title used in an account of west-coast marine invertebrates entitled A Snail's Odyssey
  Predators & defenses
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  In this section limpets as predators are considered, while studies on FISHES, WHELKS, SEA STARS, and INSECTS are found in other sections.
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Research study 1

photograph of barnacles Chthamalus dalli on a rockIn field studies in San Juan Island and Waadah Island, Washington, where limpets are caged with barnacles and predators are excluded, suvival of Chthamalus dalli is increased because of the strong, negative effects of the limpets on Balanus glandula and Semibalanus cariosus.  The settled spat of these species are larger and more susceptible to being bulldozed and eaten by limpets, while the smaller spat of Chthamalus settle in cracks and are in spatial refuge from the limpets.  Dayton 1971 Ecol Monogr 41: 351.






Two generations of barnacles Chthamalus dalli are
visible in this photo, along with a single individual of
Balanus glandula,
probably of the current-year's cohort 5X

Research study 2

graphs showing effects of presence of herbivorous limpets on survial of barnacles Balanus glandula and Chthamallus dalli at Tatoosh Island, WashingtonThe influence of limpets on differential survival of large- and small-sized barnacles is shown in an experiment in Tatoosh Island, Washington where the principal grazers, limpets Lottia digitalis, are excluded from a high-intertidal patch created in a red-algal bed.  In this experimental patch over a 3.5-yr study period the larger species B. glandula dominates in the absence of the limpets (see upper graph). However, in a nearby control patch where limpets are grazing normally there is greater survival of Chthamalus dalli than Balanus glandula (see lower graph)Paine 1981 Paleobiology 7: 553. These same data are presented in another context elsewhere in this limpet section of the ODYSSEY: LEARN ABOUT/BARNACLE: INTERSPECIFIC COMPETITION.photograph of Lottia digitalis with barnacles and littorines

NOTE  the patch, 30 x 30cm, is delineated with copper-based anti-fouling paint, which effectively excludes limpets.  A nearby area is used as a control patch.  In the control area Lottia densities are 90 . m-2

NOTE the 3 peaks in % cover in springtime represent larval recruitment of this species

Two limpets Lottia digitalis on rock with 2 generations of
barnacles Balanus glandula. The juveniles appear to be young-
of-the-year and have reached size-refuge from the limpets 3X

Research study 3

photograph of the undersurface of a limpet Lottia pelta showing the parts that can potentially dislodge a barnacle spatWhile browsing the substratum for algal and diatom foods, limpets ingest newly settled spat of barnacles with their radulae and bulldoze them off the rocks with their shells.  In laboratory studies at the Bamfield Marine Sciences Centre, British Columbia, limpets Lottia digitalis grazing on rocks are observed to kill newly attached spat of 4 species of barnacles  B. glandula, B. crenatus, S. cariosus, and Chthamalus dalli.  Of 435 spat killed in one part of the study, 26% are ingested and 74% bulldozed.  Close observation of limpets removing barnacles from oyster shells indicates that the shell is not the only instrument of bulldozing.  Of 7 barnacles removed by limpets in one session of observation, 2 are bulldozed off by the limpet's shell, 2 are knocked off by the foot, 2 by the mouth, and one is pushed off by the tentacle.  When B. glandula and B. crenatus grow to a basal diameter of 5-8mm, they enter size refuge from being killed by L. digitalis.  Semibalanus cariosus reaches size refuge at a somewhat smaller size and younger age owing to its stronger attachment.  Miller & Carefoot 1989 J Exp Mar Biol Ecol 134: 157.




Upside-down limpet, in this case, a Lottia pelta, showing
body parts used to remove barnacle spat 2X

Research study 4

graph showing mortality of spat of barnacles Balanus glandula under different experimental conditionsphotograph of slate-plate arenas used in study of limpet-barnacle interactions with Lottia digitalis and Balanus glandulaWhich offers more protection to a newly settled barnacle from being bulldozed or eaten by a limpet: a shallow depression or proximity to an adult?  This is tested at the Bamfield Marine Sciences Centre and at field sites in Barkley Sound, British Columbia using slate plates (20 x 20 x 1.9cm) divided into 4 quadrats with 3cm-high mesh fencing to prevent the limpets from escaping or moving between quadrats (see photographs upper Left). Quadrats are modified to provide one of 2 types of spatial refuge: depressions and adult barnacles.  The plates are hung from a dock at depths of 0.7m and 2m above zero chart datum to intercept, respectively, settling larvae of S. cariosus/B.crenatus (0.7m-depth plates) and B. glandula (2m-depth plates).  After the plates are colonised by barnacle spat, limpets Lottia digitalis are added to each quadrat at densities of 0, 2, 4, and 6 limpets, respectively.  The plates are left in the sea for 4wk and photographed weekly to monitor survival of the barnacle spat.  Only results for B. glandula on the high-level (2m above zero chart datum) plates will be considered here (graph upper Right).photograph of researcher workng on barnacle-settlement arenas in Barkley Sound, British Columbia

Results show, as expected, that the cyprid larvae settle in depressions in preference to flat space on the plates: 68% and 32%, respectively. The graph shows the type of mortality data collected for depression plates suspended at a high intertidal level.  Overall mortality of the spat is 39% in depressions versus 54% on open surface.  Note that mortality increases with increasing density of limpets more rapidly on the open surface than in depressions. In the “proximity to adult” part of the study, settlement of B. glandula larvae onto the slate plates is preferentially closest to the glued adult shells.   Later mortality is least for spat <2mm from an adult shell (<15%) and greatest for spat >4mm from an adult shell (up to 65%).  In control quadrats (0 limpets) mortality is <15% over the 4wk study period regardless of distance from an adult shell. The study emphasises the importance of refuges for barnacles especially during the first week of life, where depressions and proximity to adults are important, and later in life, where refuge in size becomes important. Miller & Carefoot 1989 J Exp Mar Biol Ecol 134: 157.

NOTE there are 30 depressions in each quadrat , each 6mm dia x 2.5mm deep, placed randomly and covering 8.5% of the available area. Adult barnacles consist of tests of B. glandula, 30 in each quadrat, soft parts removed and replaced with silicon cement, and glued to the substratum in random locations

NOTE mortality in control quadrats (depressions, no limpets) is <22%


Another part of the barnacle-limpet study includes field arenas
enclosing spat and juvenile barnacles and different densities of limpets.
Here, the senior author is taking photographs during weekly monitoring

Research study 5

photograph of cluster of baracles Semibalanus cariosus with whelk and limpetsThe protection offered barnacle spat by being closely sited to adults enhances their aggregation, which is beneficial because of greater mating potential.  Greater aggregation of the barnacles, however, can lead to weak attachment and increased potential for loss in storms or from log battering or predators that, in turn, frees up space for colonisation by limpets.



A close look at this group of thatched barnacles Semibalanus
reveals several Balanus glandula clustered at the bases of
the former. Survival of B. glandula is aided by the proximity of the
adults, even though they are a different species. Other "players"
visible are a whelk Nucella sp., several littorines Littorina sp.,
and a limpet Lottia sp. Whelks prey on juvenile and adult
stages of barnacles, while limpets kill off the smaller stages.
Littoriines are more or less neutral in their effects. 0.7X

Research study 6

A study by researchers from Oregon State University comparing recruitment of barnacles Balanus glandula and Chthamalus dalli onto different types of substrata shows that bulldozing by limpets has variable effects depending upon substratum and barnacle species.  Thus, while limpets (identified as several Lottia spp.) have a negative effect on recruitment of B. glandula on rock, their effect on C. dalli is inconsistent.  The authors suggest that the relative resistance of Chthamalus to bulldozing compared with Balanus may owe to faster metamorphosis and thus firmer attachment strength in the former.  Menge et al. 2010 J Exp Mar Biol Ecol 392: 160.

NOTE  the main research focus is on comparing various natural and “artificial” substrata with respect to settlement and recruitment of barnacles, to determine the extent to which an artifical surface can provide reliable estimates across space and time.  Readers who are interested in this approach to intertidal ecology will benefit from the work