Sex at sea

Anenome Anomaly

Story and photos by Glen Edney

Anchored in the shallows of Maroro Bay, I descended towards one of my favourite afternoon dive sites. At the southern end of the Gardens lies a recessed cliff I call Meditation Wall for its ability to hold me enchanted and motionless as I survey the plethora of encrusting animals vying for space on this prime real estate. I have dived this site probably a hundred times but always find something new or unexpected. This dive was to be no exception.

It was late June, with 30m visibility and fish everywhere. I was starting to wish I had put the wide angle lens on my camera. Instead I headed in towards the macro heaven of Meditation Wall, hoping to find that ‘never before photographed’ nudibranch. As I approached I noticed the water was significantly cloudier and on closer inspection I could see what appeared to be tiny eggs slowly dispersing in the water column. Excitedly I gazed around me to see if I could identify the source of this spawning activity. My first thought was that it must be fish spawn. I cursed my sieve-like memory as I tried to recall which species are midwater spawners. A male red pigfish was hovering nearby and several leatherjackets were foraging on the wall. A school of demoiselles feasted on the tiny eggs, but there was nothing that looked remotely like spawning activity. Then, out of the corner of my eye, I saw a puff of eggs emerge from the thick mass of encrusting life four metres further along the wall.

As I swam hurriedly towards the spot another puff of milky white fluid spurted forth and started mingling with the first. I guessed this must be the male’s sperm, but whose? The whole area was completely covered with everything from bryozoans, sponges and ascidians to gorgonian fans, cup corals and jewel anemones. As I was pondering this mystery, another plume of eggs burst forth, this time only a metre away. Moving in close I waited expectantly for another ejaculation of sperm and sure enough, after a few seconds, a milky cloud emerged from the wall and enveloped the spreading mass of eggs. This time I was able to identify the source of this ‘sex at sea’ display.

Perched amongst a cluster of sponges and bryozoans was a small colony of lemon-coloured jewel anemones. As I watched, another batch of eggs was ejected from one of them. A few seconds later another polyp let forth a stream of sperm directly into the expanding mass of eggs. Once the anemone polyp had unloaded its precious cargo, it immediately closed up again and shrank into the folds of the colony. I had just witnessed the anemone equivalent of the famed nocturnal coral spawning that can be seen in many of the world’s tropical seas. As I hovered, camera at the ready, many questions came to mind. What had triggered this synchronized spawning? How long would it continue? Was it just one colour variety, or would other colonies be triggered into action?

Coral spawning is triggered by the full moon at certain times of the year and can last for several days. Anemones are closely related to coral so it is possible that the anemone’s spawning behaviour was set off by the previous night’s full moon. Even though jewel anemone colonies differ in colour, they are all the same species, Corynactis haddoni. Preferring low light levels, these colonies form a rich, multi-coloured mat on the shaded walls of archways, caves and overhanging cliffs such as Meditation Wall. The accepted theory is that each colony grows asexually by new polyps budding from the basal disc of existing ones. The sexual display I was now witnessing would explain how new colonies are formed. The question is: would the new colony take on the same colouration as its parents, or would a completely new colour emerge?

Photographing the spawning proved to be rather frustrating, as each time it happened I would invariably be at the other end of the wall and by the time I got to the spot most of the action was over. Each time, though, it seemed that only one colour variety was spawning. Finally I got lucky and managed to be close enough to photograph a male polyp ejecting a stream of sperm. As it merged with the eggs the waiting demoiselles darted in to enjoy this seafood delicacy. I wondered how many eggs would survive the gauntlet of hungry mouths and all the other perils of planktonic life before eventually settling on a suitable patch of reef and starting a new colony.

Getting low on air, I reluctantly left the wall and made my way across familiar territory back to the boat. Once again this gentle, easy dive had come up with the unexpected. I know where I’ll be this time next year.

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