Catastrophic loss of tropical seagrass habitats at the Cocos (Keeling) Islands due to multiple stressors.

Seagrass habitats at the Cocos (Keeling) Islands (CKI), a remote atoll in the Indian Ocean, have suffered a catastrophic decline over the last decade. Seagrass monitoring (1996-2020) in relation to dredging and coastal development works (2009 to 2011) provide a historical baseline, and document the decline of mixed tropical seagrass Thalassia hemprichii and macroalgal (predominantly Caulerpa spp.) beds over a decadal scale time series. Attribution of loss to coastal development is confounded by lagoon-wide die-off events in 2007, 2009 and 2012 and high air and water temperatures from 2009 to 2016, with evidence of broad scale changes, visible in satellite imagery between 2006 and 2018. We conclude that up to 80% of seagrass habitats in the CKI lagoon (~1200 ha) have been lost due to multiple stressors including episodic die-off events related to high temperatures and calm conditions, and loss due to sediment disturbance and increased turbidity. Grazing pressure from the resident green sea turtles (Chelonia mydas) may have also exacerbated the loss of seagrass, which in turn poses a dire threat to their ongoing health and survival. This study highlights the fragility of tropical seagrass habitats and the cascading effect of system imbalance as a result of anthropogenic pressures and climate drivers. Although small in comparison to global estimates, the loss of seagrass habitats at CKI could change the entire ecosystem of a remote atoll. Due to the significance of the Thalassia beds for coastal stability, as food for an isolated population of green sea turtles and as a fish nursery, rehabilitation efforts are warranted.

Evaluation of barnacle (Crustacea: Cirripedia) colonisation on different fabrics to support the estimation of the time spent in water by human remains.

The estimation of the time since death (minimum Post Mortem Interval, minPMI) is an essential aspect of forensic investigations. This is particularly complex when a human body is found submerged, floating or beached in a marine environment. When a cadaver is found in a terrestrial environment the minPMI estimation is generally based on the presence of carrion insects. However, when a cadaver is found in an aquatic environment, a correct crime scene reconstruction is more complex and requires the consideration of the time the remains spent submerged underwater (minimum Post Mortem Submersion Interval, minPMSI) and/or floating (Floating Interval, FI). In marine crime scene scenarios, the use of barnacles (Crustacea: Cirripedia) has recently received some attention, due to their permanent settlement on human remains and their accompanying clothing. Previous research considered barnacle growth on human shoes, but the present research is the first to focus on the colonisation of barnacles on clothing materials (fabrics). Polystyrene floats were covered by either cotton, velvet, satin or neoprene and submerged underwater over a period of six months off the coast of Perth, Western Australia. The aims of this research were 1) the identification of marine species colonising the fabrics, with special attention to barnacles; 2) the identification of which fabric type provides the most desirable environment for colonisation; and 3) the identification of factors that affect the growth rate of the different species. Three species of barnacles, Balanus trigonus Darwin, Amphibalanus reticulatus (Utinomi) and A. variegatus (Darwin), were present in varying numbers and sizes. The colonisation process of the barnacles occurred rapidly, with the first sighting of barnacles observed within the first month on neoprene and control floats. The surface that attracted the largest number of barnacles was neoprene, followed by satin and cotton, while velvet showed an inconsistent colonisation rate. The largest size barnacles were observed on the control floats, while all fabrics showed a similar smaller size. Overall, time spent in water and water temperature had a significant positive relationship with both number and size of the colonising barnacles. This study is the first to provide information that will aid in the investigation of human remains recovered from Western Australian marine waters, using the barnacle colonisation on different fabric types.

Longevity and sustainability of tropical and subtropical restored seagrass beds among Atlantic, Pacific, and Indian Oceans.

Seagrass longevity up to 47 years in well-restored, well-sited seagrass restorations are demonstrated from 253 trials at 83 regional sites in tropical and subtropical portions of three oceans (Atlantic, Pacific, Indian Oceans). These trials include over 3.04 million planted units into 306.3 ha. Approximately 12% of the total global tropical restored seagrass by Van Katwijk, Thorhaug et al. (2016) calculations from 1786 trials are included. Almost all projects herein reviewed persisted since date of planting except several cases with harsh anthropogenic impact or forceful natural events in first post-planting months. The oldest tropical/subtropical restoration continually observed is 47 yrs, many are 35 yrs. An array of observed and/or measured restored services accompanied these. This review may provide informational background for government resource managers, legislators, scientists, and citizens concerning tropical/subtropical seagrass longevity. This data from these trials may substantiate future seagrass restoration investments. Public outreach, national & regional government training,and outreach occurred, needing continuation.

Linking Seed Photosynthesis and Evolution of the Australian and Mediterranean Seagrass Genus Posidonia.

Recent findings have shown that photosynthesis in the skin of the seed of Posidonia oceanica enhances seedling growth. The seagrass genus Posidonia is found only in two distant parts of the world, the Mediterranean Sea and southern Australia. This fact led us to question whether the acquisition of this novel mechanism in the evolution of this seagrass was a pre-adaptation prior to geological isolation of the Mediterranean from Tethys Sea in the Eocene. Photosynthetic activity in seeds of Australian species of Posidonia is still unknown. This study shows oxygen production and respiration rates, and maximum PSII photochemical efficiency (Fv : Fm) in seeds of two Australian Posidonia species (P. australis and P. sinuosa), and compares these with previous results for P. oceanica. Results showed relatively high oxygen production and respiratory rates in all three species but with significant differences among them, suggesting the existence of an adaptive mechanism to compensate for the relatively high oxygen demands of the seeds. In all cases maximal photochemical efficiency of photosystem II rates reached similar values. The existence of photosynthetic activity in the seeds of all three species implicates that it was an ability probably acquired from a common ancestor during the Late Eocene, when this adaptive strategy could have helped Posidonia species to survive in nutrient-poor temperate seas. This study sheds new light on some aspects of the evolution of marine plants and represents an important contribution to global knowledge of the paleogeographic patterns of seagrass distribution.

The movement ecology of seagrasses.

A movement ecology framework is applied to enhance our understanding of the causes, mechanisms and consequences of movement in seagrasses: marine, clonal, flowering plants. Four life-history stages of seagrasses can move: pollen, sexual propagules, vegetative fragments and the spread of individuals through clonal growth. Movement occurs on the water surface, in the water column, on or in the sediment, via animal vectors and through spreading clones. A capacity for long-distance dispersal and demographic connectivity over multiple timeframes is the novel feature of the movement ecology of seagrasses with significant evolutionary and ecological consequences. The space-time movement footprint of different life-history stages varies. For example, the distance moved by reproductive propagules and vegetative expansion via clonal growth is similar, but the timescales range exponentially, from hours to months or centuries to millennia, respectively. Consequently, environmental factors and key traits that interact to influence movement also operate on vastly different spatial and temporal scales. Six key future research areas have been identified.