As part of our study on the secondary metabolites from Mediterranean and Atlantic brown algae, we report the first chemical study of Cladostephus spongiosus f. verticillatus collected from the Algerian Mediterranean coast. The algal material was air-dried, powdered, and extracted with MeOH/CHCl3 (1:1), yielding a crude extract that was partitioned into isooctane-soluble (volatile compounds, fatty acids, sterols) and MeOH-soluble fractions. The MeOH-soluble fraction was chromatographed on silica gel and purified via HPLC, leading to the isolation of four pure compounds: fucoxanthin (1), apo-90-fucoxanthinone (2a), apo-130-fucoxanthinone (3), and loliolide (4). Their structures were elucidated using spectroscopic data (MS, IR, UV, 1D/2D NMR) and literature comparison. For compound 3, additional data (optical rotation, 13C NMR, 2D NMR) confirmed its structure, including a methylated dienic chain and E configuration of the Δ9,10 double bond. We also corrected the 13C NMR assignments of loliolide (4) compared to literature. Ecologically, compounds 2a–4 are first isolated from this species and are oxidation derivatives of fucoxanthin. Apo-fucoxanthinoids 2a and 3, known for feeding deterrent activity, likely function as grazer deterrents in the alga. Loliolide (4), with various bioactivities, may derive from β-ionone or its derivatives.