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Abstract. Demographic connectivity is a fundamental process influencing the dynamics and persistence of spatially structured populations. Consequently, quantifying connectivity is essential for properly designing networks of protected areas so that they achieve their core ecological objective of maintaining population persistence. Recently, many empirical studies in marine systems have provided essential, and historically challenging to obtain, data on patterns of larval dispersal and export from marine protected areas (MPAs). Here, we review the empirical studies that have directly quantified the origins and destinations of individual larvae and assess those studies' relevance to the theory of population persistence and MPA design objectives. We found that empirical studies often do not measure or present quantities that are relevant to assessing population persistence, even though most studies were motivated or contextualized by MPA applications. Persistence of spatial populations, like nonspatial populations, depends on replacement, whether individuals reproduce enough in their lifetime to replace themselves. In spatial populations, one needs to account for the effect of larval dispersal on future recruitment back to the local population through local retention and other connectivity pathways. The most commonly reported descriptor of larval dispersal was the fraction of recruitment from local origin (self-recruitment). Self-recruitment does not inform persistence-based MPA design because it is a fraction of those arriving, not a fraction of those leaving (local retention), so contains no information on replacement. Some studies presented connectivity matrices, which can inform assessments of persistence with additional knowledge of survival and fecundity after recruitment. Some studies collected data in addition to larval dispersal that could inform assessments of population persistence but which were not presented in that way. We describe how three pieces of empirical information are needed to fully describe population persistence in a network of MPAs: (1) lifetime fecundity, (2) the proportion of larvae that are locally retained (or the full connectivity matrix), and (3) survival rate after recruitment. We conclude by linking theory and data to provide detailed guidance to empiricists and practitioners on field sampling design and data presentation that better informs the MPA objective of population persistence.

Abstract. 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.

Table A3. 2-way ANOVA testing for differences in larval vertical distributions (depth) over the diel cycle (day/night). Day/night by depth interactions revealed whether larvae migrated into the upper water column during the night. All species of barnacles and pinnotherids occurred deep throughout the day while the remaining taxa migrated to the surface at night.

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Recent syntheses on the evolutionary causes of dispersal have focused on dispersal as a direct adaptation, but many traits that influence dispersal have other functions, raising the question: when is dispersal 'for' dispersal? We review and critically evaluate the ecological causes of selection on traits that give rise to dispersal in marine and terrestrial organisms. In the sea, passive dispersal is relatively easy and specific morphological, behavioural, and physiological adaptations for dispersal are rare. Instead, there may often be selection to limit dispersal. On land, dispersal is relatively difficult without specific adaptations, which are relatively common. Although selection for dispersal is expected in both systems and traits leading to dispersal are often linked to fitness, systems may differ in the extent to which dispersal in nature arises from direct selection for dispersal or as a by-product of selection on traits with other functions. Our analysis highlights incompleteness of theories that assume a simple and direct relationship between dispersal and fitness, not just insofar as they ignore a vast array of taxa in the marine realm, but also because they may be missing critically important effects of traits influencing dispersal in all realms.

The effect of planktivory on life history patterns of estuarine crabs was studied by determining preferences of common estuarine fishes for crab larvae in the laboratory and the upper Newport River estuary, North Carolina. Plankton samples (68) and fishes were collected from an upstream and downstream site, on spring and neap low tides, and during the day and night. Over 99.6% of the plankters collected were decapod larvae, copepods, barnacle nauplii, and cyprids. Predominant fishes in the upper estuary were silversides, Menidia menidia, anchovies, Anchoa mitchelli, and killifish, Fundulus heteroclitus, as is typical for other estuaries on the east coast of the United States. Gut contents of 1861 fishes 15—100 mm long were analyzed. Silversides and anchovies preyed upon crab larvae more often than did killifish, and are most likely to influence the life history patterns of crabs inhabiting upper estuaries. Fishes that eat crab larvae are more abundant in estuaries than coastal waters during summer. Fishes in the estuary and the laboratory showed strikingly similar preferences for prey. In order to descending preference, natural populations of fishes preferred copepods, crab larvae that are exported from estuaries (Uca, Sesarma cinereum), and decapod larvae that develop in estuaries (Sesarma reticulatum, Palaemonetes, Rhithropanopeus harrisii). In the laboratory, juvenile and adult silversides and killifish preferred Artemia nauplii to crab larvae, they fed randomly on Uca larvae, and they avoided R. harrissii larvae. These planktivores preferred zoeae that are exported to coastal waters over those that are retained because exported larvae are smaller and have shorter spines. While the large size and spines of retained larvae protect them from their predators in estuaries, vulnerable zoeae may emigrate from estuaries to coastal waters because the rate of encounter with predators offshore is less than in estuaries. The risk of predation also appears to vary spatially and temporally within the estuary. Predation generally was greatest upstream in shallow, narrow areas of the upper estuary on diurnal neap tides. The spatial gradient in predation apparently was due largely to the great abundance of fishes, and particularly small zooplanktivorous fishes, occurring upstream. In contrast, temporal patterns of planktivory were not due to differences in fish size and abundance, but to diurnal foraging of fishes and changes in the availability of prey. Resident zooplankters generally were preyed upon more during neap tides, perhaps because they remained nearer to the substrate on spring tides to prevent being swept downstream. Uca and S. cinereum zoeae were eaten in similar numbers during diurnal neap and spring tides because most zoeae had been transported downstream before dawn when fishes resumed feeding. Estuarine crabs may have responded to predictable trends in planktivory by dispersing newly hatched zoeae downstream on nocturnal ebb tides, regardless of where larvae develop. Small vulnerable zoeae eventually disperse ...

Naturalists and scientists have been captivated by the diversity of marine larval forms since they were discovered following the advent of the microscope. Because they often bear little resemblance to adults, larvae were identified initially as new life forms, classified into different groups based on the similarity of their body plans and given new names that are still with us today. The radically different body plans and lifestyles of marine larvae and adults have led most investigators historically to study the two phases of complex life cycles in isolation. More recently, important ecological insights have sprung from taking a holistic view of marine life cycles. Meanwhile, the evolutionary (phenotypic and genetic) links among life-history phases remain less appreciated. In this review, our objective is to evaluate the evolutionary links within marine life cycles, and explore their ecological and evolutionary consequences. We provide a brief overview of marine life histories, discuss the phenotypic and genetic links between the two phases of the life cycle and pose challenges to advance our understanding of the evolutionary constraints acting on marine life histories.