title for limpet section of the Odyssey
   
  Reproduction
 

Sexes are separate in most limpets.  Spawning occurs in late winter/springtime in most species, and development leads to a free-swimming, non-feeding veliger larva. 

NOTE  sex ratios in limpets are rarely mentioned.  In one study on Lottia limatula at Palos Verdes, California a ratio of 1.7 male: 1 female is reported (in 486 specimens).  Seapy 1966 Veliger 8: 300.

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  Settlement & recruitment
  Topics on reproduction in limpets & relatives include settlement & recruitment considered here, and SPAWNING & EARLY DEVELOPMENT and SETTLEMENT & RECRUITMENT considered in other sections.
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Research study 1
 

photograph of limpet Lottia fenestrata courtesy Linda Schroeder, Pacific Northwest Shell Club, SeattleA study on settlement of limpets Lottia strigatella in areas around Santa Barbara, California suggests that the larvae settle gregariously.  The author uses fenced plots to test this, half the plots containing adult L. strigatella and the other half containing L. fenestrata.  By counting recruits to each type of plot the author shows that L. strigatella larvae settle in response to the presence of conspecific adults more than to non-conspecific adults (L. fenestrata). The author recognises other possible explanations for the results and discusses these.  Dixon 1981 Veliger 24: 181. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

NOTE  other posibilities are that larvae settle randomly but: 1) suffer more mortality around L. fenestrata, 2) later disperse from plots containing L. fenestrata, and 3) later migrate into plots containing L. strigatella

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Research study 2
 

histogram showing growth of limpets Lottia scabra on mussel and rock substrataphotograph of limpet Lottia scabra in its scar
In Santa Barbara, California limpets Lottia scabra inhabit both rock and shells of sea mussels Mytilus californianus.  Given the risk of the larvae being caught up during settlement in the feeding currents of the mussels and consumed, the question arises as to whether life on a mussel shell is the best “choice” for a limpet.  A comparison of growth and survival of Lottia in the 2 habitats shows that while survivorship of limpets on mussels is much better than on rock (data not shown here), growth is significantly less (by 33%, see histogram).  Mussel shells are usually quite clean, so food would be at a premium in comparison with that growing on adjacent rocks.  The only advantage of a mussel habitat, which might help explain the greater survivorship, is that this homing limpet species may more easily etch out a protective home scar on the soft shell of a mussel than on rock.  Lohse 1993 J Exper Mar Biol Ecol 173: 133.

 
Research study 3
 

histogram showin percentage of larval limpets Lottia digitalis that settle and metamorphose on different substrataphotograph of limpet Lottia digitalisLarval limpets are thought either to settle directly into the adult habitat or too settle on another substratum and later migrate into the adult habitat. This is tested in an Oregon study on Lottia digitalis.  A third option, that the larvae settle indiscriminately in different habitats but ultimately survive only in the adult habitat is not tested in the study, but neither is it commonly known for limpet species.  In the laboratory, metamorphically competent larvae are exposed to a variety of field-collected substrata, including rock fragments from the high-level adult habitat (1-2m above MLLW) and from a lower zone, macroalgae (includes several species, including a filamentous green growing on high intertidal rock fragments and a crustose coralline), diatoms, adult mucus on rocks, and live goose barnacles Pollicipes polymerus.

The results show that larval settlement and metamorphosis is induced in the presence of rocks from the high-zone adult habitat, green filamentous algae from the high zone, rocks bearing conspecific adult mucus, and goose barnacles Pollicipes polymerus (see histogram on Right). The study is especially interesting because the larvae are from parents collected from an area devoid of goose barnacles, yet they appear to be genetically programmed to recognise and settle onto Pollicipes equally as onto rock taken from the adult habitat.

graph showing shell length of limpets Lottia digitalis
Further evidence of the suitability of the upper-intertidal region for recruitment of Lottia digitalis larvae in Oregon comes from data on growth of newly metamorphosed individuals on rock fragments from the high-level adult zone vs. rock fragments from a lower zone.  The author credits the better food resources of filamentous green algae and diatoms on the upper-intertidal rock fragments (see graph on Left).  Not only do the juveniles grow faster on these upper-level rocks, but their shells are less brittle, their adherence to the substratum more tenacious, and their escape behaviour more rapid.

The author concludes that L. digitalis larvae recruit directly into adult habitat high in the rocky intertidal region, thus supporting suggestions by other authors on settlement of this species.  Kay 2002 Mar Biol 141: 467.

NOTE for visual emphasis only representative results are presented here

 
Research study 4
 

graph relating shell width of limpets Lottia paleacea to blade widths of seagrass plants that they are inhabitingphotograph of limpet Lottia paleacea on a blade of seagrass courtesy Gary McDonald, Long Marine Laboratory, Santa Cruz, CaliforniaThe limpet Lottia paleacea is an obligate inhabitant of blades of seagrasses and feeds on the plant’s epidermis.  The species is known to exhibit morphological differences over fine geographical scales and the question arises as to whether seagrass canopies, through alteration in flow regimes, are entraining the larvae of L. paleacea and thus reducing gene flow between the seagrass beds.  To determine L. paleacea’s genetic population structure,  researchers from the University of California, Berkeley analyse 20 individuals  from each of 6 equidistant locations from La Jolla, California to Cape Arago, Oregon for partial cytochrome-oxidase b sequences.  Results reveal 81 uniquely different haplotypes with greatest diversity in southern California populations.  The only significant genetic break is found at Point Conception, California.  The authors conclude that larval entrainment is not the explanation for the species’ morphological diversity; rather, it may simply be differential eco-phenotypic expression in response to local habitat variability.  As one example of this, the authors show a significant positive correlation between width of seagrass blade inhabited and width of shell (see graph). Begovic & Lindberg 2011 PLoS ONE 6 (4): e18408. Photograph courtesy Gary McDonald, Long Marine Laboratory, Santa Cruz and CALPHOTOS.

NOTE  the authors use the genus name Tectura rather than Lottia.  However, for sake of consistency in the ODYSSEY, and recognising that the systematics of Lottia are still being reviewed, the species is referred to here as Lottia paleacea

 
Research study 5
 

map showing current and historical distributions of owl limpets Lottia gigantea along the west coast of North AmericaLarvae of owl limpets Lottia gigantea appear in the plankton in late winter and have the potential of being transported northward from their centre of distribution around Monterey, in northward-flowing currents along the California coast.  However, recent survey of 34 sites along the California and Baja Mexico coasts by researchers from Oregon and Chile show that overall distribution of owl limpets does not extend north of 39.39oN even though historical records dating as far back as 1889 show them as being as far north as Crescent City (41.74oN; see map).  The authors consider that the northern range-limit of L. gigantea is probably controlled by some type of recruitment limitation, as suitable habitat appears to be abundant.  In contrast, limits on the southern range of distribution appear to owe to absence of suitable rocky habitat.  Fenberg & Rivadeneira 2011 J Biogeogr 38: 2286.

NOTE  the study is, in part, a test of the so-called Abundant Center Hypothesis that assumes that populations in the central part of a distribution are living at optimal physical and biotic conditions -  which makes a lot of sense when you think of it

NOTE  the authors uniquely use the software programme Google Earth (v.4.1) to examine the southern shores of Baja California from a fixed elevation of 500m for suitable habitats (i.e., rocky substrata)

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