Effect of Acute Seawater Temperature Increase on the Survival of a Fish Ectoparasite

Abstract

Extreme warming events that contribute to mass coral bleaching are occurring with increasing regularity, raising questions about their effect on coral reef ecological interactions. However, the effects of such events on parasite-host interactions are largely ignored. Gnathiid isopods are common, highly mobile, external parasites of coral reef fishes, that feed on blood during the juvenile stage. They have direct and indirect impacts on their fish hosts, and are the major food source for cleaner fishes. However, how these interactions might be impacted by increased temperatures is unknown. We examined the effects of acute temperature increases, similar to those observed during mass bleaching events, on survivorship of gnathiid isopod juveniles. Laboratory experiments were conducted using individuals from one species (Gnathia aureamaculosa) from the Great Barrier Reef (GBR), and multiple unknown species from the central Philippines. Fed and unfed GBR gnathiids were held in temperature treatments of 29 °C to 32 °C and fed Philippines gnathiids were held at 28 °C to 36 °C. Gnathiids from both locations showed rapid mortality when held in temperatures 2 °C to 3 °C above average seasonal sea surface temperature (32 °C). This suggests environmental changes in temperature can influence gnathiid survival, which could have significant ecological consequences for host-parasite-cleaner fish interactions during increased temperature events.

The role of corals on the abundance of a fish ectoparasite in the Great Barrier Reef

“…More recently, Pagán et al (2020) showed that tropical cyclones are also capable of having direct effects on gnathiid populations by transporting large numbers of gnathiids, and over hundreds of kilometres, sufficient to alter the population-genetic structure. Alongside, Shodipo et al (2020) showed that gnathiid survival rates in the laboratory decrease in warmer water. Moreover, Paula et al (2020) showed that gnathiids are resilient to other environmental stressors, such as ocean acidification.…”

Access to Cleaning Services Alters Fish Physiology Under Parasite Infection and Ocean Acidification

“…But while it quickly recovered after the first extreme event (possibly due to lower coral cover, see Paula et al, 2021 ), it did not do so in 2017 and remained low postbleaching (in 2018) ( Sikkel et al, 2019 ). This overall decrease in gnathiids may have been caused by an interaction between the short-term negative impacts of thermal stress on gnathiids, as shown in laboratory studies ( Shodipo et al, 2020 ), and a decline in host availability, causing gnathiid abundance to drop ( Sikkel et al, 2019 ; Triki and Bshary, 2019 ). Since heatwave intensity and frequency is increasing ( Oliver et al, 2018 ), client fish (e.g., P. amboinensis ) population attempts of adaptation to either ocean acidification or parasite infection can quickly be erased following such extreme events, if, for example, individuals that develop tolerance to either parasite infection or OA die during such extreme events.…”

First record and molecular characterisation of two Gnathia species (Crustacea, Isopoda, Gnathiidae) from Philippine coral reefs, including a summary of all Central-Indo Pacific Gnathia species

“…While the work in the Visayas region over the past decade has resulted in extensive sampling of gnathiids ( Sikkel et al, 2014 ; Santos and Sikkel, 2017 ; Shodipo et al 2019 , 2020 ), until now, none of the species captured have been identified. Our descriptions here thus represent the first gnathiid species identified from the Philippines.…”

“…Yet, to date, only four unidentified species of gnathiid isopods have been mentioned in literature ( Santos and Sikkel, 2017 ) and no Philippine gnathiids have been described or named. Thus, especially given the high biodiversity of the region, research on coral reef gnathiids in the Philippines lags far behind other regions, with only five gnathiid studies to our knowledge being conducted to date: one study in the Luzon region the North of the Philippines ( Cruz-Lacierda and Nagasawa, 2017 ) and the other four in the Visayas region in the central Philippines ( Sikkel et al, 2014 ; Santos and Sikkel, 2017 ; Shodipo et al, 2019 , 2020 ).…”

“…In 2018, as part of an ongoing ecological study on gnathiid isopods in the central Philippines ( Sikkel et al, 2014 ; Santos and Sikkel, 2017 ; Shodipo et al, 2020 , Shodipo et al, 2019 ), gnathiids were collected from fringing coral reefs off the islands of Siquijor and Negros Oriental. Therefore, the aims of this paper were to provide detailed morphological descriptions and molecular characterisation of the adult males collected using both light and electron microscopy and to provide a summary of all known Gnathia species from the CIP.…”