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Marine Life & Conservation

Study shows krill is important food source for Mobulid Rays

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A new study by scientists at the Marine Megafauna Foundation (MMF), Large Marine Vertebrates Research Institute Philippines (LAMAVE), the University of Queensland, and Scripps Institution of Oceanography was published in Royal Society Open Science last week, providing novel insights into the food sources of four mobulid ray species found in the Bohol Sea, Philippines.

Mobulids have slow growth and reproductive rates, making them vulnerable to overexploitation. Targeted and incidental fishing continue to cause population declines in various locations worldwide, and, as a result, Manta birostris and Mobula tarapacana have been listed as ‘vulnerable’ on the IUCN Red List of Threatened Species, and Mobula japanica and Mobula thurstoni as ‘near threatened’.

Dietary studies can inform fisheries and help reduce by-catch through the identification of critical feeding areas, where the occurrence of mobulid rays and targeted fishes overlap. For direct, short-term assessment of diet through stomach contents analyses, access to dead specimens is required, which can be challenging for rare or internationally protected species such as mobulids.

For this study, scientists were granted access to a targeted mobulid fishery which operates out of Jagna, Bohol in the Philippines from November to May. Stomach contents of all examined mobulid species were dominated by the krill Euphausia diomedeae (91% of stomachs contained the species), suggesting that this zooplankton species is abundant during this period. The larger mobulids also contained small mesopelagic fishes in their stomachs in addition to krill.

“Our results show that krill can be an important food source for large filter feeders living in tropical seas with surface waters that are low in plankton at the surface during the day. Krill migrates vertically, staying deep during the day and shallow, including at the surface, at night when the mobulids were caught”, commented Dr Chris Rohner, principal scientist at the Marine Megafauna Foundation. “Some mobulids had empty stomachs, while others had just finished a huge meal, which shows that tropical mobulids have a boom-and-bust strategy, feeding in dense prey patches when they are available and then undergo a period of starvation until they find the next prey patch.”

Stomach content studies provide a direct, but short-term snapshot of a species’ diet, while biochemical analyses can provide an indirect, but longer-term view. In 2016, manta ray scientists at the Marine Megafauna Foundation in collaboration with Proyecto Mantas Ecuador published a study using non-lethal muscle tissue sampling and stable isotope analysis, which revealed that Manta birostris found in the waters off Isla de la Plata, Ecuador, largely feed on prey originating from the mesopelagic zone (200 to 1,000 meters below the ocean surface) rather than on surface zooplankton. The new study from the Philippines now provides direct evidence to the theory that large planktivores in the tropics and subtropics heavily feed on mesopelagic migrating prey.

Photo: Gonzalo Araujo, LAMAVE


The Marine Megafauna Foundation was created in 2009 to research, protect and conserve the populations of threatened marine megafauna around the world. ‘Megafauna’ are large marine species such as sharks, rays, marine mammals and sea turtles – marinemegafauna.org

Large Marine Vertebrates Research Institute Philippines (LAMAVE) is the largest independent non-stock non-governmental organization dedicated to the conservation of marine megafauna and their habitats in the Philippines. LAMAVE strive for conservation through scientific research, policy and education -
 lamave.org

Marine Life & Conservation

New report shows simple measures needed to cut beach plastic pollution

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The Marine Conservation Society has launched its annual State of our Beaches 2023 report, highlighting the need for less single-use plastic items and more refillable options.

The charity’s beach cleaning programme, now in its 30th year, asks volunteers to record all litter that they find within a 100-metre stretch of beach. By gathering vital data from across the UK and Channel Islands, the charity creates change for cleaner seas and a healthier planet through policy and industry change. Last year, over 148 kilometres of beach were surveyed by volunteers, who removed 17,208kgs of litter from our coast.

Using data collected by over 14,000 volunteers, the State of our Beaches 2023 report shows that half of all litter collected came from public sources – either dumped, blown or washed onto our beaches.

Drinks-related litter, such as plastic bottles, caps and cans were one of the most found items, with an average of 16 found per 100 metres of beach surveyed. This figure is up 14% compared to the charity’s 2022 report.

Plastics caps and lids were recorded on 89% of surveys, with over 30,000 found in total. Plastic bottles were also commonly collected, with 73% of surveys finding this single-use item – a 4% increase compared to 2022. The charity’s inland litter pick survey, Source to Sea, also reported finding plastic bottles on 92% of cleans.

However, the charity’s State of Our Beaches 2023 report also indicates that some types of litter are on a downward trend. Although still in the top 10 litter items, disposable plastic cutlery, trays and straws were found on 5% fewer beaches across the UK, showing that bans on these plastic items between 2022 – 2023 could be working. The presence of plastic cotton bud sticks also dropped by 14%.

Lizzie Price, Beachwatch Manager at the Marine Conservation Society, said, “Half of the litter found on our beaches originates from public sources, underscoring the pressing issue of single-use plastic. Evidence shows that refillable alternatives and litter return schemes effectively reduce rubbish, as demonstrated by the decline our data has shown in items like plastic bags and disposable cutlery.

“Urgent and decisive action from UK governments is needed to accelerate our shift towards a circular economy, where we reuse, repair and recycle. The public needs greater access to refillable products and systems need to be implemented in which manufacturers are responsible for their waste.”

Governments across the UK have committed to delivering deposit return schemes from October 2025. However, the proposed scheme in England does not include glass items, despite glass being found on 52% of beaches in 2023. The charity is calling for governments across the UK to introduce compatible all inclusive deposit return schemes as soon as possible. This would see aluminium cans, and plastic and glass bottles have a 20p deposit which would be returned when recycled which would reduce drinks-related pollution.

Businesses are, however, starting to take refillable and reusable options into their own hands. Supermarket chain, Aldi, the largest corporate funder of the charity’s 2024 Beachwatch programme, is already leading the charge in refillable items by trialling refillable options for cereals and porridge oats in their stores over the past 5 months.

Plastics and Packaging Director, Luke Emery, from Aldi, who are running 4 beach cleans for staff and volunteers in 2024, said, We are continually working to reduce single-use plastics and packaging, and making unpackaged product options more commonplace for our customers is a key part of this. We are really pleased with the uptake of our refillable range so far by customers. Not only are we making sustainable shopping more accessible, but we also offer refill products for a better price than the packaged alternative, helping our customers save money.”

Marine litter is one of the biggest threats to our seas, with plastic breaking down over time into microplastics and threatening marine life which can ingest or become entangled in them. The Marine Conservation Society is urging the UK Government to move faster on its policies to cut down plastic waste and prevent items from reaching our seas.

To find out more about the charity’s beach cleans and how to get involved, please visit mcsuk.org/beach-cleans

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Guarding Against Coral Invaders

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Protecting (Dutch) Caribbean Reefs from Unomia stolonifera

Recent reports highlight the concerning spread of the invasive soft coral, Unomia stolonifera, currently devastating Venezuela’s marine ecosystems and detected in Cuba. With the potential threat of its expansion to the (Dutch) Caribbean islands, urgent action and awareness are essential to safeguard marine biodiversity and local economies from possible catastrophic consequences.

Invasive species are animals or plants from another region of the world that don’t belong in their new environment. These species can have major ecological effects by decimating native flora or fauna. They can also cause large economic losses and impact human health. Invasive species also pose a significant threat to marine ecosystems worldwide, including the Dutch Caribbean. Among these invaders is the octocoral species Unomia stolonifera or “Pulsing Xenia”, originally from the Indo-Pacific. With its rapid growth and lack of natural predators, this species can outcompete native species and disrupt fragile marine habitats such as seagrass beds and coral reefs.

Background

The invasive soft coral U. stolonifera was first identified in 2014, off the coast of Venezuela. It is believed to have been introduced via the illegal aquarium trade.  Since this species can reproduce sexually and asexually (or fragment), even small pieces can regenerate to spread.  Once introduced it quickly took over shallow reefs and hard substrate at depths of 0-50 meters, outcompeting local corals and seagrass for space.  Follow on surveys found that this coral species exhibited average percentage cover as high as 80%, vastly outcompeting native corals. In highly colonized areas, fish are disappearing due to loss of habitats.

In 2022, during a survey conducted in Cuba by the University of Havana, an unknown octocoral was discovered which was later identified as the invasive Unomia stolonifera. It is suspected that the coral larvae arrived in ballast water from fossil fuel ships originating from Venezuela, as nearby sites adjacent to Venezuelan ports have been heavily affected by the invasion.

How to help

Prevention through continuous monitoring, particularly in high-risk areas such as marine harbors and oil facilities, is paramount. Early detection plays a pivotal role in mitigating the threat posed by Unomia stolonifera.

The public’s involvement and awareness are also vital. Local communities, recreational divers, tourists, and all stakeholders are urged to participate in early detection efforts by reporting sightings (photo, location and date) of this invasive coral to their respective Protected Area Management Organization (PMO’s)- the Fundacion Parke Nacional Aruba (FPNA)STINAPA BonaireCARMABI Curaçao Saba Conservation Foundation (SCF)Nature Foundation St. Maarten (NFSXM) and St. Eustatius National Parks (STENAPA). If an invaded area is confirmed, follow the recommendations by the local PMO’s.

Keys to Success

Despite the challenges, early detection is key to mitigating the threat posed by Unomia stolonifera. With continued vigilance, research, and community engagement, there is hope for containing this potential issue before it becomes a major threat.

About the DCNA

The Dutch Caribbean Nature Alliance (DCNA) supports (science) communication and outreach in the Dutch Caribbean region by making nature related (scientific) information more widely available through amongst others the Dutch Caribbean Biodiversity Database, DCNA’s news platform BioNews and through the press. This article contains the results from several scientific studies but the studies themselves are not DCNA studies. No rights can be derived from the content. DCNA is not liable for the content and the in(direct) impacts resulting from publishing this article.

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