Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, 4870, QLD, Australia; College of Science and Engineering, James Cook University, Cairns, 4870, QLD, Australia.
Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, 4870, QLD, Australia.
Mar Environ Res. 2020 Dec;162:105183. doi: 10.1016/j.marenvres.2020.105183. Epub 2020 Oct 10.
The Great Barrier Reef (GBR) contains extensive seagrass meadows with abundant and diverse herbivore populations. Typically, meadows in the region are multi-species and dominated by fast growing opportunistic seagrass species. However, we know little about how herbivores modify these types of seagrass meadows by grazing. We conducted the first megaherbivore exclusion study in the GBR at Green Island (Queensland) to understand how green turtle grazing structures these multi-species tropical seagrass meadows. After excluding green turtles for three months, we found that grazing only impacted seagrasses at one site, where green turtles created a grazing plot by actively feeding on both above and below ground seagrass structures, a rare observation for the species. Within this grazing plot at the end of the experiment, the un-caged control treatments open to grazing had a 60% reduction in both above and below ground biomass, and shoot height was reduced by 75%, but there was no impact of grazing on the seagrass species mix. Our study shows that grazing plot formation by green turtles occurs in GBR fast growing seagrass communities and reduces both above and below ground seagrass biomass, this behaviour may be targeting elevated leaf nutrients, or nutritional content of rhizomes. This study is the first documented case of grazing plot formation by green turtles in the GBR and suggests that grazing pressure has a major influence on seagrass meadow structure.
大堡礁（GBR）拥有广阔的海草草甸，拥有丰富多样的食草动物种群。通常，该地区的草地是多物种的，以生长迅速的机会主义海草物种为主。然而，我们对食草动物通过放牧来改变这些类型的海草草甸知之甚少。我们在昆士兰州绿岛（Green Island）进行了大堡礁的首次大型食草动物排除研究，以了解绿海龟放牧如何构建这些多物种热带海草草甸。在排除绿海龟三个月后，我们发现放牧仅对一个地点的海草产生影响，在该地点，绿海龟通过积极食用地上和地下的海草结构来创建放牧区，这是该物种的罕见观察。在实验结束时的放牧区内，未被笼养的对照处理区可自由放牧，地上和地下生物量分别减少了 60%，地上部分的高度减少了 75%，但放牧对海草物种组成没有影响。我们的研究表明，绿海龟在大堡礁快速生长的海草群落中形成放牧区，并减少地上和地下的海草生物量，这种行为可能针对的是叶片养分的增加，或者是根茎的营养含量。本研究首次记录了绿海龟在大堡礁形成放牧区的情况，表明放牧压力对海草草甸结构有重大影响。
