Response of reef fish populations to changes in coral cover, fishery and disruptive events in Bonaire Marine Park

Management of reef fish populations requires insight in their resilience to anthropogenic stressors. Studies on temporal variations in reef fish populations and their abundance responses to environmental changes are crucial to the development of ecosystem-based management.

Seventeen years of voluntary fish survey data of reef fish at the west coast of Bonaire Marine Park (Caribbean) were analysed to investigate the effect of environmental changes on local reef fish populations. Various anthropogenic stressors that influence the coral reefs of Bonaire were studied in recent years, this study focusses on population responses to loss of coral cover, the establishment of a fishery protected area, and reef fishery pressure. In addition, reef fish responses to specific events were analysed at species or family level.

In general fluctuations in sighting frequencies were species-specific and difficult to interpret. Three large parrotfish decreased by approximately 50% over time and there were indications of a negative trend in mid-sized parrotfish as well. In fishery targets, the most intensive fished group (large to mid-sized grouper species), decreased strongly. After their abundance decreased to near zero, two species belonging to other fish families showed signs of sequential overfishing. It is unclear if larval import will compensate for the loss in reproductive capacity of the species in decline, recent literature on recruitment distances suggest that the level of self recruitment is high in Bonaire. An exception to short recruitment distances was noted earlier in the balloon fish Diodon holocanthus. The data suggest that the balloon fish population till 2010 originated from the mass recruitment in 1994, from the start of the studied period in 2000 to 2010 their abundance steadily declined to near zero. Another event with direct effect on population dynamics is the mass mortality events in moray eels in 2008. With a lag time of a year, especially two Enchelycore species strongly declined afterwards, which could elucidate the highly variable population densities of these species over the period. A following moray eel mass mortality event in 2022, also occurred at the onset of a period of sea water warming, paralleling various reef fish species in the Red Sea. Increase in warming events carries the risk of more frequent mass mortalities.