Insights into coral growth rate trends in Fiji

Abstract

Colonies of the massive coral species, Porites lutea, located at six shallow reefs across Fiji, were cored and analysed to create a chronological growth rate record. Boosted regression tree models were used to investigate relationships between annual coral growth rates and corresponding environmental variables. An ecologically based prediction model was then created to determine expected coral growth distribution across shallow reefs in Fiji for the year 2019. Annual average growth rates for the Porites lutea colonies at coral reefs in Savusavu, Leleuvia, and Navakavu reflected typical values for the Porites genus in the Indo-Pacific. Conversely, annual average growth rates at Suva Harbour, Dennis Patch, and the Coral Coast were on the lower spectrum for the Indo-Pacific Porites genus. Porites lutea growth rates were significantly influenced by latitude, whereby growth rates decreased with increasing gradient away from the equator. Growth rates were highest in the 1940s and 1950s but declined from the 1960s onwards, with significant declines observed in more polluted sites. Growth rates in Fiji are influenced by a combination of site-specific water quality and annual average sea surface temperature, with secondary contributions from the colony’s distance to shore, chlorophyll concentration, and meteorological events such as tropical cyclones, storms, and ENSO events. Predicted coral growth distribution showed that lowest growth rates are predicted around the southern and south-eastern coast of Viti Levu, highlighting the need for better marine protection at these highly populated coastlines.