Effects of emersion on acid–base regulation, osmoregulation, and nitrogen physiology in the semi-terrestrial mangrove crab, Helice formosensis

Garett Joseph Patrick Allen, Min Chen Wang, Yung Che Tseng, Dirk Weihrauch*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Emersion limits water availability and impairs the gill function of water-breathing animals resulting in a reduced capacity to regulate respiratory gas exchange, acid–base balance, and nitrogenous waste excretion. Semi-terrestrial crustaceans such as Helice formosensis mitigate these physiological consequences by modifying and recycling urine and branchial water shifting some branchial workload to the antennal glands. To investigate how this process occurs, Helice formosensis were emersed for up to 160 h and their hemolymph and urinary acid–base, nitrogenous waste, free amino acids, and osmoregulatory parameters were investigated. Upon emersion, crabs experienced a respiratory acidosis that is restored by bicarbonate accumulation and ammonia reduction within the hemolymph and urine after 24 h. Prolonged emersion caused an overcompensatory metabolic alkalosis potentially limiting the crab’s ability to remain emersed. During the alkalosis, hemolymph ammonia was maintained at control levels while urinary ammonia remained reduced by 60% of control values. During emersion, ammonia may be temporarily converted to alanine as part of the Cahill cycle until re-immersion where crabs can revert alanine to ammonia for excretion coinciding with the crabs’ observed delayed ammonia excretion response. The presence of high hemolymph alanine concentrations even when immersed may indicate this cycle’s use outside of emersion or in preparation for emersion. Furthermore, H. formosensis appears to be uniquely capable of actively suppressing its rate of desiccation in absence of behavioral changes, in part by creating hyperosmotic urine that mitigates evaporative water loss.

Original languageEnglish
Pages (from-to)455-468
Number of pages14
JournalJournal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
Issue number3
Publication statusPublished - 2021 May
Externally publishedYes


  • Alanine-glucose cycle
  • Ammonia excretion
  • Bicarbonate
  • Carbon dioxide
  • Crustaceans
  • Free amino acids

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry
  • Physiology
  • Animal Science and Zoology
  • Endocrinology


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