Seagrass connectivity

Published on 8 May 2018

Dr Catherine Collier (James Cook University), Catherine Collier, JCU

Seagrass meadow of Cymodocea rotundata, Syringodium isoetifolium, Halodule uninervis, Cymodocea serrulata and Thalassia hemprichii at Green Island, Great Barrier Reef.

What is seagrass and why it is important?

Seagrasses are marine plants found in estuaries, reefs and deep water environments throughout the northeast Australian seascape (Figure 2). They form meadows that provide nutrient-rich habitat for many animals, for example, sea cucumbers, fish, urchins, marine turtles, dugongs, sharks and rays all use seagrass meadows at some time during their life cycle. Seagrass meadows provide important ecosystem services, such as food and shelter, nutrient cycling, nursery habitat and carbon sinks (Coles et al. 2015, Nordlund et al. 2016). The highest diversity of seagrass worldwide is in tropical waters, with an estimated 15 species of seagrasses in the northeast Australian seascape (Waycott et al. 2004).

Dr Eric Lawrey (eAtlas (Australian Institute of Marine Science)), Mr Len McKenzie (TropWATER), Robert Coles (James Cook University), Alex Carter (James Cook University), Michael Rasheed (James Cook University)

Figure 2. This map shows the distribution of shallow and deep seagrass meadows in the north east Australian seascape up to the tip of Cape York. Note: Torres Strait has a lot of seagrass meadows however these are not shown on this map.

Key concepts that relate to connectivity

Most seagrasses use water movements for pollen and seed dispersal and some species employ animal assisted seed dispersal to reproduce (Tol et al. 2017) (Figure 3). Both forms of dispersal can transport seeds long distances and support seagrass recruitment to locations many kilometres from their source (Grech et al. 2016, 2018). This long-distance dispersal also enhances the clonal diversity of meadows and therefore their resilience. This is the primary type of connectivity of seagrass meadows in the northeast Australian seascape (see Figures 4a-d). Seagrass meadows are an important coastal habitat that is threatened by human and natural disturbances, including urban and agricultural runoff, boat damage, fishing, cyclones and storms, and dredging (Waycott et al. 2009, Grech at al. 2018, McKenzie et al. 2017), and they at risk of thermal stress due to the changing climate (Collier et al. In press). Importantly, information on connectivity can provide insight into how activities in one area can impact seagrass in other areas by affecting seed stocks and distant recruitment. Any loss of seagrass habitat will have consequences for the animals that depend on it for food, shelter and breeding, such as dugongs and marine turtles.

Reproductive cycle of example seagrass species

Collier and Waycott 2009

Figure 3. Reproductive cycle of three example species of seagrass: Once seeds are set they are dispersed from the plant by water movements or animals where they can recruit to new areas many kilometres away. Depending on many biophysical factors such as currents, winds and temperature, dispersal can range from 10 to 30 days.