Produced by:
Northern Territory Government
Department of Primary Industry and Fisheries
ABN 84 085 734 992
January 2013
© Northern Territory Government, 2013
E. Lawson, A. Beatty and M. Skarlatos Simoes researched and compiled this report.
Department of Primary Industry and Fisheries
GPO Box 3000, Darwin NT 0801, AUSTRALIA
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
LIST OF TABLES ................................................................................................................................................ i
LIST OF FIGURES .............................................................................................................................................. i
BACKGROUND ................................................................................................................................................... i
METHODS ......................................................................................................................................................... 2
Annual Visual Survey ..................................................................................................................................... 2
Settlement Collector Monitoring ..................................................................................................................... 3
RESULTS AND DISCUSSION .......................................................................................................................... 4
Annual Visual Survey ..................................................................................................................................... 4
Settlement Collector Monitoring ..................................................................................................................... 5
APPENDIX ......................................................................................................................................................... 6
LIST OF TABLES
Table 1.
East Arm Wharf marine pest inspection sites detailing modifications for 2012 inspection.. ....... 2
Table 2.
A brief description of biofouling observed from a visual survey of 7 sites along the face of
East Arm Wharf 30 November 2012. Waterline is actual level of water at time of visual
inspection..................................................................................................................................... 5
Table 3.
Settlement collector inspection schedule; November 2011 - December 2012.. ......................... 6
LIST OF FIGURES
Figure 1.
A settlement collector installed at East Arm Wharf (pictured during an extremely low tide). ...... 3
Figure 2.
Locations of settlement collectors at East Arm Wharf. ................................................................ 4
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
i
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 can be 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,
NT Fisheries) regularly monitors the marine fouling communities of the 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 30 November 2012.
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 settlement collectors (deployed
with assistance from Darwin Port Corporation staff) allows for monthly assessments of biofouling
communities at chosen sites 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 30 November 2012 between 12.45 pm and
2:00 pm on a low tide of 1.07 m.
Ten sites along the East Arm Wharf face have been identified for annual inspection (Table 1). Due to the
presence of a number of commercial vessels alongside the wharf, 3 of the inspection sites were repositioned
slightly and 3 sites were omitted. At each site the fouling community was examined for the presence of
known marine pest species, photographs taken, and the general fouling assemblage recorded.
Table 1. East Arm Wharf marine pest inspection sites detailing modifications for 2012 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
Inaccessible
3
150 m north west along south western face of the wharf
Inspected at 160 m
4
250 m north west along south western face of the wharf
Inspected at 270 m
5
350 m north west along south western face of the wharf
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
Inspected at 580 m
9
780 m north west along south western face of the wharf
Inaccessible
10
Wharf pylons between 750 m and 780 m
2
Site details specific to 2012
Inaccessible
January 2013
Settlement Collector Monitoring
Settlement collectors used for the monthly inspection of fouling communities were deployed along East Arm
Wharf in November 2007. Each collector is connected to the wharf face by a steel cable attached to, and
running the length of, the ladders at the wharf face. The collector is made from PVC pipe to which artificial
settlement surfaces (settlement plates and rope mops) are attached. The collector is attached to a floating
buoy, and the steel cable runs through the centre of the pipe, allowing the collector to move vertically with
the tide (Figure 1). The settlement collectors are 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.
The 2 settlement collectors are positioned approximately half way along the wharf (at the 200-210 m mark)
and at the north-western 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).
Monthly inspections of the collectors involves noting 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.
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
3
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.
Figure 2. Locations of settlement collectors at East Arm Wharf.
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 serpullids (Table 2).
Barnacles and oysters were the most abundant organisms higher up in the intertidal regions of the wharf
face (Appendix A). At and below the waterline in areas subject to less tidal exposure, biofouling groups such
as ascidians (solitary and colonial), bryozoans (encrusting and branching), sponges and hydroids were more
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.
4
January 2013
Table 2. A brief description of biofouling observed from a visual survey of 7 sites along the face of East Arm
Wharf 30 November 2012. Waterline is actual level of water at time of visual inspection.
Site
Time
Comments
1
(south eastern
face)
1:46 pm
2
(10 m)
12.45 pm
3
(160 m)
12:47 pm
4
(270 m)
12:54 pm
5
(350 m)
1:04 pm
Sponge species (green, red, orange, purple, blue and pink) dominant below, at
and above the waterline. Hydroids present below the waterline whereas colonial
ascidians (pale green, black, white and grey), barnacles and oysters found at
and above the waterline. Serpullid species were only found 1 m above the
waterline.
6
(450 m)
1:10 pm
No access to this site.
7
(580 m)
1:13 pm
Lesser abundance of sponge species (purple, red and green) at this site than at
previous sites; present below, at and above the waterline. Barnacle species
present between 1-1.5 m, and oysters dominant between 1.5-2 m above the
waterline. Brown colonial ascidians were present at and above the waterline and
hydroids were found at and below the waterline.
8
(650 m)
1:23 pm
Sponge species (grey, pink, red and purple) dominant at and below the
waterline. Oysters, hydroids and brown colonial ascidians also present. Oysters
dominant upwards from 1 m above the waterline. Several sponge species (red,
blue, green), brown colonial ascidians, barnacle and serpullids also present.
9
(750 m)
1:31 pm
No access to this site.
10
(pylons under
wharf at 750 m)
1:35 pm
Sponge species (red, green, yellow, white, orange and pink) dominant at and
below the waterline. Hydroids only present below the waterline, brown colonial
ascidians found at the waterline and a few oysters found at and upwards
from1 m above the waterline.
Barnacle species dominant below, at and above the waterline. Oysters and a
variety of sponge species (green, white, black and red) also present. Brown
colonial ascidians and branching bryozoans were found at the waterline.
Hydroids were only found below the waterline.
No access to this site.
Hydroids and several sponge species (green, black, purple and orange)
dominant at and below the waterline. Brown and yellow colonial ascidians also
present. Barnacle species (dominant) and sponge (green and black) present
above the waterline. Oysters also present at and above the waterline.
Similar sponge species as previous site, but less frequent. Hydroids dominant
below the waterline. Hydroids and sponge species dominant at the waterline
with the presence of colonial ascidians (white, grey and pink), oysters,
barnacles and orange sponge. At 1 m above the waterline, barnacle species
were dominant with the occasional oyster, green and purple sponge and
serpullids.
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
5
Settlement Collector Monitoring
Biofouling on the settlement plates comprised of several sponge species, oysters, barnacles, hydroids,
ascidians (colonial and solitary), sabellids, serpullids, bryozoans (branching and encrusting) and amphipod
tubes. Fouling taxa on the rope mops included hydroids, algae, oysters, amphipods and the occasional
colonial ascidian. No recognised marine pest species have been detected on the settlement collectors since
commencement of monitoring in November 2007.
Marine pest monitoring at East Arm Wharf has been regular; however access to the settlement collectors at
sites 1 and 2 was prevented on numerous occasions by the presence of vessels moored alongside the
wharf, and collectors at both sites went missing and had to be replaced (Table 3).
Table 3. Settlement collector inspection schedule; November 2011 - December 2012.
Date of inspection
2011
2012
Comments
November
25
December
29
January
Collector 1 inaccessible. Collector 2 settlement surfaces inspected,
photographed, collected and replaced.
Collector 1 and 2 inaccessible due to monsoon weather.
February
22
March
30
April
26
May
30
June
6
Collector 1 inaccessible. Collector 2 settlement surfaces inspected and
photographed.
Collector 1 settlement surfaces inspected and photographed. Two missing plates
replaced. Collector 2 inaccessible.
Collector 1 settlement surfaces inspected and photographed. One missing plate
replaced. Collector 2 had become entangled as a result, the bottom arm had
broken off with plates attached; earmarked for replacement.
Collector 1 settlement surfaces inspected, photographed, collected and replaced.
Collector 2 replaced.
Collector 1 and 2 settlement surfaces inspected and photographed.
Collector 1 and 2 inaccessible.
July
11
August
31
September
26
November
(October)
5
December
(November)
4
January
2013
(December
2012)
7
Collector 1 and 2 settlement surfaces inspected and photographed.
Collector 1 and 2 settlement surfaces inspected, photographed, collected and
replaced.
Collector 1 and 2 settlement surfaces inspected and photographed.
Collector 1 inaccessible. Collector 2 settlement surfaces inspected and
photographed.
Collector 1 missing. Collector 2 settlement surfaces inspected and
photographed.
Collector 1 missing; earmarked for replacement. Collector 2 settlement surfaces
inspected, photographed, collected and replaced.
January 2013
APPENDIX
APPENDIX A:
Representative photographs of biofouling communities on the wharf face at
East Arm Wharf, Darwin Harbour on 30 November 2012.
Waterline refers to the level of the air-water interface at the time of inspection.
Site 1 - waterline
Site 1 - 1 m above waterline
Site 3 - waterline
Site 3 - 1 m above waterline
Site 4 - waterline
Site 4 - 1 m above waterline
Marine Pest Survey of Eas t Arm W harf, Darwin Harbour
7
8
Site 5 - waterline
Site 5 - 1 m above waterline
Site 7 - waterline
Site 7 - >1 m above waterline
Site 8 - waterline
Site 8 - 1 m above waterline
Site 10 - waterline
Site 10 - 1 m above waterline
January 2013