Port Hacking: an aquatic jewel adjacent to Royal National Park
Rob Williams, Bob Creese, Tim Glasby, Greg West September 2011 Tidal cross section of estuarine foreshore Life in Saltmarsh
Life in Mangroves
Life in ‘bare’ sediments
Life in Seagrass
Photos by Dave Harasti Posidonia australis
Halophila ovalis
Zosterea capricornia Estuaries are complex ecosystems
Chemical & biological processes Biodiversity Habitats Surrounded by fertile land – Rural impacts • increased sediments & nutrients Good places for harbours & cities – Industrial impacts • increased pollution, infrastructure Nice places for people to live near – Urban impacts • increased stormwater & sewage inflow Sealevel – the major driver of estuarine structure What are key estuarine habitats?
1. Natural physical features –Deep holes – Sand bars or mud banks –Rocky reefs What are key estuarine habitats? 2. Biological features – Mangrove forests - Saltmarsh – Seagrass beds - Algae What are key estuarine habitats? 3. Man-made physical features
• Marinas, jetties • Oyster farms • Port facilities • Artificial reefs NSWNSW hashas 184184 coastalcoastal waterbodieswaterbodies
Semi-enclosed embayments (6; e.g. Jervis Bay)
Drowned river valleys (13; e.g. Port Hacking)
Barrier estuary (51; e.g. Manning river estuary)
ICOLLs (110; e.g. Lake Conjola)
Brackish lakes (4) Australian Estuarine Classification Alternatives
• Roy (1984) – Geomorphological, 4 3 zones
• Rochford (1951, 1959) – Hydrological, 4 zones Hawkesbury River (DRV) DLWC photo Roy: Estuary evolution since sealevel stabilised 6,500 years ago – Catchment infilling Evolution of NSW Drowned River Valleys Proto-valley Evolutionary Stage: %Central Mud Basin Young Adolescent Adult Pensioner 90-60% 60-10% 10-1% <1% Stephens Port Stephens Hawkesbury Hawkesbury River (main channel) Pitt Pittwater Middle Harbour Middle H. Creek Parramatta Parramatta R. Georges Georges River Hacking Hacking River (main channel) Clyde Clyde River
6,500 YBP Present
(after Roy et al. 2001) Geomorphic Zones in NSW Drowned River Valleys
RC FD CMB MTD
6 218 4 Parramatta River 30km 60%
1 2103 Pittwater 16km 63%
Hacking River 35 6 14km 21%
Geo. R./ Botany Bay 28 612 2 49km 4%
Hawkesbury River 139km 100 30 8
(Total lengths from Roper et al. 2011) Rochford ‘s initial observation (1951)
MANGROVES
OPTIMUM FATTENING
OYSTERS OPTIMUM SPAWNING
ZOSTERA Rochford ‘s initial observation (1951)
ZONE FRESH- GRADIENT TIDAL MARINE WATER
MANGROVES OPTIMUM FATTENING
OPTIMUM SPAWNING OYSTERS
ZOSTERA Rochford (1951) “Estuarine System”
(River) (River/Estuary) (Estuary) Fresh- Gradient Tidal Marine water Chl. Sal.
20 35 30 25 11 20 15 10 5 00 Why map estuarine habitats?
Habitats give a guide to biodiversity – the more habitats there are, the more types of plants & animals there are likely to be.
Complex habitat arrangements are a good indicator of healthy estuaries.
The change in the amount of habitat over time can show improvement or deterioration.
Accurate spatial layers in a GIS can help in assessing risks and developing rehabilitation. Mangrove: an expanding commodity Coastal Saltmarsh, a NSW EEC
Saintilan and Williams (1999, 2000) Avicennia marina expansion in the Parramatta River (Ermington)
Photo: J. Kelleway (2007) Southward migration of mangrove in NSW: early 1980s – mid 2000s
Barrier estuary ~Distance Avicennia Aegiceras Exoecaria Rhizophora Brugeria from Qld. marina cornic- agal- stylosa border ulatum locha (km) 01 Tweed R. 0 X X X X X 05 Brunswick R. 40 X X X X X 09 Richmond R. 70 X X X X X 12 Clarence R. 135 X X X X 13 Sandon R. 165 X X X X 14 Wooli W. R. 190 X X X X X 21 Moonee Ck. 235 X X X 31 S. W. R. Ck. 310 X X X
X= West et al. (1985), X = N. Wilson, pers. comm. (2002, 2003), X = R. Glover, pers. comm. (2001) Saltmarsh 100000 In Out 10000 - 3
1000
100
10 Number of Crab Larvae m m Larvae Crab of Number
1 Mar Apr. May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
0.1
Mazumder et al. (2009) Trophic interactions between different ecosystem components and consumers at Towra Point, NSW
Mazumder et al. (2011)
Saltmarsh Recent history of estuarine macrophyte cover in Port Hacking
Photo. Land Information Centre Photo. Land Information Centre 1930 1999 Area of Port Hacking’s estuarine vegetation 1930 - 1999
Seagrass 200 Mangrove Saltmarsh 180
160
140
120
100
80 Area (ha)
60
40
20
0 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year
Williams and Meehan (2004) Cabbage Tree Basin 1942 Cabbage Tree Basin 1999
N N
Posidonia Zostera Mixed Mangrove
0500Meters 0500Meters Threats to estuarine habitats in Port Hacking
Dredging and other physical disturbance – Regular dredging of channels still occurs every 3-4 years – Damage from recreational boating still an issue
Sediment & nutrient input from catchment activities – Less of a problem than 4-5 decades ago – Still likely to be stormwater impacts
Invasive species – Fewer vectors occur (no commercial fishing, shipping or aquaculture) – But close to Botany Bay – Discards from home aquaria a high potential risk • Propeller scour •Mooring holes Area of Port Hacking’s estuarine vegetation 1930 - 1999
Seagrass 200 Mangrove Saltmarsh 180
160
140
120
100
80 Area (ha)
60
40
20
0 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year
Williams and Meehan (2004) Hacking River 1951
Zostera N
01Kilometers
Hacking River 1999
N
0 1 Kilometers Hacking River Foreshores, 2009: natural & artificial South West Arm Macrophytes, 2009 Macrophyte change at RNP locations: 1951-1999
Geom. Location Saltmarsh Mangrove Seagrass Zone 7 Cabbage -37% +420% -92% Tree Basin 8 South +186% +100% -10% West Arm (?) 9 Hacking -50% +28% -83% River
From Williams & Meehan (2004) API Presumptive map of saltmarsh
Saltmarsh 2 Sm-4 Sm-1 Mangrove-2 Mangrove-3
M-1 Sm-3 Final map FN FN
FN
FP Final map FN FN
FN
FP
Saltmarsh polygons No. patches Area (m2) Presumed to exist 4 500 False positive -1 -50 Expose joins -2 500 False negative 7 100 Total 8 1050 (Williams et al. 2011) helicopter mapping allows greater control photos are taken under optimal conditions sub 1m accuracy density & health; not just extent Wallis Lake, Snake Island: ALOS vs QuickBird unsupervised classification
ALOS AVNIR QuickBird 10m spatial resolution 2.6m spatial resolution January 2003
Posidonia
February 2008 January 2007 (Glint affected)
sand September 2008 sparse seagrass/BMA sand
CSIRO L&W Introduced Caulerpa Cumulative distribution of Caulerpa
Note: Caulerpa not always present in these areas and it is often quite sparse Caulerpa vs Posidonia: 2005-2010 20 x 20 m fixed plots in each of 2 sites
Gunnamatta Bay Jibbon Ctax Pos (canopy) 100 Pos (primary) 100
90 90
80 80
70 70
60 60
50 50
40
% cover 40 % cover
30 30
20 20
10 10
0 0 DEC05 AUG05 MAR06 AUG06 MAY07 MAR08 NOV08 DEC10 DEC05 MAR06 AUG06 MAY07 MAR08 NOV08 DEC10 Overall change in Caulerpa: 2003-2011
Data from 17 x 250 m transects throughout Port Hacking
Caulerpa abundance - Port Hacking
0.5
0.4
0.3
0.2
0.1 Mean proportion Ctax per transect (+SE) transect per Ctax proportion Mean 0.0 MAR03 AUG03 MAR04 SEP04 APR05 AUG05 MAR06 AUG06 MAR11 Salient points re Caulerpa
Caulerpa taxifolia comes and goes – Discovered April 2000 – Overall distribution and abundance in Port Hacking has changed little since 2003, slight decline if anything Zostera capricorni comes and goes, Posidonia australis is more persistent – No evidence yet of direct impacts of Caulerpa on seagrasses – Seems that Caulerpa is opportunistic – colonises where Zostera has died for some reason – Experimental work on potential impacts is continuing Concluding Points
Catchment management issues relevant to RNP: – Dredging and other physical disturbances (e.g. recreational boating) – Sediment & nutrient input from catchment activities – Invasive species – Public access & education – Aquatic macrophytes • Seagrass loss appears stabilised • Saltmarsh cover appears stable • Mangrove cover has increased slightly RNP offers stable home for complex estuarine processes – Aquatic macrophyte cover has not been stable