Papers by Jordan Grigor
Growth and reproduction of the chaetognaths Eukrohnia hamata and Parasagitta elegans in the Canadian Arctic Ocean: capital breeding versus income breeding
Journal of Plankton Research
In Arctic seas, primary production and the availability of food for zooplankton are strongly puls... more In Arctic seas, primary production and the availability of food for zooplankton are strongly pulsed over the short productive summer. We tested the hypothesis that Eukrohnia hamata and Parasagitta elegans, two similar and sympatric arctic chaetognaths, partition resources through different reproductive strategies. The two species had similar natural longevities of around 2 years. Eukrohnia hamata, which occurred at epi- and meso-pelagic depths, spawned two distinct broods in autumn and spring. Offspring production coincided with drops in the frequency of E. hamata with visible lipid reserves, characteristic of capital breeders. Growth was positive from April to January and negative in February and March. Growth and maturation were similar for the two broods. Storage reserves contained in an oil vacuole may allow E. hamata to reproduce and grow outside the short production season. Parasagitta elegans produced one brood in summer–autumn during peak production in near-surface waters, characteristic of income breeders. In winter, P. elegans co-inhabited meso-pelagic waters with E. hamata, where it neither grew nor reproduced. As the Arctic warms, the development of an autumn phytoplankton bloom could favour the summer–autumn brood of P. elegans.
Assessments of Carbon Stock Hotspots in Nicaragua and Costa Rica
Central American Biodiversity, 2015
ZOOMIE v 1.0 (Zooplankton Multiple Image Exclusion)
We deployed the Lightframe On-sight Keyspecies Investigation
(LOKI) system, a novel underwater im... more We deployed the Lightframe On-sight Keyspecies Investigation
(LOKI) system, a novel underwater imaging system providing
cutting-edge imaging quality, in the Canadian Arctic during fall
2013. A Random Forests machine learning model was built to
automatically identify zooplankton in LOKI images. The model
successfully distinguished between 114 different categories of
zooplankton and particles. The high resolution taxonomical tree included
many species, stages, as well as sub-groups based on animal
orientation or condition in images. Results from a machine learning
regression model of prosome length (R2 = 0.97) were used
as a key predictor in the automatic identification model. Model internal
validation of the automatic identification model on test data
demonstrated that the model performed with overall high accuracy
(86%) and specificity (86%). This was confirmed by confusion
matrices for external testing results, based on automatic identifications
for 2 complete stations. For station 101, from which images
had also been used for training, accuracy and specificity were 85%.
For station 126, from which images had not been used to train the
model, accuracy and specificity were 81%. Further comparisons between
model results and microscope identifications of zooplankton
in samples from the two test stations were in good agreement
for most taxa. LOKI’s image quality makes it possible to build accurate
automatic identification models of very high taxonomic detail,
which will play a critical role in future studies of zooplankton dynamics
and zooplankton coupling with other trophic levels.
Polar Biology 38:87-98, Oct 15, 2014
The annual routines and seasonal ecology of herbivorous zooplankton species are relatively well k... more The annual routines and seasonal ecology of herbivorous zooplankton species are relatively well known due to their tight coupling with their pulsed food source, the primary production. For higher trophic levels of plankton, these seasonal interactions are less well understood. Here, we study the mid-winter feeding of chaetognaths in high-Arctic fjord ecosystems. Chaetognaths are planktivorous predators which comprise high biomass in high-latitude seas. We investigated the common species Parasagitta elegans around the Svalbard archipelago (78–81°N) during the winters of 2012 and 2013. Our samples consisted of individuals (body lengths 9–55 mm) from three fjords, which were examined for gut contents (n = 903), stable isotopes, fatty acid composition, and maturity status (n = 352). About a quarter of the individuals contained gut contents, mainly lipid droplets and chitinous debris, whilst only 4 % contained identifiable prey, chiefly the copepods Calanus spp. and Metridia longa. The δ15N content of P. elegans, and its average trophic level of 2.9, confirmed its carnivorous position and its fatty acid profile [in particular its high levels of 20:1(n-9) and 22:1(n-11)] confirmed carnivory on Calanus. Observations of undeveloped gonads in many of the larger P. elegans, and the absence of small individuals <10 mm, suggested that reproduction had not started this early in the year. Its average feeding rate across fjords and years was 0.12 prey ind.−1 day−1, which is low compared to estimates of spring and summer feeding in high-latitude environments. Our findings suggest reduced feeding activity during winter and that predation by P. elegans had little impact on the mortality of copepods.
Marine Ecology Progress Series, Mar 3, 2014
Organisms residing in seasonal environments schedule their activities to annual cycles in prey av... more Organisms residing in seasonal environments schedule their activities to annual cycles in prey availability and predation risk. These cycles may be particularly pronounced in pelagic ecosystems of the high-Arctic, where the seasonality in irradiance, and thus primary production, is strong. Here we report on the seasonal ecology and life strategy of a predatory planktivore in a high-Arctic fjord (Billefjorden, Svalbard ~78°N). We studied the chaetognath Parasagitta elegans (var. arctica), an abundant zooplankter of high-latitude seas, focusing on its age structure, seasonal vertical distribution, growth and timing of reproduction. The body-length data (range: 2 to 44 mm) revealed the presence of 3 size cohorts (Cohorts 0, 1 and 2), suggesting a 3 yr life span. Spring and early summer (May/June) was the main spawning season, as revealed by inspection of gonads and the presence of well-developed seminal receptacles prior to high numbers of newborns. Both Cohorts 1 and 2 reproduced, with male gonads maturing first in this hermaphrodite. Growth rates for all cohorts were highest in spring and early summer, and at this time of the year, the youngest year class (Cohort 0) was distributed near the surface where their feeding opportunities may peak. In winter, however, all cohorts were in deeper waters, suggesting seasonal migrations, possibly to follow the distributions of overwintering copepods. Scheduling of growth, maturation and reproduction in Arctic zooplankton populations is important baseline information for predictions of zooplankton responses to environmental change, particularly those associated with timing and phenology, pinpointing the need for more high-resolution studies on zooplankton annual routines.
Recent talks by Jordan Grigor
Ecology of arrow worms in the Arctic – are they really the “tigers of the zooplankton”?
Organisms residing in seasonal environments schedule their activities to annual cycles in prey av... more Organisms residing in seasonal environments schedule their activities to annual cycles in prey availability and predation risk. These cycles may be particularly pronounced in pelagic ecosystems of the high-Arctic, where the seasonality in irradiance and thus primary production is strong. Whilst the annual activities of several herbivorous zooplankters have been relatively well-documented, much less is known about the strategies of omnivores and carnivores, including chaetognaths. Also known as arrow worms, these gelatinous animals are numerous in high-latitude seas, and may be important prey for the early life stages of some fish. Some have considered chaetognaths as strict predators, based on a few laboratory studies observing ferocious feeding on copepods, and aspects of their anatomy such as hooks and teeth. Others report that net-caught specimens in fact only rarely contain prey in their guts, and sometimes contain algae or detritus, introducing questions on their true feeding behaviours and ecological role. Here we document the life histories and annual routines of three Arctic chaetognaths: Parasagitta elegans, Eukrohnia hamata and Pseudosagitta maxima, based on studies in both Norway and Canada. We focus on diet, distribution, and on the timing of key life cycle events (e.g. reproduction, growth and energy storage). P. elegans and E. hamata are common chaetognaths above 1000m and reach maximum body lengths ~55mm in the Arctic. P. maxima individuals residing at bathypelagic depths may grow much larger. Whilst P. elegans appears to produce a single yearly cohort in spring and/or summer, multiple cohorts may be produced by E. hamata, also in winter. We discuss the potential role of a centrally positioned oil vacuole, exclusively observed in E. hamata individuals. Finally, in contrast to the accepted paradigm of chaetognaths as exclusive carnivores, we present evidence for detritivory and omnivory as additional feeding modes.
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Papers by Jordan Grigor
(LOKI) system, a novel underwater imaging system providing
cutting-edge imaging quality, in the Canadian Arctic during fall
2013. A Random Forests machine learning model was built to
automatically identify zooplankton in LOKI images. The model
successfully distinguished between 114 different categories of
zooplankton and particles. The high resolution taxonomical tree included
many species, stages, as well as sub-groups based on animal
orientation or condition in images. Results from a machine learning
regression model of prosome length (R2 = 0.97) were used
as a key predictor in the automatic identification model. Model internal
validation of the automatic identification model on test data
demonstrated that the model performed with overall high accuracy
(86%) and specificity (86%). This was confirmed by confusion
matrices for external testing results, based on automatic identifications
for 2 complete stations. For station 101, from which images
had also been used for training, accuracy and specificity were 85%.
For station 126, from which images had not been used to train the
model, accuracy and specificity were 81%. Further comparisons between
model results and microscope identifications of zooplankton
in samples from the two test stations were in good agreement
for most taxa. LOKI’s image quality makes it possible to build accurate
automatic identification models of very high taxonomic detail,
which will play a critical role in future studies of zooplankton dynamics
and zooplankton coupling with other trophic levels.
Recent talks by Jordan Grigor