Crown of Thorns Starfish – Hazardous Starfish of Okinawa by Shawn Miller

Posted on June 28, 2018 by Admin11

The crown of thorns starfish (Ancanthaster planci) plays an important role in the underwater world. They generally feed on the fastest growing corals, allowing the slower growing coral to establish ground. They are the coral moderators, the gardeners of the sea and help increase the diversity of coral species on the reef.

Mature Crown of thorns starfish © Shawn Miller

Animals that feed on coral are known as corallivores.

Natural coral bleaching © Shawn Miller

In Okinawa, we have a variety of Corallivorous marine snails ( Drupella sp). These small snails have also caused serious damage to coral reefs.

Corallivorous snails © Shawn Miller

The venomous sea star has sharply pointed spines that deliver a painful sting. The spines inject venom which causes extreme pain, discomfort and nausea. Most injuries occur because recreation Scuba divers cut up the starfish with a dive knife and the spine penetrates the hand. The starfish serves a purpose in the ecosystem so leave it alone. They are a native marine animal of the Ryukyu Islands.

COTS of Okinawa © Shawn Miller

COTS venomous spines © Shawn Miller

In Okinawa, we have had massive COTS outbreaks in the past. These outbreaks have devastated some of the most beautiful shallow water coral reefs.

Juvenile COTS feeding © Shawn Miller

Possible Outbreak Causes

A natural cycle of nature
The decrease in natural predators that feed on COTS
Increase in food source caused by agricultural runoff, causing a blooming effect.

Coral crabs are one of the natural protectors of the coral reef. The coral provides shelter and food for the coral crabs. The crabs are on call to defend against the coral-eating starfish and other marine predators.

Coral crabs (Calcinus minutus) © Shawn Miller

Coral crabs (Cymo melanodactylus) © Shawn Miller

Protective Coral crab (Trapezia sepata) © Shawn Miller

Coral hermit crab (Pagurita vittata) © Shawn Miller

Gall coral crabs © Shawn Miller

COTS have many natural predators. Over the last twenty-five years, I have observed marine snails, harlequin shrimp, sea anemones and fish feeding on healthy and injured COTS in the wild. I was not able to get photographs of all of this behavior taking place, many natural observations occurred before I purchased an underwater camera.

Marine snails feeding on COTS © Shawn Miller

The trident trumpet (Charonia tritonis) is sought after by fisherman and shell collectors worldwide. The meat is a popular food source and the beautiful shell is valuable.

These large snails are capable of eating mature COTS. Overtaking has reduced populations of this of this predatory snail. More effort needs to be directed to the protection of this species. I have personally observed populations drastically decline over the years.

Trident trumpet © Shawn Miller

Trident trumpet feeding © Shawn Miller

The Harlequin shrimp feed on juvenile COTS in the wild and captivity. Harlequin shrimp populations are decreasing as well due to the over-collecting for the pet trade market.

Harlequin shrimp feeding © Shawn Miller

Sea anemones are vicious predators and known to feed on the crown of thorns as well.

Sea anemone © Shawn Miller

Red soil runoff contributes to coral reef bleaching and fertilizers entering the water. Could fertilizers, sewage or pollution really be the cause for a massive bloom in plankton causing an outbreak of healthy numbers of baby COTS?

Okinawa agricultural runoff © Shawn Miller

My Mission: To Document and Preserve the Wildlife of the Ryukyu Islands

This site is also designed to help people identify the beautiful animals of Okinawa, basically to serve as an online nature reference guide. If you would like to make a contribution to support my mission, please click on the donation link paypal.me/maketheswitch4nature

Your donations will help conservation initiatives as well as bring solutions to the worldwide pollution issues on our beautiful shorelines. Thank you for your support, Shawn M Miller.

#MakeTheSwitch4Nature

Testing The Venus Optics Laowa 12mm f/2.8 Zero-D Lens Underwater

Posted on May 4, 2018 by Admin11

Laowa 12mm f/2.8 Zero-D Lens for Canon EF

Underwater Housing © Shawn Miller

The Laowa D-Dreamer 12mm lens is a technical lens with great optics. The specialized lens is manual focus and manual aperture selection. I decided to see what it could do underwater.

The lens was used in combination with a Canon 70d DSLR, mounted in an Ikelite housing with an eight-inch dome port. For all the underwater shots, I preset the aperture to f11 before I locked it in the underwater housing. I tested it under ambient light, with the use of modeling lights and underwater strobes. I only had time to test it four times underwater due to bad weather and family obligations. It was challenging for sure. By the fourth dive, I started getting the hang of using this manual lens underwater.

1st issue – Reflection when shooting into the sunlight. (see the bottom right corner)

Venus 12mm underwater reflection © Shawn Miller

I made an anti-reflection lens ring cover to reduce reflection and eliminate the letters and numbers in my image.

Anti-reflection lens cover © Shawn Miller

Anti-reflection lens cover attached to the lens. (Nice and simple)

Anti reflection lens cover Anti-reflection lens cover

Anti-reflection lens covering © Shawn Miller

2nd issue – Locking on focus. Many of my images were soft due to user error and malfunctions. The focus ring kept slipping off. I adapted with some orange nonstick stretch tape to prevent it from slipping again.

If you plan to use this lens underwater I would recommend a camera body that has focus peaking. I tested it without the function and had some difficulty underwater. Below are some of my favorite photographs using the Laowa D-Dreamer 12mm lens underwater. Okinawa, Japan

To be expected the Laowa 12mm f/2.8 Zero-D lens was a lot easier to use on land. Below are some of my documentation photographs of the marine debris washed ashore on local beaches.

I hope these photographs will inspire people to care more about nature and make difference in the environment