So, about my recent adventure with Koajiro Forest 小網代の森 in Miura Peninsula 三浦半島. Do you remember my post on July 15, 2016? I joyfully noticed I would go to see crabs to release their babies to the high tide sea. It was an annual “invitation only” occasion, the observation of baby crabs, aka zoea, released by their red craws crab mums (Chiromantes haematocheir) アカテガ二放仔観察会. Kanagawa Green Trust 公益法人かながわトラストみどり財団 and NPO Koajiro Activities Coordination Council NPO法人小網代野外活動調整会議 organize this event for 4 nights in July-August every year under full or new moon. Each night, only lucky 50 people are allowed to join. As the observation event is held in sea, even if a storm does not hit our region directly, when weather brings rough water to the shore of Koajiro Forest, the meeting is cancelled. We must apply to attend the event: only one application is accepted by a person per year. There always is a draw for tickets. Please calculate the probability of obtaining a ticket when the average number of application for a night is 200. By the way, August and September are storm months for Japan. On August 26, 2016, I regretfully reported in my post a super typhoon destroyed my hope to meet baby crabs of Koajiro Forest. The event was called off. *Sigh*
Since 2016, I’ve annually cast lots for the gathering. Result? 1 lose, and 2 cancellations by typhoon (including 2016). This year, I changed the strategy. To maximize my odds for the ticket, (1) we must intentionally choose a week night expecting the number of application smaller than for weekends, and (2) the choice of the day must have the least probability for a typhoon to come to Japan, i.e. the earliest schedule of the event. This year, such day was August 1st, New Moon. Hurrrrrrrrrrrrrah! I hit a jack pot! Not only I get the permit, August 1st this year had a clean sky of 30°C with very calm wind from the Pacific Ocean. Koajiro Forest was damned hot and humid. But crabs were fine.
Aside from Japanese oak wilt attacks, the environment surrounding Koajiro Forest has been changed this summer. It seems to me the City of Miura 三浦市 has decided to make the Forest one of the major tourism attractions. The traffic light to the entrance of the Forest was named “Koajiro Forest Entrance” this July. On June 9 they opened an information desk near Hikihashi Entrance 引橋入口 of the Forest. Though the brochures and videos provided down there is in Japanese, city staff are stationed, and I hope they could provide some information in foreign languages. (Please try 😉) Bonus: the info desk is in the second floor of a large supermarket called Beisia Miura ベイシア三浦. You can procure your meal there before entering the Forest. For the observation event, we started from this information desk with mini-lecture about red craws crabs, zoea releasing, and meaning of this annual event in Koajiro Forest that is very near to the downtown Tokyo. We then entered the Forest before sunset, went down the board walk to Enoki Terrace えのきテラス. (The map of Koajiro Forest is here.) At low tide, we normally go to the tideland from the Terrace to see crabs dancing on the sand. Red craws crabs do not live there, or release their zoeas in this spot. In any case, with high tide, the dancing stage for crabs is under water. We were chaperoned to another beach. (I won’t tell you where. Please apply for the event!) There were reeds (Phragmites australis) almost to the edge of seashore. This was a place hidden from the hiking road. Casual visitors are not allowed to enter there. And so, red craws crabs can come safely every summer, meandering the jungle of reeds to the sea.
When you take a bus ride from
Misakiguchi Station 三崎口 of Keikyu Line 京急,
this #1 stop is the place you have to go first.
Second stop from Misakiguchi Station
is Hikihashi Bus Stop where
We can find Beisia Miura.
The info desk for Koajiro Forest resides in the second floor.
Mini-seminar before entering the Forest
Beisia Miura has a free parking.
As long as the store is open,
you can park your car here to visit Koajiro Forest.
Newly named cross road, “Koajiro Forest Entrance.”
There is this sign when we cross the traffic light.
Please simply go straight.
The road goes down to the forest, and
The entrance to Koajiro Forest, with a map.
As long as you follow the board walk,
you cannot lose your way.
And PLEASE DO NOT DEVIATE from the board walk.
Human stomping is the most damaging
for the ecosystem in a forest.
Thank you.
Getting darker …
Red craws crab has a very peculiar life cycle as sea crab. They don’t like sea actually. The adult crabs spend almost all their life in a forest that must be by the sea. They even do not bother if water near their nest is fresh. But, just for several nights of high summer under full or new moon, and so with high tide, female red craws crab enters sea and releases babies from her belly. If she lives near the highest altitude area of Koajiro Forest, the creature walks roughly 1.2km with babies on her stomach. It’s astonishing. After the delivery in sea, a matured female is ready to fertilize next batch of eggs. Male crabs are waiting, also on seashore, for the females coming back baby-less, to mate and to continue their DNA in the next generation. Fertile eggs hatch on the belly of a mum and baby crabs, called zoea, cling to the mum’s stomach. Mothers come to visit the seashore again, vibrate their body to release zoeas. Once they leave from mum’s protection, zoeas swim in the sea for a while, eating smaller planktons for about a month to grow as megalopa. When red craws crab babies are in zoea stage, they are only 0.5mm tall with 4 legs. A toddler megalopa is about 2mm tall with 8 legs like their parents, but without craw. Before winter comes, megalopas turn into grade-schooler tiny crabs of about 4mm. They return to the forest and spend 2 years to be adult red craws crabs, about 5cm wide. According to the lecture, a female red craws crab in Koajiro lets loose 30,000-40,000 zoeas per night. Typically, they let loose zoeas 3 times in summer, so that she is a mother of roughly 150,000 babies. Out of these zoeas, only 1 or 2 individuals reach to adulthood for procreation. In sea they are eaten by bigger creatures, like fishes. Young crabs in the forest are always in danger of being a meal for animals, of desiccation on land, and from tramping of merry human tourists. Life of a crab is not at all easy. *Sigh*
A dusk of Koajiro Bay with New Moon …
“Please do not turn on your flash light before the creature enters the sea. Never. Crabs run away with your light. Also, please keep quiet. Even a slight commotion can frighten them, and they will not come here tonight.” Mr. Ichisaki of Kanagawa Green Trust gave us orientation. At around 18:30 of August 1, we softly went into the sea knee-deep; carrying good boots is the MUST for this event. We then stand and wait quietly in water, facing to the bushes of reeds expanding along the water’s edge. We strained our eyes for crabs in dark seashore of Koajiro. I understood why a far-away typhoon can cancel the meeting. Calm waves came towards and went away from us. I could feel the sand beneath my foot was shifting. Mr. Ichisaki warned us if we were in poor shape we could easily feel sea-sickness while concentrating to find the creature. According to Yabe and Kishi (2001)* red craws crabs in Koajiro start to release their zoeas roughly 20 minutes before the sun-set, suddenly increase their activity at sun-set which reached to its max 30 minutes after the sundown, and end their discharge by 30 minutes after the peak. Surprisingly, it was exactly so on August 1, 2019. Mr. Ichisaki whispered behind us “The sun has set,” and “30 minutes past” as a cue. The sun set at 18:45. “Look! One came!” “Wow, she really vibrates her entire body …” “Is this whitish smoke around her sand or zoeas?” 30 minutes later, our small conversation became like “This side of a rock is very congested.” “Hmmmmm, she’s very quick, but this one is hesitating quite a while if she can do it.” “Difference in personality?” “For crabs?” “Hey, it seems to me there is a kind of route for crabs coming out from the reeds.” “Yeah, indeed ...” It was for less-than-90-minutes, but so amazing adventure. 2 years later, only 2 zoeas will come back here as parents. How long have these crabs kept their “tradition” of baby farewell in Koajiro Forest? It must be far longer than humans use to this place …
* Kazuhiro Yabe and Yuji Kishi. Time characteristics in zoea releasing of Chiromantes haematocheir in Koajiro. Keio University Hiyoshi Bulletin: Natural Science, 30, 75-82, 2001. 矢部和弘、岸由二。「小網代におけるアカテガ二の放仔活動の時間特性」慶應義塾大学日吉紀要・自然科学、30：75-82、2001。
To the beach!
We were facing toward reeds.
She’s an early riser.
Mr. Ichisaki with his stop watch.
The staff was stationed in case medical emergency.
So, even if you could not swim, rescuers were behind you.
She’s releasing her babies.
The place is getting congested …
A person from Koajiro Activities Coordination Council captured zoeas in his plastic wine glass and showed it to us. The cup looked like a magic potion of Harry Potter where tiny twinkling stars were dancing inside vivaciously. Cute. And marvelous. Hey kids, you get bigger, you promise? Releasing zoeas in the sea is very important moment for red craws crab as species to continue. Before, when there were lots of forests reaching to the seashore, Japan had many places for the crab to thrive. People also took their existence for granted even to allow the creature for nests inside their houses. In the 21st century Japan, the condition is different. There are not many natural forests along with tideland by sea for red craws crabs. The majority of such places were deforested and dried up for reclamation of whatever human purposes. In any case, when a bay is in the vicinity of megalopolis Tokyo, the environment of tidelands and forests has experienced serious pollution during industrialization of the nation. Many crabs went into extinction. Though, with some miracle, Koajiro Forest facing to Sagami Bay 相模湾 has survived with crabs. Now it’s receiving an attack of Japanese oak wilt. How can we treasure this wondrous ecosystem so near to the Megalopolis downtown?
Magic goblets of baby crabs in Koajiro
You can see You Tube video here about the observation event last year. I guess Green Trust will upload this year’s event eventually as well. By the way, till the end of September near Enoki Terrace we can enjoy flowers of Hemerocallis fulva L. var. littorea (Makino) M.Hotta . This flower was once ubiquitous along the beach near Tokyo, but now very rare because of theft and Tsunami on March 11, 2011. Corporate money and volunteers plant the seedlings and protect their habitat in Koajiro. The Trust and the Council will welcome both CSR money and volunteers to expand their activity. If you think you can help, please enquire at the Information desk in the 2nd floor of Beisia Miura.
This year’s first flowers of
Hemerocallis fulva L. var. littorea (Makino) M.Hotta in Koajiro.
If you find an environmental issues, like Japanese oak wilt, in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121 〒243－0121 厚木市七沢657
Phone: 046-248-0323
You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/
If you sighting is in the northern part of City of Yokohama, the office you may call is
Office for Northern Parks, City of Yokohama 環境創造局公園緑地部北部公園緑地事務所
Phone: 045-353-1166
FAX： 045-352-3086
ks-hokubukoen@city.yokohama.jp
Or for the southern part, the address to call is
Office for Southern Parks, City of Yokohama 環境創造局公園緑地部南部公園緑地事務所
Phone： 045-831-8484
FAX： 045-831-9389
ks-nambukoen@city.yokohama.jp
We Really thank you, for your kindness to rescue our forest!
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