2015 11 - peter henderson
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Peter HendersonPisces Conservation Ltd &University of Oxford
Fish and Crustacean Dynamics in the Severn
Estuary & Bristol Channel
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35 years monthly sampling at Hinkley now completed..
Sampling started in October 1980 and is still ongoing. Data are available for about 80 species of fish, 17 macro-crustaceans and about 50 species of plankton including 9 mysid species.
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The results show a system with many stable features, but with individual species showing a rich and variable range of dynamics
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Species richness and diversity is notably stable
Change in the Hinkley fish community through time: overall community view. (a) species richness per year of time series (Hill’s N0 index) ; (b) exponential form Shannon index (Hill’s N1 index; (c) reciprocal of Simpson diversity index; (d) Berger-Parker index (Hill’s N infinity index);(e) mean rank shift index, sequential pairs of years; (f) Bray-Cutis dissimilarity values between sequential pairs of years. From: Magurran, A. E., & Henderson, P. A. (2010). Temporal turnover and the maintenance of diversity in ecological assemblages. Philosophical Transactions of the Royal Society B: Biological Sciences, 365(1558), 3611-3620.
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Blue are older than 1 year. Red are in first year of life
All species are seasonal – e.g. sprat, Sprattus sprattus
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The fish fall into 4 groups each abundant in a different season
The dendrogram shows the 4 seasonal groupings identified by cluster analysis. Box plots show ln scaled relative abundance for each seasonal cluster .
From:Shimadzu, H., Dornelas, M., Henderson, P. A., & Magurran, A. E. (2013). Diversity is maintained by seasonal variation in species abundance. BMC biology, 11(1), 98.
Abundance through time. The individual seasonal components are shown in the lower plot
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While the overall system attributes can show notable temporal stability There are marked differences in the stability of individual species. Abundant core species show density-dependent regulation and high stability. Lower abundance species are more variable.
However species vary greatly in temporal stability
Relationship between mean (±sd) coefficient of variation (COV) and mean (±sd) biomass. Core species showing density-dependence shown in blue. Core species with no evidence of density-dependence in red. Transient species in grey.
From: Henderson, P. A., & Magurran, A. E. (2014). Direct evidence that density-dependent regulation underpins the temporal stability of abundant species in a diverse animal community. Proceedings of the Royal Society of London B: Biological Sciences, 281, 20141336.
These blue dots are high stability core species
These grey dots are highly variable transient species
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Trends in 15 most abundant species
From : Henderson, P. A., & Bird, D. J. (2010). Fish and macro-crustacean communities and their dynamics in the Severn Estuary. Marine Pollution Bulletin, 61(1), 100-114.
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Trends in next 15 most abundant species
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In part these changes can be related to physical change in temperature, salinity and NAO
1980s rapid warming period 1990-2006
stability period
2007 start recent cooling period
The fish and crustaceans are responded to recent cooling.
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Each time series can be decomposed and break points and trends identified – for example the Atlantic prawn P. serratus
Warmer waters allowed a change in seasonality to occur around 1997 and this produced a rapid increase in abundance During the 1998-2007 period of high abundance prawns were caught in high numbers in January and February.
Cooling post 2007 has resulted in switch to
1980s/90s seasonality and a decline in
abundance