Barry Muir | Guest Contributor
In Part 1 of this series (Muir 2024a), I dealt with climate change myths. In Part 2 (Muir 2024b) I discussed the impact of climate change on endophytes, and in Part 3 (Muir 2024c), mycorrhizal fungi and their essential role in plant health and thus their importance to birds in all habitats.
The role of migratory birds in dispersal of seeds and fungal spores can be long-distance: eg, trans-equatorial; mid-distance (such as to inland lakes after rain, or even through rainforest); or short distance from one feeding place to another. This paper takes the concepts discussed in Part 3 to a more specific level: the role of mycorrhizae associated with mangroves and coastal mudflats that are used by birds along flyways.
Source: eaaflyway.net/the-flyway/
Mangrove ecosystems provide vital services including shoreline protection; water quality and climate regulation through carbon storage; pollutant uptake and nutrient cycling; and food and nursery grounds for commercially important fishes and invertebrates. Mangroves, seagrass beds and coral reefs are also interlinked because of the water that moves in and out with the tide and the animals that move with it.
Many fish, such as Barramundi, Snapper and Mackerel, and prawns, crabs, etc, that normally live offshore use mangrove habitats for part of their life cycle. Queensland Mud Crabs, for example, live in the mangroves but move out to sea to spawn. Many fish that spawn amongst mangroves provide food out at sea for larger fish such as Marlin that are strictly open ocean species.
Nutrients created amongst the mangroves fertilise the seagrass beds and coral reefs. The whole system is interlinked (Lovelock 1993). Also vital are the apparently bare mudflats! Work by Fasheng Zou et al. (2006) in China found that 69% of all waterbirds studied and 81% of all migrant birds studied used intertidal mudflats.
It is known that migratory birds transport seeds over hundreds of kilometres and mediate dispersal from mainland to oceanic islands. Up to 1.2% of birds that reached Alegranza, a small island of the Canary Archipelago, during their migration from Europe to Sub-Saharan Africa, carried seeds in their gut (Viana et al., 2016). The tens of thousands of birds making seasonal migrations each year may therefore transport millions of seeds and their associated fungi.
Birds migrating between the northern and southern hemispheres, including the East-Asian Australasian Flyway (EAAF) between Australia and northern Asia, may be involved in the transmission of fungal and bacterial endophytes and mycorrhizae. The commonality of endophytes in northern hemisphere and southern hemisphere plants is poorly known, but there is a definite possibility with respect to mangrove populations (and probably samphires and other salt-marsh species) that occur along the land margin from Australia to, at least as far north as, Kyushu in Japan (Tomomi Inoue et al., 2022).
Some birds fly non-stop from their over-wintering grounds in the southern hemisphere (and return), while others stop off at refuelling sites while going both ways, and by doing so can become “mid-distance” transporters from one mangrove location or mudflat to another.
Riza L (2020) found in a study in West Kalimantan, Indonesia, that several species of mycorrhizal fungi were associated with mangroves, and abundant spores were found around mangrove roots and in nearby mud. There are similar findings at Sungai Buloh wetlands in Singapore (see here).
Mycorrhizal fungi have been investigated in two mangrove swamps in south China and were found to be commonly associated with all the mangrove species investigated (Yutao Wang et al. 2010). They found that mycorrhizae significantly improved mangrove growth, resulting in greater plant height and biomass, as well as increased absorption of nitrogen, phosphorous and potassium. These findings suggest that mycorrhizal fungi play important roles in mangrove ecosystems.
Gupta et al. (2016) found a total of 45 mycorrhizal fungi species in mangroves including Sonneratia, Heritiera, Excoecaria, Derris, Bruguiera, Avicennia and Aegiceras, all genera that occur in Queensland. Thus, although there has been no research on Australian mangrove mycorrhizae, as far as I am aware, it is clear that there is a very high probability of mycorrhizal fungi being associated with ALL mangrove populations and their mudflats. Sengupta and Chaudhuri (2002) found that other members of the mangrove plant community were also mycorrhizal and even that many of the supposedly non-mycorrhizal plants, except the Cyperaceae, were, in fact, also mycorrhizal.
So, where do bird flyways fit in? Birds that stop off along the way while on long-distance migrations feed in mangroves and on nearby mudflats, and undoubtedly pick up fungal spores on their feathers, feet, and in their gut. They then transport these vital spores along the flyway to other locations, increasing local fungal diversity, and perhaps playing a vital role in intermixing of fungal genetics over tens to thousands of kilometres. These genetic transfers may be vital in maintaining mangrove populations, especially with the prospect of climate change forcing heat-intolerant mangrove and marsh plants to higher latitudes.
We know that protection and maintenance of mangroves and mudflats is vital (MangroveWatch Australia, 2016) to the preservation of migratory shorebirds, and a great deal of effort and money goes toward bird conservation.
However, we may not have considered that protection of these birds and maintaining of their populations may also be essential to the protection of mangrove, mudflat, seagrass beds and coral reefs that are vital to OUR economy and well-being.
References are available on email request to the author at: unit57.may@gmail.com