The Future of Scattered Trees in Agricultural Landscapes

Abstract: Mature trees scattered throughout agricultural landscapes are critical habitat for some biota and provide a range of ecosystem services. These trees are declining in intensively managed agricultural landscapes globally. We developed a simulation model to predict the rates at which these trees are declining, identified the key variables that can be manipulated to mitigate this decline, and compared alternative management proposals. We used the initial numbers of trees in the stand, the predicted ages of these trees, their rate of growth, the number of recruits established, the frequency of recruitment, and the rate of tree mortality to simulate the dynamics of scattered trees in agricultural landscapes. We applied this simulation model to case studies from Spain, United States, Australia, and Costa Rica. We predicted that mature trees would be lost from these landscapes in 90–180 years under current management. Existing management recommendations for these landscapes—which focus on increasing recruitment—would not reverse this trend. The loss of scattered mature trees was most sensitive to tree mortality, stand age, number of recruits, and frequency of recruitment. We predicted that perpetuating mature trees in agricultural landscapes at or above existing densities requires a strategy that keeps mortality among established trees below around 0.5% per year, recruits new trees at a rate that is higher than the number of existing trees, and recruits new trees at a frequency in years equivalent to around 15% of the maximum life expectancy of trees. Numbers of mature trees in landscapes represented by the case studies will decline before they increase, even if strategies of this type are implemented immediately. This decline will be greater if a management response is delayed.     

Population dynamics of Mytilicola intestinalis in Mytilus edulis in south west England

The population dynamics of Mytilicola intestinalis Steuer in mussels (Mytilus edulis L.) from the River Lynher, Cornwall, England, have been studied over 3 years. By transplanting uninfested mussels from the River Erme, South Devon, into the Lynher mussel bed, the study was extended to the growth and development of new infestations under natural conditions. Female Mytilicola intestinalis are shown to breed twice, and two generations of parasites coexist for most of the year, with recruitment taking place in summer and autumn. One generation contributes its first brood to the autumn recruits before overwintering and contributing its second brood to the following summer's recruits. The other generation overwinters as juvenile and immature stages to contribute its two broods successively to the summer and autumn recruits. Environmental temperatures are believed to control the rates of development at all stages rather than acting as triggers in the onset or cessation of breeding at specific times. There is no evidence to support the contention that heavily infested mussels are killed, and parasite mortality is shown to be density-independent.     

Determinants of habitat association in a sympatric clade of marine fishes

Triplefin fishes reach their greatest diversity in New Zealand with 26 endemic species, and habitat diversification has been implicated as a key factor in the divergence of this group. Despite this, it is unknown whether species-specific habitat patterns in these sympatric fishes are established by passive processes (e.g. differential mortality) or by habitat selection during settlement. We investigate this question by comparing the habitat associations of new recruits with those of conspecific adults in five species. In addition, the amount of variation in habitat use of conspecific recruits and adults was calculated to identify ontogenetic shifts in habitat association. The results indicated that while there were some differences between recruit and adult habitats, these differences were small in magnitude and habitat use of new recruits was similar to that of adult conspecifics. This finding was further supported by the small difference in variation of habitat use between conspecific recruits and adults. The study suggests that new recruits are actively involved in the selection of habitats at settlement and maintain the use of these throughout demersal life. Habitat use in these territorial species has a large influence on mate choice, thus habitat selection by new recruits would provide a powerful mechanism for pre-zygotic isolation between individuals with different habitat preferences. Together these findings support the notion that habitat diversification has been a major component in the radiation of this sympatric group.     

Fine-scale patchiness and genetic heterogeneity of recruits of the corallivorous gastropod Drupella cornus

The size-frequency distributions and genetic composition of recruits of the corallivorous snail Drupella cornus (Röding, 1798) were examined in outbreak populations collected from Ningaloo Reef, Western Australia in August 1990. The recruits are found in groups on digitate Acropora spp. corals. Among coral colonies, mean lengths of recruits in our samples ranged from <9 to 22 mm, but the snails within a group were generally similar in size. Despite the fact that D. cornus has planktonic larvae, there were marked genetic differences between groups of recruits on different coral colonies. The relatively large genetic subdivision among groups of recruits within sites over distances <80 m was measured as a value of F _ST (standardized variance in allelic frequencies) of 0.044. This was three times the value from comparisons of pooled samples of recruits from areas up to 119 km apart, and six times as great at the genetic subdivision among populations of adults over a distance of 180 km. Much of the genetic heterogeneity among groups of recruits is associated with mean size of the snails. Taken together, the size-frequency distributions and the genetic differences indicate that recruits within the same coral colony shared a common history of settlement, suggesting a cohesiveness of groups of larvae. Although the mechanisms for this patchiness are not understood, one implication is that studies of size-frequency distributions and genetic composition of cohorts of D. cornus must treat the group, not the individual snail, as the unit of replication.     

A “source” for asteroid larvae?: recruitment of Pisaster ochraceus,Pycnopodia helianthoides and Dermasterias imbricata in Nootka Sound,British Columbia

A major recruitment of the forcipulate asteroid Pisaster ochraceus was observed in September 1987 in the channel leading into Boca del Infierno, a semi-enclosed bay on the southeastern shore of Nootka Island, on the west coast of Vancouver Island, British Columbia, Canada. Newly settled recruits were observed at high densities subtidally in the channel (mean maximal density=1.23x10⁴m^-2) and at nearby sites. Subsequent surveys in 1988 to 1991 and size-frequency distributions of adults indicated strong yearly recruitment of P. ochraceus. Recruits of P. ochraceus were found on all available substrata, including hard and soft bottoms and on benthic algae. The initial food of the recruits included newly settled mussels (Mytilus sp.), snails and barnacles. Recruitment of the forcipulate Pycnopodia helianthoides was observed in 1987 to 1989 and in 1991, while recruitment of the spinulosan Dermasterias imbricata occurred only in 1988. High densities of planktonic bipinnaria larvae were found in the bay of Boca del Infierno in late May. We hypothesise that the high density population of adult P. ochraceus found in the channel of Boca del Infierno spawns synchronously and most of the resulting embryos and larvae are retained within the bay. This area may act as a source of larvae that then disperse locally. Post-recruitment mortality was estimated by comparing the density of recruits of P. ochraceus in 1987 with the numbers of juveniles presumed to be 1 yr old in 1988. Post-recruitment mortality was in excess of 97% with few individuals surviving to 1 yr. Moreover, even after the first year, mortality or emigration of the juveniles resulted in the almost complete loss of the 1-yr cohort at North Saavedra between 1988 and 1989. This study provides evidence that the P. ochraceus population in this area of Nootka Island may not be open, but may be regularly supplied from a source of larvae in the bay of Boca del Infierno. Post-settlement processes may, however, have significant effects on the local population, resulting in a poor correlation between the rate of recruitment and the incorporation of yr-1 + individuals into the adult population.     

Solitary behavior in a high-altitude population of the social sweat bee Halictus rubicundus (Hymenoptera: Halictidae)

In the subalpine region of the Rocky Mountains of Colorado, United States, Halictus rubicundus has a solitary life cycle, but it is social in other parts of its known range. The brood is protandrous, with a nearly equal investment in the sexes. Productivity averages 6.5 offspring per foundress female, similar to the second brood of social nests in New York, but less than the combined productivity of both New York broods. Leucophora sp. (Diptera: Anthomyiidae) is the principal cause of brood mortality in Colorado. Foundress females in about half the nests survive until brood emerge as adults. Retention of these foundresses decreases offspring mortality by 68%. Comparable abilities to express solitary behavior with a single brood may characterize other eusocial halictine lineages that have successfully invaded high altitudes in the Rocky Mountains. The apparent inability to do this may help explain the absence of other eusocial halictine bees and polistine wasps at high altitudes, despite their success at lower elevations in the same mountains. Presence or absence of this ability may help explain latitudinal distributions of these lineages in North America. Holarctic distributions of lineages with eusocial behavior can be explained by migration as solitary populations from Eurasia to North America across Pleistocene Bering land bridges, with re-expression of double-brooded, eusocial behavior when the species then extended their ranges southward in North America. Received: 4 November 1994/Accepted after revision: 23 October 1995     

Ontogenetic changes in small-scale movement by recruits of an exploited mussel: implications for the fate of larvae settling on algae

Many South African populations of the brown mussel Perna perna have been depleted through over-exploitation by subsistence harvesters. This is problematic because recovery after disturbance is very slow, partly because recruits are largely associated with adult mussels. However, unlike large recruits of 3.5–10 mm that exhibit spatial structure related to that of adults, a very high proportion of settlers and small recruits (0–3.5 mm) occur on foliose algae. We tested the hypothesis that recruits on algae move to adult mussel beds after a period of growth, with the null hypothesis that they die at a certain size. We conducted an indirect field study comparing the ratios of large to small recruits in 100% cover mussel patches at locations with high and low algal cover. A second laboratory experiment analysed whether the size of recruits on algae affects their active movement behaviour in response to nearby mussel patches. Large/small recruit ratios were slightly, but not significantly greater in high than low algal cover locations. Both small (2–2.5 mm) and medium (4.5–5.5 mm) recruits remained on algae and moved very short distances throughout the laboratory experiment, while larger recruits (9–10 mm) moved significantly further distances and more often into mussel patches. The results suggest that very large recruits are able to migrate actively to nearby mussel patches, indicating ontogenetic shifts in this behaviour. However, the absence of a significant difference in ratios between field locations with high and low algal cover suggests many large recruits are accidentally dislodged from the algae and presumably die. Thus settlement of P. perna onto algae is likely to be wasted, with consequences for sustainable management of the mussel resource.     

Induction of settlement and metamorphosis in the sand dollarEchinarachnius parma: Evidence for an adult-associated factor

Larvae of the northern sand dollarEchinarachnius parma (Lamarck), reared from adults collected from Eagle Head, Nova Scotia, Canada, in 1988 and 1989, metamorphose in significantly greater numbers on sand conditioned by adults than on non-conditioned sand. The metamorphic factor has a molecular weight < 1000 and is destroyed by heating. Larvae are capable of sensing this cue in the water column under static conditions. Substrata of varying particle size and surface texture can be conditioned by adults to induce metamorphosis. Substrata conditioned in the dark, and conditioned sand treated with antibiotics also induce metamorphosis suggesting that the factor is not produced by adult-associated bacteria or microflora. In nature, this adult-associated factor may direct settlement of larvae to established sand dollar beds resulting in the aggregated distribution of this species.     

Early life histories in the bryozoan<Emphasis Type="Italic"> Schizobrachiella sanguinea</Emphasis>: a case study

Mediterranean populations of Schizobrachiella sanguinea seem to span a wide range of contrasting benthic habitats. We have studied adult, larval, and recruit populations of S. sanguinea from sublittoral (approximately 10 m depth) communities at Blanes (Spain, NW Mediterranean). At the study site, the species colonises semi-obscure caves and, to a lesser extent, communities of sciaphilic algae. Our first goal was to show the periods of brooding, larval release, and recruitment. Plankton was collected about twice a week between July 1998 and June 2000 over an artificial reef. A total of 303 larvae were collected in 23 of the 102 days of sampling. At the study site the species shows a single, annual larval release period, which occurs from late March to June–July every year. Recruits were found from late May to late August 1999 and in late May 2000. A recruitment peak was observed in July 1999 and again in late May 2000. The presence of brooding adults corresponded to the periods of larval supply and recruitment. Our second goal was to investigate the causes of the variable distribution of the species along several communities in the north-west Mediterranean Sea. We describe adult distribution and the dynamics of larval supply, recruitment of early (15 days from settlement) and late (4 months from settlement) recruits. Patterns of larval presence and early recruit distribution along the communities on the reef did not reflect the adult distributions, whereas this was closely matched by the distribution of late recruits. Post-recruitment mortality strongly affected recruits of the PA (photophilic algae) and SA (sciaphilic algae) communities, whereas it was very low in the communities of SOC (semi-obscure caves). Mortality of recruits was density independent and colony survivorship in the SA communities, where recruitment was the highest, appeared strongly affected by competition with brown algae. Like the majority of cheilostomate bryozoans, S. sanguinea releases a coronate larva capable of active swimming and positive reaction to light. Such swimming abilities may allow larvae to actively select the substrate on which to settle and to avoid unsuitable substrates. It seems that larval behaviour does not explain the preference of S. sanguinea for sciaphilic habitats. High post-recruitment mortality due to various factors, especially competition with fast-growing algae, seems particularly relevant in determining the adult distributions observed.Communicated by S.A. Poulet, Roscoff     

Life histories of large and small murexes (Prosobranchia: Muricidae)

One can predict the major features of a muricid's life history from its adult size. Most adults do not grow, and juveniles of all species grow 1 to 2 mm/month, so that larger adults have had fonger juvenile periods. Larger females deposit larger egg capsules and, since each of these contains more eggs, their clutches are larger. Small females deposit several clutches each year, and thus have relatively large annual fecundities. However, large females live longer, so each spawns many more eggs in her life-time than would a smaller female. From 90 to 99% of the juveniles die within their first year. However hatchings of small species are much more likely to complete their first year; a newly hatched Urosalpinx cinerea is 25 times more likely to survive long enough to breed once than a newly hatched Ceratostoma foliatum (Gmelin, 1791).     

Concordance between short-term experiments and long-term censuses in tide pool fishes

Sixteen years of annual censuses (1990-2005) of an assemblage of tide pool sculpins at Tatoosh Island, Washington, USA, revealed relative constancy in the numbers of recruits and adults. However, the dominant species as a recruit (Clinocottus globiceps) was always replaced numerically as an adult by another species (Oligocottus maculosus). When mechanisms of coexistence were evaluated, little support was found for either a lottery model, because competitive interactions are hierarchical, or a storage-effect model of coexistence, because the relative ranking of recruitment varied little among years and did not covary among species with environmental variables such as ocean temperature, upwelling indices, or an estimator of ocean productivity (oyster condition index). There was also little evidence of niche partitioning based on habitat affinities. Additionally, predation-mediated coexistence had little support, given that the competitive dominant did not have the greatest rates of mortality. Instead, a competition-colonization trade-off may contribute to the coexistence of these species, where C. globiceps always recruits in the greatest numbers, while O. maculosus dominates the adult assemblage via competitive processes. The importance of post-recruitment processes in this assemblage is further suggested by some negative associations among species, the presence of density dependence, some habitat affinities, and previously published experimental work that demonstrated the competitive dominance of O. maculosus over C globiceps.     

Demography of <Emphasis Type="Italic">Halimeda incrassata</Emphasis> (Bryopsidales,Chlorophyta) in a Caribbean reef lagoon

The fate of 100 marked recruits of the rhizophytic alga Halimeda incrassata was followed in Puerto Morelos reef lagoon, Mexican Caribbean (20°52′N, 86°51′W), until death of the last individual from April 2005–2007. Juvenile mortality was relatively high (19%), the half-life of adult thalli was 13 months and maximal lifespan was 2 years. First age of sexual reproduction was 10 months, but only 6% of the marked thalli reproduced sexually. A subsequent static life-table approach (February–April 2008) at two sites indicated low spatial variation in transition probabilities between the life stages. Recruits were found throughout the year (density 2–11 thalli m⁻²) and were mostly of clonal origin. In a disturbed area, the density of sexual recruits was ~0.01 thalli m². Temporal fluctuations in population size depended on mortality rates, which increased slightly after hurricanes Emily (July 2005) and Wilma (October 2005), but might otherwise be regulated by density-dependent processes.     

Habitat patchiness and predation modify the distribution of a coral-dwelling damselfish

Fish abundance is often better predicted by microhabitat variables on continuous reefs than on isolated patch reefs. Although this was suggested to stem from reduced post-recruitment relocation, this has not been shown experimentally. We found the relationship between the presence of a coral-dwelling fish, Dascyllus marginatus, and the size of its coral host to differ between corals on continuous reefs and the sparsely distributed corals on sandy bottoms. Empty transplanted corals were colonized exclusively by new recruits when on the sandy bottom, and both by new recruits and post-recruitment dispersal of adults when on the continuous reef. New recruits settled predominantly into small corals, although analyses of recruitment patterns were confounded by low recruitment in the studied years. Both tank experiments and field survey data suggest that the presence of recruits in small corals is at least partially driven by predation by the dottyback, Pseudochromis olivaceus, which lives predominantly in large corals within both habitats. Consequently, we suggest that the relationship between fish presence and coral size differs between the habitats due to coral size dependent predation on recruits and variability in the importance of direct recruitment to replenish fish populations.     

Antipredation role of clumped nesting by marsh-nesting red-winged blackbirds

Summary Red-winged blackbirds, Agelaius phoeniceus, breed in marshes in high densities and their nests are frequently clumped. Because predation is consistently the most important cause of redwing nesting mortality, high densities of breeding individuals could be an anti-predation adaptation. In our study site predation by marsh wrens, Cistothorus palustris, was the main cause of redwing nesting losses. In situations when marsh wrens were near, predation rates on redwing nests decreased with increasing female density. Group life could reduce predation because of improved nest defense, selfish herd effects, or predator dilution effects. We differentiated between these possibilities by introducing experimental colonies consisting of 3, 6, and 9 artificial nests near and away from active redwing nests. The experimental colonies near active nests suffered less predation, but predation rates were not correlated with colony size or a nest's location within the colony. Therefore, the advantage of group life in this population is probably mutual nest protection.     

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.     

Wintering areas of adult Atlantic puffins Fratercula arctica from a North Sea colony as revealed by geolocation technology

Most seabirds die outside the breeding season, but understanding the key factors involved is hampered by limited knowledge of nonbreeding distributions. We used miniature geolocating loggers to examine the movements between breeding seasons of Atlantic puffins Fratercula arctica from a major North Sea colony where numbers have declined in recent years, apparently due to increased overwinter mortality. The most intensively used region was the northwestern North Sea but most puffins also made excursions into the east Atlantic in the early winter. Ringing recoveries previously indicated that adults from British east coast colonies remained within the North Sea and hence were spatially segregated from those breeding on the west throughout the year. Updated analyses of ringing recoveries support results from geolocators suggesting that usage of Atlantic waters is a recent phenomenon. We propose that the increased adult mortality is related to changes in distribution during the nonbreeding period and reflects worsening conditions in the North Sea.     

Settlement and recruitment of sea urchins (Strongylocentrotus spp.) in a sea-urchin barren ground and a kelp bed: are populations regulated by settlement or post-settlement processes?

I sampled recruitment of very small sea urchins (Strongylocentrotus spp.) by using the anesthetic magnesium chloride to remove individuals from substrata collected in sea-urchin barren grounds (barrens) and kelp beds at Naples Reef near Santa Barbara, California, USA. Preliminary sampling found low numbers of newly settled individuals(<0.6 mm test diam) from April–July in 1984 and 1985, and in April, 1986. In early May, 1986, I found many newly settled seaurchins (0.3 to 0.6 mm, 5 to 17 d old), and I compared the densities of the cohort on several types of natural substrata in barrens and kelp-bed habitats. Newly settled individuals of both purple sea urchins (S. purpuratus) and red sea urchins (S. franciscanus) were present in similar, high densities (1 000 S. purpuratus m^-2) on foliose red algal turf, a dominant substratum ofthe kelp bed, and on crustose coralline algae, the dominant substratum of an adjacent barrens. Larvae of S. purpuratus reared and tested in the laboratory showed high rates of settlement on both red algal turf and on crustose coralline algae, but significantly lower rates on rock. Larvae also settled in response to a partiallypurified extract of coralline algae. The reduced settlement on natural rock surfaces relative to either algal treatment and the significant settlement in response to the extract of coralline algae indicate that larvae discriminate between natural substrata and probably respond to a settlement cue other than, or in addition to, a simple microbial (bacterial) film. The similar densities of young recruits of S. purpuratus on dominant substrata of barrens and kelp bed show that, at least in this case, differential settlement cannot explain the high densities of sea urchins in the barrens habitat. Movement between barrens and kelp bed is unlikely given the small sizes of the newly recruited sea urchins relative to the large distances often involved. Reduced post-settlement mortality of newly settled individuals in the barrens remains the most likely mechanism leading to the higher densities of sea urchins in barrens relative to kelp-bed habitats.     

Population dynamics of Diadema antillarum (Echinodermata: Echinoidea) following mass mortality in Panamá

In 1983, Diadema antillarum suffered mass mortality throughout the Caribbean Sea and the western Atlantic Ocean. I followed the dynamics of populations at the San Blas Islands, Panamá from April 1983 to November 1987. Density measurements indicate that populations of D. antillarum have not recovered from the die-offs that killed nearly 97% of the individuals. There was recruitment to the 1 to 1.5 cm class immediately after the mass mortality, but there has been little additional influx of juveniles since then. The low number of observable juveniles could not be attributed to elevated rates of predation on very small individuals. Rates of recruitment did not differ between reefs with artificially increased densities of D. antillarum and reefs kept free of sea urchins; thus, the lack of recruitment did not arise from absence of adults that could provide settlement cues to the larvae or protection to newly settled juveniles. Other species of sea urchins did not show a clear pattern of increase after the demise of D. antillarum. Therefore, interspecific competition directed towards D. antillarum juveniles did not increase after the mass mortality. Two reefs where Echinometra viridis, Eucidaris tribuloides and Lytechinus williamsi, were removed showed no significant differences in recruitment of D. antillarum relative to two reefs where these species were allowed to remain at their natural densities. Resident D. antillarum after the mass mortality produced gametes with the same per capita intensity and lunar synchrony as before the mass mortality. However, it is possible that the probability of fertilization of their gametes decreased because of low population density. The most likely explanation for lack of recruitment is that the reduced numbers of reproducing adults at Panamá and upstream locations resulted in levels of larval supply that were inadequate to sustain recruitment on Panamanian reefs.     

Halogenated metabolites in two marine polychaetes and their planktotrophic and lecithotrophic larvae

This study investigated the occurrence and ontogenetic changes of halogenated secondary metabolites in planktotrophic and lecithotrophic larvae and adults of two common, infaunal polychaetes, Streblospio benedicti (Spionidae) and Capitella sp. I (Capitellidae), with different life-history traits. S. benedicti contains at least 11 chlorinated and brominated hydrocarbons (alkyl halides) while Capitella sp. I contains 3 brominated aromatic compounds. These halogenated metabolites are potential defense compounds benefiting both larvae and adults. We hypothesized that: (1) planktotrophic larvae contain halogenated metabolites because they are not protected by adult defenses, (2) quantitative and qualitative variation of planktotrophic larval halogenated metabolites parallels that of adults, and (3) brooded lecithotrophic larvae initiate the production of halogenated metabolites only after metamorphosis. To address these hypotheses, volatile halogenated compounds from polychaete extracts were separated using capillary gas chromatography and identified and quantified using mass spectrometry with selected ion monitoring. All four life stages (pre- and post-release larvae, new recruits, adults) of both S. benedicti and Capitella sp. I contained the halogenated metabolites previously identified from adults. This is the first report of halocompounds identified and quantified in polychaete larvae. Allocation of potential defense compounds to offspring varied as a function of species, feeding type and developmental stage. Pre-release larvae of S. benedicti with planktotrophic development contained the lowest concentration of total halogenated metabolites (1.75 ± 0.65 ng mm⁻³), post-release and new recruits contained intermediate concentrations (8.29 ± 1.72 and 4.73 ± 2.63 ng mm⁻³, respectively), and planktotrophic adults contained significantly greater amounts (28.9 ± 9.7 ng mm⁻³). This pattern of increasing concentrations with increasing stage of development suggests synthesis of metabolites during development. Lecithotrophic S. benedicti post-release larvae contained the greatest concentrations of halometabolites (71.1 ± 10.6 ng mm⁻³) of all S. benedicti life stages and developmental types examined, while the amount was significantly lower in new recruits (34.0 ± 15.4 ng mm⁻³). This pattern is consistent with a previously proposed hypothesis suggesting a strategy of reducing potential autotoxicity during developmental transitions. Pre-release lecithotrophic larvae of Capitella sp. I contained the highest concentration of total halogenated metabolites (1150 ± 681 ng mm⁻³), whereas the adults contained significantly lower total amounts (126 ± 68 ng mm⁻³). All concentrations of these haloaromatics are above those known to deter predation in previously conducted laboratory and field trials. As a means of conferring higher larval survivorship, lecithotrophic females of both species examined may be expending more energy on chemical defenses than their planktotrophic counterparts by supplying their lecithotrophic embryos with more of these compounds, their precursors, or with energy for their synthesis. This strategy appears common among marine lecithotrophic larval forms. Received: 14 July 1999 / Accepted: 20 January 2000     

Demography of the intertidal brown alga Pelvetia fastigiata in Southern California,USA

The demography of Pelvetia fastigiata was studied from 1973 through 1977 in the intertidal zone near La Jolla, California, USA. Populations were usually small and relatively stable as new recruits replaced older individuals that were lost; however, in 1977 high recruitment substantially increased total abundances. The survivorship of recruits was similar regardless of the season or year of recruitment. Mortality rates decreased with age, and the mean life expectancy continued to increase for at least 1 yr. Losses of juveniles were high; 50% lived 80 d and only 9% survived to the age of first reproduction (about 1.5 yr). Plants present at the start of the study had higher survivorship rates than new recruits, 19 and 7%, respectively, living more than 3 yr. Individuals within aggregations of large plants lived longer than most dispersed individuals, and aggregations remained intact throughout the study in spite of low recruitment. Established individuals had low mortality rates and populations probably relied on these persistent individuals for reproduction.