Seasonal dynamics, productivity and resilience of seagrass at the Port of Abbot Point: 2008-2010

This report details the results of seagrass baseline assessments, quarterly seagrass monitoring, and experimental research on seagrass resilience and productivity conducted between 2008 and 2010 at the Port of Abbot Point, North Queensland. This program of research and monitoring was commissioned by North Queensland Bulk Port (NQBP) Corporation in order to provide an understanding of the spatial and temporal change of seagrasses in the vicinity of the Port; their ecological and economic value, and their capacity to recover from future port related impacts. Seagrass coverage was extensive, with meadows comprising 42% of the survey area. Seagrass meadows occurred from the shoreline to a distance of approximately 10km offshore and covered an area of up to 21,000ha. The survey area contained a variety of species and meadow types ranging from low biomass coastal Halodule uninervis meadows, to higher biomass deep water Halophila spinulosa meadows. Small meadows comprising the larger leaved species Zostera capricorni and Cymodocea serrulata were also recorded. Seagrasses at Abbot Point were highly dynamic, changing as a function of season, but also influenced by extreme weather events during the life of the study. The productivity and resultant biomass of seagrasses at Abbot Point reached a maximum in the late dry season, a trend consistent with observations of seagrasses throughout Queensland. Seagrass meadows at Abbot Point were highly productive, producing 237 grams of carbon per m² per day. Although this is roughly half the productivity of seagrass meadows on reef platforms in the Torres Strait, this net productivity compares highly with many productive marine and terrestrial ecosystems worldwide. The productivity of these seagrasses supports an abundant and diverse fauna, with many species of economically important Penaeid prawns utilising the seagrass meadows of Abbot Point. This is in addition to the presence of a range of endangered and migratory mega fauna such as Dugong, Turtle and Humpback whale observed in proximity to the port. Seagrasses at Abbot Point were found to have some levels of resilience to stress, however this varied with species and community type and will be dependent in the future upon the continued availability of seed reserves. Species such as Halophila spinulosa were found to have a high capacity for recovery through the use of seed reserves in the sediment, however shallow near- shore species such as Halodule uninervis failed to recover quickly from simulated disturbance, relying on asexual propagation and were more vulnerable to longer term impacts should widespread loss occur. Seagrass meadows at the Port of Abbot Point are highly productive and provide habitat and food for a range of important fauna. These seagrass meadows are dynamic, with some habitats having a higher capacity for recovery from loss than others. They are currently subject to a range of anthropogenic and natural threats potentially reducing their resilience to increased cumulative impact. The available information indicates that future developments that may potentially disturb the local water quality (particularly light availability) at Abbot Point need to be carefully managed to ensure the longer term viability of seagrasses. The program presented here can form the basis of a seagrass assessment and monitoring strategy to aid in the management of dredge related impacts