Robert R Warner

• Ph.D.
• Professor at University of California, Santa Barbara

To support conservation practices, societal demand for understanding fundamental coastal ocean ecosystem mechanisms has grown in recent decades. Globally, these regions are among the world’s most productive, but they are highly vulnerable to extractive and non-extractive stresses. In 1999, we established the Partnership for Interdisciplinary Studie...

The life cycle of most benthic marine species includes a planktonic larval stage. Movement, largely by ocean currents, and survival during this stage drive patterns of variability and long-term persistence in adult populations, as well as connectivity among spatially separated populations. Here, we describe recent advances- many by PISCO-in underst...

Predation on parasites is an important ecological process, but few experimental studies have examined the long-term impacts on the prey. Cleaner fish prey upon large numbers and selectively feed on the larger individuals of the ectoparasitic stage of gnathiid isopods. Removal of cleaner fish Labroides dimidiatus for 1.5–12.5 years negatively affect...

Marine protected areas (MPAs) are important tools for managing marine ecosystems. MPAs are expected to replenish nearby exploited populations through the natural dispersal of young, but the models that make these predictions rely on assumptions that have recently been demonstrated to be incorrect for most species of fish. A meta‐analysis showed tha...

The pelagic larval stage is a critical component of the life cycle of most coral reef fishes, but the adaptive significance of this stage remains controversial. One hypothesis is that migrating through the pelagic environment reduces the risk a larval fish has of being parasitised. Most organisms interact with parasites, often with significant, det...

Courtship and spawning behaviors of coral reef fishes are very complex, and sufficient sampling effort and proper methods are required to draw informed conclusions on their mating systems that are grounded in contemporary theories of mate choice and sexual selection. We reviewed the recent study by Karkarey et al. (BMC Ecol 17:10, 2017) on the spaw...

In some marine ecosystems, overharvesting marine predators has triggered major changes in trophic structure and ecosystem function. However, harvest levels that are deemed sustainable for one species may still lead to unexpected impacts elsewhere in the ecosystem. For example, by imposing an additional source of mortality, even sustainable harvesti...

Mutualisms are pivotal in shaping ecological communities. Iconic images of cleaner fish entering the mouths of predatory fish clients to remove ectoparasites epitomize their mutual benefit. Experimental manipulations of cleaner wrasse reveal declines in fish size and growth, and population abundance and diversity of client fishes in the absence of...

Herbivorous fishes are being increasingly valued for their ecological function in coral reef systems, and consequently they have become the focus of management actions on many reefs around the world. Because many conservation actions require an understanding of the space use patterns of species of interest, there has been an increased effort in rec...

Herbivory by fishes and sea urchins is a powerful mechanism on coral reefs that mitigates coral-algal competition by physically removing algae and creating bare space. Spatially constrained grazing by herbivores, particularly parrotfishes, may foster coral recruitment by creating a spatially continuous refuge of bare substrate for settlement and su...

The transition between the planktonic and the benthic habitat is a critical period for the larvae of many demersal marine organisms. Understanding the potential constraints on the timing of this habitat transition, called settlement, is important to understanding their biology. Size-specific mortality can set the limits on lifestyle and help explai...

In terrestrial systems it is well known that the spatial patterns of grazing by herbivores can influence the structure of primary producer communities. On coral reefs, the consequences of varied space use by herbivores on benthic community structure are not well understood, nor are the relative influences of bottom-up (resource abundance and qualit...

Where predator–prey interactions are size-dependent, reductions in predator size owing to fishing has the potential to disrupt the ecological role of top predators in marine ecosystems. In southern California kelp forests, we investigated the size-dependence of the interaction between herbivorous sea urchins and one of their predators, California s...

Human recreational activities like hiking can elicit anti-predator responses in prey species that are similar in nature and magnitude to those elicited by hunting, sometimes triggering dramatic shifts in the surrounding ecosystem via behaviorally mediated cascades. Studies that test analogous hypotheses about the effects of recreational activities...

In ocean ecosystems, many of the changes in predation risk - both increases and decreases - are human-induced. These changes are occurring at scales ranging from global to local and across variable temporal scales. Indirect, risk-based effects of human activity are known to be important in structuring some terrestrial ecosystems, but these impacts...

Oceans currently face a variety of threats, requiring ecosystem-based approaches to management such as networks of marine protected areas (MPAs). We evaluated changes in fish biomass on temperate rocky reefs over the decade following implementation of a network of MPAs in the northern Channel Islands, California. We found that the biomass of target...

Marine defaunation, or human-caused animal loss in the oceans, emerged forcefully only hundreds of years ago, whereas terrestrial defaunation has been occurring far longer. Though humans have caused few global marine extinctions, we have profoundly affected marine wildlife, altering the functioning and provisioning of services in every ocean. Curre...

Background/Question/Methods In the last few decades, the cascading consequences of overharvesting top marine predators have become increasingly clear. However, even when it does not cause dramatic reductions in predator populations, fishing can disrupt the food web in a way rarely considered—by shrinking predator body size distributions. Because m...

Using calcified structures as natural geochemical tags to estimate levels of population connectivity is becoming increasingly common. However, the technique suffers from several logistical and statistical problems that constrain its full application. Foremost is that only a subset of potential sources is sampled, often compounded by under-sampling...

Overfishing of urchin predators, in combination with natural disturbances, has been linked to an increase in the occurrence of urchin barrens. Marine reserves have been proposed as a means to re-establish the interactions between urchins and their predators in California kelp forests. Whether increased densities of lobsters and other predators in r...

An increasing number of short-term experimental studies show significant effects of projected ocean warming and ocean acidification on the performance on marine organisms. Yet, it remains unclear if we can reliably predict the impact of climate change on marine populations and ecosystems, because we lack sufficient understanding of the capacity for...

Hermaphroditism is taxonomically widespread among teleost fishes and takes on many forms including simultaneous, protogynous, and protandrous hermaphroditism, bidirectional sex change, and androdioecy. The proximate mechanisms that influence the timing, incidence, and forms of hermaphroditism in fishes are supported by numerous theoretical and empi...

While detrital material is recognized as an important food source on coral reefs, its role in reef food webs remains unclear. We quantified standing stock and input rates to the detrital resource pool in exposed forereef and protected backreef habitats of Palmyra Atoll National Wildlife Refuge and measured the trophic structure of the overlying fis...

Several factors lead to expectations that the scale of larval dispersal and population connectivity of marine animals differs with latitude. We examine this expectation for demersal shorefishes, including relevant mechanisms, assumptions and evidence. We explore latitudinal differences in (i) biological (e.g. species composition, spawning mode, pel...

Even without selecting for large fish, the added mortality of fishing means fewer fish make it to larger sizes, leading to distributions shifted towards smaller individuals. The consequences of these shifts for single-species management have long been recognized. Because body size limits the sizes of prey a predator can eat, truncated size distribu...

Determining whether seed production is limited by pollen availability has been an area of intensive study. Past studies have focused largely on terrestrial species with biotic pollination modes, but precise causes and consequences of pollen limitation remain unknown. Here, sex ratio, seed production, seed recruitment, and viability were examined in...

Efforts to restore top predators in human-altered systems raise the question of whether rebounds in predator populations are sufficient to restore pristine foodweb dynamics. Ocean ecosystems provide an ideal system to test this question. Removal of fishing in marine reserves often reverses declines in predator densities and size. However, whether t...

Density of competitors for focal species within Central Indo-Pacific reef pairs. Upper panel (a) is blackbar damselfish (P. dickii); lower panel (b) is bullethead parrotfish (C. sordidus). Bars are means (±SE). (TIFF)

Piscivores encountered by P. dickii in relation to reef protection status. Points are means (±SE). (TIFF)

Relationship between excursion area (m2) and rate of movement (cm/s) for C. sordidus. Data are from three atolls within the Line Islands (Palmyra, Tabuaeran, Kiritimati). (TIFF)

Methodological details. (DOC)

Recent theoretical models predict that the relative allocation to advertisement and parental care depends on whether paternal care is necessary for offspring survival: In species with exclusive male care, male investment in attrac-tion is expected to reliably indicate paternal care effort and male phenotypic quality. Previous research, yielding con...

Spatial variation of trace elements in calcified structures (otoliths, statoliths, and shells) has been used to track the movements of individuals among habitats, and connectivity between marine populations. In the present study, we used laser ablation-inductively coupled plasma mass spectrometry to quantify the concentrations of trace elements in...

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The natal origin of a post-dispersal marine fish may be determined by examining the trace elemental signatures present in the core (i.e. the pre-dispersal region) of the otolith. We found distinct spatial differences in the natal elemental signatures in the core region of the otoliths of post-dispersal juvenile kelp rockfish Sebastes atrovirens col...

1. The sublethal impact of parasites on host behaviour and the mechanism linking them to population level effects remain largely unquantified. On the Great Barrier Reef, juvenile gnathiid isopods (mobile ectoparasites) are one of the most common ectoparasites of fishes. Previous laboratory studies on damselfishes suggest that a single gnathiid can...

The indirect, ecosystem-level consequences of ocean fishing, and particularly the mechanisms driving them, are poorly understood. Most studies focus on density-mediated trophic cascades, where removal of predators alternately causes increases and decreases in abundances of lower trophic levels. However, cascades could also be driven by where and wh...

We examined variability in otolith chemistry of wild caught fish in relation to in situ temperature and salinity within the California Current System. Barium, magnesium, and iron from the most recent growth zone in otoliths differentiated pelagic juvenile shortbelly rockfish (Sebastes jordani) residing in water masses with distinct temperature and...

Maternal effects are increasingly recognized as important drivers of population dynamics and determinants of evolutionary trajectories. Recently, there has been a proliferation of studies finding or citing a positive relationship between maternal size/age and offspring size or offspring quality. The relationship between maternal phenotype and offsp...

Fishing has clear direct effects on harvested species, but its cascading, indirect effects are less well understood. Fishing disproportionately removes larger, predatory fishes from marine food webs. Most studies of the consequent indirect effects focus on density-mediated interactions where predator removal alternately drives increases and decreas...

Explicit consideration of space and place in fisheries science and governance holds great promise for addressing management failures caused by inappropriately defined boundaries, disregard for spatial dynamics in assessments, and incompatible ocean uses. Most importantly, it can foster the emergence of sustainable, rights-based governance regimes a...

Recruitment variation in marine populations is clearly affected by physical processes in the ocean. We therefore examined correlations between long-term, high-frequency data on fish settlement on artificial substrates and oceanographic processes operating at different spatial and temporal scales. We sought, for example, associations with processes...

Marine reserve theory suggests that where large, productive populations are protected within no-take marine reserves, fished areas outside reserves will benefit through the spillover of larvae produced in the reserves. However, empirical evidence for larval export has been sparse. Here we use a simple idealized coastline model to estimate the expec...

Marine reserves may not only protect populations within their borders but also subsidize harvested populations outside through the spillover of either adults or planktonic larvae. The conservation benefits of marine reserves are well documented, and a growing body of evidence suggests that the spillover of large adults from reserves can enhance fis...

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To estimate connectivity between populations, we used trace-element composition in otoliths of the temperate wrasse Coris julis as a proxy for the environmental conditions experienced from hatch to settlement. Recruits collected at different sites in the Azores archipelago (northeastern Atlantic) differed significantly in their natal chemical signa...

Otolith microstructure has been shown to record valuable information about fishes including age, growth, and the timing of life history transitions, while microchemical analysis can reveal information about environmental history, dispersal, and migration. For the bluehead wrasse Thalassemia bifasciatum, a common coral reef fish on an oceanic island...

Aim Phylogeographical breaks may reflect historical or present‐day impediments to gene flow, and the congruence of these breaks across multiple species lends insight into evolutionary history and connectivity among populations. In marine systems, examining the concordance of phylogeographical breaks is challenging due to the varied sampling scales...

The study and implementation of no-take marine reserves have increased rapidly over the past decade, providing ample data on the biological effects of reserve protection for a wide range of geographic locations and organisms. The plethora of new studies affords the opportunity to re- evaluate previous findings and address formerly unanswered questi...

Despite the interest in restoring remnant populations of the Olympia oyster, Ostrea lurida Carpenter 1864, little is known about connectivity among populations. Identifying the sources of settling larvae could broaden our understanding of the degree to which particular populations are reliant on their neighbors for their persistence. Calcified stru...

We found distinct geographic differences in trace element concentrations in both the core and early larval areas of the statoliths of paralarval market squid Doryteuthis (= Loligo) opalescens at sites throughout the Southern California Bight, USA. Laser ablation inductively cou- pled plasma mass spectrometry (LA-ICPMS) of individual statoliths indi...

Geochemical signatures deposited in otoliths are a potentially powerful means of identifying the origin and dispersal history of fish. However, current analytical methods for assigning natal origins of fish in mixed-stock analyses require knowledge of the number of potential sources and their characteristic geochemical signatures. Such baseline dat...

Parasitic castration is an adaptive strategy where the parasite usurps its host’s phenotype, most notably the host’s reproductive effort. Though castrators are loosely known to be large relative to their hosts (compared to typical parasites), their mass has rarely been quantified and little is known about size variation, even if such variation exis...

Many nearshore fish and invertebrate populations are overexploited even when apparently coherent management structures are in place. One potential cause of mismanagement may be a poor understanding and accounting of stochasticity, particularly for stock recruitment. Many of the fishes and invertebrates that comprise nearshore fisheries are relative...

One of the most compelling unanswered questions in marine ecology is the extent to which local populations are connected via larval exchange. Recent work has suggested that variation in the chemistry of otoliths (earstones) of fishes may function as a natural tag, potentially allowing investigators to determine sources of individual larvae and esti...

Variation of trace elemental composition in fish otoliths has been successfully used to reconstruct the environmental history of fish, including the movement of early life stages among populations and habitats. Past studies have focused primarily on estuarine-dependent species, and information has been very limited for species that spawn along open...

There is a growing realization that the scale and degree of population connectivity are crucial to the dynamics and persistence of spatially structured populations. For marine organisms with complex life cycles, experiences during larval life may influence phenotypic traits, performance, and the probability of postsettlement survival. For a Caribbe...

Elemental signatures have been used as a tool to track individual organisms to their natal site in an attempt to understand stock structure and larval dispersal. However, factors that affect elemental signatures are not well understood. We conducted a factorial experiment using whelk Kelletia kelletii larvae from Salta Verde Point on Catalina Islan...

In coral reef fishes, density-dependent population regulation is commonly mediated via predation on juveniles that have recently settled from the plankton. All else being equal, strong density-dependent mortality should select against the formation of high-density aggregations, yet the juveniles of many reef fishes aggregate. In light of this appar...

Animals in social aggregations often spend more time foraging than solitary conspecifics. This may be a product of the relative safety afforded by aggregations: group members can devote more time to foraging and less time to antipredator behaviors than solitary animals (the "risk reduction" effect). All else being equal, risk reduction should resul...

Cleaning symbioses on coral reefs involve small cleaner fish or shrimps picking ectoparasites from the exterior surfaces of larger client organisms. These mutualisms are thought to evolve in part because the cleaner receives a reliable source of profitable prey items and immunity from predation. However, the benefits of cleaning behavior have never...

The scales of population structure in marine species depend on the degree to which larvae from different populations are mixed in the plankton. There is an intriguing trend in marine population genetic studies of significant genetic structure for larvae, recruits, or populations at fine scales that is unpatterned across space and changes through ti...

Over the past decade, researchers have used variation in the chemical composition of fish otoliths (earstones) to address a number of ecological questions, such as stock assessment and assessing rates of movement of individuals among habitats or life-history stages. However, these methods have yet to be applied successfully to the study of larval c...

An example of alternative male strategies is seen in diandric protogynous (female first) hermaphrodites, where individuals either mature directly as male (primary males) or first reproduce as female and then change sex to male (secondary males). In some sex-changing fishes, the testes of primary males appear anatomically similar to those of non-sex...

Here, we review recent empirical advances that have improved our understanding of why and when sex change occurs. We show that sex-changing animals use a greater diversity of strategies to increase their reproductive success than was previously recognized: some individuals change sex early, others change sex late, some individuals change sex more t...

The population replenishment of marine organisms is routinely characterized as highly variable and unpredictable in space and time. Using island-wide recruitment surveys of a common coral reef fish, the bluehead wrasse Thalassoma bifasciatum, in 6 summers spanning a 12 yr period (1991 to 2003), we examined whether spatial patterns of recruitment ar...

Land use, watershed processes, and coastal biodiversity are often intricately linked, yet land--sea interactions are usually ignored when selecting terrestrial and marine reserves with existing models. Such oversight increases the risk that reserves will fail to achieve their conservation objectives. The conceptual model underlying existing reserve...

We show that chemical differences found along the open coast are sufficiently strong to leave a readable natal signature in fish otoliths. Laser ablation inductively coupled plasma mass spectrometric (LA-ICPMS) analysis of individual larval otoliths taken from near-term females of the primitively viviparous rockfish Sebastes atrovirens indicates de...

Many species vary in their ecology across their geographic ranges in response to gradients in environmental conditions. Such variation, which can influence life history traits and subsequent demography of populations, usually occurs over large spatial scales. However, describing and understanding the causes of such variation is difficult precisely...

Variation in the chemical composition of fish otoliths has been used in recent years to address a range of ecological questions, including levels of stock mixing, variation in habitat use, and rates of larval exchange. While some of these questions have been answered with varying success, the degree to which discrete populations are connected via l...

How much should a female be willing to risk in any one reproductive event? Highly iteroparous females will be risk averse and very conservative in their behaviour. Such females will be expected to avoid mortality risks and seek assurance that any current reproductive activity is safe. By way of minimizing risk, these same females will not engage in...

Surprisingly little research has evaluated how habitat size may limit the population size of species that use different habitats at different stages of their lives. Here we develop simple discrete-time models to describe the population dynamics of species that use separate juvenile and adult habitats. Analytic solutions, model simulations, and elas...

Marine reserves are a spatial approach to marine management and conser- vation aimed at protecting and restoring multispecies assemblages and the structure and function of marine ecosystems. We used meta-analyses of published data to address the questions of how and over what time frames marine assemblages change within no-take marine reserves as t...

We recorded the courtship and spawning behavior of a protogynous fish, the California sheephead, Semicossyphus pulcher, throughout their spawning season at Bird Rock, Santa Catalina Island, California. We made additional observations at the Monterey Bay Aquarium and confirmed the details of behavior seen in the field. Large males held spawning terr...

Marine reserves affect areas outside reserve boundaries via the displacement of fishing effort and the export of production. Here we focus on how these key factors interact to influence the results seen once reserves are created. For a settlement-limited fishery, export of increased production from within reserves can offset the effects of dis- pla...

Arising from: Allsop, D. J. & West, S. A. Nature 425, 783–784 (2003); Allsop and West reply Organisms that change sex during their lifetime use a variety of strategies — they may be female first¹, male first² or even repetitive sex changers³. Natural selection should favour those individuals that change sex at a time when it increases their reprod...

A variety of field studies suggest that sex change in animals may be more complicated than originally depicted by the size-advantage hypothesis. A modification of the size-advantage hypothesis, the expected reproductive success threshold model, proposes that sperm competition and size-fecundity skew can strongly affect reproductive pay-offs. Size-f...