Mandahl Nights: Ragged Sea Hares Mating Aggregation
FILMED OBSERVATION PERIOD: 1:30am – 2:30am AST, July 11, 2018.
Visual no-touch identification of sea hares subject to verification. Individuals seemed to be young adults/late adolescents ranging in size from 1.5 inches to three inches.
Behold, the mighty Ragged Sea Hare of Mandahl Bay!
These attractive little beauties are responsible for the lives of practically all creatures in the Mandahl lagoon.
Without them, the lagoon would be an algae-covered stench bomb with its waters choked of life maintaining oxygen.
Ragged Sea Hares eat algae! And they love cyanobacterias or blue-green algae.
You probably see these very common mollusks a lot more often than you think.
Ragged villae stick out all over their bodies giving them the appearance of sea weeds or mats of algae when they aggregate.
Even though these sea hares have very few predators due to a noxious tasting skin coating of mucus slime, looking like an innocent pile of seaweed while mating can only help.
They track each other down using oral tentacles plus smell and taste sensitive rhinopores to follow the slimy mucus trail left behind by a soon-to-be lover.
Ragged Sea Hares do not have to worry about finding a partner of the opposite sex. They are hermaphrodites meaning that they are both male and female at the same time! The front of each animal is male and the rear is female.
During aggregations they link up in head-to-tail masses continually fertilizing each other.
Sand shallows mating aggregations occur at Mandahl usually when Ragged Sea Hares are approaching over population numbers, making deeper areas over-crowded. During this time, lagoon waters can be exceptionally clear because of so much algae feasting.
All of these births at once, however, typically means a lot of sea hares will perish of old age at same time.
Shortly after this mass die off, Mandahl lagoon will scum over again, awaiting a new generation of lagoon-cleaning Ragged Sea Hares.
27 Minute Raw Video available.
Video highlights:
00:00 – 00:30 Yellow-crowned Night Heron with hermit crab in beak runs about in front of headlights of car entering Mandahl Bay.
00:31 – First sea hare sightings … individuals stranded on sand by retreating tide. Juvenile fish.
01:16 – Possible juvenile Sphoeroides testudineus (Checkered Puffer) ??? (Positive ID of juvenile fish can be extremely tricky using no-touch observation methods. Collection and microscopic analysis is typically required for confirmation).
01:53 – First encounter with active sea hare. 2 inches of water. Within 20 minutes, the sand was covered with sea hares. Dorsal respiration and excreting activity visible.
03:31 Small hermit crab passes sea hare. Sea hare obviously responds to crab’s proximity.
Throughout: Unidentifiable juvenile fish, various shrimp, other swift moving water life
06:34 – Lighting angle and water depth optimal for best video detail and close up of sea hares. (4 inches depth). 6 1/2 in. diameter flat diffusion plate added to light to eliminate minor spotlighting.
08:00 – First mating contact of sea hares
16:55 – Attempt to get to denser patches of sea hares, not enough light to penetrate lagoon water.
17:03 – Fiddler Crab ???
18:21 – Tide stranded Cassiopea xamachana (Mangrove Upsidedown Jelly) Visual no-touch ID notes longer arm length and greater symmetry of white markings than C. frondosa (Upsidedown Jelly)
19:06 – Sea hares among unidentified lagoon plants. No obvious signs of egg strings. Will require followup observation. individuals appear younger and smaller than those in sand.
22:51 – { Middle Salt Pond beach area} Adult Sphoeroides testudineus (Checkered Puffer)
24:11 – Needlefish chases fish, appears distracted by light – Suspected Tylosurus crocodilus (T. Acus [agujon] also present in region). Identity inconclusive from dorsal view. T. crocodilus suspected because: Beak short compared to other needlefishes, dorsal fin begins set back from anal fin, known to adapt a darker blue/black/purple dorsal coloration when stalking prey close to sandy bottoms however bluish coloration may also be due to camera lighting refracting off the silvery scales.
25:10 – Sea hares washed ashore on salt pond beach plus various juvenile fish and shrimp to conclusion.
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