Jobos Bay on Puerto Rico’s southern shore, is recognized for its habitat diversity: coral reefs; mangroves; seagrass beds; and estuaries. The bay is rimmed by a peninsula and chain of small islands. Tucked between the reefs and mangrove cays, this bowl-shaped beach features grains from both land and sea.

Lithic grains here reflect Puerto Rico’s geology where carbonate rocks overlay volcanics. Biotic grains reflect nearby reef and estuary habitats. The green nerite snail is an algal grazer; high-spired snails feed on detritus. The brownish U-shaped fragment, a vermetid snail, attaches to hard surfaces and feeds using mucus nets. The glassy oval near center and ribbed fan shape center top are bivalve remains. Sea urchin parts include the skeleton fragment, bottom left, with the raised boss that once supported a moveable spine, and green, purple and tan longitudinal-grooved spine fragments. Swirled discs with tight rows of pores are forams like Heterostegina, brick-red chunks are Homotrema. Large chalky flakes with porous interiors are blades from coralline alga Halimeda.