Video frame capture: Shark Egg Case – Maybe a Bamboo Shark?
This is a frame capture from a video I shot earlier this year in Anilao, Philippines. I have found empty egg cases washed up on the beach (beachcombers call them mermaid’s purses), but never one with its little living treasure: a yolk and developing shark embryo. I have no idea what species this is – maybe a bamboo shark, one of several small species of oviparous (egg-laying), bottom dwelling sharks found throughout the Indo-Pacific. I’m familiar with the Brownbanded Bamboo Shark (Chiloscyllium punctatum) and the Whitespotted Bamboo Shark (Chiloscyllium plagiosum); both species are found in the Philippines.
At the beginning of our dive, I was distracted by spawning coral (unusual for the middle of the day) and got separated from Ned and our group. I surfaced and told the boat crew I would stay under the anchored boat, at 15 feet depth, and re-board when I heard them start the engine to pick the others up. The boat was anchored away from the reef, in a spot that was mainly rubble; what we call “alternate habitat”. There are advantages to slowly examining one small area, so I was content to spend my hour in the shallows directly under the boat.
The egg case was firmly attached to the top of a small rubbly coral mound but didn’t look like the shiny, clean cases I’ve found on the beach and seen in aquarium exhibit photographs. It was covered in a thin coat of algae but I could clearly see something bright orange undulating inside. When I gently rubbed a little of the algae off, the embryo stopped moving and I realized I was looking at a developing shark! To my relief, it wasn’t long before it started the undulating motion again.
Back on shore, a quick Internet search turned up quite a few images of shark egg cases and an interesting paper, “Survival of the Stillest: Predator Avoidance in Shark Embryos”. The embryo’s undulating motion aids in moving fresh seawater in and out of the egg case, which aids in respiration. Using Bamboo Shark eggs, the researchers found that the embryonic sharks react to possible predators with a freeze response, possibly to avoid alerting the predator by scent or water movement. If the little embryo froze because it perceived I was a predator, I’m glad it resumed its normal behavior so quickly.
It was difficult to shoot video because there was no place to set my camera down to steady it – but here’s a short bit:
Bonaire, September 2015 ~ Although our tally shows that we saw a number of species spawning last month, the September coral spawning event was just not very robust compared to past years (others who dive regularly in Bonaire agree). One of the things I had on my wish list was spawning Flower Coral, Eusmilia fastigiata, but this year, I never managed to catch any in the act of spawning. I have footage from our observations in previous years but I had hoped to fill in gaps. It didn’t happen, so I’m sharing what I have.
I first saw Flower Coral spawn years ago in the Florida Keys when Lauri MacLaughlin, a resource manager with the Florida Keys National Marine Sanctuary, pointed it out to me. We were on a mission to see other corals spawn so I didn’t take the time to set up my video but what I remembered most was how clearly I could see the little round “eggs”, collecting in the translucent tentacles of the cup-shaped corallites, long before they were actually released.
One of the things we look for in spawning coral is the “setting” of the eggs or egg/sperm bundles. We say the coral eggs are “setting” when they become visible to us, usually in the mouth of the coral polyp. Corals, like the Staghorn and Elkhorn (genus Acropora) and some star corals will set about 30 minutes prior to release. With many other species, the setting isn’t as apparent until shortly before the release.
During coral spawning week, we try to be conservative with our diving because so much happens between 7:30 and 11:30 p.m. and we want to be underwater for as much of that time as possible, so the shallower the dive, the better. In Bonaire, we usually work a reef where the Flower Coral colonies are between 40 and 50 feet deep. If I spend a lot of time at 50 feet then that cuts my total bottom time short for the evening, plus I don’t want to be sprinting to shore to change tanks right when something exciting, like spawning brittle stars, starts (that was a bitter experience in 2009). While some things are fairly predictable, there are no guarantees and to complicate matters, spawning corals have to be in spots where I can set up my tripod without damaging any reef. Oh, the calculations and decisions! So, we spend a lot of time cruising around the reef, looking for signs of spawning and often getting distracted by things other than spawning corals. This year, I was determined to bypass all other spawning and look for one thing only, Flower Coral, but I never found any with setting eggs. Bummer.
But that brings me to the eggs. For years, I have been calling the tiny white spheres in the clear tentacles of the Flower Corals, eggs. Well, they are technically not eggs because this species of coral is a brooder not a broadcast spawner. This means we are looking at female colonies, whose eggs have already been fertilized and the little round spheres we see in the tentacles are zygotes, already on their way to becoming planula larvae. A 1999 paper documented that unlike other brooders that release well-developed planula larvae, The Flower Coral releases zygotes in “early developmental stages”. Not to digress too much, but an example of a broadcast spawning species is the Giant or Great Star Coral, Montastraea cavernosa. Male colonies release sperm into the water and about fifteen to twenty minutes later, female colonies release clumps of eggs that hopefully meet up with the sperm, become fertilized and become planula larvae that find a good spot to settle and become new coral colonies.
Larva emerging from mouth (this is a video frame capture)
That same paper observed that the Flower Coral released its supposed gametes (they still thought they were gametes at that point in their paper) from the tentacles of its colonies. Ever since I read that, I have been trying to see them released from the tentacles but all I have been able to observe is the zygotes being released through the mouth of the corallite. In fact I have seen them gather in the clear tentacles (the swirling movement is quite beautiful) then move down small canals to the mouth. In my video, you can see the zygotes exiting the mouth and I have even gotten close-ups of a few individuals being released through the mouth. I finally had a chance to talk to our friend, Ellen Muller, who assured me that Flower Coral releases the zygotes through the mouth. Has anyone else ever observed release through the tentacles? We’d love to hear from you.
Here is my video, also viewable over at our BlennyWatcher YouTube channel:
Two weeks ago, I posted about a dive at the Blue Heron Bridge where I watched a female box crab molt while in the grasp of a male. Ned had good luck too. Bumblebee shrimp are known to feed on the tube feet of echinoderms, so we usually see them on or under urchins and sea cucumbers. He had stopped to watch an octopus feeding on a gastropod whose shell was too large to fit into the den. Imagine his delight when several of the tiny, striped shrimp bimbled across the front of the octopus.
Bluelip Parrotfish, Cryptotomus roseus, male in normal color
Even though the Blue Heron Bridge in Riviera Beach, Florida is only a three and a half hour drive from our home, we don’t have a chance to make the trip more than once or twice a year. But when we do, we are never disappointed and over the years, have had some amazing dives there. Although there are areas around the bridge that can be dived any time, the areas directly under the bridge spans are only manageable during slack tide, so a little planning is required. Last month, we managed to squeeze in a quick, two-day trip.
A male Bluelip Parrotfish flashing his courting colors
We’ve started work on updating the Reef Fish Behavior book, so spawning Bluelip Parrotfish, Cryptotomus roseus, was exciting. The males are normally pretty anyway, but during courting and spawning they get even flashier.
Bluelip Parrotfish male, courting harem
The Blue Heron Bridge is one of the few places we’ve dived where Trunkfish, Lactophrys trigonus (formerly known by the common name, Buffalo Trunkfish), can regularly be found. The black juvenile is more commonly seen, but we were delighted when our friend Deb Devers showed us a tiny, bright green one.
Trunkfish, formerly commonly known as Buffalo Trunkfish, Lactophrys trigonus juvenile
Trunkfish, formerly called the Buffalo Trunkfish, Lactophrys trigonus, green juvenile
My video lights can be pretty annoying at night, attracting all kinds of worms and other assorted plankton that can totally screw up my video. One advantage though, is among the worms and isopods and occasional settling fish, we see some pretty cool settling crustaceans. I think the second is a settling lobster, but I’m not certain. The second is a stomatopod larva (thanks to Dr. Peter Wirtz for the confirmation).
Night settling stomatopod
We close with a nudibranch, Dondice occidentalis, identified for us by nudi expert, Anne Dupont, who noted that there are two color forms found at the bridge, one of which is this “sparkly” one:
We are on the island of Bonaire, where one dare not touch a rock, even in the gentlest of ways. So, for International Rock Flipping Day, I decided to follow some fishes that are the best at rock flipping: goatfishes. My video contribution starts with a Spotted Goatfish and ends with another species, the Yellow Goatfish. Goatfishes got their common name from a pair of highly sensitive appendages (barbels) just under their chin that they use to detect small crustaceans and other prey under the sand and rocks. In my video, the goatfishes are accompanied by jacks, that sometimes hunt opportunistically with the goatfishes.
A very large part of Bonaire’s beautiful hard coral stands along the west side of the island were destroyed by two storm events, Lenny, in 1999 and Omar in 2009. The coral rubble, silted over, offers very little stable base for new corals to settle so most divers swim over it to reach the reef. We spend a lot of time meandering over the rubble looking for tiny treasures, like the Sailfin Blenny, that makes homes of holes in the rocks. And we can see just how adept goatfish are at flipping rocks to catch a meal.
International Rock Flipping Day2015 is this Sunday, September 13. Get yourselves outside and turn over a few rocks and share your finds. This was founded in 2007 by Dave Bonta and Bev Wigney (you can see the original post here) and now held the second Sunday of September. Hosted each year by different bloggers – this year over at Wanderin’ Weeta. To participate, check out the instructions on her post, including the important precautions – you know, like watching for snakes under rocks and hornets nests and stuff. My own caution is: don’t break any rules. Also use proper etiquette: remember rocks often cover someone’s home, so take extra care to gently return a rock to the position in which you found it without squishing the resident.
On Beqa Island, Fiji – tide pooling and turning rocks
You can post your photos on the rockflippingday FLICKR group. If you blog, you can send a link to Wanderin’ Weeta (see instructions on her page). Tweet your finds to #rockflip. and yes, there is a Facebook page to follow: International Rock Flipping Day
Nailed by a bristle worm – hazard of rock turning
Ned and I are habitual rock turners above and below water. Here we are this past March in Beqa Lagoon, Fiji, where Ned got nailed by a bristle worm that was living under a rock that he turned over (hello… precautions)! On Sunday, I’ll update this post with my finds. Until then, happy flipping!