Environmentally Driven Ecological Fluctuations on the Faroe Shelf Revealed by Fish Juvenile Surveys

Jacobsen, Sólvá; Gaard, Eilif; Hátún, Hjálmar; Steingrund, Pétur; Larsen, Karin Margretha Húsgarð; Reinert, Jákup; Ólafsdóttir, Sólveig Rósa; Poulsen, Meinhard; Vang, Helga Bára Mohr

doi:10.3389/fmars.2019.00559

Cited by 11 publications

(17 citation statements)

References 52 publications

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“…chlorophyll concentration) (Jacobsen et al 2018). In addition, cod 0-group indices, which are based on the June survey, closely resemble the local primary production index (Jacobsen et al 2019). Together, these observations suggest that sub optimal feeding conditions during the late larval period may be a main critical phase for survival to the end of the pelagic stage in Faroe Plateau cod.…”

Section: The Late Larval Periodmentioning

confidence: 57%

“…The neritic copepods are more abundant in years with high primary production (Jacobsen et al 2018), while the summer abundance of C. finmarchicus is related to inter-annual differences in predation pressure from 0-group fish e.g. cod (Jacobsen et al 2019), the variable exchange rate between on-and offshelf waters (Gaard and Hansen 2000) as well as the general production in the open ocean and on the shelf (Gaard 2000). Thus the difference in the mean size of prey ingested compared with the preferred size of prey ingested by early juvenile cod is most likely caused by a combination of high abundance of small prey together with a low abundance of preferred sized prey depending on the contemporary environmental conditions.…”

Section: The Early Juvenile Periodmentioning

confidence: 99%

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Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

et al. 2020

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The availability of suitable prey during the early life of fish may determine recruitment to the adult population. Since larval and juvenile feeding can be highly selective, their preferences for certain prey species and sizes should be considered when estimating the availability of prey. In this study, diet composition (and prey preferences) of 4984 (1366) Faroe Plateau cod (Gadus morhua) larvae and juveniles between 3 and 63 mm sampled on the central Faroe shelf (62°N, 6.8°W) over an 8-year period was investigated. Cod preyed on successively larger food items as they grew. Yolk-sac larvae consumed phytoplankton, copepod eggs and nauplii before the yolk sac was exhausted. Copepod eggs followed by calanoid nauplii were the predominant and preferred food items in the early larval stage. In the late larval stage these were replaced by small to medium sized (0.6-1.2 mm) copepod species mainly Pseudocalanus sp., Acartia sp. and early stage Calanus finmarchicus, of which the two former species appeared most preferred. Temora longicornis was highly abundant in juvenile cod, but the preference for this species was neutral. Positive selection and high abundance of late stage (≥ 1.5 mm) C. finmarchicus was observed in early juveniles, but C. finmarchicus was replaced by decapod larvae in late juveniles. Other abundant prey species such as Oithona sp. and barnacle larvae occurred in varying numbers in the guts, but were generally not positively selected at any stage. Late larval and early juvenile cod appeared to suffer from unfavourable feeding conditions as they fed on smaller prey than what they prefer potentially indicating bottle necks in the feeding at these development stages.

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Section: The Late Larval Periodmentioning

confidence: 57%

Section: The Early Juvenile Periodmentioning

confidence: 99%

Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

et al. 2020

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“…Corresponding changes in the strength and properties of the Slope Current are likely to reverberate downstream. Expansion and contraction of the subpolar gyre have already been shown to be correlated with salinity variations on an interannual and decadal timescale in the northern North Sea, strongly linked to pulses in nutrient availability, with a lag of approximately 2 years (Pätsch et al, 2020;Hátún et al, 2021Hátún et al, , 2017Jacobsen et al, 2019). Nitrate and phosphate fluxes in the North Sea have been linked to the local and regional wind fluxes (Pätsch et al, 2020).…”

Section: Implications Of the Observed Changes On The Slope Current An...mentioning

confidence: 98%

Weakening and warming of the European Slope Current since the late 1990s attributed to basin-scale density changes

2022

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Abstract. Oceanic influences on shelf seas are mediated by flow along and across continental slopes, with consequences for regional hydrography and ecosystems. Here we present evidence for the variable North Atlantic influence on European shelf seas over the last 4 decades using ocean analysis and reanalysis products, as well as an eddy-resolving ocean model hindcast. To first order, flows oriented along isobaths at the continental slope are related to the poleward increase in density in the adjacent deep ocean that supports a geostrophic inflow towards the slope. In the North Atlantic, this density gradient and associated inflow have undergone substantial, sometimes abrupt, changes in recent decades. Inflow in the range 10–15 Sv is identified with eastward transport in temperature classes at 30∘ W in the latitude range 45–60∘ N. Associated with major subpolar warming around 1997, a cool and fresh branch of the Atlantic inflow was substantially reduced, while a warm and more saline inflow branch strengthened, with respective changes of the order of 5 Sv. Total inflow fell from ∼ 15 Sv pre-1997 to ∼ 10 Sv post-1997. In the model hindcast, particle tracking is used to trace the origins of poleward flows along the continental slope to the west of Ireland and Scotland before and after 1997. Backtracking particles up to 4 years, a range of subtropical and subpolar pathways is identified from a statistical perspective. In broad terms, cold, fresh waters of subpolar provenance were replaced by warm, saline waters of subtropical provenance. These changes have major implications for the downstream shelf regions that are strongly influenced by Atlantic inflow, in particular the northern North Sea, where “subtropicalization” of ecosystems has already been observed since the late 1990s.

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“…Zooplankton biomass was determined by drying at ~60°C until a constant weight was attained. The time series for zooplankton biomass represents an average over 20-25 stations that were distributed throughout the shelf inside the 100 m bottom depth contour (Jacobsen et al, 2019).…”

Section: Zooplanktonmentioning

confidence: 99%

Relationship between plankton dynamics and growth of the long-lived clam Arctica islandica on the Faroe shelf

et al. 2022

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Marine ecosystem dynamics can vary on timescales ranging from months to centuries, but many observational data are limited to just a few decades. The bivalve Arctica islandica may live up to five centuries depositing annual growth increments in its shells which can serve as an indicator for ecosystem productivity. In the present study, 154 specimens of A. islandica were collected on the Faroe Shelf and standardised annual growth increments for 143 of them – 44 from coastal stations and 99 from shelf stations – were compared with climatic, oceanographic and biological variables. A. islandica growth from coastal and shelf stations was not correlated with basin-scale climate indices (the AMO index, the NAO index, the AO index or the subpolar gyre index) or, more locally, with windspeed or sea surface temperature on the Faroe Shelf. For the shelf stations there was a significant negative correlation between A. islandica growth and the volume transport of the Faroe Current flowing just north of Faroe Islands (r = -0.62). There was a weak nonsignificant positive correlation with an index of primary production on the Faroe Shelf (r = 0.31) and a strong negative correlation with a zooplankton biomass index in mid-summer (r = -0.76). There was also a strong positive correlation between A. islandica growth and the biomass of the bottom-feeding fish species Melanogrammus aeglefinus two years later (r = 0.62). These results seem to suggest that A. islandica growth may represent the amount of fresh phytoplankton that reaches the near-bottom water layers and could probably be regarded as a proxy for the strength of pelagic-benthic coupling that is modulated through phytoplankton-zooplankton interactions in the overlying water. Our results highlight the potential for A. islandica to serve as a long-term proxy for linking variability in pelagic ecosystem dynamics to demersal fish stocks.

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Environmentally Driven Ecological Fluctuations on the Faroe Shelf Revealed by Fish Juvenile Surveys

Cited by 11 publications

References 52 publications

Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

Diet and prey preferences of larval and pelagic juvenile Faroe Plateau cod (Gadus morhua)

Weakening and warming of the European Slope Current since the late 1990s attributed to basin-scale density changes

Relationship between plankton dynamics and growth of the long-lived clam Arctica islandica on the Faroe shelf

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