Well I just checked the latest copy of the Fish and Game Code so let me see if I can cover this. Please note, I am not a lawyer or a warden, just a biologist. There is one code that pertains to importation of aquatic plants and animals, and hobbiests are exempt. I have also included the code regarding caulerpa. I couldn't find anything else that would apply to importation of algae. I checked with a wildlife management co-worker who also happens to be a reefer and she hadn't heard anything about that. She did suggest that perhaps the supplier can not guarantee their cheato doesn't have caulerpa mixed in, or perhaps they just don't want to deal with shipping macro algae to California because they don't know the codes and don't want to risk it. Hopefully All About Fish can share where they obtained this information from, and I'll see if I can find out more from anyone else.
CA FISH & GAME CODE DIVISION 3,
Chapter 3. Importation and Transportation of Live Plants and Animals
Article 3. Aquatic Plants and Animals
2271. (a) No live aquatic plant or animal may be imported into this state without the prior written approval of the department pursuant to regulations adopted by the commission. A written application for the importation, submitted in conformance with the procedural requirements established by the commission, is deemed approved where it has not been denied within 60 days.
(b) This section does not apply to the following plants or animals unless the plants or animals are or may be placed in waters of the
state:
(1) Mollusks.
(2) Crustaceans.
(3) Ornamental marine or freshwater plants and animals that are not utilized for human consumption or bait purposes and are maintained in closed systems for personal, pet industry, or hobby purposes.
(c) The section does not apply to any live aquatic plant or animal imported by a registered aquaculturist.
Chapter 3.5 Aquatic Invasive Species
2300. (a) No person shall sell, possess, import, transport, transfer, release alive in the state, or give away without consideration the salt water algae of the Caulerpa species: taxifolia, cupressoides, mexicana, sertulariodes, floridana, ashmeadii, racemosa, verticillata, and scapelliformis.
(b) Notwithstanding subdivision (a), a person may possess, for bona fide scientific research, as determined by the department, upon
authorization by the department, the salt water algae of the Caulerpa species: taxifolia, cupressoides, mexicana, sertulariodes, floridana, ashmeadii, racemosa, verticillata, and scapelliformis.
(c) In addition to any other penalty provided by law, any person who violates this section is subject to a civil penalty of not less than five hundred dollars ($500) and not more than ten thousand dollars ($10,000) for each violation.