Understanding North Sea ecosystem

dynamics: Is 3 decades enough?

Chris FridSchool of Biological Sciences

The North Sea is a semi-enclosed, highly productive (>300 g C m-2 yr-1), relatively shallow, temperate sea.

A variety of human activities affect the marine ecosystem:• nutrient enrichment,• coastal developments,• the fisheries.

The North Sea

The Dove Time Series:

Zooplankton – Station Z

Macro-benthos – two stations M1 and P

Main Nephrops ground

M1

PZ

Benthos Buchanan initiated in

1971-72 Two stations remain

from an extensive grid 6 and 12 miles offshore 50 and 70 m deep M1 sampled March and

September P sampled March

Benthos – M1 At M1 the first decade

showed stable biennial cycle.

Buchanan interpreted thisas evidence of density dependence (?food limitation).

Broke down in 1981. From 1981-91 correlation

of benthic abundance with phytoplanktonproductivity two years previous (r2=55%) [whole series r2~33%]

Benthos Station P

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25000P Swept area Station P tracks phytoplankton until fishing increases in the 1980’s then declines.

Little year to year variation in species composition at Stn M1 (1986 decreased abundance of many taxa)

Stn P the same until mid 1980’s when fishing increased and inter-annual variability increased. 60

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Stn P Stn M1

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Stn P Stn M1%

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M1- 35 years of “natural” variation

Since September 1972 Have missed 3 September (1987,1991,

2002) and 1 March (1998) sampling 516 taxa recorded Genera richness: Sept: mean 105 (70-129)

Mar: mean 94 (63-124) Abundance: Sept: mean 605 (224-1310)

(per grab) Mar: mean 380 (104-720)

Some biology

Worms dominate,

with brittlestars, burrowing urchins and

clams (bivalve molluscs)

Levinsenia gracilis

Prionospio

ThyasiraAmphiura

After 35 years: Top genera

Meanindiv. m2

1 Prionospio 495.11 10.09%

2 Levinsenia gracilis 257.79 5.26%

3 Chaetozone setosa 198.19 4.04%

4 Amphiura 193.54 3.95%

5 Thyasira 191.03 3.89%

6 Abra 186.98 3.81%

7 Mysella bidentata 158.62 3.23%

8 Phoronis muelleri 153.67 3.13%

9 Pholoe 150.86 3.08%

10 Nuculoma tenuis 140.81 2.87%

TOTAL 4906.64 43.35%

Total Abundance – altered variability and

mean?

Tota

l N

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Time Series Plot of Total N

Total abundance – seasonal signal

Data

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s. A

dj. D

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Component Analysis for Fit NAdditive Model

Original Data

Seasonally Adjusted Data

Genera Richness – A shifted baseline

Genera

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Time Series Plot of Genera richness S

Genera Richness – seasonal signal

Data

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Seas.

Adj. D

ata

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Component Analysis for Fit gen SAdditive Model

Original Data

Seasonally Adjusted Data

Changes in time No significant change in total abundance

over time nor between decades Indication of altered variability and multi-

annual shifts

Significant change (ANOVA p<0.001) in genera richness, significantly higher in the 1990s and 2000s.

Global Climate Change

•Clear evidence of warming

•Rate of change is increasing

•Kicks off in late 1970s

•Clear evidence of warming

•Rate of change is increasing

•Kicks off in late 1970s

Climatic variation: Winter NAO

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2002199719921987198219771972

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Time Series Plot of Winter NAO

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Data

2002199719921987198219771972

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Std Gen Rich

Std NAOStd Abun

Time Series Plot of Std NAO, Std Abun, Std Gen Rich

Time Series – Std NAO, Abundance and Richness

(genera)

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Data

2002199719921987198219771972

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Std Gen Rich

Std NAOStd Abun

Time Series Plot of Std NAO, Std Abun, Std Gen Rich

Time Series – Std NAO, Abundance and Richness

(genera)

March

Climate Variation – A driver?Winter NAO and

March AbundanceMarch Genera richnessSept. AbundanceSept. Genera richness

No relationship with any variable (<5% variance explained)

Biological detail

Top 2 taxaData

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VariablePrionospio allLevinsenia gracilis

Time Series Plot of Prionospio all, Levinsenia gracilis

Not synchronisedNot synchronised

Total Abundance

Variation in the abundance of the polychaete Levinsenia (rank 2) accounts for over 31% of the variation in the total abundance

A multiple regression of Levinsenia and the brittlestars Amphiura (rank 4) together accounts for over 50% of the variation in the total abundance

Tota

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200520021999199619931990198719841981197819751972SepSepSepSepSepSepSepSepSepSepSepSep

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Time Series Plot of Total N

Genera richness

Total abundance explains around 28% of the variation in Genera Richness

35% with a quadratic fitted to logged data

Amphiura abundance explains 11% of the variation in genera richness

Total N

Genera

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S

14000120001000080006000400020000

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Scatterplot of Genera richness S vs Total N

Total N

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14000120001000080006000400020000

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S 0.0544469R-Sq 36.5%R-Sq(adj) 34.4%

Fitted Line Plotlogten(Genera richness S) = - 0.402 + 1.139 logten(Total N)

- 0.1317 logten(Total N)**2

MDS ordination top genera

Transform: Log(X+1)Resemblance: S17 Bray Curtis similarity

Month93

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2D Stress: 0.16

March – Decadal progression

Transform: Log(X+1)Resemblance: S17 Bray Curtis similarity

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2D Stress: 0.14

September – Decadal progression

Transform: Log(X+1)Resemblance: S17 Bray Curtis similarity

Decade7890

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2D Stress: 0.14

Shifts in community structure

March shows shifts in: 1985-1986, 1990-1991, 1991-1992 1998-1999, 1999-2000

September shows shifts in: 1984-1985 1998-1999, 1999-2000

Something happened between Sept 1984 and March 1985

And1999 was an odd year (especially September)

CPR silk greenness – index of phytoplankton

Mean G

reenness

YearMonth

2000199119821973196419551946JanJanJanJanJanJanJan

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Time Series Plot of Mean Greenness

Food as a driver?CPR greenness (2 years previous) and

Total (March) abundance1970s ns r2=6%1980s Signif. r2=24%1990s ns r2=<1%

Total Series: March Abundance – ns r2= 5% March Genera richness - Signif. r2=15% Sept. Abundance - ns Sept. Genera richness - Signif. r2=17.7%

Drivers of Biodiversity March – Greenness and Total Abundance

explain over 25% of Genera Richness

Sept – Greenness and Total Abundance explain over 40% of Genera Richness

35 years of study shows.. Decadal scale variation in total abundance,

species richness and community composition No trend in abundance i.e. due to warming

or eutrophication ‘Trend’ in community composition and

hence deliver of ecological functions Indication of importance of climatic drivers

(variation) and food supply in setting limits on total abundance and patterns of richness

Decadal scale variation in total abundance, species richness and community composition

No trend in abundance i.e. due to warming or eutrophication

‘Trend’ in community composition and hence deliver of ecological functions

Indication of importance of climatic drivers (variation) and food supply in setting limits on total abundance and patterns of richness

Take home message 10 taxa account for over 40% of the

individuals recorded Richness and total abundance tend to

change together: Richness has increased over time

Climatic variation directly and the variation in food supply (which is influenced by climate) are important drivers

Our understanding of this system continues to develop as the series lengthens

And where next?

We continue, in conjunction with Newcastle University, to extend the time series

We have also, in 2006, initiated benthic sampling twice a year at two of the Coastal Observatory stations

Acknowledgements For initiating the series Jack Buchanan

and for collecting the data: various PhD students and Peter Garwood, masters and crew of the RV Bernicia

For funding it at various times: DEFRA (DoEnv, DETR), NERC, University of Newcastle

For intellectual input: Leonie Robinson, Robin Clark, Kirsty Nicholas.