The Spotted Shrimp and its fascinating symbiotic interactions with sea anemones and reef fishes.

Spotted Shrimp on a Sea Anemone by Nuno Simões
July 31, 2023
Marine Science
Reef Aquariums

Periclimenes yucatanicus, commonly known as the Spotted shrimp, is one of the fascinating species of marine invertebrates that inhabit the waters of the Caribbean Sea and the Gulf of Mexico in the Western Atlantic. This small crustacean, measuring only about 3 cm in length, belongs to the select group of reef shrimps known for their role as cleaners of fishes that inhabit coral reefs. Cleaner shrimps, along with certain small cleaner fishes, play a fundamental role in the biological stability of small ecosystems as they are responsible for controlling and eliminating ectoparasites that infect the gills, mouths, and other external parts of many fishes, protecting them from diseases, reducing stress, and their mere presence affects the fishes habitat choice and, therefore, the biodiversity of the entire community. However, the activity of these species as cleaners is only possible thanks to their ability to establish close symbiotic relationships with sea anemones, animals belonging to the group of cnidarians closely related to corals and jellyfishes.

Whether due to their special biological and ecological capabilities or their beautiful color patterns, the Spotted Shrimp has attracted great attention and interest from both scientists and aquarium enthusiasts. Here we will explore some of the most interesting aspects of this inter-specific system of interactions between the Spotted Shrimp, sea anemones, and reef fishes.

Table Of Content

Symbiotic Relationships Between Spotted Shrimp And Sea Anemones

The Spotted Shrimp inhabits waters associated with coral reefs and is commonly found at depths ranging from 1 to 30 m. Its distribution in the Caribbean Sea extends from South Florida to Venezuela, while in the Gulf of Mexico, it has been recorded in reefs of the Campeche Bank and around the Yucatán Peninsula.

In coral reefs, the Spotted Shrimp has been observed living in association with various species of sea anemones, including Corkscrew Anemone (Bartholomea annulata), Giant anemone (Condylactis gigantea), Pale anemone (Exaiptasia diaphana), Branching anemone (Lebrunia neglecta), and Atlantic Carpet anemone (Stichodactyla helianthus). It has also been observed coexisting with the coralimorpharians Rhodactis osculifera and Ricordea florida, the Upside-down jellyfish (Cassiopea xamachana) and even with the Great Star coral (Montastraea cavernosa). However, it appears to have a certain preference for Atlantic Carpet Anemone and Giant Anemone. The association of Periclimenes yucatanicus with anemones is presumably a mutualistic symbiotic relationship, which means that both species benefit from it.

A Spotted Shrimp on a sea anemone by Ricardo González-Muñoz

On one hand, the shrimp benefits from the protection provided by the anemone against predators, thanks to the toxic substances produced by the anemones. Sea anemones, like all cnidarians, have thousands of cells that produce stinging organelles called nematocysts, which are microcapsules with tiny filamentous spines containing venom. Sea anemones use these nematocysts to capture prey and defend themselves against predators. It would be logical to think that these nematocysts could harm and even kill the shrimp. However, the shrimp is not affected by the nematocysts because it acquires immunity through a process known as acclimation. In this process, the shrimps gradually approach to interact with the anemones' tentacles. Initially, they may get stung by the nematocysts, but as the acclimation process progresses, they learn to avoid the capture response by moving away from the tentacles or migrating towards their base, where the capture response is less pronounced. The shrimps explore the tentacles, peck at the areas where the anemones secrete mucus, and apparently, this mucus also adheres to their appendages. Additionally, they seem to ingest the mucus. This mucus seems to consist of a mixture of secretions and discharged nematocysts. Over time, the tentacle capture behavior diminishes, and the shrimps can move more freely around the anemone. The observed acclimation process in some species lasts between 2 to 5 hours. It has been observed that the shrimps' level of protection can be lost if they are separated from their anemones for extended periods, demonstrating that their protection is closely related to their constant interaction with the anemone. Other benefits attributed to the shrimp include camouflage, stability, and the potential expansion of the distribution range, as the distribution patterns of the shrimps depend on those of the sea anemones. If the range of anemones expands, there is a chance for shrimp distribution to expand as well.

On the other hand, the anemones benefit from the removal of parasites and dead tissue by the shrimp. In addition, many species of anemones habitants of coral reef also have photosynthetic unicellular endosymbionts called zooxanthellae, which provide the anemones with oxygen and an alternative source of energy. Since the shrimp excrete nitrogenous waste in the form of ammonia, it has been proposed that this additional nitrogen input may benefit the growth and development of the zooxanthellae living within the anemone and, in turn, benefit the anemone with increased energy. Thus, the small nitrogen contributions from the shrimp could be very important, as coral reefs are oligotrophic environments with very low levels of nutrients, such as inorganic nitrogen, which may be present in limited quantities.

Interaction of Spotted Shrimp As a Cleaner Species Of Fishes

Although the Spotted shrimp was reported as a cleaner species almost from its first records, its activity as an actual cleaner species remained in doubt for a long time. While the shrimp was reported almost exclusively among the tentacles of symbiotic anemones, it had not been observed engaging in cleaning behavior with any fish, unlike other cleaner shrimp species like the well-known Pederson's cleaner shrimp (Ancylomenes pedersoni), an efficient cleaner of fishes that can be found in the same reefs as P. yucatanicus and even shares almost all the same host anemone species.

Thus, although the Spotted Shrimp was classified by some as a "cleaner or possibly cleaner species", other researchers suggested that there was not enough evidence to confirm that P. yucatanicus exhibited such behavior. It was even proposed that it possibly "mimicked" the cleaning behavior of A. pedersoni to enhance its food capacity or reduce predation pressure.

Although some observations supported the idea that P. yucatanicus is indeed a cleaner species, it was not until a recently research provided compelling field observations that demonstrate that the Spotted Shrimp effectively engages in cleaning activity with representatives of at least nine families of fishes.

In its cleaning behavior, the Spotted Shrimp communicates with reef fishes. The shrimp waves its long white antennae, signaling to the client fish that it is available for cleaning. The fish, in turn, approach to within a few centimeters of the anemones and adopt reciprocal postures, accepting the cleaning. Here, the anemones also play a crucial role as the fishes use them as visual signals and reference points to locate the symbiotic shrimps. It has even been proposed that larger anemones seem to attract more client fishes than smaller anemones, probably because they are more visible to them.

The Spotted Shrimp For Aquarium Enthusiasts

The Spotted shrimp has garnered significant attention and interest from scientists and aquarium enthusiasts, thanks to its captivating shapes, color patterns, and ecological interactions. Its ability to associate and live with sea anemones makes P. yucatanicus a popular and desirable species in marine aquariums. However, it is important to note that not all species of sea anemones are suitable for establishing this relationship with cleaner shrimps. Careful research and selection of suitable species of sea anemones are necessary to maintain this symbiotic relationship in an artificial environment. Both the Spotted Shrimp and all the species of anemones with which it has symbiotic interactions in habit environments associated with coral reefs, which implies that they are accustomed to warm, clear, and shallow waters. In addition to adequately recreating the conditions of the natural environment in the aquarium to promote the establishment and maintenance of this symbiotic relationship, it is crucial to consider that cleaner shrimps need an acclimation period to adapt to the new environment and avoid potential harm.

Spotted shrimp with an anemone by Ricardo Gonzalez

It is important to highlight that the acquisition of sea anemones and cleaner shrimps should be done responsibly and ethically. Some species of sea anemones may be collected in a destructive manner from the wild, which can have a negative impact on marine ecosystems. Therefore, it is recommended to acquire these species from reliable sources that, whenever possible, cultivate them sustainably in captivity.

About the author:
Ricardo González-Muñoz

Ricardo is an enthusiastic biologist specialized in the taxonomic, biological, and ecological study of sea anemones and other marine cnidarians. He holds a PhD in Marine Biology from the National Autonomous University of Mexico and currently works as a researcher at the National Council for Scientific and Technical Research (CONICET) in the Marine and Coastal Research Institute (IIMYC-UNMDP) in Mar del Plata, Argentina.

About the Author
Ricardo González-Muñoz

Ricardo is an enthusiastic biologist specialized in the taxonomic, biological, and ecological study of sea anemones and other marine cnidarians. He holds a PhD in Marine Biology from the National Autonomous University of Mexico and currently works as a researcher at the National Council for Scientific and Technical Research (CONICET) in the Marine and Coastal Research Institute (IIMYC-UNMDP) in Mar del Plata, Argentina.

Sources:

Ricardo González-Muñoz's Research Gate profile

Instituto de Investigaciones Marinas y Costeras (IIMYC), National University of Mar de Plata, CONICET

Laboratorio de Biología de Cnidarios (LABIC), (IIMYC), National University of Mar de Plata, CONICET

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