Low susceptibility of invasive Indo-Pacific lionfish Pterois volitans to ectoparasitic Neobenedenia in the eastern Caribbean

Since its introduction to the tropical western Atlantic in the 1980s, the Indo-Pacific lionfish, Pterois volitans , has become one of the most devastating species invasions in the marine environment. It remains unclear whether release from parasitism has played a role in its success. The capsalid monogenean Neobenedenia pargueraensis is a common Caribbean ectoparasite with a broad host range that, in high numbers, can kill hosts. However, previous research found that lionfish collected from the Bahamas, Puerto Rico and the US Virgin Islands were not parasitized by N. pargueraensis . Possible explanations for this are that 1) lionfish do not occupy habitat where infective stages are present; and 2) lionfish are not susceptible to this parasite. The goal of this project was to determine the susceptibility of lionfish to N. pargueraensis . Experiments were conducted in spring and summer of 2012 and 2013 on St. Thomas, US Virgin Islands. Lionfish ( n  = 24) and control blue tang, Acanthurus coeruleus ( n  = 19) were caught from nearby shallow reefs, treated to remove pre-existing ectoparasites, and exposed to high concentrations of N. pargueraensis for 14 days. Despite exposure to high concentrations of parasites, only one of 24 lionfish was parasitized, and only one individual parasite was found on the infected fish. In contrast, all blue tang were infected with an average of ten parasites per fish. These results suggest that invasive lionfish are not highly susceptible to N. pargueraensis , which may contribute to their successful invasion of the Caribbean

Nocturnal migration reduces exposure to micropredation in a coral reef fish

Tropical Atlantic reef fishes in the family Haemulidae (grunts) remain quiescent on reefs during the day and migrate to seagrass beds or sand flats at night. Hypothesized advantages of such nocturnal migrations are increased food availability and/or decreased predation risk. Here, we tested predictions of an alternative hypothesis that nocturnal migrations of French grunt, Haemulon flavolineatum (Desmarest, 1823), reduce exposure to blood-feeding gnathiid isopods. The departure of grunts from the reef coincides with increasing gnathiid activity. In field experiments, subadult fish placed in cages and deployed on the reef at night harbored significantly more gnathiids than those placed in the seagrass habitat. However, this was not the case during the day when gnathiid activity in all habitats is low. In another experiment, the timing of return to the reef was determined to coincide with the postdawn decrease in gnathiid activity. Estimates of cumulative gnathiid exposure at two sites revealed that grunts remaining in reef habitat at night would experience an average of 3 and 44 times more gnathiids than if they spent the night in the seagrass bed, and could reach more than 300 gnathiids on a single fish. In a final field experiment, even recently-settled (<2 cm) juvenile grunts were infested by gnathiids, supporting previous laboratory experiments showing that a single third-stage gnathiid will infest and kill grunts of this size. Combined, these findings suggest that nocturnal feeding migrations of French grunts and ecologically similar fishes result in reduced exposure to blood-feeding gnathiid isopods

The relationship between lunar periodicity and activity of fish-parasitic gnathiid isopods in the Caribbean

Gnathiid isopod larvae are members of the marine demersal zooplankton community and are common ectoparasites of coral reef fishes, emerging from the substratum, mostly at night and crepuscular periods to feed on fish blood. Given that the activity of many marine organisms is often linked to changes in the phase of the moon, we examined the relationship between lunar phase and activity in gnathiid isopods on Caribbean reefs. We employed two sampling methods to quantify gnathiid activity: (1) Emergence traps set on reefs over a 24 h period; and (2) live fish placed in cages on reefs and retrieved during night and dawn peaks in gnathiid activity. These were compared during discrete phases as well as a continuous metric, the lunar "angle", and an estimate of ambient light availability (luminance). Lunar phase and angle varied in their statistical effect on gnathiid activity patterns by sampling method and/or year. Luminance had a significant but inconsistent effect on measures of gnathiid activity. Our results suggest that changes in the lunar cycle are not a strong predictor of gnathiid activity at our shallow reef study sites