resulted in the mats being covered by fine sediment shortly after being placed, making them difficult
to find on subsequent dives (Fig. 4A). This prevented follow up sampling of chlorine levels, inspection
of the efficacy of the mats in killing exotic Caulerpa, and removal of the mats once mortality of exotic
Caulerpa  was  confirmed.  This  could  be  addressed  by  marking  the  mats  with  sub-surface  floats  to
increase  their  visibility,  however  implications  for  vessel  navigation  safety  and  suction  dredge
operation would need to be considered.
Patch size / dynamics. The procedure for placing mats was time consuming and subsequently was not
considered  to  be  an  efficient  method  for  addressing  very  small  patches  of  exotic  Caulerpa.  Hand
removal could be more effective in these scenarios; however this method is challenged by the delicate,
fragmentary nature of exotic Caulerpa. There were also instances where free-floating balls of exotic
Caulerpa  were  encountered  for  which,  again,  benthic  matting  was  not  considered  the  optimum
response.

5. Conclusion

Delimitation surveys confirmed that the spatial extent of exotic Caulerpa in Te Rāwhiti Inlet and Albert
Channel was concentrated primarily in the vicinity of Omākiwi Cove. Some distinct infestations were
found adjacent to and beyond the boundaries of the Te Rāwhiti CAN, however these were targeted
with a combination of benthic mats and chlorine tablets. Of the mats that were recovered, mortality
of exotic Caulerpa was noted, thus this approach helped to reduce the spatial extent of exotic Caulerpa
infestation in the outer region of the Te Rāwhiti  CAN. Given the speed and ease with which exotic
Caulerpa can spread, continued surveillance and treatment of infestations will be key to containing
the spatial extent of exotic Caulerpa in Te Rāwhiti Inlet and Albert channel.

References
Biosecurity New Zealand. (2024) Exotic Caulerpa seaweeds in New Zealand. Available online at:
https://www.mpi.govt.nz/biosecurity/exotic-pests-and-diseases-in-new-zealand/pests-and-
diseases-under-response/exotic-caulerpa-seaweeds-caulerpa-brachypus-and-caulerpa-
parvifolia-in-new-zealand/. Last accessed May 15th 2024.

Botting, S. (2023) Superspreader seaweed found in more than 10 spots in Northland’s Bay of Islands.
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