Are vent crab behavioral preferences adaptations for habitat choice?

Area of Science:

• Marine Biology
• Chemical Ecology
• Behavioral Ecology

Background:

• Hydrothermal vent (HV) organisms inhabit extreme, patchy environments and possess specialized adaptations for survival.
• Understanding habitat selection mechanisms in HV crustaceans, like brachyurans, is crucial due to limited knowledge on their recruitment.
• The endemic HV crab Xenograpsus testudinatus dominates the Turtle Island vent fauna, making it an ideal model for studying habitat choice.

Purpose of the Study:

• To investigate the behavioral responses of Xenograpsus testudinatus to various vent-associated and non-vent cues in a laboratory setting.
• To identify specific chemical and physical cues that influence the habitat selection of HV crabs.
• To determine the relative importance of different cues and their combinations in attracting HV crabs.

Main Methods:

• A two-choice experimental chamber was used to present individual HV crabs with vent-specific cues (sulfuric sediment, air-bubbling, elevated temperature, dead zooplankton, other crabs, shade) and non-vent cues (quartz sediment, dead fish, light).
• Crab behavior was monitored by recording initial and final choices, and resident time in each compartment.
• Cues were tested individually and in combination against a control (no cue) to assess their attractiveness.

Main Results:

• Sulfuric sediments and dead fish attracted females, while other crabs attracted males. Crabs generally avoided light but were attracted to air-bubbling, sulfuric sediment, elevated temperature, dead fish, dead zooplankton, and quartz sediments.
• A combination of sulfuric sediment, elevated temperature, and air-bubbling elicited the strongest attractive response across all measured variables.
• First choice and resident time were consistent indicators of preference, unlike final choice, suggesting 'resident time' is a reliable measure of habitat selection.

Conclusions:

• Multiple vent-associated cues act as significant attractors for HV crabs, influencing their habitat selection behavior.
• The findings provide the first evidence of specific attractants for HV crabs, contributing to the understanding of vent ecosystem dynamics.
• Observed larval distribution patterns near the seafloor in the field support the laboratory findings on habitat selection cues.