Welcome to PB. Here is a link to the algae. I don't think that is a problem that would cause the LMB to disappear. It reflects a nutrient rich pond.
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=92633#Post92633 archives on Filamentous Algae (FA) identification and control
If you have seen yoy LMB then you have adult LMB. The pic you posted looks like a healthy LMB. Can you give us some info on the situation - like a time line and description of events from stocking to now ?