Thermal reaction norms and the scale of temperature variation: latitudinal vulnerability of intertidal Nacellid limpets to climate change

The thermal reaction norms of 4 closely related intertidal Nacellid limpets, Antarctic (Nacella concinna), New Zealand (Cellana ornata), Australia (C. tramoserica) and Singapore (C. radiata), were compared across environments with different temperature magnitude, variability and predictability, to test their relative vulnerability to different scales of climate warming. Lethal limits were measured alongside a newly developed metric of “duration tenacity”, which was tested at different temperatures to calculate the thermal reaction norm of limpet adductor muscle fatigue. Except in C. tramoserica which had a wide optimum range with two break points, duration tenacity did not follow a typical aerobic capacity curve but was best described by a single break point at an optimum temperature. Thermal reaction norms were shifted to warmer temperatures in warmer environments; the optimum temperature for tenacity (Topt) increased from 1.0°C (N. concinna) to 14.3°C (C. ornata) to 18.0°C (an average for the optimum range of C. tramoserica) to 27.6°C (C. radiata). The temperature limits for duration tenacity of the 4 species were most consistently correlated with both maximum sea surface temperature and summer maximum in situ habitat logger temperature. Tropical C. radiata, which lives in the least variable and most predictable environment, generally had the lowest warming tolerance and thermal safety margin (WT and TSM; respectively the thermal buffer of CTmax and Topt over habitat temperature). However, the two temperate species, C. ornata and C. tramoserica, which live in a variable and seasonally unpredictable microhabitat, had the lowest TSM relative to in situ logger temperature. N. concinna which lives in the most variable, but seasonally predictable microhabitat, generally had the highest TSMs. Intertidal animals live at the highly variable interface between terrestrial and marine biomes and even small changes in the magnitude and predictability of their environment could markedly influence their future distributions

Antarctic Cartography: The mapping of the Terra Australis Incognita , 1531-2007

‘It hath euer offended mee to looke vpon the Geographicall mapps and find this Terra Australis, nondum incognita. The vnknown Southerne Continent. What good spirit but would greeue at this? If they know it for a Continent, and for a Southerne Continent, why then do they call it vnknowne? But if it bee vnknowne; why doe all the Geographers describe it after one forme and site?’ -Joseph Hall, 1605. (Quoted by Richardson 1993: 67 – 68). ‘A team of researchers have unveiled a newly completed map of Antarctica that is expected to revolutionise research of the continent's frozen landscape. The map is a realistic, nearly cloudless satellite view of the continent at a resolution 10 times greater than ever before with images captured by the NASA-built Landsat 7 satellite. The mosaic offers the most geographically accurate, true-colour, high-resolution views of Antarctica possible.’ -NASA ScienceDaily excerpt, 2007. The above quotes give an insight into the exciting and complicated history of Antarctic cartography. They represent a paradigm shift from an unexplored ‘Terra Australis Incognita’ whose existence was portrayed in detailed but inaccurate topographic maps, to the representation of the Antarctic continent in the modern era using high-resolution, highly accurate satellite technology. The following article comprehensively reviews the evolution of Antarctic cartography and gives an insight into the processes and problems associated with mapping of the polar regions

The Iron Wedge and a Climate on the Edge: The potential for artificial iron fertilisation of the Southern Ocean as a viable carbon dioxide mitigation strategy

Although it still remains a misunderstood concept amongst the majority of the world’s population, ‘climate change’ is a term which sticks in the minds of people from all walks of life. Scientists have proven that CO2 levels in the atmosphere are increasing due to anthropogenic activity, although it remains uncertain just how much of an effect this increase may have in the future, due to the lag time associated with the increase and the consequent response.   Countless mitigation schemes have been put forward that could be used either to cut down the amounts of CO2 entering the atmosphere, or alternatively remove significant amounts of CO2 using the worlds natural carbon sinks. Terrestrial ecosystems are thought to be the largest sink, fixing 1 – 2 tonnes of carbon per km2 annually through photosynthesis (Myers and Kent 2005). In the past, it has been assumed that oceans have a minor role to play in the carbon cycle, contributing only to small carbon fluxes. It has since been proven that the ocean has the potential to hold up to sixty times more inorganic carbon than the atmosphere (Bathmann et al. 2000). The ocean’s role in the carbon cycle is illustrated below

The temperature limits for tenacity and upper lethal limits correlated with environmental temperatures of the four subtidal limpet species.

<p>Pearson’s correlation co-efficient (R²) and significance (p). Significant correlations in bold.</p

Temperature limits for survival (functional mortality) of A) Antarctic (intertidal <i>N. concinna</i>; upper limit from Morley et al, 2009) B) New Zealand (<i>C. ornata</i>), C) Melbourne (<i>C. tramoserica</i>) and D) Singapore (<i>C. radiata</i>) Nacellid limpets (Mean ±95%CI).

<p>Temperature limits for survival (functional mortality) of A) Antarctic (intertidal <i>N. concinna</i>; upper limit from Morley et al, 2009) B) New Zealand (<i>C. ornata</i>), C) Melbourne (<i>C. tramoserica</i>) and D) Singapore (<i>C. radiata</i>) Nacellid limpets (Mean ±95%CI).</p

Thermal reaction norm of duration tenacity in Nacellid limpets.

<p>Fitted curves are shown. A) Antarctic (<i>N. concinna</i>), B) New Zealand (<i>C. ornata</i>), C) Melbourne (<i>C. tramoserica</i>) and D) Singapore (<i>C. radiata</i>). (Mean ±95%CI). Linear regressions are shown with break points calculated using the R-package strucchange (Zeileis et al., 2002).</p