Ecology of mesophotic macroalgae and Halimeda kanaloana meadows in the Main Hawaiian Islands.

摘要

This dissertation focused on the distribution and abundance of mesophotic macroalgal assemblages (MMA) in mesophotic coral ecosystems (MCE) in the Main Hawaiian Islands (MHI), with an emphasis on the natural history and recovery response of Halimeda kanaloana meadows.;Submersibles, a remotely operated vehicle, and technical diving were used to survey MMA at 59 sites from 40 to 212 m depths around O'ahu, Maui, Lana'i, Kaho'olawe and Moloka'i. Seventy-six species of frondose macroalgae were described. Thirty species were new records for Hawai'i or new species, with 45% of the flora only found at mesophotic depths. Eleven dominant algal assemblages were encountered, covering several hundred meters to kilometers squared. Mesophotic algal meadows of an invasive species (Avrainvillea amadelpha) and a proposed new genus (resembling Udotea) were discovered off O'ahu. MMA in the MHI are abundant, diverse, and spatially heterogeneous. The biology of mesophotic macroalgae will have substantial implications for tropical food web ecology, biodiversity, and biogeography. MCE in Hawai'i offer decades of research potential given their areal extent, ecological importance, and reservoir of genetic diversity.;H. kanaloana meadows cover large portions of the sand-dominated environment in the MHI, yet little is known about their ecology or contribution to carbonaceous sediments. To help close this gap, the growth, densities, lifespan, herbivory, quantity of calcium carbonate (CaCO3), and reproduction of Halimeda meadows were surveyed at multiple locations over a four year period around Maui from 10 to 85 m depths. Halimeda were generally long-lived perennials, with rapid growth and high densities (up to 314 plants per m2), producing up to 1883 g CaCO3 m-2 y-1. Deep psammophytic algal meadows appear to be an integral and highly productive part of the tropical ecosystem in Hawai'i.;Both natural and anthropogenic disturbance were observed in H. kanaloana meadows, stimulating a manipulative experiment on the recovery of Halimeda to anchor scar damage at 23 m depth. Recovery in a near-by anchor scar at 27 m depth was also monitored. Recovery in the experiment and anchor scar occurred in 1½ to 2 years. The use of moorings would be beneficial to the health and stability of deep Halimeda meadows.