Long term seagrass monitoring in Port Curtis: quarterly permanent transect monitoring progress report 2009 to 2014

Davies, Jaclyn, Sankey, Tonia, Jarvis, Jessie, Bryant, Catherine, and Rasheed, Michael (2015) Long term seagrass monitoring in Port Curtis: quarterly permanent transect monitoring progress report 2009 to 2014. Report. James Cook University, Cairns, QLD, Australia.

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This report details results from the assessment of seagrass change at a range of permanent transect sites that were established as part of the Western Basin Dredging and Disposal Project (WBDDP). These sites are assessed regularly throughout the year (quarterly since the completion of dredging) and will continue for 3 years after the completion of the dredging program. This work is in addition to the long term annual seagrass monitoring that has been conducted since 2002 which examines and re‐maps the full extent of seagrasses each November at the time of their maximum distribution. The results of that program are presented in a separate report (see Carter et al. 2015).

Monitoring at permanent transects revealed that seagrasses in the Western Basin and Rodds Bay underwent distinct seasonal changes as well as significant inter‐annual changes in seagrass distribution, abundance and species composition.

Over the duration of the monitoring program (since November 2009), Gladstone has received higher than average rainfall during the majority of wet seasons, punctuated by two of the most extreme flood events on record.

Significant declines in seagrass abundance occurred at all sites during the monitoring program, particularly following the 2010/2011 floods. Some sites showed substantial recovery, particularly in the outer harbour the following year; however inner harbour sites have yet to recover to preflood levels.

The timing of flood related declines in seagrass during 2010 and 2011 immediately prior to the onset of the major WBDDP dredging activities makes it difficult to ascertain what additional impact dredging may have had on seagrass condition at the permanent transect sites. However, light information collected at the sites indicates seagrasses were receiving enough light for their growing requirements during the dredging program. Similar losses of seagrasses in other Queensland locations were also recorded in response to the flooding and cyclone impacts.

In January 2013, the Calliope River again discharged at record levels and declines in seagrass were detected across most of the monitoring sites. Recovery over the 2013 and 2014 growing seasons varied with some sites (e.g. Pelican Banks South) remaining atypically low in seagrass cover.

During 2014, seagrass C:P, N:P and C:N ratios remained low at outer harbour sites following declines in 2013, indicating that seagrasses were existing in a nitrogen limited, low light and a relatively phosphorous rich environment.

Seed banks for Halophila ovalis and Zostera muelleri subsp. capricorni were detected at some locations in the harbour from which recovery could be initiated when conditions are favourable for germination, seedling survival and for subsequent clonal growth and colonisation.

At the reference site in Rodds Bay, mean Z. muelleri subsp. capricorni seed density generally increased in 2014 following a gradual downward trend in seed density from 2011 to 2013, possibly enabling the increase in seagrass percent cover observed in the November 2014 assessments.

Gladstone seagrasses were capable of rapid clonal growth and the production of flowers, fruits and seeds. However this varied substantially between meadows and time of year. It is likely that propagule limitation at some sites may be inhibiting seagrass recovery.

The November 2014 monitoring has revealed substantial recovery at the out of Port reference sites in Rodds Bay and many of the inner and outer harbour sites also showed increasing cover. In the absence of another extreme wet season in 2014/2015, further increases in Rodds Bay and the Western Basin region are expected.

Results of seagrass monitoring over the post‐dredging phase of the project will continue to provide insight into the capacity of seagrass resilience to human activities. If low levels of resilience detected at many sites persist then the tools and thresholds established through the Gladstone seagrass research programs will be critical in ensuring successful management of their recovery. Currently seagrasses have shown a capacity to recover from impacts in Gladstone, but as has been seen in other Queensland locations repeated disturbances over multiple years may lead to long term loss, with recovery trajectories far less certain. The extensive and detailed seagrass monitoring and research efforts in Gladstone means we are well placed to understand these processes and can look to implement measures to reduce the chances of exacerbating natural impacts by human activities.

Item ID: 45228
Item Type: Report (Report)
Keywords: recovery, resilience, management, environmental monitoring, marine monitoring, marine water quality, seagrass, reproduction, seagrass habitats, Great Barrier Reef, port development, dredging
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A report for Gladstone Port Corporation Limited Report. No. 15/05

Funders: Gladstone Ports Corporation Limited
Date Deposited: 30 Aug 2016 04:57
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050206 Environmental Monitoring @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050205 Environmental Management @ 50%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments @ 50%
96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 50%
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