Guadalcanal was not fought by all marines.
According to wikipedia:(which is not always entirely accurate)
Order of Battle United States
The US landing force on Guadalcanal was under the command of Marine Major General Alexander Archer Vandegrift. On December 8th he was replaced by Army Major General Alexander McCarrell Patch, who took command of the U.S. XIV Army Corps on January 2nd.
Marines
1st Marine Division1
1st Marine Regiment
5th Marine Regiment
7th Marine Regiment
11th Marine Regiment
1st Amphibian Tractor Battalion
1st Aviation Engineer Battalion
1st Parachute Battalion2
1st Pioneer Battalion
1st Raider Battalion
1st Special Weapons Battalion
1st Tank Battalion
2nd Marine Division3
2nd Marine Regiment
6th Marine Regiment
8th Marine Regiment
10th Marine Regiment
2nd Amphibian Tractor Battalion
3rd Defense Battalion
9th Defense Battalion
2nd Raider Battalion
2nd Special Weapons Battalion
2nd Tank Battalion
Notes:
The 1st Marine Division was commanded by Major General Alexander Archer Vandegrift. The majority of the division arrived on Guadalcanal August 7th. 2nd Battalion 5th Marines and elements of the 1st Pioneer Battalion arrived later in August. 7th Marines and 1st battalion/11th Marines arrived September 18th. The division began withdrawal from the island December 12th.
Arrived September 8th; departed September 18th.
The 2nd Marines were attached to the 1st Marine Division for the initial landing on August 7th, although the 1st and 3rd battalions were initially employed on Tulagi and Gavutu-Tanambogo islands. The entire regiment was on Guadalcanal by November. On November 4 the 8th Marines landed, and the remainder of the division followed in December. The division came under the command of Brigadier General Alphonse De Carre.
Army
25th Infantry Division1
27th Infantry Regiment
35th Infantry Regiment
161st Infantry Regiment
8th Field Artillery Battalion
64th Field Artillery Battaltion
89th Field Artillery Battalion
90th Field Artillery Battalion
65th Engineer Combat Battalion
Americal Division2
132nd Infantry Regiment
164th Infantry Regiment
182nd Infantry Regiment
221st Field Artillery Battalion
245th Field Artillery Battalion
246th Field Artillery Battalion
247th Field Artillery Battalion
57th Engineer Combat Battalion
147th Independent Infantry Regiment3
97th Field Artillery Battalion
214th Coast Artillery Regiment
244th Coast Artillery Regiment
Notes:
The 25th division arrived by January 4th, 1943, under the command of Major General Joseph Lawton Collins.
The 164th arrived October 13th; the 182nd on November 12th, and the division HQ and 132nd on December 8th. The division was under the command of Major General Alexander McCarrell Patch.
Arrived November 4th.