Sure, here are the correct forms of the words in parentheses:

Up to now, the (0) **difficulties** in a fisherman's working life have been quite obvious, but now they face a new threat from (**MICROSCOPIC**) plant-like organisms. These creatures, which are (**INVISIBLE**) to the naked eye have been (**IDENTIFIED**) as causing American fishermen to 'lose their memory'. (**SCIENTISTS**) investigating the phenomenon observed that the fishermen affected became so (**FORGETFUL**) that their lives were thrown into (**CONFUSION**). Amongst other things, they were unable to remember to take important fishing (**EQUIPMENT**) with them when they left for work and they (**FREQUENTLY**) forgot where they were going in the middle of a journey. (**LUCKILY**) the memory loss is reversible. Within six months the fishermen's (**BEHAVIOR**) had returned to normal.