The Use of Chemical Cues by Sargassum Shrimps Latreutes fucorum and Leander tenuicornis in Establishing and Maintaining a Symbiosis with the Host Sargassum Algae

Jaime L Frahm,William Randy Brooks

doi:10.3390/d13070305

Abstract

A mutualistic symbiosis exists between the alga Sargassum spp. and two shrimp species, Latreutes fucorum and Leander tenuicornis. However, little is known about how these shrimp locate and establish their host alga. Both visual and chemical cues are potentially available. A previous study has looked at both cue variables with results that are mixed. Specifically, these same shrimp species used chemical cues only when visible cues were available simultaneously. Visual cues would be presumably restricted at night, but chemical cues are potentially available continuously. This current research elaborates on the previous study to fully understand Sargassum shrimp chemoreception. Increases in sample sizes and both a 4-chambered and Y-maze apparatus were used to test whether the shrimp could detect Sargassum cues, dimethylsulfoniopropionate (DMSP) (a chemical excreted by some marine algae), and conspecific cues. Neither shrimp species showed a strong directional response to any of the chemical cues, but the Sargassum and DMSP cues did cause more shrimp to exhibit searching behavior. Additionally, several differences in responses between male and female shrimp were found for each cue. A lowered dilution of DMSP was also tested to determine sensitivity of L. fucorum shrimp to the chemical cue; although searching behavior was triggered, conclusions about quantifying the sensitivity could not be made. Overall, these results show the shrimp can detect chemical cues—in the absence of visual cues—that could affect initiating and maintaining this shrimp/algal symbiosis.

Highlights

Pelagic, floating mats of primarily Sargassum fluitans and Sargassum natans algae are found in both tropical and temperate waters of the Atlantic Ocean [1,2]
This increase in movement did not show more shrimp moving into the radial chamber with the Sargassum chemical source but rather more shrimp moved into all of the four radial chambers in the presence of Sargassum compared to the other treatments. This result suggests L. fucorum increased its general searching behavior but was not precise in locating the directional aspects of the chemical cue source. This slight difference between the past study and the current study, both of which used the same shrimp species, apparatus, and chemical cue type, could be related to improvements made on the preparation of the chemical cue in this study
Results of these trials for Latreutes fucorum and Leander tenuicornis were compelling in that they showed a clear ability of both shrimp species to detect and respond to chemical cues associated with Sargassum and conspecifics Such a strong response with the Y-maze compared to outcomes with the 4-chambered apparatus are likely related to notable differences between the experimental procedures used with these two different types of apparatus

Summary

Introduction

Pelagic, floating mats of primarily Sargassum fluitans and Sargassum natans algae are found in both tropical and temperate waters of the Atlantic Ocean [1,2]. These species are characterized with highly branched thalli and small air bladders (pneumatocysts) that keep the algae afloat [1]. S. natans differs from S. fluitans with thinner blades and a spine located on the pneumatocysts [3] (see Figure A1 in Appendix A) These floating mats range greatly in size from small patches less than 0.5 m in horizontal diameter up to huge mats 50 m in diameter [1,4]. Sargassum can be found in the Sargasso Sea in high quantities [1,6]

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Conclusion