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.     

Modeling the Effects of Fishing and Implications for the Design of Marine Protected Areas: Juvenile Fish Responses to Variations in Seafloor Habitat

Abstract: A number of recent studies have linked post-settlement survivorship of Atlantic cod (  Gadus morhua ) with the complexity of the seafloor to which fish settle. Survivorship is greater in habitats of higher complexity (e.g., pebble-cobble substratum with emergent epifauna> pebble-cobble> sand), where cover provides shelter from predators. Fishing with mobile gear such as bottom trawls and dredges reduces the complexity of seafloor habitats. We used a dynamic model to (1) link patterns in habitat-mediated survivorship of post-settlement juvenile cod with spatial variations in habitat complexity, (2) simulate habitat change based on fishing activities, and (3) determine the role of marine protected areas in enhancing recruitment success. Density-dependent natural mortality was specified as three alternative functional response curves to assess the influence of different predator foraging strategies on juvenile survivorship during the first 12 months of demersal existence. We applied the model to a theoretical patch of hard-bottom substrata and to a case study based on seafloor habitat distributions at Stellwagen Bank National Marine Sanctuary (Gulf of Maine, Northwest Atlantic). Our results demonstrate that patterns in the shape of response surfaces that show the relationship between juvenile cod survivorship and density as well as movement rate were similar regardless of functional response type, that juvenile cod movement rates and post-settlement density were critical for predicting the effects of marine protected-area size on survivorship, and that habitat change caused by fishing has significant negative effects on juvenile cod survivorship and use of marine protected areas can ameliorate such effects.     

Intensive fishing of marine consumers causes a dramatic shift in the benthic habitat on temperate rocky reefs

Intensive fishing can cause dramatic, long-lasting shifts in benthic habitat. This study used three approaches to test whether overharvesting of blacklip abalone (Haliotis rubra) can cause a shift in benthic habitat to a configuration that is unsuitable for abalone, on the east coast of Tasmania, Australia. After 18 months of removing abalone from rocks, encrusting red algae (ERA) became overgrown by filamentous and foliose algae, sessile invertebrates and accumulated sediment. The differences in the community composition between locations, sites nested within locations and rocks were minor. Throughout the study, abalone were largely associated with areas of rock covered in ERA but avoided other habitats. A transplant experiment demonstrated that abalone preferred areas of rock covered in ERA but move away from overgrown rocks. These results suggest overharvesting of abalone results in a shift to benthic habitat poorly preferred by abalone. This could form a positive feedback loop that limits recovery of abalone populations and ERA.     

Habitat complexity modifies post-settlement mortality and recruitment dynamics of a marine fish

For species that have an open population structure, local population size may be strongly influenced by a combination of propagule supply and post-settlement survival. While it is widely recognized that supply of larvae (or recruits) is variable and that variable recruitment may affect the relative contribution of pre- and post-settlement factors, less effort has been made to quantify how variation in the strength of post-settlement mortality (particularly density-dependent mortality) will affect the importance of processes that determine population size. In this study, I examined the effects of habitat complexity on mortality of blue rockfish (Sebastes mystinus) within nearshore reefs off central California. I first tested whether variation in habitat complexity (measured as three-dimensional complexity of rocky substrate) affected the magnitude of both density-independent and density-dependent mortality. I then used limitation analysis to quantify how variation in habitat complexity alters the relative influence of recruitment, density-independent mortality, and density-dependent mortality in determining local population size. Increased habitat complexity was associated with a reduction in both density-independent and density-dependent mortality. At low levels of habitat complexity, limitation analysis revealed that mortality was strong and recruitment had relatively little influence on population size. However, as habitat complexity increased, recruitment became more important. At the highest levels of habitat complexity, limitation by recruitment was substantial, although density-dependent mortality was ultimately the largest constraint on population size. In high-complexity habitats, population dynamics may strongly reflect variation in recruitment even though fluctuations may be dampened by density-dependent mortality. By affecting both density-independent and density-dependent mortality, variation in habitat complexity may result in qualitative changes in the dynamics of populations. These findings suggest that the relative importance of pre- vs. post-settlement factors may be determined by quantifiable habitat features, rather than ambient recruitment level alone. Because the magnitude of recruitment fluctuations can affect species coexistence and the persistence of populations, habitat-driven changes in population dynamics may have important consequences for both community structure and population viability.     

Influence of habitat on abundance and size structure of a large temperate-reef fish, Achoerodus viridis (Pisces: Labridae)

The relationship between densities of Achoerodus viridis (Pisces: Labridae) and reef habitats at various localities within New South Wales (NSW), Australia was examined. Types of habitats were quantified at inner, mid and outer estuarine locations in each of two estuaries (Botany Bay and Port Jackson) to determine whether purported patterns of movement from estuaries could be related to differences in habitat. Although the same types of habitat were generally found at all locations, differences in the proportion of habitat types were found between shallow and deep reefs and among inner, mid and outer estuarine locations for both estuaries. Shallow habitats were usually dominated by Ecklonia radiata, turf and/or fringe habitat in Botany Bay, whereas deep sites were generally dominated by urchin-grazed barrens habitat and, sometimes, sponge- and ascidian-dominated deep reef. Shallow sites in Port Jackson were dominated by a mixture of habitats, as were deep reefs at mid-estuarine locations. Other deep reefs in Port Jackson were dominated by E. radiata (inner estuarine) or barrens (outer estuarine) habitat. Thus, patterns of habitat cover were not consistent between estuaries and numbers of fish could not be related to proportional representation of habitat on reefs along estuarine gradients. Univariate and multivariate analyses showed that there was little evidence that any size class of fish was correlated with the proportional representation of a particular habitat or group of habitats. Counts of fish that focused on barrens and E. radiata forest habitats over a period of 10 yr showed that similar numbers and all sizes of fish were found in the two types of habitat. Greater numbers of small fish were, however, found in the E. radiata forest habitat than in the barrens habitat. Estimates of abundance along the coast of NSW (100s to 1000 km) in a range of habitats (e.g. ascidian-dominated reef, kelp forest, urchin-grazed barrens) showed that there was no indication that a particular habitat consistently had greater numbers of A. viridis than other habitats. Therefore, A. viridis of a range of sizes appears to be flexible in its use of habitats on reefs. Received: 24 December 1997 / Accepted: 23 June 1998     

Predator biomass,prey density,and species composition effects on group size in recruit coral reef fishes

Group incidence and size are described for recruit parrotfishes, wrasses, and damselfishes on Hawaiian reefs over 3 years (2006–2008) at sites spanning the archipelago (20–28°N, 155–177°W). Coral-poor and coral-rich areas were surveyed at sites with both low (Hawaii Island) and high (Midway Atoll) predator densities, facilitating examination of relations among predator and recruit densities, habitat, and group metrics. Predator and recruit densities varied spatially and temporally, with a sixfold range in total recruit densities among years. Group (≥2 recruits) metrics varied with time and tracked predator and recruit densities and the proportion of schooling species. Groups often included heterospecifics whose proportion increased with group size. A non-saturating relationship between group size and recruit density suggests that the anti-predator benefits of aggregation exceeded competitive costs. Grouping behavior may have overarching importance for recruit survival–even at high recruit densities–and merits further study on Hawaiian reefs and elsewhere.     

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.     

Reducing per capita food supply alters urchin condition and habitat

When food supply declines or population density increases, the per capita food availability is reduced causing a decline in condition of consumers. Many consumers alter their feeding behaviour and ultimately the surrounding community (e.g. overgrazing and formation of urchin barrens). This study tested the hypothesis that sea urchin populations are of greater density and poorer condition in barrens (little food) than forest habitat (lots of food). We then tested the hypothesis that a decrease in per capita food supply to urchins has a negative effect not only on their condition but also on their surrounding habitat. We experimentally assessed the effect of limited food supply and increased density of a subtidal Australian sea urchin (Heliocidaris erythrogramma) on their condition (i.e. gonad index) and surrounding benthic habitat (i.e. turf-forming algae). Our results show that a reduction in food supply led to poorer consumer condition and greater herbivory on surrounding local habitat. We provide evidence that per capita food reduction is one of the necessary conditions for the over-consumption by urchins (i.e. urchin barrens), a proposed but previously untested mechanism.     

Reproduction in the diadematoid sea urchin Centrostephanus rodgersii in contrasting habitats along the coast of New South Wales, Australia

Reproduction in the sea urchin Centrostephanus rodgersii was examined in two types of habitats (“barrens”, i.e. habitats characterised by the high crustose coralline algal cover typical of urchin-barren grounds, and by the absence of macroalgae; and “fringe”, i.e. habitats characterised by a high macroalgal biomass and few C. rodgersii) at four locations in New South Wales. The four locations: the Solitary Islands, Sydney, Ulladulla and Eden, span the distribution of C.␣rodgersii from the subtropics at its northern limit to temperate waters near its southern limit. Histology and estimates of gonad retrieval rate (GRR) from January 1994 to October 1995 indicated that reproduction was synchronous at all locations. An increase in the tempo of gametogenesis in May and onset of spawning in June at all locations is consistent with entrainment in response to exogenous factors. Over the range studied, C. rodgersii experienced relatively similar daylength cycles and contrasting sea-temperature cycles. Short days and lunar conditions coinciding with the solstice appear likely proximate cues for the onset of spawning. The major difference in reproduction among locations was in the duration of spawning. In the southern parts of its range breeding occurred over a 5 to 6 mo period, whereas at the Solitary Islands it lasted ≃1 mo. At most locations the GRRs were significantly higher in the fringe habitat than in the barrens habitat. The lower reproductive output of urchins in the barrens habitat was attributed to the food-poor conditions typical of this habitat. The developing fishery for C. rodgersii is likely to be most effective from March to early May. Urchins from barrens areas may not provide sufficient yield to warrant harvesting. Received: 29 October 1997 / Accepted: 18 May 1998     

Megafaunal-habitat associations at a deep-sea coral mound off North Carolina,USA

Deep-sea corals provide important habitat for many organisms; however, the extent to which fishes and other invertebrates are affiliated with corals or other physical variables is uncertain. The Cape Fear coral mound off North Carolina, USA (366–463 m depth, 33° 34.4′N, 76° 27.8′W) was surveyed using multibeam sonar and the Johnson-Sea-Link submersible. Multibeam bathymetric data (2006) were coupled with in situ video data (2002–2005) to define habitat associations of 14 dominant megafauna at two spatial scales. Results suggested greater habitat specificity of deep-reef fauna than previously documented, with fishes showing greater affinity for certain habitat characteristics than most invertebrates. High vertical profile, degree of coral coverage, and topographic complexity influenced distributions of several species, including Beryx decadactylus, Conger oceanicus, and Novodinia antillensis on the smaller scale (30 × 30 m). On the broad scale (170 × 170 m), several suspension feeders (e.g., N. antillensis, anemones), detritivores (Echinus spp.), and mesopelagic feeders (e.g., Beryx decadactylus, Eumunida picta) were most often found on the south-southwest facing slope near the top of the mound. Transient reef species, including Laemonema barbatulum and Helicolenus dactylopterus, had limited affiliations to topographic complexity and were most often on the mound slope and base. Megafauna at deep-water reefs behave much like shallow-water reef fauna, with some species strongly associated with certain fine-scale habitat attributes, whereas other species are habitat generalists. Documenting the degree of habitat specialization is important for understanding habitat functionality, predicting faunal distributions, and assessing the impacts of disturbance on deep-reef megafauna.     

Ontogenetic habitat shift,population growth,and burrowing behavior of the Indo-Pacific beach star, <Emphasis Type="Italic">Archaster typicus</Emphasis> (Echinodermata; Asteroidea)

Archaster typicus, a common sea star in Indo-Pacific regions, has been a target for the ornamental trade, even though little is known about its population biology. Spatial and temporal patterns of abundance and size structure of A. typicus were studied in the Davao Gulf, the Philippines (125°42.7′E, 7°0.6′N), from February 2008 to December 2009. Specimens of A. typicus were associated with intertidal mangrove prop roots, seagrass meadows, sandy beaches, and shoals. Among prop roots, specimens were significantly smaller and had highest densities (131 ind. m⁻²) between November and March. High organic matter in sediment and a relatively low predation rate seemed to support juvenile life among mangroves. Size and density analyses provided evidence that individuals gradually move to seagrass, sandy habitats, and shoals as they age. Specimens were significantly larger at a shoal (maximum radius R = 81 mm). New recruits were found between August and November in both 2008 and 2009. Timing of recruitment and population size frequencies confirmed a seasonal reproductive cycle. Juveniles had relatively high growth rates (2–7 mm month⁻¹) and may reach an R of 20–25 mm after 1 year. Growth rates of larger specimens (R > 30 mm) were generally <2 mm month⁻¹. The activity pattern of A. typicus was related to the tidal phase and not to time of day: Specimens moved over the sediment surface during low tides and were burrowed during high tides possibly avoiding predation. This is one of the first studies to document an ontogenetic habitat shift for sea stars and provides new biological information as a basis for management of harvested A. typicus populations.     

Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus

Allozyme electrophoresis was used to characterize genetic variation within and among natural populations of the red sea urchin Strongylocentrotus franciscanus. In 1995 to 1996, adult urchins were sampled from twelve geographically separated populations, seven from northern California and five from southern California (including Santa Rosa Island). Significant population heterogeneity in allelic frequencies was observed at five of six polymorphic loci. No geographic pattern of differentiation was evident; neighboring populations were often more genetically differentiated than distant populations. Northern and southern populations were not consistently distinguishable at any of the six loci. In order to assess within-population genetic variation and patterns of recruitment, large samples were collected from several northern California populations in 1996 and 1997, and were divided into three size classes, roughly representing large adults (>60 mm), medium-sized individuals (31 to 60 mm, “subadults”) and individuals <2 yr of age (≤30 mm test diam, referred to as “recruits”). Comparisons of allelic counts revealed significant spatial and temporal differentiation among size-stratified population samples. Recruit samples differed significantly from adult samples collected at the same locale, and showed extensive between-year variation. Genetic differentiation among recruit samples was much higher in 1997 than in 1996. Between-year differences within populations were always greater for recruits than for adults. Potential explanations for the differentiation of recruit samples include pre- and post-settlement natural selection and high interfamily variance in reproductive success or “sweepstakes” recruitment. Unless recruit differentiation can be attributed to an improbable combination of strong and spatially diverse selection, such differentiation across northern California populations indicates that the larval pool is not well mixed geographically (even on spatial scales <20 km), despite long planktonic larval duration. Received: 6 July 1999 / Accepted: 25 January 2000     

Balancing the edge effects budget: bay scallop settlement and loss along a seagrass edge

Edge effects are a dominant subject in landscape ecology literature, yet they are highly variable and poorly understood. Often, the literature suggests simple models for edge effects-positive (enhancement at the edge), negative (enhancement at the interior), or no effect (neutral)--on a variety of metrics, including abundance, diversity, and mortality. In the marine realm, much of this work has focused on fragmented seagrass habitats due to their importance for a variety of commercially important species. In this study, the settlement, recruitment, and survival of bay scallops was investigated across a variety of seagrass patch treatments. By simultaneously collecting settlers (those viable larvae available to settle and metamorphose) and recruits (those settlers that survive some period of time, in this case, 6 weeks) on the same collectors, we were able to demonstrate a "balance" between positive and negative edge effects, resulting in a net neutral effect. Scallop settlement was significantly enhanced along seagrass edges, regardless of patch type while survival was elevated within patch interiors. However, recruitment (the net result of settlement and post-settlement loss) did not vary significantly from edge to center, representing a neutral effect. Further, results suggest that post-settlement loss, most likely due to predation, appears to be the dominant mechanism structuring scallop abundance, not patterns in settlement. These data illustrate the complexity of edge effects, and suggest that the metric used to investigate the effect (be it abundance, survival, or other metrics) can often influence the magnitude and direction of the perceived effect. Traditionally, high predation along a habitat edge would have indicated an "ecological trap" for the species in question; however, this study demonstrates that, at the population level, an ecological trap may not exist.     

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.     

Population dynamics,reproduction and growth of the Indo-Pacific horned sea star, <Emphasis Type="Italic">Protoreaster nodosus</Emphasis> (Echinodermata; Asteroidea)

The horned sea star (Protoreaster nodosus) is relatively common in the Indo-Pacific region, but there is little information about its biology. This study of the population biology of P. nodosus was carried out in Davao Gulf, The Philippines (7°5′N, 125°45′E) between September 2006 and May 2008. Protoreaster nodosus was found in sand and seagrass dominated habitats at a mean density of 29 specimens per 100 m² and a mean biomass of 7.4 kg per 100 m², whereas a significantly lower density and biomass was found in coral and rock dominated habitats. Adult specimens (mean radius R = 10.0 cm) were found at depths of 0–37 m, whereas juveniles (R < 8 cm) were only found in shallow sandy habitats with abundant seagrass (water depth ≤2 m). Increased gonad weights were found from March to May (spawning period), which coincided with an increasing water temperature and a decreasing salinity. Density and biomass did not change significantly during reproduction, but sea stars avoided intertidal habitats. All specimens with R > 8 cm had well developed gonads and their sex ratio was 1:1. Protoreaster nodosus grew relatively slowly in an enclosure as described by the exponential function G = 7.433 e^{−0.257 × R} . Maturing specimens (R = 6–8 cm) were estimated to have an age of 2–3 years. Specimens with a radius of 10 cm (population mean) were calculated to have an age of 5–6 years, while the maximum age (R = 14 cm) was estimated as 17 years. Potential effects of ornamental collection on the sea star populations are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Contrasting effects of habitat loss and fragmentation on coral-associated reef fishes

Disturbance can result in the fragmentation and/or loss of suitable habitat, both of which can have important consequences for survival, species interactions, and resulting patterns of local diversity. However, effects of habitat loss and fragmentation are typically confounded during disturbance events, and previous attempts to determine their relative significance have proved ineffective. Here we experimentally manipulated live coral habitats to examine the potential independent and interactive effects of habitat loss and fragmentation on survival, abundance, and species richness of recruitment-stage, coral-associated reef fishes. Loss of 75% of live coral from experimental reefs resulted in low survival of a coral-associated damselfish and low abundance and richness of other recruits 16 weeks after habitat manipulations. In contrast, fragmentation had positive effects on damselfish survival and resulted in greater abundance and species richness of other recruits. We hypothesize that spacing of habitat through fragmentation weakens competition within and among species. Comparison of effect sizes over the course of the study period revealed that, in the first six weeks following habitat manipulations, the positive effects of fragmentation were at least four times stronger than the effects of habitat loss. This initial positive effect of fragmentation attenuated considerably after 16 weeks, whereas the negative effects of habitat loss increased in strength over time. There was little indication that the amount of habitat influenced the magnitude of the habitat fragmentation effect. Numerous studies have reported dramatic declines in coral reef fish abundance and diversity in response to disturbances that cause the loss and fragmentation of coral habitats. Our results suggest that these declines occur as a result of habitat loss, not habitat fragmentation. Positive fragmentation effects may actually buffer against the negative effects of habitat loss and contribute to the resistance of reef fish populations to declines in coral cover.     

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.     

Differences in abalone growth and morphology between locations with high and low food availability: morphologically fixed or plastic traits?

Many species of sedentary marine invertebrates exhibit large spatial variation in their morphology, which allow them to occupy a broad geographic distribution and range of environmental conditions. However, the detection of differences in morphology amongst variable environments cannot determine whether these differences represent a plastic response to the local environment, or whether morphology is genetically fixed. We used a reciprocal transplant experiment to test whether ‘stunted’ blacklip abalone (Haliotis rubra) are the result of a plastic response to the environment or fixed genetic trait. Furthermore, we related environmental factors, that affect food availability (density of abalone, water movement, algal cover and reef topography), to differences in growth and morphology. Morphological plasticity was confirmed as the mechanism causing morphological variation in H. rubra. Individuals transplanted to sites with ‘non-stunted’ H. rubra grew significantly faster when compared to stunted controls, whilst individuals transplanted to stunted sites grew significantly slower compared to non-stunted controls. The growth response was greater for individuals transplanted from ‘non-stunted’ to ‘stunted’ sites, suggesting that the environmental stressors in morphologically ‘stunted’ habitat are stronger compared to locations of faster growing morphology. We propose that these differences are related to resource availability whereby low algal cover and topographic simplicity results in stunted populations, whereas high algal abundance and topographic complexity results in non-stunted populations.     

Genetic structure of natural populations of California red abalone (<Emphasis Type="Italic">Haliotis rufescens</Emphasis>) using multiple genetic markers

Mitochondrial cytochrome oxidase subunit one (COI) sequence, nuclear microsatellites, and amplified fragment length polymorphisms (AFLPs) were used to evaluate connectivity among nine red abalone (Haliotis rufescens) populations sampled between August 1998 and November 2003 along approximately 1,300 km of California coastline from Crescent City (41°46′N, 124°12′W) to San Miguel Island (34°02′N, 120°22′W). COI sequences and microsatellite genotypes did not show significant genetic divergence among nine sampled populations. A subset of five populations spanning the geographic range of the study was scored for 163 polymorphic AFLP markers. Of these, 41 loci showed significant divergence (P < 0.001) among populations. Still, no AFLP markers were diagnostic for any of the study populations, and assignment tests did not consistently assign individuals to the correct population. Although the AFLP data are the first to suggest there is significant genetic differentiation among California red abalone populations, the discordance between the different genetic markers needs further study before unambiguous conclusions can be drawn with respect to connectivity among the populations. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seasonal distribution patterns of juvenile loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) following capture from a shipping channel in the Northwest Atlantic Ocean

Thirty-four juvenile loggerhead sea turtles captured by trawling from the Charleston, South Carolina (USA), shipping channel (32°42′N; −79°47′W) between May 2004 and August 2007 were tagged with satellite transmitters to assess the extent to which they remained near the capture location given their collection along a seasonal migratory corridor. Seventy-five percent of juveniles were classified as seasonal residents. Migrants predominantly swam north in the spring and nomads wandered south in the summer, but predictive indicators for non-resident status were not identified. All but one juvenile generally remained south of 34°N, within 40 km of shore, and in waters <30 m deep throughout the year. Nine of 14 loggerhead sea turtles monitored during the winter remained exclusively over the continental shelf, three briefly occurred in oceanic habitats, and two foraged extensively in oceanic habitats. Residents distributed >15 km from shore between spring and autumn were three times as likely to occur in oceanic habitats in winter. Modest seasonal movements contrasted with adults tagged at similar latitudes and with juveniles tagged further north and suggest distinct foraging groups within a regional foraging ground.