SEAGRASS MAPPING FOR THE PENRHYN ESTUARY HABITAT ENHANCEMENT PLAN

Transcription

1 SEAGRASS MAPPING FOR THE PENRHYN ESTUARY HABITAT ENHANCEMENT PLAN PREPARED FOR SYDNEY PORTS CORPORATION By D. E. Roberts, S. R. Murray, G. R., Sainty August 2008

2 TABLE OF CONTENTS INTRODUCTION...3 METHODS...3 RESULTS AND DISCUSSION...4 CONCLUSIONS AND RECOMMENDATIONS...17 ACKNOWLEDGEMENTS...19 REFERENCES...19 APPENDICES

3 INTRODUCTION Sydney Ports Corporation has developed a monitoring programme for various components of the seagrass habitat associated with the Penrhyn Estuary Habitat Enhancement Plan (Maunsell, 2006). The seagrass monitoring plan was compiled by the Ecology Lab Pty Ltd (TEL), which detailed the requirements and methodology to be used for monitoring of seagrass associated with the expansion of the port (TEL, 2006). Part of this monitoring was to include seagrass mapping using the same techniques previously used to map seagrasses along Foreshore Beach (see Roberts et al., 2006). The aim of the seagrass mapping is to document changes in the seagrass habitat prior to the expansion of the port and to identify any seagrasses that may require transplanting prior to the commencement of construction works. METHODS The methods described here conform to the Seagrass Monitoring Plan produced by TEL (2006) using the same techniques outlined in Roberts et al. (2006; 2007). This was done to ensure that the seagrass maps produced were directly comparable to previous maps prepared for the project. Two seagrass maps were produced for this report. Seagrass mapping was done in November 2007 and again in May The most recent air photographs of the estuary were used for baselines to map the seagrass meadows. Since most of the seagrass meadows had disappeared, isolated patches of seagrass were marked with a float and their location, size and makeup were fixed and recorded using the D-GPS (see Appendices). The aerial photographs supplied by Sydney Ports Corporation (SPC) were imported into AutoCAD. Survey data were plotted over the aerial photographs. Colour maps were produced and areas of seagrass calculated using AutoCAD. Air photographs of the footprint of the port expansion and area to be dredged were also superimposed on the seagrass maps and the areas of seagrass to be directly impacted were also calculated for each time. 3

4 RESULTS AND DISCUSSION The seagrass meadow along Foreshore Beach continues to be reduced since it was mapped in 2006 and 2007 (see Roberts et al., 2006, Roberts et al., 2007). Most of the Zostera capricorni that was recorded in 2006 had disappeared and the remaining shoots were quite sparse with covers generally ranging between 0-1%. This sparse coverage of seagrass occurred within the area that was previously mapped in 2006 (Roberts et al., 2006). The reason for the extensive loss of seagrass along Foreshore Beach is due to burial by sand. The source of the sand is most probably from erosion along Foreshore Beach. The cause of increased wave energy leading to this erosion is not known. Whilst there has been a complete loss of the functional seagrass meadow along Foreshore Beach, there are still small remnant patches of seagrass (see Roberts et al., 2007). These patches were identified and their size (in square metres) and the relative cover of the species present estimated. For the purpose of identifying and mapping the seagrass patches, the air photo was divided into a number of sheets for each time (see Fig. 1 & Fig. 6). Patches of seagrass were identified as Halophila ovalis, Zostera capricorni, Posidonia australis or as a mixed bed comprised of two or more of these species (see Figs. 2 4, Nov 2007; Figs. 7 10, May 2008). In November 2007, the total area of seagrass patches was calculated to be around 365 m 2. There was approximately 93 m 2 of Zostera capricorni and 43 m 2 of Posidonia australis (see Figs. 2 4) located within individual patches. Mixed patches of Zostera capricorni and Halophila ovalis were calculated to be around 217 m 2. Mixed patches of Zostera capricorni and Posidonia australis were calculated to be around 8 m 2, whilst mixed patches comprising all three species were calculated to be around 4 m 2 (Figs. 2 4). The extent of works (dredging, boat ramp, port and estuary enhancement) was overlayed on the November 2007 seagrass map (Fig. 5). At this time, it was calculated that approximately 331 m 2 of total seagrass would be directly impacted by the works. This included 93 m 2 of Zostera capricorni and 40 m 2 of Posidonia australis. 4

5 Approximately 195 m 2 of small mixed patches of Zostera capricorni and Halophila ovalis and 3 m 2 of Posidonia australis and Zostera capricorni (Fig. 5) were also located within the works area. In May 2008, the total area of seagrass patches was calculated to be around 352 m 2. There was approximately 86 m 2 of Zostera capricorni and 36 m 2 of Posidonia australis (see Figs. 7 10) located within individual patches. Mixed patches of Zostera capricorni and Halophila ovalis were calculated to be around 221 m 2. Mixed patches of Zostera capricorni and Posidonia australis were calculated to be around 5 m 2, whilst mixed patches comprising all three species were calculated to be around 4 m 2 (Figs. 7 10). The extent of works (dredging, boat ramp, port and estuary enhancement) was overlayed on the May 2008 seagrass map (Fig. 11). At this time, it was calculated that approximately 317 m 2 of total seagrass would be directly impacted by the works. This included 84 m 2 of Zostera capricorni and 26 m 2 of Posidonia australis. Approximately 207 m 2 of mixed patches of Zostera capricorni, Halophila ovalis and Posidonia australis (Fig. 11) were also located within the footprint. It is clear from these mapping exercises that there continues to be significant changes in the seagrass meadows along Foreshore Beach (see Roberts et al., 2006; Roberts et al., 2007). The total area of seagrass to be directly impacted by the works in 2006 was calculated to be Ha, comprised of approximately 1.13 Ha of Zostera capricorni and an overlapping area of 0.9 Ha of Halophila ovalis. The seagrass monitoring plan outlined techniques and designs to sample seagrasses at small spatial scales, before, during and after construction (TEL, 2006). As a result of this mapping, the monitoring programme will need to be revised, as the TEL (2006) plan made the assumption that there would be more extensive seagrass meadows to be monitored. A monitoring site selection report was prepared (Roberts and Lincoln Smith, 2007) however, given the loss of seagrass along Foreshore Beach, this is now considered redundant. The revised monitoring plan should be discussed with DPI Fisheries. 5

6 Figure 1. Map sheet for seagrass patch mapping in November

7 Figure 2. Location of seagrass patches (western end of Foreshore Beach) in November

8 Figure 3. Location of seagrass patches (eastern end of Foreshore Beach) in November

9 Figure 4. Location of seagrass patches (outer Penrhyn Estuary) in November

10 Figure 5. Extent of works directly impacting on seagrasses in November

11 Figure 6. Map sheet for seagrass patch mapping in May

12 Figure 7. Location of seagrass patches (western end of Foreshore Beach) in May

13 Figure 8. Location of seagrass patches (eastern end of Foreshore Beach) in May

14 Figure 9. Location of seagrass patches (eastern end of Foreshore Beach and outer Penrhyn Estuary) in May

15 Figure 10. Location of seagrass patches (outer Penrhyn Estuary) in May

16 Figure 11. Extent of works directly impacting on seagrasses in May

17 CONCLUSIONS AND RECOMMENDATIONS Total seagrass coverage in November 2007 was 365 m 2 comprised of: o Individual patches - 93 m 2 of Zostera capricorni and 43 m 2 of Posidonia australis. o Mixed patches m 2 of Zostera capricorni and Halophila ovalis. o Mixed patches 8 m 2 of Zostera capricorni and Posidonia australis. o Mixed patches 4 m 2 of all three species. As of November 2007, approximately 331 m 2 of seagrass were to be directly impacted by dredging and the expansion of the port, comprised of: o 93 m 2 of Zostera capricorni. o 40 m 2 of Posidonia australis. o 195 m 2 of mixed Zostera capricorni and Halophila ovalis. o 3 m 2 of mixed Zostera capricorni and Posidonia australis. Total seagrass coverage in May 2008 was 352 m 2 comprised of: o Individual patches - 86 m 2 of Zostera capricorni and 36 m 2 of Posidonia australis. o Mixed patches m 2 of Zostera capricorni and Halophila ovalis. o Mixed patches 5 m 2 of Zostera capricorni and Posidonia australis. o Mixed patches 4 m 2 of all three species. As of May 2008, approximately 317 m 2 of seagrass were to be directly impacted by dredging and the expansion of the port, comprised of: o 84 m 2 of Zostera capricorni. o 26 m 2 of Posidonia australis. o 202 m 2 of mixed Zostera capricorni and Halophila ovalis. o 5 m 2 of Zostera capricorni and Posidonia australis. Transplantation of the Posidonia australis (26 m 2 ) from within the dredge works area along Foreshore Beach and within Penrhyn Estuary will begin in early July 2008, just prior to port construction. 17

18 Summary of changes to total seagrass coverage (m 2 ) along Foreshore Beach and in Penrhyn Estuary through time. Species EIS 2003 Jan 2006 Feb 2007 Nov 2007 May 2008 Zostera (Z) Halophila (H) Posidonia (P) Mixed Z+H Mixed Z+P 8 5 Mixed Z+P+H Total Coverage Summary of changes to seagrass coverage (m 2 ) that will be directly impacted along Foreshore Beach and in Penrhyn Estuary through time. Species EIS 2003 Jan 2006 Feb 2007* Nov 2007 May 2008 Zostera (Z) Halophila (H) Posidonia (P) Mixed Z+H Mixed Z+P 3 5 Mixed Z+P+H Total Coverage * does not include seagrass to be impacted by Penrhyn Estuary enhancement works 18

19 ACKNOWLEDGEMENTS We wish to thank Marika Calfas (SPC) for managerial support of the project and Ben Gray (SPC) for assistance in the field. Marcus Lincoln Smith and Peggy O Donnell (TEL) are thanked for technical advice on the project. REFERENCES Maunsell (2006). Vegetation Management Plan. Port Botany Expansion. Maunsell Australia Pty Ltd. Roberts, D. E., Lincoln Smith, M. P. (2007). Seagrass monitoring programme for the Penrhyn Estuary Habitat Enhancement Plan: selection of reference seagrass meadows. Report prepared for Sydney Ports Corporation. BIO-ANALYSIS Pty Ltd: Marine, Estuarine & Freshwater Ecology, Narara Roberts, D. E., Sainty, G. R., Murray, S. R. (2006). Saltmarsh and seagrass mapping associated with the Port Botany expansion. Report prepared for Sydney Ports Corporation., Narara and Sainty & Associates Pty Ltd, Potts Point. Roberts, D. E., Murray, S. R., Sainty, G. R. (2007). Seagrass mapping for the Penrhyn Estuary habitat enhancement plan. Report prepared for Sydney Ports Corporation., Narara. TEL (2006). Seagrass monitoring plan: Penrhyn Estuary Habitat Enhancement. Report to Maunsell Australia Pty Ltd. The Ecology Lab Pty Ltd, Brookvale. 19

20 APPENDICES 20

21 Appendix 1. Mapping data for November Works* No Eastings Northings Zostera Halophila Posidonia Area % % % M 2 Comment Mixed 2 No P No Mixed 3 No Mixed 1 No Mixed 1 No P No Mixed 1 No Mixed 1 No P Yes P Yes Mixed 2 Yes Mixed 1 Yes P Yes P Yes P Yes P Yes P Yes P Yes Z Yes P Yes P Yes P Yes P Yes Z Yes Mixed 1 Yes Z Yes Z Yes Z Yes Z Yes Z Yes Z Yes Z Yes Mixed 1 Yes P Yes Z Yes Total 365 Total Works Area Seagrass Zostera 93 Zostera 93 Posidonia 43 Posidonia 40 Mixed Mixed Mixed 2 8 Mixed 2 3 Mixed 3 4 Mixed 3 0 Total 365 Total 331 *No outside works area; Yes within works area. 21

22 Appendix 2. Mapping data for May Works* No Eastings Northings Zostera Halophila Posidonia Area % % % M 2 Comment P No P No Mixed 3 No Mixed 1 No Z No P No Mixed 1 No Mixed 1 No P Yes Z Yes Mixed 1 Yes Mixed 2 Yes Mixed 1 Yes P Yes P Yes P Yes Mixed 1 Yes P Yes P Yes P Yes P Yes Z Yes Z Yes Z Yes Z Yes P Yes Z Yes Z Yes Z Yes Mixed 1 Yes P Yes Z Yes Total 352 Total Works Area Seagrass Zostera 86 Zostera 84 Posidonia 36 Posidonia 26 Mixed Mixed Mixed 2 5 Mixed 2 5 Mixed 3 4 Mixed 3 0 Total 352 Total 317 *No outside works area; Yes within works area. 22