Physiological ecology
  Topics considered here include metabolic demands in larvae, desiccation, and temperature effects. Effects of intertidal temperatures on HEAT-SHOCK PROTEINS in turban snails are considered in another section.
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Metabolic demands in larvae

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Research study 1
 

graph showing mass of body components during larval development in abalone Haliotis rufescensAn abalone larva is non-feeding and the energy it contains must last it through metamorphosis to a feeding juvenile stage.  But are veliger larvae truly in energy balance? That is, does their store of yolk fully meet their energy needs?  Studies on the energetics and growth of veliger larvae of Haliotis rufescens in southern California attempt to answer this.  First, the larvae actually increase in dry organic mass during the first 2d after hatching, and dry mass of ash increases steadily during the 7d of larval life (see graph on Left). Second, the decrease in organic mass (representing metabolism histogram showing uptake rates by larval abalone Haliotis rufescens of different amino acidsof energy stores) from hatching to metamorphosis only accounts for about 48% on average of the total energy required during this period as measured by oxygen consumption.  The authors suggest that the larvae are utilising nutrients obtained as DOM, specifically amino acids, to make up this deficiency.  Based on estimates of amounts of amino acids in the total pool of DOM in seawater and on measured rates of uptake of amino acids by abalone trochophores and veligers (see uptake rates in graph on Right), the authors calculate that an uptake of only 4% of the total amino-acid pool would satisfy 100% of the missing energy. The authors conclude that these lecithotrophic larvae are not energetically independent of their environment.  Jaeckle & Manahan 1989 Biol Bull 177: 237; Jaeckle & Manahan 1989 Mar Biol 103: 87.

NOTE data obtained in laboratory culture at 16-17oC and presented for egg (0d of age), trochophore larva (1d), early veliger larva (2d), and for several later veliger stages up to the metamorphically competent one (7d)

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Research study 2
 

photograph of a post-metamorphic juvenile abalone Haliotis rufescens courtesy Shilling et al. 1996 Biol Bull 191: 402In a later paper researchers investigate the energy demands of metamorphosis in 6-9d-old red abalone Haliotis rufescens and determine that the proportion of total metabolic demand supplied from aerobically catabolised biomass is less than 40%.  Thus, metamorphosing veligers have a theoretical shortfall of 60%. Based on measured rates of transport of dissolved alanine from seawater, the authors determine that the energy shortfall could once again be met by uptake of DOM from the environment.  In fact, their data show that the cumulative transport of DOM during development to the early juvenile stage could supply an amount of energy equivalent to the entire maternal endowment of energy reserves in the form of yolk to the egg.  Shilling et al. 1996 Biol Bull 191: 402.

NOTE dissolved organic matter, equated here to amino acids in the surrounding seawater, but in general terms also including fatty acids and perhaps some sugars

Post-metamorphic juvenile Haliotis already feeding on epiphytes on coralline algae
(0.8mm shell length). The red arrow indicates the larval shell; yellow arrow, the juvenile shell.
Photo courtesy Sabine Daume, from Heasman & Savva 2007 Manual for intensive
hatchery production of abalone
Fisheries Res & Dev Corp, Australian Gov

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Desiccation

 

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Research study 1

  By tagging individual Chlorostoma funebralis and monitoring their movements during daily tidal cycles, researchers Hopkins Marine Station, Pacific Grove, California report that populations move to the tops of rocks during high tides at night, but not during high tides in the daytime.  Even light from a full moon appears to inhibit the movement.  The significance of the behaviour is not known, but may relate to temperature effects on feeding and/or reproduction.  Wara & Wright 1964 Veliger 6(Suppl): 30.
 

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Research study 2

 

Black turban snails Chlorostoma funebralis often aggregate during periods of low tide.  Is this for defense against predators or for protection against desiccation?  The last is investigated at Bodega Marine Laboratory, California by measuring the photogaph of a cluster of black turban snails Chlorostoma funebralissalt concentration of water1 held within the closed shell during low tide periods in both solitary and aggregated individuals.  We know that this species cannot regulate the salt concentration of internal fluids, so this water should be a direct reflection of the internal osmolarity2

The histogram indicates a trend of higher values in animals exposed to open air as compared with animals in protected sites (such as within crevices or beneath algae). In both exposed and protected microhabitats there is no significant difference3 between solitary or aggregated individuals. The authors conclude that microhabitat effects are more important than being solitary or aggregated.  Marchetti & Geller 1987 Veliger 30: 127.

NOTE1  also known as “extra-corporeal” water (lit. “outside body” L.). 

NOTE2 salt concentration is expressed here as “osmolarity”, although the two units are not quite the same, and defined as mOsM per liter.  Full-strength seawater is around 1000 mOsM per liter

NOTE3 internal body temperatures are about 4oC lower in aggregated individuals than in solitary ones

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Temperature effects

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Research study 1
 

map showing collecting sites for black turban-shells Chlorostoma funebralis for use in study on temperature effectson activityTemperature should affect locomotion, food-consumption, and gut-passage rates in snails as predicted from Q10 principle and temperatures characteristic of the snails’ geographic distributions.  This is examined in 3 Chlorostoma species with distinct thermal distributions: C. brunnea (cold water), C. aureotincta (warm water), and C. funebralis (both warm and cold water).  Rates for each species are tested at 4 temperatures: 11, 15, 19, and 23oC. 

Results for C. aureotincta, the warm-water species, show that activity and consumption rates increased with increasing temperature.  For C. brunnea, the cold-water species, rates are lowest at 11oC and highest at 19oC, a temperature rarely experienced in its natural habitat.  For cold-water C. funebralis, overall activity is highest at 15oC and food-consumption is highest at 23oC.  For warm-water C. funebralis, activity and food-consumption is lowest at 11oC.  Gut-passage times are little affected by temperature in these species.  Overall, and as might be expected, activity and food-consumption in the more broadly distributed C. funebralis are less affected by temperature than those of the 2more narrowly distributed species.  The authors discuss their data in the context of temperature effects on distributions in the various species. Yee & Murray 2004 Mar Biol 145: 895.

NOTE  rates are tested after acclimation periods of 10d in the laboratory

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Research study 2
 

histogram comparing thermal-tolerance ranges of snails Chlorostoma spp.Three commonly occurring west-coast Chlorostoma species live at different tidal heights on the shore of Pacific Grove, California.  Thus, funebralis inhabits the low- to mid-intertidal zone, while brunnea and montereyi live in low intertidal or subtidal regions.  What are the thermal limits of heart function in these snails and how do these relate to their vertical zonation?  This is investigated in 3 populations of Chlorostoma at Hopkins Marine Station, California. 

Results show that the thermal range of field-acclimatised C. funebralis is greater than those of the 2 lower-occurring species. Thus, ABT and FLThot are higher (see histogram on Left), and FLTcold is lower (data not shown).  If snails of each species are acclimated to lower (14oC) and higher (22oC) temperatures, all 3 species show increases in ABT and FLThot, with the largest changes occurring in brunnea and montereyi.  The authors note that while funebralis is more eurythermal than its co-occurring congeners, it may sometimes encounter body temperatures that impair or even stop heart function, that is, exceed ABT.  Stenseng et al. 2005 Biol Bull 208: 138.graph showing how the Arrhenius Break Temperature of ABT is determined for heart-beat response to rising temperature in snails Chlorostoma funebralis

NOTE  the authors use 3 indices to provide an estimate of the thermal range within which Chlorostoma’s heart function is maintained: 1) temperature at which heart rate initially decreases rapidly during heating, also known as the Arrhenius break temperature or ABT; see graph on Right), 2) temperature at which the heart ceases to beat during heating, termed the flatline temperature or FLThot, and 3) temperature at which the heart ceases to beat during cooling, termed FLTcold

NOTE  heart rate is monitored using an impedance converter with electrodes inserted via 2 1mm diameter holes drilled into the shell close to the heart and glued in place with cyanoacrylate adhesive

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Research study 3
 

histogram showing effects on gonadal indices in red and green abalone of various combinations of temperature, and food quality and quantityphotographs of Haliotis rufescens & H. fulgens, courtesy Kevin Lee, Fullerton, CaliforniaCan predicted climate-change effects be simulated in the laboratory? This approach has been growing in popularity1 and is examined here for red abalone Haliotis rufescens and green abalone H. fulgens at the Scripps Institution of Oceanography in La Jolla, California using treatments that mimic El Niño and La Niña conditions in the California current.  Haliotis rufescens is a cool water-inhabiting species, while H. fulgens prefers warm water. The researchers simultaneously test the possible synergistic effects of temperature, and food quality and quantity on survivorship, growth, and reproduction in the 2 species, with special emphasis on exacerbation of disease2 susceptibility.  The design of the experiments is complex and only a brief summary of results is presented here.  Basically 7 individuals of each species are housed in each of 9 floating plastic-mesh cages in larger tanks maintained at 3 temperatures.  The 9 cages represent a 3 x 3 combination of food3 quality and quantity.  Over a 50-wk treatment period the test abalone are measured periodically for changes in shell length, live mass, and gonadal maturation.  At the end of the experiment, 3 individuals from each treatment are assessed for gonad index, done by cross-sectional measurement, and intensity of withering syndrome disease.  Results for H. rufescens show that warm temperatures increase the onset of withering disease, and halt growth and reproduction (see histograms for effects on gonadal indices).  In comparison, temperature has little effect on these parameters in H. fulgens, with growth and reproduction being most influenced by food quantity.  Overall, then, the cool-water red abalone suffer more in warm water than do green abalone.  The authors conclude that ocean warming will have significant adverse effects on California abalone populations. Vilchis et al. 2005 Ecol Appl 15: 469. Photograph of H. rufescens courtesy Kevin Lee, Fullerton, California diverKevin.

NOTE1  a later and similar study also compares health and survival of H. rufescens in laboratory simulations of El Niño and La Niña conditions.  It differs from the earlier study in using wild abalone from San Miguel Island, Channel Islands, California, an area characterised by generally cooler water temperatures throughout the year, rather than cultured abalone.  Results are similar to the earlier study, with higher temperatures leading to elevated expression of withering syndrome (now identified as Candidatus Xenohaliotis californiensis).  Based on their results the authors predict that strong El Niño events will result in significant mortality of red abalone at San Miguel Island.  Moore et al. 2011 J Aquat Anim Health 23: 78.

NOTE2  the disease, withering syndrome, is a Rickettsiales-like prokaryote found in the gastroinstestinal epithelia.  The disease is invariably fatal.  In order to eliminate it from experimental animals (purchased from hatcheries), all are treated with antibiotics over 7wk prior to the start of the experiment. For more on the disease see Friedman et al. 2002 J Shellf Res 21: 817

NOTE3  food is kelp Macrocystis pyrifera collected at different vertical levels in the kelp bed, and treated or not for 72h in nitrogen-enriched seawater to make high-, medium-, and low-quality diets.  The 3 diets vary from about 1.5-3.5% dry mass in nitrogen.  The 3 quantities are high (ad libitum), medium (30% of ad labitum), and low (10% of ad labitum). Temperatures vary over the time span of the experiment, but are maintained at about 2oC separation for the 3 treatments.  Each combination is replicated 3 times

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