I gave one above already for my reluctant case for Marwell.
I would add that the in-situ / ex-situ conservation of desert species like the Arabian and Scimitar horned oryx, the addax, Dorcas gazelles, the Grevy's zebra, the Somali wild ass, Egyptian tortoises and sand cat make this biome a particularly strong point for Marwell.
This is unfortunately just not a biome or biogeographical region that Jersey specialize in at all so it is another cup that isn't in Jersey or the Durrell trusts favour in terms of deserts.
In terms of grasslands things are slightly better as Jersey has historically had maned wolves and Przewalski's horse and once again their ex-situ / in-situ work with the pygmy hog in the grasslands of India gives them a point up.
However, Marwell still has the trump card on grasslands with sheer amount of species from this biome and ex-situ / in-situ conservation with Bactrian camel, Przewalski's horse and many East African ungulates (whether this conservation work is in the league of Jersey with the pygmy hog though, I dont know, but I would tend to think that it wouldn't be anywhere near it).