Parasites in the cleaning interactions between Labroides dimidiatus and fish

Grutter, Alexandra Sara (1994) Parasites in the cleaning interactions between Labroides dimidiatus and fish. PhD thesis, James Cook University.

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Abstract

Parasites are removed from host fish by cleaner fish but their significance in cleaning interactions is still not well understood. This study investigated the significance of parasites in cleaning interactions between the cleaner wrasse Labroides dimidiatus and its host fish at Lizard Island and Heron Island, Great Barrier Reef, Australia. Detailed information on the external parasite assemblages of several fish species, L. dimidiatus diet analyses and parasite removal rates, host cleaning rates (how often individual host fish are cleaned by L. dimidiatus), and an experiment involving the removal of all cleaner fish from reefs were used.

Host fish had species-specific parasite assemblages which were consitent among localities and time. These parasite assemblages were diverse and included copepods, isopods, monogeneans, digeneans, turbellaria, and unidentified platyhelminths. Host species identity explained most of the variation in the composition of these parasites, while host size was of secondary importance. Patterns of parasite abundance among fish species were similar between widely separated locations although the northern location (Lizard Island) had more species of parasites.

Labroides dimidiatus fed largely on crustaceans, similar to the feeding behaviour of most tropical labrids. However, they selectively fed on parasitic crustaceans rather than benthic crustaceans. Gnathiid isopod larvae were the most abundant crustaceans in the diet. At Lizard Island they selectively fed on larger gnathiids while at Heron Island their diet included fewer gnathiids but more mucus and benthic copepods. The number, size, and biomass of gnathiids at Lizard Island varied temporally with a greater proportion of small gnathiids and less biomass during the austral summer. Variability in the diet suggests both spatial and temporal flexibility in the foraging habits of L. dimidiatus. Host cleaning rates were estimated for 11 fish species by following individuals and recording the number of times and duration that they were inspected by Labroides dimidiatus. Individuals of Siganus doliatus were cleaned the most and spent an estimated 32 minutes per day being cleaned.

Host cleaning rates were positively correlated with the parasite load and surface area of the host. However, surface area explained slightly more of the variation in cleaning rates. This may be because cleaner fish use size of fish as an indicator of food availability. In the fish species Hemigymnus melapterus, larger fish had more parasites and were cleaned more often and for a longer duration. The finding that larger fish with more parasites are cleaned more suggests that size and parasites play an important part in the cleaning behaviour of host fish.

The rate at which parasites (mainly gnathiids) were removed from host fish by Labroides dimidiatus was investigated. To examine the effect of parasite removal on parasites, the number of parasites removed per individual Hemigymnus melapterus per day was estimated and compared to the infection rate and abundnace of gnathiids on H. melapterus. Observations of cleaner fish feeding rates, estimates of host cleaning rates, stomach content analyses, and an experimental manipulation of gnathiid abundances on fish were used. Labroides dimidiatus inspected an estimated 2297 (±SE 83) fish per day and ate large numbers of parasites (mainly gnathiid isopods) each day (1218 ±SE 118). The estimated predation rate by L. dimidiatus was 4.8 (±SE 0.4) parasites per minute of inspection or 0.5 (±SE 0.05) parasites per fish inspected. However, the infection rate of gnathiids onto fish was high with reduced gnathiid loads (about 50%) on fish returning to levels similar to control fish within 1-6 days. These infection rates suggest that a significant proportion of gnathiids removed by cleaner fish are quickly replaced. However, the estimated number of gnathiids removed per H. melapterus per day by L. dimidiatus was 61 (±SE 5) which was over 5 times the standing crop of gnathiids on H. melapterus (11 ±SE 3). Such a high predation rate relative to the number of gnathiids on fish and their infection rates onto fish, implies that cleaner fish may have an effect on the abundance of gnathiids on fish. However to what extent gnathiid abundances are suppresed is unclear.

An experimental evaluation of the effect of Labroides dimidiatus on the fish Pomacentrus moluccensis was done by removing all L. dimidiatus from several reefs for 6 months. The subsequent effect on parasites (total number, number per taxonomic category of parasite, and size of parasite) and host fish abundance was estimated and compared to control reefs with L. dimidiatus. This was the first time this experiment has been conducted in an area where L. dimidiatus has high densities of parasites in its diet. The absence of L. dimidiatus had no effect on total parasite abundance per fish, number per category of parasite per fish, and size of the most abundant copepod per fish. The abundance of P. moluccensis also did not differ among reefs with and without L. dimidiatus. Thus P. moluccensis did not leave reefs to seek cleaning elsewhere nor suffer increased mortality in the absence of L. dimidiatus. The absence of an effect of L. dimidiatus on the parasites of P. moluccensis is compatible with L. dimidiatus foraging behaviour as L. dimidiatus selectively fed on larger gnathiids not present on P. moluccensis. Why fish, such as P. moluccensis, which do not benefit from cleaning, seek cleaning may be due to factors other than ectoparasite removal, such as tactile stimuli provided by cleaners.

This study suggests that cleaner fish foraging patterns determine the effect cleaner fish have on parasites. Thus, although cleaning behaviour may be driven by tactile stimuli provided by cleaners, the effect of cleaners on hosts may vary according to the foraging patterns of cleaner fish and the parasite loads of hosts.

Item ID: 27392
Item Type: Thesis (PhD)
Keywords: Labroides dimidiatus; Lizard Island; Heron Island; cleaner fish motivations; fish behaviour; ectoparasites; cleaning symbiosis
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Appendix 1: Grutter, A. S. (1994) Spatial and temporal variations of the ectoparasites of seven reef fish species from Lizard Island and Heron Island, Australia. Marine Ecology Progress Series 115. pp. 21-30.

Appendix 1: Grutter, A. S. (1995) Relationship between cleaning rates and ectoparasite loads in coral reef fishes. Marine Ecology Progress Series 118. pp. 51-58. Appendix 1: Grutter, A. S. (1995) A comparison of methods for sampling ectoparasite from coral reef fishes. Marine and Freshwater Research 46. pp. 897-903.

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Date Deposited: 25 Jun 2013 04:07
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 90%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 10%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 49%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 51%
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