THE MARINE FAUNA OF THE BLACKWATER ESTUARY 35
Carcinus maenas Linne Shore Crab
Very common on the sea shore, in saltings and on the bottom
of the Blackwater, breeding in spring and summer. Juveniles are
abundant on the shores in the autumn, but later migrate below
low water mark as they out-grow the limited cover provided by
the small shells and stones. Recorded from the Blackwater by
Cole (1888) and Walne (1956). Numerous in 1960 but declined
during the winters of 1961-62 and 1962-63. Generally more
abundant in 1965 than in 1960 showing a rapid recovery from the
effects of the winter.
PINNOTHERIDAE
Pinnotheres sp. Pea Crab
Occasional records. A commensal inside the mantle cavity of
the mussel Modiolus modiolus on stations C.1 (18.8.1960), C.2
(18.8.1960), C.3 (18.8.1960), and North Buxey Beacon (19.7.1962),
and in Mytilus edulis fouling ships anchored in the Blackwater
(25.4.1960). The species may be P. pinnotheres.
Maiidae
Hyas araneus (Linne) Spider Crab
Commonly taken in dredge and trawl samples from bottoms of
shell and stones. Recorded as occasional by Cole (1888) and as
present between Osea Island and Bradwell by Walne (1956). It
has been found from Thirslet seawards in the recent survey. The
species was not adversely affected by the severe winter of 1962-63
and showed some increase in numbers subsequently, perhaps in
response to the decline of Carcinus maenas. In 1964 and 1965
there appears to have been a decline in both inshore and off-
shore populations. 'Berried' females are common in the winter
and spring and juveniles may be found in the benthos in late
summer.
Macropodia rostrata (Linne)
Originally recorded from the Blackwater by Cole (1888) as
Stenorhynchus tenuirostris. Normally found on clean shelly
bottoms in association with hydroids. Common in 1960, 'berried'
females were observed in June, and more common in 1961 and
1962. After the winter of 1962-63 the species declined to an un-
detectable level but there was some recovery by 1965.
Sub-Phylum ARACHNIDA
Class ACARINA
Order Prostigmata
Halacaridae
Possibly two species, not fully identified, obtained from
hydroids dredged in Thirslet Creek and on stations N.1 and N.2
in May 1965. Probably common where hydroids occur.