Foods, feeding, digestion, & growth
 

photo/diagram of the gut system of a generalist herbivore, as sea hare, Aplysia
Nudibranchs and other opisthobranchs are mostly carnivorous, but some eat seaweeds. Many species have fairly specific preferences for prey types eaten.  As most of the prey is sessile or sedentary, the predator follows a chemical-scent gradient upstream using its paired rhinophores or oral tentacles, depending upon species.  The opisthobranch crawls up, bites with its jaws, and draws food into its gullet with its radula.  From the stomach, which in gastropods is more of a sorting area than a digestive, the food is conveyed along ciliated ducts to a large digestive gland for processing.  Undigested matter moves back into the stomach and thence into the intestine for release as fecal pellets from the anus.

Depending on the type of food being eaten by the opisthobranch, there may be ancillary digestive organs, for example, buccal pumps for plant-cell suckers or, as shown for the sea hare here, storage crops and grinding gizzards for processing of extra-tough foods.

NOTE  lit. “nose-bearing”.  The rhinophores are generally layered for greater surface area for chemoreception and are held upright in the current.  By moving its head back and forth, and thus changing the orientation of the paired rhinophores to the current, the nudibranch can track the location of its prey upstream

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Preferred foods, feeding ecology, & growth: genera A-C

 

Nudibranchs mostly eat sponges, bryozoans, and different types of  cnidarians.  Anaspids (Phyllaplysia, Aplysia) are generally herbivorous, while sacoglossans, with one or two exceptions, are mostly plant-suckers.  Information on diets and feeding ecology of west-coast genera is provided below and in 6 other sections:
PREFERRED FOODS FEEDING ECOLOGY & GROWTH: GENERA D-G
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PREFERRED FOODS FEEDING ECOLOGY & GROWTH: GENERA H-M,
PREFERRED FOODS FEEDING ECOLOGY & GROWTH: GENERA N-P
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PREFERRED FOODS FEEDING ECOLOGY & GROWTH: GENERA R-T,
PREFERRED FOODS FEEDING ECOLOGY & GROWTH: SACOGLOSSANS, and INGESTIVE CONDITIONING.

NOTE  the following review of diets of west-coast nudibranchs & relatives brings together data from many sources; but see McDonald & Nybakken 1978 Veliger 21: 110 for a list of food habits of California nudibranchs

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Aeolidia

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Research study 1
 



photograph of sea-anemon species that are always eaten by the aeolid nudibranch Aeolidia papillosa
photographs of sea anemones that are rarely eaten by the aeolid nudibranch Aeolidia papillosaAeolidia papillosa
preferentially eats sea anemones and worldwide its diet includes at least 26 species.  In central California, Aeolidia displays varying preferences for 7 species of anemones and one corallimorpharian.  The author divides these preference into 3 groupings of "always eaten", "sometimes eaten", and "rarely eaten" shown by the clusters of photos. The author provides descriptions of the role that the anemone's defenses may play in determining these preferences. Waters 1972 Veliger 15: 174. Photo of Diadumene sp. courtesy Chesepeake Bay Program.

NOTE  most generalities in natural science seem to have exceptions: in the Netherlands, Aeolidia papillosa prefers the acontiate species Metridium senile over other actiniarian species.  Stehouwer 1951 Arch Neerl Zool 10:161.

photograph of sea anemones that are sometimes eaten by the aeolid nudibranch Aeolidia papillosa

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Research study 2
 

The accompanying photos confirm that Aeolidia papillosa will readily eat an acontiate anemone Metridium senile that it encounters in an aquarium tank at Bamfield Marine Sciences Centre, British Columbia.

 

The first 2 photographs show the initial
encounter, withAeolidia almost immediately
protruding its mouth.. Photos 3 & 4 show the
anemone being eaten, but the jaws and radula
are not visible. In the last photogaph the
anemone has extended many acontia,
some of which appear to be clinging to
the predator. Within 90min the anemone is
completely consumed. 3X for all photos

photograph of a series showing first contact of the aeolid nudibranch Aeolidia papillosa with an intended prey anemone Metridium senile photograph of a series showing contact of the aeolid nudibranch Aeolidia papillosa with an intended prey anemone Metridium senile
photograph in close view  showing biting contact of the aeolid nudibranch Aeolidia papillosa with a prey anemone Metridium senile photograph in close view  showing biting contact of the aeolid nudibranch Aeolidia papillosa with a prey anemone Metridium senile photograph in close view  showing biting contact of the aeolid nudibranch Aeolidia papillosa with a prey anemone Metridium senile
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Research study 3
 

photograph of an aeolid nudibranch Aeolidia papillosahistogram showing reates of photosynthesis of zoochlorellae and zooxanthellae symbionts in the cerata of a nudibranch Aeolidia papillosa as compared with that in the nudibranch's feces and in the host anemoneOne of Aeolidia papillosa’s preferred species Anthopleura elegantissima is also one that contains high concentrations of photosynthesising symbionts.  Interestingly, passage through Aeolidia’s gut apparently does not kill all the anemone’s symbionts.  Some of these are retained by the snail and positioned in the digestive lining of the dorsal cerata where they continue to photosynthesise.  Note in the graph that rates of photosynthesis of the two types of symbionts is only slightly less in the cerata than in the anemone’s tentacles (compare CERATA vs. ANEMONE).  Many more symbionts pass out of the snail in its feces, where they remain healthy for some time and may provide a source for inoculation of other anemones, either adults or larvae.  Seavy & Muller-Parker 2002 Invert Biol 121: 115; McFarland & Muller-Parker 1993 Biol Bull 184: 223.

NOTE  lit. “horns”.  The cerata are dorsal projections on the body of aeolid nudibranchs that contain extensions of the digestive gland.  Not only do the tissue linings of these digestive-gland extensions sometimes contain photosynthesising symbionts as described here, but in other species of nudibranch they may also contain functional nematocysts also derived from their prey.  More information on this potential defense is located in another section of NUDIBRANCHS & RELATIVES entitled DEFENSE

NOTE  as each snail can eat up to 3 small anemones per day, the number of symbionts released in this way can number in the 10’s of millions daily

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Aplysia

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Research study 1
 

An early study of foods of sea hares Aplysia californica in southern California reveals that juveniles almost exclusively eat “fleshy red algae”, but can be fed green algae Ulva and Enteromorpha in the laboratory.  The authors could find no evidence that eelgrass Zostera marina is eaten by A. californica.  A second Californian sea-hare species, Aplysia vaccaria, that is sometimes found with A. californica, exclusively eats the brown alga Egregia and thus is unlikely to interact competitively with the latter species for food.  Winkler & Dawson 1963 Pac Sci 17: 103.

NOTE  the most predominant algae identified in contents of crops and fecal pellets are Centroceras clavulatum, Ceramium eatonianum, Gelidium coulteri, Gigartina canaliculata, and Plocamium pacificum (names of algae are not corrected to current nomenclature)

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Research study 2.1
 

In early publications on feeding behaviour in sea hares Aplysia spp., researchers at the University of Oregon demonstrate learned behavioural discriminations of food objects by both A. californica and A. vaccaria.  In trials where a glass rod or metal forceps are offered alternatively with edible green alga Ulva sp. to naïve individuals they at first seize and try to ingest the inanimate objects as often as they ingest the algae.  After several days at 20 trials per day, an individual will refuse contact with the inanimate objects up to about 90-100% of the time.  The memory is retained in A. californica for at least 9d, and in A. vaccaria for 4d.  Lickey & Berry 1966 The Physiologist : 230; Lickey 1968 J Comp Phys Psych 66 (3): 712.

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Research study 2.2
 

drawing of gut of Aplysia showing crop and other partsEarly research on digestive capabilities of Aplysia vaccaria at San Diego State College, California reveals that a cellulase is present in the crop fluids.  Initially, the authors identify the enzyme’s presence from the presence of glucose after treating filter paper with crop fluid.  In a later, more refined study, they use a radioactively labeled substrate, cellulose-14C, instead of filter paper, and obtain glucose-14C as a product.  Although the results indicate the presence of a cellulase, the authors note that they do not know whether its presence is endogenous or from another source such as bacteria.  Koningsor & Hunsaker 1971 Veliger 13: 285; Koningsor et al. 1972 Comp Biochem Physiol 43B: 237.

NOTE  Whatman brand filter paper is described by the manufacturer as being made of pure cellulose

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Research study 3
 

photograph of sea hare Aplysia californica in typical upside-down feeding postureSea hares Aplysia detect algal foods from a distance, with the most sensitive receptors involved in this being predominantly located in the anterior tentacular groove area of the oral veil.  The author uses the mouth-opening-reponse in Aplysia californica to identify particular sensitivities to the amino acids glutamic acid and aspartic acid at concentrations of 10-6 to 10-7, and suggests that these may serve as feeding attractants. Jahan-Parwar 1972 Am Zool 12: 525.

 

 

A sea hare Aplysia californica in typical upside-down feeding posture.
The predominant structure visible in the open mouth is the pair of
jaws. The radula can be extended out of the jaws to draw in food

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Research study 4
 

diagram of T-maze food-choice apparatus used in studies of food preferences of sea haresdrawing showing sensitivity of various body parts of the sea hare Aplysia californica to food-extract stimuulationA series of experiments on feeding behaviour in sea hares Aplysia californica show, firstly, that individuals perceive food from a distance using head-waving for orientation.  T-maze choice experiments show that individuals readily move up the stem of a maze and make a correct turn into the seaweed arm 78% of the time (see diagram on Left).  In this experiment the water in the maze compartment is still, but if a current bearing food-extract is present then success rises to 92%.  By stimulating various parts of the sea-hare’s body with a fine-diameter stream of extract-bearing seawater, the authors determine that food sensation is mainly by the tips of the rhinophores and leading edges of the oral tentacles (see drawing on Right). Preston & Lee 1973 J Comp Physiological Psychol 82: 368.

NOTE  commercial dry laver (Porphyra sp.) soaked in seawater to produce a tainted solution for application

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Research study 5
 

drawing showing where sensory parts are excised on head of sea hare Aplysia californicaIf  the oral veil is used for distance location of food in sea hares, what role do the rhinophores and tentacles play? This is tested in a Y-maze apparatus at the Santa Cataline Marine Biological Laboratory using Aplysia californica with rhinophores removed, tentacles removed, or with both sets of structures removed.  Normal intact animals when tested with red algae Plocamium coccineum alone or with Laurencia pacifica in one arm of the maze, and with another alga Gelidium nudifrons, not known to be eaten by A. californica, in the other arm, choose the correct arm about 90% of the time.  If only rhinophores are removed, individuals choose correctly 90% of the time, the same as sham-operated animals.  If only tentacles are removed, individuals choose correctly only 67% of the time, but the difference is not statistically significant.  However, with both sets of organs removed, correct performance declines significantly to 25-46%.  The author speculates that the scent of a suitable food may be perceived by the rhinophores and this alerts the animal to the upstream presence of food. However, it is the tentacles located closer to the substratum that play the dominant role in locating and identifying the algal foods.  Head-waving is a common behaviour in food-seeking Aplysia and, in the present study, occurs mostly in animals whose tentacles are intact. Audesirk 1975 Behav Biol 15: 45.

NOTE  only the distal tips are cut off with a single snip of scissors (see drawing). Sham operations, involving comparable-sized snips of tissue from a parapodium, are also done to assess whether trauma of the operation may bias the results. The dimensions shown in the drawing are for a 570g individual

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Research study 6
 

graph showing growth of sea hares Aplysia californica at 2 sites in Santa Catalina Island, CaliforniaSea hares Aplysia californica in southern California prefer red algae of the genera Plocamium and Laurencia, and growth is fastest on diets of these species.  The accompanying graph shows rapid springtime growth of A. californica at 2 sites in Santa Catalina Island, California. The author notes that one tagged individual gained more than 2kg of mass during Feb-Apr and average monthly gains for the entire study population from Jan-May, inclusive, range from 40-100g.  After maturity is reached in late summer, individuals spawn and most die by the end of autumn.  Mid-summer live mass rarely exceeds 3kg in this Santa Catalina population, but much larger sizes are recorded for the species elsewhere, for example, up to 6.8kg in Elkhorn Slough, California. Reproductive activity peaks in August and at that time, perhaps through a combination of lack of grazing opportunity because of copulation and production of massive amounts of eggs, live mass drops precipitously. Audesirk 1979 Biol Bull 157: 407.

NOTE  data from MacGinitie & MacGinitie 1968 Natural history of marine animals McGraw-Hill, San Francisco.

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Research study 6.1
 

graph showing relationship between age and shell length in sea hares Aplysia californicaResearchers at the University of Kentucky, Lexington attempt to find a morphological feature of sea hares Aplysia californica that reliably correlates with age.  The authors maintain a batch of animals in laboratory culture for 235d, kill some of them every few weeks, and record total live mass, and masses of various organs, including reproductive tract, radula, gill, and internal shell of each individual killed.  Length of internal shell is also recorded.  Correlation between age and all measurements save shell length are too variable to be useful; only data on shell length provide a reliable indicator of age (see graph).  Peretz & Adkins 1982 Biol Bull 162: 333.

NOTE  a single individual lives for another 85d and is included in the graph.  All other data points represent the mean of 8-28 individuals

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Research study 6.2
 

graph showing survival against age for laboratory-reared sea hares Aplysia californicaIn a typical life span an animal grows, reproduces, ceases to grow, then dies.  The penultimate part is manifested by senescence or “aging”, where body parts begin to fail both physiologically and physically, leading ultimately to loss of function of some critical part or process, and death ensues.  Given this, is it possible that an animal can both continue to grow and senesce at the same time?  This question is addressed by the same research group featured in Research Study 6.1 above who note that a typical age/growth curve for a population of Aplysia tends to be more of a straight line than a declining exponential curve as seen for other animal species.  In their main experiment the researchers maintain a batch of 112 Aplysia californica in the laboratory and dissect each individual when it dies. The shell's size is used to estimate age as described in Research Study 6.1 above.  The researchers separate their data into “bins”, basically a statistical smoothing technique considered in detail in the article. Results show that survival is linear for 102 members of the laboratory population, with a few outliers representing a some early and late deaths, and an especially long-lived individual that survives for 316d.  As defined by the authors, senescence therefore commences in this population at a post-metamorphic age of 100d.  The authors conclude that in A. californica, senescence is accompanied by a constant rate of growth that is maintained to the end of life.  Unfortunately for our appreciation of this paper, the researchers never measure growth in their population, and the fact that “growth..is maintained to the very end of life” must, perforce, be taken on faith.  Hirsch & Peretz 1984 Mech Ageing Dev 27: 43.

NOTE  the presentation is made less clear by the authors’ propensity to synonomise “senescence” with “aging”.  Most biologists would agree that an organism “ages” progressively from its appearance as an egg, with “senescence” occurring as a degenerative stage leading to death.  Perhaps there are particular preferences of the Journal in which the article is published that have influenced the way in which these words are used by the authors

NOTE  sea hares spawn at a young age and size, and continue to spawn until they die.  As spawn is part of production, its mass should be incorporated with somatic mass to give total mass-change over time.  It is actually not clear how spawn is dealt with in the sudy.  Its only mention comes as a note regarding a 316 day-old individual that apparently did not spawn at all.  In fact, as mentioned later in this synopsis, growth appears not to be measured in the study at all

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Research study 7
 

graph showing growth of newly metamorphosed sea hares Aplysia californica on different species of algaeA later study on diets of sea hares Aplysia californica in Santa Catalina Island, California confirm that they prefer to eat red algae Plocamium cartilagineum and Laurencia pacifica.  Do they prefer these algal species because they grow best on them, or because they obtain from them certain secondary compounds that protect them from predators?  Results of experiments to test these ideas support both possibilities.  Newly metamorphosed animals eat only Plocamium of 6 algal species tested, and this is the alga that stimulates the larvae to settle and metamorphose (see graph).  Later, at a size of 1-3cm body length, the diet spectrum is broadened, and good growth is attained on Plocamium, Laurencia pacifica, and the green alga Ulva sp. Most of the other seaweed diets tested by the author are not eaten at all by the juveniles.  Tissues of individuals fed on the 2 red-algal species are rich in terpenes, while those of individuals fed only green algae Ulva sp. are terpene-free.  When these 2 types of sea hares are presented to hungry rock wrasses Halichoeres sesmicinctus, the Ulva-fed ones are more likely to be eaten than the Plocamium-fed ones.  Pennings 1990 Oecologia 82: 192.

NOTE  if A. californica is raised on an exclusive diet of green algae, such as Ulva spp., not only do they lack terpenes, but they lose the capacity to produce purple ink.  See the section on DEFENSE: INK & OPALINE SECRETIONS for more information

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Research study 8
 

histogram showing attractiveness of species of red algae to post-metamorphic sea hares Aplysia californicaA companion study by the same researcher examines ontogenetic changes in food preferences in Aplysia californica in Santa Catalina Island.  Results of field and laboratory studies show that dietary specialisation decreases with size and age.  Thus, new recruits eat only the red alga Plocamium cartilagineum, juveniles eat P. cartilagineum and the green alga Ulva sp., and adults eat generally Plocamium, Ulva, and Codium.  The larvae settle preferentially onto Plocamium in the field, so the preference for this alga is expected.  Interestingly, in the laboratory larvae settle on a wide variety of algal species, but, if Plocamium is present, the post-metamorphic juveniles soon gather onto this alga; individuals metamorphosing in the presence of other algae tend to be found on the culture-container walls.  As found in other studies on sea photograph of a juvenile sea hare Aplysia californica courtesy Kevin Lee, Fullerton, Californiahares, feeding preferences of A. californica of different sizes change in a manner consistent with the ability of the algae to promote growth.  Pennings 1990 J Exp Mar Biol Ecol 142: 43. Photograph courtesy Kevin Lee, Fullerton, California diverKevin.

NOTE  although used in laboratory experiments, the author notes that this alga is almost never found at the study sites in Santa Catalina Island

Juvenile sea hare Aplysia californica
crawling on red algae 2X

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Research study 9
 

drawing of sea hare Aplysia vaccariagraph showing size change in a population of sea hares Aplysia vaccaria annuallyA 1yr study by researchers at the University of California, San Diego confirms that mating in sea hares Aplysia vaccaria occurs in late spring, with recruitment in June-July, and senescence and death by October. The life span is therefore one year. The authors tag 19 individuals with subcutaneous transponders and follow the feeding and copulatory behaviour, as well as growth, of 14 of these at various times during the study period.  Growth on a mixed diet of seaweeds is on average 5g per day and, in this particular population, peaks in June at an average live mass of 1100g (see graph). The species forms copulatory aggregations of up to 20-24 individuals that tend to occupy the same general area year-after-year (as found by other authors for A. californica).  At any given time up to 45% of individuals in the population may be copulaating.  Angeloni et al. 1999 Veliger 42: 1. Drawing courtesy Beeman 1963 Veliger 5: 145.

NOTE  for other details on the use of these microchip transponders for sea hares see  LEARN ABOUT NUDIBRANCHS & RELATIVES: COPULATION: APLYSIA & OTHER ANASPIDS

NOTE  in other areas of California, such as Elkhorn Slough, individuals may top out at live masses exceeding 10kg.  One individual of 14kg was 1m in length, making the species a good candidate for the largest gastropod in the world (however, other close candidates must be bailer and trochid shells collected from the Marianas Trench, shells so large that they require to be held in both arms). Note in the graph that the decrease in live mass of the population in late summer is not a "shrinking"; rather, it results from the older, larger individuals dying off. The authors provide some specific data on growth for tagged animals but, because they could not retrieve all individuals at regular intervals, the data are rather spotty and are not included here

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Research study 10
 

graph comparing natural abundance ratios of sea hares Aplysia californica and various food and non-food seaweedsNatural abundance ratio”, or the ratio of 13C/12C isotopes (=delta13C, expressed as ‰)  in a tissue, has been used in terrestrial and a few marine studies to define broadly the diets of herbivores, that is, the extent to which they have been feeding on C3-type or C4-type photosythesisers. Given the known wide range of isotopic ratios between different species of macroalgae and the fact that a consumer’s delta13C value is usually within ±2‰ of that of its food source, it should be possible to determine dietary selectivity in a marine herbivore by comparing isotopic ratios in available food species and the animal’s body tissues.  Fast-growing tissues like gonads will reflect the ratios of algae most recently eaten, while slow-growing tissues like muscles will be a composite of algae eaten over a longer time period. 

Results of a study on dietary specialisation in sea hares Aplysia californica at the Wrigley Institute for Environmental Studies, Santa Catalina Island, California, however, are mixed.  While the isotopic compositions of sea hares do NOT reflect those of their favoured red-algal foods Plocamium cartilagineum and Laurencia pacifica, as expected (see graph, all values differ significantly), those of individuals held in seawater tanks and fed diets of constant isotopic composition do exhibit delta13C values similar to their food (data not shown).  This is especially true for fast turnover tissue, such as muscle in actively growing juveniles or eggs in adults, where values are within ±2‰ of the algal diet, but not in muscle tissue of large adults, which presumably reflected the diet over several months (see graph lower Right, based on 14d of growth).  The author notes that the apparent absence of the favoured red-algal foods P. cartilagineum and L. pacifica from Aplysia’s diet may, in fact, reflect its almost complete absence from the habitat at the time of the study, possibly eaten up by the sea hares.  Korb 2003 J Mar Biol Ass UK 83: 501.

NOTE  plants differ in their contents of stable carbon isotopes depending on which photosynthetic type they are, either C3 or C4.  The ratio is expressed as delta13C in parts per thousand (‰).  Macroalgae have C3-type photosynthesis with d13C values ranging from -2.5 to -35‰ for different species

NOTE  the study is really a test of the efficacy of the technique in determining dietary specialisation of a marine-invertebrate herbivore.  However,if one wants to know what A. californica, specifically, is eating, it’s much easier and certainly more accurate to sample food directly from the crop.  However, the author does note that the isotope-ratio technique is essentially non-destructive, and it may have promise as a static technique for determining diets over long term 

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Research study 11
 

graph showing growth rates of juvenile sea hares Aplysia californica on diets with different contents of nitrogenBecause of its importance in nutrition, specifically, for production of proteins, content of nitrogen in a seaweed should be an important factor in determining its nutritional value to an herbivore.  This is tested by researchers at Harbor Branch Oceanographic Institution, Florida with juvenile sea hares Aplysia californica by feeding them on red seaweeds Gracilaria ferox containing differing levels of nitrogen.  By pulsing the seaweeds in culture with different amounts of nitrogen-containing compounds the researchers are able to create algae with high, medium, and low nitrogen contents.  Not only do test individuals significantly prefer to eat the nitrogen-enriched alga over the other 2 treatments, their growth over a 30d test period is significantly enhanced - by two-fold over the “medium”-N diet, and four-fold over the “low”-N diet.  Although the enrichment approach used in the study is familiar to seaweed biochemists, it represents a novel use in the study of sea-hare nutrition, and the authors should be complimented for bringing the technique to the attention of fellow scientists.  Barile et al. 2004 J Exp Mar Biol Ecol 303:  65.

NOTE  only the high and medium treatments involve N pulsing; the low treatment is simply Gracilaria grown in field seawater, but under full natural irradiance to promote growth and thus deplete N content.  The 2 nitrogen-enriched diets have carbon/nitrogen ratios less than 10, while the naturally grown seaweed has a C/N ratio > 20

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Research study 12
 

graph comparing growth and maturation of sea hares Aplysia californica at high and low culture temperatures in the laboratoryA study by researchers at the University of Miami provides useful data on growth, reproduction, and life span of Aplysia californica in laboratory culture.  Best performance overall is at a temperature of about 13oC where individuals live twice as long, grow 4 times as large, and spawn longer than at a temperature of about 18oC (see graph focussing on growth performance at these particular temperatures).  Other notable statistics include sexual maturation after about 245d at 13oC as compared with after about 201d at 18-20oC.  As predicted, lifespan is inversely correlated with temperature, while aging rate is highest for animals raised at the highest temperature of 21oC.   Regardless of temperature, A. californica has a lifespan of usually less than 1yr.  Stommes et al. 2005 Contemp Topics  44 (3): 31.

NOTE  the same researchers at the same facility provide other potentially useful data on effects of stocking density on growth, maturation, and reproductive output of laboratory-cultured A. californica, not presented here: Capo et al. 2002 Contemp Top Lab Anim Sci 41 (6): 18 and Capo et al. 2003 Contemp Top Lab Anim Sci 42 (5): 31

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Armina

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Research study 1
 

photograph of several opisthobranchs Armina californica eating a sea pen Ptilosarcus guernyi
In this photograph several Armina californica appear to be attacking a sea pen Ptilosarcus guernyi, which has withdrawn into the soil, but the diet of this species is not well known.
Photo courtesy Kevin Lee, Fullerton, California diverkevin.

 

 

 

 

 

 

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Cadlina

 

photograph of dorid nudibranch Cadlina luteomarginata eating sponge Pleraplysilla sp.A study at the Bamfield Marine Sciences Centre, British Columbia shows that Cadlina luteomarginata in Barkley Sound eats at least 10 species of sponges, with Clione californiana and Mycale sp. being most common.  Penney 2013 J Moll Stud 79: 64.

 

 

Cadlina luteomarginata eating a sponge Pleraplysilla sp. 2X

 

 

 

 

 

 

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Corambe (Doridella)

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Research study 1
  photograph of the nudibranch Corambe steinbergae on its host bryozoan Membranipora sp.Corambe (Doridella) steinbergae feeds on zoids of bryozoans Membranipora membranacea growing on kelp blades.  An individual Doridella of 2-4mm body length will consume an average of 27 zooids per day at 13oCYoshioka 1986 Mar Ecol Progr Ser 31: 179. Photo courtesy Clinton Bauder, California and seaslugforum.
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Research study 2
  Observation of Corambe steinbergae in San Juan Islands, Washington provides this description of feeding.  The nudibranch approaches a zooecium of Membranipora, presses its mouth against the frontal membrane, and forms a seal with its lips.  The radula then creates a slit in the frontal membrane of the zooecium and the predator sucks out the soft parts using its buccal pump.  The radula does not extend far into the body cavity of the zooecium.  McBeth 1968 Veliger 11: 145.
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Research study 3
 

histograms showing distribution of prey Membranipora sp. colonies on the fronds of Laminaria saccharina and the positions of predatory nudibranchs Corambe steinbergae on the same frondsdiagram showing sampling quadrats for Membranipora sp. on the frond of a brown alga Laminaria saccharina
Studies in at Friday Harbor Laboratories, Washington show that a single surface of a 90cm kelp frond Laminaria saccharina in summer may host as many as 238 individual Corambe steinbergae. The figure above shows fourteen 5x5cm sampling quadrats that the researcher uses to assess densities and % cover of predator and prey. 

The data show that colonies of the nudibranch’s preferred prey Membranipora spp. are distributed fairly evenly along the length of the fronds, with highest densities of zooids being at the distal, or older, ends (top histogram). The nudibranchs are distributed on the kelp in almost direct proportion to the percentage cover of Membranipora colonies (compare middle and bottom histograms on Right). The author queries as to how such high densities of Corambe can be maintained, and whether food might be a limiting factor.  Counts of Membranipora colonies show that each Laminaria frond surface bears 386,000 zooids which, during the July-August study period, would produce 22,000 new zooids per day.  Thus, each of the 238 Corambe would theoretically have 92 zooids available each and every day as food.  While adult-sized Corambe (6mm body length) will eat as many as 150 zooids per day in the lab, the fact that many of the 238 individuals counted are less than 1mm in length, suggests that this level of food provision would be more than ample to sustain the population.  Seed 1976 J Exp Mar Biol Ecol 24: 1.

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Research study 4
 

scanning electron microscopic view of the colony edge of a bryozoan Membranipora sp.
The presence of Corambe steinbergae on or near a colony of its principal food, the bryozoan Membranipora membranacea, stimulates the prey species to grow defensive spines, both at the corners of individual zoecia and along their frontal membranes. The spine-inducing substance is water-soluble and spines develop within 48h of exposure.  The authors note that the spines deter feeding by Corambe, although obviously not with 100% effectiveness (see Research Study 3 above). Do spines form only in response to Corambe, or only to predators of Membranipora, or perhaps to all nudibranch species? 

Tests at Friday Harbor Laboratories, Washington of spine-inducing potential of 14 nudibranch species, including ones known to prey on Membranipora (for example, Corambe steinbergae, Triopha catalinae, and Onchidoris muricata) and ones known to eat other prey species, reveal that only C. steinbergae consistently induces spines to form.  Spines are never induced by Dialulasandiegensis, Dendronotus frondosus, D. diversicolor, Tritonia festiva, Flabellina trilineata, or Hermissenda crassicornis, but some other supposedly “benign” species do induce spines to form.  No phylogenetic pattern exists.  The authors conclude that M. membranacea often produces spines in response to predators that are deterred by spines, but seems surprisingly responsive to cues from some benign species.  Iyengar & Harvell 2002 Mar Ecol Progr Ser 225: 205; photo of spines from Harvell 1992 Ecology 73: 1567.

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Crimora

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Research study 1
 

photograph of
photograph of a nudibranc Crimora coneja eating a bryozoan Hincksina sp. courtesy Jeff Goddard, U C Santa Barbara, CaliforniaCrimora coneja is a rarely seen relative of Triopha species.  In the Punta Gorda region of northern California it apparently subsists on the encrusting bryozoan Hincksina minuscula.  Goddard 1987 Veliger 29: 267. Photos courtesy Jeff Goddard, UC Santa Barbara, California and seaslugforum.

 

 

 

Crimora eating the bryozoan Hincksina.
The inset shows empty zoecia after
Crimora
has finished with them

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Cuthona

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Research study 1
 

photograph of the nudibranch Cuthona divae eating hydroids Hydractinia spp. courtesy Jeff Goddard, Santa Barbara, CaliforniaIn the Punta Gorda region of northern California Cuthona divae preys mainly on hydroids Hydractinia spp.  Goddard 1987 Veliger 29: 267. Photo courtesy Jeff Goddard, Santa Barbara, California and seaslugforum.

 

 

 

 

OTHER HYDROID-EATING WEST-COAST AEOLIDS:

 

photograph of nudibranch Flabellina verrucosa crawling on a hydroid
Flabellina verrucosa crawling on, and likely feeding on, an unknown species of hydroid 1X

photograph of a nudibranch Doto columbiana crawling on its prey hydroid Aglaeophenia sp.  courtesy Jeff Goddard, Santa Barbara, California
Doto columbiana on its prey hydroid Aglaeophenia sp. 9X. Photo courtesy Jeff Goddard, Santa Barbara, California
photograph of an aeolid nudibranch Flabellina picta eating hydroids Eudendrium spp. courtesy Bruce Wight, California
Flabellina picta eats Tubularia spp. & Eudendrium spp. 2X. Photo courtesy Bruce Wight, CA and seaslugforum
photograph of several aeolid nudibranchs Flabellina triophina eating a large solitary hydroid courtesy Kevin Lee, Fullerton, California
2 or 3 Flabellina triophina eating a large solitary hydroid 0.5X. Photo courtesy Kevin Lee, Fullerton diverkevin
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