When I was a kid (so this was about 10 years ago, give or take) I read
a book about some undersea creatures - I want to say a lobster and a
crab but could be totally wrong on this.  All I remember is, the main
characters *weren't* fish.  They collected human stuff left on the
beach and made a museum in a cave under the water.  I really want to
find the name and author of this book!

Some of the parts I remember are

1)  There was a hermit crab that the main characters knew but weren't
really friends with

2)  There was a tortoise who was wise and something like the honorary
king of the sea.  The main characters look up to him and invite him to
live in their museum but he declines

3)  One of the main characters finds 3 ear plugs on the beach and gets
scared because he thinks that means there is a 3 eared human wandering
around

4)  A meteor hits the beach.  The humans want to take it but it's too
hot.  When they go to sleep, the main characters drag it down under
the sea and put it in their museum

5)  At some point, one of the main characters is captured or rescued
by the humans, depending on how you look at it.  They give him salt
water in a bucket for the night, then either return him to the sea or
he escapes, I don't remember which

I don't know if the characters called their museum a museum - they may
have just referred to it as their collection

I have no idea how long ago this was published - it could have been
old when I read it.  I read it about 10 years ago, give or take.

Hi baerana,

Okey dokey, here you go - 

The book you are looking for has been published under two titles, each
having different illustrators. So if the illustrations matter to you,
hopefully you'll be able to recognize the title of the book you had.

"OSCAR LOBSTER'S FAIR EXCHANGE" and "GARDEN UNDER THE SEA"
by George Selden.

Main characters: Peter Starfish, Oscar Lobster and Hector Crab
Location: Crescent Beach, Long Island

Publications: "Oscar Lobster's Fair Exchange":
Illustrated by Peter Lippman.
Publishers:
1) New York, N.Y. : Avon Books, [1982], ©1966. ISBN: 0380007037
2) New York : Harper & Row, ©1966, 1973 printing. ISBN: 0060252650
Photo:
http://dogbert.abebooks.com/servlet/BookDetailsPL?ph=2&bi=199141034

Previously published as "The Garden Under the Sea".
Illustrated by Garry Mackenzie.
1) Publisher: New York, Viking Press [1957]

"This is a book about a group of sea creaturess a lobster a crab a
fish and a star fish and all their friends who help them in the many
encounters they have trying to scavenge materials for their under
water garden ."
http://www.book.nu/0060252650

Selden, George
Oscar Lobster's Fair Exchange
Juvenile wonder, a different kind of a garden, a different kind of a
party. A starfish and a lobster decide to have an underwater garden,
filled with treasure gleamed from the summer folk above tide, like
shovels and pails. A shooting star provides a meteorite, and James
Fish grows the kelp and anemonies. Illustrated by Peter Lippman.
http://dogbert.abebooks.com/servlet/BookDetailsPL?bi=169713126

>>>>>>>>>>>>>>

BOOKS FOR SALE: Here are a few possibilities but there are many to
choose from. Following these books for sale I've added some book
search websites where you can comparison shop (depending on where you
are located, cost of postage, condition preferences, etc.)

GARDEN UNDER THE SEA: Good ex-libary, no dustjacket: $8.95:
http://www.biblio.com/details.php?dcx=16314674&aid=bkfndr&t=1

OSCAR LOBSTER'S FAIR EXCHANGE: Paperback, Very Good, $6.95:
http://www.tomfolio.com/bookdetails.asp?book=972444

OSCAR LOBSTER'S FAIR EXCHANGE: Hardcover, Very Good ex-library w/dustjacket: $4.28:
http://www.biblio.com/details.php?dcx=12478342&aid=bkfndr&t=1

OSCAR LOBSTER'S FAIR EXCHANGE: Hardcover, Good ex-library, $4.75, Canada
"Story was originally published under the title "the Garden Under the
Sea". Another Selden story of the animal world, this time a maritime
story at the bottom of Long Island Sound with Peter Starfish, Oscar
Lobster and Hector Crab."
http://www.choosebooks.com/item_details.jsp?refer_code=bookfinder&item_id=6565407

>>>>>>>>>>>>>>

Comparison shop:
http://www.abebooks.com or http://www.abebooks.co.uk
http://www.tomfolio.com 
http://www.biblio.com
http://www.choosebooks.com
http://www.bibliophile.net
http://www.bookavenue.com
http://www.antiqbook.com
http://www.usedbookcentral.com
http://www.zshops.com
http://www.bookfinder.com  Searches forty sites but often doesn't show all results.
http://used.addall.com/  Also searches many sites but often doesn't
show all results.

>>>>>>>>>>>>>>>>

About the author:

George Selden: thumbnail bio with photo:
http://www.students.bucknell.edu/japarker/selden.html

George Selden: pseudonym of George Selden Thompson (1929-1989):
Children's Fantasy:
  * The Garden Under the Sea [1957] a.k.a. Oscar Lobster's Fair Exchange
  * The Genie of Sutton Place [1973]
  * The "Chester, Harry and Tucker" series illustrated by Garth Williams:
      * The Cricket in Times Square [1960]
      * Tucker's Countryside [1969]
      * Harry Cat's Pet Puppy [1974]
      * Chester Cricket's Pigeon Ride [1981]
      * Chester Cricket's New Home
      * Harry Kitten and Tucker Mouse [1986]
http://www.magicdragon.com/UltimateSF/authorsS.html

"George Selden is George Selden Thompson's pseudonym. He is an
American author whose stories take place in areas he knows well - New
York and Connecticut. Selden has written many books, but the two that
distinguish themselves from the rest are Cricket in Times Square and
the sequel, Tucker's Countryside. The former won the Newbery Honor
Book Award in 1961, while the latter won the Christopher Award in
1969. Selden has immortalized Chester, Tucker, and Harry the Cat, by
giving them endearing human characteristics."
http://quickplace.sd91.bc.ca/resources/resource.nsf/0/23a81eab42548b7586256d9000053592?OpenDocument

Library of Congress: George Selden:
# 7: Garden Under the Sea
# 16 & 17: Oscar Lobster's Fair Exchange
http://catalog.loc.gov/cgi-bin/Pwebrecon.cgi?Search_Arg=selden+george&Search_Code=NAME_&PID=716&CNT=25&BROWSE=2&HC=20&SID=2

>>>>>>>>>>>>>>>

I was very happy to have found the book for you - I hope you enjoy
seeing it again (it sounds like a neat story). If you have any
questions, please post a clarification request before closing/rating
my answer and I will be happy to respond.

Thank you,
hummer

Search Strategy:
I tried many keyword search terms (crab, beach, cave, juvenile,
collections, lobsters, turtles, tortoise, etc) in various combinations
on Google, Amazon, and book search websites. My success came when I
searched on Abebooks for the keywords "lobster juvenile". I went down
the list of books until I came across the one above with the great
description (with the word meteorite) and I knew I had found it.

Fantastic!! You are the greatest!! Thanks so much and thanks for being so fast!!!!!

Thank you, baerana, for your nice note, rating, and tip - all are
appreciated. Enjoy your book! Sincerely, hummer