In intertidal poikilotherms with wide geographic distribution, physiological variations are ubiquitous, due to phenotypic plasticity and/or individual geographic variation. Using the grapsid crab, Cyclograpsus cinereus as a study model, acclimatization differences in respiratory physiology were evaluated among populations along the Chilean coast, covering a latitudinal gradient of about 2000 km. This species inhabits the supratidal zones and, therefore, is subject to constant immersion and emersion periods, producing physiological acidification due to CO2 retention, mainly in the branchial cavity. Individuals of six populations were collected along the coastline of Chile and were exposed to air for different time periods in the laboratory. The following parameters were measured: pH, Ca2+, Cl− and haemolymphatic lactate dehydrogenase (LDH) enzyme activity. Populations from lower latitudes were significantly different from those from central and southern Chile, with a higher haemolymphatic pH variation and higher Ca2+ level, along with lower levels of Cl− and LDH enzyme activity. This indicates that the populations from lower latitudes, which are subject to higher air temperatures during emersion, have a higher homeostatic capacity during emersion periods than those of intermediate and higher latitudes. This response seems to be determined by genetic bases due to adaptation to the local environment.

The common starfish, Asterias rubens, occurs in fluctuating environments in the North Atlantic. To better understand energy allocation dynamics, we recorded gonad, body wall, and pyloric caeca (storage organ) indices between 2000 and 2004 from three different habitats. We applied a Fourier transform to the data to evaluate and compare the seasonal variation in these indices. Specific effects of emersion and salinity variation were examined in two laboratory studies. Differences in energy allocation were found between sites and temporally within sites. Food availability appeared to be the most important factor controlling allocation dynamics while fluctuating salinity and/or emersion had a significant but smaller impact. Only severe food shortage reduced reproductive investment indicating a preferential energy allocation to gonads. This study is the first to encompass a broad range of populations over several reproduction cycles and emphasizes the ability of A. rubens to adapt to a fluctuating environment.

The dynamics of intertidal populations of the starfish Asterias rubens, living in contrasted habitats and over a broad geographical range, were studied from March 2000 to November 2002 using modal analysis. As only 1 juvenile (first year after recruitment) and 1 adult (subsequent years) modes could be distinguished; only juvenile growth was quantified. Concomitantly, experiments were carried out to test several factors assumed to influence juvenile growth: food quantity and quality, emersion, salinity variations and temperature. Three different juvenile growth patterns were evidenced: (1) a fast and protracted growth linked to high food availability and lack of disturbance; (2) a winter cessation of growth likely due to a seasonal increase of emersion-related stress and salinity variations; and (3) disrupted juvenile dynamics, which was encountered in 2 populations. In the first one, estuarine salinity conditions limited growth and, combined with food depletion, led to the extinction of the population. In the second one, wave action confined most of the population to a restricted area with low food levels. In the third scenario, intraspecific competition for food was probably at the source of an unusual growth pattern in which most juveniles did not grow while a small proportion achieved a medium growth rate.

The effects on photosynthesis of CO2 and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO2 on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO2 level (about 350 ml m−3), and doubling the CO2 concentration (700 ml m−3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700 ml m−3 CO2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO2 concentration during emersion.

Inorganic carbon acquisition under emerged conditions was studied in the red macroalga Bostrychia scorpioides by investigating the effects of changes in the pH of the water film surrounding the thalli when emerged and of inhibitors of carbonic anhydrase (CA; EC 4.2.1.1). The CO2 uptake rate increased by approximately 150% when the pH of the water film was changed from 8·1 to 10·5. Acetazolamide (AZ), an inhibitor of the external CA, inhibited CO2 uptake by 50% at pH values higher than 8·7. The effect of ethoxyzolamide (EZ), an inhibitor of both external and internal CA, was more pronounced than that of AZ, inhibiting the CO2 uptake rates by 80% at all the pH values assayed. At pH 10·5, CO2 flux into the cells exceeded by several orders of magnitude the flux supported by the spontaneous dehydration of HCO3− to CO2 in the water film. From these results it was concluded that the main source of inorganic carbon was atmospheric CO2. The driving force for the flux of atmospheric CO2 into the cell must be the CO2 concentration gradient. Therefore, low internal CO2 concentration might be necessary to account for the CO2 fluxes measured. The function of the internal CA could be to speed up the transformation of CO2 into HCO3− inside the cell. The function of the external CA could not be fully described from the experiments although it was demonstrated that the external enzyme enhanced the CO2 flux from air to cell surface.

Littorella uniflora (L.) Ascherson is a small, perennial, amphibious rhizophyte of rosette life-form which is common along the margins of lakes, tarns and reservoirs where water-level fluctuations are often rapid and unpredictable. The majority of plants are continuously submersed and reproduce vegetatively, but a small proportion become completely emersed for variable lengths of time, when flowering and seed set occur. To find out how L. uniflora adjusts to sudden emersion we studied the plants at a reservoir where water level falls each spring and remains low throughout the summer; L. uniflora adjusted very quickly showing a degree of phenotypic plasticity not expected in a ‘stress tolerator’, including the production of a new set of terrestrial leaves with reduced lacunal volume and increased stomatal density, a rapid increase in leaf growth rate, and flowering within 3–4 wk. Comparison of terrestrial L. uniflora with aquatic plants growing permanently submersed in lake and tarn habitats showed that three to fourfold more carbon (C) and nitrogen (N) was incorporated into above-ground biomass by emersed plants. However, ramet production in the aquatic environment appeared to be more costly, in terms of C and N invested, than terrestrial flower and seed production. The combination of continuous, submersed vegetative spread with the capacity for a high degree of phenotypic plasticity allowing some flower and seed production to occur during brief periods of emersion seems to account for the success of this plant in the amphibious niche.