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Crust Aging and Mechanisms of Crust Death
In observing Mastocarpus crusts, about the biggest you will see
is 1.0 meter in diameter. I found a few that were almost 70 cm on the shore
along the marine station. I heard about people making estimates for crustose
lichen ages by knowing their growth rate and measuring crust diameters.
Mastocarpus tetrasporophytes can grow from 1-2 cm in diameter
in a year under laboratory regulated conditions. Taking this as a rough
estimate of natural growth rate, some of those large crusts could be
almost 70 years old. Considering that most of the algae are annuals
or live only a few years, 70 years is ancient. Considering that bull
kelp will grow a thick stipe about 20m in one year, 1-2cm per year
is really slow. An experiment showed that flies with a higher metabolism
died earlier than flies with a lower metabolism. Could the same thing
be true for algae?
Finding out that an alga might grow to be 70 years old is really neat,
but why not older? What are mechanisms of crust death?
Epiphyte smothering can occur, and other intertidal organisms could crowd
out the slow-growing crust, but how then do we get a 70 cm wide crust?
Some other crustose algae have been observed to shed their cuticle to slough
off epiphytes. Mastocarpus has not been observed to do the same, but
it is a possibility. The crust could also produce secondary metabolites that
ward off epiphyte colonization. There has to be some explanation.
Mastocarpus pages copyright W. Ludington 1999