Habitat partitioning and thermal tolerance in a tropical limpet, Cellana grata

Abstract

Populations of the tropical limpet Cellana grata Gould were studied on exposed shores around Cape d'Aguilar, Hong Kong. C. grata is a high shore species, the zonation pattern of which varies seasonally, shifting downwards in association with increasing summer temperatures. C. grata is a non-homing species and was active (foraging) whilst awash by the tide, moving up and down the shore with the flood and ebb tides, respectively. Limpets moved up to 1 m in the vertical plane over a tidal cycle. When not foraging limpets took refuge in habitats that reduced the effects of high temperature and desiccation stress. Temperature measurements of individuals and their physical environment showed that the quality of these refuges varied both spatially and temporally. Horizontal rock surfaces were hotter than vertical surfaces; limpet body temperatures and habitat temperatures in refuges (crevices, pool interfaces and east-facing vertical surfaces) were consistantly cooler than adjacent habitats by 3 to 8°C and limpet body temperatures were usually 2°C warmer than the rock they rested on. Experimental manipulations with specimens restrained 0.5 m above their normal resting height or on horizontal rock surfaces and prevented from returning to refuges caused desiccation, osmotic stress and, in many cases, death as a consequence of prolonged emersion In these sub-optimal habitats. Tndividuals on horizontal surfaces lost water more rapidly than those on vertical surfaces and showed higher mortality. C. grata does not adopt many of the behavioural adaptions to reduce heat stress shown by other gastropod species. It does, however, exhibit 'mushrooming' behaviour, lifting its shell from the rock surface, although the exact benefits of this behaviour are unclear. Summer physical extremes may strongly select for limpet activity rhythms entrained by wave splash and the selection of refuges from high temperatures and desiccation when inactive. Variation in the quality of these refuges can lead to selective mortality during very hot periods.

Topographic complexity and landscape ­temperature patterns create a dynamic habitat structure on a rocky intertidal shore

“…temperature and microclimate landscape; Jones & Boulding 1999). In contrast, the link between static habitat structure (surface topography) and body size may be associated with the suitability of habitats for growth and survival over much longer time scales (Williams & Morritt 1995, Jones & Boulding 1999. However, temperature landscape was ranked second amongst the habitat structure variables in the modelling for abundance patterns of the barnacle Tesseropora rosea, suggesting that movement between habitats was not the only explanation for the observed decoupling of habitat effects on size and abundance patterns.…”

“…This is particularly evident on intertidal shores, where sun, wave and tidal exposure create a highly dynamic environment with substantial fluctuations in conditions over time and pronounced gradients in microclimates (Helmuth 1999, Harley & Helmuth 2003. Mobile invertebrates such as gastropods can respond to environmental extremes by moving between microhabitats to ameliorate thermal and desiccation stress (Garrity 1984, Moran 1985, Williams & Morritt 1995, Jones & Boulding 1999, whereas the distribution of sessile species is driven by the longer-term processes of settlement, growth and mortality (Underwood & Fairweather 1989, Hills et al 1998.…”

Can acclimation of thermal tolerance, in adults and across generations, act as a buffer against climate change in tropical marine ectotherms?

“…Whilst intertidal organisms live in a complex environment with a mosaic of exposed and sheltered micro-habitats (Helmuth et al, 2002), they are regularly subject to a wide range of temperatures as they are alternately immersed and emersed through each tidal cycle. The tropical intertidal environment can be extremely variable, with temperatures ranging between 25 and 50°C (Williams and Morritt, 1995) requiring animals to have high acute temperature limits. This contrasts to the very stable 27 to 31°C temperature range experienced by Singapore subtidal species throughout the year (Chou and Lee, 1997).…”

Fighting for mates: the importance of individual size in mating contests in rocky shore littorinids

“…It is unclear at this stage why there is such interspecific behavioural variation in this family, but we speculate that lifetime mating opportunities may be a plausible explanation. The mating opportunities of Echinolittorina and Littoraria species in Hong Kong, for example, are heavily constrained by physical factors on these tropical shores, such as heat and desiccation stresses (see Williams and Morrittt 1995). The two Echinolittorina species in this study mate mostly during the rising tide, and when the tide is receding, there is high selection pressure for them to search for refuges and aggregate to avoid thermal and desiccation stresses (Williams 1994;Stafford et al 2008Stafford et al , 2012.…”