Fróðskaparrit - 01.01.2002, Page 153

NÝTT INNAN VÍSINDI 2001
151
Ritgerðin lýsir sambandið ímillum tey
einstøku liðini í føðiketunum og møguligar
orsøkir til broytingarnar millum árini.
Abstract
This thesis is a study of the plankton com-
munity on the Faroe Shelf during the peri-
od 1989-1999. The Shelf essentially has its
own plankton community, which is rela-
tively well isolated from those in the sur-
rounding oceanic environment. On the
Faroe Shelf, the hydrographic conditions,
nutrient concentrations, and the phyto- and
zooplankton production, abundance, and
species composition are markedly different
from those in the oceanic environment out-
side the Shelf. The water mass is very tur-
bulent and since the pool of nutrients in the
Shelf water is limited, the nutrient concen-
trations may decrease much during spring
and summer.
During spring, diatoms dominated
among the phytoplankton on the Faroe
Shelf. During summers with high nutrient
concentrations, diatoms continued to dom-
inate throughout the productive season.
However, in years with low nutrient con-
centrations (1993-1995), diatoms were out-
competed during summer by the prymne-
siophyte, Phaeocystis pouchetii. The zoo-
plankton community is basically neritic.
During spring and summer, while the zoo-
plankton in the surrounding oceanic envi-
ronment is dominated by the copepod
Calanus jinmarchicus, the zooplankton in
the Shelf water is largely dominated by ner-
itic copepods, mainly Acartia longiremis
and Temora longicornis. C. finmarchicus
occurs in interannually, highly variable
abundance in the Shelf water. Meroplank-
tonic larvae, mainly barnacle larvae, may
also be abundant, and decapod larvae and
ichthyoplankton are common on the Shelf
during spring and summer.
During the period 1989-1997, the mid-
summer abundance of C. fmmarchicus
(which originally is advected onto the Shelf
from the open ocean) fluctuated between ~
400 copepods m'3 in 1989 and ~ 25 cope-
pods m'3 in 1994. During the same time pe-
riod, the neritic copepods increased from
-120 m'3 to 450 m'3i. Hence, the system
gradually switched from a highly oceanic
influence to a much more neritic ecosystem
in regards to zooplankton species composi-
tion. Consequently, the midsummer zoo-
plankton biomass on the Shelf fluctuated
by a factor of ten during the same period. A
variable inflow rate (largely induced by
wind) is likely a major explanation for the
variable abundance of C. finmarchicus.
The main advective area is considered to be
on the western and north-western shelf re-
gions.
Primary production usually increases
earlier in spring on the Shelf than offshore.
However, the timing of the spring bloom
development, as well as the phytoplankton
biomass and primary production, may fluc-
tuate considerably between years. An in-
dex of the calculated mean potential new
primary production in the Shelf ecosystem
during spring and early summer showed
variability by a factor of four, from very
low productivity at the beginning of the
studied period to the highest level in 1995.
There is a clear inverse relationship be-
tween the calculated new primary produc-