Fig. 14.29 Histogram bars: time-series estimates of particulate organic-carbon flux
from traps at 3000 m above the Porcupine Abyssal Plain (49°N, 16°30′W) in the NE
Atlantic. Continuous line (mostly above the bars): satellite estimates of chlorophyll
concentration averaged for a 200 km radius around the trap station.
(^) (After Lampitt et al. 2010b).
Lampitt et al. (2009) have suggested, based on continuous plankton recorder data,
that late-summer population bursts of phaeodarians, 0.1 to 1 mm protists with
siliceous skeletal bits embedded in a protein matrix and that feed with sticky
pseudopods along fine opal spines, are likely to be responsible for bringing down
large POC flux. Neither phaeodarians nor their spicules are abundant in trap materials,
spicules are thought to dissolve during descent, but mini-pellets (protozoan feces) can
be abundant in late summer trap samples. They were in 1990. Unfortunately, the 1999
and 2001 samples were not suitable for the necessary microscopic examination.
Nevertheless, speculations of this sort do provide hypotheses for later testing.
(^) No SCOC data were gathered with the PAP flux time-series, but a very close
examination was made of the variations in abundance and composition of trawl-
captured megafauna by Billett et al. (2010). Swaths of 6 to 15 hectares were swept
with an 8.6 m wide otter trawl in the vicinity of PAP, but spread out enough on the
abyssal plain to evaluate the generality of faunal shifts. Sea cucumbers (holothurians)
were the dominant group, >60% of individuals and ∼90% of biomass. Up to 1995,
this dominance was shared by six species. Probably starting in 1995, but not sampled
until 1996, there was an increase of the sea cucumber Amperima rosea. It had not
been present before, but by 1996 it was the numerical dominant. Also increasing were
Ellipinion molle (holothurian) and Ophiocten hastatum (ophiuroid). Amperima was
present for four years, declined, and then went through a shorter uptick – not shared
with E. molle – in 2001 to 2003. Then both species dropped to low levels; the