FAUNA AND FLORA O F MANGROVE SWAMPS
209
worms on the land and lugworms (Arenicola spp.) on temperate zone
mud flats.
The digging techiiiqucs used are perhaps best described as shovelling
and bulldozing. The maxillipeds and anterior walking legs are normally
held in thc position shown in Fig. 51, and the container formed by these
would appear to scoop up the mud somewhere down below. The mud
is then brought LIP and deposited outside one of the entrances on the
mound.
Feeding has never been described for Thalassina, and nothing is
known apart from a note by Johnson (1961) to state that its gut is
always full of mud, a statement which 1 can confirm. One can only
presume that it makes use of the bacteria and other micro-organisms
which live in the mud.
b. Effects of temperuture and humidity on crustaceans
The crabs living in the mangal are above ground and foraging for
much of the ebb tide. But there may be days on end when, for one
reason or anothcr, only a very few crabs are encountered. They tend to
be more numerously visible on the days of high spring tides, and
scarcely dppear at all on the days around the lowest neap tides. To
what is this due? They tend also to be more numerously visible in
warmer weather. At Inhaca, July 1964 was, taken by and large, colder
than is usual and between 21 June a3d 2 July few specimens were seen
a t any time during a spring tide series. Was i t temperature that kept
them down? Thc air temperatures during that period were between
12" and 23"C, which are well above the lethal minimum. The crabs
were not moulting for they were hard when dug up and no moulting
specimens were obtained.
The temperature relationships of species of Xesarma do not appear
to have becn studied. The relationships of the five species of Uca
common at Inhaca werc studied by Edney (1961). He showed that the
normal body temperature of each species was lower than that of the air
a t the timc of measurement. Each showed an upper lethal temperature
which was quite sharp. For Uca inversa which lives on open sunny
sandflats the upper lethal temperature was 43.3"C. For Uca lactea
f. annulipes which lives in sunny glades or along the fringes of the
mangal or among the plant cover of Xesuvium, or Arthrocnemum, all
places where shelter is close by, the upper lethal temperature was
42.1"C. For Uca gaimardi (= U . chlorophthalmus of Edney's paper) it
was 40.8"C and for U . urvillei, 40°C : both of these live in the shelter of
bushes and often occur together. Uca vocans (= U . marionis) was
intermediate a t 41.4"C. This quite high level puzzled Edney but in fact
209
worms on the land and lugworms (Arenicola spp.) on temperate zone
mud flats.
The digging techiiiqucs used are perhaps best described as shovelling
and bulldozing. The maxillipeds and anterior walking legs are normally
held in thc position shown in Fig. 51, and the container formed by these
would appear to scoop up the mud somewhere down below. The mud
is then brought LIP and deposited outside one of the entrances on the
mound.
Feeding has never been described for Thalassina, and nothing is
known apart from a note by Johnson (1961) to state that its gut is
always full of mud, a statement which 1 can confirm. One can only
presume that it makes use of the bacteria and other micro-organisms
which live in the mud.
b. Effects of temperuture and humidity on crustaceans
The crabs living in the mangal are above ground and foraging for
much of the ebb tide. But there may be days on end when, for one
reason or anothcr, only a very few crabs are encountered. They tend to
be more numerously visible on the days of high spring tides, and
scarcely dppear at all on the days around the lowest neap tides. To
what is this due? They tend also to be more numerously visible in
warmer weather. At Inhaca, July 1964 was, taken by and large, colder
than is usual and between 21 June a3d 2 July few specimens were seen
a t any time during a spring tide series. Was i t temperature that kept
them down? Thc air temperatures during that period were between
12" and 23"C, which are well above the lethal minimum. The crabs
were not moulting for they were hard when dug up and no moulting
specimens were obtained.
The temperature relationships of species of Xesarma do not appear
to have becn studied. The relationships of the five species of Uca
common at Inhaca werc studied by Edney (1961). He showed that the
normal body temperature of each species was lower than that of the air
a t the timc of measurement. Each showed an upper lethal temperature
which was quite sharp. For Uca inversa which lives on open sunny
sandflats the upper lethal temperature was 43.3"C. For Uca lactea
f. annulipes which lives in sunny glades or along the fringes of the
mangal or among the plant cover of Xesuvium, or Arthrocnemum, all
places where shelter is close by, the upper lethal temperature was
42.1"C. For Uca gaimardi (= U . chlorophthalmus of Edney's paper) it
was 40.8"C and for U . urvillei, 40°C : both of these live in the shelter of
bushes and often occur together. Uca vocans (= U . marionis) was
intermediate a t 41.4"C. This quite high level puzzled Edney but in fact