CiguaHAB will initially concentrate sampling efforts in the northern half of the GCR, extending from St. Thomas to the south, up to Flower Garden Banks National Marine Sanctuary (FGBNMS) and coastal Alabama to the north (see accompanying figure). In order to best utilize our resources, we have divided our seven study sites into two tiers. The first tier (St. Thomas and the Florida Keys, representing end-points in the connectivity pathway), will be the most intensively-studied locations, involving monthly sampling of a full-breadth of parameters. Due to the labor and costs associated with sampling this broad geographic region, each of the second tier sites (oil rigs off the coast of LA, MS, and AL, FGBNMS, Veracruz, Yucatan, and the Bahamas) will only be sampled during two years of the project; during those years samples will be collected biannually (every six months) to account for seasonal variability at each site. Each sampling event at the Tier 2 sites comprises the collection of Gambierdiscus cells for a variety of analyses and limited fish collections for toxin analysis.