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Title: Disentangling the effects of fishing and environmental forcing on demographic variation in an exploited species
Description: Species targeted by fishing often recover in abundance and size within marine protected areas (MPAs) resulting in increased reproductive potential. However, in some situations, concomitant changes in the abundance of predators, competitors, or prey within MPAs, or strong gradients in the surrounding environmental seascape may counteract the purported benefits making it more difficult to predict how species will respond to protection. We used a network of MPAs in California, spanning a large temperature gradient, to investigate the drivers of demographic variability in the commercially important red sea urchin Mesocentrotus franciscanus. We investigated how demographic metrics varied geographically in response to protection, temperature, and the main sea urchin resource, the giant kelp Macrocystis pyrifera. We found significant conservation benefits to this fished sea urchin within MPAs designated six years prior to the beginning of this study. Within MPAs, red sea urchins were generally larger resulting in greater adult biomass density and reproductive biomass density. In addition, kelp density was an important explanatory variable of all red sea urchin demographic traits examined (adult size, gonadosomatic index [GSI], density, adult biomass density, and reproductive biomass density). Kelp density was positively correlated with red sea urchin GSI and adult size, but the relationships with density, adult biomass density, and reproductive biomass density were complex and the directionality changed depending on the region (or environmental setting) examined. Our results demonstrate that kelp, red sea urchin reproduction, and the effects of spatial management on demographic processes are tightly coupled with the oceanographic regime. © 2017 Elsevier Ltd
Author: Teck, Lorda, Shears, Bell, Cornejo-Donoso, Caselle, Hamilton, Gaines

Title: Dietary niche expansion of a kelp forest predator recovering from intense commercial exploitation
Description: Marine ecosystems are increasingly at risk from overexploitation and fisheries collapse. As managers implement recovery plans, shifts in species interactions may occur broadly with potential consequences for ecosystem structure and function. In kelp forests off San Nicolas Island, California, USA, we describe striking changes in size structure and life history traits (e.g., size at maturation and sex change) of a heavily fished, ecologically important predator, the California sheephead (Semicossyphus pulcher). These changes occurred in two phases: (1) after intense commercial fishery exploitation in the late 1990s and (2) following recovery in the late 2000s, nearly a decade after management intervention. Using gut contents and stable-isotope values of sheephead and their prey, we found evidence for a dietary niche expansion upon recovery of population size structure to include increased consumption of sea urchins and other mobile invertebrate grazers by larger sized fish. By examining historical diet data and a time series of benthic community composition, we conclude that changes in dietary niche breadth are more likely due to the recovery of size structure from fishing than major shifts in prey availability. Size-dependent predator-prey interactions may have ecosystem consequences and management measures that preserve or restore size structure, and therefore historical trophic roles of key predators, could be vital for maintaining kelp forest ecosystem health. © 2014 by the Ecological Society of America., Fish and Fisheries
Author: Hamilton, Newsome, Caselle

Title: Natural History Observations of Hawaiian Garden Eels, Gorgasia hawaiiensis (Congridae: Heterocongrinae), from the Island of Hawai'i, Natural History Observations of Hawaiian Garden Eels
Description: Garden eels occur worldwide in the tropics, but little is known about their biology and ecology. We studied Hawaiian garden eel (Gorgasia hawaiiensis) colonies near Kawaihae, Hawai'i, to investigate multiple aspects of basic biology of this species. Colonies of G. hawaiiensis occurred at depths from 16 to 36 m in soft-bottom habitat adjacent to rocky reefs. Highest burrow densities (up to 40 eels m-2) were in shallower water, and large (~10 mm diameter) burrows were more abundant, less dense, and commonly found in pairs in deeper water. Eels emerged around sunrise and withdrew and covered burrow entrances around sunset. Age was estimated from annual rings in sectioned otoliths (n = 17) and modeled to suggest fast growth to a maximum size of ~600 mm total length and a maximum age of 6 yr. Prey size and eel anatomy suggest that these fish feed by ingesting planktonic prey and processing them in the esophagus. The most common food items were small (<0.5 mm) demersal harpacticoid, cyclopoid, and calanoid copepods and unidentified fish eggs. These and other observations indicate that G. hawaiiensis is abundant, has a high population turnover rate, and may enrich sandy-bottom habitat within their beds by facilitating energy flow from the water column to the benthos. © 2017 by University of Hawai'i Press., Export Date: 17 April 2017, Article
Author: Donham, Foster, Rice, Cailliet, Yoklavich, Hamilton

Title: First quantification of subtidal community structure at Tristan da Cunha Islands in the remote South Atlantic from kelp forests to the deep sea
Description: Tristan da Cunha Islands, an archipelago of four rocky volcanic islands situated in the South Atlantic Ocean and part of the United Kingdom Overseas Territories (UKOTs), present a rare example of a relatively unimpacted temperate marine ecosystem. We conducted the first quantitative surveys of nearshore kelp forests, offshore pelagic waters and deep sea habitats. Kelp forests had very low biodiversity and species richness, but high biomass and abundance of those species present. Spatial variation in assemblage structure for both nearshore fish and invertebrates/algae was greatest between the three northern islands and the southern island of Gough, where sea temperatures were on average 3-4o colder. Despite a lobster fishery that provides the bulk of the income to the Tristan islands, lobster abundance and biomass are comparable to or greater than many Marine Protected Areas in other parts of the world. Pelagic camera surveys documented a rich biodiversity offshore, including large numbers of juvenile blue sharks, Prionace glauca. Species richness and abundance in the deep sea is positively related to hard rocky substrate and biogenic habitats such as sea pens, crinoids, whip corals, and gorgonians were present at 40% of the deep camera deployments. We observed distinct differences in the deep fish community above and below ~750 m depth. Concurrent oceanographic sampling showed a discontinuity in temperature and salinity at this depth. While currently healthy, Tristan's marine ecosystem is not without potential threats: shipping traffic leading to wrecks and species introductions, pressure to increase fishing effort beyond sustainable levels and the impacts of climate change all could potentially increase in the coming years. The United Kingdom has committed to protection of marine environments across the UKOTs, including Tristan da Cunha and these results can be used to inform future management decisions as well as provide a baseline against which future monitoring can be based.
Author: Caselle, Hamilton, Davis, Thompson, Turchik, Jenkinson, Simpson, Sala

Title: Recovery trajectories of kelp forest animals are rapid yet spatially variable across a network of temperate marine protected areas
Description: 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 targeted (i.e. fished) species has increased consistently inside all MPAs in the network, with an effect of geography on the strength of the response. More interesting, biomass of targeted fish species also increased outside MPAs, although only 27% as rapidly as in the protected areas, indicating that redistribution of fishing effort has not severely affected unprotected populations. Whether the increase outside of MPAs is due to changes in fishing pressure, fisheries management actions, adult spillover, favorable environmental conditions, or a combination of all four remains unknown. We evaluated methods of controlling for biogeographic or environmental variation across networks of protected areas and found similar performance of models incorporating empirical sea surface temperature versus a simple geographic blocking term based on assemblage structure. The patterns observed are promising indicators of the success of this network, but more work is needed to understand how ecological and physical contexts affect MPA performance. © 2015, Nature Publishing Group. All rights reserved., Export Date: 2 October 2015
Author: Caselle, Rassweiler, Hamilton, Warner
Date: 2015-01-01T00:00:00Z

Title: Fishing top predators indirectly affects condition and reproduction in a reef-fish community
Description: To examine the indirect effects of fishing on energy allocation in non-target prey species, condition and reproductive potential were measured for five representative species (two-spot red snapper Lutjanus bohar, arc-eye hawkfish Paracirrhites arcatus, blackbar devil Plectroglyphidodon dickii, bicolour chromis Chromis margaritifer and whitecheek surgeonfish Acanthurus nigricans) from three reef-fish communities with different levels of fishing and predator abundance in the northern Line Islands, central Pacific Ocean. Predator abundance differed by five to seven-fold among islands, and despite no clear differences in prey abundance, differences in prey condition and reproductive potential among islands were found. Body condition (mean body mass adjusted for length) was consistently lower at sites with higher predator abundance for three of the four prey species. Mean liver mass (adjusted for total body mass), an indicator of energy reserves, was also lower at sites with higher predator abundance for three of the prey species and the predator. Trends in reproductive potential were less clear. Mean gonad mass (adjusted for total body mass) was high where predator abundance was high for only one of the three species in which it was measured. Evidence of consistently low prey body condition and energy reserves in a diverse suite of species at reefs with high predator abundance suggests that fishing may indirectly affect non-target prey-fish populations through changes in predation and predation risk. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles., Cited By (since 1996):1, Export Date: 24 September 2013, Source: Scopus, CODEN: JFIBA
Author: Walsh, Hamilton, Ruttenberg, Donovan, Sandin
Date: 2012-01-01T00:00:00Z

Title: Historical ecology and the conservation of large, hermaphroditic fishes in Pacific Coast kelp forest ecosystems
Description: The intensive commercial exploitation of California sheephead (Semicossyphus pulcher) has become a complex, multimillion-dollar industry. The fishery is of concern because of high harvest levels and potential indirect impacts of sheephead removals on the structure and function of kelp forest ecosystems. California sheephead are protogynous hermaphrodites that, as predators of sea urchins and other invertebrates, are critical components of kelp forest ecosystems in the northeast Pacific. Overfishing can trigger trophic cascades and widespread ecological dysfunction when other urchin predators are also lost from the system. Little is known about the ecology and abundance of sheephead before commercial exploitation. Lack of a historical perspective creates a gap for evaluating fisheries management measures and marine reserves that seek to rebuild sheephead populations to historical baseline conditions. We use population abundance and size structure data from the zooarchaeological record, in concert with isotopic data, to evaluate the long-term health and viability of sheephead fisheries in southern California. Our results indicate that the importance of sheephead to the diet of native Chumash people varied spatially across the Channel Islands, reflecting modern biogeographic patterns. Comparing ancient (~10,000 calibrated years before the present to 1825 CE) and modern samples, we observed variability and significant declines in the relative abundance of sheephead, reductions in size frequency distributions, and shifts in the dietary niche between ancient and modern collections. These results highlight how size-selective fishing can alter the ecological role of key predators and how zooarchaeological data can inform fisheries management by establishing historical baselines that aid future conservation.
Author: Braje, Rick, Szpak, Newsome, McCain, Elliott Smith, Glassow, Hamilton

Title: Spatial and temporal variation in the natal otolith chemistry of a Hawaiian reef fish: Prospects for measuring population connectivity,
Description: , , , 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 estimate larval connectivity. We analyzed the spatial and temporal variation in natal otolith chemistry of a benthic-spawning reef fish from the Hawaiian Islands. We found no consistent chemical variation at the largest scale (>100 km, among islands), but found significant variation at moderate scales (sites within islands, tens of kilometres) and small scales (clutches within sites), and chemistry of otoliths was not stable between years. These results imply that we may be able to use otolith chemistry to track larval dispersal only if the scales of dispersal match those of variation in natal otolith chemistry, and that separate natal otolith collections may be needed to track different cohorts of larvae. Finally, we found that elemental composition of recruit cores often did not match that of natal otoliths, suggesting that additional methodological development is required before we can effectively apply methods in otolith chemistry to the study of larval dispersal., ,
Author: Ruttenberg, Hamilton, Warner
Date: 2008-01-01T00:00:00Z

Title: Elevated levels of trace elements in cores of otoliths and their potential for use as natural tags,
Description: , , , 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 larval exchange remains unknown. To identify larval sources using natural variation in otolith chemistry, we must distinguish and measure the chemical composition of the otolith core, the portion of the otolith formed at the spawning site. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we found that the core regions of otoliths from 6 different species of fishes were highly enriched in manganese (Mn), and elevated in magnesium (Mg) and barium (Ba), relative to adjacent regions of the otolith. These patterns were consistent for species drawn from different taxonomic groups, which inhabit temperate and tropical regions, are found in marine and freshwater, and utilize a variety of spawning modes. Variation among species in Mn concentration in the core also corresponds to maternal investment, measured by egg size. These data suggest that core enrichment may be a general characteristic of otoliths, and that the chemical composition of the otolith core is fundamentally different from other regions of the otolith. The localized elemental enrichment of the core underscores the importance of methods that analyze the core region in small, discrete samples if otolith chemistry is used to address questions of larval exchange among populations., ,
Author: Ruttenberg, Hamilton, Hickford, Paradis, Sheehy, Standish, Ben-Tzvi, Warner
Date: 2005-01-01T00:00:00Z

Title: Postsettlement survival linked to larval life in a marine fish,
Description: , , , 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 Caribbean reef fish (Thalassoma bifasciatum) on an oceanic island, we used otolith (ear stone) elemental profiles of lead (Pb) to assign recent settlers to a group that developed in waters elevated in Pb concentrations throughout larval life (i.e., nearshore signature) and a group that developed in waters depleted in Pb (i.e., offshore signature), potentially dispersing from upstream sources across oceanic waters. Larval history influenced early life history traits: offshore developers initially grew slowly but compensated with fast growth upon entering nearshore waters and metamorphosed in better condition with higher energy reserves. As shown in previous studies, local production contributed heavily to settlement: at least 45% of settlers developed nearshore. However, only 23% of survivors after the first month displayed a nearshore otolith profile. Therefore, settlers with different larval histories suffered differential mortality. Importantly, selective mortality was mediated by larval history, in that the postsettlement intensity of selection was much greater for fish that developed nearshore, potentially because they had developed in a less selectively intense larval environment. Given the potential for asymmetrical postsettlement source-based survival, successful spatial management of marine populations may require knowledge of “realized connectivity” on ecological scales, which takes into account the postsettlement fitness of individuals from different sources., ,
Author: Hamilton, Regetz, Warner
Date: 2008-01-01T00:00:00Z

Title: From a sea of phenotypic traits, fast reaction and boldness emerge as the most influential to survival in marine fish
Description: Predation is arguably the most consequential of ecological interactions in determining fitness and thus natural selection; prey that do not escape a predator encounter become dinner and can no longer pass their genes on to the next generation. For organisms with complex life histories (e.g. plants, insects, amphibians, marine fish, invertebrates and algae; Wilbur, 1980), processes occurring during transitions between life stages are particularly important for subsequent survival and reproduction (e.g. Berven, 1990; Johnson, Grorud‐Colvert, Sponaugle, & Semmens, 2014; Pechenik, 2006). Mortality is intense at these vulnerable developmental stages (Almany & Webster, 2006; Hjort, 1914), especially when those life‐history transitions involve a habitat shift (i.e. pelagic larva to benthic‐associated juvenile for marine species) where individuals are naïve about new predators and other risks. In marine systems, early results showed that bigger, faster growing, or better‐conditioned individuals were more likely to survive the larval‐juvenile transition (Hamilton, Regetz, & Warner, 2008; Hoey & McCormick, 2004; Searcy & Sponaugle, 2001; Vigliola & Meekan, 2002). Understanding which individuals survive periods of selective mortality, from birth to reproduction, remains fundamental to our understanding of both demographic and evolutionary processes.
Author: Hamilton

Title: Geographic variation in natal and early larval trace-elemental signatures in the statoliths of the market squid Doryteuthis (formerly Loligo) opalescens,
Description: , , , 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 coupled plasma mass spectrometry (LA-ICPMS) of individual statoliths indicated detectable levels of Mg, Mn, Sr, and Ba, with marginal levels of Cr and Pb. While these paralarvae showed considerable within-sample differences in elemental concentrations, there was significant between-site discrimination of natal (core) and early larval signatures for collection sites up to 100 km apart. In 2002 and 2003, levels of Ba and Sr in the statolith cores were significantly different among sites, suggesting differences in the natal environment or local maternal effects. Site specific differences in elemental signatures were also apparent for Mg and Mn in samples taken from outside the core in the early post-hatching period. These same portions of the statolith can be analyzed from adult squid collected on spawning grounds. We showed that concentrations of trace elements in the statolith cores of adults closely resembled the core signatures of squid paralarvae, which opens the possibility of identifying the source populations for stocks of this commercially important species., ,
Author: Warner, Hamilton, Sheehy, Zeidberg, Brady, Caselle
Date: 2009-01-01T00:00:00Z

Title: The interaction of retention, recruitment, and density-dependent mortality in the spatial placement of marine reserves,
Description: Population density can affect rates of mortality and individual growth. We measured these for the nonexploited bluehead wrasse, Thalassoma bifasciatum, at three sites around St. Croix, US Virgin Islands. Previous work demonstrated that differences in the degree of larval retention in these sites results in very large differences in recruitment intensity. Post-settlement mortality differed among sites and was positively related to recruitment density. Post-settlement growth differences were small. Because of strong mortality effects early in life, adult densities and size/age distributions differed among sites and did not reflect differences in recruitment rate. The site with the highest retention and recruitment (Butler Bay) had many small fish, while the two other sites with lower recruitment rates (Jacks Bay and Green Cay) had proportionally more large fish. These differences resulted in large differences in egg production. Per capita production was highest at the lowest density site (Green Cay). Total egg production at Green Cay was 75% that at Butler Bay, despite only having half the population size, and the highest overall production was at Jacks Bay, with low retention and moderate recruitment. In terms of marine reserve location, sites predicted to have high retention and recruitment may not always be the sites of highest egg production due to density-dependent processes, and it is important to consider the relative values of self-recruitment and larval export in reserve design., , ,
Author: Caselle, Hamilton, Warner
Date: 2003-01-01T00:00:00Z

Title: Utilizing spatial demographic and life history variation to optimize sustainable yield of a temperate sex-changing fish
Description: Fish populations vary geographically in demography and life history due to environmental and ecological processes and in response to exploitation. However, population dynamic models and stock assessments, used to manage fisheries, rarely explicitly incorporate spatial variation to inform management decisions. Here, we describe extensive geographic variation in several demographic and life history characteristics (e.g., size structure, growth, survivorship, maturation, and sex change) of California sheephead (Semicossyphus pulcher), a temperate rocky reef fish targeted by recreational and commercial fisheries. Fish were sampled from nine locations throughout southern California in 2007-2008. We developed a dynamic size and age-structured model, parameterized separately for each location, to assess the potential cost or benefit in terms of fisheries yield and conservation objectives of changing minimum size limits and/or fishing mortality rates (compared to the status quo). Results indicate that managing populations individually, with location-specific regulations, could increase yield by over 26% while maintaining conservative levels of spawning biomass. While this local management approach would be challenging to implement in practice, we found statistically similar increases in yield could be achieved by dividing southern California into two separate management regions, reflecting geographic similarities in demography. To maximize yield, size limits should be increased by 90 mm in the northern region and held at current levels in the south. We also found that managing the fishery as one single stock (the status quo), but with a size limit 50 mm greater than the current regulations, could increase overall fishery yield by 15%. Increases in size limits are predicted to enhance fishery yield and may also have important ecological consequences for the predatory role of sheephead in kelp forests. This framework for incorporating demographic variation into fisheries models can be exported generally to other species and may aid in identifying the appropriate spatial scales for fisheries management. © 2011 Hamilton et al., Cited By (since 1996):3, Fish and Fisheries, Art. No.: e24580
Author: Hamilton, Wilson, Ben-Horin, Caselle
Date: 2011-01-01T00:00:00Z

Title: Benthic processes and overlying fish assemblages drive the composition of benthic detritus on a central Pacific coral reef,
Description: 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 fish assemblage. While detrital standing stock was 1.6 times higher on the backreef than on the forereef, detrital input rates were 1.7 to 2.9 times higher on the forereef. Planktivores were the most abundant guild in the fore reef habitat, and stable isotope signatures of detritus reflected a greater input from pelagic sources (i.e. depleted in 13C). In contrast, herbivores and detritivores numerically dominated the backreef habitat and detrital stable isotope signatures appeared to be predominately of benthic origin (i.e. enriched in 13C). Through total organic carbon (TOC) and nitrogen analyses we found that benthic detritus may represent a significant nutritional source. Converting total nitrogen into maximum protein estimates, we found high benthic deposition of protein (104 to 124 mg m-2 d-1) and organic carbon (184 to 190 mg m -2 d-1), but very low standing stocks of these materials (protein: 5 to 6 mg m-2, organic carbon: 46 to 63 mg m-2). While high water flow rates may explain low standing stocks of detritus in forereef habitats, the lower flow rates in backreef habitats suggest that removal of this material is via consumption by abundant roving detritivorous fishes. Our results provide support for the hypothesis that reef fish detritivory represents a significant consumer-mediated energy pathway, promoting nutrient recycling by linking many elements of a complex food web. © Inter-Research 2013., Cited By (since 1996):1, Fish and Fisheries, CODEN: MESED, ,
Author: Max, Hamilton, Gaines, Warner
Date: 2013-01-01T00:00:00Z

Title: Variable responses of temperate calcified and fleshy macroalgae to elevated pCO2 and warming
Description: Anthropogenic carbon dioxide (CO2) emissions simultaneously increase ocean temperatures and reduce ocean surface pH, a process termed ocean acidification (OA). OA is expected to negatively affect the growth and physiology of many calcified organisms, but the response of non-calcified (fleshy) organisms is less well understood. Rising temperatures and pCO2 can enhance photosynthetic rates (within tolerance limits). Therefore, warming may interact with OA to alter biological responses of macroalgae in complicated ways. Beyond thresholds of physiological tolerance, however, rising temperatures could further exacerbate negative responses to OA. Many studies have investigated the effects of OA or warming independently of each other, but few studies have quantified the interactive effects of OA and warming on marine organisms. We conducted four short-term independent factorial CO2 enrichment and warming experiments on six common species of calcified and fleshy macroalgae from southern California to investigate the independent and interactive effects of CO2 and warming on growth, carbonic anhydrase (CA) enzyme activity, pigment concentrations, and photosynthetic efficiency. There was no effect of elevated pCO2 on CA activity, pigment concentration, and photosynthetic efficiency in the macroalgal species studies.However,we found that calcareous algae suffered reduced growth rates under high pCO2 conditions alone, although the magnitude of the effect varied by species. Fleshy algae had mixed responses of growth rates to high pCO2, indicating that the effects of pCO2 enrichment are inconsistent across species. The combined effects of elevated pCO2 and warming had a significantly negative impact on growth for both fleshy and calcareous algae; calcareous algae experienced five times more weight loss than specimens in ambient control conditions and fleshy growth was reduced by 76%. Our results demonstrate the need to study the interactive effects of multiple stressors associated with global change on marine communities., http://icesjms.oxfordjournals.org/content/early/2015/09/25/icesjms.fsv168.abstract, Advanced view
Author: Kram, Price, Donham, Johnson, Kelly, Hamilton, Smith
Date: 2015-09-25T00:00:00Z

Title: Exploitation and recovery of a sea urchin predator has implications for the resilience of southern California kelp forests
Description: Size-structured predator–prey interactions can be altered by the history of exploitation, if that exploitation is itself size-selective. For example, selective harvesting of larger sized predators can release prey populations in cases where only large individuals are capable of consuming a particular prey species. In this study, we examined how the history of exploitation and recovery (inside marine reserves and due to fisheries management) of California sheephead (Semicossyphus pulcher) has affected size-structured interactions with sea urchin prey in southern California. We show that fishing changes size structure by reducing sizes and alters life histories of sheephead, while management measures that lessen or remove fishing impacts (e.g. marine reserves, effort restrictions) reverse these effects and result in increases in density, size and biomass. We show that predation on sea urchins is size-dependent, such that the diet of larger sheephead is composed of more and larger sized urchins than the diet of smaller fish. These results have implications for kelp forest resilience, because urchins can overgraze kelp in the absence of top-down control. From surveys in a network of marine reserves, we report negative relationships between the abundance of sheephead and urchins and the abundance of urchins and fleshy macroalgae (including giant kelp), indicating the potential for cascading indirect positive effects of top predators on the abundance of primary producers. Management measures such as increased minimum size limits and marine reserves may serve to restore historical trophic roles of key predators and thereby enhance the resilience of marine ecosystems.
Author: Hamilton, Caselle
Date: 2015-01-01T00:00:00Z

Title: Predator-induced demographic shifts in coral reef fish assemblages,
Description: In recent years, it has become apparent that human impacts have altered community structure in coastal and marine ecosystems worldwide. Of these, fishing is one of the most pervasive, and a growing body of work suggests that fishing can have strong effects on the ecology of target species, especially top predators. However, the effects of removing top predators on lower trophic groups of prey fishes are less clear, particularly in highly diverse and trophically complex coral reef ecosystems. We examined patterns of abundance, size structure, and age-based demography through surveys and collection-based studies of five fish species from a variety of trophic levels at Kiritimati and Palmyra, two nearby atolls in the Northern Line Islands. These islands have similar biogeography and oceanography, and yet Kiritimati has ~10,000 people with extensive local fishing while Palmyra is a US National Wildlife Refuge with no permanent human population, no fishing, and an intact predator fauna. Surveys indicated that top predators were relatively larger and more abundant at unfished Palmyra, while prey functional groups were relatively smaller but showed no clear trends in abundance as would be expected from classic trophic cascades. Through detailed analyses of focal species, we found that size and longevity of a top predator were lower at fished Kiritimati than at unfished Palmyra. Demographic patterns also shifted dramatically for 4 of 5 fish species in lower trophic groups, opposite in direction to the top predator, including decreases in average size and longevity at Palmyra relative to Kiritimati. Overall, these results suggest that fishing may alter community structure in complex and non-intuitive ways, and that indirect demographic effects should be considered more broadly in ecosystem-based management. © 2011 Ruttenberg et al., , , ,
Author: Ruttenberg, Hamilton, Walsh, Donovan, Friedlander, DeMartini, Sala, Sandin
Date: 2011-01-01T00:00:00Z

Title: Species-specific consequences of ocean acidification for the calcareous tropical green algae Halimeda
Description: Ocean acidification (OA), resulting from increasing dissolved carbon dioxide (CO2) in surface waters, is likely to affect many marine organisms, particularly those that calcify. Recent OA studies have demonstrated negative and/or differential effects of reduced pH on growth, development, calcification and physiology, but most of these have focused on taxa other than calcareous benthic macroalgae. Here we investigate the potential effects of OA on one of the most common coral reef macroalgal genera, Halimeda. Species of Halimeda produce a large proportion of the sand in the tropics and are a major contributor to framework development on reefs because of their rapid calcium carbonate production and high turnover rates. On Palmyra Atoll in the central Pacific, we conducted a manipulative bubbling experiment to investigate the potential effects of OA on growth, calcification and photophysiology of 2 species of Halimeda. Our results suggest that Halimeda is highly susceptible to reduced pH and aragonite saturation state but the magnitude of these effects is species specific. H. opuntia suffered net dissolution and 15% reduction in photosynthetic capacity, while H. taenicola did not calcify but did not alter photophysiology in experimental treatments. The disparate responses of these species to elevated CO2 partial pressure (pCO2) may be due to anatomical and physiological differences and could represent a shift in their relative dominance in the face of OA. The ability for a species to exert biological control over calcification and the species specific role of the carbonate skeleton may have important implications for the potential effects of OA on ecological function in the future. © 2011 Inter-Research., Cited By (since 1996):12, Seaweeds, CODEN: MESED
Author: Price, Hamilton, Tootell, Smith
Date: 2011-01-01T00:00:00Z

Title: Reassessment of the fecundity of California sheephead,
Description: Fecundity estimates used in a 2004 stock assessment to evaluate the overall health of the population of California sheephead Semicossyphus pulcher were based primarily on two studies. The first estimated the total fecundity of only nine individuals captured near Santa Catalina Island, California, and the second estimated batch fecundity of individuals taken from only one artificial reef. In order to develop a current and more comprehensive estimate of fecundity, we collected California sheephead from seven locations off southern California throughout the spawning season (July through September). To estimate both total fecundity and batch fecundity, we categorized and counted oocytes from ovarian subsamples of 28 and 24 (respectively) mature females (stage 3, spawning capable; determined by histological analysis). Total and batch fecundity increased with somatic mass, standard length, and ovary mass. We found total fecundity to increase with somatic mass to a power of 5.5, which is considerably greater than the value (2.95) reported previously. Our observations therefore highlight the importance of large females in the reproductive potential of the California sheephead stock. Regression analysis indicates that ovary mass is the most accurate biological indicator of fecundity for California sheephead and should be used for subsequent stock analyses., , ,
Author: Loke-Smith, Floyd, Lowe, Hamilton, Caselle, Young
Date: 2012-01-01T00:00:00Z

Title: Extensive geographic and ontogenetic variation characterizes the trophic ecology of a temperate reef fish on southern California (USA) rocky reefs,
Description: Interactions between predator and prey act to shape the structure of ecological communities, and these interactions can differ across space. California sheephead Semicossyphus pulcher are common predators of benthic invertebrates in kelp beds and rocky reefs in southern California, USA. Through gut content and stable isotope (δ 13C and δ 15N) analyses, we investigated geographic and ontogenetic variation in trophic ecology across 9 populations located at island and mainland sites throughout southern California. We found extensive geographic variation in California sheephead diet composition over small spatial scales. Populations differed in the proportion of sessile filter/suspension feeders or mobile invertebrates in the diet. Spatial variation in diet was highly correlated with other life history and demographic traits (e.g. growth, survivorship, reproductive condition, and energy storage), in addition to proxies of prey availability from community surveys. Multivariate descriptions of the diet from gut contents roughly agreed with the spatial groupings of sites based on stable isotope analysis of both California sheephead and their prey. Ontogenetic changes in diet occurred consistently across populations, despite spatial differences in size structure. As California sheephead increase in size, diets shift from small filter feeders, like bivalves, to larger mobile invertebrates, such as sea urchins. Our results indicate that locations with large California sheephead present, such as many marine reserves, may experience increased predation pressure on sea urchins, which could ultimately affect kelp persistence. © Inter-Research 2011., Cited By (since 1996):6, CODEN: MESED, ,
Author: Hamilton, Caselle, Lantz, Egloff, Kondo, Newsome, Loke-Smith, Pondella II, Young, Lowe
Date: 2011-01-01T00:00:00Z

Title: Synthesizing mechanisms of density dependence in reef fishes: Behavior, habitat configuration, and observational scale,
Description: , , , Coral and rocky reef fish populations are widely used as model systems for the experimental exploration of density-dependent vital rates, but patterns of density-dependent mortality in these systems are not yet fully understood. In particular, the paradigm for strong, directly density-dependent (DDD) postsettlement mortality stands in contrast to recent evidence for inversely density-dependent (IDD) mortality. We review the processes responsible for DDD and IDD per capita mortality in reef fishes, noting that the pattern observed depends on predator and prey behavior, the spatial configuration of the reef habitat, and the spatial and temporal scales of observation. Specifically, predators tend to produce DDD prey mortality at their characteristic spatial scale of foraging, but prey mortality is IDD at smaller spatial scales due to attack-abatement effects (e.g., risk dilution). As a result, DDD mortality may be more common than IDD mortality on patch reefs, which tend to constrain predator foraging to the same scale as prey aggregation, eliminating attack-abatement effects. Additionally, adjacent groups of prey on continuous reefs may share a subset of refuges, increasing per capita refuge availability and relaxing DDD mortality relative to prey on patch reefs, where the patch edge could prevent such refuge sharing. These hypotheses lead to a synthetic framework to predict expected mortality patterns for a variety of scenarios. For nonsocial, nonaggregating species and species that aggregate in order to take advantage of spatially clumped refuges, IDD mortality is possible but likely superseded by DDD refuge competition, especially on patch reefs. By contrast, for species that aggregate socially, mortality should be IDD at the scale of individual aggregations but DDD at larger scales. The results of nearly all prior reef fish studies fit within this framework, although additional work is needed to test many of the predicted outcomes. This synthesis reconciles some apparent contradictions in the recent reef fish literature and suggests the importance of accounting for the scale-sensitive details of predator and prey behavior in any study system., ,
Author: Wilson White, Samhouri, Stier, Wormald, Hamilton, Sandin
Date: 2010-01-01T00:00:00Z

Title: Consistent long-term spatial gradients in replenishment for an island population of a coral reef fish
Description: 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 are consistent or variable through time on St. Croix, US Virgin Islands. Despite annual fluctuations in the magnitude of replenishment, recruitment intensity follows a distinct and consistent spatial gradient that differs in direction between the north (leeward) and south (windward) shores; recruitment declines from west to east on the north shore and east to west on the south shore. The rank ordering of sites on each shore was concordant when recruitment was either pooled across years (monthly variation) or pooled across months (annual variation). When the 2 highest recruitment sites on each shore were considered alone, consistent seasonal effects were also apparent, with higher recruitment from June through August on the north shore, and higher recruitment in September on the south shore. Thus, while the magnitude of recruitment is indeed variable in space and time, its qualitative pattern is predictable in this area. Results of prior investigations of larval dispersal and coastal oceanography around St. Croix shed light on the origin of the consistent recruitment patterns documented in this study. The potential for consistent spatial and temporal patterns in recruitment is an important consideration in the spatial management of marine resources.
Author: Hamilton, White, Caselle, Swearer, Warner

Title: Otolith barium profiles verify the timing of settlement in a coral reef fish,
Description: , , , 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 Thalassoma bifasciatum, a common coral reef fish on an oceanic island, we examined whether otolith chemistry could be used to identify the timing of settlement from the pelagic larval phase to the reef-based juvenile phase. This species has a distinct settlement mark visible in its otolith microstructure. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we found that Ba:Ca ratios increased abruptly at the time of settlement. On average, Ba:Ca ratios were 6.5× greater in the juvenile than the larval phase. Other elements (Mg, Mn, and Sr) also displayed ontogenetic changes in concentration; however, those changes were not associated with the settlement mark. We demonstrate the potential utility of otolith chemistry as a method to identify the timing of settlement (and thereby the larval duration) in other marine fishes with similar early life histories, whose otoliths may not produce distinct settlement checks or those whose settlement stage larvae may not be captured by other means., ,
Author: Hamilton, Warner
Date: 2009-01-01T00:00:00Z

Title: Larval history influences post-metamorphic condition in a coral-reef fish
Description: Upon settlement, many Wshes undergo an energetically costly metamorphic period that requires substantial nutritional reserves. Larval growth and the accumulation of lipids prior to metamorphosis are likely to infuence growth and survival following this critical period. On the Caribbean island of St. Croix, I investigated relationships between larval growth, early life-history characteristics, and post-metamorphic lipid content in the bluehead wrasse Thalassoma bifasciatum. Lipid reserves remaining after metamorphosis were positively related (r2 = 0.62) to the width of the metamorphic band; thus, this otolith-derived trait may be used to estimate the condition at emergence of survivors collected at some later time. In contrast, pelagic larval duration, average larval growth, and otolith size at settlement were negatively related to postmetamorphic lipid content. Interestingly, the trend for slower growth among fish in good condition was not consistent over the entire pelagic larval duration. Analyses of daily larval growth histories indicated that Wsh with high lipid reserves grew rapidly in the last week prior to settlement, but relatively slowly during the early phases of larval life; those emerging with low lipid concentrations, however, displayed strikingly opposite patterns. These contrasting patterns of growth and energy storage were consistent at two sites and over three recruitment events. Otolith chemistry data suggested that diVerences in growth histories and body condition were consistent with the hypothesis of larval development in distinct oceanic environments (characterized by Pb concentration); but, within a water mass, differences reflected life-history trade-offs between growth and energy storage. The results have implications for understanding the processes driving juvenile survival, which may be condition dependent.
Author: Hamilton

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