Preprint volume - SIBM

Pre-print Volume - Oral presentations
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
N. RAUH 1,2 , C. BROWNLEE 2 , S.J. HAWKINS 3 , A.M. HETHERINGTON 2
1 The Marine Biological Association, The Laboratory, Citadel Hill, Plymouth, PL1 2PB, U.K.
niauha@mba.ac.uk
2 Universtiy of Bristol, United Kingdom.
3 University of Bangor, Wales.
HYPO-OSMOTIC STRESS TOLERANCE AMONG THREE INTERTIDAL
FUCUS SPECIES: EFFECTS ON SURVIVAL, RECRUITMENT AND
COMMUNITY COMPOSITION
TOLLERANZA ALLO STRESS IPOOSMOTICO IN TRE SPECIE INTERTIDALI
DI FUCUS: EFFETI SU SOPRAVIVENZA, RECLUTAMENTO E
COMPOSIZIONE DELLA COMUNITÀ
Abstract – These studies aimed to test the extent to which the distribution of fucoid algae is determined by
recruitment and survival of early developmental stages (zygotes and embryos); in particular the influence
of abiotic (osmotic) stress at early development stages on subsequent growth and survival. Comparative
physiological experiments have been carried out on three dominant fucoid species native to the UK. A
further investigation into the acute responses to hypo-osmotic treatment, has shown that embryos are
susceptible to osmotic stress caused both by exposure to rainfall at low tide and re-immersion into seawater
following periods of desiccation. This work has also shown that zygotes and embryos of the three most
common fucoid species (Fucus spiralis, F. vesiculosus and F. serratus) display dramatically different
physiological strategies for tolerating osmotic stress.
Key-words: Ecological zonation, osmotic pressure, seaweed embryo.
Introduction - Temperate rocky shore habitats comprise complex interacting physical
gradients and show temporal fluctuations in a number of environmental variables
(Stephenson & Stephenson, 1949; Lewis, 1964). The varying levels of stress associated
with these gradients and fluctuations contribute to the competitive interactions between
organisms in this habitat (Baker, 1909, 1910; Davison & Pearson, 1996). On the other
hand, physical heterogeneity creates numerous potential ecological niches that may
underlie both high biodiversity and biomass (Helmuth & Hofmann, 2001). Hypoosmotic
stress is likely to be encountered with every tidal cycle, either through
sporadic events of rainfall or re-immersion into seawater following periods of
desiccation. The resistance to physical stress of fucoid algae has previously been
demonstrated through adaptive mechanisms within established adult populations
(Chapman, 1995; Davison & Pearson, 1996). However, this has not been fully
examined in early developmental stages, such as zygotes and embryos that are
potentially exposed to the same physical factors as adults and are likely to be more
vulnerable to stresses. Higher shore levels experience exposure to emersion,
specifically osmotic, stresses more frequently and for longer periods of time than lower
shore levels (Stephenson & Stephenson, 1949). We have demonstrated that zygotes and
embryos of Fucus species from higher shore levels display very different physiological
strategies for tolerating osmotic stress than neighbouring species lower down the shore
gradient. We have developed new approaches to monitor fucoid propagule supply and
recruitment in situ. Field studies reveal that physiological tolerance mechanisms
identified from laboratory experiments have real ecological relevance in terms of
survival, recruitment, and community.
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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