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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.

Climate-driven changes are altering production and functioning of biotic assemblages in terrestrial and aquatic environments. In temperate coastal waters, rising sea temperatures, warm water anomalies and poleward shifts in the distribution of tropical herbivores have had a detrimental effect on algal forests. We develop generalized scenarios of this form of tropicalization and its potential effects on the structure and functioning of globally significant and threatened seagrass ecosystems, through poleward shifts in tropical seagrasses and herbivores. Initially, we expect tropical herbivorous fishes to establish in temperate seagrass meadows, followed later by megafauna. Tropical seagrasses are likely to establish later, delayed by more limited dispersal abilities. Ultimately, food webs are likely to shift from primarily seagrass-detritus to more direct-consumption-based systems, thereby affecting a range of important ecosystem services that seagrasses provide, including their nursery habitat role for fishery species, carbon sequestration, and the provision of organic matter to other ecosystems in temperate regions.

Seagrass ecosystems are inherently dynamic, responding to environmental change across a range of scales. Habitat requirements of seagrass are well defined, but less is known about their ability to resist disturbance. Specific means of recovery after loss are particularly difficult to quantify. Here we assess the resistance and recovery capacity of 12 seagrass genera. We document four classic trajectories of degradation and recovery for seagrass ecosystems, illustrated with examples from around the world. Recovery can be rapid once conditions improve, but seagrass absence at landscape scales may persist for many decades, perpetuated by feedbacks and/or lack of seed or plant propagules to initiate recovery. It can be difficult to distinguish between slow recovery, recalcitrant degradation, and the need for a window of opportunity to trigger recovery. We propose a framework synthesizing how the spatial and temporal scales of both disturbance and seagrass response affect ecosystem trajectory and hence resilience.

species (e.g., Halodule uninervis). Those biotic effects also impacted multiple consumer populations including turtles and dugongs, with implications for species dynamics, food web structure, and ecosystem recovery. We show multiple stressors can combine to evoke extreme ecological responses by pushing ecosystems beyond their tolerance. Finally, both direct abiotic and indirect biotic effects need to be explicitly considered when attempting to understand and predict how ECEs will alter marine ecosystem dynamics.

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The responses of the seagrass Amphibolis griffithii to different experimental shading conditions were examined by characterising biomass, morphological and physiological features. In an in situ experiment, the intensity (ambient, moderate shading [13 to 19% of ambient] and high shading [5 to 11% of ambient]), duration (3, 6, 9 mo) and timing (post-summer, post-winter) of light reductions were manipulated. We observed interactive effects of all 3 factors, the most notable being with timing. When moderate shading was imposed at the end of summer there was a 57% loss of leaf biomass and 67% loss of rhizome carbohydrates within 3 mo. The same shading imposed at the end of winter caused no loss of leaf biomass and only a 25% decline in rhizome carbohydrates. This contrasting effect of time reflects the plant's photo-physiological characteristics under the water temperature and light conditions. More prolonged or higher intensity shading produced more consistent responses at both times of year: moderate shading resulted in more than 93% loss of leaf biomass after 9 mo and high intensity shading resulted in more than 99% loss after 9 mo. The results highlight the importance of time of year when attempting to predict seagrass responses to shading. The study identified 14 potential early indicators of light reduction; these included leaf δ 15 N, which may reflect changes in the allocation of nitrogen in the photosynthetic apparatus. There is no evidence that A. griffithii is more susceptible to shading than larger seagrasses such as Posidonia spp.

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