Living on the edge: high-latitude Porites carbonate production under temperate eutrophic conditions

Non-framework building high-latitude coral communities have recently received increased attention as a result of their potential to act as refugia during global change, as proxies for such change and for testing the environmental tolerance limits of various species of coral. In this study, we report on high-resolution in situ measured environmental factors influencing the development of monospecific (Porites panamensis) non-framework building coral communities and the resulting coral-derived carbonate sediment production in the northern Gulf of California, Mexico (Bahía de Los Angeles, 29°N, 113°E). Half-hourly measurements of temperature and chlorophyll a (a nutrient proxy) for a 1-year period indicate temperature extremes ranging from 14°C to 30°C, and average chlorophyll a values of 2.2 mg Chl a/m³ (eutrophic). Even though P. panamensis only occur as small massive and encrusting colonies, they nonetheless show a significant carbonate sediment production potential (0.14 kg CaCO₃/m²/year). A calculation of carbonate production rates vs amount of coral found in the sediment shows that this high-latitude community must have persisted for an extended period of time.