climate change

impacts of climate change on the sea

  • ocean warming

  • sea level rise (from ice melt and thermal expansion)

  • changes to currents

  • acidification

  • deoxygenation

  • more frequent and intense storms

  • habitat loss

why should biologists care?

  • major distribution shifts

  • more biological invasions

  • higher extinction rates

  • phenology disruption (timing of spawning, migration, blooms)

  • acidification impacts (especially calcifiers)

  • low oxygen impacts

global warming stripes

  • atmospheric temperatures have been rising dramatically since teh 1970s

  • ocean temperature rise in all basins since 1901

  • warming is already happening everywhere

marine heatwaves (MHV)

  • marine heatwaves are sudden periods of abnormal high sea surface temperature, which may last weeks to months

  • these cause more biological damage than slow warming

how climate change affects fish

  • physiological effects:

    • metabolism increases with temperature

    • growth efficiency changes

    • higher risk of disease

  • changes in recruitment, migration, distribution

    • fish follow their preferred thermal habitat

    • larvae and juveniles have different optimal temperatures than adults

  • food web effects:

    • changes in prey abundance

    • changes in predator abundance

    • phenological mismatch (fish larvae hatch when food isnt available)

temperature window changes through life

  • eggs and larvae have the narrowest temperature tolerances

  • juveniles wider

  • adults wide

  • spawners narrow again

  • this shows why early life stages are the most vulnerable

spatial dynamics during progressive warming

  • poleward expansion at northern range limits

  • equator ward contraction at southern range limits

  • phenology shifts in warmer regions (timing changes)

  • temperature dependent windows narrowing at low latitudes

biomass projections

  • high latitude regions may temporarily see more biomass, but tropical reginos collapse

  • under low emissions (1.5˚C-2˚C) → moderate loss globally

  • under high emissions (3-4˚C) → massive loss in many regions

ecosystem risks by habitat type

  • warm water corals are at the highest risk

  • followed by kelp forests, seagrass meadows, rocky shores

warm water corals

  • they are extremely vulnerable for a few reasons

    • narrow thermal limit

    • acidification weakens skeletons

    • pollution

    • diseases

    • overfishing

    • even rats (predation on seabird eggs → less guano → nutrient decline)

  • just an increase in 1.5˚C threatens tropical reefs

ocean acidification

  • CO2 + H2O → carbonic acid → releases H+ → binds carbonate

  • as pH decreases

    • less carbonate available for calcification

    • existing shells dissolve

    • organisms must spend more energy maintaining structure

  • particularly affectes:

    • pteropods (type of free swimming pelagic sea snail)

    • bivalves

    • corals

    • foraminifera

regional and local impacts

  • climate change is global in cause but local in impact, affecting

    • coastal floods

    • storm surges

    • local fisheries

    • local ecosystem

arctic ocean

  • rapid ice loss, meaning smaller area + thinner ice gives a huge reduction in ice volume

  • acidification hits the arctic first; cold water holds more CO2 → early undersaturation

  • the effects of wamring in the arctic ocean are felt by:

    • marine mammals

    • zooplankton

    • fish communities

    • ice algae

    • seabirds

    • fisheries

    • shipping

  • cod and haddock are expanding northward into arctic water, causing borealisation of the barents sea

  • threats to arctic species

    • slow growing

    • specialist feeders

    • high vulnerability

    • competition from boreal species

    • phenological mismatch

    • new pathogens

  • will the arctic biome dissapear?

    • probably not because the light regime is extremely unique (midnight sun, polar night)

    • seasonal light cues limit boreal species survival

    • some physical barriers remain

future projections and models

  • climate scenarios

    • SSP1-1.9, SSP1-2.6 → low emissions

    • SSP2-4.5 → moderate

    • SSP3-7.0, SSP5-8.5 → high/extreme

  • the need for downscaling the models; global models are too coarse. instead switch to more regional models

  • the barents sea and norwegian sea are projected to warm rapidly under all scenarios

  • winning and losing species in norwegian waters

    • some stocks will increase (e.g. mackerel), while other decline (e.g. cold water species)

marine heatwaves in norway

  • increasing with frequency and severity

  • extreme anomalies (>5˚C or above)

  • strong ecosystem effects

  • salmon lice outbreaks worsened by heatwaves

MHV impacts on coral and seagrass

  • coral bleaching

  • seagrass die off

  • loss of habitat complexity

  • food web collapse

adaptation vs mitigation

  • adaptation:

    • adjust to changing climate:

      • ecosystem based management

      • changing fish quotas

      • long term planning

      • reducing vulnerability

  • mitigation:

    • reduce climate change itself:

      • CO2 reduction

      • blue carbon habitats (kelp seagrasses)

      • international climate policy

fisheries adaptation 

  • move toward ecosystem based fisheries management

  • accept short term quota reduction for long term stability

  • manage for multiple species and environmental risk

  • international cooperation needed

ocean based mitigation opportunities

  • potential CO2 sequestration contributions:

    • renewable energy

    • ecosystem restoration

    • kelp carbon capture

    • marine spatial planning

the papers - all together (Smale 2019, Sandø 2024, European marine board)

focus

  • smale 2019 → extreme events (marine heatwaves) and ecosystem collapse

  • sandø 2024 → long term climate projections for plankton and fish stocks

  • EMB biodiversity chapter → biodiversity changes + risk assessment

the ocean is warming gradually and suddenly

  • all the papers mention how climate warming is now universal across all oceans

  • two types of warming occur:

    • long term gradual warming

    • sudden warming spikes - marine heatwaves (MHW)

long term gradual warming

  • shift species poleward

  • changes timing of biological events (phenology)

  • shrinks thermal windows for tropical species

sudden warming spikes - marine heatwaves (MHW)

  • the smale (2019) paper shows that:

  • MHVs have increased in frequency, intensity, and duration over the last century

  • many regions now experience > 50% more MHW days compared to the early 1900s

  • MHWs destroy foundation species:

    • corals (bleaching)

    • kelp forests

    • seagrass meadows

  • these foundation species hold ecosystems together, so their collapse affects entire food webs

marine heatwaves as acute disturbances

(smale 2019)

  • across 685 species-level observations, most taxonomic groups respond negatively to MHWs

  • the most vulnerable are

    • corals

    • seagrass

    • macroalgae

    • sessile invertebrates

  • fish responses may vary: some tropical species expand into temperate areas during MHWs

  • key finding: MHWs causes sudden ecosystem reconfiguration and range contractions - not slow, predictable changes

biodiversity redistribution and collapse

(EMB biodiversity chapter)

  • The EMB report focuses on how warming and heatwaves rearrange biodiversity, especially in European seas

  • main outcomes

    • polewards and depthward shifts of thousands of species

    • warm-edge species decline

    • cold adapted arctic species lose habitat entirely

    • invasive species increase due to warming

  • these changes are a major threat to:

    • ecosystem services

    • fisheries

    • habitat structure

    • food-web stability

  • climate change redistributes who lives where. some species expand, others collapse

plankton at the centre of everything

(sandø 2024)

  • this paper used climate models (SSP scenarios) to analyse how primary production and plankton communities will change in northern seas

  • findings

    • warming and stratification reduces nutrient mixing, lowering productivity in many areas

    • phytoplankton composition shifts (diatoms → smaller flagellates)

    • zooplankton (calanus spp.) declines in some reginos → less food for fish

  • bottom up control

fish stocks respond to both direct and indirect climate effects

  • direct physiological effects:

    • temperature affects metabolism, growth, and survival

    • thermal windows differ by life stages (echoes your lecture slides)

  • distribution shifts:

    • boreal fish expand northward

    • arctic species retreat or decline

  • recruitment effects via heatwave:

    • MHWs cause mass mortality of eggs, larvae, or key habitat forming species

    • coral/seagrass/kelp loss reduces nursery habitat for many fish

  • food web restructuring:

    • changes at the plankton level propagate upward

    • some fish stocks gain biomass, some lose, depending on shifting productivity

  • fish populations change in growth, survival, and distribution becaue the whole food web is changing

climate scenarios - what the future looks like

  • under low warming scenarios:

    • moderate changes in productivyt

    • some shifts in fish distribution

    • arctic retains some cold water habitats

  • under high warming scenarios:

    • drastic increases in MHWs

    • substantail biomass loss in many regions

    • strong northward movement of species

    • collapse of coldwater fish populations

    • food web simplification becomes severe

climate change threatens ecosystem services

  • both papers (smale 2019 + EMB) emphasize losses to:

    • fisheries

    • coastal protection

    • tourism

    • carbon sequestration

    • biodiversity-based cultural value

  • smale 2019 provides table 1 summarizing impacts on 

    • provisioning services (fish stocks)

    • regulating services (carbon storage, nutrient cycling)

    • cultural services (tourism decline)