“In another trial, daily astaxanthin doses of 6, 12, or 18 mg decreased triglycerides and increased HDL cholesterol and improved blood flow in microcirculation models [15].”*
*[15] Yoshida H, Yanai H, Ito K, et al. Administration of natural astaxanthin increases serum HDL-cholesterol and adiponectin in subjects with mild hyperlipidemia. Atherosclerosis. 2010;209:520–3.
Peter Attia said on a recent (sometime in the past year, on an CVD-focused podcast) that there have been many tests of compounds that increase HDL, but no evidence that boosting HDL reduces risk of atherosclerosis. It seems associative, but not causal.