DIVE DRY WITH DR. BILL #678: SEE ANOTHER SEA HORSE!
Last week I wrote about the beautiful little Pacific seahorse (Hippocampus ingens) discovered by Ruth Harris in our dive park. I said I knew of two others that had been seen in Catalina waters over the last year. Then last week I went up to the harbormaster's office to obtain some water temperature data for a video I'm producing (thanks Brian) and was informed that another one had been discovered dead on one of the floats!
One of my earliest research interests when I arrived on Catalina back in 1969 was how critters get to offshore islands like ours. Yes, many fish can swim over but there are some that stick close to home and don't. There are few invertebrates that can crawl along the deep bottom from Newport Beach to Catalina in a lifetime. After all "Twenty Six Miles" is a long way if you are a sea cucumber or crab.
Many species of fish and invertebrates have dispersal stages that exist temporarily in the plankton. These may include both egg and larval stages. We refer to them as meroplankton. Those with reasonably long planktonic stages can drift over to the island in the currents and settle here. We see this when young life stages of species like sea stars and our little whitetail damsel arrive in Catalina waters.
However some species brood their eggs and sometimes their young and do not disperse far from home. Others reproduce asexually (what fun is that?) and cannot colonize far away places without a helping hand.
My first major research project in Catalina waters involved looking at drifting rafts of giant kelp and other algae to identify all the species that might hitch a ride on them. My Toyon students and I sampled rafts from 1969 to 1977 under an NSF grant to my Harvard mentor, Dr. H. Barraclough Fell. The results were pretty eye opening and kelp pioneer and expert Dr. Wheeler North, formerly of Cal Tech, called the paper I published "ground breaking."
Now sea horses are often seen with their tails entangled on different species of algae, or in the case of the one I filmed, on a gorgonian colony. Their appearance often makes them blend in with the seaweed offering them camouflage. Therefore it is quite possible that a seahorse could drift over here either on seaweed, or associated with such drift material.
The males brood the eggs in their belly pouch (no, I'm not a "pregnant seahorse) and when they hatch after about two weeks, the little ones are tiny miniatures of the parents. I found a source that reported these youngsters are pelagic, drifting with the currents to see the world before they have to settle down and raise a family. Dispersal could certainly occur during this life stage.
Even adult Pacific seahorses apparently spend part of their lives in the open ocean despite being largely reef associated. They are often found in numbers in the bellies of yellow-fin and bluefin tuna which are largely pelagic feeders. I just can't see the tuna scrounging around in beds of seaweed or eelgrass to pick them out.
Another factor affecting seahorse populations is collection for the aquarium trade. This has probably been one reason why the IUCN considers them a vulnerable species. In addition, shrimp fleets working off Mexico reported taking hundreds of thousands of them a month as by-catch, although that has declined to almost none in recent years. Habitat degradation due to development along coastlines has also impacted them. Fortunately my home is 150 feet above sea level, a habitat they are rarely seen in.
© 2016 Dr. Bill Bushing. For the entire archived set of over 650 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Crown and lack of belly pouch indicating a female; small dorsal fin on back and hanging on to soft coral with tail.
Last week I wrote about the beautiful little Pacific seahorse (Hippocampus ingens) discovered by Ruth Harris in our dive park. I said I knew of two others that had been seen in Catalina waters over the last year. Then last week I went up to the harbormaster's office to obtain some water temperature data for a video I'm producing (thanks Brian) and was informed that another one had been discovered dead on one of the floats!
One of my earliest research interests when I arrived on Catalina back in 1969 was how critters get to offshore islands like ours. Yes, many fish can swim over but there are some that stick close to home and don't. There are few invertebrates that can crawl along the deep bottom from Newport Beach to Catalina in a lifetime. After all "Twenty Six Miles" is a long way if you are a sea cucumber or crab.
Many species of fish and invertebrates have dispersal stages that exist temporarily in the plankton. These may include both egg and larval stages. We refer to them as meroplankton. Those with reasonably long planktonic stages can drift over to the island in the currents and settle here. We see this when young life stages of species like sea stars and our little whitetail damsel arrive in Catalina waters.
However some species brood their eggs and sometimes their young and do not disperse far from home. Others reproduce asexually (what fun is that?) and cannot colonize far away places without a helping hand.
My first major research project in Catalina waters involved looking at drifting rafts of giant kelp and other algae to identify all the species that might hitch a ride on them. My Toyon students and I sampled rafts from 1969 to 1977 under an NSF grant to my Harvard mentor, Dr. H. Barraclough Fell. The results were pretty eye opening and kelp pioneer and expert Dr. Wheeler North, formerly of Cal Tech, called the paper I published "ground breaking."
Now sea horses are often seen with their tails entangled on different species of algae, or in the case of the one I filmed, on a gorgonian colony. Their appearance often makes them blend in with the seaweed offering them camouflage. Therefore it is quite possible that a seahorse could drift over here either on seaweed, or associated with such drift material.
The males brood the eggs in their belly pouch (no, I'm not a "pregnant seahorse) and when they hatch after about two weeks, the little ones are tiny miniatures of the parents. I found a source that reported these youngsters are pelagic, drifting with the currents to see the world before they have to settle down and raise a family. Dispersal could certainly occur during this life stage.
Even adult Pacific seahorses apparently spend part of their lives in the open ocean despite being largely reef associated. They are often found in numbers in the bellies of yellow-fin and bluefin tuna which are largely pelagic feeders. I just can't see the tuna scrounging around in beds of seaweed or eelgrass to pick them out.
Another factor affecting seahorse populations is collection for the aquarium trade. This has probably been one reason why the IUCN considers them a vulnerable species. In addition, shrimp fleets working off Mexico reported taking hundreds of thousands of them a month as by-catch, although that has declined to almost none in recent years. Habitat degradation due to development along coastlines has also impacted them. Fortunately my home is 150 feet above sea level, a habitat they are rarely seen in.
© 2016 Dr. Bill Bushing. For the entire archived set of over 650 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Crown and lack of belly pouch indicating a female; small dorsal fin on back and hanging on to soft coral with tail.
