Wednesday, November 13, 2024

New video shows sharks making an easy meal of spiky sea urchins, shedding light on an undersea mystery

New video shows sharks making an easy meal of spiky sea urchins, shedding light on an undersea mystery

From The Conversation by Jeremy Day

Long-spined sea urchins have emerged as an environmental issue off Australia’s far south coast. Native to temperate waters around New South Wales, the urchins have expanded their range south as oceans warm. There, they devour kelp and invertebrates, leaving barren habitats in their wake.

Lobsters are widely accepted as sea urchins’ key predator. In efforts to control urchin numbers, scientists have been researching this predator-prey relationship. And the latest research by my colleagues and I, released today, delivered an unexpected result.

We set up several cameras outside a lobster den and placed sea urchins in it. We filmed at night for almost a month. When we checked the footage, most sea urchins had been eaten – not by lobsters, but by sharks.

This suggests sharks have been overlooked as predators of sea urchins in NSW. Importantly, sharks seem to very easily consume these large, spiky creatures – sometimes in just a few gulps! Our findings suggest the diversity of predators eating large sea urchins is broader than we thought – and that could prove to be good news for protecting our kelp forests.

A puzzling picture

The waters off Australia’s south-east are warming at almost four times the global average. This has allowed long-spined sea urchins (Centrostephanus rodgersii) to extend their range from NSW into waters off Victoria and Tasmania.

Sea urchins feed on kelp and in their march south, have reduced kelp cover. This has added to pressure on kelp forests, which face many threats.

Scientists have been looking for ways to combat the spread of sea urchins. Ensuring healthy populations of predators is one suggested solution.

Overseas research on different urchin species has focused on predators such as lobsters and large fish. It found kelp cover can be improved by protecting or reinstating these predators. 

 
Sea urchins feed on kelp. Nathan Knott

In NSW, eastern rock lobsters are thought to be important urchin predators. The species has been over-fished in the past but stocks have significantly bounced backin recent years.

But despite this, no meaningful reduction in urchin populations, or increase in kelp growth, has been observed in NSW.

Why not? Could it be that lobsters are not eating urchins in great numbers after all? Certainly, there is little empirical evidence on how often predators eat urchins in the wild.

What’s more, recent research in NSW suggested the influence of lobsters on urchin populations was low, while fish could be more important.

Our project aimed to investigate the situation further.

Eastern rock lobsters are thought to be major urchin predators. Flickr/Richard Ling, CC BY
 
 What we did

We tied 100 urchins to blocks outside a lobster den off Wollongong for 25 nights. This tethering meant the urchins were easily available to predators and stayed within view of our cameras.

Then we set multiple cameras to remotely turn on at sunset and turn off after sunrise each day, to capture nocturnal feeding. We used a red-filtered light to film the experiments because invertebrates don’t like the white light spectrum.

We expected our cameras would capture lobsters eating the urchins. But in fact, the lobsters showed little interest in the urchins and ate just 4% of them. They were often filmed walking straight past urchins in search of other food.

Sharks, however, were very interested in the urchins. Both crested horn sharks (Heterodontus galeatus) and Port Jackson sharks (H. portusjacksonii) entered the den and ate 45% of the urchins.

As the footage below shows, sharks readily handled very large urchins (wider then 12 centimetres) with no hesitation.

Until now, it was thought few or no predators could handle urchins of this size. Larger urchins have longer spines, thicker shells and attach more strongly to the seafloor, making them harder to eat.

But the sharks attacked urchins from their spiny side, showing little regard for their sharp defences. This approach differs from other predators, such as lobstersand wrasses, which often turn urchins over and attack them methodically from their more vulnerable underside.

In fact, some sharks were so eager to eat urchins, they started feeding before the cameras turned on at sunset. This meant we had to film by hand.
Footage captured by the researchers showing crested horn sharks eating sea urchins. Horn sharks generally do not pose a threat to humans.
 
Footage captured by the researchers showing crested horn sharks eating sea urchins.
Horn sharks generally do not pose a threat to humans.
 
A complex food web

Our experiment showed the effect of lobsters on urchins in the wild is less than previously thought. This may explain why efforts to encourage lobster numbers have not helped control urchin numbers.

We also revealed a little-considered urchin predator: sharks.

Lobsters are capable but hesitant predators, whereas sharks seem eager to eat urchins. And the shark species we filmed are abundant, hardy and not not actively fished.

When interpreting these findings, however, a few caveats must be noted.

First, sharks (and lobsters) are not the only animals to prey on urchins. Other predators include bony fishes, and more are likely to be identified in future.

Second, other factors can control urchin numbers, such as storm damage and the influx of fresh water.

And finally, it is unsurprising that we found a key predator when we intentionally searched for it by laying out food. Tethering urchins creates an artificial environment. We don’t know if the results would be replicated in the wild.

And even though we now know some shark species eat sea urchins, we don’t yet know if they can control urchin numbers.

But our research does confirm predators capable of handling large urchins may be more widespread than previously thought.

Tuesday, November 12, 2024

Philippines : new map redraws maritime boundaries

NAMRIA nautical raster chart

The Philippines will release soon a new map that will include the West Philippine Sea within its jurisdiction, the National Mapping and Resource Information Authority (Namria) said Friday.

 
A new Philippine map that includes the West Philippine Sea (WPS) as part of its jurisdiction will be released soon, the National Mapping and Resource Information Authority (Namria)
This map is not to scale and is for visual representation purposes only.
Graphics by: Samuel Yap / INQUIRER.net


Speaking during a press conference in Malacañang, Namria Administrator Peter Tiangco said the map will be published after the implementing rules and regulations (IRR) for the newly signed Republic Act (RA) 12064, or the Philippine Maritime Zones Act, is released.

"We already have the maps prepared. We are just waiting for the implementing rules and regulations in order for us to modify or revise the maps we have prepared accordingly until its final publication," Tiangco said.

Asked to compare the new map with that one issued by China in August 2023, which incorporates Taiwan and most of the West Philippine Sea, Tiangco said: "The big difference here is that our map has a legal basis supported by existing laws."

Earlier on Friday, President Ferdinand Marcos Jr. signed the Philippine Maritime Zones Act that aims to declare the country's maritime zones in accordance with the standards set by the United Nations Convention on the Law of the Sea (Unclos).
 

 
The Maritime Zones Law uses the archipelagic baselines under the 2009 Philippine Baselines Law as the basis upon which the country's maritime zones are measured.

Apart from identifying the Philippine internal waters, the law also defines the archipelagic waters, full entitlement of a 12 nautical miles territorial sea, declaration of a 24 nautical miles contiguous zone from the baselines, and the 200 nautical miles exclusive economic zone and continental shelf where the Philippines can exercise sovereign rights and jurisdiction.


During the same press briefing, Sen. Francis Tolentino said the signing of the Philippine Maritime Zones Act was an enforcement of the 2016 arbitral ruling that invalidated China's massive claims in the South China Sea.

Tolentino, who sponsored the measure in the Senate, also expressed elation over the enactment of the law as well as the Philippine Archipelagic Sea Lanes Act.

He said the newly inked law would also mean "legislating the West Philippine Sea."
 
Philippines EEZ in the GeoGarage platform
 
 
NAMRIA including outer limits of the Extended Continental Shelf in the Benham Rise Region
 
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Sunday, November 10, 2024

Vendée Globe 2024 : the 10th edition is coming


 
The Vendée Globe covers 45,000 km (24,300 miles) around the world! 
Starting from Les Sables d'Olonne, the race passes through the Atlantic, Indian, and Pacific Oceans, before returning to Vendée.
To protect marine wildlife (whales, sharks...), Biodiversity Protection Zones have been established by the Share the Ocean consortium with support from the Vendée Globe Foundation.
The goal? To minimize the risk of collisions between IMOCA yachts and marine megafauna in these crucial feeding and breeding areas.
 
40 Skippers 6 Women, 34 Men
Average age: 42 
(Youngest Violette Dorange 23 with oldest boat Devenir FRA 1 (2006), 
oldest Jean Le Cam 67 with newest boat Virgile FRA 29 (2023)
16 IMOCA daggerboards / 24 IMOCA foils  (13 boats have not made a VDG)

Links :