Produced by:
Northern Territory Government
Department of Primary Industry and Fisheries
April 2015
© Northern Territory Government, 2015
M. Skarlatos Simoes conducted this survey and compiled this report with survey assistance from Jonathan
Taylor and Samantha Tonissoo.
Department of Primary Industry and Fisheries
GPO Box 3000, Darwin NT 0801, AUSTRALIA
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
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Disclaimer
While all care has been taken to ensure that information contained in this Report is true and correct at the time of publication, the
Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or
advice contained in this publication, or that it is suitable for your intended use. No serious business or investment decisions should be
made in reliance on this information without obtaining independent and/or professional advice in relation to your particular situation.
TABLE OF CONTENTS
TABLE OF CONTENTS....................................................................................................................................... i
LIST OF TABLES ................................................................................................................................................ i
LIST OF FIGURES .............................................................................................................................................. i
BACKGROUND ................................................................................................................................................. 1
METHODS ......................................................................................................................................................... 1
Annual Visual Survey ..................................................................................................................................... 1
Settlement Collector Monitoring ..................................................................................................................... 2
RESULTS AND DISCUSSION .......................................................................................................................... 4
Annual Visual Survey ..................................................................................................................................... 4
Settlement Collector Monitoring ..................................................................................................................... 6
APPENDIX A ..................................................................................................................................................... 7
LIST OF TABLES
Table 1. East Arm Wharf marine pest inspection sites detailing modifications for 2014 inspection. ................. 1
Table 2. Description of biofouling observed from a visual survey of 8 sites along the face of East Arm
Wharf on 6 November 2014. ............................................................................................................... 4
Table 3. Settlement collector inspection schedule; November 2013- December 2014. .................................... 6
LIST OF FIGURES
Figure 1. A settlement collector installed at East Arm Wharf (pictured during an extremely low tide). ............. 2
Figure 2. Locations of settlement collectors at East Arm Wharf. ....................................................................... 2
Figure 3. Current design of settlement collector ................................................................................................ 3
November 2014
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BACKGROUND
The Port of Darwin, the closest Australian port to South East Asia, experiences a significant amount of
international shipping traffic. As a number of recognised marine pest species are widely distributed
throughout South East Asia, the risk of marine pests being introduced to Darwin Harbour is high.
Invasive marine pests can cause significant environmental and economic damage. Economic impacts are
associated with increased costs for the removal of unwanted fouling from ships and wharf structures, and
vessels carrying marine pests being restricted from entering certain ports. Marine pests also present an
environmental problem threatening native communities through predation, by overtaking habitats and food
sources, or by spreading disease. Once established, it is very difficult to eradicate pests from an aquatic
environment. It is therefore important that the initial introduction of marine pests is prevented.
Aquatic Biosecurity, within the Fisheries Division of the Department of Primary Industry and Fisheries (DPIF)
regularly monitors the marine fouling communities of the Northern Territory (NT) coastline in areas of high
international shipping and yachting activity, enabling early detection of marine pest invasions. As part of its
marine pest monitoring program, Aquatic Biosecurity has undertaken annual surveys of the fouling
organisms growing on East Arm Wharf since 2001. This report presents the findings from a visual survey of
East Arm Wharf conducted on 6 November 2014.
In addition to the annual survey, monthly monitoring for targeted marine pests was established in November
2007. This monitoring was initiated in response to the detection of a marine pest, the Asian green mussel, on
the hull of a rig tender whilst the vessel was alongside the wharf. The use of a settlement collector (deployed
with assistance from Darwin Port Corporation staff) allows for monthly assessments of biofouling
communities at one site (780m) along the wharf face, with particular attention paid to the detection of marine
pest species.
METHODS
Annual Visual Survey
Prior to undertaking the survey, permission was sought from Darwin Port Corporation (DPC) to access the
wharf face. DPC was advised of the time and duration of the inspection and facilitated access to the wharf
front. A visual survey of the wharf face was undertaken on 6 November 2014 between 11 am to 12 noon on
a low tide of 1.00 m.
Ten sites along the East Arm Wharf face have been allocated for annual inspection (Table 1). Each site is
inspected at 3 positions; <0 m, 0-1 m and >1 m above the waterline. The waterline is the actual level of water
at time of visual inspection. Due to the presence of a number of commercial vessels alongside the wharf, 2
of the inspection sites were omitted and 1 site was repositioned slightly. At each site, the fouling community
was examined for the presence of known marine pest species, photographs were taken, and the general
fouling assemblage was recorded.
Table 1. East Arm Wharf marine pest inspection sites detailing modifications for 2014 inspection.
Site
Site location
1
Middle of south eastern face of the multipurpose wharf
2
10 m north west along south western face of the wharf
3
150 m north west along south western face of the wharf
4
250 m north west along south western face of the wharf
Inaccessible
5
350 m north west along south western face of the wharf
Inspected at 380m
6
450 m north west along south western face of the wharf
7
550 m north west along south western face of the wharf
8
650 m north west along south western face of the wharf
9
750 m north west along south western face of the wharf
10
Wharf pylons between 750 m and 780 m
November 2014
Site details specific to 2014
Inaccessible
1
Settlement Collector Monitoring
In November 2007, 2 settlement collectors were deployed along East Arm Wharf and used for the monthly
inspection of fouling communities. Each collector was connected to the wharf face by a steel cable attached
to, and running the length of, the ladders at the wharf face (Figure 1). One settlement collector was
positioned approximately half way along the wharf (at the 200-210 m mark) and the other at the northwestern end of the wharf face (at the 780-790 m mark) as depicted in Figure 2 by locations 1 and 2
respectively.
Figure 1. A settlement collector installed at East Arm Wharf (pictured during an extremely low tide).
Figure 2. Locations of settlement collectors at East Arm Wharf.
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
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Towards the end of 2013, this design was modified due to restricted access (vessel traffic) along the wharf
face when accessing the collectors via a boat. To resolve this issue, DPC approved the deployment of the
settlement collectors from the top of the wharf which enabled their access from land. Currently, 1 settlement
collector has been installed at the 780 m mark (Figure 2- Settlement Collector 2).
The collector is made from PVC pipe to which artificial settlement surfaces (settlement plates and rope
mops) are attached (Figure 3). The collector is attached to a floating buoy, via a length of rope allowing the
collector to move vertically with the tide. The settlement collector is installed in such a manner as to allow
maximum travel with the tidal movement, and minimum exposure of settlement surfaces during extreme low
tides. The 2 different types of artificial surface allow for the targeting of a more diverse assemblage of
biofouling species.
Figure 3. Current design of settlement collector
Monthly inspections of the collectors involves documenting whether or not any marine pests were present on
the settlement surfaces, recording a brief description of fouling organisms growing on the plates and within
the rope mop, and photographing the plates (front and back) and rope mops using a digital camera.
Every 4 months, the settlement surfaces are removed for closer examination in the laboratory, which
involves an inspection for known marine pests and analysis of the biofouling community. Settlement surfaces
are replaced with clean surfaces, which allow for the settlement of more opportunistic biofouling species.
November 2014
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RESULTS AND DISCUSSION
Annual Visual Survey
The marine fouling organisms observed along the East Arm Wharf face were generally consistent with
observations made during previous surveys and included taxonomic groups such as barnacles, bivalves,
sponges, hydroids, bryozoans, ascidians and anemones (Table 2).
Barnacles, oysters and sponge were the most abundant organisms at and below the waterline and higher up
in the intertidal regions of the wharf face (Appendix A). At and below the waterline in areas subject to less
tidal exposure, different biofouling groups such as ascidians (colonial), bryozoans (branching), sponges and
hydroids were also prevalent (Appendix A).
No attempt was made to identify every individual species within the fouling community. Only when unusual
or suspicious species were observed, were samples collected for identification. In general, the species
observed at East Arm Wharf are consistent with those observed throughout Darwin Harbour, and no known
marine pest species were detected.
Table 2. Description of biofouling observed from a visual survey of 8 sites along the face of East Arm Wharf
on 6 November 2014.
Site
Site
Location
Time
Comments
1
Middle
south
eastern
face of
wharf
11:57am
Barnacle and oyster species were dominant below, at and above the waterline.
A variety of sponge species were also present (green and brown above the
waterline, pink, white, orange, green, red, black, brown, white, and purple at
the waterline and brown below the waterline). Branching bryozoans and
hydroids were present at and below the waterline.
2
10 m
11:55am
Inaccessible.
3
150 m
11:38am
Sponge (all colours previously observed), barnacles and oysters were the
dominant taxa, at and above the waterline. Branching bryozoans and colonial
ascidians were found below the waterline and hydroids were found below and
0-1m above the waterline.
4
250 m
11:36am
Inaccessible.
5
380 m
11:31am
Barnacles, oysters and sponge (all colours below the waterline and black,
green, red, white and brown at and above the waterline) were the dominant
taxa below, at and above the waterline. Branching bryozoans were found
below the waterline and hydroids were observed at 0-1 m.
6
450 m
11:27am
Sponge, barnacles and oysters were dominant below, at and above the
waterline. Below the waterline and at 0-1 m above the waterline, the sponge
species were more diverse and included all colours, however black, brown,
green and red sponge dominated at 0-1 m and >1m above the waterline. An
anemone and hydroids were observed below the waterline and branching
bryozoans were found at >1m mark.
7
550 m
11:21am
Barnacles, oysters and sponge dominant below, 0-1 m and >1 m above the
waterline. The sponge species varied at different depths. White, red, purple
and pink sponges were dominant below the waterline. Red, white, black,
green, purple and brown sponge species dominated at 0-1m above the
waterline. At >1 m, purple, green, brown and orange sponge species
dominated. Hydroids were also found below the waterline and branching
bryozoans were found at 0-1m above the waterline.
8
650 m
11:17am
Oysters, sponge and barnacles were the dominant taxa below, at and 1 m
above the waterline. Hydroids and an anemone were also present below the
waterline and colonial ascidians were observed at 0-1 m above the waterline.
Sponge species were present below the waterline (green, white and orange)
as well as 0-1 m above the waterline (orange, purple, green, brown and pink).
Above 1 m, brown, green and red sponge species dominated.
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
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9
750 m
11:12 am
Barnacles, sponge and oysters dominated at all water levels. Hydroids were
observed below the waterline and up to 1 m. Branching bryozoans were found
below the waterline also. The sponges found below the waterline were green,
red, orange and pink. Up to the 1 m mark, brown, grey, pink, green, orange
and red sponges dominated.
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Pylons
under
wharf
between
750 m and
780 m
11:06 am
Barnacles, oysters and sponge species (brown, pink, white, green and orange)
were dominant below, at and above the waterline. Colonial ascidians and
hydroids were found below the waterline.
November 2014
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Settlement Collector Monitoring
As the monitoring of the settlement collector at East Arm Wharf was conducted by land for the period of
November 2013- December 2014, it was possible to conduct inspections every month (apart from May) on
the settlement devices.
Biofouling on the settlement plates comprised of oysters, barnacles, amphipod tubes, sponge, colonial and
solitary ascidians, hydroids, algae, encrusting and branching bryozoans. No recognised marine pest species
have been detected on the settlement collectors since commencement of monitoring in November 2007.
Table 3. Settlement collector inspection schedule; November 2013- December 2014.
Date of inspection
Collector 2 comments
26th November 2013
Settlement surfaces inspected and photographed.
20th December 2013
Settlement surfaces inspected, photographed, collected and new surfaces re-deployed.
11th February 2014
Settlement surfaces inspected and photographed.
(January inspection)
25th February 2014
Settlement surfaces inspected and photographed.
1st April 2014
Settlement surfaces inspected and photographed.
(March inspection)
8th May 2014
Settlement surfaces inspected, photographed, collected and new surfaces re-deployed.
(April inspection)
May 2014
Inspection not conducted.
17th June 2014
Settlement surfaces inspected and photographed.
9th July 2014
Settlement collector missing.
15th August 2014
Settlement collector re-surfaced. Settlement surfaces inspected, photographed, collected and
new surfaces re-deployed.
19th September 2014
Settlement surfaces inspected and photographed.
17th October 2014
Settlement surfaces inspected and photographed.
14th November 2014
Settlement surfaces inspected and photographed.
16th December 2014
Settlement surfaces inspected, photographed, collected and new surfaces re-deployed.
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
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APPENDIX A
Representative photographs of biofouling communities on the wharf face at East Arm Wharf, Darwin
Harbour on 6 November 2014.
Site 1: 0-1 m above waterline
Site 2: Inaccessible
Site 3: 0-1 m above waterline
Site 4: Inaccessible
November 2014
Site 1: >1 m above waterline
Site 2: Inaccessible
Site 3: >1 m above waterline
Site 4: Inaccessible
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Site 1: 0-1 m above waterline
Site 5: 0-1 m above waterline
Site 6: 0-1 m above waterline
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
Site 1: >1 m above waterline
Site 5: >1 m above waterline
Site 6: >1 m above waterline
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Site 1: 0-1 m above waterline
Site 1: >1 m above waterline
Site 7: 0-1 m above waterline
Site 7: >1 m above waterline
Site 8: 0-1 m above waterline
Site 8: >1 m above waterline
November 2014
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Site 1: 0-1 m above waterline
Site 1: >1 m above waterline
Site 9: 0-1 m above waterline
Site 9: >1 m above waterline
Site 10: 0-1 m above waterline
Site 10: >1 m above waterline
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
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