Pretterebner K et al. (2012), Hermit crabs and their symbionts: Reactions to ...

ECB-ART-42315

J Exp Mar Biol Ecol 2012 Jan 10;4115:23-33. doi: 10.1016/j.jembe.2011.10.027.

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Hermit crabs and their symbionts: Reactions to artificially induced anoxia on a sublittoral sediment bottom.

Pretterebner K , Riedel B , Zuschin M , Stachowitsch M .

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Hermit crabs play an important role in the Northern Adriatic Sea due to their abundance, wide range of symbionts, and function in structuring the benthic community. Small-scale (0.25 m(2)) hypoxia and anoxia were experimentally generated on a sublittoral soft bottom in 24 m depth in the Gulf of Trieste. This approach successfully simulates the seasonal low dissolved oxygen (DO) events here and enabled studying the behaviour and mortality of the hermit crab Paguristes eremita. The crabs exhibited a sequence of predictable stress responses and ultimately mortality, which was correlated with five oxygen thresholds. Among the crustaceans, which are a sensitive group to oxygen depletion, P. eremita is relatively tolerant. Initially, at mild hypoxia (2.0 to 1.0 ml l(- 1) DO), hermit crabs showed avoidance by moving onto better oxygenated, elevated substrata. This was accompanied by a series of responses including decreased locomotory activity, increased body movements and extension from the shell. During a moribund phase at severe hypoxia (0.5 to 0.01 ml l(- 1) DO), crabs were mostly immobile in overturned shells and body movements decreased. Anoxia triggered emergence from the shell, with a brief locomotion spurt of shell-less crabs. The activity pattern of normally day-active crabs was altered during hypoxia and anoxia. Atypical interspecific interactions occurred: the crab Pisidia longimana increasingly aggregated on hermit crab shells, and a hermit crab used the emerged infaunal sea urchin Schizaster canaliferus as an elevated substrate. Response patterns varied somewhat according to shell size or symbiont type (the sponge Suberites domuncula). Mortality occurred after extended anoxia (~ 1.5 d) and increased hydrogen sulphide levels (H(2)S ~ 128 μmol). The relative tolerance of crabs and certain symbionts (e.g. the sea anemone Calliactis parasitica) - as potential survivors and recolonizers of affected areas - may influence and promote community recovery after oxygen crises.

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Species referenced: Echinodermata
Genes referenced: LOC100887844 LOC105441782 LOC576114

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	Supplementary Fig. 1. Fig. 1. (A) Extension and (B) emergence from shell (average number of the selected behaviour per hour) during deployment 11. n = 3 crabs in open, n = 4 in closed configuration. White and black bars: day and night. White and black arrowheads: death (50 % and 100 % of individuals).
	Supplementary Fig. 2. Fig. 2. (A) Paguristes eremita (pa) in Aporrhais pespelecani shell on top of ascidian Phallusia mammilata (ph) at 13.6 h after anoxia (H2S 18.3 µmol l–1). The holothurian Ocnus planci (op) on left. (B) P. eremita (pa) extending from an overturned Murex brandaris shell (mu) at 16.1 h after anoxia (H2S 36.7 µmol l–1). Note extended sea anemone (Cereus pedunculatus, ce) at top. (C) Atypical interactions: shell-less hermit crab P. eremita (pa) on top of emerged infaunal sea urchin Schizaster canaliferus (sc) at 35 h after anoxia (H2S 243.2 µmol l–1). Note abandoned, overturned M. brandaris (mu) shell on the sediment. Bent-over C. pedunculatus partially extended from tube on right. (D) Dead P. eremita (pa) (curved abdomen visible on bottom) next to its abandoned shell (overturned A. pes-pelecani (ap) at top left). Note typical serpulid-encrusted aperture.
	Fig. 1. Presence of hermit crabs on multi-species clumps (mean percentage) related to five oxygen thresholds: (A) all individuals, (B–D) specific responses. n: number of evaluated crabs in closed configuration. Numbers in parentheses under oxygen thresholds indicate total photographs evaluated in each oxygen category.
	Fig. 2. Reactions of all hermit crab individuals (mean percentage) related to five oxygen thresholds: (A–D) selected behaviours. Normoxia n = 51; hypoxia/anoxia n = 25. Numbers in parentheses under oxygen thresholds indicate total photographs evaluated in each oxygen category (valid for A–D). Note different scales.
	Fig. 3. Average number of locomotions per hour during deployment 11. n = 3 crabs in open, n = 4 in closed configuration. White and black bars: day and night. White and black arrowheads: emergence from shell and death, respectively (50% of individuals).
	Fig. 4. Average number of interactions per hour during deployment 11. n = 3 crabs in open, n = 4 in closed configuration. White and black bars: day and night. White and black arrowheads: emergence from shell and death (50% of individuals). P1–3: interaction peaks.
	Fig. 5. Sequence of behavioural responses to oxygen thresholds, anoxia duration and H2S development: (A) normal body posture, (B) crab extended from upright shell, (C) crab extended from overturned shell, (D) crab outside shell, and (E) mortality. Hours in pictograms are mean values from onset of anoxia.

References [+] :

CÔtÉ, Less choosy or different preference? Impact of hypoxia on hermit crab shell assessment and selection. 1998, Pubmed