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This paper not to be eited without prior reference to the author
International Council for
The Exploration of the Sea
C.M.l988/L: 3D
Biologieal Oceanography
Committee
Ceratium fusus in the North Sea in 1987.
by
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J.M.Colebrook
Plymouth Marine Laboratory
Prospect Plaee, West Hoe, Plymouth PLl 30H
England
The da ta from the Continuous Plankton Recorder survey for 1987.
have 1ndicated a substantial increase in the abundance' of the
dlnoflagellate Ceratium fusus in the open waters of .the North Sea
especially in central and northern areas. With respect to this kind of
event 1n the survey da ta it is preferable to wait for a seeond if not
a third year to provide data to conflrm or deliniate the event.
However, 1n v1ew of the occurrence and nature of a number of widely
reported 1ncidents (sea birds, seals, blooms) in the North Sea over
the last year and a half or so, and also in view of the uncertain
future of the Continuous Plankton Recorder survey. it was decided to
prepare this brief report.
Figure 1 contains graphs of annual means of abundance of C. fusus
for th1rty years from 1958 to 1981 for s1x areas coverlng the Horth
Sea. In the northern areas the abundance of C. fusus 1n 1987 was aore
than 5 tlmes the long term-average-(l958 ·to-1986} __In-the_central__
areas 1t,was about 3 times and in the south It was about twice the.
long term average.
(
Figure 2 conta1ns graphs, for the same" areas. of the average-·-seasonal cycles of C. fusus for 1985 "tol981 (dashed lines) cOIIpared
with 1958 to 1984 (solid lines). The graphs show that there were no
marked differences in the form of the seasonal cycles between the two
periods other than in amplitude. although the cycles -were perhaps
slightly earlier in the period 1985 to 1987.
Flgure 1 showi that C fusus has; on the whole. been inereasing in
abundanee slnee about 1980. Ouring this period there has been an
increase in the abundance of manyspec1es of both phytoplankton and
zooplankton and It i9 only in 1987 that.the inerease 1n numbers .of C.
fusus has been partieularly marked in relation to the general upward
trend. Figure 3 eontains graphs of the first pr1ncipal components of
the annual fluetuat10ns in the abundance ;-- of. zooplankton
and ..__
phytoplankton for the north-east Atlantic and the North Sea for 1948
to 1987. These are updates of graphs presented 1n Colebrook et Al.
1984.
Over the last thirty years, a coherent group of Ceratium species.
iricludlng. C. fusus. C', furea. C. l1neatum. C. triPos and C. horrldum,
have tended to show basically s1milar patterns ofyear-to-year change
in abundanee. in the north-east Atlantie as weIl as in the North Sea
(Colebrook. 1982). C. fusus in the North Sea in 1987 presents a clear
break in this pattern. The marked 1nerease in abundanee is conflned to ~
the North Sea and eonf1ned to C. fusus, aithough C. furea does showar,
s1mllar pattern. It ls noth1ng like as pronounced.
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lt is worth noting that C. fusus has oecurred in phytoplankton
blooms in the coastal waters of the North Sea on several occaslons.
Mommaerts (1985-86) lists six oeeurrences of blooms of C. fusus in the
lCES area in the period 1980 to 1983.
lt has been argued that whlle the _year-to-year .. ehanges In the
abundance of plankton in the North Sea are reflected 1n similar
ehanges taking p1aee in the open waters of the north-east Atlantlc,
then these changes can be attributed to 1ong~term variations in
climate (Colebrook, 1985. 01ckion •. et Al. 1988) as opposed to
anthropogenie influences. The marked iricrease in theabundanee of
CeratiUm fusus, if this eontinues, may be presumed to· represent a
response to nutrient enricrument on a much larger seale than has
previously been observed.
REFERENCES
Colebrook, J.M. 1982 Continuous plankton records: phytoplankton,
zooplankton and environment. north-east - -Atlantic and North Sea,
1958-1980. Oceanologica Acta. 5:473-480.
Colebrook. J.M •• 1985. Sea surface temperatureand zooplankton.
Sea, 1948 to 1983. J. Coris. int. Explor. Mer; 42: 179-l85~
North
Colebrook. j .M.. Robinson. G.A. ,Hunt ~ H.G. ,_.Roskell._J. ,John." A.W .G~ •
Bottrell, H.H.~ Litidley,J~A.,ColUtis. N~R. aiidHalliday. N~C. 1984
Continuous plankton reeords:.a pOssible reversal in.the.downward trand
in the abuDdance of the plankton of the North Ses and the Northeast
Atlantlc. J. Cons. Int. Explor. Mer. 41: 304:306.
01ckson. i.R. KellY. P.M~, Colebrook.J .K~. Wooster, W.S. snd Cushing~
D.R .. 1988. North winds aud production
the eastern North-Atlantlc.--J. Planke Res., 10: 151-169.
in
Mommaerts. J~P. 1985-1986. Observations of phytoplankton blooms in the
leES area. Annales Biologiques, vols 39-41.
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