Mangrove seedlings collected in muddy shallows in the pond. Clumps of Gracilaria have also floated in, and some collect near the new roots.
There are some new project developments at hand! In addition to examining invasive algal canopies, I've also started some preliminary work on a new structure-forming alien species: red mangrove (Rhizophora mangle). Mangroves, while important nutrient sources and nursery grounds in their native habitats, are alien species in Hawai'i, with quite different effects on the native ecosystem. Though mangroves are a vascular plant, they have some similarities to the Gracilaria canopy. Like Gracilaria, mangroves slow down water flow. They are also incredibly effective at trapping fine sediments and drawing down nutrients and heavy metals. This ability to trap particles is what led people to introduce them to the fishpond in 1922: upstream agriculture and land development was releasing large amounts of sediment and excess nutrients into the stream, and mangroves seemed to be a good biological solution. However, now the mangroves have grown over many parts of the pond, and their negative impacts on pond function are more obvious. As mangrove roots trap fine sediment and shed leaves, they make the underlying sediment anoxic, so that worms and other sediment-dwelling organisms can't survive. The mangrove canopy provides habitat for other alien species (like tilapia; more on these later) which threaten fish stocks. Currently I'm examining the distribution of infauna (organisms that live inside the sediment) in the pond in areas where mangroves have invaded and areas where mangroves have been removed.
A sediment core before being sieved. After a core is taken, the contents are run through a 500 µm sieve to remove fine sediments. Macrofauna (organisms visible to the naked eye) are retained on the mesh, counted and classified.
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