Diurnal activity patterns of the temporary fish ectoparasite,Gnathia africanaBarnard, 1914 (Isopoda, Gnathiidae), from the southern coast of South Africa

Rachel L Welicky,Paul Sikkel,Nico J Smit,Maryke L Ferreira

doi:10.1017/s0025315417001369

Abstract

Gnathiid isopods are one of the most common fish ectoparasites, and are found in both temperate and tropical oceans. On coral reefs, gnathiids are most active at dusk and dawn, and contribute significantly to trophic dynamics, as they are a prey resource for cleaner fish and parasitize numerous fishes. Gnathiids also inhabit temperate intertidal waters, but their activity patterns and contribution to intertidal trophic dynamics remain unstudied. To provide the first ecological data on temperate intertidal gnathiid activity patterns, 172 gnathiid-freeClinus superciliosuswere set in an intertidal system in Tsitsikamma National Park, South Africa, during early morning, morning, afternoon, early evening, and evening, high and low tide, and within the inter- and infra-tidal zone to examine gnathiid infestation levels. After exposure, gnathiids from each fish were identified to the species level, counted, and their developmental stage was recorded. All gnathiids were identified asGnathiia africana. On average, 1 ± 5SD gnathiids were collected from each fish, and the majority of gnathiids collected were stage 1. Significantly more gnathiids were collected during morning and afternoon compared with all other time periods. The number of gnathiids collected was not influenced by the fish's exposure to high or low tide, or placement within the tide zone. AlthoughG. africanais free from cleaner fish predation because cleaner fish do not reside in temperate intertidal habitat,G. africanaabundance is surprisingly small. Future studies should examine what regulatesG. africanapopulation size and the role they play in temperate intertidal food webs.

Highlights

Many marine organisms undergo daily shifts in activity
The diel activity patterns of zooplankton may be in part related to endogenous cues, there is evidence that they can moderate their activity levels based on factors such as light availability, which in turn are associated with season and time of day (Hays, 1995; Cohen & Forward, 2009)
The goal of this study is to provide the first steps towards understanding the ecology of intertidal gnathiids by examining the interactions between G. africana and its host Clinus superciliosus

Summary

Introduction

Many marine organisms undergo daily shifts in activity. These daily shifts are often associated with the exploitation of food, avoidance of predators, and reproductive efforts (e.g. Sancho et al, 2000; Zemke-White et al, 2002). Many marine organisms undergo daily shifts in activity These daily shifts are often associated with the exploitation of food, avoidance of predators, and reproductive efforts The diel activity patterns of small, mobile, benthic invertebrate zooplankton are well-documented. These organisms regularly undergo daily vertical migrations. In both marine and freshwater environments, they find refuge from fish predators in the benthos during daytime, and move up the water column at night, where food is typically more dense and easier to locate (Gilbert & Hampton, 2001; Hays, 2003). The diel activity patterns of zooplankton may be in part related to endogenous cues, there is evidence that they can moderate their activity levels based on factors such as light availability, which in turn are associated with season and time of day (Hays, 1995; Cohen & Forward, 2009)

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