Last week we celebrated Chinese New Year, the festival that marks the start of the New Year according the lunar Chinese calendar. Humans are not the only creatures to time activities by the waxing and waning of the moon’s light. Many species of invertebrates have behaviors that are timed based on the moons rhythms. Here are a few fun examples.
A spawning stony coral from Flower Garden Banks National Marine Sanctuary (Photo Credit: Emma Hickerson, National Ocean Service)
Corals are a diverse group of animals with a wide range of reproductive strategies. Depending on the species, individual corals can be male, female or both. They can reproduce asexually or sexually, and sexual reproduction can take place either internally or externally. Stony corals are mostly broadcast spawners, which is a form of external fertilization. Many of these corals undergo mass spawning events. In a spectacular show coral colonies release huge numbers of eggs and sperm that float toward the surface.
For this type of fertilization to be effective, corals have to closely coordinate their reproductive timing. They do this through the use of three cues, the full moon, sunset, and a pheromone released by other spawning corals. The National Museum of Natural History’s own Nancy Knowlton has been studying coral reefs and their spawning patterns for years, at the Smithsonian Tropical Research Institute's Bocas del Toro field station.
For my money, the palolo worm, has possibly the most fun name to pronounce in the animal kingdom. But these worms are interesting for reasons other than their delightfully rhythmic moniker.
Like corals, these animals use the moon to sync their spawning. Palolo worms, are marine annelid worms of the Eunicidae family that can be found in tropical and temperate oceans worldwide. The species Palola virdis from the south pacific are probably the most well-known as their unusual mating behaviors attract a lot of attention, and were documented in the scientific literature more than 100 years ago! Before breeding, the animal undergoes a partial metamorphosis (epitoky), the back half of the animal transforms and becomes laden with gametes.
When the appropriate part of the lunar cycle arrives, the back section, now called an epitoke, breaks off from the front portion (the atoke) in a process called schizogamy. The epitoke then swims on its own to the surface where it begins to disintegrate, releasing either sperm or eggs. In some places, for instance Samoa and Vanuatu, the aggregations of spawning epitokes are collected and used as a food source. Considered a delicacy, they are prepared in a variety of ways, even eaten raw!
Lunar animal aggregations can have less delicious consequences for humans. Though you may think of jellyfish as animals that are at the mercy of the current, box-jellyfish are actually quite strong swimmers. Box-jellyfish species in the genus Alatina aggregate eight to twelve days after the full moon in parts of Hawaii, Australia, and Bonaire.
These aggregations pose a serious threat to beachgoers, often resulting in mass sting events and beach closures. Not just consequences of the current, evidence suggests that these groupings are spawning aggregations. Still curious? We have several previous posts about jellyfish taxonomy, field-collections, research, and outreach. You can even get involved in box-jellyfish research yourself!
As it turns out, many species of marine invertebrates use lunar cycles to synchronize breeding patters, including some species of sea urchins, oysters, various polychaete worms, and crustaceans. But romantic rendezvous under the moonlight are not the only thing invertebrates set their lunar calendars for. Many species of crustacean have been observed to time their molting to certain parts of the lunar and tidal cycle. Crustaceans like all arthropods have a hard exoskeleton; in order to grow they have to molt their old exoskeleton (a process called ecdysis). There are several reasons why syncing molting to lunar/tidal cycles might be advantageous. Firstly, this may allow crustaceans to time their molting to align with favorable tide conditions. Secondly, it is possible that having all the individuals in an area molt at once, decreases individual risk of predation or conspecific aggression -- this is known as the selfish herd hypothesis. The thinking goes that there is safety in numbers; if you are all vulnerable at the same time, predators cannot pick you off one by one. For a specific example take a look at Pseudosquilla ciliata, a mantis shrimp or stomatopod.
You may remember a bit about these remarkable creatures from our recent post. Research has shown that these mantis shrimp molt during the last lunar phase. Since these animals are highly aggressive towards one and other, molting at the same time reduces the chance of individual mortality. If you molt at the same time as everyone else, you will not be left defenseless, while others are armored and ready for a fight!
So while you usher in the year of the goat, take a moment to think about our invertebrate friends, and the myriad ways that their biology is tied to lunar cycles.
By Frances Farabaugh, Intern Invertebrate Zoology Department NMNH
Thank you Kelly Drinnen. We've have cited the original source now. Much appreciated.
Posted by: Allen Collins | 01 March 2015 at 01:14 PM
The top image of Stony Coral Spawning is also from Flower Garden Banks National Marine Sanctuary.
Posted by: Kelly Drinnen | 27 February 2015 at 04:15 PM