3/25/11

More Sea Jellies 101

This is a follow-up to a previous blog post. Learn about different kinds of sea jellies and their unique characteristics here.

 
Black Sea jelly, via Wikimedia Commons

"True Jelly" reproduction 
One remarkable trait of most Scyphozoans is their dual reproductive strategies. They can produce asexually by budding and sexually after a process called strobilation. The fertilized egg becomes a planula larva that quickly settles and morphs into a polyp. This polyp then becomes a strobila – almost looking like a stack of coffee filters. Each of these detaches and becomes an ephyra which then transitions into either a male or female medusa to begin the process all over again.




Jellies are beauties, adaptors, predators, survivors, neighbors...
If this year is anything like last we will see a fairly large population of jellies in the harbor pretty soon.  They thrive in warmer water, but humans also play a role in helping jelly populations.

Credit: NancyHeise, via Wikimedia Commons

Overfishing – Humans can overfish the natural predators of jellies, creating a host of problems. By removing their predators, namely large fish, it allows populations of jellies to grow exponentially.  Since jellies in turn eat larval fish, increased jelly populations further reduces already overfished populations.




Pollution and runoff – Pollution and runoff can cause what's known as "dead zones," areas that are severely depleted of oxygen. While these conditions are inhospitable to fish, they are a fine environment for jellies.








Invasive species – Many invasive species are introduced to oceans around the world through the ballast
waters of boats; and invasive jellies are no exception. A famous example is the comb jellies that were introduced into the Black Sea in the 1980's. They have no natural predators and have wiped out many commercial fisheries. By 2000, the total weight of the comb jellies in the Black Sea was more than 10x all the commercial fish caught there throughout the entire year.

What can you do?
There are lots of ways you can support healthier oceans, including hoofing it now and then and choosing ocean-friendly seafood. Explore ways you can LiveBlue™ at the Aquarium. Come see jellies up close and learn even more about these fascinating creatures in The Trust Family Foundation Shark and Ray Touch Tank area, opening April 15!

3/24/11

Sea jellies 101: What is a sea jelly?

Most people think of jellies as clear, squishy blobs of goo that sting and ruin your day at the beach. You can see them in several places throughout the Aquarium. The common image in most people's minds looks somewhat like an umbrella with long strings dangling. While this is what many jellies look like, to a biologist the term "jelly" can refer to a huge range of animals that have existed on the planet for around 650 million years! Let's explore...



Jelly Classification
When classifying jellies the best place to start is the phylum Cnidaria, so named because of the venomous cells called cnidocytes that are unique to animals in this phylum. Cnidaria is most commonly divided into four classes and perhaps the most well known class is Scyphozoa – sometimes referred to as "true jellies," or those umbrella-shaped jellies mentioned earlier.



Some examples at the Aquarium would be moon jellies and our pacific sea nettles. Another well represented class at the Aquarium that you may not have even realized is a cnidarian is the class Anthozoa – the corals and sea anemones. The last two classes are Hydrozoa (hydroids, Portuguese man-o-war) and Cubozoa (box jellies, sea wasps).

Moon jelly © Hans Hillewaert / CC-BY-SA-3.0 , via Wikimedia Commons

The second most prominent phylum referred to by the name "jelly" is Ctenophora, the "comb jellies." The most prominent feature of these animals is their comb-like cilia that they use to swim. Ctenophores differ from cnidarians in a few ways, perhaps the most important being that ctenophores do not have cnidocytes, and thus they cannot sting.



Comb jellies, credit: Überraschungsbilder, via Wikimedia Commons

Common Characteristics
Jellies are invertebrates made of about 95% water, so as you can imagine they are pretty fragile. Jellies consist of two or three layers of cells formed around a central opening – this organization of similar parts around an axis is known as radial symmetry. Despite the fact that they do not have a brain, heart, real digestive system, complex eyes OR a respiratory system they are still effective predators of mainly zooplankton. Jellies that move do so by pulsations of their bell, but many species are sessile and don’t move at all. Or, some species are sessile at one stage of their life and then begin to free swim.

Which leads us to sea jelly reproduction! As the weather warms up, you'll likely see loads of jellies in Boston Harbor (see this blog post for evidence). Keep checking the Exhibits Blog to learn how sea jellies reproduce and to find out why there are just so many jellies in oceans today!

3/14/11

The Lesser-Known Sharks and Rays at the Aquarium

It's high time that we meet some of the smaller shark and ray relatives that are lurking about the Aquarium. You can find many of these cool creatures in the Northern Waters Gallery.

First up, lets meet the chain dogfish! Note the distinctive chain pattern on their body. This local New England species can be found in the Sandy Bottom exhibit in Northern Waters. These small bottom dwelling sharks can grow to about two feet long (though they more likely grow to 15 to 18 inches) and can be found from New England to Florida feasting on small prey such as crustaceans, worms and fish. You can find them living in areas built up with piers and other man-made structures.

These types of environments make it hard for fishermen to trawl for their catch, which in turn makes for a great nursery for chain dogfish. Females will lay two cases at a time, using the sticky tendrils on the ends of the cases to secure them to the bottom (another reason that they prefer areas with lots of structure and habitat). After about eight months, the young will hatch and be on their own.


And here's an interesting tidbit: Did you know that chain dogfish are thought to have fluorescent properties after being observed by a deep sea exploration in 2005? Scientists were able to take photographs of these sharks emitting a greenish glow, though they still aren’t sure what the purpose is.

Next up, the spotted ratfish. This animal, also called the chimera, is a cartilaginous fish, just like sharks and can be found in the Boulder Reef exhibit.

This species of ratfish can be found in the eastern Pacific (Alaska to Baja Mexico) and can be found both near shore and offshore. Their colors make for great camouflage: the white spots and dark brown back help to blend in with the ocean floor. They can use their grinding plate teeth to crush food like clams, crabs, shrimp and worms.



Don't forget about the skates! These animals look like rays and act like rays but skates are a different type of animal. The cartilaginous fishes live in the colder waters of the world, and unlike their tropical cousins, skates do not have a venomous spine along their tail.

There are five different species currently in the Sandy Bottom exhibit of the Northern Waters exhibit. In the wild, they all can be found in roughly the same geographic region, inhabiting waters from the Gulf of St Lawrence and Nova Scotia in Canada down to the waters off North and South Carolina. Their diets (worms, crabs, fish, crustaceans and squid) are also similar. The next time you visit, see if you can find the little skate (about a foot and a half), the thorny skate (about three feet long), the clearnose skate (about 3 feet long), the winter skate (about three and a half feet long) and the barndoor skate (one of the largest skates in the Atlantic)! Most of the skates are all the same size so you have to look at body shape and color pattern to tell who is who in the tank, which can be most challenging when the skates bury themselves in the sand to hide.

On your next visit, ask someone with an Aquarium shirt to point out some of these interesting species and get to know some shark and ray relatives. And don't forget to say hi to their relatives in The Trust Family Foundation Shark and Ray Touch Tank!

3/11/11

A hatching event!

Aquarist Dave Wedge recently grabbed some special video of a female Acadian hermit crab (Pagurus acadianus) hatching her eggs. You can see her remove her tail from her shell to fan the eggs so the larvae can disperse into the water column. Those larvae are tough to see, but look carefully and you can spot them sparkling at the surface of the water during the close-up!



Female hermit crabs carry their eggs for a couple weeks before releasing the larvae into the water. You might be able to spot this kind of behavior at the Aquarium's Edge of Sea exhibit the next time you visit! Just ask anyone with the Aquarium logo on their shirt to point out a hermit crab in this hands-on touch tank.


Edge of the Sea exhibit