17
ON THE VARIATIONS IN NUMBERS AND
HABITAT OF MARINE ANIMALS ON THE
COAST OF ESSEX DURING THE LAST
TEN OR TWELVE YEARS.
By H. O. SORBY, L.L.D., F.R.S. F.L.S. &c.
During the last ten or twelve years I have spent a good deal
of time in collecting marine animals along the coast, and in the
estuaries, of Essex and the adjoining parts of Suffolk, as they
were floating near the surface or by using a dredge or small
trawl, or by examining the mud or shores exposed at low water;
but paying little attention to such as are less than 1/2-inch in
length. In doing this, I have been much struck by the great
variations that have occurred from year to year, and with the
remarkable contrast between what I now find in some localities,
and what I found 10 or 12 years ago, or even more recently.
Some of the changes may be, and probably are, of a temporary
character, and the original conditions may be restored in years to
come; but some seem as if likely to be permanent. In the
earlier years I did not expect to be in the district so long and so
continuously, and never anticipated that I should witness any
striking changes, and so unfortunately I omitted to take such
detailed notes as would now have been very valuable. It was
only by degrees that the great extent of the changes became
apparent. In any case it now appears to me desirable to put
some of the facts on record, since they may be of much interest
in years to come.
I have not noticed any material change in the number of
some animals. Of these I may mention the Common Shore
Crab (Carcinus maenas), the Hermit Crab (Pagurus bernhardus), the
common Nereis (N. versicola), Nepthys hombergii, Arenicola marina,
Sabella pavonia, Lanice conchilega, Cirratulus cirratus, Doris pilosa,
Echinus miliaris, Solaster papposus, Asterias rubens, Ophiura texturata,
Ophiothrix fragilis, and several species of simple and compound
Ascidians, such as Ascidiella virginea and aspersa, Ciona intestinalis,
done grossularia, Molgula arenosa, Botrytioides rubrum and leachii
and Botryllus schlosseri and polyclyclus.
There has, however, been a great change in the case of some
other animals. I do not take into account such as are so rare
that very few specimens have been seen, since in such cases too