Featured Creature: Whale Shark

What creature is the largest of its kind, sports beautiful patterns, and holds a reputation for being a ‘gentle giant’? 

The whale shark!

Photo by Shiyam ElkCloner (CC BY-SA 3.0 via Wikimedia Commons)

Filter feeding for giants 

The majestic whale shark is famed for being the largest fish in existence. With a length of up to 33 feet and weight up to 20 tons, they are not only the largest living fish, but thought to be the largest fish that ever lived on this planet. Though their name might suggest otherwise, whale sharks are not a type of whale at all, but instead a member of the shark family. It is their enormous size (akin to a school bus) that led them to be compared with whales. 

Like their other shark relatives, these creatures are excellent swimmers and true masters of the deep. People are coming to recognize that all sharks, even carnivorous species that hunt marine mammals, fish, or other invertebrates, have been unfairly mischaracterized as threatening, and whale sharks are another species you need not be afraid of. 

In fact, one of the most fascinating traits of the whale shark is its diet. Despite their own large size, whale sharks subsist on some of the smallest ocean inhabitants, plankton. Much like the enormous blue whale, whale sharks are a living example of one of the most interesting links in the food chain, where nutrients are cycled from microscopic life to macroscopic organisms. 

They filter-feed by opening their mouths and letting plankton-rich waters pass through, as well as ingesting other small fish or unlucky invertebrates along the way. But even in this habit they are unique. Whale sharks use a technique called “cross-flow filtration,” in which particles do not actually catch on the filter (the way it works when we drain pasta through a strainer or breathe through an N95 mask). Instead, water is directed away through the gills while particles move towards the back of the mouth. A bolus (or a spinning ball of food) grows in size as more particles are concentrated, finally triggering a swallowing reflex in the throat. This avoids clogging any filters in the process and is a particularly efficient method of filter feeding. 

Because they are so large, whale sharks need a lot of food to sustain themselves, and so they journey long distances in order to eat enough for their great big appetites. They can be observed throughout the world in warm tropical waters and tend to lead solitary lives. Where there is an abundance of plankton, however, whale sharks are sure to follow. For example, in the Springtime many whale sharks migrate to the continental shelf of the Central West Coast of Australia, where Ningaloo Reef is the site of a great coral spawning that produces water rich with plankton for our giant fishy friends to enjoy.

Photo by Leonardo Lamas from Pexels

Big fish in a complex sea

The whale shark contributes to nutrient cycling throughout its lifespan, providing important benefits to the ecosystems they are a part of. Some of the warm tropical waters that whale sharks call home tend to be low in nutrients and productivity, and in these areas whale sharks can make a big difference due to their size and force. As they undertake migrations or even as they go about daily swimming and feeding activities, their motion stimulates small ocean currents that can help nutrients travel from areas of high productivity to waters where they are much less concentrated. 

Their own eating habits rely on an abundance of microscopic creatures and the nutrients they metabolize, and eventually each mighty whale shark passes on and becomes food itself, returning those nutrients to the ocean food web. After death, whale sharks sink to the ocean floor and the benthic organisms that reside there find food and shelter in the great carcasses. It can take decades for this decomposition to occur, and in the meantime hundreds of creatures benefit from the habitat and nutrients left behind.  

In life as well, whale sharks can provide refuge to smaller species of fish that travel around their great bodies, taking advantage of the shelter these gentle giants create. As largely docile creatures, whale sharks can be quite approachable and playful with divers who are also interested in tagging along: 

In a couple of instances, humans have even pushed their luck so far as to ride along on a whale shark’s back! Such close contact is discouraged by conservationists to protect the personal space of these beautiful animals, but whale sharks’ friendly reputation remains. 

Though they may be steady, generous members of the ocean community, whale sharks are struggling to survive in changing conditions. They are an endangered species, and while some protections for these creatures have been enacted across the coastal waters of the world, they are still hunted for meat, fins, and oil, or captured or killed as bycatch in industrial fishing operations. Whale sharks also suffer from the plastic pollution in our oceans, as microplastics mingle with the food they rely on. Like the rest of us, whale sharks need clean, healthy, abundant environments in which to live and co-create. 

Whale shark in the Maldives (Photo by Sebastian Pena Lambarri from Unsplash)

Unique beauties

Whale sharks may be known for their size, but that’s not the only special thing about their anatomy and appearance. Each whale shark sports a beautiful pattern of white markings on its dark gray back. Not only does this make these creatures look like giant mobile modern art pieces, but the patterns also uniquely identify whale shark individuals.

It is not conclusively determined why whale sharks carry these unique signatures, their own version of the human fingerprint. Some scientists speculate that the patterns, which tend to be common among carpet sharks and other species that find such markings useful for camouflage as they traverse the ocean floor, indicate a close evolutionary link among these organisms.  

The World Wildlife Fund has used these markings to identify individuals in the waters around the Philippines and keep track of whale shark population numbers there, so that humans can make the interventions needed to mindfully coexist with our marine friends. Whatever its distant origin or function today, this feature makes it clear that each whale shark is a special and irreplaceable member of our blue planet. 

For gentle giants and filtering friends,
Maya


Maya Dutta is an environmental advocate and ecosystem restorer working to spread understanding on the key role of biodiversity in shaping the climate and the water, carbon, nutrient and energy cycles we rely on. She is passionate about climate change adaptation and mitigation and the ways that community-led ecosystem restoration can fight global climate change while improving the livelihood and equity of human communities. Having grown up in New York City and lived in cities all her life, Maya is interested in creating more natural infrastructure, biodiversity, and access to nature and ecological connection in urban areas.


Sources and Further Reading:
https://www.worldwildlife.org/species/whale-shark
https://www.georgiaaquarium.org/animal/whale-shark/
https://www.nationalgeographic.com/animals/fish/facts/whale-shark
https://en.wikipedia.org/wiki/Whale_shark
https://earth.org/endangered-species/whale-sharks/
https://www.4ocean.com/pages/whale-shark-cause-of-the-month

Featured Creature: Clamworm

Photo by Alexander Semenov

What sort of worm is festooned with sensitive tentacles all the way down its sides and – though it can’t bark – has a nasty bite?


That would be the “clam worm” or alitta succinea, a denizen of estuarial waters.

Alternative names

I’ve always called them “seaworms” but they are normally known as “clam worms,” “ragworms,” “sand worms” or “pile worms”, and they are a species of annelid, the phylum of segmented worms.

Size and habitat

The clam worm can reach up to 15 cm (almost 6 inches) but most are smaller. This worm is reddish-brown in color, and has four eyes, tentacles or flaps all the way down its sides which can also function as gills, and sensory feelers at its head. 

When hungry, it uses a long internal mouthpart called a proboscis, along with two hooks that unfold to capture and then draw prey into a mouth at its front end. These worms are themselves an important food source for fish and crustaceans, and are widely used as fishing bait. Their typical habitat is rocks, vegetation, reefs, and mud. They burrow into the mud or sand, or hide under rocks, to be safe from many potential predators.

Photo from wikimedia.org

My own first encounter 

In my early teens, my father and I used to fish for striped bass with a flashy lure with a seaworm strung on a hook behind it. “Here’s how you do it,” my father counseled me. “Just poke the worm in its mouth and, as soon as it opens, insert the hook point.”

“Owww!!!” I exclaimed. “This worm bit me!” My father laughed, almost as hard as during one of my earlier ‘learning moments’ in a Maine field, when halfway over an electric fence I got shocked! On neither occasion did I expect the bite, but I eventually learned to be more careful. Those pincers were sharp! 

The pincers’ zinc content makes them strong while keeping them very lightweight. They certainly drew my blood that first time! The fish surely liked these worms, but eventually I gave them up for flies (less messy and easier on the worms).

Spawning behavior 

During the full and new moon tides in the late spring and early summer, these clam worms undergo a process called epigamy, which enlarges their parapodia (tentacles) so they can swim more easily to the surface to release their eggs and sperm, at which point their bodies rupture and disintegrate. Talk about dying to reproduce! One hopes at least they have fun on their way out. Their fertilized eggs then settle to the bottom and hatch into a new generation.

Replacement parts 

These worms can replace various body parts, and make new worms from broken pieces, such as when their tails are pulled off by a predator. But rear body segments are more readily repaired than heads, which are much harder to replace – those of us our heads still on can probably relate!

Check out a short video on clam worms and their special properties:

Their role in marine ecosystems 

The tunneling and boring of marine worms irrigate and oxygenate the shallow water pools encouraging beneficial plant and algae growth. Whether it’s in tide pools, lowland waters or oceanic reefs, the marine worm’s primary ecological contribution is as sustenance for aquatic animals further up the food chain. Species of these worms respond quickly to increased amounts of pollution in the water and on the ocean bottom. Their presence or absence may indicate important changes in the marine environment.

Some subspecies are at risk, but clam worms are OK 

Most of this species is doing just fine, at least when not being used for bait or eaten by humans. However, you might just want to think twice before skinny dipping on May-June new or full moon tides!

By Fred Jennings

Featured Creature: Giant Barrel Sponge

What creature grows tall and sturdy, cleans up its neighborhood, and defends itself from predators – all without moving a muscle?

The Giant Barrel Sponge, or Xestospongia muta!

Photo By Twilight Zone Expedition Team 2007, NOAA-OE – NOAA Photo Library (Public Domain, via Wikimedia Commons)

A Giant Barrel by any other name… 

Giant barrel sponges are aptly named for their shape and great size. They grow over 1 m tall, but only grow an average of about 1.5 cm a year. After all, good things take time! 

Giant barrel sponges come in a range of colors, depending on the presence of the cyanobacteria that they work with in symbiosis. They can be pink, purple, brown, reddish brown, and gray, and tend to be different colors at different depths. 

You may be wondering why this “giant barrel” doesn’t look very much like Spongebob Squarepants, or the sponge you use to clean up in the kitchen. Well sponges, or animals of the phylum Porifera, come in all shapes and sizes, and there is great diversity among the 8,550 species of them. Sponges are quite ancient, with their oldest fossil records dating back 600 million years, so they’ve had time to differentiate and find their own ecological niches.

The giant barrel sponge is known as the “Redwood of the Sea.” The phrase comes from the fact that giant barrel sponges share the tendency for individuals to live long lives, from a few hundred to thousands of years old. In fact, the oldest known giant barrel sponge is over 2000 years old. 

Old age isn’t the only thing they have in common with their counterparts on land. Like the magnificent redwoods, they do wonders to clean up and support the environment around them. Giant barrel sponges can filter up to 50,000 times their own volume in water in a single day. They also provide habitat to several small fish and other invertebrates that can be found living inside or on the surface of the sponge.

Photo by Andre Oortgijs (CC BY-SA 3.0 via Wikimedia Commons)

How does such a giant creature sustain itself?

Although giant barrel sponges are, well, giant, their diet is anything but. These creatures, like many species of whales, sustain their size not by eating very large sources of food, but by eating large volumes of it. Giant barrel sponges are filter feeders, and consume microorganisms from the water around them that they pump through their bodies. The sponges have special cells along their inner cavities called choanocytes, which work to facilitate the movement of water and the capture of food from it.

In their ocean food chain, giant barrel sponges take their place above their symbiotic partners cyanobacteria, and are consumed in turn by macroorganisms like fishes, turtles, and sea urchin. They try to defend themselves by releasing chemicals to repel their predators, but there’s only so much they can do when stuck in one place, waiting to be ingested by so many types of marine life. Like other filter feeders, giant barrel sponges ultimately form an important branch in the transfer of nutrients from very small to much larger life forms.  

They don’t even have tissues, let alone organs, but their simple structure is more than enough to ensure their survival and proliferation. Giant barrel sponges reproduce by spawning, and are one of the few species of sponge that undertake sexual reproduction. Males and females release sperm and egg cells into the ocean synchronously, so that when the time comes, they have a chance of contributing to a fertilized egg that grows into a larva and, after being carried by currents to a new spot of the ocean floor, establishes itself as an independent sponge. 

Check out this short video of the spawning phenomenon:

A valued community member

Giant barrel sponges are native to the oceans of the Americas, found primarily in the Caribbean Sea, and observed as far south as the coasts of Venezuela. 

Due to their filtration capabilities, giant barrel sponges are real assets to the ecosystems they are a part of, but boosting water quality is not the only ecological role they play. As mentioned, many other creatures live in and around the cavernous sponges, and giant barrel sponges are one of the largest organisms in the coral reef environments where they are found. They are thought to help coral anchor to substrate (the mix of mineral, rock, and skeleton that binds reefs together), and themselves make up about 9% of coral reef substrate in certain areas where they are found. By helping in this binding process, giant barrel sponges can play an important role in reef regeneration. 

Though the giant barrel sponge is not currently classified as threatened, like all of us, it is living in vulnerable times, as reef habitats are weakened in warming, acidifying waters. It is susceptible to a disease called Sponge Orange Band disease that afflicts all kinds of sponges. They can also be damaged or killed by human activities that disturb reefs and break sponges off from their surroundings. 

On the flip side, when these great creatures are doing well, they enable the thriving of life all around them. May all of us aspire to say the same.

With one giant smile,
Maya


Maya Dutta is an environmental advocate and ecosystem restorer working to spread understanding on the key role of biodiversity in shaping the climate and the water, carbon, nutrient and energy cycles we rely on. She is passionate about climate change adaptation and mitigation and the ways that community-led ecosystem restoration can fight global climate change while improving the livelihood and equity of human communities. Having grown up in New York City and lived in cities all her life, Maya is interested in creating more natural infrastructure, biodiversity, and access to nature and ecological connection in urban areas.


Sources and Further Reading:
https://animaldiversity.org/accounts/Xestospongia_muta
https://oceana.org/marine-life/corals-and-other-invertebrates/giant-barrel-sponge
https://en.wikipedia.org/wiki/Giant_barrel_sponge
https://www.americanoceans.org/species/giant-barrel-sponge
https://oceanservice.noaa.gov/facts/sponge.html