Marine ecosystem and human impacts

Question 1

The impacts

Answer 1

1. Land-based impacts
2. Commercial activity taking place at sea
3. Climate change
4. Fisheries
5. By-catch

Question 2

Land-based impacts

Answer 2

Things on land with a direct impact on the ocean
-coastal development = habitat destruction
-mangroves are a great defence system and spp rich area (fish juveniles etc.), lost 20% between 1980-2005
-seagrass - 30% decline since 1970s and is continuous, its a C store and good for protection
Replaced by hard structures

Question 3

Commercial activity taking place at sea

Answer 3

Oil rigs, gas and communication pipelines
Shipping, direct impacts (collisions)
Invasive species on hulls or in ballast waters
Pollution - noise, oil and rubbish
Acute pollution - more insidious, the Pacific garbage patch
Huge increase in microplastics
-samples found more micro plastics than plankton & has huge impacts of food web
-1/10 fish had plastics in gut, not yet know ecological consequences

Question 4

Climate change

Answer 4

Increased atmospheric CO2 has caused temp increases, sea level rise and depleted [carbonate]
Looking at sea surface temp (SST) - almost all increasing
Direct consequences = sea ice melting
Zooplankton assemblages changing - no cold-preferring around UK anymore (was in 1990s)
North Sea fish going deeper
Coral bleaching
Ocean acidification

Question 5

Coral bleaching

Answer 5

Healthy corals have a symbiont - zooxanthellae
• When coral is stressed, will expel this leaving the skeletal coral exposed
• Can recover - but if repeated or for extended periods it will cause death
• Coral then colonised by filamentous algae = different ecosystem

Question 6

Acidification

Answer 6

C emitted often ends up in seas (would’ve rose by 30°C by now)
• 500+ billion tonnes dumped
• Reacts with water = carbonic acid, lowers sea pH
• Reduces carbonate available for marine organisms, need for skeletons
• Very important for phytoplankton
• More [CO2] = less suitable for coral, obvious impacts on ecosystem and spp dependent on it

Question 7

Fisheries

Answer 7

• Industrial scale of hunting wild animals - little farming
• Fish catches increased, peaking in 1990s - now stabilising at 8-70mil/ton/yr
-interesting as global efforts are on the rise
• Makes declines in individual species
-bluefin tuna 200,000 to few 1000s - sought-after fish
• See declines in entire functional groups like predatory fish and large pelagic predators

Question 8

Have consumers noticed a decline in fish?

Answer 8

No - why?
• Overfishing in developed worlds overcome by importing from developing worlds
-“spatial subsidies” - travel further, fish deeper
• Fishing down food web - start at predators and go lower, now harvesting
• Shifting baselines - fisheries record started in 20th century
-exploiting oceans for well-over 1000yrs
-can look at different ages of fishermen
-older said fishing grounds = more degraded
-younger hadn’t noticed
-similar data (unpublished) by Webb and Selim - cod abundance

Question 9

What was natural?

Answer 9

• Abundances of marine mammals
• Larger fish
• Overfishing been in place for >1000yrs
-found using unorthodox data:
eye-witness accounts
-ship logs
-archaeological finds
• Most groups of species have now been reduced, but some are recovering - whales; pinnipeds; otters and coastal birds
• Computer modelling how rare fish are and relationship with size shows large fish should not be as rare as they are now

Question 10

By-catch

Answer 10

• No fishing gear is perfectly selective
• Large numbers of non-target organisms caught by mistake - fish untargeted or undersized, marine inverts, sea birds, mammals and reptiles
• It rarely survives
• Shrimp, prawn and crab trawls by-catch exceeds targets
• Albatross population endangered…
• Fishermen aiming for swordfish got 95% blue sharks and chucked all back >40% dead, >20% injured
• North-sea trawling - mainly inverts
• Habitat destruction - worse than cutting down forests and can happen several times/yr
-ruins seabed structure and ecosystems