Friday, November 29, 2013

The Sargasso Sea and the North American Eel: An Interview With Dr. Joe Richardson

In our last post, we looked at the difference between anadromous and catadromous fish, as well as several examples of each type of fish.  Eager to learn more, I contacted several people who have been very helpful to me in the past so that I could learn more.  One of these people was Dr. Joe Richardson, a marine biologist who gives Ecology Tours (which I highly recommend) on Tybee Island in Georgia, and whose Facebook page can be reached by clicking HERE.  Dr. Joe has helped me out a lot in the past, including providing a guest post about moon snails way back in February (which can be reached by clicking HERE!  When my family and I were on the Ecology Tour several years ago, I remember Dr. Joe mentioning something about the Sargassum seaweed that could be found on the beach.  Therefore, when I was researching the North American eel for the anadromous/catadromous post and I came across mentions of this same seaweed, I decided to ask Dr. Joe a few questions about the eel and the seaweed.  I wanted to make sure that you all could benefit from his knowledge as well, so I am reproducing the interview here!  
The Natural World:  First off, what is it you're holding in the picture above?

Dr. Joe:  It's a Portuguese Man of War.  They sting real bad.  They are more of an open water, tropical species, but they float (I'm holding it by the float) so they go wherever the wind blows them. We don't get many on Tybee Island, but on some Florida beaches they can be a real problem.

TNW: Didn't you guys find another one pretty recently on one of your Ecology Tours?

Dr. Joe: Yes, within this past week. We found two of them washed ashore during one of my Tybee Beach Ecology Trips. I sure didn't expect to see them; but most anything is likely to wash ashore.
A picture of this weeks Portuguese Man of War.
TNW:  In a recent post, I discussed the North American eel. I was wondering whether you have any pictures or stories regarding the eel that you'd like to share!

Dr. Joe:  I don't have any pictures of the American eel; but my experience with them is that I always hated to catch one when fishing because they were so slimey.  And they would invariably wrap themselves around the rig and line so they were a mess to get unhooked.  The slime was also thick and would stay on the line even after you got them off.  Many years ago, while in college, I worked one summer in North Carolina on a shrimp boat and was involved in a few research projects on the side.  One involved developing eel traps to be used for catching eels in the inshore waters.  They were trying to create a business opportunity for catching eels, then somehow shocking them so they would die straight before flash freezing them.  By being straight, they could pack more of them in boxes than if they were all curvy.
The North American eel.  Photo Credit:
TNW: I also found that the eel spawns in the Sargasso Sea, and I recall you talking about all of the Sargassum seaweed washing up on shore when we went with you on the tour several years ago.  What can you tell me about this type of seaweed?

Dr. Joe:  This species of Sargassum (a brown seaweed) is unlike most seaweeds, that have to grow attached to a hard bottom or structure in shallow water where they get enough light to do photosynthesis. This Sargassum actually grows unattached, floating in open water, generally well out in the Atlantic Ocean. In fact some charts refer to the middle of the Atlantic Ocean as the “Sargasso Sea” because there is lots of it floating around out there. The small berry-looking structures on the Sargassum are actually air floats that keep it floating near the surface. Clumps of Sargassum in the open ocean serve as places to hide for some animals and as structure for some small animals to attach on to. During late June, we found lots of those small animals (Sargassum shrimp, Sargassum Swimming crabs, small file fish, baby flying fish) on the beach and in tide pools because they have washed in with the seaweed clumps. All these animals are yellow-orange in order to camouflage or blend in with the seaweed. So the Sargassum has brought with it lots of interesting animals from far offshore, that we normally don’t see on our beach.
Pile of Sargassum seaweed along the high tide line at North Beach.
The berry-like structures on the Sargassum are actually air floats that keep the seaweed at the sun-lit surface.   
Sargassum shrimp (this one carrying eggs under her abdomen) were abundant in some of the clumps of seaweed.
This was one of many Sargassum swimming crabs that were common for a few days on Tybee's ocean beach. 
Small filefish with camouflage colors matching the seaweed were found among many of the Sargassum clumps. 
Although only about an inch long, what appears to be a baby flying fish was another type of fish found among the drifting seaweed.
TNW: Besides the eels and the other small animals you mentioned above, what other animals live in the Sargassum?

Dr. Joe: The floating clumps of Sargassum in the open ocean also serve as places to hide for small young animals that will eventually become larger as they age and grow. When the baby Loggerhead Sea Turtles hatch on Tybee’s beach later this summer, they will head out to sea, and many will hide among clumps of floating Sargassum far offshore. Many years ago, while on a research cruise offshore, we anchored overnight and found ourselves among a large area of floating Sargassum. Being curious scientists, we used some long dip nets to catch some clumps of the floating seaweed to see what sort of animals were among it. This was how I caught the only Sailfish I’ve ever caught!
Baby sailfish hide among the floating clumps of Sargassum far offshore.
TNW:  Do you know why Tybee was inundated with Sargassum when we visited in the summer of 2012?

Dr. Joe: I don’t recall our having a prolonged period of strong winds from the east, so I don’t think it was necessarily a wind-blown event. Instead, I’ve got a different hypothesis. The Gulf Stream current flows from the south toward the north well offshore of Georgia’s coast. It doesn’t flow in a straight line, but meanders a lot. Sometimes those meanders can be almost like huge hair-pin curves, and sometimes those big meanders, like loops, can break off and form large circular or oval water masses of warm off-shore water. If such a large ring of Gulf Stream and warm Atlantic Ocean water (and possibly water that recently had been in the tropics) happened to break off on our side of the Gulf Stream, it could gradually move toward our coast, and bring with it things like Sargassum. This is my guess: one of these offshore water masses, with its floating Sargassum, broke off and had moved into our coastal waters.
Laying among a pile of Sargassum seaweed along the high tide line was this lumber that had been drifting offshore long enough for these Goose-neck Barnacles to settle and grow. This species of barnacle only grows on drifting, open-water objects.
TNW:  What other ecological or biological effects did this inundation of Sargassum have on the coastline?

Dr. Joe:  Since the Sargassum seaweed event on Tybee, I’d been noticing (almost daily while conducting my Tybee Beach Ecology Trips) additional tropical and offshore species of animals. There was a group of Sargent Majors, a small black and white striped damsel fish that is common around coral reefs and rocky shorelines in the Caribbean and Florida Keys. They don’t belong this far north. We also got a Ballyhoo, a strange looking fish with a long extended lower jaw; and they usually live offshore where they are food for large gamefish like sailfish, marlins and dolphins.  So I’ve got a feeling that the Sargassum and all these other interesting tropical and offshore animals are signs that Tybee had been the landfall of a large warm water, open-ocean water mass. It sure made beach ecology on Tybee interesting this spring and summer!!
Small Sargent Major damselfish, common on coral reefs and tropical rocky shorelines, have shown up on Tybee in the last week. 
We've been seeing Ballyhoo in the beachwater, but they normally live in warm offshore open waters.
I would like to take this opportunity to thank Dr. Joe for taking the time out of his schedule to chat with me for a bit about these fascinating animals, and the importance of the Sargassum!  I look forward to hearing more from you in the future, but in the meantime, make sure you like the Facebook page for his Tybee Beach Ecology Tours by clicking HERE, and make sure you check out his website HERE.

Unless otherwise noted, the photo credit for all of the pictures in this post goes to Dr. Joe Richardson.

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