The beach office was called to assist a woman who reported being stung by a jellyfish in Lancing last week.
Staff attended Widewater beach to find a woman had been stung on her leg by a compass jellyfish, which had then beached on the cobbles.
Compass jellyfish are native to UK waters and after breeding in May they are venturing closer ashore with the rising temperatures, a council spokesman said.
They have been seen around the Lancing and Shoreham area recently.
The jellyfish, which are recognisable by their brown/beige colour, bold dots and striking lines around the main body, can cause harm to humans with the venom in their tentacles, confirmed the spokesman.
The attached tentacle was removed with tweezers and the affected area was flushed with hot water to release the toxins, before the woman was taken home, the spokesman said.
The spokesman issued this advice for anyone is stung by a jellyfish: “Remain calm and call the Beach Office on 01903 238977.
“Sit down and flush the affected area with hot water.
“Pick any tentacles off with tweezers only and hydrate yourself with water.
“Stay with someone until all symptoms pass and if symptoms become more severe, or a more sensitive part of the body has been stung, seek medical help.”
The spokesman added: “Our local waters are very safe below and on top, get out there enjoy it as you would.
“Be prepared for the adverse should it happen, look out for each other and have fun.”