Also not a statistician, but I think this is unpaired t-test for sure. Like you say, you have different numbers of samples in each time point. I guess you want to see if there is a systematic difference (increase or decrease) from season to season, which would be a good case for paired. If it was paired, it would have to be on the means, since the individual replicates can’t really be linked to each other I don’t think. Do you have to do ANOVA also?