Hamelin Cockle

Domain: Eukarya
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Cardiida
Family: Cardiidae
Genus: Fragum
Species: Fragum erugatum

When I wrote about Shell Beach, Australia, I mentioned the Hamelin cockle, Fragum erugatum. Today, I want to expand on what I wrote.

The Hamelin cockle is a bivalve that belongs to the phylum Mollusca, along with oysters, snails, and squids, to name a few. It’s native to the shallow shores of Western Australia, though it is prevalent in Shark Bay and Shell Beach.

Shark Bay is a hypersaline marine environment. Its seagrass beds restrict tidal movement, and the rate of evaporation is higher than the rate of precipitation, which makes the water really salty. In fact, the water is plankton-deficient because the high salinity makes it hard for plankton to survive.

So what does the cockle do for food? Isn’t it a filter feeder like many of its bivalve brethren?

Hamelin cockles are not strict filter feeders. Instead, they have a partnership with our favorite oceanic BFFs, zooxanthellae. Like coral, the cockle receives leftover food from the zooxanthellae in exchange for protection in well-lit waters. Fragum erugatum will siphon plankton from the water when they can, but it’s never enough to sustain them.

The soft body of the cockle is brown, and the photosynthetic algae live in the soft tissue. The shells are white and appear translucent in the light. Fun fact, zooxanthellae also help to collect calcium carbonate that the cockle uses to make its shell. The entire organism is less than 20 millimeters, which is a little smaller than an inch.

Hamelin cockles are hermaphrodites, meaning they have both male and female sex organs; however, they still need other individuals to reproduce. Between winter and spring, F. erugatum will release their gametes, or eggs, into the water to be fertilized by other Hamelin cockles. The fertilized eggs develop into zooplankton that float around in the water before they settle to the ground and further develop into cockles.

I find these bivalves to be every interesting. They entered Shark Bay over 4000 years ago and really put forth the effort to make the bay and Shell Beach their home. Most living things do not prosper in extreme conditions, especially in areas of high salinity. However, the Hamelin cockle not only adapted to the hypersaline water, but they prospered so beautifully that they left a noticeable mark in the local geology.

Four thousand years’ worth of cockle shells replaced the sandy beach of Shell Beach. Building material was made from the dense accumulation of these shells that, over time, became cemented together. It just blows my mind to think how successful these tiny little organisms are, and that makes them special!

Sources and links:
Ocean the Definitive Visual Guide made by the American Museum of Natural History

Sponges pt.1

A yellow tube sponge (Aplysina fistularis) growing on a Caribbean coral reef. Photo taken by Dr. Alex Mustard. More can be found at www.amustard.com

“Oooooooooooh! Who lives in a pineapple under the sea? SPONGEBOB SQUAREPANTS!”

Actually, pineapples are terrible places for sponges to live. If SpongeBob wanted the best place to survive and be successful, he would have lived on top of Patrick’s rock. I know, I know, it’s a show for kids and therefore isn’t accurate, but what better way to introduce the topic than with a relevant pop culture reference?

I just have to say that sponges are weird.

Like coral, they were first thought to be plants, which to be fair is quite understandable. Sponges don’t possess appendages, eyes, noticeable mouths, or reproductive parts, so if I had come across my first sponge without knowing its biology, I would have thought it was a plant too.

Sponges are the simplest multi-cellular creatures of the animal kingdom, and they’re so cool that they have their very own phylum, Porifera. In fact, sponges are so unique that they have no other close relatives.

Like other marine invertebrates, such as coral, barnacles, and oysters, sponges will permanently attach themselves to hard surfaces like rocks or shipwrecks. Some species of sponge will even burrow themselves into whatever substrate they want to call home. Once they’ve attached, there’s no second guessing, so hopefully they picked a good spot!

Unlike coral, sponges are a bit hardier and have fewer requirements to be successful. Sponges can live in a variety of different places that vary in temperature, salinity, and depth. About 2% of sponges can live in freshwater!

Sponges can be found almost everywhere: on rocks, shipwrecks, and coral reefs; they can be found in the tropics and higher attitudes, though a good portion of them live in Antarctic waters. Unlike coral, sunlight is a limiter for sponges. Too much sunlight exposure can be harmful for sponges, so they tend to prefer caves, crevices, and other places that don’t get a lot of direct sunlight.

However, there are a lot of sponges that live in areas with a few feet or less of water above them and in direct sunlight. These sponge species possess a special relationship with a species of algae that will dwell in the sponge. The sponge protects the algae from herbivores while the algae secretes pigments in the outer most layer of the sponge. These pigments act like sunscreen, thereby helping to protect the sponge from the sun.

Like most animals, a good place for a sponge to live will have a steady supply of food. Areas with strong tidal currents can support large sponge populations because all that water movement brings in extra food. Like whale sharks, sponges are filter-feeders, but how they feed is a bit more complicated. I will therefore have a whole post dedicated to how sponges eat!

For being the simplest multi-cellular animals you can find, sponges can be very complicated. I’ve barely scratched the surface of what make sponges unique and what they can do for their environments. But like all things, it wouldn’t be fun or interesting if it were easy!

Sources and fun links for those who want to dive right in to sponges:
Ocean: The Definitive Visual Guide made by the American Museum of Natural History


I just wanted to take a quick moment and talk about symbiosis. I know it’s a topic you learn about in school; I first learned about it in middle school, then again in high school biology, and then a few more times in college. If you already know about symbiosis feel free to pick another post from the sidebar or glance over this one for a quick refresh. For those of you who haven’t learned about it yet or have simply forgotten, I’ll try to explain it in the best way possible—through the human experience!

There are many forms of symbiosis that we see and experience every day, but first let me explain what it is.

Symbiosis is any long-term and personal relationship between two or more individuals, and the relationship can be between the same or different species, such as between you and another human or a pet. Each participant in the symbiotic relationship is called a symbiont.

There are different types of symbiosis that are defined by the kind of interactions between symbionts. If you’ve read my post about coral and zooxanthellae, you’ve already been introduced to a form of symbiosis called mutualism. In a mutualistic relationship, such as coral and zooxanthellae, both parties benefit without inflicting harm on each other. Think of mutualism as the relationship you have with a project partner: if done right you both benefit from each other’s hard work. It can also be viewed in a relationship between humans and dogs or cats: the animal gains a home and a reliable food source while, the human gets companionship and additional health benefits.

A female oceanic whitetip shark (Carcharhinus longimanus) is accompanied by a group of pilotfish (pilot fish: Naucrates ductor) as it swims overhead. Photo taken by Dr. Alex Mustard, find more of his photos at www.amustard.com

Commensalism is a type of symbiotic relationship wherein one individual benefits and the other remains unaffected. An example of this is the pilot fish that ride on or near sharks or larger fish: the pilot fish feed on the leftovers of their hosts while the hosts remain unaffected. In the human experience, it’s like when you let a classmate copy off your homework: you gain nothing while they get all the right answers.

Not every relationship is healthy though. And this last relationship may be disturbing for some people.

Parasitism occurs when the parasite benefits from the host and the host suffers. An example of this relationship can be found in all species of parasitic wasps. The wasp will find another insect (caterpillars, spiders, other wasps, etc.), paralyze them, and then lay their eggs inside the host. The host will then go about the rest of their lives while incubating the eggs, and when the eggs hatch, they burst from the host like a scene from the movie Alien. And sometimes the host will survive only to protect the hatchlings until the host dies of starvation. This is an extreme example, but one of the more fascinating ones I learned about in one of my ecology classes. In human terms, parasitism is like the one cousin (or friend) that always comes to you asking for money and claiming they’ll pay you back but they never do.

Mutualism, commensalism, and parasitism are the main types of symbiosis. There are others that I will probably mention as I talk about the various other species, or if I want to dedicate another post to symbiosis. I know it’s a lot of word vomit, but I hope I made a bit more palatable than standard textbook explanations. Personally, I find symbiotic relationship like parasitism really interesting, especially with parasitoid wasps. I could easily see myself studying the wasps that may have inspired the Xenomorphs from Alien in an alternate universe!

In another alternate universe, I think I’d dedicate my life to researching sloths too. Sloths are maddeningly adorable, I could spend hours watching them. I wish there was a way to watch what my alternate selves were doing with their lives. Wouldn’t that make for some fun reality TV!

Golden Jellyfish

Photo of a Golden Jellyfish taken by Dr. Alexander Mustard. More of his photos can be found at http://www.amustard.com

Domain: Eurkaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Rhizostomeae
Family: Mastigiidae
Genius: Mastigias
Species: papua etpisoni

Last time, we talked about Jellyfish Lake in the Palau region of the Caroline Islands archipelago. We learned that the meromictic lake, which has distinct layers of water that do not intermix, is the only place you can find Golden Jellyfish.

I highly recommend putting this place on your bucket list, not only would you get killer pictures but you’ll experience something unlike anywhere else in the world! Now, let’s move on to the special guest of the day.

Golden Jellyfish (Mastigias papua etpisoni) are a species of jellyfish that are closely related to the spotted jellyfish that can be found in the lagoons near Jellyfish Lake. Like coral, they benefit from a close relationship with zooxanthellae. What, did you think coral were the only ones to be best friends with the greatest algae of the ocean?

Like coral, the jellyfish house the zooxanthellae in their tissue which gives the jellyfish their golden color. They also have a mutualistic relationship with the algae; the golden jellies provide housing, waste that the algae uses for nutrients, and sunlight in exchange for the sugar that the zooxanthellae don’t use from photosynthesis.

In fact, it’s the sugar that gives the jellies all the energy they need to grow and reproduce, because they don’t gather food on their own since they lost their ability to sting prey through untold years of evolution. It also allows them to propel and migrate through the water, giving the zooxanthellae access to sunlight throughout the day as the sun moves across the sky, casting shadows on the lake.

This migration has a positive effect on the lake’s ecosystem, by stirring up the nutrients and microorganisms found in the water, providing one of the only sources of circulation in the layers they inhabit. So in this scenario everyone wins: the zooxanthellae get everything they need to make food, the jellies get all the leftovers, and the surface of the lake gets stirred up for the other organisms that call it home.

But the jellies aren’t without predators. They’re preyed upon by anemones that concentrate in areas that the jellies frequently migrate through, creating a bottleneck effect. Thankfully, the sheer number of Golden Jellyfish provide their predators a healthy diet without affecting the population too much.

I find these guys to be really cool creatures to study just because of their relationship with the zooxanthellae and their ecosystem. In general, the whole lake is fascinating and worth the time to read about. It’s a wonderful example of how crazy nature can become when isolated from what used to be similar environments and/or species.

Sources and cool links to check out:


If you’ve ever had the opportunity to dive or snorkel at a coral reef, you might’ve seen impressive coral structures. In Jamaica, I saw massive Boulder Coral, Acrapora species (like the Elkhorn Coral) that looked like alien trees, and Pillar Coral that appeared to be the main feature of the reef, from the perspective of a photographer.
In fact, if you look at pictures of reefs online, a lot of them have huge corals that draw the eye. Now, how do coral get that big? They only eat plankton and there’s only so much one can eat in a day, but they require a lot of energy for everything they do. Lucky for the coral, at least the reef building varieties, they don’t have to acquire all that necessary energy by themselves.
Let me introduce you to what is, in my opinion, one of the best examples of a mutualistic relationship in the animal kingdom. High on the to-do list of most coral polyps is to acquire the best of best friends in the ocean, zooxanthellae (zo-zan-THEL-ee).
This organism, or group of organisms, is a type of dinoflagellate (a special kind of algae) that forms a positive symbiotic relationship with creatures like coral and jellyfish. A symbiotic relationship is defined as any relationship between two or more individuals of the same or different species that lasts over an extended period of time. You and a pet have a symbiotic relationship.
For coral and zooxanthellae, they’re like best friends; not only do they live together, but they help each other, making it a mutualistic relationship. In exchange for a safe haven from predators like zooplankton, and necessary ingredients for health and photosynthesis like carbon dioxide and nitrogenous waste products (they eat coral poop), the zooxanthellae give coral their excess food.
That’s right, zooxanthellae are like those friends that bring huge amounts of food to your party or potluck and leave the leftovers with you, giving you meals for days. In fact, zooxanthellae provide up to 90% of the energy needed for coral growth and reproduction; they are the reason those Pillar Coral can grow as tall as you are and why coral reefs exist.
In summation, zooxanthellae are friends, not food! No, wait; that’s not quite right. Zooxanthellae are totally the friends you want to have in order to build a successful community, or if you want to mooch off their leftovers because you can’t make enough food on your own.