Low Earth Orbit (LEO) satellite communication presents a promising solution for data backhaul from oceanic buoys. However, due to the power-limited buoys and large path loss between the buoy and LEO satellites, the received signal at the LEO satellites is critically weak, which poses severe challenges to both signal detection and localization of the buoys. To make things worse, the high mobility of LEO satellites introduces large Doppler frequency shifts that complicate signal detection, while ocean currents exacerbate the positional uncertainty of buoys. The interaction of these factors highlights the inadequacy of conventional approaches that fail to address detection and localization jointly. To address these challenges, we propose a direct detection and localization algorithm based on the Generalized Likelihood Ratio Test (GLRT). To reduce the complexity of the exhaustive grid search algorithm, we employ Particle Swarm Optimization (PSO) as a low-complexity search algorithm. Furthermore, the theoretical analysis is proposed from the perspective of closed-form expressions for the probability of detection PD and the Earth-surface-constrained CRLB. Numerical simulation results demonstrate that the proposed algorithms can attain the CRLB at high SNR.