Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

We sampled the gut contents of 709 fishes, representing 61 species and including both cleaner and non-cleaner fishes by opportunistic shore-based or small craft day trips to shallow reef sites in Caribbean waters by the Virgin Islands, and Puerto Rico to compare their consumption of gnathiid isopods, the most common fish ectoparasites

Sampling sites: St Thomas, usvi (18°20′25.3ʺ N, 64°58′36.8ʺ W): "baby", St. John, usvi (18°19’0.2” N, 64°43’20.8” W): "donkey", "jum", "lam", "tektite", La Parguera, Puerto Rico (17°57′18.1ʺ N, 67°03′08.1ʺW): "Enrique", "Mario", "Medialuna".

Fish Collection Methods
A variety of methods and net types were used to collect fish while on snorkel or SCUBA. All fish were caught between sunrise and approximately 11:00 h. This time block was selected to maximize the interface between when diurnal fishes begin to feed and when gnathiids may still be active. Details on sampling for each site can be found in supplementary material (Supplementary Table 1 in Nicholson et al. in review). We did not account for any effect of site because all sites are similar in composition regarding biodiversity and benthic composition, and all have been confirmed to have substantial gnathiid populations (Artim et al. 2020).

Sample Processing
Gut content samples were collected via lavage (stomach pump, Artim et. al 2017), dissection, or feces collection. Fish that were large enough to have surgical tubing (either 6mm or 3mm outer diameter) safely inserted were gut lavaged. They were then returned to the location on reef where they were caught after recovering in an aerated bin of fresh seawater. Fish that were too small to be lavaged were brought back to the lab and humanely euthanized prior to dissection. However, when possible, fish were placed in aerated tanks for ~24hrs and allowed to defecate. Fecal matter was collected, and the fishes were subsequently returned to the same area reef where they were caught. Samples were screened with a dissecting scope. Since their chitinous exoskeletons are not able to be digested, remnants of gnathiids (specifically the heads, Fig. 1 in Nicholson et al. in review), can be reliably identified by any of the sample collection methods detailed above.

Known Issues:
There were some issues with data transcription but these were resolved in data analysis. These include:
Misspelled “Tetraodontidae”, “Eucinstmus lefroyi”, and “Nicholsina usta” in some cells.

BCO-DMO Processing Description:
- Missing data identifier ‘NA’ replaced with 'nd' (BCO-DMO's default missing data identifier) 
- Adjusted field/parameter names to comply with BCO-DMO naming conventions
- Added a conventional header with dataset name, PI names, version date
- Added columns for “Latitude” and “Longitude”
- Rounded columns: “Latitude” and “Longitude” to 3 decimal places (or to the thousandth place)

NSF Award Abstract:
Most research on the complex biological interactions that inhabit coral reefs has focused on larger organisms that are easily observed by divers. However, marine scientists are increasingly aware of the importance of the tiny organisms that make up the "smaller majority." This includes parasites, organisms that feed on other organisms without killing them, which may make up as many as 80% of the species on coral reefs. Among the most important parasitic organisms on coral reefs are gnathiid isopods, so-called 'ticks of the sea', that share many similarities with blood-feeding ticks and other arthropods on land. Like ticks and mosquitoes, gnathiids transmit malaria-like blood parasites. In high numbers, they can remove enough blood to kill adult fish, but even a single gnathiid can kill a juvenile fish. Thus, gnathiids may have a significant effect on coral reef communities through their effects on coral reef fishes. This project will use an integrative interdisciplinary approach involving field and laboratory observations and experiments, and molecular tools. In addition to contributing to our understanding of life in our oceans, this research will provide continued support for U.S. Doctoral and Masters students and will create valuable research opportunities for undergraduates from multiple institutions. The project will further build on the investigators existing relationships with resource managers, local divers, fishers, and boat operators, as well as K-12 schools and environmental education programs, and will contribute to local economies. A major goal of our outreach efforts will include an exhibit featuring our research at Coral World Ocean Park on St. Thomas, participation in Virgin Islands radio programs, and hosting high school students from South Carolina Governor's School.

The overall goal this investigation is to understand the ecology of fish-parasite interactions on coral reef and associated ecosystems. This project focuses on fish-parasitic gnathiid isopods, the most common ectoparasites of coral reef fishes that are best known for their role in cleaning symbiosis, as the major food item of cleaner fishes. However, their abundance, host range, role as micropredator, disease vector, and potential prey item for other species, as well as their strong association with the benthos suggests the potential for much stronger community impacts. The goals for this project are to: 1) characterize the factors influencing local gnathiid isopod density by examining the role of fish-hosts, benthic cover, gnathiid predators including cleaners, and gnathiid conspecific attraction; 2) determine and quantify variation in host exploitation and the effects of gnathiid density on larval fish-host recruitment. To accomplish the first objective, the investigators will trap gnathiids from the substrate at sites in the Caribbean, Australia, and the Philippines. Variables associated with benthic habitat as well as local fish communities will be quantified and compared with local gnathiid abundance. Laboratory experiments will be conducted to determine the effects of different host species on gnathiid growth and reproduction and to determine the role of conspecific attraction in the formation of aggregations. Predators of gnathiids will be identified through examination of gut contents and through laboratory feeding studies. To accomplish the second objective, patterns of host-exploitation will be determined by DNA barcoding of blood meals from wild-caught gnathiids and results compared with the availability of different host species. To determine the effects of gnathiids on early life history stages of coral reef fishes, gnathiid abundance will be manipulated on small artificial patch reefs onto which newly-settled reef fishes will be transplanted.