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Baltic biodiversity: out of balance, but are we out of time?

Aug. 19, 2024

Photo generated by AI at DreamStudio

“The Baltic Sea’s ecosystem is out of balance”

 – Gustaf Lind, Secretary General of the WWF

Previously we introduced you to the groups that make up the Baltic Sea ecosystem, and showed how habitats are still in poor condition even after years of assessment and management. We want to show you there is still hope, and demonstrate how collective change can turn this situation around. 

So how is our marine life doing?

If you’ve read our blogs you already know that our partner, HELCOM, conducts research on the Baltic Sea. Sadly, this shows imbalance in almost all marine groups. Thanks to a nasty combination of eutrophication, plastic pollution, and hazardous substances, scientists have observed six main changes:

Increasing harmful algal blooms 

Phytoplankton can be really blooming cool (pun intended), turning the sea into a sparkling mass with their bioluminescent properties pictured below. But this is not always the case. Picture this. The sea turns from blue to green as harmful algae, ‘cyanobacteria’, multiply at record speed. This occurs due to higher nutrient loads entering the marine environment, called ‘eutrophication’. Linked to poor agricultural practices, wastewater treatment, and climate change, more harmful algal blooms (HABs) have been returning to the Baltic Sea in recent years and have already reached Sweden this summer [1]. HABs often look like a green stringy soup, seen below, hanging around for several days before the algae decompose and sink to the seafloor.

Source: Studying Bioluminescent Blooms in the Arabian Sea – State of the Planet (columbia.edu)

Source: Harmful Algal Blooms (HABs) and Cyanobacteria (iolight.co.uk)

Impacts

  • Large areas of coast become unsafe for bathing during HABs, which are toxic to both humans and animals
  • Decomposing algae uses up available oxygen in the sea, resulting in “dead zones” where no marine life can survive [2]

How do we fix it?

  • The work starts at your kitchen table. Since the agricultural industry is a factor in HAB occurrence, you can make impacts through adjusting your weekly food shop.
  • Farmers are taking steps to reduce nutrient runoff to the Baltic Sea, recognised here by the WWF Baltic Sea Farmer Award [3]. 
  • As a consumer, actively choosing to support farms making efforts to reduce eutrophication in the Baltic Sea is a big win for biodiversity. 
  • If you’re a farmer, find out what you can do to reduce eutrophication here..  

Hard times for habitat-builders

Coastal-meadow forming species, like eelgrass, are suffering. Especially in the southern Baltic Sea where pollution and eutrophication are the worst. Known as the “coral reefs of the Baltic Sea”, coastal meadows are “severely threatened by agricultural abandonment and environmental change” [5]. Estonia, despite having the densest coastal meadows in the Baltic, has seen ~200km² of this habitat disappear since the ‘60s. Sea-level rise and increased storm surge frequency are the main culprits for this, stemming from greenhouse gas emissions and climate change.

Source: Eelgrass proves to be much younger than we thought – DOE Joint Genome Institute

Impact 

  • Loss of microhabitats for fishes to lay eggs, invertebrates to spawn, and young predators to learn how to hunt in before entering the open sea. 
  • Economic losses in the fishing industry due to fewer nurseries for commercially important species, i.e. prawns.
  • Coastal meadows oxygenate the Sea by producing food from the sun, called photosynthesis. This reduces the impacts of Ocean acidification, a critical issue in the Baltic stemming from climate change. Without this oxygenation, life would be inhospitable for many other species.

How do we fix it?

Reducing our emissions. This is a huge topic, so let’s start with changes that begin in your house and continue when you go out.

  • Maximising energy efficiency. Baltic buildings tend to have poor energy performance, but small improvements can reduce emissions by up to 900 kg CO2e a year [6]! Save energy and money by:
  • Keeping appliances up-to-date 
  • Improving your insulation
  • Switching off unused plug sockets 
  • Travel mindfully. Allowing more time to reach your destination and using slower forms of transport also provides a mental break from hectic daily life.
  • If it’s nice out, walk or cycle
  • In harsh weather, take public transport (and you get to read that book you’ve been meaning to finish).
  • If the journey calls for a car, try carpooling!. It cuts daily expenses on average by 20-30%, reducing CO2 emissions by 50% per passenger mile. Here’s how to carpool safely.. 

Predator shifts lead to floundering fisheries

A lack of large predatory fish coupled with eutrophication has led to imbalance in the Baltic fish community. We’ve seen shifts from large bottom-dwellers (e.g. cod) to smaller pelagic species (e.g. herring, sprat) since the ‘80s, resulting in only 4/15 commercial fish stocks having a “good” status between 2016-2021. The European eel remains critically endangered, and efforts to reintroduce the regionally extinct sturgeon are ongoing [9].

Source: Press Release: New study presented on dramatic decline of cod in the Baltic Sea – FishSec

Impact

  • Declining predator levels within fish populations often result from overfishing, so food webs are more likely to crash. 
  • This leads to economic losses in the fishing industry, directly impacting the price of fish. Nobody wants salmon to get any more expensive! 
  • Marine mammals rely on healthy fish stocks for survival, and are already at risk of decline due to a lack of food sources.

How do we fix it?

  • Be informed. As mentioned in our last blog, use the Good Fish Guide and Baltic Fish [11] to make informed decisions about what goes on your plate. 
  • Cut your food waste. The way you cook and dispose of food, including fish, leads to greater or lesser demand on the fishing industry. By only buying what you need and using it up, you save money, reduce emissions, and improve food security for future generations.

Seabirds aren’t doing well

Overall, seabird status is “not good” in the Baltic sea [9]. The great black-backed gull and velvet scoter, seen below, have decreased in abundance over the past decades. One of the greatest threats to seabirds is fisheries by-catch, followed by shrinking available habitats due to climate change, and overfishing of their main food sources. The graph below shows countries with highest estimated annual seabird bycatch, four of which are Baltic. It also shows poor data quality in Sweden and Germany, indicating a lack of research.

Source: EU Seabird Bycatch Action Plan – Good intentions, little action! (birdlife.org)

Source: Seabird bycatch in European waters – Ramírez – Animal Conservation – Wiley Online Library

Impact 

  • Seabirds connect land and sea, transporting nutrients between the two in the form of nest materials, eggshells, and of course poop. 
  • Intrepid explorers and foragers of marine environments, seabirds are often used as indicators of Ocean health. 
  • Seabirds are vital elements of coastal ecosystems, but remain poorly understood in comparison with other groups of organisms [12]. Let’s make sure they stick around so we can get to know them better.

How do we fix it?

Getting seabirds off the hook? Tricky. As consumers, it’s hard to tell what’s accidentally caught in the net used to catch your fillet of fish. But you can:

  • Lobby for implementation of mitigation measures onboard fishing vessels. Here are the methods that need integrating to reduce bycatch.
  • Vote with your pocket. Donations made to Save The Baltic Sea directly improve our ability to hold important educational workshops on sustainable fishing practices. Donate here to support our cause.  
  • Eat less fish, or adopt a vegetarian diet. This directly reduces seabird bycatch as you lower the overall demand for fish. 
  • Become a citizen scientist and improve our chances of successfully monitoring seabird health. DOF-Birdlife Denmark is just one example of this, linked here. This is especially needed in Poland, Sweden, Germany and Denmark where bycatch rates are high and data quality is low.

Marine mammals: declining and threatened

In HELCOM’s 2009 biodiversity report, 59 Baltic Sea species fell into this category including all present marine mammals. Their status in 2023 is still “not good”, with overall population growth remaining “too low” [9]. 

  • Harbour porpoise populations are in a vulnerable state due to by-catch, lack of prey availability, noise pollution and entry of hazardous substances to the sea.
  • The Baltic Sea grey seal population has been increasing since 1988, but their recovery is still “too slow”.
  • Behavioural changes in the Baltic ringed seal population has led to poor quality monitoring data, meaning we can’t accurately assess their wellbeing.

Source: WWF Finland: Endangered Saimaa ringed seals begin crucial breeding season | Yle News | Yle

Impact

  • As we learned previously, marine mammals sit at the top of the food-chain as predators, regulating the distribution and health of prey species. 
  • Highly mobile and often migratory, marine mammals also regulate nutrient transfer throughout the Baltic Sea. 
  • Loss of predatory species, i.e. the ringed seal, impacts our ability as humans to exploit organisms lower down the food-chain such as fish and invertebrates (e.g., shrimp). 

How do we fix it?

  • The Sea begins in your home. Being aware of what goes down your sink can lead to fewer hazardous substances ending up in the Baltic Sea. This already reduces the threats marine mammals face in their watery home. 
  • Implement new habits. We’ve highlighted key lifestyle changes you can make with our campaign “The Sea Begins Here”, to help you lower your impact on marine mammals and other wildlife.

Alien invasions on the rise

You might be surprised to hear that the mud crab, pictured below, is non-native to the Baltic Sea. Whilst this little fella is not currently harmful, since the early 19th century around 120 non-native, alien marine species have made it to the Baltic. 

Source: AquaNIS: Information system on aquatic non-indigenous and cryptogenic species (ku.lt)

Shipping traffic, contaminated fishing vessels and gear are the main culprits for new invasions. Despite mainly impacting coastal areas, several species have made it out into the open ocean. How does this happen? As cargo ships move from coast to coast, ballast water is released into the Sea and refilled to maintain buoyancy. Any organisms trapped inside are introduced to the environment, and new ones are picked up. Whilst there are management strategies in place to avoid this, they aren’t totally watertight.

Impact

  • Most invasive species in the Baltic Sea have yet to become invasive and outcompete native species, but remain a threat to biodiversity through depletion of native resources and space. 
  • Risk of new invasions remains high due to a high level of maritime transport in the Baltic Sea. 
  • When established, invasive species might have an unnatural advantage in their new environment compared with native species, i.e. they are more efficient predators. 
  • Native species must then compete for precious resources, a bit like when your girlfriend asks for a bite of your cookie and then takes the whole thing.

How do we fix it?

  • If you own a boat, clean it! Invasive species spread through unclean boat hulls and often go unnoticed, so make sure you check things over now and again. 
  • Don’t release aquatic pets into the sea. They may not survive and if they do, they could overcome native species and become invasive.
  • Scrub your fishing equipment down after each use. It really is easy to prevent invasive species from spreading, with a little extra care. 

You’re not alone! 

There are so many choices we can make as individuals, but what about our industries? You’re right, we can’t do everything ourselves. That’s why our partner Ignitis Renewables are driving sustainable energy solutions such as on and offshore wind farms. We’ve only partnered with companies we trust and want to support, so we’d love it if you read more about their pathway to a green, sustainable economy here.

Written by marine biologist Eloise M. K. Holmes.

Sources

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