Long-term effects of flooding events on the resilience and recovery of tropical seagrass habitats

In the summer of 2010/2011 Queensland experienced some of the worst floods on record. Plumes associated with flooding have the potential to negatively impact seagrass habitats through high nutrient loads, burial, sediment destabilisation, reducing light availability and lowering salinity. Over the last 17 years a network of long-term monitoring sites have been established around Queensland to examine the condition and trend of the state's valuable seagrass habitats. Results have shown major declines in seagrass across the east coast of Queensland since the 2010/2011 floods. Many of these seagrass communities were already in decline prior to the 2010/2011 floods meaning that these communities were likely to be less resilient to further impacts and may have had a reduced capacity for recovery. Our long-term monitoring data has previously demonstrated seagrass loss related to flood events, however tropical seagrass meadows have shown a capacity for recovery returning to pre-flood levels within 4 months to 5 years. Recovery was dependent on the presence of locally available propagules and established seed banks from which recovery could occur. While seagrasses along the urban east coast were in poor condition, in other regions of the state including northern Cape York, the Torres Strait and the Gulf of Carpentaria seagrass remained in relatively good condition. The vulnerable state of seagrass habitats on the east coast of Queensland, and differences between regions underscores the need for continued monitoring across regions to ensure the long-term viability of these ecologically important marine habitats and appropriate management of the resource. Long-term monitoring programs can play an important role in providing quality data on seagrass status which can assist managers to make decisions on how to respond with greater confidence

Long-term effects of flooding events on the resilience and recovery of tropical seagrass habitats

In the summer of 2010/2011 Queensland experienced some of the worst floods on record. Plumes associated with flooding have the potential to negatively impact seagrass habitats through high nutrient loads, burial, sediment destabilisation, reducing light availability and lowering salinity. Over the last 17 years a network of long-term monitoring sites have been established around Queensland to examine the condition and trend of the state's valuable seagrass habitats. Results have shown major declines in seagrass across the east coast of Queensland since the 2010/2011 floods. Many of these seagrass communities were already in decline prior to the 2010/2011 floods meaning that these communities were likely to be less resilient to further impacts and may have had a reduced capacity for recovery. Our long-term monitoring data has previously demonstrated seagrass loss related to flood events, however tropical seagrass meadows have shown a capacity for recovery returning to pre-flood levels within 4 months to 5 years. Recovery was dependent on the presence of locally available propagules and established seed banks from which recovery could occur. While seagrasses along the urban east coast were in poor condition, in other regions of the state including northern Cape York, the Torres Strait and the Gulf of Carpentaria seagrass remained in relatively good condition. The vulnerable state of seagrass habitats on the east coast of Queensland, and differences between regions underscores the need for continued monitoring across regions to ensure the long-term viability of these ecologically important marine habitats and appropriate management of the resource. Long-term monitoring programs can play an important role in providing quality data on seagrass status which can assist managers to make decisions on how to respond with greater confidence

Seagrass habitat of Cairns Harbour and Trinity Inlet: Annual Monitoring Report 2017

Seagrasses have been monitored annually in Cairns Harbour and Trinity Inlet since 2001. Each year all seagrass monitoring meadows representing the range of different seagrass community types found in Cairns are mapped and assessed for changes in biomass and species composition. These metrics are then used to develop a seagrass condition index (Map 1). In addition to the established annual monitoring program, regular assessments of seagrass condition (quarterly), seed bank density and viability, and benthic light (continuously logged) are conducted at a key seagrass recovery site within the Ellie Point to the Esplanade intertidal meadow (site E; Map 1) from June 2014

Seagrass habitat of Mourilyan Harbour: Annual Monitoring Report – 2017

Seagrasses in Mourilyan Harbour have been monitored annually since 2000 following baseline surveys and initial assessments conducted between 1993 and 1996. Each year all seagrasses within 5 seagrass meadows representing the range of different seagrass community types found in Mourilyan Harbour are assessed for changes in biomass, aerial coverage and species composition. Changes to area, biomass and species composition are used to develop a seagrass condition index (see sections 2.2 & 3.2 of this report for further details)

Gladstone Western Basin and Channel Dupliaction BPAR Monitoring May - July 2014

The dredging projects associated with port expansion in the Western Basin were identified as potentially posing a high level of environmental risk to the marine habitats of the area, particularly to seagrass meadows. A detailed seagrass and light assessment program has been established for the Western Basin project to assist in management of the project to ensure seagrass meadows are appropriately managed during dredging. This program includes a requirement for continued assessment of seagrasses and Benthic Photosynthetically Active Radiation (BPAR) following the end of dredging activities to assess seagrass recovery. These post dredge seagrass and BPAR monitoring requirements are outlined in several conditions and plans connected with the Western Basin Dredging and Disposal Project (WBDDP) and a strategy to meet them was developed and endorsed by the Dredge Technical Reference Panel. This report presents results of the third quarter (May to July 2014) of post dredge monitoring to address BPAR requirements outlined in the "Western Basin Dredging & Disposal Projec t: Water Quality and Seagrass Monitoring Strategy – Post TSHD & completion of dredging in 2013." In May 2014, BPAR monitoring equipment was also established at additional sites to expand the seagrass and light assessment program to areas most likely to be impacted by dredging associated with the proposed Channel Duplication project. In order to put any changes to seagrasses that occur during the project into perspective it is critical to collect pr e-dredge background information on the natural seasonal and inter annual changes in seagrasses in relation to benthic irradiance at the intended sensitive receptor monitoring sites for as long a period as possible

Gladstone Western Basin and Channel Dupliaction BPAR Monitoring May - July 2014

The dredging projects associated with port expansion in the Western Basin were identified as potentially posing a high level of environmental risk to the marine habitats of the area, particularly to seagrass meadows. A detailed seagrass and light assessment program has been established for the Western Basin project to assist in management of the project to ensure seagrass meadows are appropriately managed during dredging. This program includes a requirement for continued assessment of seagrasses and Benthic Photosynthetically Active Radiation (BPAR) following the end of dredging activities to assess seagrass recovery. These post dredge seagrass and BPAR monitoring requirements are outlined in several conditions and plans connected with the Western Basin Dredging and Disposal Project (WBDDP) and a strategy to meet them was developed and endorsed by the Dredge Technical Reference Panel. This report presents results of the third quarter (May to July 2014) of post dredge monitoring to address BPAR requirements outlined in the "Western Basin Dredging & Disposal Projec t: Water Quality and Seagrass Monitoring Strategy – Post TSHD & completion of dredging in 2013." In May 2014, BPAR monitoring equipment was also established at additional sites to expand the seagrass and light assessment program to areas most likely to be impacted by dredging associated with the proposed Channel Duplication project. In order to put any changes to seagrasses that occur during the project into perspective it is critical to collect pr e-dredge background information on the natural seasonal and inter annual changes in seagrasses in relation to benthic irradiance at the intended sensitive receptor monitoring sites for as long a period as possible

Seagrass habitat of Mourilyan Harbour: Annual Monitoring Report – 2018

Seagrasses in Mourilyan Harbour have been monitored annually since 2000 following initial assessments conducted between 1993 and 1996. Each year a subset of 5 seagrass meadows (annual monitoring meadows) representing the range of different seagrass community types found in Mourilyan Harbour are assessed for changes in biomass, aerial coverage and species composition. These indicators are used to develop a seagrass condition index (see section 2.5.1 of this report for further details). This report also includes an extended survey encompassing all seagrasses within the harbour to capture the health and condition of the whole system

Seagrass habitat of Cairns Harbour and Trinity Inlet: Annual Monitoring Report 2018

Seagrasses have been monitored annually in Cairns Harbour and Trinity Inlet since 2001. Each year six seagrass monitoring meadows representing the range of different seagrass community types found in Cairns are mapped and assessed for changes in biomass and species composition. These metrics are then used to develop a seagrass condition index (Map 1). Every 3 years all seagrasses within the port limits are also remapped (conducted in this 2018 survey). In addition to the established annual monitoring program, regular assessments of seagrass condition (quarterly), seed bank density and viability, and benthic light (continuously logged) are conducted at a seagrass site within the Ellie Point to the Esplanade intertidal meadow (site E; Map 1)

Seagrass habitat of Mourilyan Harbour: Annual Monitoring Report – 2021

1. Seagrass was in a very poor condition in Mourilyan Harbour in 2021. 2. All meadows were classified as in a very poor condition as the biomass and extent were well below the long-term average, even though seagrass was present in three of the five monitoring meadows. 3. Two of the monitoring meadows received a very good condition grade for species composition, a return to Halophila ovalis in Seaforth bank (3) and the Bradshaw meadow (1) which saw a return of foundation species Zostera muelleri through restoration trials for the first time since 2009. 4. The whole of port survey looked for overall seagrass distribution in the harbour area. Two additional meadows were mapped, a decline from the 11 previously found in 2018. 5. Above average rainfall and river flow in the months leading up to the survey may have reduced the environmental conditions favourable to seagrass growth and survival prior to the survey. 6. A return of the foundation species Zostera muelleri in Mourilyan Harbour is a promising sign that preliminary restoration efforts were successful and can be scaled up for a full restoration program for Bradshaw and Lily meadows. 7. Current seagrass condition was unlikely to be related to port operations with the major losses and declines associated with previous La Niña climate events and more recent wet weather and river flows

Seagrass habitat of Cairns Harbour and Trinity Inlet: Annual Monitoring Report and Cairns Shipping Development Project Monitoring Report 2021

• Seagrass meadows in Cairns Harbour and Trinity Inlet are monitored annually to assess their condition and as an indicator of marine environmental health in the Port of Cairns. • The three large meadows in Cairns Harbour were in a good condition and remained stable in 2021. • Due to reductions in area and or biomass the three smaller Estuarine Trinity Inlet monitoring meadows were collectively in a poor condition. o Two of these small meadows consist of ephemeral species and are highly variable in density and distribution each year. o The third meadow of larger growing species has improved in condition over the last two years following its complete loss between 2010 and 2015. • The whole of port assessment in 2021 mapped 1,488 ha of seagrass, the fourth year in a row recording some of largest areas of seagrass in the Cairns region, but a slight reduction compared to the past 3 years. • Two years after completion of the Cairns Shipping Development Project (CSDP) there were no signs of impacts on the extensive seagrass monitoring meadows adjacent to the harbour works. • The meadows closest to the dredge operation remained in a good condition and both area and biomass have been stable since the CSDP works were completed