Early Benthic Phase Research Articles

The impact of ocean warming on juvenile American lobster recruitment off southeastern Massachusetts

AbstractDuring the 1990s, coastal habitat off southeastern Massachusetts (SEMA) supported commercially viable fisheries for American lobster (Homarus americanus). Over the past two decades, landings and post‐larval settlement of lobsters in this region, which is near the southern edge of the species' range, have declined substantially, concurrent with a period of significant warming of the coastal waters off southern New England. Previous work has suggested that rising ocean temperatures may adversely impact the survival of larval and early benthic phase (EBP) lobsters and may cause adult lobsters to seek cooler offshore waters during the critical time of larval release. To investigate the manner in which the observed decline in lobster abundance may be linked to warming coastal waters, a high‐resolution hydrodynamic model was used to quantify the increase in water temperature experienced by EBP lobster off SEMA and to supply input to an individual‐based model of lobster larval transport from release areas delineated using fishery‐dependent data of late‐stage egg‐bearing lobsters. The results indicate that rising coastal water temperatures may have adversely impacted EBP lobster recruitment off SEMA by (1) causing an offshore shift in the area of larval release that resulted in a reduction in the delivery of larvae to suitable nearshore EBP habitat and (2) dramatically increasing thermal stress experienced by recently settled EBP lobsters. These findings highlight the implications of warming coastal waters on southern New England lobster population connectivity and provide insight to an understudied mechanism by which climate change affects marine species recruitment.

Role of initial energy reserves in stress tolerance thresholds during the early benthic phase in intertidal invertebrates

Although depleted energy reserves are not a major direct cause of early benthic phase mortality for many species of marine invertebrates, initial energy reserves might nevertheless play a role in early benthic phase mortality through indirect effects on physiological tolerance thresholds, a mechanism that has not been tested. We therefore examined the extent to which energy reserves affect acute tolerance thresholds of early benthic phase individuals of 2 species (Balanus glandula and Nucella ostrina) to 2 of the most challenging intertidal stressors: desiccation and high emersion temperature. Energy reserve levels were estimated by maintaining individuals without food for different durations of time or using individuals of different body mass. Individuals in each energy level treatment were then exposed to a range of desiccation periods and emersion temperatures. Lower estimated energy levels had no effect on tolerance to emersion temperature, but did significantly reduce the ability to tolerate desiccation. This suggests the survival of individuals through the early benthic phase is likely dependent on initial energy content through an indirect effect on tolerance to desiccation. Also, habitats experiencing intense desiccation likely impose a selective pressure on intertidal invertebrates favoring the evolution of greater energy reserves at the onset of the early benthic phase. These findings suggest depleted energy reserves at the onset of the early benthic phase can influence early benthic phase mortality through indirect effects by making individuals more vulnerable to environmental stressors. In this way, energy reserves may impact recruitment rates and thus influence population dynamics and intertidal community structure.

Role of depleted initial energy reserves in early benthic phase mortality of six marine invertebrate species.

Insufficient energy reserves are widely considered to be a primary factor contributing to high rates of early benthic phase mortality among benthic marine invertebrates, but this hypothesis has been based mostly on indirect, observational evidence, and remains largely untested. We therefore examined the role of initial energy reserves in regulating survivorship and growth during the early benthic phase. Recently settled or hatched individuals of six invertebrate species were collected from natural populations, maintained without food, and their survivorship was monitored. Contrary to expectations, starved individuals of all six species had high survivorship through the critical first 10 days of the early benthic phase, with half of the species experiencing <2% mortality, and the remaining three species experiencing only 6%–12% mortality. For five of the six species, 50% mortality was reached only after ≥50 days of starvation. Additionally, no difference in short‐term survivorship was detected among starved individuals of three different size classes (a proxy for energy reserves) of N. ostrina hatchlings. Finally, the effect of different durations of delayed feeding (0–50 days) on recovery (i.e., growth and survivorship) once food was made available revealed that duration of starvation prior to feeding can nevertheless have significant longer‐term impacts on the proportion of individuals that survive or their ability to grow. Together, these findings suggest that depleted energy reserves are not a primary cause of high mortality at the start of the early benthic phase, as had previously been hypothesized. Levels of energy reserves did influence growth, however, suggesting a possible indirect influence on performance by leaving individuals vulnerable for longer periods.

Ontogenetic shifts and interspecies variation in tolerance to desiccation and heat at the early benthic phase of six intertidal invertebrates

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 634:15-28 (2020) - DOI: https://doi.org/10.3354/meps13189 Ontogenetic shifts and interspecies variation in tolerance to desiccation and heat at the early benthic phase of six intertidal invertebrates Hilary J. Hamilton, Louis A. Gosselin* Department of Biological Sciences, Thompson Rivers University, 805 TRU Way, Kamloops, BC, V2C 0C8, Canada *Corresponding author: lgosselin@tru.ca ABSTRACT: During the early benthic phase of intertidal invertebrates, desiccation and elevated temperature are increasingly recognized as the most significant stressors, but it is not known whether all species are equally sensitive during this phase. In this study, involving 6 co-occurring rocky intertidal species (Nucella ostrina, Littorina scutulata, Mytilus trossulus, Chthamalus dalli, Balanus glandula, Petrolisthes cinctipes), we examined interspecific variation in (1) tolerance to desiccation and temperature at the early benthic phase and (2) the magnitude of ontogenetic shifts in tolerance. Ontogenetic shifts in temperature tolerance were significant but modest, whereas desiccation tolerance thresholds changed considerably throughout ontogeny in all species, and shifts were greatest in species that changed microhabitats during ontogeny. Tolerance at the early benthic phase also varied markedly among species; temperature tolerance thresholds ranged from 32.3 to 45.8°C, and juveniles were able to survive exposure to desiccation for durations ranging from 10 min to 29 h. Ontogenetic shifts in desiccation tolerance were largely explained by differences in body mass; thus individuals achieve increased tolerance through growth. However, variation among species was unrelated to body mass; rather, interspecific variation in tolerance thresholds of the early benthic phase was related to the upper limit of intertidal distribution of the species and to microhabitat use during this phase. The study revealed desiccation to be a greater threat to early benthic phase individuals than temperature in all species, but also discovered considerable interspecific differences in tolerance thresholds, such that species are likely to respond differently to present and future extremes in desiccation and temperature. KEY WORDS: Ontogenetic shifts · Tolerance threshold · Early benthic phase · Juveniles · Environmental stress · Mortality factors · Microhabitat use · Interspecific variation Full text in pdf format Supplementary material PreviousNextCite this article as: Hamilton HJ, Gosselin LA (2020) Ontogenetic shifts and interspecies variation in tolerance to desiccation and heat at the early benthic phase of six intertidal invertebrates. Mar Ecol Prog Ser 634:15-28. https://doi.org/10.3354/meps13189 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 634. Online publication date: January 23, 2020 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2020 Inter-Research.

Evidence that mud seafloor serves as recruitment habitat for settling and early benthic phase of the American lobster Homarus americanus H. Milne Edwards, 1837 (Decapoda: Astacidea: Nephropidae)

Abstract Structurally complex cobble seafloor protects against predators, and is generally assumed to be the only meaningful habitat for settlement and benthic recruitment of American lobsters (Homarus americanus H. Milne Edwards, 1837). Accordingly, historical surveys on featureless substrates such as mud have found few and only older juveniles. Mud, however, is far more common than cobble across the lobster’s range, and may be of increasing importance in regions where the lobster population has been growing over the past few decades. As a first step to determining whether mud seafloor serves as meaningful recruitment habitat for juvenile lobsters, we deployed artificial habitats (bio-collectors) at five locations varying from 100% mud to mostly cobble, in Maces Bay, Bay of Fundy, NB, Canada, to capture young lobsters. A broad size range of lobsters, from new settlers up to adolescents, colonized bio-collectors in all locations, suggesting that lobsters settle and spend at least some of their juvenile life on mud. Differences in body condition (length-standardized mass) of lobsters sampled from the different locations suggest that some individuals must reside on mud for at least months to years, long enough to show differential growth between habitats. The greater relative abundance of adolescents in bio-collectors on mud also suggests their net movement from densely populated cobble beds into mud habitat. We propose that mud seafloor may be a more important habitat for settlement and early survival of American lobsters than is currently appreciated, especially given the current potential saturation of scarce cobble nursery habitat by growing lobster populations and, in some regions, reduced predation on mud seafloor due to overfishing of groundfish.

Competitive and agonistic interactions between the invasive Asian shore crab and juvenile American lobster.

Invasive species can have profound ecological and evolutionary impacts on native fauna, particularly those from overlapping guilds. Intraguild predation and competition often occur simultaneously, and ontogenetic shifts in competitive strength can dictate the magnitude and direction of species interactions. The recent introduction of the Asian shore crab Hemigrapsus sanguineus to the Atlantic coast of North America has resulted in the potential for considerable intraguild interactions with juvenile American lobsters Homarus americanus, with which it now co-occupies rocky intertidal and shallow subtidal habitats. We present data from 5 yr of monthly (May-October) field sampling revealing a significant decline in lobster density as H.sanguineus density increased in the low intertidal. To investigate potential mechanisms behind this pattern, we conducted three mesocosm experiments designed to examine whether competitive interactions between H.americanus and H.sanguineus are size- or density-dependent. Larger early benthic phase lobsters (16-34mm CL) outcompeted H.sanguineus for both food and shelter resources. These lobsters fed faster and more in the presence of H.sanguineus, effectively defended shelter, were responsible for the majority of agonistic interactions, and, in multiple instances, killed and consumed H.sanguineus. Effects on sheltering and agonstic interactions by these lobsters were independent of H.sanguineus density; however, prior shelter residency increased lobster agonistic behavior towards crabs. In contrast, H.sanguineus outcompeted smaller, early benthic phase lobsters (7.2-11.2mm CL) for shelter, and these interactions were density dependent. Displacement of lobsters from shelter by crabs and cumulative agonistic interactions instigated by crabs towards lobsters scaled positively with H.sanguineus density. Given the similarity of the invasion documented here and others occurring globally, these experiments demonstrate the importance of considering how factors such as ontogeny, density-dependence, and primacy influence the outcomes of interactions between intraguild predators. Disentangling how these factors structure intraguild interactions between invasive and endemic species will both advance our fundamental understanding of community ecology and enhance efforts to conserve and manage natural resources.

Decreased growth and increased shell disease in early benthic phase Homarus americanus in response to elevated CO2

Decreased growth and increased shell disease in early benthic phase Homarus americanus in response to elevated CO2

Ontogenetic habitat shift in Pugettia quadridens on the coast of Sagami Bay, Japan

Population dynamics of the kelp crab Pugettia quadridens, a potential predator of juvenile abalone, were investigated on the coast of Nagai, Sagami Bay, to examine its cryptic ontogenetic habitat shift. Monthly quantitative sampling over 2 years, which was carried out in 11 different subtidal habitats (< 0.1–8 m deep), revealed that P. quadridens changes ontogenetically according to its habitat: P. quadridens occurred in shallow lower subtidal (1–4 m) small red algal turfs (mainly Grateoloupia cornea) almost all year around, when the population was dominated by juveniles and stage I (immature) individuals; on the other hand, in the shallow upper subtidal (0.1–1 m) habitat (mainly Sargassum fusiforme beds near the low tidal mark), P. quadridens occurred only during winter to early spring, when the population was dominated by individuals of senior ontogenetic stages. These finding suggest that P. quadridens inhabit subtidal small red algal turfs during their early benthic phase, and then, the majority of larger individuals of stages II and III migrate to Sargassum beds. Our results suggest that the impact of P. quadridens predation on abalone stocks is limited in the present study site, primarily because the habitat of P. quadridens is segregated from that of juvenile abalone.

Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 562:53-63 (2016) - DOI: https://doi.org/10.3354/meps11975 Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates Samantha D. Sandee, Jonathan D. Van Hamme, Louis A. Gosselin* Department of Biological Sciences, Thompson Rivers University, 900 McGill Road, Kamloops, BC V2C 0C8, Canada *Corresponding author: lgosselin@tru.ca ABSTRACT: Microbial pathogens such as bacteria, viruses, fungi, and protozoa are potentially important causes of mortality during the critical first days of juvenile life in benthic invertebrates, but their effect on early juveniles in natural habitats remains unexplored. We therefore placed newly-settled mussels (Mytilus trossulus) and barnacles (Balanus glandula, Chthamalus dalli), and newly-hatched snails (Nucella ostrina) in screened cages submerged in the field, exposing them to ambient microbial organisms while isolating them from most non-microbial mortality factors. Mortality over a 5 d period was only 0-3% in M. trossulus and N. ostrina and 0-10% in B. glandula and C. dalli. Mortality was consistent among replicate trials in the same summer and between 2 different years, and was much lower than previously reported natural early juvenile mortality in these species. We then examined whether bacterial infection caused the few juvenile deaths in our field experiment. Dosage testing in the laboratory with 5 antibiotics resulted in an antibiotic cocktail providing broad-spectrum antibacterial protection without affecting the health of juveniles. In a second field experiment, early juvenile M. trossulus and N. ostrina exposed to the antibiotic cocktail 3 times daily did not experience reduced mortality relative to controls. Our findings suggest that, at least in some species, microbial pathogens are not a direct cause of juvenile mortality in the field, thus narrowing the list of potential causes of early juvenile mortality to the non-microbial factors excluded from our experiments. KEY WORDS: Early benthic phase · Natural mortality · Bacteria · Viruses · Antibiotics · Immune response · Survivorship · Mussels · Barnacle cyprids · Snails Full text in pdf format PreviousNextCite this article as: Sandee SD, Van Hamme JD, Gosselin LA (2016) Testing microbial pathogens as a cause of early juvenile mortality in wild populations of benthic invertebrates. Mar Ecol Prog Ser 562:53-63. https://doi.org/10.3354/meps11975 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 562. Online publication date: December 29, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Evaluation of Effectiveness of Fixed‐Station Sampling for Monitoring American Lobster Settlement

AbstractThe American lobster Homarus americanus supports one of the most valuable fisheries in the USA. One of the important monitoring programs is for benthically settled lobsters, which closely relates to recruitment. The lobster settlement sampling program follows a fixed‐station design. However, the performance of this design has not been evaluated, and we are unclear if the design can capture the temporal dynamics of settlers, in particular in response to changes in spatial distribution of lobster in the last 2 decades. In this study, we compared the fixed‐station design with a random sampling design for the mid‐coast region of the Gulf of Maine. We developed a generalized additive model (GAM) to quantify the relationship between habitat variables and density of early benthic phase and older juvenile lobsters by using the data from inshore trawl surveys from 1989 to 2012. The GAM model was then used to simulate putative true populations using the habitat variables. The two different sampling designs were applied to sample the simulated true populations. The fixed‐station sampling design tended to underestimate the true density but could capture the temporal trends in settler density. A persistence index analysis suggests that the fixed‐station design could identify interannual change of the lobster settler density. This study suggests that fixed‐station sampling design is effective in monitoring temporal changes in settler density but could not be used for the estimation of absolute density of settlers.Received December 16, 2014; accepted July 9, 2015

Differential Response of the American LobsterHomarus americanusto the Invasive Asian Shore CrabHemigrapsus sanguineusand Green CrabCarcinus maenas

The American lobster Homarus americanas shares rocky shore habitats and resources with two common invasive crab species in the northwest Atlantic: the green crab Carcinus maenas and the Asian shore crab Hemigrapsus sanguineus. Juvenile or early benthic phase (EBP) lobsters live under the same boulders as these crabs and are potentially vulnerable to crab predation and competition. Time-lapse photography was used to quantify aggressive interactions between EBP lobsters and invasive crabs in the laboratory. Lobsters behaved far more aggressively toward Asian shore crabs (initiating 11.8 attacks/h) than green crabs (4.9 attacks/h). Crab behavior varied widely as well, as green crabs were five times more likely to attack EBP lobsters than were Asian shore crabs. Thus, lobsters initiated 75.5% of aggressive interactions with Asian shore crabs, compared with only 22.3% with green crabs. Invasion history was a possible reason for this disparity, as green crabs have shared geographic range with American lobsters for more than 100 y. compared with only more than 10 y for Asian shore crabs. Differences in lobster responses to the two crab species suggest that aggressive behavior is the default for EBP lobsters and that they attacked the novel species (H. sanguineus) because they had not developed avoidance behavior to the potential crab threat. Green crabs posed more of a predation threat than Asian shore crabs, consuming over 80% of lobsters in 24-h trials. These results suggest that invasion history and predator—prey adaptation may shape the behavior and ecological interactions of native and invasive species.

Actions for restocking of the European lobster (Homarus gammarus): a case study on the relevance of behaviour and welfare assessment of cultured juveniles

Restocking and stock enhancement of marine organisms are increasingly becoming a common practice to replenish populations of fish and invertebrates. As for aquaculture, they raise several conservation and welfare issues. Here, we focus on lobsters (Homarus sp.), crustacean decapods that have been cultivated and released since the end of the nineteenth century. In Europe (H. gammarus), in the last three decades these actions have been prompted by dramatic stock depletion and efficient rearing technology, yet often overlooking ecological and behavioural data. We emphasize the relevance of behaviour and welfare assessment of cultured juveniles during the early benthic phase and report an experimental case study in which rearing conditions of juveniles were varied shaping distinct profiles in sheltering behaviour. Simple rearing procedures of environmental enrichment coupled with behavioural tests may allow improving and assessing the survival skills of individuals that will be released, at the same time ameliorating their welfare conditions and eventually increasing restocking success.

Settlement and early survival of southern rock lobster, Jasus edwardsii, under climate-driven decline of kelp habitats

Abstract Kelp habitats provide food, refuge, and enhance the recruitment of commercially important marine invertebrates. The southern rock lobster, Jasus edwardsii, supports valuable fisheries in southern Australia and New Zealand. Kelp habitats once covered large areas of inshore reef around Tasmania, Australia, but coverage has reduced over the last few decades due to climate change, especially off the eastern coast of the island. We investigated whether the kelp influences the settlement of lobster post-larvae to artificial collectors and how the presence of kelp affected the overnight predation on the early benthic phase (EBP). Settlement of lobster was tracked over 6 months using crevice collectors that had either natural or artificial giant kelp, Macrocystis pyrifera attached, or nothing attached (control). Collectors with natural kelp had higher catches than those with artificial kelp or controls (p = 0.003), which suggested enhanced settlement through chemical attraction. Additionally, we measured overnight predation of the EBP in barren and kelp habitats individually tethered to artificial shelters. The kelp habitat was dominated by brown macroalgal species of Ecklonia radiata, Phyllospora comosa, and M. pyrifera, while the barren was devoid of macroalgae. Survival of the EBP was higher (∼40%) in the kelp habitat than in the barren habitat (∼10%) due to differences in predation (p = 0.016). These results suggest that the kelp habitat improves the recruitment of J. edwardsii and that decline in this habitat may affect local lobster productivity along the east coast of Tasmania.

Inter-Cohort Cannibalism of Early Benthic Phase Blue King Crabs (Paralithodes platypus): Alternate Foraging Strategies in Different Habitats Lead to Different Functional Responses

Blue king crabs (Paralithodes platypus) are commercially and ecologically important in Alaska, USA, but population abundances have fluctuated over the past several decades likely resulting from a combination of environmental and biological factors, including recruitment variability. Cannibalism between cohorts may be a source of mortality limiting recruitment success in the wild, but the degree of inter-cohort cannibalism is unknown for early benthic phase blue king crabs. In laboratory experiments, we evaluated the effects of habitat type (sand and shell) on the predator functional response and foraging behavior of year-1 blue king crabs as predators of year-0 conspecifics and examined the effects of predator presence on crypsis of prey crabs. In sand, consumption rates increased with predator size and prey density until satiation, while predation rates in shell were low regardless of predator size or prey density. These differential predation rates yielded a type III functional response in sand but a type I functional response in shell habitat. Crypsis of prey crabs was generally high and did not change in the presence of predators. Predator foraging activity was reduced in shell and may be an adaptive behavior to balance foraging efficiency and susceptibility to larger predators. Our results demonstrate that early benthic phase blue king crabs are cannibalistic between cohorts in the laboratory and that shell material is extremely effective for reducing encounter rates with conspecific predators. The distribution and abundance of such habitat may be important for recruitment success in some populations. Future studies should compare benthic habitat and species assemblages in areas with variable abundances, such as the Pribilof Islands and Saint Matthew Island in the eastern Bering Sea, to better understand possible mechanisms for recruitment variability.

Intra-guild predation among early benthic phase red and blue king crabs: Evidence for a habitat-mediated competitive advantage

The apparent shift in predominance of commercial crab species from blue king crab (Paralithodes platypus) to red king crab (Paralithodes camtschaticus) around the Pribilof Islands, Alaska, USA, may be driven by ecosystem-level processes such as competitive displacement or predation during early life stages. Specifically, intra-guild predation among species during the early benthic phase might be a source of mortality limiting blue king crab population recovery. In a laboratory experiment, we evaluated how varying ratios of prey species (year-0 blue and red king crabs) and habitat type (shell and cobble) affect prey preference of year-1 red king crabs. Year-0 red king crabs were preferentially consumed over blue king crabs in shell habitat, but not cobble, likely because the smaller interstitial spaces in shell reduced predator foraging efficiency and predator–prey encounter rates. Blue king crabs had high levels of crypsis regardless of habitat type or predator presence/absence, while red king crabs were less cryptic overall compared to blue king crabs, but crypsis increased when predators were present. Preference for red king crabs in shell may reflect divergent adaptations between species for minimizing predation. Blue king crab's light, mottled coloration and relatively smooth, flat carapace is well adapted for visual and physical crypsis in shell habitat, while the monochromatic, dark coloration and pronounced spination of red king crabs may make them more conspicuous. Our results show that habitat can mediate intra-guild predation between Paralithodes species and suggest that shell material may provide blue king crabs a competitive advantage over red king crabs. The extent of shell habitat may be an important factor regulating blue king crab distribution or the recovery of depleted populations around the Pribilof Islands.

Early benthic phase mortality of the barnacle Balanus glandula is influenced by Fucus spp. cover but not by weather-related abiotic conditions

This study aimed to improve our understanding of the factors that influence mortality of the acorn barnacle, Balanus glandula, during the first days after the transition from pelagic to benthic environments. This was accomplished by examining the mortality of barnacle cyprids from settlement to metamorphosis, as well as mortality of early juveniles up to the age of 10 d after metamorphosis. A field survey of B. glandula recruitment was conducted from 1 to 23 June 2011 at Wizard Islet in Barkley Sound, British Columbia, Canada. We also documented the range of weather-related abiotic conditions that occurred in the intertidal zone during the recruitment survey. These weather-related abiotic conditions were highly variable during the survey, indicating that each daily cohort of barnacle settlers experienced conditions after settlement that differed from those experienced by the other daily cohorts. Cyprid cohort mortality was high, averaging 52.7±22.7% (SD), and differed greatly among the daily cohorts. Contrary to expectations, cyprid mortality was not significantly influenced by weather-related abiotic conditions. This was likely due to the study being conducted during a La Niña cycle that may have had lower temperature and desiccation levels than are typical for Barkley Sound. Overall, an average of 70.6±16.3% (SD) of all metamorphosed individuals were alive 10d after metamorphosis. Although the direct cause of high mortality could not be determined, Fucus spp. cover negatively influenced the survival of both newly-settled cyprids and juveniles. A decline of fucoid algae populations due to changing climate may therefore result in an increase in barnacle survival through the early benthic phase and may subsequently affect annual variation in barnacle population abundance.

Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 481:147-159 (2013) - DOI: https://doi.org/10.3354/meps10221 Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality Brittany T. Jenewein1, Louis A. Gosselin1,2,* 1Department of Biological Sciences, Thompson Rivers University, 900 McGill Road, Kamloops British Columbia V2C 0C8, Canada 2Department of Biology, University of Victoria, Victoria British Columbia V8W 3N5, Canada *Corresponding author. Email: lgosselin@tru.ca ABSTRACT: We examined the sensitivity of newly settled Mytilus trossulus to heat and desiccation, as well as the ontogeny of sensitivity through the early benthic phase. Laboratory experiments were conducted to determine the sensitivity of mussels to the full range of temperatures and desiccation levels experienced in the field. Mussels of 1 to 2 mm shell length (SL) experienced a threshold of heat tolerance at 34°C and a threshold of desiccation tolerance at vapour pressure deficit levels of 1.01 kPa. Extended periods of temperatures reaching or exceeding lethal levels for newly settled M. trossulus occurred relatively rarely in Barkley Sound, British Columbia, Canada, whereas lethal levels of desiccation occurred often during the recruitment season and were usually sustained for several hours. Desiccation, therefore, appears to be a substantially greater threat to recently settled M. trossulus than heat. A final laboratory experiment characterized the changes in sensitivity to desiccation that occur as mussels increase in size. Mussels became highly tolerant to desiccation when they reached a size of 2 to 3 mm SL. This size closely corresponds to the size at which juvenile M. trossulus relocate from protective filamentous algal habitat to adult habitat, suggesting ontogenetic shifts in habitat use by juvenile M. trossulus are a response to changing sensitivity to desiccation. If so, the future survival of newly settled mussels, and thus possibly the local persistence of mussel populations, may depend upon the persistence of protective algal microhabitats under changing climate conditions. KEY WORDS: Early post-settlement mortality · Mortality factors · Physiological stress · Weather · Settlement · Recruitment · Population regulation · Climate change Full text in pdf format PreviousNextCite this article as: Jenewein BT, Gosselin LA (2013) Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality. Mar Ecol Prog Ser 481:147-159. https://doi.org/10.3354/meps10221 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 481. Online publication date: May 07, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Ocean-Based Nurseries for Cultured Lobster (Homarus americanusMilne Edwards) Postlarvae: Initial Field Experiments off the Coast of Eastern Maine to Examine Effects of Habitat and Container Type on Growth and Survival

The commercial fishery for American lobster Homarus americanus Milne Edwards in Maine has experienced the highest landings during the past 2 decades than at any time since the 1950s. However, there is no scientific consensus on why landings have increased nearly 250% from 1990 to 2010, and no one can predict how long landings can be expected to remain at current levels. This uncertainty has sparked a renewed interest in lobster stock enhancement using cultured individuals. Historically, lobster stock enhancement in North America has focused primarily on releasing early benthic phase (stage IV) animals. It is not cost-effective to feed and maintain animals in the laboratory or hatchery until they are larger (ca. stage X–XI), as is typical of enhancement efforts with cultured individuals of Homarus gammarus (L.) in Europe, even though survival to commercial size presumably would be greater. One difficulty with releasing early benthic phase animals is that they have the capacity to swim away from the release site, making tests to determine the efficacy of such programs logistically difficult and expensive. A low-cost, low-maintenance, ocean-based nursery grow-out system for stage IV H. americanus was tested in waters off eastern Maine using technology first developed and implemented successfully for cultured individuals of H. gammarus in Ireland. A single individual was added to a plastic soda bottle (ca. 350 mL) or Petri dish (440 mL) containing a series of small holes to allow continuous flow of seawater into and out of the units. Bottles (n = 630) and dishes (n = 420) were added to rigid nursery cages constructed of traditional vinyl-coated lobster trap wire and deployed in July 2002 ca. 2 m off the bottom in depths of 10 m, 15 m, and 25 m in and around Chandler Bay near Jonesport. After nearly 70 days, survival in the bottles varied from 20% at the deepwater site to 90% at the shallow-water site; however, after an additional 244–288 days, most bottles had filled with muddy sediments, and mortality rate was nearly 100%. Conversely, survival rates after 448 days in the dishes varied, on average, from 21.5–47.2% per cage originally deployed at the deepest and shallowest site, respectively. Growth rates in the dishes generally doubled during the 14-mo field trial from a carapace length of 4.2 mm to that of 8.9 mm. Results suggest that ocean nurseries can be used to rear cultured lobsters to larger sizes prior to release for stock enhancement purposes; however, these animals are too small to apply visible tags (i.e., streamer or T-bar tags) that fishers could discern easily.

DENSITY-DEPENDENT SETTLEMENT AND MORTALITY STRUCTURE THE EARLIEST LIFE PHASES OF A CORAL POPULATION

The local densities of heterospecifics and conspecifics are known to have profound effects on the dynamics of many benthic species, including rates of settlement and early post-settlement survivorship. We described the early life history of the Caribbean coral, Siderastrea radians by tracking the population dynamics from recently settled planulae to juveniles. Through three years of observation, settlement correlated with the abundance of other benthic organisms, principally turf algae (negatively) and crustose coralline algae (positively). In addition, adult density showed independent effects on coral settlement and early post-settlement survivorship. Settlement rates increased across low levels of adult cover and saturated at a maximum around 10% cover. Early post-settlement survivorship decreased with adult cover, revealing structuring density dependence in coral settlers. The earliest life stages of corals are defined by low survivorship, with survivorship increasing appreciably with colony size. However, recent settlers (one-polyp individuals, < 1-year-old) are more likely to grow into two-polyp juveniles than older single polyps (> 1-year-old) that were delayed in their development. The early benthic phase of corals is defined by a severe demographic bottleneck for S. radians, with appreciable density-dependent and density-independent effects on survivorship. For effective management and restoration of globally imperiled coral reefs, we must focus more attention on this little studied, but dynamic, early life history period of corals.

Spatial and temporal dynamics of reproduction and settlement in the Pompeii worm Alvinella pompejana (Polychaeta: Alvinellidae)

The tubicolous polychaete Alvinella pompejana (Desbruyeres & Laubier) inhabits deep- sea hydrothermal vents. To assess its reproductive and recruitment strategies in response to such extreme conditions, populations of A. pompejana were sampled at various spatial scales: among hydrothermal vents within the 13°N/East Pacific Rise vent field and among vent sectors along the southern East Pacific Rise. Additional samples were collected at 1 vent 31 d apart to determine short- term temporal variations. Such a sampling strategy allowed us to conduct an integrated study of both the spatial variation of the reproductive dynamics (i.e. fecundity, oocyte distribution) and the popula- tion structure of this polychaete. Despite a 1:1 sex ratio for each population, a male-biased sex ratio was found at sexual maturity, which could maximise reproductive success in this spermathecae- bearing species. Oocyte size distributions in mature females distinguished 5 maturity stages related to the presence of 1 to 5 distinct oocyte size groups. Coelomic fecundity, which is among the highest known in polychaetes (max. 978 000 oocytes), depends on the maturity stage, but not on the size of the female. The analysis of oocyte distributions strongly highlighted that reproduction is semi- continuous. Mature oocytes are however discretely recruited in the gonoducts from a massive stock of coelomic oogonia and spawned in pulses that may be synchronised between reproductive females. Size-frequency distributions of organisms displayed polymodal structure, suggesting discontinuous recruitment that may be locally affected by the vent dynamics or variations in larval supply. The dis- crepancy between semi-continuous reproduction and a polymodal size-frequency distribution may be explained by: (1) a limited amount of recruits within populations, (2) rapid growth during the early benthic phase, and/or (3) an accumulation of individuals of different ages in the adult cohort. Nearly continuous production of gametes and storage of mature oocytes and/or sperm seem to be a general trend selected in hydrothermal-vent polychaete species.