There's a fact sheet in the app Pacific Pests Pathogens & Weeds on algal leaf spot (148). Images look a little different from yours. They are usually quite furry. The fact mentions Samoa. Younger leaves might show more definite symptoms.
Looking at what's recorded in Samoa and other Pacific island countries, other than algal leaf spots, there are a number of other causes of leaf spots worth considering. In Samoa, there is Pestalotiopsis, and elsewhere Colletotrichum, and Cercospora. So look at the spots on the fruits and leaves and see if you can see any sporulation. The spores of all these fungi are fairly distinct.
If in doubt have a look at the excellent manuals of Eric McKenzie - Pathogen Identification Manual 2&3 Export Commodities. Pest identification workshop. Landcare Research. NZ. There are nice images of Cephaleuros (sporangiophores and sporangia) on other crops as well as the equivalent structures of those three fungi I mention. I am sure Biosecurity would have copies, if they are not at SROS.