Development of the gooseneck barnacle Pollicipes polymerus (Cirripedia: Lepadomorpha): Fertilization through settlement

Pollicipes polymerus (Sowerby, 1833) is a common barnacle in rocky intertidal zones of the West Coast of North America whose development has been previously undescribed in detail. In the present study, certain aspects of the development of P. polymerus are recorded from fertilization through settlement. In vitro fertilization has been accomplished using already-implanted sperm plus ovulating eggs and oviducal gland fluid. The eggs are small (about 100 μ diameter at fertilization; 90 x 140 μ at first cleavage) and somewhat yolky. Embryos obtained from brooding adults and from in vitro fertilization were reared in glass dishes until hatching. Cleavage was total, asynchronous and unequal. Division of the D macromere lagged behind division of the other blastomeres, and gastrulation occurred by epiboly so that blastoderm surrounded the macromeres. The nauplii hatched an average of 25.4 days (range was 20.3 to 30.1 days) after fertilization, and molted within 1 day to Stage II nauplii. From Stages II through VI the nauplii required food. As they grew from stage to stage, the number of setae per appendage increased. Nauplii have feathery and hispid-type setae, previously described only in Chthamalus aestuarii. In contrast to other pedunculate larvae which have been described, P. polymerus nauplii are small and have specialized feathery setae. Cypris-larva settlement was stimulated only when healthy adult peduncles were available, thus showing an affinity for its own species.     

Effects of settlement density on spatial arrangement in four intertidal barnacles

Balanus amphitrite was studied in an estuary (Halifax River) in central Florida from October to November 1990, while three other barnacle species were studied on the central coast (Monterey Bay) of California from April 1988 to July 1989. Mean nearest-neighbor distances indicated that in the majority of cases the spatial arrangement of settlers was random for three different balanomorph barnacles-B. amphitrite, B. glandula, and Chthamalus dalli. In Pollicipes polymerus, a lepidomorph species, strong aggregation among settlers was almost always observed. In the three balanomorph species there was no apparent relationship between settler density and the degree of aggregation. In P. polymerus there was a significant positive correlation between settler density and the degree of aggregation. Morphological differences between balanomorph and lepidomorph barnacles may influence the evolution of settlement behavior.     

Thermal tolerance of larvae of Pollicipes elegans, a marine species with an antitropical distribution

For the antitropical gooseneck barnacle Pollicipes elegans, population-specific physiological temperature tolerance of larvae may serve as a barrier to larval dispersal across the warmest regions of the tropical Pacific Ocean. Thermal tolerance ranges of larvae of three different populations of P. elegans sampled in 2011 and 2012 (Mexico [MX], El Salvador [ES], and Peru [PE]) were investigated by measuring three indicators of physiological performance: swimming activity, oxygen consumption, and lethality or LT₅₀. The thermal tolerance profiles, which include measurable optimum (maximum aerobic performance), pejus (“getting worse”) and pessimum (worst aerobic performance) ranges, of larvae from the three populations were consistent with their characteristic environmental temperatures. In MX, larvae live close to the upper border of their optimum during warm months and so have a limited capacity to tolerate higher-than-normal temperatures. Larvae from the ES population likewise appear to live within their optimum temperature range, but these larvae lack a detectable pessimum range, suggesting they would be unable to cope with temperatures above their pejus range. Larvae from PE have a broad optimum but no pejus range. Different thermal tolerance ranges provide strong evidence for population-dependent physiological adaptations in P. elegans. For the southern (PE) and northern (MX) P. elegans populations, high tropical temperatures are likely to be a strong direct physiological barrier to larval survival and dispersal, which is in contrast to the more thermally tolerant ES population.     

Effects of algal and larval densities on development and survival of asteroid larvae

Effects of larval and algal culture density and diet composition on development and survival of temperate asteroid larvae were studied in the laboratory at Santa Cruz, California, USA, during summer and fall of 1990. Larvae of Asterina miniata were reared at two densities, 0.5 or 1.0 ml^-1, and fed one or two species of cultured phytoflagellates — Dunaliella tertiolecta alone or mixed with Rhodomonas sp. — at three concentrations of 5x10², 5x10³, and 5x10⁴ total cells ml^-1. Algal concentration strongly influenced larval development; however, larval density also had a marked effect. Development progressed further with increasing algal concentration. Larval growth and differentiation were sometimes uncoupled; i.e., growth measures were directly related to food level, while differentiation indicators were less so. At the lowest food level, growth was negative and differentiation was arrested at early precompetent stages; these larvae never formed juvenile rudiments or brachiolar attachment structures. Development times of larvae given more food ranged from 26 to 50 d and depended directly on food availability. Development time to metamorphosis at the highest food concentration was similar for siblings fed D. tertiolecta alone or mixed with Rhodomonas sp. In contrast, when food level was an order of magnitude lower, larvae fed the algal mixture metamorphosed significantly earlier than larvae fed the unialgal diet. This suggests interactive effects of food quantity and food quality. Survival was little affected by larval or food density, except at the lowest ration. Feeding experiments in well-controlled laboratory conditions are useful to predict and compare the physiological or developmental scope of response of larvae to defined environmental factors; however, results from such studies should not be extrapolated to predict rates and processes of larval development in nature.     

Inhibition of attachment of larval barnacles,Balanus amphitrite,by bacterial surface films

Films of bacteria on solid substrata can positively or negatively influence the attachment of marine invertebrate larvae. Effects of marine bacteria on the attachment of cypris larvae of the barnacle Balanus amphitrite Darwin were examined in the laboratory. Bacteria, grown to mid-exponential phase and allowed to adsorb irreversibly to polystyrene petri dishes, attached in densities of 10⁷ cells cm^-2. Assays (22h) were used to compare the effects of adsorbed cells of 18 different bacterial species on larval barnacle attachment. Most of the adsorbed bacteria either inhibited or had no effect on larval attachment compared to clean surfaces. Experiments testing the effect of larval age on barnacle attachment were conducted with six species of bacteria and showed that older larvae attached in higher percentages to clean surfaces and that bacterial films generally inhibited larval attaschment. Both the species of bacteria and the in situ age of the adsorbed bacteria affected barnacle attachment response: older films of Deleya (Pseudomonas) marina were more inhibitory. Bacterial extracellular materials may be involved in the inhibitory process.     

Effects of limiting access to prey on development of first zoeal stage of the brachyuran crabs Cancer magister and Hemigrapsus oregonensis

We tested the influence of limiting access to prey on larval development of the crabs Cancer magister and Hemigrapsus oregonensis by raising their Stage 1 larvae in the laboratory on different prey densities and with various periods of access to prey. Experiments were conducted in 1995 and 1996 at the Shannon Point Marine Center in Anacortes, Washington, USA. Our results show that crab larvae do not require continuous access to prey for optimal development nor do they appear to require light for prey capture. Survival and duration of Stage 1 C. magister fed continuously on only one-fourth the amount of the control density of prey and those fed at the control density for only 6 h per day were the same as for larvae fed continuously at the control density (20 ml⁻¹). Larvae with cyclic access to prey at the control density for 24 h and then starved for 72 h showed significantly lower survival and longer instar duration to Stage 2. Experiments on Stage 1 H. oregonensis which investigated a combination of prey density, period of access to prey and light/dark conditions during feeding revealed that survival decreased with decreasing prey density or with decreasing feeding period, but no differences were observed during periods of limited prey availability as a function of light or dark conditions. Stage duration was not affected by reduced prey density nor by the light/dark condition at the time of feeding, but it was prolonged when the period of access to prey was limited. The period of access to prey did not affect the weight of Day 1 Stage 2 larvae. Larvae fed high densities of prey for 4 h followed by 20 h of reduced-density diet exhibited the same survival and stage duration as controls that were continuously fed high-density prey. Our results define sub-optimal diets that can be used experimentally to determine the nutritional contributions made by naturally-occurring prey organisms during larval development in the two species. In nature, larvae may satisfy nutritional requirements through periodic encounters with dense prey patches during vertical migrations by day or night. Received: 12 August 1997 / Accepted: 5 February 1998     

Relationship between larval and juvenile growth rates in two marine gastropods,Crepidula plana and C. fornicata

Previous studies on various marine mollusc species have shown that both larval and juvenile growth rates are substantially heritable, but few workers have examined the extent to which larval and juvenile growth rates covary. We examined the relationship between larval and juvenile growth rates in seven laboratory experiments conducted between 1986 and 1993, using the prosobranch gastropods Crepidula plana Say and C. fornicata (L.). In most experiments larvae were reared individually, measured twice nondestructively to determine larval grwoth rate, allowed or stimulated (daily 5-h exposure to 20 mM excess K⁺ in seawater) to metamophose, and then measured at least twice after metamorphosis to determine juvenile growth rates. Generally, there was no significant (p >0.10) relationship between larval and juvenile growth rates, suggesting that in these two species selection can act independently on the two stages of development. A positive correlation (p=0.007) between larval and juvenile growth rates was observed for C. fornicata in one experiment, but only for offspring from females maturing the most rapidly in laboratory culture. Even for these larvae, however, variation in larval growth rate explained<2% of the variation in juvenile growth rate, so that larval and juvenile growth rates are at most only weakly associated in this species.     

Developmental physiology of Antarctic asteroids with different life-history modes

Rates of respiration and protein synthesis were measured during embryonic and larval development of Antarctic asteroids with different life-history modes (non-feeding and feeding larvae: Acodontaster hodgsoni, Porania antarctica, Odontaster meridionalis). Patterns of respiration for these species all show an increase during embryogenesis, with subsequent maintenance of routine respiration (“starvation resistance”), even in the absence of food for ~4 months (O. meridionalis). Fractional rates of protein synthesis (i.e., rate per unit mass of whole-body protein content) in the Antarctic larvae are essentially identical to those of temperate species. Larvae of O. meridionalis had an average fractional synthesis rate of 0.52% ± 0.05 h⁻¹ at −1.0°C, which is comparable to the temperate asteroid Asterina miniata at 0.53% ± 0.14 h⁻¹ at 15°C. For embryos of the asteroids A. hodgsoni and P. antarctica, fractional rates of protein synthesis (~0.2% h⁻¹) also are comparable to those reported for embryos of temperate echinoderm species. While rates of synthesis are high, rates of protein deposition are relatively low (percent of protein synthesized that is retained for growth). During a ~4 month growth period for larvae of O. meridionalis, the average protein depositional efficiency was 5.2%. This contrasts with higher rates of depositional efficiency reported for similar developmental stages of temperate echinoderm species. The biological significance of maintaining high rates of macromolecular synthesis for species with low rates of cell division and low protein depositional efficiencies is intriguing in the context of understanding the mechanistic bases of extended life spans and dispersal potential in response to changing Antarctic environments.     

Size regulation in larvae of the crustacean Balanus eburneus (Cirripedia: Thoracica)

We tested the hypothesis that larval size in the acorn barnacle Balanus eburneus Gould (Cirripedia Thoracica) varies in relation to food availability. In March–November 1980, and March–July 1981, larvae were obtained from adult Balanus eburneus collected in the Newport River, North Carolina, USA. Carapace length and width of larvae reared at three different food concentrations were measured. Mean naupliar instar size was independent of food concentration. Mean size of the cypris instar increased with increasing food level. Greater cypris size could be attributed to increased food reserves in the preceding naupliar stage, and was coinciden with inmarked increase in metamorphic success. Variation in instar size remained constant or declined during naupliar development, but increased sharply at the molt to the cyprid. Naupliar size regulation involved: (1) conservation of a molt increment specific for each naupliar-naupliar molt, (2) an inverse relationship between premolt size and the molt increment during the first five naupliar instars, and (3) an increase in the precision of the molt increment at the molt to the sixth naupliar instar. Experimental evidence implies that size regulation in Balanus eburneus limits variation about a fixed final naupliar size (e.g. volume). Measurement of naupliar size, accumulated energy reserves, survival and development time, and cypris metamorphic success indicated that naupliar cuticular growth is the most conservative feature of larval development. The data suggest that maximum naupliar size is limited by escalating metabolic costs during development, while minimum naupliar size is limited by size-related feeding effectiveness.     

Recruitment in the intertidal limpet Lottia digitalis (Patellogastropoda: Lottiidae) may be driven by settlement cues associated with adult habitat

The ribbed limpet, Lottia digitalis, is found high in rocky intertidal habitat throughout its geographic range. In order to identify likely natural settlement locations for larvae of this species, laboratory-reared larvae were settled onto substrata collected from within and near an adult L. digitalis habitat. Of larvae exposed to rock chiseled from within high-intertidal adult habitat, 31.0% and 23.3% underwent metamorphosis during two separate experiments. Similarly, an unidentified filamentous green alga that was isolated from this rock induced metamorphosis in 26.6% and 8.7% of larvae during additional experiments. In contrast, larvae did not metamorphose upon bare rocks or upon rocks encrusted with a crustose corraline alga (CCA) that were collected from lower intertidal zones, nor did they metamorphose upon the macroalgae Ulva sp., Enteromorpha contorta, Alaria marginata, or Polysiphonia sp. The presence of mucus from adult conspecifics during these experiments did not enhance metamorphosis onto rock taken from adult habitat, but it did induce metamorphosis in an average of 13.5% and 7.0% of larvae introduced to the mid-intertidal bare rock and CCA substrata, respectively. Finally, 38.0% and 34.4% of larvae from two experiments underwent metamorphosis when exposed to the high-intertidal barnacle Pollicipes polymerus. These results suggest that larval settlement, rather than differential post-settlement mortality and/or migration, drives recruitment of L. digitalis in high-intertidal habitats.     

Feeding by larvae of intertidal invertebrates: assessing their position in pelagic food webs

One of the leading determinants of the structure and dynamics of marine populations is the rate of arrival of new individuals to local sites. While physical transport processes play major roles in delivering larvae to the shore, these processes become most important after larvae have survived the perils of life in the plankton, where they usually suffer great mortality. The lack of information regarding larval feeding makes it difficult to assess the effects of food supply on larval survival, or the role larvae may play in nearshore food webs. Here, we examine the spectrum of food sizes and food types consumed by the larvae of two intertidal barnacle species and of the predatory gastropod Concholepas concholepas. We conducted replicated experiments in which larvae were exposed to the food size spectrum (phytoplankton, microprotozoan and autotrophic picoplankton) found in nearshore waters in central Chile. Results show that barnacle nauplii and gastropod veligers are omnivorous grazers, incorporating significant fractions of heterotrophs in their diets. In accordance with their feeding mechanisms and body size, barnacle nauplii were able to feed on autotrophic picoplankton (<5 microm) and did not consume the largest phytoplankton cells, which made the bulk of phytoplankton biomass in spring-summer blooms. Balanoid nauplii exhibited higher ingestion rates than the smaller-bodied chthamaloid larvae. Newly hatched C. concholepas larvae also consumed picoplankton cells, while competent larvae of this species ingested mostly the largest phytoplankton cells and heterotrophic protozoans. Results suggest that persistent changes in the structure of pelagic food webs can have important effects on the species-specific food availability for invertebrate larvae, which can result in large-scale differences in recruitment rates of a given species, and in the relative recruitment success of the different species that make up benthic communities.     

Comparative larval development of the shipworms Bankia gouldi and Teredo navalis

Larvae of Bankia gouldi (Bartsch) and Teredo navalis L. were reared in the laboratory at various temperatures and salinities. T. navalis spawned at lower temperatures than B. gouldi. T. navalis larvae were released at temperatures from 13° to 30°C; in B. gouldi, spawning occurred from 17.5° to 30°C. Both species released offspring at salinities of 20 and 30‰. Larvae of the two species can be distinguished morphometrically at the earliest pelagic veliger stage and in the pediveliger stage. Average dimensions of newly released T. navalis larvae are 88 x 75 μ (length x height), while the youngest B. gouldi veligers measure 61 x 50 μ. Pediveligers of T. navalis (205 x 239 μ) are smaller than those of B. gouldi (221 x 260 μ). At other stages of larval development the two species appear so similar that they cannot yet readily be distinguished. Under laboratory conditions of 25°C and 30 ‰, the free-swimming life of B. gouldi to the pediveliger stage was about 10 days longer than that of T. navalis (25 and 15 days, respectively). Incubated larval development of T. navalis was estimated to be 5 days at 25°C. Potential competition between larval stages of the two species, and modification of settling behavior by dissolved humic material (Gelbstoff), is discussed.     

RNA-DNA ratio: an index of larval fish growth in the sea

Data on water temperature, RNA-DNA ratio, and growth of eight species of temperate marine fish larvae reared in the laboratory were fit to the equation: $$G_{pi} = 0.93{\text{ }}\operatorname{T} + 4.75{\text{ RNA - DNA}} - 18.18$$ where G_pi is the protein growth rate in % d^-1 and T is the water temperature. Water temperature and larval RNA-DNA ratio explained 92% of the variability in growth rate of laboratory-reared larvae. The model is useful over the entire range of feeding levels (starvation to excess), temperatures (2° to 20°C) and fish species studied. Estimates of recent growth of larval cod, haddock, and sand lance caught at sea based on water temperature and RNA-DNA ratio ranged from negative to 26% d^-1. These data demonstrate the importance of food availability in larval fish mortality and suggest that short-term growth under favorable conditions may be considerably higher than expected from long-term indicators. RNA-DNA ratio analysis offers new possibilities for understanding larval growth and mortality, and their relation to environmental variability.     

Characteristics of feeding on dinoflagellates by newly hatched larval crabs

The zoeal larvae of brachyuran crabs must feed soon after hatching on a diet that includes large micro- and mesozooplankton in order to satisfy nutritional requirements. However, newly hatched larvae have been shown to ingest a variety of dinoflagellates, perhaps using microbial carbon sources to sustain them until they encounter more favored prey. Ingestion of dinoflagellates by larval crabs has been documented previously under conditions in which the larvae were exposed to algae provided in monoculture or in defined mixtures of cells. We report here on experiments conducted on the hatching stage of five crab species to determine if ingestion of dinoflagellates occurred when they were provided in combination with Artemia sp. nauplii or after a period of feeding on mesozooplankton. Quantitative measurements of chl a in the larval guts provided evidence of ingestion of algal cells. Active ingestion of the dinoflagellate Prorocentrum micans at specified intervals during an extended feeding period was determined on larvae of two crab species using fluorescently labeled cells provided for brief periods at prescribed time intervals. Stage 1 larvae of four of the five crab species ingested dinoflagellates when they were provided in combination with nauplii and larvae of all five species ingested cells after feeding solely on nauplii for 24 h. Ingestion of algal cells was first evident in the larval guts after 6 h of feeding at both low (200 cell ml⁻¹) and high (1,000 cells ml⁻¹) prey densities. Higher prey densities resulted in higher gut chl a. Larvae continuously exposed to dinoflagellates actively ingested cells at every 3 h interval tested over a 36 h period. Results confirm previous studies that larvae will ingest dinoflagellates even when they are encountered in a mixed prey field or when having previously fed. Ingestion of cells may occur on a continual basis over time.     

Decreased pH does not alter metamorphosis but compromises juvenile calcification of the tube worm Hydroides elegans

Using CO₂ perturbation experiments, we examined the pre- and post-settlement growth responses of a dominant biofouling tubeworm (Hydroides elegans) to a range of pH. In three different experiments, embryos were reared to, or past, metamorphosis in seawater equilibrated to CO₂ values of about 480 (control), 980, 1,480, and 2,300 μatm resulting in pH values of around 8.1 (control), 7.9, 7.7, and 7.5, respectively. These three decreased pH conditions did not affect either embryo or larval development, but both larval calcification at the time of metamorphosis and early juvenile growth were adversely affected. During the 24-h settlement assay experiment, half of the metamorphosed larvae were unable to calcify tubes at pH 7.9 while almost no tubes were calcified at pH 7.7. Decreased ability to calcify at decreased pH may indicate that these calcifying tubeworms may be one of the highly threatened species in the future ocean.     

Essential fatty acid (docosahexaenoic acid, DHA) availability affects growth of larval herring in the field

Larval fish growth and survival depends not only on prey quantity, but also on prey quality. To investigate effects of prey fatty acid concentration on larval herring growth, we collected different prey organisms and larval herring (Clupea harengus L.) in the Kiel Canal during the spring season of 2009. Along with biotic background data, we analysed fatty acids both in prey organisms and in the larvae and used biochemically derived growth rates of the larvae as the response variable. Larval herring reached their highest RNA/DNA derived growth rates only at high docosahexaenoic acid (DHA) concentration. When the ratio of copepodids to lesser quality cirriped nauplii was low, larval growth and larval DHA concentration were both significantly negatively affected. This was true even as prey abundance was increasing. This finding indicates that even in mixed, natural feeding conditions, growth variations are associated with DHA availability in larval fish.     

Physiological development of brooded larvae from two pocilloporid corals in Taiwan

In southern Taiwan, brooded larvae of Pocillopora damicornis and Seriatopora caliendrum are released year-round in synchrony with new moons, and each larval release occurs over multiple days. Using P. damicornis and S. caliendrum as a model system, we describe within-brood variation in larval phenotypes and test for release-day effects that influence larval performance in the pelagic phase. Research was conducted in 2010 using larvae from corals collected in June and July from Nanwan Bay (21°56.179??N, 120°44.85??E). In June, larval phenotypes of both species were characterized immediately following release, and their competency to settle assessed. In July, larvae of P. damicornis were collected on 3?days over the peak release period and incubated for 7?C11?days at 28.0?°C and 320???mol?quanta?m^?2?s^?1; their phenotypes and settlement competency were measured every 2?days. P. damicornis larvae released close to peak release were 1.6 times larger in size, contained twice the number of Symbiodinium larva^?1, and were 44?% more likely to settle in the first 24?h than larvae released early in the brood. In addition, peak-release larvae respired at a lower rate than larvae released late in the brood. Similarly, S. caliendrum larvae released close to peak release were 1.4 times larger in size and were 33?% more likely to settle in the first 5?h than larvae released early in the brood. In July, P. damicornis larvae differed between early (2?days prior to peak), peak, and late (2?days after peak) release. Protein content of early-release larvae was lower than peak- and late-release larvae, and this difference persisted throughout the development. Further, release day affected the way larval respiration varied throughout development. By showing that brooded coral larvae differ between release days and display maternal effects influencing performance in the swimming phase, our results suggest that pocilloporid corals utilize bet-hedging to increase reproductive success.