Abstract
Quantifying changes to coral reef fish assemblages in the wake of cyclonic disturbances is challenging due to spatial variability of damage inherent in such events. Often, fish abundance appears stable at one spatial scale (e.g. reef-wide), but exhibits substantial change at finer scales (e.g. site-specific decline or increase). Taxonomic resolution also plays a role; overall stability at coarse taxonomic levels (e.g. family) may mask species-level turnover. Here we document changes to reef fish communities after severe Tropical Cyclone Ita crossed Lizard Island, Great Barrier Reef. Coral and reef fish surveys were conducted concurrently before and after the cyclone at four levels of exposure to the prevailing weather. Coral cover declined across all exposures except sheltered sites, with the largest decline at exposed sites. There was no significant overall reduction in the total density, biomass and species richness of reef fishes between 2011 and 2015, but individual fish taxa (families and species) changed in complex and unpredictable ways. For example, more families increased in density and biomass than decreased following Cyclone Ita, particularly at exposed sites whilst more fish families declined at lagoon sites even though coral cover did not decline. All sites lost biomass of several damselfish species, and at most sites there was an increase in macroinvertivores and grazers. Overall, these results suggest that the degree of change measured at coarse taxonomic levels masked high species-level turnover, although other potential explanations include that there was no impact of the storm, fish assemblages were impacted but underwent rapid recovery or that there is a time lag before the full impacts become apparent. This study confirms that in high-complexity, high diversity ecosystems such as coral reefs, species level analyses are essential to adequately capture the consequences of disturbance events.
Highlights
Cyclones are large meteorological events that can have variable effects on coral reef communities, from minimal impacts [1, 2] to severe damage [3, 4]
Positive Negative Positive Positive Positive Positive Positive Negative Negative Negative Negative Negative Negative Negative Positive Negative Positive Negative biomass and species richness at pre-disturbance levels, especially as it is becoming clear that the relationship between habitat complexity and fishes is stronger than the relationship between fish assemblages and benthic biota such as corals [15, 18, 25, 41]
Rapid change is possible in coral reef fish communities, as evidenced by changes in target fish abundance and biomass within two years after the establishment of MPAs [46]
Summary
Cyclones are large meteorological events that can have variable effects on coral reef communities, from minimal impacts [1, 2] to severe damage [3, 4]. While storm swell associated with these events can reach upwards of 10m (33ft), damage to benthic communities can vary around individual reefs, due to shifts in wind direction (and associated storm swell) as a cyclone passes any given point [5, 6] This means that cyclone damage will affect different parts of a reef at different times and importantly, sites normally sheltered from the prevailing weather may be heavily impacted by cyclones. More delicate coral morphologies are generally found in sheltered environments, such as lagoons or the leeward sides of reefs, which are rarely impacted by the prevailing weather conditions Due to their nature, cyclones have the potential to impact such sites as the wind and associated swells change direction as a cyclone passes. It is rare for a study to document the effects of a severe tropical cyclone on reef communities across different degrees of wave exposure
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