Beach Blobs

Recently a reader sent me some pictures of yellowy-green blobs at Pui O beach and asked me if I knew what they could be. Beach blobs turn up on beaches all over the world and are actually a pretty interesting topic. Type ‘beach blob’ into a google image search and you will find a range of blobs from tiny and inconspicuous to giant and downright frightening blobs.


Blobs can be or be produced by any number of organisms including the egg cases of marine polychaete worms, dead jellyfish and any number of other partly decomposing marine animals.

After I looked at the pictures closely it seemed to me these particular blobs are most likely the remains of small jellyfish. The tentacles have either already decomposed and broken off or we’re very tiny to begin with. Only the “bell” is left.  The bell of the jellyfish is made of two firm layers of skin-like tissue sandwiching a layer of connective tissue called mesoglea. 

This mesoglea is a translucent, non-living, jelly-like substance  and is mostly water. Other than water, it contains several other substances including fibrous proteins like collagen. The mesoglea also contains muscle bundles and nerve fibres. It acts like an internal skeleton, supporting the bell and its elastic properties help restore the shape after it is deformed by the contraction of muscles when the jellyfish swims. If you have ever watched a jellyfish swim you’ll know it moves by opening and flattening the bell to draw water in, followed by contracting and closing of the bell to expel the water.
When I zoomed in on the pictures I could just make out 4 faint circular structures arranged in a cross in the middle of some of the blobs. These I am pretty sure are the gonads or sex organs of the jellyfish.

Anatomy of a jellyfish

The gonads are the cross-shaped circle-like structure in the center of this jellyfish.
The gonads are the cross-shaped circle-like structure in the center of this jellyfish.

Look very very closely and you may be able to spot 4 tiny circle outlines inside some of the yellow-green blobs. These are the gonads or sex organs of the jellyfish.

Unfortunately without the actual blobs in my hand or under a microscope I can’t say anymore than that. Jellyfish come in all sorts of sizes from microscopic to more than 2 m across so these could be juveniles or they could be adults.

Thanks to my reader for sending me this fun little mystery. If anyone else out there has any mystery pics that need identifying, please leave a comment and I’ll get in touch.

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