While swimming one morning across Coogee Bay in New South Wales, we came across thousands of these strange creatures (see photo) floating at depths down to about 2 metres.

They were hard but also flexible, with water inside and a small hole at one end. Their length varied from about 3 to 30 centimetres and their walls were between 2 and 5 millimetres thick. Their skin was marked with many small protrusions, the size of which varied from one creature to another. Unlike jellyfish they appeared to be completely harmless.

No one I've spoken to from the area has ever come across anything like this. So what were they and why were they there?

Philippe Wilmotte, Maroubra, New South Wales, Australia

I noticed this creature floating near the recreational pier at Rocky Point Park, in Port Moody, BC. It appeared to swim by curving/swinging its body side-to-side, as if it were a tail, and appeared to be similar in size to the fist of a child. There were a number of jellyfish in the waters at the same time, and at first, I assumed it was a type of jellyfish. Can anyone identify this creature?

Peter Buckley, Toronto, Canada

During the last 100 years, humans have been burning oil, natural gas, peat and coal. In the next 50 years we will burn even more. Burning hydrocarbons produces carbon dioxide and water. How much has this water added to sea-level rise?

Alfred Jacobsen, The Netherlands

Last week me & my family were down the beach in Suffolk, UK and as soons as we packed up a storm appeared. As we got soaked walking back we saw a fork of lightning strike the sea (North Sea).

My question is what happens when lighting strikes the sea? Or more to the point; how much of the sea is affected by the strike? Will it kill the fish? What would have happened if a human was in the sea? 

I am guessing that it would affect the wildlife but I am not sure if the large mass of water would disperse the energy and affect it less.