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Increasing picocyanobacteria success in shelf waters contributes to long-term food web degradation.

Abstract：

:Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota-large diatoms, dinoflagellates and copepods-that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico- and nanophytoplankton biomass in coastal areas. Among the pico-fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico- and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light-harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega-3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition-related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters.

journal_name

Glob Chang Biol

journal_title

Global change biology

authors

Schmidt K,Birchill AJ,Atkinson A,Brewin RJW,Clark JR,Hickman AE,Johns DG,Lohan MC,Milne A,Pardo S,Polimene L,Smyth TJ,Tarran GA,Widdicombe CE,Woodward EMS,Ussher SJ

doi

10.1111/gcb.15161

subject

Has Abstract

pub_date

2020-10-01 00:00:00

pages

5574-5587

issue

eissn

1354-1013

issn

1365-2486

journal_volume

pub_type

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Increasing picocyanobacteria success in shelf waters contributes to long-term food web degradation.