Corals thriving in dynamic environments may hold key insights into future coral reefs

The coastal waters of Texas have dynamic environmental conditions and are heavily influenced by anthropogenic stressors, which are not conducive for corals. However, cryptic coral species (Astrangia poculata and Oculina diffusa) have been documented in this ecosystem, particularly within manufactured channels on jetty rocks connecting the Gulf of Mexico and Corpus Christi Bay. This research explored the strategies these corals utilize to survive with varying fluctuations in environmental conditions. Extensive in-water-field surveys were conducted in Packery Channel over one year to 1) characterize physical environment fluctuations within Packery Channel over an annual cycle, 2) characterize the physiological condition of the corals by, a) understand autotrophic contribution through symbiont density and chlorophyll concentrations, b) understand heterotrophic contribution through corallite sizing and assessing zooplankton presence to understand food availability for corals and c) describe coral tissue isotopic signatures of the symbionts, coral host, and the coral holobiont to understand contributions to heterotrophic and autotrophic feeding mechanisms, and 3) classify the corals located on the jetty rocks at Packery Channel through morphological and genetic analyses. Physical environmental data (e.g., turbidity, temperature, salinity, etc.) was measured weekly during each season (e.g., winter, spring, summer, and fall). Additionally, plankton abundance and diversity measurements were assessed each season at the highest tide and the lowest tide of the full moon cycle. Corals were collected seasonally (total n=64). This work revealed the species present are Astrangia poculata and Oculina diffusa and that these corals utilize both heterotrophy and autotrophy year-round to withstand extreme environmental conditions, including large temperatures (9.4-31.5°C) and turbidity (0-95.3 NTU) ranges. Stable isotope analyses suggest heterotrophy to be the dominant feeding mechanism year-round and autotrophy secondarily. Specifically, the autotrophic contribution is more prominent during the summer and fall seasons than in the spring and winter seasons which correlates with the environmental data fluctuating the least in the summer and fall. Understanding the nutritional sources of corals in extreme environmental conditions could provide insights into potential phenotypic plasticity and adaptability to anthropogenic influence. Therefore, corals thriving in dynamic environments could provide researchers with the insight they need to understand coral adaptation amid rapidly changing environmental conditions.