Port of Abbot Point long-term seagrass monitoring: interim report 2008-2011

This report summarises the results of the coastal and deep water seagrass monitoring program conducted between June 2008 and September 2011 at the Port of Abbot Point. The report also discusses the status of light and temperature assessments, and recovery experiments that have been included as part of the monitoring program in the Port. The seagrass monitoring program at Abbot Point was developed in 2008 following two baseline assessments of the marine habitat within the port limits. Seagrass distribution and density at Abbot Point has been highly dynamic, changing as a function of season, and further influenced by extreme weather events during the life of the study. Seagrass biomass and distribution was generally lowest at the end of the wet season and greatest in the late dry season, a trend consistent with observations of seagrasses throughout Queensland. Results of the latest survey indicate that seagrasses at Abbot Point are in a vulnerable state. Significant losses of density and distribution of seagrasses at Abbot Point were observed after the November 2010 survey, particularly in the coastal monitoring meadows. The La Niña events of 2010/11 combined with severe Tropical Cyclone Yasi are the most likely factors that caused these significant losses. Consecutive above average wet seasons since late 2009 have also potentially left seagrasses with substantially reduced resilience to further stressors. The cumulative impacts of natural stressors, combined with a potential increased level of impact from future port activities and development, places these seagrasses at a heightened risk. Seagrasses at Abbot Point have the potential to recover, however this recovery is dependent upon the species present and the availability of seed reserves. Studies at Abbot Point between 2008 and 2010 found that Halophila spinulosa, the dominant seagrass species in the offshore meadows, has a high capacity for recovery through the use of seed reserves in the sediment. In contrast the shallow near shore species Halodule uninervis failed to recover quickly from simulated disturbance, relying on asexual propagation making them more vulnerable to longer term impacts should widespread loss occur. The seagrass monitoring and research program findings demonstrate the importance of developing effective management strategies for future developments that may potentially disturb the local water quality (particularly light availability) at Abbot Point. Water quality management linked to the local ecological requirements of seagrasses will help ensure the resilience of seagrasses in the area during planned capital works in the port. This monitoring program provides the basis for such assessments which will be critical should the current vulnerable state of seagrasses continue