Tag: Oceanography

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Attachment

muscles need iron
so do mussels it appears
such sticky anchors

Iron is an essential element for almost all living organisms. The majority of iron in mammals is found in red blood cells (haemoglobin) and muscle cells (myoglobin), supporting the transport, storage and release of oxygen. In humans, iron deficiency is the most common nutritional deficiency in the world and can lead to iron-deficiency anaemia, symptoms of which include fatigue, headaches, weakness, angina, breathlessness, complications during pregnancy and delayed growth in infants and children.

Iron is also important for many animals, utilised to help strengthen hard materials such as rodent teeth or the carbonate armour of some gastropods. Yet iron can be found in soft biological materials too, including the sticky anchors that mussels use to attach to rocks and the threads that connect those adhesives to the mussels’ inner tissues.

To investigate the importance of iron in mussel anchors, Hamada et al. (2020) varied seawater iron levels in a controlled environment and examined adhesive thread samples from Blue mussels (Mytilus edulis) which had been living in the water for 3 days. The researchers measured thread strength by securing the entire length of the threads and measuring how much force was required to pull them until the adhesive failed.

Adhesive strength increased as the iron level of the water increased until an optimal amount was reached, after which the adhesive strength declined. Examination of the plaques themselves also revealed differences in morphology, including colour and microstructural features, arising from the different iron levels of the water.

The results confirm that iron is a key component of how mussels anchor themselves to rocks and demonstrate how changing ocean chemistry might affect these molluscs in the future.

Further reading: https://doi.org/10.1021/acs.est.0c02392

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Hadal Mercury

Quicksilver sinking.
Sediments sequestering
in the cold, dark deep.

Mercury pollution can cause huge environmental damage, accumulating in the food chain and causing harm to wildlife and humans. Reducing mercury pollution is vitally important and monitoring mercury levels in the environment is crucial for understanding how mercury travels through ecosystems. Yet measuring mercury levels isn’t always easy.

Recent research by Sanei et al. (2021) examined some of the most challenging areas to access on the planet – the deep-ocean trenches. The researchers collected sediment core samples from areas of the Kermadec and Atacama Trench Systems in the Pacific Ocean, over 6km below the surface in the hadal zone.

The researchers found that some areas were mercury hotspots, with levels 6–56 times higher than the previously inferred deep-ocean average. Whilst the hadal zone comprises only around 1% of the deep-ocean area, the findings suggest that it may account for 12–30% of the mercury estimate for the entire deep-ocean.

The findings raise serious questions about levels of mercury pollution in the oceans, highlighting the need for further research into deep-ocean mercury pollution. There is one bright spark in this worrying cold, dark news – mercury in trench sediments is effectively locked away, buried for millions of years as plate tectonics shifts it deep into the earth’s upper mantle.

Original research: http://dx.doi.org/10.1038/s41598-021-90459-1

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Rigs to Reefs

Oh puffing pig fish –
torn between disturbance and
piscine temptations.

Noise pollution from oil and gas drilling platforms can have huge negative impacts upon marine life. However, such rigs can also act as artificial reefs, providing shelter and a hard substrate for predators and prey alike. Moreover trawling isn’t permitted close to rigs, meaning that the seabeds around them are mostly untouched.

Harbour porpoises, Phocoena phocoena, have previously been shown to change their behaviour or avoid areas as a result of unnatural noise levels. Yet a recent study by Tubbert Clausen et al. (2021) has revealed that the temptations of high prey availability can overcome such affects. The team use 21 acoustic loggers, placed on the seabed for up to 2 years to monitor noise levels and harbour porpoise activity.

They found that despite the high noise levels from the largest rig in the Danish North Sea, the porpoises were still found close to the rig, emitting echolocation noises that indicate they were hunting for fish. The platform’s artificial reef effect appeared to increase fish numbers which drew the porpoises closer.

The findings suggest that as platforms come to the end of their lifespans, they could be partially left in place to continue acting as artificial reefs – the rigs-to-reefs concept.

The first line of the sciku refers to two names for the harbour porpoise:

– The ‘pig fish’ from the Medieval Latin porcopiscus, a compound of porcus (pig) and piscus (fish).

– The ‘puffing pig’ which comes from the noise the porpoises makes when surfacing to breathe.

Original research: https://doi.org/10.1002/2688-8319.12055

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Mapping Seagrass Loss

Quantifying our
marine meadows – past, present.
A threadbare carpet.

Everyone knows their own science interests, the areas of research that they find thought-provoking. Sometimes I think that there are also subjects that we don’t realise we find fascinating. I never knew I was interested in seagrasses but this is the third sciku I’ve published about them, the second that I’ve written myself. It’s curious that I wouldn’t have known this about myself before today when this research paper caught my eye.

Seagrasses are hugely important ecosystems. In the sciku ‘Forgotten value’ I wrote about how seagrass meadows provide a nursery habitat for over a fifth of the world’s largest 25 fisheries. And as Dr Phil Colarusso showed with his sciku ‘Blue Carbon’, seagrass meadows collect and sequester large amounts of carbon, removing it from the global carbon cycle. As a result seagrass meadows are referred to as blue carbon habitats, along with salt marshes and mangroves.

Today’s sciku is based on a study by Green et al (2021), which examines the historical loss of seagrasses from the waters around the United Kingdom. By scrutinising multiple accounts from as early as 1831 and using data collected from 1900 onwards the researchers were able to estimate the UK’s seagrass losses. It makes for sobering reading:

“At least 44% of United Kingdom’s seagrasses have been lost since 1936, 39% since the 1980’s. However, losses over longer time spans may be as high as 92%.”

The research shows that the UK currently has only 8,493 hectares of seagrass meadows remaining. That’s approximated 0.9 Mt (million tonnes) of carbon, equivalent to around £22 million in the current carbon market. Whilst that may seem a lot, it’s worth considering that historic seagrass meadows could have stored 11.5 Mt of carbon, supporting around 400 million fish.

These losses are catastrophic but the information from this study can be used to inform future monitoring and restoration efforts. What’s more, by quantifying the benefits we gain from seagrass meadows as well as what we’ve lost from their disappearance, the findings also provide an impetus for improved conservation efforts, beyond ‘softer’ arguments such improving biodiversity.

Original research: https://doi.org/10.3389/fpls.2021.629962  

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Sawfish Decline

Shout from the rostrum:
‘Poor Carpenters in the soup!’
Such dentistry snared.

Tracking declining animal populations can be tricky enough on land, but in the ocean it’s an even harder proposition. Yet without knowledge of marine animal populations, conservation efforts can’t be directed effectively. One way to solve this issue is to examine drivers of site occupancy – what causes some populations to thrive or decline in an area. Understanding these drivers can allow researchers to predict population declines and gain insight into the probability of local population extinctions.

Sawfish are a family of rays with distinctive long, flat snouts which have horizontal teeth running along the length to resemble saws. Known as rostrums (an alternative definition to the more common meaning of a raised platform for speaking or performing from) they are packed with electroreceptors that allow them to detect prey, whilst the teeth are thought to be used in a swiping motion to incapacitate fish.

Sadly, three of the five sawfish species are Critically Endangered and the other two are Endangered. Since sawfish aren’t commonly sighted keeping track of their populations is hard and there’s little systematic monitoring. To address this Yan et al. (2021) combined data from occurrence surveys with indices of ecological carrying capacity, fishing pressure and management capacity to predict local population extinctions and identify regions where conservation efforts might be most effective.

Overfishing of sawfish is a particular threat: their fins are prized for shark fin soup (whilst sawfish are known as Carpenter sharks, they aren’t actually sharks), their teeth are used as spurs for cockfighting, their rostrum are frequently sold as novelties or trophies, and parts of them are used in traditional medicines in countries including China, Mexico, Brazil, India, Kenya and Iran.

Accidental overfishing is an issue too: their iconic rostrum and teeth are easily tangled in fishing nets and lines. What’s more, untangling sawfish from nets can be difficult and dangerous so some fishermen will kill them before bringing them aboard.

By understanding issues like overfishing and habitat loss Yan et al. were able to show that sawfish are likely to be extinct off the coasts of 55 of the 90 countries where they previously existed. Their findings also suggest that if eight nations prioritise sawfish conservation (Cube, Tanzania, Colombia, Madagascar, Panama, Brazil, Mexico and Sri Lanka), then up to 71.5% of the sawfish family’s historical global distribution would be protected.

Original research: https://doi.org/10.1126/sciadv.abb6026

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Diving for Science by Dr. Phil Colarusso

Collecting data
Breathing air underwater
They pay me for this!

By Phil Colarusso

The US Environmental Protection Agency (EPA) uses scuba diving as one of many tools to study and monitor aquatic systems.  EPA currently supports 65 divers spread throughout the United States. 

Divers are involved in a wide range of scientific pursuits, including studying, monitoring and restoring valuable aquatic habitats (coral reefs, seagrass meadows, shellfish beds), tracking invasive species, collecting sediment and water samples for chemical analysis and a wide range of other duties. 

Photo credit: Phil Colarusso

EPA divers go through a rigorous training program and are required to maintain high levels of diving proficiency and safety protocols.  For more information on EPA’s scientific diving program go to: https://www.epa.gov/diving

Dr. Phil Colarusso is a marine biologist with US EPA Region I.  He has been working on eelgrass restoration, conservation and research for 31 years.  He and his team just recently had a paper on carbon sequestration rates in eelgrass in New England accepted for publication.

Enjoyed Phil’s sciku? Check out his previous sciku Blue Carbon and Invasive Species.

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Invasive Species by Dr Phil Colarusso

Misplaced visitors
Cryptic hitchhikers on boats
Food webs are altered

By Phil Colarusso

While doing eelgrass restoration work in Gloucester, I became aware of a bluish-gray growth appearing on a large number of shoots. Shortly thereafter, I read in the Woods Hole journal Oceanus about a researcher who was seeing a new species of invasive tunicates (Diplosoma listeria) appearing on scallops, boat hulls, mooring lines and eelgrass on Martha’s Vineyard. The photo was of exactly the same thing I was seeing in Gloucester.

Tunicates are filter feeding organisms that can grow as small zooids in extensive colonies or as large solitary individuals. The colonial forms tend to be prolific breeders and filter enormous quantities of water. They can grow quickly and will cover just about any surface that is bare, including pilings, clam shells, algae and eelgrass. Recent research has shown that literally miles of the seafloor can be covered by one of these colonial species, smothering other sessile life and altering the availability of the habitat.

Photo credit: Phil Colarusso

My team decided to conduct a study in a salt pond on Martha’s Vineyard, where these organisms had appeared to be particularly abundant. We initially had focused on the impact of these animals to the eelgrass in the pond, but quickly realized their prolific filter feeding may pose an additional risk to the food web of this small coastal pond.

Using stable isotopes, we determined the tunicates were feeding on the same resources as several commercially important shellfish species. Based on their high abundance, their prolific feeding rates and the small volume of the pond, our modelling suggested the tunicates could potentially filter a volume of water equivalent to the entire pond in somewhere between 1 and 17 hours. This represents a significant challenge for commercial shellfish stocks in these waters. You can see a video on this project here.

Photo credit: Phil Colarusso

It is not always clear where and how these invaders arrive, but shipping is believed to be a major vector. Planktonic life forms and small creatures are carried in ballast water and along the hulls or larger vessels. Globalization has significantly increased shipping all over the planet and as a result the unintentional transportation of organisms as well. Early detection may allow for some level of control, but often once a new species is detected in the ocean, control options are untenable. Persistent monitoring is the most prudent tool in identifying and controlling the spread of non-native species.

Original research:

Colarusso, P. et al. (2016) Quantifying the ecological impact of invasive tunicates to shallow coastal water systems. http://dx.doi.org/10.3391/mbi.2016.7.1.05

Valentine, P.C. et al. (2007) The occurrence of the colonial ascidian Didemnum sp. on Georges Bank gravel habitat – Ecological observations and potential effects on groundfish and scallop fisheries. https://doi.org/10.1016/j.jembe.2006.10.038

Dr. Phil Colarusso is a marine biologist with US EPA Region I.  He has been working on eelgrass restoration, conservation and research for 31 years.  He and his team just recently had a paper on carbon sequestration rates in eelgrass in New England accepted for publication.

Enjoyed Phil’s sciku? Check out his other of his sciku Blue Carbon and Diving for Science.

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Blue Carbon by Dr. Phil Colarusso

Climate change buffer
Particles settle in grass
Seagrass meadows rule

By Phil Colarusso

Seagrass meadows collect and sequester large amounts of carbon in the sediments below the meadows.  The carbon accumulates through 2 different pathways.  First, through photosynthesis and tissue growth, seagrasses extract carbon from the water column and incorporate it into its own tissues. The root and rhizome structures and some cast leaf material end up being incorporated into the sediments.  In most cases, this provides less than half of the carbon found in those sediments.  The majority of the carbon in the sediments originates from outside of the meadow.  The canopy of the meadow functions as a filter, facilitating the settlement of organic particles as the tide passes over the meadow going in and out. 

As long as the meadow stays intact, the carbon in the sediments remains isolated and out of the global carbon cycle.  Data shows that the age of carbon in meadows can be hundreds of years old.  Seagrass meadows, salt marsh and mangroves all perform the same carbon sequestration function and collectively are referred to as blue carbon habitats.  This is still a relatively young field of research.

Photo credit: Phil Colarusso

In the above photo, you can see the seafloor in the foreground, which is primarily sandy cobble.  The eelgrass meadow has a dark organic layer indicating the large carbon component that has accumulated due to the presence of the plants.

Further reading on seagrass blue carbon: https://doi.org/10.1038/ngeo1477

Dr. Phil Colarusso is a marine biologist with US EPA Region I.  He has been working on eelgrass restoration, conservation and research for 31 years.  He and his team just recently had a paper on carbon sequestration rates in eelgrass in New England accepted for publication.

Interested in seagrass meadows? They’re also hugely important for the world’s fisheries. Find out more in the sciku Forgotten Value here. You can also check out Phil’s sciku Invasive Species and Diving for Science.

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Backlit Billboards in the Sea by Prof Teena Carroll

Sending messages,

luminescent Humboldt Squid

flicker in the deep.

by Teena Carroll

A group of scientists at the Monterey Bay Aquarium Research Institute conducted a study of Humboldt squid using remote operated vehicles.  They wanted to determine how a group of squid could execute complex behaviors in low light deep sea conditions.  For instance, the squid avoid body contact with each other even when pursuing the same prey.

Burford and Robison (2020) found that the squid used specific color patterns on their bodies primarily when they were hunting in groups.  Normally, such color changes would not be visible in the deep sea; Humboldt squid are bioluminescent which researchers hypothesize essentially provides backlighting to highlight the color changes.

The complexity of the color changes prevented the researchers from translating exactly what the squid are communicating.  However they were able to document that the patterns are a consistent and effective communication method.  After observing repeated patterns, they think that the visual language of the squid may be evolved enough to use syntax.

Original research: https://doi.org/10.1073/pnas.1920875117

Additional information: https://www.mbari.org/humboldt-squid-signaling/

Teena Carroll is a mathematics professor at Emory & Henry College in Southwest Virginia and has been a poet longer than she has been a mathematician. @Teena Carroll

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Holdfast

Marine forests sway,
sheltering, pristine, unchanged.
For how much longer?

Giant kelp forests are some of the most diverse, productive and dynamic ecosystems on the planet. A marine algae (not a plant), giant kelp anchors itself to the seabed and grows up towards the surface, with some species growing up to 30-60 centimetres vertically a day to reach heights of 45 meters. Whilst typically found in temperate and polar coastal oceans, deep water kelp forests have been discovered in clear tropical waters where the sunlight can penetrate far enough below the water surface for the kelp to grow, potentially as far down as 200 meters.

Kelp forests are home to a vast number of species, from those living in the surface canopy to those on the seafloor. This makes them key areas to protect for species richness, much like rainforests and coral reefs. Yet many kelp forests are under threat due to marine pollution, water quality, kelp harvesting, overfishing, invasive species and climate change.

This makes the recent survey of kelp forests in southern South America heartening. Friedlander et al. (2020) re-surveyed 11 locations at the easternmost extent of Tierra del Fuego and compared their findings to surveys originally conducted in 1973. They found no differences in kelp densities or anchor diameter. Sea urchins, if not kept in check, can decimate kelp forests but the researchers also found no difference in sea urchin numbers. Additionally, comparisons of satellite imagery showed no long-term trends over the past 20 years.

It’s thought that the remoteness of the location has meant these kelp forests have been relatively unaffected by human disturbance, although increases in sea temperature as a result of climate change are likely to have an impact in the future.

A note about ‘Holdfast’ – The title refers to both the wish that kelp forests such as the one surveyed in this study persist and survive, and to the root-like mass that anchors kelp to the seafloor which is known as the kelp’s holdfast.

Original research: http://dx.doi.org/10.1371/journal.pone.0229259

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Amid fields of rubble

Seamounts amid fields
of rubble, scars and lost gear.
A glimmer of hope.

Seamounts are underwater mountains that rise at least 1,000 meters above the seafloor with their peaks hundreds or even thousands of meters underwater. Seamounts are often thriving areas of marine life, based around high levels of plankton and deep-sea corals.

However the fishing practice of trawling can decimate these areas, destroying corals and causing huge population crashes in the species that depend on them. Deep-sea coral growth rates can be as little as micrometres a year meaning that recovery, if possible, could be very slow. As a result it’s unknown whether protecting areas damaged by trawling is worthwhile or whether once lost these deep-sea communities are unlikely to recover.

New research by Baco et al. (2019) sheds comforting light on this dimly known area. Whilst little evidence supports seamount recovery over 10 years, their study examined recovery following 30-40 years protection from trawling. Encouragingly many of the sites surveyed showed multiple signs of recovery, including coral regrowth and higher levels of animal life compared to areas still being trawled. The research is clear and much needed evidence to support continued seamount protection efforts.

Author’s note: I thought that the research study’s title was too poetic to improve upon so used part of it in this sciku. The full title is ‘Amid fields of rubble, scars, and lost gear, signs of recovery observed on seamounts on 30- to 40-year time scales’ by Amy R. Baco, E. Brendan Roark and Nicole B. Morgan.

Original research: http://dx.doi.org/10.1126/sciadv.aaw4513

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Flocks of new markers

Little white sponges,

filtering in mining zones:

Flocks of new markers.

 

New species are being discovered all the time and even the most innocuous can be important. A new species of sponge has been discovered and recorded by Lim et al (2017) at a depth of 4000m on the abyssal seafloor of the central Pacific Ocean. Morphologic and genetic analysis of the sponges (Plenaster craigi) has revealed they are a new genus, currently placed within the family Stelligeridae.

The region where the sponges are found is rich in polymetallic (metal-rich) nodules and may well be subjected to deep-sea mining. The sponges could be useful indicators of the impacts of such mining efforts – they are abundant on the nodules, are easily identified and are filter-feeders so sensitive to changing conditions.

The Latin name Plenaster is due to the abundance of star-shaped microscleres within their bodies, whilst the species name of craigi is in honour of the Chief Scientist on the expeditions that sampled the species Professor Craig R. Smith of the University of Hawaii.

Original research: http://dx.doi.org/10.1080/14772000.2017.1358218