Abstract:

Data is reported from four investigative studies into the effects of oil on juvenile blue crabs in southern Louisiana marshes: 1) field and abundance data from crab collections on oiled and unoiled sites on four dates in 2015 and six dates in 2016, 2) field predation avoidance study at oiled and unoiled sites using crabs not previously exposed to oil, 3) field predation avoidance study at LUMCON using crabs that were exposed to oil in a laboratory, and 4) a laboratory experiment examining the effects of water accommodated fractions (WAFs) on the foraging behavior of juvenile blue crabs.

Suggested Citation:

Robinson, Elizabeth, Rabalais, Nancy N.. 2019. The effects of oil on juvenile blue crab (Callinectes sapidus) settlement, foraging, and predator avoidance: Field and laboratory experiments from 2015-07-19 to 2016-09-03. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-gvrv-na16

Purpose:

To determine how oil affects the settlement, foraging, and predator avoidance of blue crabs.

Data Parameters and Units:

Worksheet "Crab Abundance": Site: User-defined identifier assigned to field sites; Latitude (decimal degrees): Latitude of the field site; Longitude (decimal degrees): Longitude of the field site; Collection Date: Date of data collection (MM/DD/YYYY); Year: Year of data collection (YYYY); Replicate: sampling replicate at each site (1, 2, 3); Site Classification : User-defined classification of the site at the beginning of the project, in regards to possible Macondo oil exposure (unoiled or oiled); Salinity (ppt): water quality variable; Water Temperature (deg C): water quality variable; Dissolved Oxygen (mg l-1): water quality variable; Chlorophyll a (µg l-1): water quality variable; Juvenile Crabs: Total number of juvenile blue crabs collected. Worksheet "Pred. Avoidance-residual oil": Site: User-defined identifier assigned to field sites; Latitude (decimal degrees): Latitude of the field site; Longitude (decimal degrees): Longitude of the field site Collection; Date: Date crabs were retrieved from the field after 24 hours (MM/DD/YYYY); Replicate: sampling replicate at each site (1, 2); Site Classification: User-defined classification of the site at the beginning of the project, in regards to possible Macondo oil exposure (unoiled or oiled); Total Preyed Upon: Indicates the number of crabs gone after 24 hours in the field. Total number cannot exceed 6 (the number of crabs tethered at each replicate at the beginning of the experiment); Carapace: Indicates the number of crab carapaces after 24 hours. Carapace is a subset of the Total Preyed Upon and is an indicator of the type of predator. If a carapace is available, then it was more likely preyed upon by a crab rather than a fish that removes the entire crab. Worksheet "Pred. Avoidance-laboratory oil": Collection Date: Date crabs were retrieved from the field after 24 hours (MM/DD/YYYY); LUMCON Site: User-defined identifier assigned to the experimental sites established around LUMCON; Crab Treatment: Indicates exposure treatment of crabs (control=crabs not exposed to oil, exposed=crabs exposed to oil); Total Preyed Upon: Indicates the number of crabs gone after 24 hours in the field. Total number cannot exceed 3 (the total number of crabs exposed to each treatment at each site). Worksheet "Crab Foraging Time": Collection Date: Date of data collection (MM/DD/YYYY); Concentration (%): WAF concentration exposure for an individual crab; Exposure Duration (hr): Duration of WAF exposure; 48 or 96 hr. Crabs were exposed to WAFs for 48 hours, tested, returned to clean salt water for 48 hours, then re-tested indicated by 96 hrs; Foraging Time (s): Indicates the amount of time in seconds it took an individual crab to successfully locate and eat prey. Worksheet "Crab Foraging Success": Collection Date: Date of data collection (MM/DD/YYYY); Concentration (%): WAF concentration exposure for an individual crab; Exposure Duration (hr): Duration of WAF exposure; 48 or 96 hr. Crabs were exposed to WAFs for 48 hours, tested, returned to clean salt water for 48 hours, then re-tested indicated by 96 hrs; Success: Indicates if a crab successfully foraged for food; (1) = success, (0) = not successful.

Methods:

Crabs for the two field predation avoidance tethering experiments and the laboratory foraging time and success experiment were collected in the marshes around LUMCON (Latitude 29.254, Longitude -90.664). Crab Abundance Juvenile crabs were collected at six sampling sites (three oiled/unoiled pairs) in Terrebonne Bay, LA, using baited minnow traps that were recovered every 24 hours to collect the crabs and rebait. All sites were visited on the same day for all four trips in 2015, except for TB1 on 8/25/15. All sites were visited on the same day for all six trips in 2016, except for TB1 & TB2 on 7/8/16 and 8/26/16. Sites were not accessible on these days due to low tide or weather conditions. Predation Avoidance – Terrebonne marsh (crabs exposed to residual field oiling) Crabs were collected in the marshes around LUMCON and transported to the six sites (three oiled/unoiled pairs) in Terrebonne Bay, LA. Twelve crabs were tethered to two PVC poles placed at least 10 m apart at each site. Crabs were recovered after 24 hours to record predation. Carapace data was also collected (as an indicator of predator type; if a carapace was available, then it was more likely preyed upon by a crab rather than a fish that removes the entire crab). These tethering experiments were conducted six times in 2016. Predation Avoidance – LUMCON marsh (crabs exposed in a laboratory to oil) Crabs were collected in the marshes around LUMCON and exposed to either a control solution (clean seawater) or a WAF (25%) solution for 48 hours. Crabs were then tethered at six to ten sites (depending upon captured crab availability) along the marsh edge near LUMCON (Lat/Longs for each site were not recorded). Three control crabs and three oil-exposed crabs were tethered at each site. Crabs were recovered after 24 hours to document predation. These tethering experiments were conducted two times in 2015 and two times in 2016. Crab Foraging Time and Foraging Success Water accommodated fractions (WAFs) were prepared using Singer er al. (2000). To make WAF, oil was added at 3.45 g L‌-1. WAFs were diluted into six concentrations; 0% (control, no oil), 6.25%, 12.5%, 25%. 50%, and 100% WAF. Crabs were exposed to these concentrations for 48 hours, after which crab foraging ability was tested using a closed, re-circulatory flume (2 m x 1 m x 0.5 m), with foraging time recorded in seconds (s). After the trial, crabs were exposed to clean salt water for another 48 hours before undergoing another foraging trial. The recovery trials are referred to as 96 hour trials. Foraging success was recorded using (0) and (1) data: 1=foraging success, 0=failure. If the crab foraged successfully, there was a foraging time to coincide with it. Foraging time is not available for crabs that unsuccessfully foraged because they did not find prey items. Note that the 100% WAF concentration was not used in the crab foraging time portion of the experiment (only the foraging success experiment) due to very low success rates in trials. Foraging time is dependent upon foraging success. Up to four crabs were exposed to a treatment at a time. If the crab was successful in foraging, then the foraging time was recorded. There can be up to four replicates per collection date.

Instruments:

A YSI 6820 sonde was used to obtain water quality data (O‌2, salinity, and temperature data chlorophyll a).

Provenance and Historical References:

Singer, M. ., Aurand, D., Bragin, G. ., Clark, J. ., Coelho, G. ., Sowby, M. ., & Tjeerdema, R. . (2000). Standardization of the Preparation and Quantitation of Water-accommodated Fractions of Petroleum for Toxicity Testing. Marine Pollution Bulletin, 40(11), 1007–1016. doi:10.1016/s0025-326x(00)00045-x

Individual Files: