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Surf zone hydrodynamics vary along shorelines potentially affecting the delivery of larvae and zooplankton subsidies to intertidal communities, and, hence, the intensity of postsettlement interactions, growth and reproduction of filter-feeding foundation species and planktivorous fishes. We investigated the ability of zooplankton assemblages to enter the wide surf zone of the rip-channeled, more dissipative beach at Sand City, California, and the narrow surf zone of the steep reflective beach at nearby Carmel River State Beach. Every day for a month, we surveyed zooplankton inside and outside the surf zone and concomitant larval settlement of the dominant invertebrate onshore at each site in this upwelling regime. At the more dissipative surf zone, all zooplankters were far more concentrated inside than outside the surf zone. Many taxa increased in the surf zone and the predominant invertebrate on beaches, Emerita analoga, settled abundantly when prevailing northwesterly winds relaxed and waves were small. At the reflective surf zone, concentrations of zooplankters of most taxa were far greater outside than inside the surf zone, and many taxa increased in the surf zone when waves were small. Twice as many taxa were positively correlated inside and outside the surf zone at the dissipative than the reflective surf zone, indicating that zooplankters were more freely exchanged although behavior also played a role. Thus, spatial and temporal variation in surf zone hydrodynamics may regulate subsidies of zooplankton food and larval recruits to nearshore communities with potential cascading effects on community dynamics and structure. [ABSTRACT FROM AUTHOR]

Larvae in the coastal ocean are transported toward shore by a variety of mechanisms. Crossing the surf zone is the last step in a shoreward migration and surf zones may act as semipermeable barriers altering delivery of larvae to the shore. We related variation in the structure of intertidal barnacle populations to surf zone width (surf zone hydrodynamics proxy), wave height, alongshore wind stress (upwelling proxy), solar radiation, and latitude at 40 rocky intertidal sites from San Diego, California to the Olympic Peninsula, Washington. We measured daily settlement and weekly recruitment of barnacles at selected sites and related these measures to surf zone width. Chthamalus density varied inversely with that of Balanus, and the density of Balanus and new recruits was negatively related to solar radiation. Across the region, long-term mean wave height and an indicator of upwelling intensity and frequency did not explain variation in Balanus or new recruit densities. Balanus and new recruit densities, daily settlement, and weekly recruitment were up to three orders of magnitude higher at sites with wide (>50 m), more dissipative surf zones with bathymetric rip currents than at sites with narrow (<50 m) more reflective surf zones. Surf zone width explained 30-50% of the variability in Balanus and new recruit densities. We sampled a subset of sites <5 km apart where coastal hydrodynamics such as upwelling should be very similar. At paired sites with similar surf zone widths, Balanus densities were not different. If surf zone widths at paired sites were dissimilar, Balanus densities, daily settlement, and weekly recruitment were significantly higher at sites with the wider, more dissipative surf zone. The primary drivers of surf zone hydrodynamics are the wave climate and the slope of the shore and these persist over time; therefore site-specific stability in surf zone hydrodynamics should result in stable barnacle population characteristics. Variations in surf zone hydrodynamics appear to play a fundamental role in regulating barnacle populations along the open coast, which, in turn, may have consequences for the entire intertidal community. [ABSTRACT FROM AUTHOR]

Larvae of intertidal species develop at sea and must return to adult habitats to replenish populations. Similarly, nutrients, detritus and plankton provide important subsidies spurring growth and reproduction of macroalgae and filter-feeding invertebrates that form the foundation of intertidal communities. Together, these factors determine the density and intensity of interactions among community members. We hypothesized that spatial variation in surfzone hydrodynamics affects the delivery of plankton subsidies. We compared entire zooplankton communities inside and outside the surf zone daily while monitoring physical conditions for one month each at two shores with different surfzone characteristics. Opposite cross-shore distributions of larvae and other zooplankters occurred at the two sites: zooplankton was much more abundant inside the mildly sloping dissipative surf zone (DSZ) with rip currents and was more abundant outside the steep reflective surf zone (RSZ). Biophysical numerical simulations demonstrated that zooplankters were concentrated in rip channels of the DSZ and were mostly unable to enter the RSZ, indicating the hydrodynamic processes behind the observed spatial variation of zooplankters in the surf zone. Differences in the concentration of larvae and other zooplankters between the inner shelf and surf zone may be an underappreciated, key determinant of spatial variation in inshore communities. [ABSTRACT FROM AUTHOR]

Abstract: Larvae of intertidal species develop in the coastal ocean, and the last body of water they must cross while migrating back to shore is the surf zone. We hypothesized that the surf zone is a semipermeable barrier to this shoreward migration and that differences in water exchange across the surf zone result in temporal and spatial variation in larval delivery to the shore. We tested the hypotheses that larval delivery 1) should increase with larger waves and 2) should be higher on more dissipative beaches than on more reflective beaches. We found a significant positive correlation between the daily averaged ratio of wave height to wave period (H/T) and daily cyprid settlement at Dike Rock, California and Bastendorff Beach, Oregon, USA. We tested the second hypothesis by comparing populations of barnacles, limpets, and benthic algae on rocks on four more dissipative and six more reflective sandy beaches in northern California and southern Oregon. Newly recruited barnacles and limpets were significantly more abundant at more dissipative than reflective beaches, and the higher abundance was most likely due to differences in settlement rather than post-settlement mortality. The density and percent cover of barnacles and the density of limpets were significantly higher at more dissipative beaches. In contrast, the density and percent cover of algae were significantly higher at more reflective beaches. The results are consistent with the hypothesis that the surf zone is a semipermeable barrier to the shoreward migration of larvae and that differences in water exchange across the surf zone as function of the beach hydrodynamics result in temporal and spatial variation in larval delivery to the shore. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Morphological defences of plankton can include armour, spines and coloration. Spines defend from gape‐limited fish predators, while pigmentation increases visibility to fishes but defends from ultraviolet radiation (UVR).Planktonic crab larvae (zoeae) exhibit inter‐ and intraspecific variability in the lengths of defensive spines, extent of pigmentation and body size. The determinants of this variability and the relationships among these traits are largely unknown.Larvae may employ generalized defences against the dual threats of UVR and predation or specialized defences against their primary threat, with an unknown role of allometric or phylogenetic constraints. Generalization would result in longer spines compensating for the increased predation risk imposed by darker pigments, while specialization would lead to more investment in either defence from predation (long spines) or UVR (dark pigments), at the expense of the other trait.We examined (a) the relationship between spine lengths and pigmentation, (b) the scaling of spine lengths with body size, and (c) phylogenetic constraint in spine lengths, pigmentation, and body size, among and within 21 species of laboratory‐hatched and 23 species of field‐collected crab larvae from Panama and California.We found a negative relationship between spine length and pigmentation among species from laboratory and field. Within species, we found a marginally significant negative relationship among field‐collected larvae.Spine lengths showed positive allometric scaling with carapace length, while spine and carapace lengths, but not pigmentation, had significant phylogenetic signals.The negative relationship we observed between pigmentation and spine length supports our defence specialization hypothesis.Positive allometric scaling of spine lengths means larger larvae are better defended from predators, which may indicate that larvae face greater predation risk as they grow larger.Phylogenetic constraint may have arisen because related species encounter similar predation threats. Conversely, phylogenetic constraint in the evolution of spine lengths may induce convergent behaviours resulting in related species facing similar predation threats.Our results improve understanding of the evolution of the larval morphology of crabs, morphological defences in the plankton and evolutionary responses of morphology to multiple spatially segregated selective forces. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Plankton live under the countervailing selective pressures of predation and ultraviolet radiation (UVR). In lakes, zooplankton are transparent reducing visibility to predatory fishes but are pigmented in the absence of fishes, hypothetically reducing UVR damage. In the sea, planktivorous fishes are widespread, so plankton typically are transparent and ascend to productive surface waters at night to forage and descend during the day to reduce visibility to predators. However, larvae of some species face the unique constraint of traveling in surface currents in the daytime during migrations between adult and larval habitats. We would expect these larvae to be transparent since companion studies demonstrated increased predation risk of pigmented larvae under strong sunlight. Paradoxically, larvae range from being darkly to lightly pigmented. We hypothesize that some larvae are more heavily pigmented to reduce UVR damage, while other species travelling in subsurface currents with low UVR might be more transparent. Linking larval morphology to depth‐dependent selective pressures would add a key element to help improve predictions of larval vertical distributions, which are important for simulating larval transport trajectories. We quantitatively tested the hypothesis that selection may have favored photoprotective pigmentation for larvae in the predominantly transparent plankton community while testing the differential effects of UVA and UVB radiation. We measured larval pigmentation of 12 species of crabs and exposed them to visible light only, visible + UVA, or visible + UVA + UVB in the tropics. Controlling for phylogeny, more pigmented species survived UVR better than less pigmented species, especially on sunnier days, though intraspecific comparisons for four species were equivocal. Most species died even from UVA exposure, which has long been regarded as relatively harmless despite penetrating deeper underwater than UVB. Thus, we demonstrate with a phylogenetically controlled analysis that crab larvae are pigmented in the predominantly transparent planktonic community to protect from UVR, improving our understanding of the selective forces acting on animal coloration and the factors determining planktonic distributions, survival, and dispersal. This linkage of morphology with susceptibility will be important for developing mechanistic models of environmental stress responses to better predict larval dispersal in current and future climates. [ABSTRACT FROM AUTHOR]