Seagrass surveys October 2018 - MF236 Okehampton Bay · in the 2018 Annual Environment Report...

MF236 Okehampton Bay

Seagrass surveys October 2018

(VERSION 1.0)

Summary Report to:

Tassal Limited

July 2019

A Q U E N A L

www.aquenal.com.au

MF236 Okehampton seagrass surveys October 2018

Document Control and Distribution

Date Name Company Document

Type Version Copies

23/7/2019 Matt Barrenger Tassal Electronic 1.0 1

23/7/2019 Claudia Russman EPA Electronic 1.0 1

COPYRIGHT: The concepts and information contained in this document are the property of

Aquenal Pty Ltd. Use or copying of this document in whole or in part without the written

permission of Aquenal Pty Ltd constitutes an infringement of copyright.

DISCLAIMER: This report has been prepared on behalf of and for the exclusive use of Aquenal

Pty Ltd’s client and is subject to and issued in connection with the provisions of the agreement

between Aquenal Pty Ltd and its Client. Aquenal Pty Ltd accepts no liability or responsibility

whatsoever for or in respect of any use of or reliance upon this report by any third party.


Contents

1. Introduction .................................................................................................................................................................... 6

2. Methods .......................................................................................................................................................................... 6

2.1. Sampling design ......................................................................................................................................................... 6

2.2. Survey Transects ........................................................................................................................................................ 8

2.3. Laboratory Assessment .............................................................................................................................................. 8

3. Results and interpretation .............................................................................................................................................. 9

4. Reference ...................................................................................................................................................................... 14

Appendices

Appendix 1 Survey coordinates ........................................................................................................................................ 15

Appendix 2 Co-location of ‘outer’ October 2018 transects with seagrass cover transects surveyed in 2016 ................. 16

Appendix 3 Indicative horizontal screen grabs for October 2018 seagrass surveys. ........................................................ 16

Appendix 4 Indicative vertical screen grabs for October 2018 seagrass surveys. ............................................................ 18

Appendix 5 Raw data for October 2018 seagrass survey ................................................................................................. 19

Appendix 6 Results from the September 2017 seagrass survey ....................................................................................... 23


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Operational Summary

Contractor: AQUENAL PTY LTD

ABN 74 151 011 157

244 Summerleas Road,

Kingston, Tasmania 7050

Phone 03 6229 2334 Fax 03 6229 2335

Client: Tassal Limited

GPO Box 1645

Hobart 7001

Phone: Hobart 03 6244 9099 Huonville 03 6244 8102

Fax: 1300 880 239

Fieldwork: Filming for this assessment was carried out by Tassal using a Seabotix VLBV300 Remote Operated Vehicle (ROV), with supplementary high definition GoPro footage also collected.

Field conditions:

Date: 4/10/2018

Wind: Light, Variable

Sky: Clear

Rain: Nil

Sea: Calm

Current: Moderate

Video analysis: Aquenal Pty Ltd


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1. Introduction

Environmental Licence 10172/2 for Okehampton Bay specifies a range of broad scale

monitoring activities. As part of the broad scale monitoring program, licence conditions

require seagrass surveys to be conducted in the spring of each year. These seagrass surveys

take place along a series of transects in locations specified by the EPA. Surveys consisted of

remote video recordings to assess seagrass, macroalgae and epiphyte cover along survey

transects. The first seagrass survey was conducted in September 2017 and was documented

in the 2018 Annual Environment Report (Aquenal 2018). This document reports on the

results of the October 2018 seagrass survey.

2. Methods

2.1. Sampling design

The October 2018 seagrass survey was conducted across nine sites in Mercury Passage

(Figure 1). This sampling design constituted a more comprehensive survey than conducted

in September 2017 according to schedule 3V of the Environmental Licence 10172/2 where

only two sites were surveyed in east and west Okehampton Bay (Figure 1). Site locations

and survey design was overseen by the EPA and the new sites supersede site locations in

3F6 and associated attachments 4A and 4B of the Environmental Licence (Claudia Russman,

pers. comm. 01/10/2018).

The October 2018 survey included (a) three ‘inner’ sites within seagrass beds in the inner

margins of Okehampton Bay (OB1, OB2, OB3); (b) three ‘outer’ sites on the outer margins of

the seagrass beds of Okehampton Bay (OB4, OB5, OB6); and (c) three ‘control’ sites (CB1,

CB2, CB3) in seagrass beds within Chinamans Bay (Figure 1; Appendix 1). The ‘outer’ sites

were co-located with three transects (T2, T5, T6) surveyed for seagrass cover in 2016

(Marine Solutions 2016; see Appendix 2). The spatial arrangement of sites was intended to

capture changes in the overall health of seagrass beds (inner sites), the seagrass bed growth

or retreat (outer sites) and the dynamics of seagrass beds distant from fish farming activities

(control sites). Where practical, depth profiles among sites were matched.


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Figure 1 (a) Location of nine survey sites in Mercury Passage surveyed in October 2018 and two sites surveyed in October 2017. (b) Location of inner and outer sites in Okehampton Bay. (c) Location of control sites in Chinamans Bay, Maria Island.


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2.2. Survey Transects

At each site, a 50 m transect marked at 5 m intervals was deployed from the vessel with the

start and end coordinates recorded using a GPS. The transect was filmed slowly with a

Remote Observation Vehicle (ROV). Filming was conducted with two high definition GoPro

cameras mounted to the ROV, which captured footage both vertically and horizontally. The

vertically orientated GoPro provided a field of view of approximately 1 m2 and facilitated the

assessment of seagrass, macroalgae and epiphyte cover. The horizontally orientated GoPro

provided contextual imagery to improve assessments of habitat condition.

The methodology described for October 2018 differed from that used in the September

2017 surveys. In September 2017, spot dives were conducted with a ROV, which recorded

three minutes of video footage along a transect aligned by a compass bearing. It was

considered that this survey methodology was difficult to replicate in subsequent surveys,

hence its replacement with defined transects of a set length in October 2018. These changes

were approved by the Tasmanian EPA (Claudia Russman, pers. comm. 01/10/2018).

2.3. Laboratory Assessment

In the laboratory, GoPro video footage was systematically reviewed for the purpose of

estimating the cover of seagrass and macroalgal communities and the relative abundance of

epiphytes. A screen grab was taken from the vertically orientated GoPro every 5 m and for

each screen grab, the percent cover was assessed for the following aspects: (a) seagrass; (b)

macroalgae from the genus Caulerpa; and (c) any other macroalgae. Epiphytes were also

assessed every 5 m using a qualitative scale from 1-5 (Table 1). Where Caulerpa or other

macroalgae were present, the epiphyte assessment was made across all vegetation present.

Representative vertical and horizontal imagery of the seafloor at each sites is shown in

Appendix 3 and Appendix 4 respectively.


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Table 1 Qualitative scale for epiphytic coverage.

Scale Description

1. Very low, virtually clean plants

2. Low, minimal epiphytic growth

3. Medium, obvious epiphytic growth

4. High, most plants covered

5. Very high, plants completely covered

3. Results and interpretation The October 2018 seagrass survey provides baseline data for assessing future changes in

seagrass health and extent. The results are described according to relative seafloor cover

and community composition with a focus on differences between sampling locations. Future

analyses will describe changes in community composition and extent through time. Raw

data from October 2018 surveys are included in Appendix 5.

The composition of plant communities (Figure 2; Figure 3) differed between transects

located in the ‘inner’ Okehampton Bay (seagrass and macroalgae), ‘outer’ Okehampton Bay

(macroalgae only) and the control sites in Chinamans Bay (seagrass only). Plant cover was

particularly low at OB4 and OB5 (Figure 3) which were dominated by bare sand and shells

(Figure 4). The dominant species of seagrass at all sites was Zostera tasmanica. Seagrass

cover ranged between 5% and 75% along inner Okehampton Bay and Chinamans Bay

transects (Figure 2), with mean seagrass cover being highest at OB1 and CB3 and lowest at

OB2 and CB2 (Figure 3).

Three species of the green macroalgae genus Caulerpa were observed: Caulerpa

scalpelliformis, C. trifaria and C. flexilis (Figure 4). Caulerpa was dominant at OB3 and OB6

(Figure 3) with high Caulerpa cover evident along the extent of these two transects (Figure

2). Caulerpa cover did not exceed 10% for any other site (Figure 2; Figure 3). Other

macroalgae species (including Ulva spp. Caulocystis uvifera, Sargassum spp., Cystophora

retroflexa, Asparagopsis armata, Ecklonia radiata and Sargassum fallax) were dominant at

OB2 (along with seagrass) and were important at OB1, OB3 and OB4 (Figure 2; Figure 3).


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Epiphyte cover scores for the nine transects varied between 1 (very low; virtually clean

plants), 2 (low; minimal epiphytic growth) and 3 (medium; obvious epiphytic growth). Scores

of 4 and 5 were not recorded. Epiphyte growth was lower at control sites in Chinamans Bay

compared to Okehampton Bay (Figure 5; Figure 6). In general, inner sites had overall lower

epiphyte growth than outer sites at Okehampton Bay (Figure 5; Figure 6). When considering

the relationship between seagrass health and epiphyte growth it is important to note that

epiphyte measures implemented here include epiphyte growth on all plant types, including

macroalgae and seagrass.

Results of seagrass surveys for September 2017 are included in Appendix 6. Seagrass cover

was high at Okehampton Bay West and low at Okehampton Bay East where Caulerpa

species instead dominated (Appendix 6). Epiphyte cover along both transects was classified

as ‘medium’ with obvious epiphytic growth (Epiphyte Score = 3; Appendix 6). The transects

surveyed for seagrass in October 2018 and September 2017 were not co-located. The

nearest sites to Okehampton Bay East (i.e. OB1) and Okehampton Bay West (i.e. OB3) were

>100 m away (Figure 1) and therefore meaningful comparisons in cover was not possible.

Figure 2 Percent cover of three plant communities (seagrass, Caulerpa macroalgae, other macroalgae) at five-meter intervals along nine transects (inner = OB1-3; outer = OB4-6; control = CB1-3) surveyed in Mercury Passage in October 2018.


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Figure 3 Average percent cover of three plant communities (seagrass, Caulerpa macroalgae, other macroalgae) for nine transects (inner = OB1-3; outer = OB4-6; control = CB1-3) surveyed in Mercury Passage in October 2018.

The three ‘inner’ transects in Okehampton Bay and the control sites appear well positioned

to track changes in the density and health of seagrass beds. However, the effectiveness of

the three ‘outer’ transects to describe fluctuations in the extent of the seagrass bed through

time within Okehampton Bay is questionable.

The intention for the three ‘outer’ transects in Okehampton Bay (OB4; OB5; OB6) was to

position them at the edge of the seagrass beds and to track the growth and/or retreat of the

edge over time. Coordinates for the start and end of the transects were provided by EPA

and were based on the transition zone between areas of high and low seagrass cover shown

in benthic habitat mapping surveys conducted in 2016 (see Appendix 2). Unfortunately, this

approach was ineffective for the current October 2018 survey, with no seagrass recorded at

these sites. This scenario may have arisen for the following reasons: (1) seagrass beds may

have retreated since 2016; (2) provision of inaccurate or poorly located coordinates for the

ROV survey (see Appendix 2); or (3) inaccuracy in the application of coordinates in the ROV

survey (see Appendix 2). Regardless for the reasons behind the lack of seagrass at these

sites, the ‘outer’ transects in Okehampton Bay are unlikely to serve their intended purpose

for tracking fluctuations at the edge of the seagrass beds.


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Figure 4 Observations of macroalgae species and habitat characteristics at five-meter intervals along nine transects (inner = OB1-3; outer = OB4-6; control = CB1-3) surveyed in Mercury Passage in October 2018. Observations are overlaid on percent cover of three plant communities (seagrass, Caulerpa macroalgae, other macroalgae) for each transect.


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Figure 5 Epiphyte cover score at five-metre intervals along nine transects (inner = OB1-3; outer = OB4-6; control = CB1-3) surveyed in Mercury Passage in October 2018.

Figure 6 Mean (crosshairs) and individual observations (points) for epiphyte cover score for nine transects (inner = OB1-3; outer = OB4-6; control = CB1-3) surveyed in Mercury Passage in October 2018.


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4. Reference Aquenal (2018) MF236 Okehampton Seagrass surveys September 2017. Summary Report to:

Tassal Limited December 2017, 8pp.

Marine Solutions (2016) Baseline seagrass and Macrocystis surveys in the vicinity of proposed

finfish farming, Okehampton Bay Tasmania. Report to Tassal, November 2016, 21pp.


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Appendix 1 Survey coordinates

Site Region Location Start End Field Notes

Easting Northing Easting Northing

OB1 Okehampton Bay Inner 579605 5291902 579634 5291943 Thick seagrass.

OB2 Okehampton Bay Inner 580453 5292393 580503 5292393 Patchy seagrass.

OB3 Okehampton Bay Inner 580772 5292262 580788 5292215 Thick seagrass

OB4 Okehampton Bay Outer 579999 5291679 580039 5291650 One or two blades of seagrass.

OB5 Okehampton Bay Outer 580348 5291820 580333 5291772 Sparse Caulerpa.

OB6 Okehampton Bay Outer 580642 5291834 580621 5291788 Dense Caulerpa.

CB1 Chinamans Bay Control 585796 5276562 585841 5276539

CB2 Chinamans Bay Control 586112 5276386 586148 5276351 Patchy seagrass.

CB3 Chinamans Bay Control 586377 5276165 586413 5276129 Thick patches of seagrass.


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Appendix 2 Co-location of ‘outer’ October 2018 transects with seagrass cover transects surveyed in 2016*

* Seagrass cover transects conducted in 2016 (points coloured according to seagrass cover) overlaid with the location of October 2018 seagrass survey transects (start and end boxes connected by lines). Note that the georeferencing of the 2016 survey points with October 2018 survey points is approximate only and the figure is intended to show the concept of co-location with transect seagrass transitions zones rather than the precise positioning of survey points.


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Appendix 3 Indicative horizontal screen grabs for October 2018 seagrass surveys. Representative imagery includes inner (OB1, OB2, OB3), outer (OB4, OB5, OB6) and control (CB1, CB2, CB3) taken from the horizontally orientated GoPro.

OB1 OB2 OB3

OB4 OB5 OB6

CB1 CB2 CB3


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Appendix 4 Indicative vertical screen grabs for October 2018 seagrass surveys. Representative imagery includes the inner (OB1, OB2, OB3), outer (OB4, OB5, OB6) and control (CB1, CB2, CB3) taken from the vertically orientated GoPro.

OB1 OB2 OB3

OB4 OB5 OB6

CB1 CB2 CB3


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Appendix 5 Raw data for October 2018 seagrass survey. Position is position along transect. Epiphyte scores are given in Table 1.

Site Location Position Seagrass Caulerpa Other Algae Epiphytes Comments

(m) (% Cover) (% Cover) (% Cover) (Score)

OB1 Inner 5 60 5 2 1 Caulerpa scalpelliformis, Ulva sp., filamentous red algae, bare sand

OB1 Inner 10 30 20 10 2 Sargassum sp., filamentous red algae, bare sand

OB1 Inner 15 10 2 20 2 Caulocystis uvifera, bare sand

OB1 Inner 20 60 15 10 2 Caulerpa trifaria, Ulva sp., filamentous red algae

OB1 Inner 25 50 10 2 2 Caulerpa flexilis, C. trifaria, Ulva sp. filamentous red algae, bare sand

OB1 Inner 30 80 10 5 2 Caulerpa flexilis, C. trifaria, Ulva sp. filamentous red algae, Sargassum sp.

OB1 Inner 35 60 15 10 2 Caulerpa flexilis, C. trifaria, Ulva sp. filamentous red algae, bare sand

OB1 Inner 40 5 0 25 1 Seirococcus axillaris, filamentous red algae, bare sand, shells and pebbles

OB1 Inner 45 25 20 30 2 Caulerpa scalpelliformis, C. trifaria, Ulva sp. filamentous red algae, bare sand and pebbles

OB1 Inner 50 30 0 20 2 Caulocystis uvifera, Ulva sp., filamentous red algae, Sargassum sp.

OB2 Inner 5 25 0 30 2 Cystophora retroflexa, Ulva sp., filamentous red algae, bare sand

OB2 Inner 10 5 2 60 2 Cystophora retroflexa, Caulerpa sp., Ulva sp., filamentous red algae, bare sand

OB2 Inner 15 2 0 50 2 Cystophora retroflexa, Ulva sp., filamentous red algae, bare sand and pebbles

OB2 Inner 20 20 2 10 3 Caulerpa sp., filamentous red algae, bare sand and pebbles

OB2 Inner 25 40 5 10 2 Caulerpa scalpelliformis, Cystophora retroflexa, filamentous red algae, bare sand and shells

OB2 Inner 30 35 2 30 3 Caulerpa scalpelliformis, Sargassum fallax, filamentous red algae, bare sand and shells

OB2 Inner 35 20 2 25 3 Caulerpa scalpelliformis, Asparagopsis armata, filamentous red algae, bare sand and shells

OB2 Inner 40 20 0 25 2 Cystophora retroflexa, filamentous red algae, bare sand and shells

OB2 Inner 45 20 2 10 3 Filamentous red algae, bare sand and shells

OB2 Inner 50 20 5 10 3 Caulerpa flexilis, filamentous red algae, bare sand and shells

OB3 Inner 5 15 35 10 1 Caulerpa flexilis, Caulerpa scalpelliformis, Asparagopsis armata, filamentous red algae, bare sand and shells

OB3 Inner 10 20 40 15 2 Caulerpa flexilis, Asparagopsis armata, filamentous red algae, bare sand and shells

OB3 Inner 15 70 10 15 2 Caulerpa flexilis, Caulerpa trifaria, Asparagopsis armata, filamentous red algae

OB3 Inner 20 50 35 15 1 Caulerpa flexilis, Caulerpa scalpelliformis, Asparagopsis armata, filamentous red algae


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OB3 Inner 25 15 75 10 1 Caulerpa flexilis, Caulerpa scalpelliformis, Caulerpa trifaria, Asparagopsis armata, filamentous red algae

OB3 Inner 30 40 30 30 1 Caulerpa flexilis, Caulerpa trifaria, Asparagopsis armata, filamentous red algae

OB3 Inner 35 10 80 5 1 Caulerpa flexilis, Caulerpa scalpelliformis, filamentous red algae

OB3 Inner 40 10 70 10 1 Caulerpa flexilis, Caulerpa scalpelliformis, Cystophora sp., filamentous red algae

OB3 Inner 45 5 85 10 1 Caulerpa flexilis, Caulerpa scalpelliformis, Ecklonia radiata, Sargassum fallax, Asparagopsis armata, filamentous red algae

OB3 Inner 50 5 90 5 1 Caulerpa flexilis, Caulerpa scalpelliformis, filamentous red algae

OB4 Outer 5 0 0 15 3 Filamentous algae, bare sand

OB4 Outer 10 0 5 5 3 Caulerpa flexilis, filamentous red algae, bare sand

OB4 Outer 15 0 5 5 2 Caulerpa sp., filamentous red algae, bare sand

OB4 Outer 20 0 5 5 3 Caulerpa trifaria, filamentous red algae, bare sand



OB4 Outer 35 0 0 10 2 Filamentous red algae, bare sand

OB4 Outer 40 0 5 15 2 Caulerpa longifolia, Caulerpa trifaria, filamentous red algae, bare sand

OB4 Outer 45 0 5 10 2 Caulerpa trifaria, Asparagopsis armata, filamentous red algae, bare sand

OB4 Outer 50 0 5 5 2 Caulerpa sp., Asparagopsis armata, filamentous red algae, bare sand

OB5 Outer 5 0 0 0 NA Bare sand and shells


OB5 Outer 15 0 0 2 2 Bare sand and shells



OB5 Outer 30 0 0 5 2 Filamentous algae, bare sand and shells





OB6 Outer 5 0 50 20 3 Caulerpa scalpelliformis, Caulerpa trifaria, filamentous red algae, bare sand

OB6 Outer 10 0 50 10 3 Caulerpa scalpelliformis, Caulerpa trifaria, filamentous red algae, drift Ecklonia radiata, bare sand


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OB6 Outer 20 0 40 20 2 Caulerpa scalpelliformis, filamentous red algae, bare sand




OB6 Outer 40 0 20 5 3 Caulerpa scalpelliformis, filamentous red algae, bare sand



CB1 Control 5 2 0 0 1 Bare sand, bivalve shells





CB1 Control 30 5 0 0 1 Bare sand, bivalve shells, scallops





CB2 Control 5 25 0 0 3 Bare sand, bivalve shells, gastropod egg mass

CB2 Control 10 5 0 0 2 Bare sand, bivalve shells, gastropod egg mass

CB2 Control 15 50 0 0 1 Bare sand

CB2 Control 20 0 0 0 1 Bare sand, drift Cystophora








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CB3 Control 10 90 0 0 1

CB3 Control 15 25 0 0 1 Bare sand, gastropod egg mass


CB3 Control 25 90 0 0 1







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Appendix 6 Results from the September 2017 seagrass survey. (a) Bar chart representing percentage cover of two

plant communities (seagrass, Caulerpa macroalgae) assessed at thirty second intervals along two transects

(Okehampton East; Okehampton West) in Mercury Passage; (b) Epiphyte score at thirty second intervals along two

transects (Okehampton East; Okehampton West).

(a)

(b)

Seagrass surveys October 2018 - MF236 Okehampton Bay · in the 2018 Annual Environment Report...

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