Polymetallic nodules are essential for food-web integrity of a prospective deep-seabed mining area in Pacific abyssal plains.

Polymetallic nodule fields provide hard substrate for sessile organisms on the abyssal seafloor between 3000 and 6000 m water depth. Deep-seabed mining targets these mineral-rich nodules and will likely modify the consumer-resource (trophic) and substrate-providing (non-trophic) interactions within the abyssal food web. However, the importance of nodules and their associated sessile fauna in supporting food-web integrity remains unclear. Here, we use seafloor imagery and published literature to develop highly-resolved trophic and non-trophic interaction webs for the Clarion-Clipperton Fracture Zone (CCZ, central Pacific Ocean) and the Peru Basin (PB, South-East Pacific Ocean) and to assess how nodule removal may modify these networks. The CCZ interaction web included 1028 compartments connected with 59,793 links and the PB interaction web consisted of 342 compartments and 8044 links. We show that knock-down effects of nodule removal resulted in a 17.9% (CCZ) to 20.8% (PB) loss of all taxa and 22.8% (PB) to 30.6% (CCZ) loss of network links. Subsequent analysis identified stalked glass sponges living attached to the nodules as key structural species that supported a high diversity of associated fauna. We conclude that polymetallic nodules are critical for food-web integrity and that their absence will likely result in reduced local benthic biodiversity.

Discorhabdin alkaloids from Antarctic Latrunculia spp. sponges as a new class of cholinesterase inhibitors.

The brominated pyrroloiminoquinone alkaloids discorhabdins B, L and G and 3-dihydro-7,8- dehydrodiscorhabdin C, isolated from methanol extracts of two specimens of Latrunculia sp. sponges collected near the Antarctic Peninsula, are here demonstrated for the first time to be reversible competitive inhibitors of cholinesterases. They showed Ki for electric eel acetylcholinesterase of 1.6-15.0 µM, for recombinant human acetylcholinesterase of 22.8-98.0 µM, and for horse serum butyrylcholinesterase of 5.0-76.0 µM. These values are promising when compared to the current cholinesterase inhibitors used for treatment of patients with Alzheimer's disease, to counteract the acetylcholine deficiency in the brain. Good correlation was obtained between IC50 data and results by molecular docking calculation on the binding interactions within the acetylcholinesterase active site, which also indicated the moieties in discorhabdin structures involved. To avoid unwanted peripheral side effects that can appear in patients using some acetylcholinesterase inhibitors, electrophysiological experiments were carried out on one of the most active of these compounds, discorhabdin G, which confirmed that it had no detectable undesirable effects on neuromuscular transmission and skeletal muscle function. These findings are promising for development of cholinesterase inhibitors based on the scaffold of discorhabdins, as potential new agents for treatment of patients with Alzheimer's disease.