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Open Access Publications from the University of California

Scholarly Works (11 results)

  • Article
Research Theses and Dissertations (2011)

In an era of increasing governmental protection of marine resources and accelerating climate change, knowing how benthic populations of marine organisms are connected is of paramount importance. However, little is known about connectivity in the nearshore environment, particularly at ecologically and demographically relevant scales. Because the dispersive larval stage is the key to understanding population connectivity, my dissertation focused on developing a new technique for tracking larvae and determining how larval swimming behaviors can influence their cross-shelf distributions in the dynamic upwelling environment of northern California. This information is relevant not only to the applied fields of invasive species management, stock assessment, and marine protected area establishment, but also to the academic pursuit of understanding how life evolved in the sea.

In Chapters 1 and 2, I focused on investigating the role of swimming behavior in regulating larval transport in upwelling regimes. I observed in the laboratory the larvae of four crab species from open coast and estuarine habitats that develop either nearshore or offshore. Larval vertical positions in acrylic columns were recorded for up to three days, and I determined whether (1) depth preferences differed for the four species, (2) larvae undertook tidal and diel vertical migrations, (3) vertical migrations were timed endogenously or exogenously, and (4) maternal habitat influenced larval swimming behavior. Regardless of light or tidal phase, larvae of three species (Hemigrapsus oregonensis, Lophopanopeus bellus bellus, and Pachygrapsus crassipes) that develop offshore stayed high in the water column, where they would be transported seaward in the field. In contrast, larvae of one species (Petrolisthes cinctipes) that develop nearshore stayed low in the water column, where they would remain in shoreward-flowing bottom waters. None of the species from the open coast exhibited tidal or diel vertical migrations, but one estuarine species (H. oregonensis) exhibited reverse tidal vertical migrations that would expedite their transport to the open ocean. Furthermore, larvae hatched from estuarine populations of P. crassipes exhibited tidal swimming behaviors, while larvae hatched from coastal populations showed no tidally based behavior. Thus, larvae of species that hatch in different locations and develop different distances from shore exhibited diverse larval swimming behaviors that regulate transport, and these behaviors are phenotypically plastic.

In Chapters 3 and 4, I determined the utility of using trace element signatures in larval soft tissues as natural tags to track larval dispersal and population connectivity. As larvae develop as embryos and then pass through water masses throughout their development, they incorporate natural trace element signatures into their bodies. Many previous studies have successfully used the signatures in calcified structures, such as mollusc shells or fish otoliths, so my research instead concentrated on determining the utility of trace element signatures in larval soft tissues. The ability to track larvae based on trace element signatures in soft tissues would dramatically increase the diversity of taxa that could be investigated using this established tool.

A successful trace element study requires a natal site atlas with high reclassification success, but selecting sites to create an atlas is time consuming and expensive, with no guarantee that trace element signatures will differ among sites and remain consistent over time. In Chapter 3, I determined whether natal site atlases could be used repeatedly and identified site characteristics that yielded the best results by building atlases in five consecutive years using crab embryos from 15 sites that spanned 190 km of the northern California coast. I analyzed the elemental composition of embryos using a discriminant function optimization procedure to determine the suite of elements that resulted in the best reclassification success for individual sites and groups of sites each year. No element or group of elements was useful in discriminating the origins of embryos every year, and the reclassification success of the atlas varied at all spatial scales among years. Average reclassification success at the site level ranged annually from 39.5% to 54.3% correct, and combining sites into three areas or two regions improved overall reclassification success to 72.5% to 97.7% correct. Sites with unique geology, consistent freshwater runoff, or high anthropogenic influences had the highest individual reclassification success (up to 86.7% correct), and variation in these factors helped account for the variability in reclassification success among sites. Targeting differences in these factors when selecting sites in future trace element studies will increase the resolution of population connectivity estimates and infoinform explorations on the usefulness of these types of studies in a given area.

Finally, Chapter 4 focused on whether or not trace element signatures were retained in larval soft tissues throughout their pelagic development, to determine whether trace element analysis could be applied to larvae of the vast majority of species that do not retain larval calcified structures. To determine whether natal signatures are retained in soft tissues throughout larval development, I collected embryos of the porcelain crab, Petrolisthes cinctipes, from two to four locations along the coast of northern California in two years and reared larvae in a common water source for 6-8 weeks until they metamorphosed to postlarvae. Twenty elements were analyzed in extractions of soft tissues from embryos for the two larval and one postlarval stages. Elemental signatures of these planktonic stages were compared to those of embryos from the different collection sites using discriminant function analysis to determine if they could be accurately assigned to their site of origin. Overall reclassification success of postlarvae was poor (average 39.7% correct), though individual site success ranged from 86.2% correct to 0% correct. Reclassification success improved to 81.7% correct overall (ranging from 35.7% correct to 94.4% correct) when using each larval stage as a training set for the same larval stage. Thus, the same trace element signatures were not consistently maintained from embryos to postlarvae, but differences in signatures among natal sites were maintained. Trace element signatures in soft tissues could be useful in tracking dispersal from one stage to the next and determining how many sites, rather than which sites, contributed to a cohort of settlers.

These studies, taken as a whole, reveal new insights on larval behavior in upwelling regimes and highlight new approaches to determining population connectivity. Larvae from the open coast of northern California have evolved simple swimming behaviors in the face of complex oceanography, while estuarine species exhibit complex swimming rhythms based on the tidal stage; these differences persist even between populations of the same species. This finding reinforces the importance of understanding how populations are connected through their larval stage, and stokes the discussion about the importance of phenotype versus genotype in determining the success of larvae.

Finally, my work provides novel information about the utility of soft tissue trace element signatures and how to incorporate them into future studies. Marine ecologists constantly seek new and better tools to help determine larval dispersal patterns and population connectivity, and trace element signatures are an important component of the ecologist’s tool box. By determining the best way to utilize trace element signatures in soft tissues, my work opens the door to employing this tool on a whole new suite of taxa and dramatically broadens its utility. Investigators will now be able to use trace element signatures in soft tissues to inform the placement of marine reserves based on source/sink dynamics and an understanding of the locations of larval nursery areas, as well as determine how populations of invasive species are spreading from their points of introduction. Beyond these applied uses, my findings broaden our knowledge of the complexities of larval life in the ocean and inform our understanding of the persistence of sedentary and sessile populations in the sea.

    Cover page: Larval Behavior and Natural Trace Element Signatures as Indicators of Crustacean Population Connectivity
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2013)
    The timing of vertical migrations by newly-hatched larvae determines the extent of transport away from adult populations and exposure to predatory fishes, but it is largely unknown whether larval swimming behavior is a fixed trait or changes adaptively in response to different ocean conditions that are encountered between habitats. We determined whether larvae of the shore crab, Pachygrapsus crassipes, hatched in the San Francisco Estuary and those hatched nearby on the outer coast undertake tidal and diel vertical migrations. Vertical swimming of larvae that were released by females collected from the two locations were recorded in the laboratory for up to four days in constant darkness without a tidal cycle to detect the presence of endogenous tidal and diel vertical migrations. P. crassipes larvae from the outer coast population did not exhibit rhythmic vertical migrations, remaining near the surface throughout the day, whereas larvae from the estuarine population did undertake complex vertical migrations relative to tidal and diel cycles. Although current patterns differ on the open coast and in the estuary, remaining in surface waters at both locations would favor seaward transport of larvae to offshore nursery areas. However, undertaking tidal vertical migrations in estuaries would expedite seaward transport while increasing the risk of fish predation during the daytime. The differences in behaviors are likely phenotypic, because larvae came from neighboring populations and intermingle in offshore larval nursery areas. This spatial variation in larval swimming behavior among habitats enhances transport to offshore nursery areas. © 2013.
      Cover page: Phenotypic plasticity in larval swimming behavior in estuarine and coastal crab populations
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2015)
      Larvae of benthic marine organisms are released amid high densities of suspension feeding and predatory adults and are highly subject to being consumed, even by conspecifics or their own parent. During laboratory feeding trials conducted in June 2006, female shore crabs (Hemigrapsus oregonensis) from Stege Marsh in San Francisco Bay (37°54.530' N, 122°19.734' W) that released their larvae during the previous 24 h ate fewer conspecific larvae than females that had not recently released larvae, though the behavior was not repeated during similar trials in 2007. Additionally, the number of larvae eaten increased with increasing starvation time, and hungrier females showed a trend toward eating more larvae from a different species (Carcinus maenas) than larvae of conspecifics. Thus, suppression of suspension feeding may reduce conspecific predation of newly released larvae, but this response partially depends on hunger level. This is the first time crabs have been shown to suppress feeding to reduce cannibalism of larvae, and this behavior could affect reproductive success and population dynamics. © 2014 Blackwell Verlag GmbH.
        Cover page: Temporal variation in cannibalistic infanticide by the shore crab Hemigrapsus oregonensis: implications for reproductive success
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        • Peer Reviewed
        UC Davis Previously Published Works (2016)
        Demographic connectivity is fundamental to the persistence and resilience of metapopulations, but our understanding of the link between reproduction and recruitment is notoriously poor in open-coast marine populations. We provide the first evidence of high local retention and limited connectivity among populations spanning 700 km along an open coast in an upwelling system. Using extensive field measurements of fecundity, population size and settlement in concert with a Bayesian inverse modelling approach, we estimated that, on average, Petrolisthes cinctipes larvae disperse only 6.9 km (±25.0 km s.d.) from natal populations, despite spending approximately six weeks in an open-coast system that was once assumed to be broadly dispersive. This estimate differed substantially from our prior dispersal estimate (153.9 km) based on currents and larval duration and behaviour, revealing the importance of employing demographic data in larval dispersal estimates. Based on this estimate, we predict that demographic connectivity occurs predominantly among neighbouring populations less than 30 km apart. Comprehensive studies of larval production, settlement and connectivity are needed to advance an understanding of the ecology and evolution of life in the sea as well as to conserve ecosystems. Our novel approach provides a tractable framework for addressing these questions for species occurring in discrete coastal populations.
          Cover page: Inverse approach to estimating larval dispersal reveals limited population connectivity along 700 km of wave-swept open coast
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2009)
          The ability of miniscule larvae to control their fate and replenish populations in dynamic marine environments has been a long-running topic of debate of central importance for managing resources and understanding the ecology and evolution of life in the sea. Larvae are considered to be highly susceptible to offshore transport in productive upwelling regions, thereby increasing dispersal, limiting onshore recruitment, and reducing the intensity of community interactions. We show that 45 species of nearshore crustaceans were not transported far offshore in a recruitment-limited region characterized by strong upwelling. To the contrary, 92% of these larvae remained within 6 km from shore in high densities throughout development along two transects sampled four times during the peak upwelling season. Larvae of most species remained nearshore by remaining below a shallow Ekman layer of seaward-flowing surface waters throughout development. Larvae of other species migrated farther offshore by occurring closer to the surface early in development. Postlarvae evidently returned to nearshore adult habitats either by descending to shoreward-flowing upwelled waters or rising to the sea surface where they can be transported shoreward by wind relaxation events or internal waves. Thus wind-driven offshore transport should not limit recruitment, even in strong upwelling regions, and larvae are more likely to recruit closer to natal populations than is widely believed. This study poses a new challenge to determine the true cause and extent of recruitment limitation for a more diverse array of species along upwelling coasts, and thus to further advance our understanding of the connectivity, dynamics, and structure of coastal populations.
            Cover page: Nearshore larval retention in a region of strong upwelling and recruitment limitation
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2018)
            Planktonic larvae are thought to be very susceptible to offshore advection in upwelling regimes, increasing dispersal and decreasing recruitment. However, larvae of 42 species of nearshore benthic crustaceans primarily developed on the inner shelf at locations both in (98.5%) and away (99.8%) from a perennial upwelling center in the upwelling season of a recruitment-limited region characterized by persistent, strong, upwelling. During three cross-shelf cruises conducted at each location, larvae of 21 species remained on the inner shelf at both sites by occurring beneath seaward-flowing surface currents while larvae of other species migrated to midshelf (four species) or offshore (14 species) by initially developing near the surface. Postlarvae apparently returned to shore either deep in landward-flowing upwelled water or near the surface where behavior allows them to be transported shoreward by internal waves, diel wind cycles or wind relaxation events. Thus, recruitment limitation in upwelling regimes does not appear to be caused by larval mortality from offshore transport, requiring new research directions to advance our understanding of population dynamics, structure and connectivity.
              Cover page: Nearshore Larval Retention and Cross-Shelf Migration of Benthic Crustaceans at an Upwelling Center
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2013)
              Genetic diversity has emerged as an important source of variation in the ecological properties of populations, but there are few studies of genetic diversity effects on colonisation processes. This relative scarcity of studies is surprising given the influence of colonisation on species coexistence, invasion, and population persistence. Here, we manipulated relatedness in experimental populations of colonising larvae in four sessile marine invertebrates. We then examined the influence of coloniser relatedness on the number, spatial arrangement and phenotype of colonisers following permanent settlement. Overall, relatedness influenced colonisation in all four species, but the effects of relatedness on colonisation differed among species. The variable responses of species to manipulations of relatedness likely reflect differences in intensity of inter- and intra-specific competition among adults, as well as the differential consequences of larval behaviours for each species. Relatedness appears to play an underappreciated role in the colonisation process, and we recommend that future studies of genetic diversity effects consider not only adult stages - the focus of most work to date - but also the importance of genetic diversity in early life history stages. © 2012 The Authors. Oikos © 2012 Nordic Society Oikos.
                Cover page: Relatedness affects the density, distribution and phenotype of colonisers in four sessile marine invertebrates
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2014)
                Future climate change is predicted to alter the physical characteristics of oceans and estuaries, including pH, temperature, oxygen, and salinity. Investigating how species react to the influence of such multiple stressors is crucial for assessing how future environmental change will alter marine ecosystems. The timing of multiple stressors can also be important, since in some cases stressors arise simultaneously, while in others they occur in rapid succession. In this study, we investigated the effects of elevated pCO2 on oxygen consumption by larvae of the intertidal porcelain crab Petrolisthes cinctipes when exposed to subsequent salinity stress. Such an exposure mimics how larvae under future acidified conditions will likely experience sudden runoff events such as those that occur seasonally along portions of the west coast of the U.S. and in other temperate systems, or how larvae encounter hypersaline waters when crossing density gradients via directed swimming. We raised larvae in the laboratory under ambient and predicted future pCO2 levels (385 and 1000 µatm) for 10 days, and then moved them to seawater at ambient pCO2 but with decreased, ambient, or elevated salinity, to monitor their respiration. While larvae raised under elevated pCO2 or exposed to stressful salinity conditions alone did not exhibit higher respiration rates than larvae held in ambient conditions, larvae exposed to elevated pCO2 followed by stressful salinity conditions consumed more oxygen. These results show that even when multiple stressors act sequentially rather than simultaneously, they can retain their capacity to detrimentally affect organisms.
                  Cover page: Effect of elevated pCO2 on metabolic responses of porcelain crab (Petrolisthes cinctipes) Larvae exposed to subsequent salinity stress.
                  • Article
                  • Peer Reviewed
                  UC Santa Cruz Previously Published Works (2014)
                  Ocean acidification (OA) is occurring across a backdrop of concurrent environmental changes that may in turn influence species' responses to OA. Temperature affects many fundamental biological processes and governs key reactions in the seawater carbonate system. It therefore has the potential to offset or exacerbate the effects of OA. While initial studies have examined the combined impacts of warming and OA for a narrow range of climate change scenarios, our mechanistic understanding of the interactive effects of temperature and OA remains limited. Here, we use the blue mussel, Mytilus galloprovincialis, as a model species to test how OA affects the growth of a calcifying invertebrate across a wide range of temperatures encompassing their thermal optimum. Mussels were exposed in the laboratory to a factorial combination of low and high pCO2 (400 and 1200 µatm CO2) and temperatures (12, 14, 16, 18, 20, and 24°C) for one month. Results indicate that the effects of OA on shell growth are highly dependent on temperature. Although high CO2 significantly reduced mussel growth at 14°C, this effect gradually lessened with successive warming to 20°C, illustrating how moderate warming can mediate the effects of OA through temperature's effects on both physiology and seawater geochemistry. Furthermore, the mussels grew thicker shells in warmer conditions independent of CO2 treatment. Together, these results highlight the importance of considering the physiological and geochemical interactions between temperature and carbonate chemistry when interpreting species' vulnerability to OA.
                    Cover page: The Role of Temperature in Determining Species' Vulnerability to Ocean Acidification: A Case Study Using Mytilus galloprovincialis
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2014)
                    The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast. © 2014 Coastal and Estuarine Research Federation.
                      Cover page: Transport of Crustacean Larvae Between a Low-Inflow Estuary and Coastal Waters
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