TIME FOR DINNER

 

 

BRITTLESTARS  ARE MMMM, MMMM, GOOD!!

 

 

Ophiuroids are  so cryptic and difficult to spot, you might think that even fish  can't find them. But in fact, they play a vital role in the food  chain! Ophiuroids are extremely popular prey items for fish and  invertebrates like crabs. Though there doesn't appear to be very much  to eat inside an ophiuroid, we know that they are eaten  because parts  of arms compose a large percentage of the gut contents of fish. We  can also study the percentage of arm regeneration in a population of  ophiuroids as a basic measure of predation pressure (with the  assumption that most predatory attacks are not lethal).

 

Since brittle  stars are so inconspicuous, it may seem that they are of little  significance. I can't argue that they are economically important to  humans- the aren't edible and, unlike sea stars, don't make very good  home decorations (only because they are too fragile of course)! But  they are important in the economy of the  coral reef, in that of the  deep-sea (where they are incredibly numerous) and in any habitat they  occur in. So, what are they good for?

WHAT DO OPHIUROIDS DO?

OPHIUROIDS AT WORK!

Burrowing  ophiuroids are also very important because of their role in  bioturbation, or stirring  up the sediment. The mud bottom in many  environments can become anoxic (lacks oxygen) just below the surface.  Few things can live there, but bioturbation by worms, molluscs and  other burrowing animals (brittle stars!) introduces oxygenated water  further into the mud because the water enters their burrows. The  stirring of the sediment not only introduces oxygen and other water  soluble compounds, but also organic nutrients (just like earthworms  are good for a garden). The brittle stars which live in this  environment have extraordinary adaptations of their respiratory  system to survive in this nonetheless harsh environment.

OPHIUROIDS ARE GREAT HOUSEKEEPERS!

Some ophiuroids  have a more specialized role  than just being prey! They are a partner  in mutualistic relationships with other animals, particularly sponges  and sessile cnidarians (such as black corals). In these  relationships, both the brittle star and the  host animal benefit.  Ophiuroids that live in sponges inhabit the large canals or openings  in the sponges (called ostia). Sponges survive by filtering water and  capturing small food particles. After a time, the  surface of the  sponge may become clogged with particles that are too large to  efficiency of the sponge's feeding currents. During the night, the  arms of brittle stars are often visible "sweeping" over  the  surface of the sponge. The rest of the brittle star remains safely  hidden inside the sponge. The brittle star removes the large debris  clogging the sponge and consumes it. So, the sponge is cleaned, and   the ophiuroid gets a meal and a safe place to live.

ITS LIKE HAVING A PARAMEDIC  AROUND THE HOUSE...

BRITTLE STARS SAVE LIVES!

Other brittle  stars are associated with some types of corals, especially black  corals. These corals are also  subject to being clogged by debris or  sediment because of the environment they live in. This is a  particularly dangerous situation for the coral, which might be  killed. The ophiuroids clean the coral of this sediment and debris,  and in some cases, this has been though to save the life of the coral  host colony! Click below for a photo of this unusual ophiuroid!