It's that time of year. A perplexing question: when will be Millepora platyphylla first go off, on Guam, in Spring 2025?

 [This blog is intended to store keepers, both my own work, and found material.  ]

 [Update, 6 April 2025: My gut feeling trends toward the next mass release of medusoids on Guam about three to five days after the next Full Moon--between April 18 and 18, 2025.]  

 

It is the second day of spring, 2025.  I am in California.  In 2023 and 2024, I wrote lengthy pieces around my predictions for potential dates for Millepora platyphylla's reproductive output.  I still have received no affirmation or confutation of my predictions.  

2025 presents a baffling puzzle.  Let me explain briefly.

 In 1984, soon after my arrival at the University of Guam Marine Laboratory, to commence graduate study.  Professor Richard Randall took me aside and suggested that corals would make a good thesis study.   I told him I was interested in reproductive timing, and I probably told him that I was interested in Tridacnid clams.  He called attention to an important detail of the life history, the fact that the hard parts (the skeleton) of these species bear markers of reproductive status: ampullae, small pits in which develop the medusoids---the reproducing adult stage.  I could easily, so I reasoned, collect a few small fragments of these corals every time I snorkeled.  This would make an interesting side project, requiring little effort.  After a year or two, I would have sufficient fragments to study them and perform a statistical analysis of the times of reproductive effort.  

Indeed, I began collecting fragments, cleaning them in Professor Randall's blue tank of Calcium Hypochlorite (swimming pool bleach) on the lanai, behind his lab.  I enjoyed snorkeling, and did so frequently during the coming months.  Over time;  I visited a number of reefs.  Over time a number of fragments (each between a couple of inches and perhaps 8 inches across) accumulated over the months in a large drawer in my desk.  Each of them bore pencil markings recording the place and date of collection. 

In April of 1985, about 3 or 4 days after Full Moon, a fellow student invited me to join his party on a night fishing foray in Southern Guam, and I tagged along.  By this time I had developed an efficient technique for collecting my fragments.  A fellow student, Doug Markell, introduced me to the use of a child's swim ring as a flotation collar for the five gallon white buckets that were ubiquitous and  cheap at local hardware stores.   Spare flashlights and large Ziploc bags, a geologist's hammer, a  masonry chisel, and a handmade acrylic slate made up my kit.  I probably was a hindrance to my friend and his cousins, but by the time I left the water I brought a few bags of seawater and fragments to my car.  

I was amazed: as I prepared to treat the specimens, in the beam of the flashlight could be seen swarms of medusoids in some of the bags!  Statistics would not be necessary to determine at least one date of reproductive effort!  

This was the first event I was to observe.  The next morning, I visited several of my snorkeling spots along the West (leeward) coast of Guam, and at each site, evidence presented itself that indicated recent spawning.  It seemed to me that such an event would be tightly syncronized, to ensure successful fertilization.  (You see, each medusoid is either male or female, and I had read reports that these ephemeral adults did not more than a few hours.)  

I kept on it, collecting fragments into the summer and fall.   I observed the sibling species M. dichotoma, with medusoids popping out of their ampullaee, swarmed by young Oxymonacanthus sp. filefish.  Could it be that these fish timed their production of young to coincide with the availability of such a food source?  The mouths, after all, of these young fishes were undoubtedly the ideal size to suck the medusoids out of their holes. 

As it happened, my study of Millepora spp. intensified, and I began to learn to prepare the tissues for microscopic study.  I had spent time at UCSB, during my last year prior to graduation, learning about microscopic methods that, I reasoned, would be possible even on a remote island.  My interest in reproductive timing led me to research methods for study of neurosecretion, which involved release of hormones that stimulated the development of gametes, a process called gametogenesis.  The next year found me in the microscope laboratory, processing specimens of Millepora spp.  

And the next year, 1986, I was not disappointed.  Millepora platyphylla went off about 4 or 5 nights after Full Moon, but in March.  My collecting and study now became the entire focus of my time, even until I left Guam in November 1986.  

A hypothesis about timing.

These observations  led me to hypothesize that Millepora platyphylla released the medusoids in either late March or early April, three to five nights after Full Moon, just after dusk.  The date of this event would be some time during a window in the calendar, depending on when Full Moon fell.  I did not realize at the time that this mode of timing conincides in at least some details to the timing of many marine invertebrates, including Scleractinian corals, the kind that gets most of the attention, due to mass spawnings at various places around the world.  Easter, in fact, is reckoned by a similar algorithm, sometimes in March  and sometimes in April.

 Perplexing Question

 

This year Full Moon falls near the middle of March and again in April.  One is baffled.  

 

???