# Ecological Interactions on Sandy Beach Ecosystems: A Global Synthesis of Mole Crabs and New Insights into Emerita brasiliensis and Emerita rathbunae (Crustacea, Decapoda, Anomura, Hippidae)

## TL;DR

This study explores how mole crabs interact with other organisms on sandy beaches, revealing new relationships that affect their behavior and survival.

## Contribution

The study provides new empirical observations on previously undocumented ecological interactions involving two species of mole crabs.

## Key findings

- Mole crabs are commonly preyed on and parasitized, with new associations of hydrozoans and parasites recorded.
- Ecological interactions influence key biological processes like burrowing, reproduction, and survival of mole crabs.
- These interactions affect species distribution and highlight the importance of protecting sandy beach ecosystems.

## Abstract

Sandy beaches are dynamic environments where many animals interact, shaping how they live, grow, and survive. Mole crabs of the genus Emerita are small crustaceans that live buried in the sand, and they take part in a surprising variety of interactions with other organisms. In this study, we gathered information from scientific publications worldwide and added new observations from beaches along the Atlantic and Pacific coasts of the Americas. We found that these crabs are commonly preyed on and parasitized, and they can also host algae and other small organisms on their bodies. Some of these interactions had never been recorded before, such as the association of certain hydrozoans and parasites with these crabs. These relationships can change how the crabs feed, move, and reproduce and may even alter where they are found along the coast. Understanding these interactions underscores the importance of mole crabs to sandy beach ecosystems and the need to protect these habitats, especially as human activities increasingly impact coastal areas.

Sandy beaches are dynamic intertidal ecosystems where ecological interactions play a critical yet often overlooked role in shaping community structure and population dynamics. This study presents a global synthesis of ecological interactions involving mole crabs of the genus Emerita (Crustacea: Decapoda: Hippidae), complemented by new field and laboratory findings. Through a literature review and targeted sampling, we documented multiple interaction types, including predation, parasitism, epibiosis, competition, and symbiosis, highlighting their ecological and potential evolutionary implications. Predation and parasitism were the most frequently reported interactions worldwide. Our new empirical observations revealed, for the first time, the association of Eucheilota (Hydrozoa) and Maritrema sp. (Digenea) with E. rathbunae, as well as annual infection patterns by Profilicollis altmani (Acanthocephala) and algal epibiosis in E. brasiliensis. These interactions influence key biological processes such as burrowing, reproduction, and survival, ultimately affecting species distribution and population structure. Overall, our findings reinforce the central role of ecological interactions in the functioning and conservation of sandy beach ecosystems, particularly under growing anthropogenic pressures.