title for whelk section of A SNAIL'S ODYSSEY
title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Physiological ecology
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  Temperature & light effects
  Topics in this section on physiological ecology include temperature & light effects, considered here, and TRAIL-FOLLOWING, GAS EXCHANGE, and HEAT-SHOCK PROTEINS considered in other sections.
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Research study 1

graph showing growth rates of embryos of whelks Nucella emarginata in Alaska and southern CaliforniaLatitudinal compensation for temperature is seen commonly in physiological and other studies of invertebrates. Whelks, Nucella spp., inhabit rocky shores of Alaska and southern California, and seasonal seawater temperatures are greater by 6-10oC in the southern habitats. Most scientists would predict that growth of embryos of Nucella emarginata would thus be faster in the warmer waters of the south, although not so fast as the temperature differences would suggest because of of such latitudinal compensatory adaptation. It is surprising, then, that growth measurements actually show the reverse, with rates about 9 times faster in Alaska than in southern California (see graph). The reason for the difference photograph of hatchling whelks Nucella ostrina courtesy Louis Gosselin, Thompson Rivers University, British Columbiais not known.  Dehnel 1955 Physiol Zool 28: 115. Photograph courtesy Louis Gosselin, Thompson Rivers University, British Columbia.

NOTE  we now know that the experiments were likely done on different species of Nucella: lima or ostrina in Alaska and emarginata in southern California.  Still, this is unlikely to have accounted for the large differences shown

Hatchlings of Nucella ostrina from Barkley Sound, British Columbia 50X

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Research study 2

graph showing oxygen uptake for whelks Nucella lamellosa when immersed and emersed over a temperature rangeIn the Lummi Island area of Washington, Nucella ostrina lives about 0.5m higher on the shore than N. lamellosa.  Both species are often openly exposed to solar irradiation and, as a result, tissue temeratures may be much higher than air temperatures. The authors note that lower humidities at higher tidal heights may aid in cooling through greater evaporative water loss.  Both species take photograph showing a single whelk Nucella ostrina foraging amongst a selection of barnacle speciesup oxygen when emersed but, as shown here for N. lamellosa, at rates about 3 to 4-fold less than when immersed (see graph). Bertness & Schneider 1976 Veliger 19: 47. Photograph courtesy Dave Cowles, Walla Walla University, Washington www.wallawalla.edu.

NOTE  data are presented here only for large-sized N. lamellosa, but data for large-sized N. ostrina show similar differences


Nucella ostrina forages amongst prey barnacles Balanus glandula, Semibalanus cariosus, and Chthamalus dalli 1X

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Research study 3

photograph of shell-less whelks Nucella lamellosa, courtesy Koy 2007 J Shellf Res 26: 267.An unusual behaviour in whelks Nucella lamellosa is described by a researcher at Friday Harbor Laboratories, Washington.  The behaviour involves loss of the shell a few days to weeks after collection and transport to the laboratory.  The shell-less individuals crawl about and appear to exhibit normal behaviours, including, in 2 of 7 instances of shell loss out of a collection of several hundred, the drilling and eating of prey mussels and barnacles.  Although the author discusses the possibility that the autotomy is defensive, along the lines of limb loss in crustaceans or arm loss in sea stars, she acknowledges that it is more likely to be a response to stressful conditions, such as temperature or oxygen deprivation. Koy 2007 J Shellf Res 26: 267. Photograph courtesy the author.

Two shell-less whelks
Nucella lamellosa.

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Research study 4

photograph of whelk Nucella canaliculata courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattlemap showing collection sites for whelks Nucella canaliculata for study of thermal tolerancesWhat is the geographic variation in thermal limits of a marine snail?  This is investigated in whelks Nucella canaliculata from 7 similar mid-intertidal sites ranging from Oregon to central California (see map).  By rearing eggs in capsules to maturity from each of the 7 populations under standard conditions at the Bodega Marine Laboratory, California, then mating up to 28 non-sibling pairs within each population, the researchers are able to produce test hatchlings minimally influenced by potential past field-acclimatisation and other non-genetic effects. 

histogram comparing thermal tolerances of whelks Nucella canaliculata from sites in Oregon and CaliforniaResults of thermal-or lethal-tolerance (LT50) assays on the F2 progeny reveal that hatchling snails from central California are, surprisingly, less heat tolerant than conspecifics from Oregon (see histogram; capital letters indicate statistical homogeneity). The authors conclude that the differences in upper thermal limits existing among the populations of N. canaliculata are likely genetically based.  As to explanation for the differences, we have to conclude that Oregon whelks are exposed to higher potential thermal stresses than central California whelks.  Kuo & Sanford 2009 Mar Ecol Progr Ser 388: 137. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE the temperature at which 50% of the test subjects are killed

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Research study 5

Studies of temperature effects on feeding in intertidal animals are common, but it is rare for an investigation simultaneously to include rates for an organism both emersed and submersed.  Researchers at Friday Harbor Laboratories, Washington measure feeding rates of whelks Nucella photograp of whelk Nucella ostrina feeding courtesy Emily Carrington, Friday Harbor Laboratories, Washingtonostrina on barnacles Balanus glandula at different and varying temperatures.  Results show, interestingly, that while feeding and growth over a 20d experimental period are greatest at higher submersion temperatures of 13oC as compared with 11oC, they are actually lowest at higher emersion temperatures of 28oC as compared with 20oC or 12oC.  Thus, warm weather may lead to greater predation on the barnacle population, but is significantly released if air temperatures become too warm.  The authors suggest that at the highest experimental air temperatures the whelks may be so physiologically stressed that feeding becomes secondary to seeking shelter within their shells or in cooler microhabitats, or in devoting needed energy to cellular maintenance and repair.  Yamane & Gilman 2009 Mar Ecol Prog Ser 393: 27. Photograph coutesy Emily Carrington, Friday Harbor Laboratories, San Juan Island, Washington CARRINGTON LAB.

NOTE  temperature regimes imposed are in the range that the whelks normally experience during summer in San Juan Island, Washington

A whelk Nucella ostrina feeds on
a barnacle Balanus glandula 1X

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Research study 6

If you live in Alaska it’s hard to avoid freezing temperatures in winter, and even harder if you are a whelk Nucella lima living intertidally in Lynn Canal, Alaska where -0oC air temperatures are common during October-April.  Individuals in the upper part of the intertidal zone will photograph of a whelk Nucella lima courtesy Gerald and Buff Corziexperience more than twice the daily exposure to freezing temperatures than individuals in the lower part (7 vs. 3h, respectively).  Behavioral mechanisms to minimize freezing include cessation of feeding, hiding in crevices or beneath boulders, and burrowing into sediments during periods of tidal emersion.  Physiologically, the snails can supercool to almost -5oC but, as the researchers record several incidents of air temperatures during intertidal exposure below this during Dec-Feb (to -13oC), it is evident that freezing of tissues must occur and is tolerated by the snails.  When a snail’s temperature falls below the supercooling point, ice forming in the extracellular-fluid compartments will draw water from the intracellular compartments thus protecting the cells from damage.  In this regard, tolerance to freezing may owe in large part to the seasonal winter increase in hemolymph concentration of total free-amino acids, including most notably taurine and glycine.  The authors suggest that upper limits of intertidal zonation of N. lima may be set by their freeze tolerance to emersion during winter low tides.  Stickle et al. 2010 J Exp Mar Biol Ecol 395: 106. Photograph courtesy Gerald & Buff Corzi, and the California Academy of Sciences CALPHOTOS

NOTE  seawater temperatures in the Canal range seasonally from 1-15oC

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Research study 7

schematic showing latitudinal compensation for temperature stress in whelks Nucella ostrinaLatitudinal compensation for temperature stress is common in adult intertidal invertebrates, but is it present in larval stages?  This is investigated by researchers at the University of California, Santa Barbara for veliger larvae of whelks Nucella ostrina obtained from capsules collected at 7 sites from northern Washington to central California. The authors determine LT50 values for mature veligers and, as expected, find a significant latitudinal trend (see graph and map).  Note that first to die are veligers from Cattle Point, Washington Gulf Islands and the last, from 2 sites in central California. Zippay & Hofmann 2010 Mar Biol 157: 707.

NOTE  for data on temperature effects on growth of N. ostrina embryos, see Research Study 1 above

NOTE  this is the temperature at which 50% of the larvae are killed by heat treatment.  Different samples of veliger larvae still in their capsules are exposed for 1h periods to a range of temperatures from 13-34.5oC.  Only if the veligers upon examination afterwards are in an advanced stage of development (i.e., shell, foot, operculum, eyespots) are the data used in analysis 


The small letters above each datum
point indicate statistical similarity

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Research study 8

graph showing effect of light intensity on distribution of horn snails Cerithidea californica on beaches in CaliforniaAn investigation of horn snails Cerithidea californica in Mugu Lagoon and Goleta Sloughby researchers at the University of California, Santa Barbara reveals that light plays a strong role in their distribution.  After observing that densities seem greater in lighted areas of the shore than in shaded areas (see graph), the researchers experimentally manipulate light regimes by clipping vegetation and installing shade structures.  Within a few days, snail densities in areas of the shore with higher light levels increase significantly.  The authors hypothesise that shading reduces the numbers of surface-inhabiting diatoms on which the snails feed and the snails soon move away.  Lorda & Lafferty 2012 J Exp Mar Biol Ecol 432/433: 148.

NOTE confirmed in other experiments