208 research outputs found
The Interaction of Retention, Recruitment, and Density-Dependent Mortality in the Spatial Placement of Marine Reserves
Population density can affect rates of mortality and individual growth. We measured these for the non-exploited 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
Variabilidad temporal del crecimiento, talla y duración larvaria, y reclutamiento de un lábrido, Coris julis (Pisces: Labridae), de las Azores
Temporal variability in the size at settlement (SAS), age at settlement (PLD), larval growth and recruitment patterns of a temperate wrasse, Coris julis, were examined over two recruitment seasons for a single island site from the Azores archipelago in the northeastern Atlantic. Relationships between these early life-history traits and recruitment variability over time were also investigated. Average PLD and SAS varied significantly among sampling dates over the settlement season, increasing consistently over time. This pattern was persistent over two consecutive summers. Larval growth was not a good predictor for PLD or SAS, which were in turn positively correlated with each other. Differences in recruitment magnitude over time were not related to SAS, PLD or larval growth. Instead, we found that recruits whose early pelagic stage (first 30 d) overlapped part of a period of enhanced growth (above average and independent of larval age), tended to result in the largest recruitment events; these tended to occur in the mid season. Larvae from earlier and later settlement events, overlapping periods of depressed growth, were linked to more modest recruitment events. We hypothesize that short PLD, with resulting small SAS is favoured early in the season, when post-settlement density is lowest. Over the course of the settlement season, as recruits accumulate competition may increase, and larger SAS (associated with longer PLD), may provide a competitive/survival advantage.La variabilidad temporal en la talla de reclutamiento (SAS), edad de reclutamiento (PLD), crecimiento larvario y patrón de reclutamiento en un lábrido de aguas templadas, Coris julis, fueron examinados en dos épocas de reclutamiento consecutivas, en una isla de las Azores (Atlántico nordeste). Se examinaron también las relaciones entre estas características y la variabilidad de reclutamiento temporal. La PLD y la SAS medios aumentaron significativamente a lo largo del período de reclutamiento en los dos veranos consecutivos. La PLD y la SAS se correlacionaron positivamente, pero el crecimiento larvario no fue un buen predictor de estas características. Las diferencias en magnitud de reclutamiento entre fechas de muestreo sucesivas no fueron explicadas por las SAS/PLD medias, ni tampoco por el crecimiento larvario. En cambio, encontramos que los reclutas cuyos primeros estadios de desarrollo pelágico (30 días) se solapaban, en parte, con un periodo de crecimiento intenso (por encima del promedio e independiente de de edad) resultaron en los mayores reclutamientos; que tienden a suceder a mitad de la estación. Las larvas de asentamientos tempranos o tardíos (periodos de solapamiento, con crecimiento disminuido), se asociaron a reclutamientos modestos. Se plantea la hipótesis de que las PLD cortas, con las resultantes pequeñas SAS deberían ser favorecidas en la fase más temprana del período de reclutamiento, cuando la densidad de juveniles es menor. A lo largo del período de asentamiento, a medida que los reclutas se acumulan, la competición puede aumentar, y las mayores SAS (asociadas a mayores PLD), pueden proporcionar una ventaja competitiva o de supervivencia
Herbivorous Fish Populations Respond Positively to a Shipwreck Removal and Associated Alteration of Benthic Habitat
Shipwrecks can have significant localized effects when grounded on shallow coral reefs. These effects are not limited to the immediate physical damage, but can have wide-spread and lasting impacts due to alteration of the chemical makeup of the surrounding water column. This can subsequently impact the growth of benthic organisms, often leading to phase shifts and high levels of mortality of corals in the vicinity of the wreck. At Palmyra atoll, the grounding of a longline fishing vessel on the shallow reef terrace is associated with a phase shift to the corallimorph, Rhodactis howesii. In 2013, a wreck removal effort initiated by the US Department of Fish and Wildlife resulted in the successful extraction and disposal of the wreckage, after which the density and percent cover of R. howesii in the immediate vicinity of the wreck site dropped precipitously. Here, we document the response of the fish community to the wreck removal and localized decline in R. howesii. We show that the biomass of scarid parrotfishes and acanthurid surgeonfishes and unicornfishes (primarily herbivores) increased after the removal of the wreck, while biomass of chaetodontid butterflyfishes (primarily invertivores, many species are known to feed on coelenterate polyps) declined over the study period. The density of small scarids and acanthurids also increased, but only after a few years post removal. Overall these results indicate that Palmyra’s unfished herbivore population has rapidly responded to the removal of the wreck and associated decrease in corallimorph cover, can maintain high levels of grazing where space is made available for colonization of early successional algae species, and may have the potential to facilitate reef recovery
Umbrella species in marine systems: using the endangered humphead wrasse to conserve coral reefs
Extinction risk is closely tied to body size, home range, and species distribution. Quantifying home range is critical for conservation, and can enable the use of concepts such as \u27umbrella species\u27, whose conservation protects other species due to shared habitat. To determine the value of the humphead wrasse as an umbrella species for coral reef conservation, we conducted a multi-year study of humphead wrasse home range at Palmyra Atoll, Central Tropical Pacific, tagging juvenile, female, and male individuals with acoustic transmitters. We quantified home range using 2 metrics, length and area, and determined if these metrics were related to the sex and maturity status of the individual. We recorded individual movements during 5030 fish days, yielding detailed records for 14 individuals comprising 3 juveniles, 5 females, and 6 males. The home range of humphead wrasse measured over a 2 yr study was 0.4 to 14 km and changed with ontogeny. Females had larger home ranges than other reef fishes studied to date (n = 68), indicating value as an umbrella species for coral reefs. We compared the home range of the species to the size distribution of tropical marine protected areas (MPAs), and used a model to estimate the MPA length necessary to retain humphead wrasse. Most MPAs are too small to effectively protect the humphead wrasse
Tropicalization of fish assemblages in temperate biogeographic transition zones
Biogeographic transition zones in marine temperate systems are often hotspots of biodiversity, with high levels of resilience to short-term climate shifts due to naturally occurring cyclic oscillations of oceanographic conditions. However, these environments are likely vulnerable to a steady global warming scenario in which these cyclical conditions could be disrupted. Here, we evaluate how changes in local oceanography affect the structure of rocky reef fish assemblages over a period of 50 yr in a biogeographic transition zone. Using a 12 yr time series of rocky reef fish assemblage structure, we identified the set of oceanographic variables that most influenced assemblage dynamics. Descriptive and predictive models (multivariate regression trees) were compared to observed data using the area under the curve. Winter northward wind stress and sea surface temperature (SST) were the most important drivers of change in assemblage structure. Only warmer years had indicator species with warm-temperate or tropical affinities. A fish assemblage 'tropicalization' index was developed in response to both local-spatial resolution and short-term environmental variation (1993-2011), and to regional spatial resolution and long-term SST (1960-2012). Predictive modelling for the last 50 yr revealed that species with tropical affinities have increased in frequency compared to cold-temperate species, coinciding with the trend of increasing mean winter SST. Since the mid-1980s, warm-temperate and tropical species have responded rapidly to more frequent warm winters, suggesting that species distributions are shifting polewards. Our results support a hypothesis that cold species retreat more slowly than the advance of warm species. We discuss the importance of transition zones as ` barometers' of climate change
Drivers of Daily Routines in an Ectothermic Marine Predator: Hunt Warm, Rest Warmer?
Animal daily routines represent a compromise between maximizing foraging success and optimizing physiological performance, while minimizing the risk of predation. For ectothermic predators, ambient temperature may also influence daily routines through its effects on physiological performance. Temperatures can fluctuate significantly over the diel cycle and ectotherms may synchronize behaviour tomatch thermal regimes in order to optimize fitness. We used bio-logging to quantify activity and body temperature of blacktip reef sharks (Carcharhinus melanopterus) at a tropical atoll. Behavioural observations were used to concurrently measure bite rates in herbivorous reef fishes, as an index of activity for potential diurnal prey. Sharks showed early evening peaks in activity, particularly during ebbing high tides, while body temperatures peaked several hours prior to the period of maximal activity. Herbivores also displayed peaks in activity several hours earlier than the peaks in shark activity. Sharks appeared to be least active while their body temperatures were highest and most active while temperatures were cooling, although we hypothesize that due to thermal inertia they were still warmer than their smaller prey during this period. Sharksmay be most active during early evening periods as they have a sensory advantage under low light conditions and/ or a thermal advantage over cooler prey. Sharks swaminto shallow water during daytime low tide periods potentially to warm up and increase rates of digestion before the nocturnal activity period, which may be a strategy to maximize ingestion rates. Hunt warm, rest warmer may help explain the early evening activity seen in other ectothermic predators
Growth and life history variability of the grey reef shark (Carcharhinus amblyrhynchos) across its range
For broadly distributed, often overexploited species such as elasmobranchs (sharks and rays), conservation management would benefit from understanding how life history traits change in response to local environmental and ecological factors. However, fishing obfuscates this objective by causing complex and often mixed effects on the life histories of target species. Disentangling the many drivers of life history variability requires knowledge of elasmobranch populations in the absence of fishing, which is rarely available. Here, we describe the growth, maximum size, sex ratios, size at maturity, and offer a direct estimate of survival of an unfished population of grey reef sharks (Carcharhinus amblyrhynchos) using data from an eight year tag-recapture study. We then synthesized published information on the life history of C. amblyrhynchos from across its geographic range, and for the first time, we attempted to disentangle the contribution of fishing from geographic variation in an elasmobranch species. For Palmyra’s unfished C. amblyrhynchos population, the von Bertalanffy growth function (VBGF) growth coefficient k was 0.05 and asymptotic length L∞ was 163.3 cm total length (TL). Maximum size was 175.5 cm TL from a female shark, length at maturity was estimated at 116.7–123.2 cm TL for male sharks, maximum lifespan estimated from VBGF parameters was 18.1 years for both sexes combined, and annual survival was 0.74 year-1. Consistent with findings from studies on other elasmobranch species, we found significant intraspecific variability in reported life history traits of C. amblyrhynchos. However, contrary to what others have reported, we did not find consistent patterns in life history variability as a function of biogeography or fishing. Ultimately, the substantial, but not yet predictable variability in life history traits observed for C. amblyrhynchos across its geographic range suggests that regional management may be necessary to set sustainable harvest targets and to recover this and other shark species globally
Resetting predator baselines in coral reef ecosystems
What did coral reef ecosystems look like before human impacts became pervasive? Early efforts to reconstruct baselines resulted in the controversial suggestion that pristine coral reefs have inverted trophic pyramids, with disproportionally large top predator biomass. The validity of the coral reef inverted trophic pyramid has been questioned, but until now, was not resolved empirically. We use data from an eight-year tag-recapture program with spatially explicit, capture-recapture models to re-examine the population size and density of a key top predator at Palmyra atoll, the same location that inspired the idea of inverted trophic biomass pyramids in coral reef ecosystems. Given that animal movement is suspected to have significantly biased early biomass estimates of highly mobile top predators, we focused our reassessment on the most mobile and most abundant predator at Palmyra, the grey reef shark (Carcharhinus amblyrhynchos). We estimated a density of 21.3 (95% CI 17.8, 24.7) grey reef sharks/km2, which is an order of magnitude lower than the estimates that suggested an inverted trophic pyramid. Our results indicate that the trophic structure of an unexploited reef fish community is not inverted, and that even healthy top predator populations may be considerably smaller, and more precarious, than previously thought
Where the Weird Things Are: A Collection of Species Range Extensions in the Southern California Bight
A large-scale monitoring program associated with the establishment of a marine protected area network in southern California provided an opportunity to observe and document unique or rare species across the region. Scientists and students from several educational and research institutions surveyed 145 subtidal reefs, 39 intertidal reefs, and five sandy beaches from 2011-2017, a period of time where oceanographic and climatic conditions changed serially and dramatically. In conjunction with an increase in monitoring frequency and locations, dramatic shifts in oceanographic climate during this same time period likely caused shifts in tolerable habitat conditions for many nearshore species. Here we describe range extensions – both to the north and south – of fourteen marine fish, invertebrate, and algae species as observed during the 2011-2012 South Coast MPA Baseline Program and subsequent monitoring efforts
Marine Biodiversity in Juan Fernández and Desventuradas Islands, Chile: Global Endemism Hotspots
22 páginas, 6 tablas, 5 figurasThe Juan Fernández and Desventuradas islands are among the few oceanic islands
belonging to Chile. They possess a unique mix of tropical, subtropical, and temperate
marine species, and although close to continental South America, elements of the biota
have greater affinities with the central and south Pacific owing to the Humboldt Current,
which creates a strong biogeographic barrier between these islands and the continent. The
Juan Fernández Archipelago has ~700 people, with the major industry being the fishery for
the endemic lobster, Jasus frontalis. The Desventuradas Islands are uninhabited except for
a small Chilean military garrison on San Félix Island. We compared the marine biodiversity
of these islands across multiple taxonomic groups. At San Ambrosio Island (SA), in Desventuradas,
the laminarian kelp (Eisenia cokeri), which is limited to Desventuradas in Chile,
accounted for >50% of the benthic cover at wave exposed areas, while more sheltered sites
were dominated by sea urchin barrens. The benthos at Robinson Crusoe Island (RC), in the
Juan Fernández Archipelago, comprised a diverse mix of macroalgae and invertebrates, a
number of which are endemic to the region. The biomass of commercially targeted fishes
was >2 times higher in remote sites around RC compared to sheltered locations closest to
port, and overall biomass was 35% higher around SA compared to RC, likely reflecting fishing
effects around RC. The number of endemic fish species was extremely high at both
islands, with 87.5% of the species surveyed at RC and 72% at SA consisting of regional
endemics. Remarkably, endemics accounted for 99% of the numerical abundance of fishes
surveyed at RC and 96% at SA, which is the highest assemblage-level endemism known
for any individual marine ecosystem on earth. Our results highlight the uniqueness
and global significance of these biodiversity hotspots exposed to very different fishing
pressures.ES received funding from Blancpain,
Davidoff Cool Water and The National Geographic
Society. Oceana provided funding to ATP. CFG was
suported by Grant NC120030 from the Millennium
Scientific Initiative.Peer reviewe
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