Foraging Behavior under Starvation Conditions Is Altered via Photosynthesis by the Marine Gastropod, Elysia clarki

It has been well documented that nutritional state can influence the foraging behavior of animals. However, photosynthetic animals, those capable of both heterotrophy and symbiotic photosynthesis, may have a delayed behavioral response due to their ability to photosynthesize. To test this hypothesis we subjected groups of the kleptoplastic sea slug, Elysia clarki, to a gradient of starvation treatments of 4, 8, and 12 weeks plus a satiated control. Compared to the control group, slugs starved 8 and 12 weeks displayed a significant increase in the proportion of slugs feeding and a significant decrease in photosynthetic capability, as measured in maximum quantum yield and [chl a]. The 4 week group, however, showed no significant difference in feeding behavior or in the metrics of photosynthesis compared to the control. This suggests that photosynthesis in E. clarki, thought to be linked to horizontally-transferred algal genes, delays a behavioral response to starvation. This is the first demonstration of a link between photosynthetic capability in an animal and a modification of foraging behavior under conditions of starvation

Uptake of Dissolved Organic-Matter by Larval Stage of the Crown-of-Thorns Starfish Acanthaster Planci

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particulate food. It has been proposed, however, that particulate food (e.g. microalgae) is scarce in tropical water columns relative to the nutritional requirements of the larvae of A. planci, and that periodic shortages of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requirements of the larval development of A, planci as well. The present study addresses the ability of A, planci larvae to take up several DOM species and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and antarctic waters. Transport rates (per larval A, planci) increased steadily during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. Maximum transport rates (J(max)(in)) for alanine increased from 15.5 pmol larva(-1) h(-1) (13.2 pmol mu g(-1) h(-1)) for gastrulas (J(max)(in) = 38.7 pmol larva(-1) h(-1) or 47.4 pmol mu g(-1) h(-1)) to 35.0 pmol larva(-1) h(-1) (13.1 pmol mu(-1) h(-1)) for early brachiolaria (J(max)(in) just prior to settlement = 350.0 pmol larva(-1) h(-1) or 161.1 pmol mu g(-1) h(-1)) at 1 mu M substrate concentrations. The instantaneous metabolic demand for substrates by gastrula, bipinnaria and brachiolaria stage larvae could be completely satisfied by alanine concentrations of 11, 1.6 and 0.8 mu M, respectively. Similar rates were measured in this study for the essential amino acid leucine, with rates increasing from 11.0 pmol larva(-1) h(-1) (or 9.4 pmol mu g(-1) h(-1)) for gastrulas (J(max)(in) = 110.5 pmol larva(-1) h(-1) or 94.4 pmol mu g(-1) h(-1)) to 34.0 pmol larva(-1) h(-1) (or 13.0 pmol mu g(-1) h(-1)) for late brachiolaria (J(max)(in) = 288.9 pmol larva(-1) h(-1) or 110.3 pmol mu g(-1) h(-1)) at 1 mu M substrate concentrations. The essential amino acid histidine was transported at lower rates (1.6 pmol mu g(-1) h(-1) at 1 mu M for late brachiolaria). Calculation of the energy contribution of the transported species revealed that larvae of A, planci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from external concentrations of 1 mu M of glucose, alanine, leucine and histidine, respectively. These data demonstrate that a relatively minor component of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and development of A. planci during larval development

Ecological and Physiological Differences Between 2 Color Morphs of the Coral Pocillopora-Damicornis

Pocillopora damicornis (Linnaeus) is a ubiquitous branching coral found throughout the Indo-Pacific region. Like many other species of coral, P. damicornis displays a large range of morphologies. At One Tree Island, it occurs as two distinct morphs that are easily distinguished by the presence or absence of pink pigmentation. The two colour morphs of P. damicornis were found to differ in their distribution and abundance in the One Tree Island Lagoon. The brown morph was more abundant than the pink morph in the shallows (3 m). The two morphs also differed physiologically. The brown morph tended to have a greater calcification rate than the pink morph, regardless of environmental conditions. However, the difference in the calcification rate between the two morphs became non-significant under shaded conditions (5% full sunlight), indicating some degree of physiological plasticity of the morphs. The pink colour in P. damicornis was due to a hydrophilic pigment with a major peak absorbance at 560 nm. The expression of pink pigment had both genetic and phenotypic components. The brown morph has a reduced genetic capacity to express the pigment relative to the pink morph. On the other hand, pigment expression could be induced by light in the pink morph. Although genetic differences ultimately determine the differences between the two morphs of P. damicornis, the extent of pigment expression is under some degree of environmental influence

Effects of egg size on postlarval performance: Experimental evidence from a sea urchin

Many life-history and developmental studies of marine invertebrates assume that eggs of species with nonfeeding larvae are large because they provide materials for rapid development. Using the sea urchin Heliocidaris erythrogramma which has 400 mu m eggs and nonfeeding larvae, we removed an acellular, lipid-rich component from the blastula equivalent to ca. 40% of the egg volume and ca. 50% of the organic mass. Experimentally manipulated, reduced-lipid larvae survived well, developed in the usual time (3.5 d), and high percentages of the original numbers metamorphosed into anatomically normal juveniles. Control juveniles were larger at metamorphosis, grew more, and survived longer than siblings that lacked this lipid-rich material. Moderate increases in egg size in species with nonfeeding larvae may enhance postlarval performance significantly and therefore may reflect selection on early juvenile traits. The contrasts of our results and comparable experiments with feeding larvae suggests that egg size may play fundamentally different roles in species with feeding and nonfeeding larvae. The accommodation of materials reserved for the juvenile stage should be considered among hypotheses on evolutionary modification of developmental patterns

Host-Zooxanthella Interactions in 4 Temperate Marine Invertebrate Symbioses - Assessment of Effect of Host Extracts On Symbionts

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