Reproduction in Anthelia glauca (Octocorallia: Xeniidae). I. Gametogenesis and larval brooding

Anthelia glauca Lamarck, 1816 is a gonochoric, external-brooding soft coral found in KwaZulu-Natal. It is reproductively active in the summer months. The development of gametes produced in late summer is arrested in winter. Several stages of gametes are found at the base of the polyps, and female polyps produce several cycles of larvae over an extended breeding period of 4 to 5 months. Larvae are brooded in a unique pharyngeal brooding pouch not yet described in other coral species. The brood pouch consists of an expansion of the pharynx with constrictions proximal and distal to the embryos and larvae. Our data suggest that egg transfer and fertilization occur at full moon and the mature larvae are released after new moon. Zooxanthellae are absent in A. glauca oocytes, but zooxanthella infestation commences at the immature larval stage. Received: 15 July 1997 / Accepted: 12 March 1998     

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far. Received: 7 May 1995 / Accepted: 19 November 1997     

Intracolonial behavioral variation in worker oviposition,oophagy, and larval care in queenless honey bee colonies

Summary Two experiments were performed to determine whether worker reproduction in queenless honey bee colonies is influenced by colony genetic structure. In Experiment 1, allozyme analyses of workers and worker-derived drone larvae revealed that in half the colonies, there were genotypic differences in worker egg-laying behavior (presumed to involve actual oviposition), but biases in drone production were not always consistent with biases in egg-laying behavior. In Experiment 2, allozyme analyses again revealed intracolonial differences in egg-laying behavior and in behavior patterns thought to involve oophagy and larval care. Data support the hypothesis of a genetic influence on this intracolonial behavioral variation. Differences in the genotypic distributions of worker-derived drones relative to workers engaged in oviposition behavior in queenless colonies may be a consequence of genetic variability for egg production or for treatment of eggs and larvae (possibly coupled with kin recognition), or both. Offprint requests to: G.E. Robinson     

On living in cold water: K-strategies in antarctic benthos

Comparison of the life-histories of two species pairs of caridean decapods, each pair containing a polar and a more temperate-water species (Chorismus antarcticus (Pfeffer, 1887)/Pandalus montagui Leach, 1814 and Notocrangon antarcticus (Pfeffer, 1887)/ crangon crangon (Linnaeus, 1758), suggested that in each case the polar species was more of a K-strategist than was the temperate species. In particular there were striking differences in brood size, egg weight and maturity of the newly hatched larvae. Measurements of individual annual reproductive effort, RE, as g fresh weight eggs per g fresh weight female indicated that in both species pairs the RE of the polar K-strategist was significantly less than that of the comparable temperate water r-strategist. Results expressing RE as g total egg lipid per g fresh weight female were equivocal. These data are discussed in relation to available autecological information for Anterctic marine invertebrates and it is concluded that many features of the polar benthos are explicable in terms of a general evolution of typical K-strategies. The role of low temperature in the widespread evolution of K-strategies may be crucial; consideration of this leads to a re-appraisal of cold-adaptation.     

Intra- and interannual variability in the larval fish assemblage off Gran Canaria (Canary Islands) over 2005–2007

The present study provides the longest and most intensive plankton and larval fish seasonal variability analysis in the Canary Islands and forms a basis for understanding life cycle scheduling and interactions among species, as well as the potential variability in transport processes of early life stages. Larval fish assemblages were studied weekly at Gran Canaria Island, Canary Islands, from January 2005 to June 2007, which represented two contrasting hydrological and biological periods. The former year was characterized by lower temperature and salinity that increased through 2006 and 2007. In contrast, chlorophyll concentration and mesozooplankton biomass decreased through the same period, especially when only the late winter bloom period was evaluated. However, ichthyoplankton abundance did not exhibit any clear pattern, as larger values were observed during 2006. The larval fish community of this oceanic island, located near the NW African upwelling, was composed of both neritic and oceanic taxa. Two families accounted for almost half of the collected larvae: Clupeidae (21.9%) and Myctophidae (20.5%). Although total larval concentration did not exhibit any seasonal peak linked to changes in zooplankton, the ichthyoplankton composition gradually changed during the year due to the high diversity and extended spawning periods of the fish species represented in samples. “Winter” and “summer” larval assemblages were identified, corresponding to the mixing and stratification periods of the water column, respectively. These assemblages were characterized by changes in the contribution of the most abundant annual taxa (Sardinella aurita, Cyclothone braueri, Ceratoscopelus spp. and Gobids) and by the presence of larvae of winter (Pagellus bogaraveo, Pomacentridae sp1) or summer spawners (Pomacentridae sp2, Trachinus draco, Arnoglossus thori, Tetraodontidae sp1). Upwelling filaments shed from the NW African coast reached the sampling area three times during this study, but changes in the local larval community were only detected in August 2005.     

Seasonal growth and composition of fronds of Macrocystis pyrifera in the Falkland Islands

Frond growth of Macrocystis pyrifera in the Falkland Islands was monitored in shallow coastal water from December 1985 to March 1987, and at a different site in deeper water from December 1985 to June 1986. Growth rates in the deeper bed were generally higher than those recorded in the coastal zone. At both sites, node initiation and elongation rate fluctuated according to the seasonal pattern of light or water temperature. In the shallow coastal area, nitrate was abundant in the winter and below detection levels during late spring and summer. Correlation analysis suggests that the production of the fronds of the giant kelp in this area was probably inhibited during the summer months by extremely low concentrations of nutrients. Internal nitrogen was exhausted approximately one month after a sharp decline in ambient nitrate concentration, and carbon reserves were formed. In the deeper bed of M. pyrifera, nitrogen was abundant all year round and the production of the fronds reflected the seasonal pattern of light or water temperature. The nitrogen content of the tissue probably did not drop below a level that limited production, and no internal carbon reserves were accumulated.     

Breeding and larval distribution of the pteropod Clione limacina in the North Atlantic,Subarctic and North Pacific Oceans

The pteropod Clione limacina (Phipps, 1774) is an arcticboreal, circumpolar species, which is widely distributed in the North Atlantic and Subarctic Oceans; it also occurs in the North Pacific Ocean (in the Oyashio and neighbouring waters) and along the Atlantic coast of North America in the waters of the cold Labrador current to the Cape Hatteras region (35° N). The distribution of C. limacina larvae in the plankton of the Norwegian, Barents and White Seas, the Bear Island-Spitsbergen region of the Greenland Sea, the Newfoundland Grand Bank and the Flemish-Cap Bank region of the North-western Atlantic Ocean, and the Kurile-Kamchatka region of the North-western Pacific Ocean has been studied, and information from literature concerning the reproduction and larval occurrence of the species is summarized. Throughout its distributional are, spawning of C. limacina is characterized by the same general ecological pattern. This species breeds and spawns in all types of water masses occurring within the vertical range which it commonly inhabits — from surface layers to 500 m water depth. In all local populations of the species, the most intensive spawning is correlated with the spring/summer period of annual heating of the local waters, and the highest abundance parallels maximum growth of phytoplankton which serves as food for veligers and early polytrochous larvae. After the end of this period, spawning intensity in all local C. limacina populations declines sharply, but spawning continues at low intensity during the autumn/winter season, being practically continuous throughout the year. Distribution patterns of C. limacina larvae are determined by those of their parental forms (the parental forms spawn in the zones permanently inhabited). The earliest larval stages of C. limacina (veligers) are present predominantly in the upper 100 or 200 m water layer, i.e. in the zone of high phytoplankton abundance. Polytrochous larvae, after becoming predaceous feeders, are distributed throughout the whole water column from the surface to 500 m depth, similar to adult C. limacina. As with the adults, larvae are present (within the species' distribution area) in all types of water masses. Since the beginning of the twentieth century, in the course of the warming of the Arctic Ocean, the southern race of C. limacina (formerly a summer/autumn seasonal invader in the Norwegian Sea) has become a permanent component of the plankton fauna of the Norwegian and Barents Seas in regions influenced by the Norwegian-Northcape Current System.     

Autecology of Fucus distichus ssp. distichus (Phaeophyceae: Fucales) in Nova Scotia,Canada

The autecology of Fucus distichus L. ssp. distichus was investigated at several sites on the Atlantic coast of Nova Scotia, Canada, throughout a 2-year period. This species is confined to high-littoral rock pools at exposed sites, where there appears to be little competition from other organisms. Water temperature, salinity, dissolved oxygen, and hydrogen-ion concentrations underwent both considerable seasonal and short-term variation. Pools with extremes of salinity did not contain F. distichus ssp. distichus. Receptacles are formed during winter, and by late spring they are cast. Sporelings were first visible during September; their development was slow, and these plants did not become reproductive until the second year. During the period February to May, rapid growth of new fronds occurred; an increase in both length and bulk of the plants resulted from this growth. Fronds of mature plants continued to elongate slowly throughout the summer and the early autumn with the formation of receptacles in winter. Plants were frequently damaged, which resulted in regeneration of new fronds from the wounded surface.Issued as NRCC No. 14510     

Queen–worker–brood coadaptation rather than conflict may drive colony resource allocation in the ant Temnothorax curvispinosus

Conflicts of interest among genetically heterogeneous nestmates in social insect colonies have been emphasized as driving colony resource allocation. However, potential intracolonial conflicts may not actually be realized so that resource allocation could be shaped primarily by among-colony selection that maximizes colony productivity. To elucidate the causal basis of patterns of resource allocation, I experimentally manipulated three fundamental aspects of colony social structure (relatedness among workers, relatedness among larvae, and queen presence) in the ant Temnothorax curvispinosus and measured effects on colony resource allocation to new workers, gynes, and males. The experimental manipulations had widespread effects on patterns of colony resource allocation, but there was little evidence for realized conflicts over the sex ratio and caste ratio. Decreasing nestmate relatedness caused decreased colony productivity, suggesting that more closely related nestmates have more favorably interacting phenotypes. Together, these results suggest that resource allocation in T. curvispinosus may be shaped more by among-colony selection than intracolonial conflict, leading to queen–worker–brood coadaptation.     

Population biology ofMacrocystis integrifolia from British Columbia,Canada

Aspects of the population dynamics ofMacrocystis integrifolia Bory were determined from harvested wild populations over a 26-month period and cultivated plants over a 40-month period. Mean wild plant size varied from 0.1 wet kg and two fronds in the winter to 3.1 wet kg and mine fronds in the summer. Plant recruitment probably occurred year-round with recruits making up 20 to 86% of the total population. Plant half-lives, estimated from population data, ranged from 1 to 3 months, with few plants exceedings 2 to 3 years in age. Standing crop ranged from 1.6 plants m^-2 and 0.1 wet kg m^-2 in winter to 8.3 plants m^-2 and 8 wet kg m^-2 in summer.     

Electrophoretic identification and genetic analysis of bivalve larvae

Taxonomic identification and genetic analysis of larval marine invertebrates have been vexing problems. We describe a polyacrylamide mini-gel electrophoresis technique for resolving proteins from individual larval bivalves (shell length 250 to 350 m) and apply this technique to three species of laboratory-cultured larval oysters [Ostrea edulis L., 1758, Crassostrea gigas (Thunberg, 1793) and c. virginica (Gmelin, 1791)] reared during summer 1989. Electrophoretic patterns of proteins clearly discriminate among the three species and allow genetic analysis of a polymorphic allozyme locus (Pgi) in field-collected larvae and juveniles of C. virginica. This technique provides an economical tool for largescale taxonomic, ecologic, and genetic studies of meroplanktonic stages of various species.     

Cycles and rates of reproduction of six Baltic Sea bivalves of different zoogeographical origin

All bivalves investigated (Astarte borealis, Astarte elliptica, Macoma calcarea, Cyprina islandica, Macoma baltica, Cardium lamarcki) are dioecious. The mean egg-diameters were determined by a series of measurements for 6 bivalves and compared with data from other authors. M. calcarea does not have a direct non-pelagic larval development as previously assumed, but probably produces pelagic planktotrophic larvae. The arctic species exhibit no modification of their mode of development in the boreal area. The boreal forms spawn over a relatively short period in spring and summer. The arctic forms revealed, over long periods, ripe eggs and sperms. Apparently they begin to spawn in winter or early spring. This extension and shift of the spawning season represents adaptation of the Aretic species to the specific conditions of the Baltic Sea. The number of eggs laid by the most important bivalves were determined and correlated with the larval ecology and length of generation time.     

Comparison of laboratory rates of predation of five species of marine fish larvae by three planktonic invertebrates: effects of larval size on vulnerability

Rates of predation by the invertebrates Aurelia aurita, Thysanoessa raschi and Euchaeta norvegica on larval stages of cod (Gadus morhua L.), flunder (Platichthys flesus L.), plaice (Pleuronectes platessa L.), herring (Clupea harengus L.), and turbot (Scophthalmus maximus L.) were determined. Experiments were conducted in late winter and early spring 1982 with predators collected in Loch Etive, Scotland and prey obtained from several locations in Great Britain. Early stages of the smallest species, cod, flounder and turbot, tended to be most vulnerable to all three predators, while the early stages of the larger species, plaice and herring, and older stages of all species, were less vulnerable. For all stages and species of larvae, predation rates by the three predators were most closely related to larval length and escape swimming speed. Larval length itself was closely correlated to indices of larval escape ability. Low predation rates on large larvae by E. norvegica could be due to handling difficulties, whereas for A. aurita and T. raschi these low rates were due to escape abilities of the larger larvae. Prey movement is an important stimulus eliciting predation in E. norvegica but not in A. aurita or T. raschi.     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.     

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic,abbreviated and direct development

The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.     

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 and facilitation of bryozoan and ascidian settlement by natural multi-species biofilms: effects of film age and the roles of active and passive larval attachment

Sessile marine invertebrate larvae can recognize suitable settlement substrata by using various environmental cues, including organic/microbial biofilms. In laboratory choice assays, the effect of biofilms of varying ages on the settlement behaviour of two fouling organisms was assessed. The species included the arborescent cheilostome bryozoan Bugula flabellata (Thompson) and the solitary ascidian Ciona intestinalis (L.), both of which are characteristic of temperate sublittoral hard substratum assemblages in northwest Europe. Experiments were carried out using polystyrene petri dish substrata preconditioned with multispecies biofilms from natural laboratory-aquarium seawater for 1, 3, 6 or 12 d. Unfilmed (new, initially sterile) dishes were used as control substrata. Whereas the coronate larvae of B. flabellata generally were inhibited by biofilming, irrespective of film age, the settlement of tadpole larvae of C. intestinalis was facilitated on biofilmed substrata, and numbers of settled larvae generally increased with biofilm age: the highest mean numbers were counted on 12 d-old biofilms. In C. intestinalis, settlement and metamorphosis are processes which can be temporally separate and are possibly induced by different environmental cues. This study therefore distinguished between C. intestinalis larvae which were attached to the biofilm surface by the anterior, and those larvae entrapped by the biofilm but not settled in the conventional meaning of the term. As reported in previous studies, we did observe that such entrapped larvae could subsequently attach and develop successfully into sessile juveniles. Both the numbers of “attached” and “trapped” tadpoles increased with biofilm age. Assuming that “settlement” is essentially a process involving the active behavioural response of larvae to environmental cues, it seems that the facilitated attachment of C. intestinalis onto biofilmed substrata is due to the combined effect of active habitat selection and passive deposition/“entrapment” of larvae onto the “sticky” substratum. Received: 21 August 1996 / Accepted: 21 November 1996     

Combined effects of temperature and salinity on the survival and growth of the larvae of Pandalus jordani (Decapoda: Pandalidae)

Survival and growth over an environmental range of temperature and salinities were examined in order to help assess the importance of these environmental factors in affecting the distribution, abundance and survival of larvae and provide greater understanding of factors affecting fluctuations in adult Pandalus jordani Rathbun population sizes. Larvae were shown to have a wide tolerance to salinity, especially in the early stages, but a relatively narrow tolerance to temperature. The optimal temperatures for survival, 8° to 11°C, were also optimal for growth as reflected by maximal growth increments and body size. It is therefore felt that fluctuations in temperature as seen within and between successive larval seasons would have profound effects on larval survival, growth rates and size at metamorphosis to the benthic juvenile phase.     

Siphon size and burying depth in deposit- and suspension-feeding benthic bivalves

This paper analyses the significance of siphon investment in the life strategy of benthic bivalves. It describes the relationships between siphon weight, burying depth and shell size in Mya arenaria, Cerastoderma edule. Scrobicularia plana and Macoma balthica. All data were collected on an intertidal flat in the Dutch Wadden Sea during seven successive winter and summer periods. The four species have in common that (1) the increase of depth in relation to size can be described with an S-curve; (2) there is a linear relationship between log siphon weight and log shell size; (3) siphon investment is maximal for the size classes with the greatest increase in their depth; (4) siphon weight, in proportion to total body weight, decreases gradually for the larger size classes whose depth does not increase; (5) burying depth increases with siphon weight if individuals within a same size class are compared, but burying depth levels off above a certain siphon weight. Macoma balthica and Scrobicularia plana live twice as deep in winter as in summer, although siphon weight for both seasons is about the same. In summer both species use a part of the siphon to graze the surface around the burrow, whereas deposit feeding does not occur in winter. This might explain the seasonal variation in burying depth. On the other hand Cerastoderma edule and Mya arenaria, which are both suspension feeders, show hardly any increase of depth in winter as compared to summer. For benthic bivalves the risk of being taken by a predator decreases with depth. The burying depth levels off where individuals reach the depth refuge (though in winter Scrobicularia plana live at greater depth). The conclusion is that siphon size is one of the main factors determining the burying depth of benthic bivalves and thus plays a critical role in their survival.     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.