Monitoring
Biogeography
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(Click to enlarge) |
The accumulation of data by the CPR
survey has demonstrated clear patterns in the distribution of
plankton on a broad geographical scale, relating to latitudinal
gradients, the position of the current systems and the proximity of
the shelf seas. A wealth of data has been acquired on diurnal,
annual and long-term changes of the plankton community.
An 'Atlas of Plankton for the North Atlantic' has been produced
from decades of past data sets and continues to be improved and
added to as the survey proceeds. Preferred ranges of plankton
species now help us to determine changes in distribution that may
be effected by changes in sea temperature and climate.
Monitoring unusual events
and
non-indigenous species
The introduction of non-indigenous marine plankton species can
have considerable ecological and economic impact on regional seas.
Efforts to monitor invasive marine species are at best fragmented,
as they are typically only noticed when the species reaches
nuisance status, so there are few case histories of their spatial
and temporal expansion. In recent years there were a number of
species recorded in the CPR survey that were outside their expected
range. These included Penilia avirostris (a cladoceran),
Stomatopoda (mantis shrimp) and Clausocalanus sp (Johns,
unpublished). These three species are more commonly found in the
warmer waters of the Bay of Biscay and the Mediterranean Sea. Their
appearance in the North Sea may indicate a significant
environmental change.
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| Coscinodiscus wailseii. |
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| C.wailesii distribution map from 1985. |
The CPR survey has been used to trace the expansion and subsequent persistence of the large diatom, Coscinodiscus wailesii, which was first recorded in the English Channel in 1977. C.wailesii was originally known only from the Pacific coast of North America, and in Chinese and Japanese waters of the North Pacific. It is presumed that it made its way from its native seas via the ballast water of international ships. Since its first appearance it has become a significant member of the diatom community and is now well established in the continental shelf seas of NW Europe. In the southern North Sea it may now reach such high abundance that it can dominate the phytoplankton biomass. The ecological importance of such invasive species can therefore have potential ecosystem effects by out-competing native species for resources and space, reducing biodiversity, and effecting the exploitation of native herbivores (Edwards et al, 2001)