These straps are used to bind the batim to one's arm/hand (Tefillin shel Yad) and to one's head (Tefillin shel Rosh) in obedience to Deuteronomy 6:8 (And thou shalt bind them for a sign upon thine hand, and they shall be as frontlets between thine eyes).
Given that a single mangrove area can produce as much as four tons of detritus per year, the mud crab's work as a decomposer is a primary part of the detritus-based food ecology that supports fisheries populations.
A decomposer is an organism that breaks down waste and dead organisms into nutrients for the producers. These can be fungi, animals, bacteria, etc... An ecological niche is the role or function the organisms has in its ecosystem. For example, an owl's niche would be that of a hunter in his ecosystem. I hope this helps a bit.