MEPS 293:143-153 (2005)  -  doi:10.3354/meps293143

Morphodynamics and habitat safety in sandy beaches: life-history adaptations in a supralittoral amphipod

Omar Defeo1,2,*, Julio Gómez2

1CINVESTAV IPN Unidad Mérida, AP 73 Cordemex, 97310 Mérida, Yucatán, Mexico
2UNDECIMAR, Facultad de Ciencias, Iguá 4225, PO Box 10773, Montevideo 11400, Uruguay
*-Authors are in alphabetical order. Email:

ABSTRACT: Understanding the relationships between beach morphodynamics and descriptors of macrofauna assemblages has been a major step in theoretical development in sandy beach ecology. However, the role of morphodynamics in shaping life-history traits is still uncertain. Here, we test the predictions of the habitat harshness hypothesis (HHH) on the life-history traits of the sandhopper Atlantorchestoidea brasiliensis, based on information compiled from 7 Uruguayan sandy beaches spanning a continuum from reflective to dissipative states, over a period of almost 2 yr. A. brasiliensis showed clear population responses to physical variables in a trend opposite to that predicted by the HHH, including an increase in abundance (total, ovigerous females and juveniles) and individual sizes from dissipative to reflective beaches. A generalized additive model explained 46.1% of the deviance in sandhopper abundance and retained all 4 physical descriptors in the model as significant. Sandhopper abundance increased with grain size and beach face slope, and decreased with low values of water content and compaction of the sand. Per capita rate of recruitment increased linearly with adult abundance, i.e. there was a positive density-dependent effect of adults on recruitment rates, which exponentially decreased from reflective to dissipative beaches. Only the proportion of ovigerous females increased towards the dissipative domain. We conclude that the HHH did not accurately predict spatio-temporal fluctuations in population features of A. brasiliensis, particularly because of a limited appreciation of the role played by life-history strategies in explaining population responses to the environment. Our results have important implications for sandy beach macrofauna, particularly supralittoral organisms, and suggest a novel hypothesis (termed here the ‘hypothesis of habitat safety’), which states that the combination of narrow swashes and steep slopes makes reflective beaches a more stable and safer environment for supralittoral species.

KEY WORDS: Sandhopper · Atlantorchestoidea brasiliensis · Life history · Sandy beaches · Morphodynamics · Habitat safety

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