Dataset: Field experiments of gnathiid isopods and Caribbean reef fish hosts

Name: Field experiments to determine the ability of gnathiid isopods to detect and locate Caribbean reef fish hosts using chemosensory cues in John Brewers Bay, St Thomas, US Virgin Island from June to August, 2019
Published: 2023-01-25
Keywords: Gnathiid isopod, parasite, chemical cues, host attraction, host finding, biota, oceans

Cite This Dataset

DOI:10.26008/1912/bco-dmo.887304.1

Spatial Extent: N:18.333 E:-64.967 S:18.333 W:-64.967

Temporal Extent: 2019-06-03 - 2019-08-14

Project:

Beyond Cleaning and Symbiosis: Ecology of 'Ticks of the Sea' on Coral Reefs (Gnathiid isopod ecology)

Principal Investigator:

Paul C. Sikkel (Arkansas State University)

Student:

Amber J. Packard (University of the Virgin Islands Center for Marine and Environmental Studies)

Clayton Vondriska (Arkansas State University)

Contact:

Clayton Vondriska (Arkansas State University)

BCO-DMO Data Manager:

Taylor Heyl (Woods Hole Oceanographic Institution, WHOI BCO-DMO)

Version:

Version Date:

2023-01-25

Restricted:

Validated:

Yes

Current State:

Final no updates expected

Field experiments to determine the ability of gnathiid isopods to detect and locate Caribbean reef fish hosts using chemosensory cues in John Brewers Bay, St Thomas, US Virgin Island from June to August, 2019

Abstract:

Gnathiid isopods are common crustacean parasites that inhabit all oceans from shorelines to depths of over 3000 m and use chemical cues to find their marine fish hosts. While gnathiids are host-generalists, hosts vary in their susceptibility to infestation. However, the mechanisms that mediate differential susceptibility are unknown. Here we used field experiments to investigate if the chemical attractiveness of hosts explains differences in the susceptibility of Caribbean reef fishes to infestation by a common Caribbean gnathiid isopod, Gnathia marleyi. We showed that while G. marleyi can detect and locate hosts using only chemical cues, they do not exhibit a preference for chemical cues produced by more susceptible fish species. We conclude that species-specific chemical cues are not the main mechanism driving differences in host susceptibility to gnathiid isopod infestation and that visual or post-attachment factors such as ease of obtaining a blood meal are likely mediators.

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Archival Copy

Version Date	Archive	Persistent Identifier	Date Assigned
2023-01-25	Marine Biological Laboratory/Woods Hole Oceanographic Institution Library (MBLWHOI DLA)	10.26008/1912/bco-dmo.887304.1	2023-01-25

Methods & Sampling

Host species: Host fishes selected for testing were French grunt (Haemulon flavolineatum: Haemulidae), lane snapper (Lutjanus synagris: Lutjanidae), longspine squirrelfish (Holocentrus rufus: Holocentridae), and longfin damselfish (Stegastes diencaeus: Pomacentridae). French grunt and lane snapper are carnivorous, nocturnal fish that forage in seagrass and sandy areas at night and school on reefs during the day. Both species are highly and similarly susceptible to gnathiids. French grunts are locally abundant and are known to be able to attract gnathiids with only chemical cues and therefore were used as a standard for the experiments (see below). Longspine squirrelfish are nocturnal invertivores that forage at night and shelter in or near refuges on reefs during the day. Finally, longfin damselfish are diurnal herbivores that are highly territorial. Longspine squirrelfish and longfin damselfish represent moderate and low susceptibility to gnathiids, respectively.

Field collection: Juvenile Gnathia marleyi and adult host fishes were collected from John Brewers Bay, St. Thomas, United States Virgin Islands (18°20’ N, 64°58’ W) from May to August 2019 and January to March 2020. Gnathiids were collected using zooplankton light traps similar to those de- scribed by Artim and Sikkel (2016). They were held at the University of the Virgin Islands’ MacLean Marine Science Center in small colonies in 150-milliliter (ml) containers filled with filtered seawater. All host fishes were caught by free-divers using cast nets and were held in a 2800-liter tank with continuously flowing seawater, at 28 degrees C. Fish were held for no longer than 24 hours and all were returned to the original capture site.

Field experiments: To determine the ability of gnathiid isopods to detect and locate hosts using chemosensory cues and whether they used these cues to distinguish between host species, traps similar to those described in Sikkel et al. (2011) and Santos and Sikkel (2019) were used. These traps were constructed using a PVC tube (20 centimeters × 5 centimeters) with two removable, inward-facing funnels. The hole in the bottom of the funnel was sealed and four 1 centimeter diameter holes were drilled in the side of the funnels, allowing chemical cues to be released without the gnathiids being able to see the fish from outside the trap. Traps were placed haphazardly on the reef in pair-wise choice arrays. Pairings included: 1) French grunt versus empty (Control); 2) French grunt versus lane snapper (high vs high susceptibility); 3) French grunt versus longspine squirrelfish (high vs medium susceptibility); and 4) French grunt versus longfin damselfish (high vs low susceptibility). Fishes of similar size were paired for trials. The traps were placed more than 1 meter apart 1 hour before sunset and collected 1 hour after sunrise. This ensured that traps were deployed at times of peak gnathiid activity. Water from the traps was then filtered through 55-micrometer (μm) plankton mesh and fish were checked to assure no gnathiids were still feeding. The number of gnathiids in each trap was counted and all gnathiids were categorized by stage. In total, 66 pairs of traps were deployed (Control: n = 10; lane snapper: n = 15; longspine squirrelfish: n = 20; longfin damselfish: n = 21).

Data Processing Description

Statistical analysis: All statistical analyses were performed using RStudio (Version 1.2.1335). For field experiments, gnathiid counts within traps did not conform to and could not be transformed to a normal distribution, so a Kruskal-Wallis test was used to compare the differences between treatment levels. The differences within each treatment were calculated by subtracting the number of gnathiids found in a French grunt trap from the number of gnathiids found in its paired trap. A Dunn’s Multiple Comparison Test was then used to determine any differences between treatments (e.g. Control versus lane snapper, lane snapper versus longspine squirrelfish, etc.). Independently, Mann-Whitney U tests were used within each treatment to detect any differences between French grunt and its paired treatment (e.g. French grunt versus lane snapper, French grunt versus longspine squirrelfish, etc.). Data were also analyzed using permutation resampling (see Online Resource 1).

Video data was collected using a DLSR camera. Video data was analyzed manually. Statistical analyses were conducted in RStudio (Version 1.2.1335).

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 based on sampling site location
- Converted dates to ISO date format (YYYY-MM-DDThh:mmZ)

Data Files

File
field_data.csv (Comma Separated Values (.csv), 4.06 KB) MD5:75c19ebbed344c6346e496d354e7507d Primary data file for dataset ID 887304

Supplemental Files

File
Permutation resampling resource filename: 887304_Summary_Permutation_Resampling_Vondriska.pdf (Portable Document Format (.pdf), 9.83 KB) MD5:2f647a1b88ee4adfb30145ef989550bb Summary of permutation resampling of field experiment results

More Information about this dataset

Funding Sources

Funding Source	Award Number
NSF Division of Ocean Sciences	OCE-1536794

Deployments

None available yet

Instruments

Camera

Supplied Name: DLSR camera

Supplied Description:

Instrument Type

Generic Name: Camera

Acronym: camera

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/311/

Generic Description:

All types of photographic equipment including stills, video, film and digital systems.

Fish Cage

Supplied Name: Host-attraction trap

Supplied Description:

Host-attraction traps: PVC tubing with a reversed funnel on each side. An individual host is placed within the trap to test chemical attraction for gnathiids.

Instrument Type

Generic Name: Fish Cage

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/90/

Generic Description:

Used to catch fish.

Plankton Net

Supplied Name: Lighted plankton trap

Supplied Description:

Lighted plankton traps: PVC tubing with a reversed funnel. A light is shined out the funnel to attract plankton (including gnathiids) into the trap.

Instrument Type

Generic Name: Plankton Net

Community Identifier: http://vocab.nerc.ac.uk/collection/L05/current/22/

Generic Description:

A Plankton Net is a generic term for a sampling net that is used to collect plankton. It is used only when detailed instrument documentation is not available.

Self-Contained Underwater Breathing Apparatus

Supplied Name:

Supplied Description:

Instrument Type

Generic Name: Self-Contained Underwater Breathing Apparatus

Acronym: SCUBA

Generic Description:

The self-contained underwater breathing apparatus or scuba diving system is the result of technological developments and innovations that began almost 300 years ago. Scuba diving is the most extensively used system for breathing underwater by recreational divers throughout the world and in various forms is also widely used to perform underwater work for military, scientific, and commercial purposes.

Reference: http://oceanexplorer.noaa.gov/technology/diving/diving.html

Parameters

Date and time formats are described in python strftime() syntax.

Supplied Name	Supplied description	Supplied Units	Standard Name
Date	Date of trial Format: %Y-%m-%d	unitless	date
Latitude	Latitude of sample site North (South is negative)	decimal degrees	lat
Longitude	Longitude of sample site East (West is negative)	decimal degrees	lon
Treatment	Host placed in comparison trap (Control = empty trap; Ls = Lutjanus synagris; Hr = Holocentrus rufus; Sd = Stegastes diencaeus)	unitless	treatment
Hf_Total	Total number of gnathiids found in trap containing a Haemulon flavolinieatum	unitless	number
Treatment_Total	Total number of gnathiids found in comparison Treatment trap	unitless	number
Difference	Difference between Hf Total and Treatment Total	unitless	number
Hf_Z1	Number of unfed stage 1 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Hf_Z2	Number of unfed stage 2 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Hf_Z3	Number of unfed stage 3 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Hf_P1	Number of fed stage 1 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Hf_P2	Number of fed stage 2 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Hf_P3	Number of fed stage 3 gnathiids found in the Haemulon flavolineatum trap	unitless	number
Treatment_Z1	Number of unfed stage 1 gnathiids found in the Treatment trap	unitless	number
Treatment_Z2	Number of unfed stage 2 gnathiids found in the Treatment trap	unitless	number
Treatment_Z3	Number of unfed stage 3 gnathiids found in the Treatment trap	unitless	number
Treatment_P1	Number of fed stage 1 gnathiids found in the Treatment trap	unitless	number
Treatment_P2	Number of fed stage 2 gnathiids found in the Treatment trap	unitless	number
Treatment_P3	Number of fed stage 3 gnathiids found in the Treatment trap	unitless	number

Database

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Dataset: Field experiments of gnathiid isopods and Caribbean reef fish hosts