Publications

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2018
Navarro, MO, Parnell PE, Levin LA.  2018.  Essential market squid (Doryteuthis opalescens) embryo habitat: A baseline for anticipated ocean climate change. Journal of Shellfish Research. 37:601-614.   10.2983/035.037.0313   AbstractWebsite

The market squid Doryteuthis opalescens deposits embryo capsules onto the continental shelf from Baja California to southern Alaska, yet little is known about the environment of embryo habitat. This study provides a baseline of environmental data and insights on factors underlying site selection for embryo deposition off southern California, and defines current essential embryo habitat using (1) remotely operated vehicle-supported surveys of benthos and environmental variables, (2) SCUBA surveys, and (3) bottom measurements of T, S, pH, and O-2. Here, embryo habitat is defined using embryo capsule density, capsule bed area, consistent bed footprint, and association with [O-2] and pH (pCO(2)) on the shelf. Spatial variation in embryo capsule density and location appears dependent on environmental conditions, whereas the temporal pattern of year-round spawning is not. Embryos require [O-2] greater than 160 mu mol and pH(T) greater than 7.8. Temperature does not appear to be limiting (range: 9.9 degrees C-15.5 degrees C). Dense embryo beds were observed infrequently, whereas low-density cryptic aggregations were common. Observations of dense embryo aggregation in response to shoaling of low [O-2] and pH indicate habitat compression. Essential embryo habitat likely expands and contracts in space and time directly with regional occurrence of appropriate O-2 and pH exposure. Embryo habitat will likely be at future risk of compression given secular trends of deoxygenation and acidification within the Southern California Bight. Increasingly localized and dense spawning may become more common, resulting in potentially important changes in market squid ecology and management.

2017
Parnell, EP, Fumo JT, Lennert-Cody CE, Schroeter SC, Dayton PK.  2017.  Sea urchin behavior in a Southern California Kelp Forest: Food, fear, behavioral niches, and scaling up individual behavior. Journal of Shellfish Research. 36:529-543.: National Shellfisheries Association   10.2983/035.036.0224   Abstract

ABSTRACT Red and purple sea urchins (Mesocentrotus francisanus and Strongylocentrotus purpuratus) cohabit the west coast of North America and exhibit behavioral switching between sheltering, when food is abundant, and emergence and overgrazing, when food is scarce. To better understand individual urchin foraging behavior, we conducted a series of time-lapse behavioral studies within and at the edge of a resilient sea urchin barren. Photographs were taken at 15-min intervals for weeklong periods to observe behavior (1) in different microtopographic settings, (2) in response to food additions, and (3) along a spatial gradient from the leading edge of a sea urchin grazing front to ?100 m behind it. Movement was limited for both species when crowded or in complex microtopography. Consistent differences in sheltering behaviors and diel movement patterns were observed between species in the presence and absence of food indicating behavioral niche differentiation. Red sea urchins responded to food falls at distances of at least 3m and exhibit an ability to return to shelters at similar distances. Both species exhibit (1) local movement for up to weeklong periods indicating constraints on bulk movement and grazing front formation, (2) decreased movement rates owing to crowding and microtopography analogous to traffic jams, and (3) consistent instraspecific differences in individual movement behaviors (i.e., personality). We propose how small-scale behavioral modes may scale to larger-scale local population movements and affect the dynamics of sea urchin overgrazing.

2016
Dayton, P, Jarrell S, Kim S, Thrush S, Hammerstrom K, Slattery M, Parnell E.  2016.  Surprising episodic recruitment and growth of Antarctic sponges: Implications for ecological resilience. Journal of Experimental Marine Biology and Ecology. 482:38-55.   10.1016/j.jembe.2016.05.001   AbstractWebsite

Sponges are the most conspicuous component of the Antarctic benthic ecosystem, a system under stress both from climate change and fishing activities. Observations over four decades are compiled and reveal extremely episodic sponge recruitment and growth. Recruitment occurred under different oceanographic conditions on both sides of McMurdo Sound. Most of the sponges appear to have recruited in the late 1990s-2000. Observations from 2000 to 2010 follow thirty years of relative stasis with very little sponge recruitment or growth followed by a general pattern of recruitment by some forty species of sponges. That there was almost no recruitment observed on natural substrata emphasizes the contrast between potential and realized recruitment This unique data set was derived from a region noted for physical stasis, but the episodic ecological phenomena highlight the importance of rare events. Against a background of intermittent food resources and the low metabolic costs of stasis, understanding the causes of irregular larval supply, dispersal processes, recruitment success and survivorship becomes critical to predicting ecosystem dynamics and resilience in response to increasing environmental change. Our time-series emphasizes that long-term data collection is essential for meaningful forecasts about environmental change in the unique benthic ecosystems of the Antarctic shelf. (C) 2016 Elsevier B.V. All rights reserved.

Switzer, RD, Parnell EP, Leichter JL, Driscoll NW.  2016.  The effects of tectonic deformation and sediment allocation on shelf habitats and megabenthic distribution and diversity in southern California. Estuarine, Coastal and Shelf Science. 169:25-37.   10.1016/j.ecss.2015.11.020   Abstract

Landscape and seascape structures are typically complex and manifest as patch mosaics within characteristic biomes, bordering one another in gradual or abrupt ecotones. The underlying patch structure in coastal shelf ecosystems is driven by the interaction of tectonic, sedimentary, and sea level dynamic processes. Animals and plants occupy and interact within these mosaics. Terrestrial landscape ecological studies have shown that patch structure is important for ecological processes such as foraging, connectivity, predation, and species dynamics. The importance of patch structure for marine systems is less clear because far fewer pattern-process studies have been conducted in these systems. For many coastal shelf systems, there is a paucity of information on how species occupy shelf seascapes, particularly for seascapes imbued with complex patch structure and ecotones that are common globally due to tectonic activity. Here, we present the results of a study conducted along a myriameter-scale gradient of bottom and sub-bottom geological forcing altered by tectonic deformation, sea level transgression and sediment allocation. The resulting seascape is dominated by unconsolidated sediments throughout, but also exhibits increasing density and size of outcropping patches along a habitat patch gradient forced by the erosion of a sea level transgressive surface that has been deformed and tilted by tectonic forcing. A combination of sub-bottom profiling, multibeam bathymetry, and ROV surveys of the habitats and the demersal megafauna occupying the habitats indicate (1) significant beta diversity along this gradient, (2) biological diversity does not scale with habitat diversity, and (3) species occupy the patches disproportionately (non-linearly) with regard to the proportional availability of their preferred habitats. These results indicate that shelf habitat patch structure modulates species specific processes and interactions with other species. Further studies are needed to examine experimentally the mechanics of how patch structure modulates ecological processes in shelf systems. Our results also provide further support for including multiple spatial scales of patch structure for the application of remote habitat sensing as a surrogate for biological community structure.

2015
Parnell, PE.  2015.  The effects of seascape pattern on algal patch structure, sea urchin barrens, and ecological processes. Journal of Experimental Marine Biology and Ecology. 465:64-76.   10.1016/j.jembe.2015.01.010   AbstractWebsite

Seascapes are the marine analog of terrestrial landscapes, and their importance for ecological processes in marine ecosystems is generally poorly known. This is especially true for giant kelp (Macrocystis pyrifera) forests for which the acquisition of high resolution acoustic terrain data is problematic due to canopy cover. The goal of this study was to determine the effects of geologically forced seascape structure on algal patch structure, and to address the potential for seascape pattern to affect higher order ecological processes within giant kelp forests. The difficulty of terrain data acquisition within giant kelp forests was overcome using a narrow single beam sonar system and the development of processing algorithms that resulted in high resolution (10 m) models of bathymetry and algal patch structure. Algal patch structure was determined for the canopy kelps Macrocystis pynfera and Pelagophyais porra, and pooled understory algal species. The analysis also enabled estimation of the spatial distribution of a large (> 2 ha) persistent sea urchin barrens. The results highlight the importance of bottom topography and bottom depth distributions on algal distributions, algal patch structure, and the dynamics of the sea urchin barren. Large scale topographic features (ca. 500 m), depth, and their interaction are significantly related to canopy and understoty distributions among the forests and known patterns of algal resiliency and persistence. Canopy is preferentially distributed toward large scale topographic highs, whereas understory is preferentially distributed towards topographic lows. Pelagophycus porra, however, does not exhibit a distributional preference among hard bottom topographic features. Large scale topography clearly controls algal patch structure. Greater algal patch density and complexity are associated with topographic highs and lows, whereas patches in planar areas exhibit large core areas with less edge habitat and less interspersion with different canopy guilds. Comparisons of the joint probability distributions of bottom and algal depth distributions among forests indicates that density dependent positive feedback processes potentially reinforce the predominance of their differential canopy guild composition. Seascape structure (1) controls and interacts with algal patch structure to define edge habitat structure and potentially foraging and migration pathways, and (2) defines the margins of the large persistent sea urchin barrens and likely the dynamics of sea urchin feeding and movement. The results reinforce the need for adequate sampling design and replication for probability based benthic assessments when high resolution habitat structure is not available, or the utilization of model based purposive sampling strategies when habitats are known. (C) 2015 Elsevier B.V. All rights reserved.

2014
Cook, GS, Parnell PE, Levin LA.  2014.  Population connectivity shifts at high frequency within an open-coast marine protected area network. Plos One. 9   10.1371/journal.pone.0103654   AbstractWebsite

A complete understanding of population connectivity via larval dispersal is of great value to the effective design and management of marine protected areas (MPA). However empirical estimates of larval dispersal distance, self-recruitment, and within season variability of population connectivity patterns and their influence on metapopulation structure remain rare. We used high-resolution otolith microchemistry data from the temperate reef fish Hypsypops rubicundus to explore biweekly, seasonal, and annual connectivity patterns in an open-coast MPA network. The three MPAs, spanning 46 km along the southern California coastline were connected by larval dispersal, but the magnitude and direction of connections reversed between 2008 and 2009. Self-recruitment, i.e. spawning, dispersal, and settlement to the same location, was observed at two locations, one of which is a MPA. Self-recruitment to this MPA ranged from 50-84%; within the entire 60 km study region, self-recruitment accounted for 45% of all individuals settling to study reefs. On biweekly time scales we observed directional variability in alongshore current data and larval dispersal trajectories; if viewed in isolation these data suggest the system behaves as a source-sink metapopulation. However aggregate biweekly data over two years reveal a reef network in which H. rubicundus behaves more like a well-mixed metapopulation. As one of the few empirical studies of population connectivity within a temperate open coast reef network, this work can inform the MPA design process, implementation of ecosystem based management plans, and facilitate conservation decisions.

Edgar, GJ, Stuart-Smith RD, Willis TJ, Kininmonth S, Baker SC, Banks S, Barrett NS, Becerro MA, Bernard ATF, Berkhout J, Buxton CD, Campbell SJ, Cooper AT, Davey M, Edgar SC, Forsterra G, Galvan DE, Irigoyen AJ, Kushner DJ, Moura R, Parnell PE, Shears NT, Soler G, Strain EMA, Thomson RJ.  2014.  Global conservation outcomes depend on marine protected areas with five key features. Nature. 506:216-+.   10.1038/nature13022   AbstractWebsite

In line with global targets agreed under the Convention on Biological Diversity, the number of marine protected areas (MPAs) is increasing rapidly, yet socio-economic benefits generated by MPAs remain difficult to predict and under debate(1,2). MPAs often fail to reach their full potential as a consequence of factors such as illegal harvesting, regulations that legally allow detrimental harvesting, or emigration of animals outside boundaries because of continuous habitat or inadequate size of reserve(3-5). Here we show that the conservation benefits of 87 MPAs investigated worldwide increase exponentially with the accumulation of five key features: no take, well enforced, old (>10 years), large (>100 km(2)), and isolated by deep water or sand. Using effective MPAs with four or five key features as an unfished standard, comparisons of underwater survey data from effective MPAs with predictions based on survey data from fished coasts indicate that total fish biomass has declined about two-thirds from historical baselines as a result of fishing. Effective MPAs also had twice as many large (>250 mm total length) fish species per transect, five times more large fish biomass, and fourteen times more shark biomass than fished areas. Most (59%) of the MPAs studied had only one or two key features and were not ecologically distinguishable from fished sites. Our results show that global conservation targets based on area alone will not optimize protection of marine biodiversity. More emphasis is needed on better MPA design, durable management and compliance to ensure that MPAs achieve their desired conservation value.

2012
Konotchick, T, Parnell PE, Dayton PK, Leichter JJ.  2012.  Vertical distribution of Macrocystis pyrifera nutrient exposure in southern California. Estuarine Coastal and Shelf Science. 106:85-92.   10.1016/j.ecss.2012.04.026   AbstractWebsite

We examined water column temperature time series profiles for several years at two locations in a single kelp (Macrocystis pyrifera) forest to characterize the alongshore variability of the nutrient climate that giant kelp is exposed to and compare it to the response of giant kelp. The differences in nutrient climate are due to differential alongshore vertical variations in temperature, a well-established proxy of nitrate, due to the topographically induced internal wave dynamics within the kelp forest. We observed the greatest temperature variability during summer and most of this variability occurred near the surface. The 14.5 degrees C isotherm, indicating the presence of nitrate, ranged the entire vertical extent of the water column, and was shallowest during the winter and in the southern portion of the kelp forest. Predicted water column integrated nitrate varies from 0 mu mol NO3-/m(2) to 431 mu mol NO3-/m(2) yielding a time series daily average of 0.12 gN/m(2)day (North La Jolla) and 0.18 gN/m(2)day (South La Jolla). Redfield conversion of these values puts the time series daily average for carbon production (upper limit) between 0.8 and 1.2 gC/m(2)day for the north and south parts of the bed respectively, and shows considerable variation at several time scales. Giant kelp in the southern portion of the forest exhibited greater stipe densities (a proxy for kelp production) than individuals in the northern portion, corresponding with the alongshore nutrient climate variability. The depth of the nutricline varied by up to 10 m over time scales as short as hours. Variability was greatest at diurnal and semi-diurnal frequencies, with shallower water column depths showing greatest variability. These depth-specific variations in temperature and nutrient exposure may have biologically important consequences for M. pyrifera especially during low nutrient seasons. (C) 2012 Elsevier Ltd. All rights reserved.

2010
Parnell, PE, Miller EF, Lennert-Cody CE, Dayton PK, Carter ML, Stebbins TD.  2010.  The response of giant kelp (Macrocystis pyrifera) in southern California to low-frequency climate forcing. Limnology and Oceanography. 55:2686-2702.   10.4319/lo.2010.55.6.2686   AbstractWebsite

The nutrient climate on the inner shelf off southern California changed markedly across the 1976-1977 North Pacific climate regime shift. With respect to giant kelp (Macrocystis pyrifera) canopies off southern California, the nitrate climate shifted from relatively replete conditions prior to the regime shift to depleted conditions afterward, and the dynamics of 14 giant kelp forests appeared to change as a result. The response of giant kelp to nutrient-replete years before the regime shift was dampened compared to their response afterward. The sensitivity of these kelp-forest canopies to nutrient limitation appears to have increased since the regime shift. This intensification of physical control after 1977 is evident in the strong correlation of seawater density (sigma(t)) and M. pyrifera density. The linear fit of the percent of time the 25.1 sigma(t) isopycnal bathes the inner shelf, accounted for similar to 71% of the variability in kelp density off Point Loma, and the median depth of this isopycnal has deepened similar to 5 m since the regime shift. The wave climate also intensified beginning in the early 1970s. The dampened kelp response prior to the regime shift was likely due to greater biological control of kelp canopies via consumer and competitive processes (i.e., biological modulation) or decreased physical control at possibly many trophic levels. Our results suggest that the response of kelp forests to El Nino Southern Oscillation events is mediated by lower frequency climate modes that may modulate the regulatory importance of biological and physical processes on giant kelp.

Parnell, PE, Dayton PK, Fisher RA, Loarie CC, Darrow RD.  2010.  Spatial patterns of fishing effort off San Diego: implications for zonal management and ecosystem function. Ecological Applications. 20:2203-2222.   10.1890/09-1543.1   AbstractWebsite

The essence of ecosystem-based management is managing human practices to conserve the ecosystem. Ecologists focus on understanding the ecosystem, but there are fundamental information gaps including patterns of human exploitation. In particular, the spatial distribution of fishing effort must be known at the scales needed for ecologically relevant management. Fishing is a primary impact on coastal ecosystems, yet catch distribution at scales relevant to habitats and processes are not well known for many fisheries. Here we utilized photographic time series, logbook records, and angler surveys to estimate the intensity and spatial pattern of commercial and recreational fishing. Effort was clearly aggregated for most types of fishing, the motivating factors for effort distribution varied among areas, and effort was coupled or uncoupled to habitat depending on the area and type of fishing. We estimated that similar to 60% and similar to 74% of private recreational and recreational charter vessel fishing effort, respectively, were concentrated into two small areas that also included similar to 78% of commercial sea urchin effort. Exploitation and effort were considerably greater in one kelp forest, which has important implications for patterns of kelp persistence, productivity, and ecosystem function. Areas subject to the greatest recreational fishing pressure appeared to have lower diversity. Our results indicate that fine-scale patterns of fishing effort and exploitation have profound consequences for ecosystem functioning and biodiversity. Ecosystem-based management of nearshore ecosystems depends on an understanding of the fine-scale patterns of exploitation.

2008
Parnell, PE, Groce AK, Stebbins TD, Dayton PK.  2008.  Discriminating sources of PCB contamination in fish on the coastal shelf off San Diego, California (USA). Marine Pollution Bulletin. 56:1992-2002.   10.1016/j.marpolbul.2008.08.023   AbstractWebsite

Management of coastal ecosystems necessitates the evaluation of pollutant loading based on adequate source discrimination. Monitoring of sediments and fish on the shelf off San Diego has shown that some areas on the shelf are contaminated with polychlorinated biphenyls (PCBs). Here, we present an analysis of PCB contamination in fish on the shelf off San Diego designed to discriminate possible sources. The analysis was complicated by the variability of species available for analysis across the shelf, variable affinities of PCBs among species, and non-detects in the data. We utilized survival regression analysis to account for these complications. We also examined spatial patterns of PCBs in bay and offshore sediments and reviewed more than 20 years of influent and effluent data for local wastewater treatment facilities. We conclude that most PCB contamination in shelf sediments and fish is due to the ongoing practice of dumping contaminated sediments dredged from San Diego Bay. (C) 2008 Elsevier Ltd. All rights reserved.

2007
Parnell, PE, Dayton PK, Margiotti F.  2007.  Spatial and temporal patterns of lobster trap fishing: a survey of fishing effort and habitat structure. Bulletin Southern California Academy of Sciences. 106:27-37.   10.3160/0038-3872(2007)106[27:SATPOL]2.0.CO;2   Abstract

ABSTRACT The patterns of distribution and abundance for the California spiny lobster (Panulirus interruptus) within the kelp forest off La Jolla, CA (USA) were compared to the distribution of fishing effort during the 2005/2006 lobster season over an area of 20.25 km2. Fishing intensity was greatest at the beginning of the season (3333 traps on opening day) decreasing to 258 traps a few days before the end of the 24 week-long season. The collective effort of the trap fishermen primarily targeted the best habitats at the scale of the kelp forest, but fishing effort at smaller scales (250m, the smallest scale of our study) was less correlated to the best lobster habitats, especially near the beginning of the season. Fishing efficiency (CPUE) decreased linearly throughout the season, decreasing by more than an order of magnitude despite the fact that the distribution of fishing effort was better correlated with habitat quality and distribution near the end of the season. Fishing effort was greatest throughout the season at the edge of a small no-take marine protected area indicating possible fishing of spillover.

2006
Parnell, PE, Dayton PK, Lennert-Cody CE, Rasmussen LL, Leichter JJ.  2006.  Marine reserve design: optimal size, habitats, species affinities, diversity, and ocean microclimate. Ecological Applications. 16:945-962.   10.1890/1051-0761(2006)016[0945:mrdosh]2.0.co;2   AbstractWebsite

The design of marine reserves is complex and fraught with uncertainty. However, protection of critical habitat is of paramount importance for reserve design. We present a case study as an example of a reserve design based on fine-scale habitats, the affinities of exploited species to these habitats, adult mobility, and the physical forcing affecting the dynamics of the habitats. These factors and their interaction are integrated in an algorithm that determines the optimal size and location of a marine reserve for a set of 20 exploited species within five different habitats inside a large kelp forest in southern California. The result is a reserve that encompasses similar to 42% of the kelp forest. Our approach differs fundamentally from many other marine reserve siting methods in which goals of area, diversity, or biomass are targeted a priori. Rather, our method was developed to determine how large a reserve must be within a specific area to protect a self-sustaining assemblage of exploited species. The algorithm is applicable across different ecosystems, spatial scales, and for any number of species. The result is a reserve in which habitat value is optimized for a predetermined set of exploited species against the area left open to exploitation. The importance of fine-scale habitat definitions for the exploited species off La Jolla is exemplified by the spatial pattern of habitats and the stability of these habitats within the kelp forest, both of which appear to be determined by ocean microclimate.

2005
Parnell, PE, Lennert-Cody CE, Geelen L, Stanley LD, Dayton PK.  2005.  Effectiveness of a small marine reserve in southern California. Marine Ecology-Progress Series. 296:39-52.   10.3354/meps296039   AbstractWebsite

While relatively small, the San Diego-La Jolla Ecological Reserve is one of the oldest in California, and it contains giant-kelp-forest, boulder-reef, submarine-canyon and sandy-shelf habitats. We evaluated the effectiveness of this 'no-take' marine reserve and gauged its success according to the goals implicit in its design. To overcome the lack of data prior to its establishment, we employed habitat-specific analyses. Our study comprised 4 components: (1) an historical review of its establishment; (2) a survey of conspicuous species in kelp-forest, submarine-canyon, and boulder-reef habitats; (3) comparisons with historical data; (4) a public survey regarding awareness, knowledge, and support of the reserve. Despite 30 yr of protection, only a few sessile or residential species exhibit positive effects of protection, and most fished species have decreased in abundance inside the reserve. However, the reserve protects the largest remaining populations of green abalone Haliotis fulgens and vermillion rockfish Sebastes miniatus in the area, which therefore represent important sources of larvae. Implementation and enforcement of coastal reserves depends on public support, but the results of the public survey indicated a lack of knowledge of the reserve, highlighting the need for improved public education in this respect. The results of the study reflect the limited value of small reserves and document the inadequacy of inside/outside comparisons as tests of reserve effectiveness when baseline and historical data are lacking.

2004
Tapia, FJ, Pineda J, Ocampo-Torres FJ, Fuchs HL, Parnell PE, Montero P, Ramos S.  2004.  High-frequency observations of wind-forced onshore transport at a coastal site in Baja California. Continental Shelf Research. 24:1573-1585.   10.1016/j.csr.2004.03.013   AbstractWebsite

We investigated the effect of the daily sea breeze on the surface flow at Bahia Salsipuedes, Baja California, Mexico. Drifter-tracking experiments were conducted over a 2-week period in July, 1999. Surface drifters were deployed daily and their trajectories tracked from a small boat for 3-7 h. Wind speed and direction, as well as the vertical distribution of temperature and current velocities were measured throughout the observation period. Our results indicate that strong winds associated with the daily sea breeze at the study area can produce onshore surface currents with velocities of up to 10 cm s(-1) (net transport of up to 2 km in a diurnal cycle). There was a hyperbolic relationship between onshore wind stress and net onshore transport of the drifters. A decrease in stratification and more consistent pattern of onshore transport were associated with sustained winds > 6 in s(-1) towards the end of the study. Progressive vector diagrams computed from near-surface currents failed to predict the trajectory of drifters, especially on days where wind forcing was more consistent in terms of direction and magnitude. We discuss the implications of these results regarding the collection of settlement data and their interpretation in terms of larval supply to coastal populations. (C) 2004 Elsevier Ltd. All rights reserved.

2003
Parnell, PE.  2003.  The effects of sewage discharge on water quality and phytoplankton of Hawai'ian coastal waters. Marine Environmental Research. 55:293-311.   10.1016/S0141-1136(02)00275-1   AbstractWebsite

The effects of sewage discharge on algal populations and the quality of Hawai'ian coastal waters were investigated. Two outfalls were studied. One discharges primary treated sewage and the other discharges secondary treated sewage but are otherwise similar. This enabled comparisons of the effects of these different levels of treatment on the water quality and algal productivity of receiving waters. Plumes were followed and repeatedly sampled in a time-series manner. Rhodamine dye was used as a conservative tracer to compare the dilution behavior of the plume constituents MRP, NO3 + NO2, NH4, Silicate, TDP, TDN, total bacteria, PC, and PN. Rates of initial dilution ranged from two to almost three orders of magnitude, and were in reasonable agreement with engineering model predictions. Dilution of plume constituents approximated that of Rhodamine until background concentrations were reached, typically within 10 min of discharge. Chl a concentrations did not increase through time in the primary sewage plume but did increase up to 30% in the secondary sewage plume. However, rates of far-field dilution were so rapid that the increase could not have been due to algal growth. The increase Was attributed to the plume mixing with a water mass whose relative chl a concentrations were greater. Rates of secondary dilution ranged from 2 to 3 orders of magnitude. resulting in total dilutions of 10(5)-10(6) within 3 h of discharge. These rates of secondary dilution were much greater than model predictions. From a nutrient standpoint, secondary treatment exhibited no advantages over primary treatment because dilutions were so rapid. (C) 2002 Elsevier Science Ltd. All rights reserved.

2002
Parnell, PE.  2002.  Larval development, precompetent period, and a natural spawning event of the pectinacean bivalve Spondylus tenebrosus (Reeve, 1856). Veliger. 45:58-64. AbstractWebsite

The artificial induction of spawning, and the development of larval Spondylus tenebrosus, a spondylid pectinacean bivalve, is described. A combination of warming and injections of serotonin into the adductor muscle of these animals produced spawning within 1.5 hours. Larvae were cultured at temperatures ranging from 22-24degreesC. Pediveligers were first observed within 12 days of fertilization, and settlement was first observed 21 days after fertilization. Pediveligers that were not allowed to settle were healthy 60 days after fertilization, when culture ended, indicating that larval S. tenebrosus can delay settlement, and remain planktonic for at least 2 months. In addition, a spawning event of natural populations on the southern shore of Oahu, Hawaii was indirectly observed. This spawning event occurred during a period of maximum annual temperature, suggesting that warming may be a natural spawning cue for Spondylus tenebrosus.

2001
Parnell, PE.  2001.  The distribution of estuarine and oceanic water masses on the southern shore of O'ahu, Hawai'i: Ecological and coastal management implications, and novel methodology. Limnology and Oceanography. 46:1468-1485. AbstractWebsite

The distribution of estuarine and oceanic water masses along the shelf of Mamala Bay, O'ahu, Hawaii, were determined by use of larval supply and recruitment patterns of benthic invertebrate species, stable C and N isotopic compositions of the suspension-feeding bivalve, Spondylus tenebrosus, turbidity, drifter, and CTD data. The recruitment of different species among estuaries was used to associate larval species with particular estuarine waters. Recruitment patterns of these species along the shelf were then used to infer water-mass distributions along the shelf. The spatial recruitment pattern of an oceanic lepadomorph barnacle, Conchoderma virgatum, was useful to infer shelf areas exposed to oceanic waters. Water-mass distributions inferred from the recruitment distribution of these species concurred with spatial patterns of turbidity and stable C and N isotopic compositions of S. tenebrosus, as well as drifter observations. Water-mass distributions observed in this study also concurred with biological distributional patterns observed in other studies, such as distributions of phytoplankton and zooplankton and the distribution of coral bio-erosion in the Bay. The ecological implications of this work include further evidence of the physical control of recruitment and biological pattern and the possible control of patch dynamics on the scale of kilometers due to significant recruitment variability at this scale. The prevailing distribution of water masses determined in this study also has important implications for the management of watersheds associated with Mamala Bay.

1998
Southward, AJ, Burton RS, Coles SL, Dando PR, DeFelice R, Hoover J, Parnell PE, Yamaguchi T, Newman WA.  1998.  Invasion of Hawaiian shores by an Atlantic barnacle. Marine Ecology-Progress Series. 165:119-126.   10.3354/meps165119   AbstractWebsite

A largely vacant niche in the upper mid-littoral zone of sheltered Hawaiian shores is now occupied by Chthamalus proteus Dando & Southward, 1980 (Crustacea, Cirripedia), otherwise found in the Caribbean, the Gulf of Mexico and Brazil. The identity of the species was established by morphological details and confirmed by allozyme electrophoresis. Previously, chthamaline barnacles have rarely been found fouling hulls of ships; this is the first recorded instance of regular occurrence on ships as well as of remote dispersal in the genus. While the introduction of C. proteus apparently has had little impact so far, there is a need to step up monitoring programs so as to prevent rather than simply detect future introductions.

1992
Dayton, PK, Tegner MJ, Parnell PE, Edwards PB.  1992.  Temporal and spatial patterns of disturbance and recovery in a kelp forest community. Ecological Monographs. 62:421-445.   10.2307/2937118   AbstractWebsite

This paper addresses questions of community and patch stability as defined by the population biology of dominant plants in the context of different areas within a large kelp forest. We ask (1) "Do large-scale episodic events override biological mechanisms as major community structuring processes?", (2) "Are different local areas characterized by different processes?", and (3) "How persistent are the patches or biological structure over decadal and local spatial scales?" We evaluate these questions with regard to the effects of various types of disturbance for as much as three decades on the populations of several species of kelp in the large kelp forest off Point Loma, San Diego, California. The most sensitive population factors we studied include recruitment, density, and survivorship. Patch stability was evaluated with regard to the persistence of patches already well established in 1971-1972. The study sites offer a cross-shore transect through the central part of a large kelp forest at depths of 8, 12, 15, 18, and 21 m; two additional sites at the north and south ends of the forest offer a longshore transect along the 18-m contour. There were marked differences among the decades with regard to the intensity of the disturbances. Compared with the 1980s, the two preceding decades were relatively benign. The 1980s had two extreme disturbance events: the 1982-1984 El Nino-Southern Oscillation (ENSO) was the most severe El Nino event in the last century, which included very warm, nutrient-depleted water, and a short but intense storm in January 1988 appeared to have been the most severe in perhaps 200 yr. The storm changed age-specific kelp mortality patterns and caused the first large-scale understory mortality in several decades. By sweeping away drift algae it caused intense local urchin grazing. The storm was followed by a strong La Nina event marked by cool, nutrient-rich water in 1988-1989. Differences in kelp recruitment and survivorship in different areas of the kelp forest are influenced by gradients in longshore currents, temperature, light, wave energy, floc, planktonic propagules, and physical disturbance. The areas are characterized by different plant Population patterns and the effects of several species of herbivores. The massive disturbances of the 1980s obliterated much of the structure in the kelp forest. Certainly the disturbances caused many lag effects including outbreaks of understory algae such as Desmarestia ligulata, intraspecific competition, changes in grazing patterns, etc., which in tum resulted in between-area variation in recovery rates. However, in all cases this variation was overshadowed by the overwhelming competitive dominance of Macrocystis pyrifera. Most of the understory patches on the transect lines, some of which had persisted for 7 yr, died out by the end of 1990. The population biology of Macrocystis was remarkably similar in most areas, as the cohort longevity and survivorship curves were very similar, and the plant and stipe densities tended to level off in only a few years. Thus large-scale episodic events such as El Ninos, La Ninas, and rare storms exert dramatic impacts, but small-scale responses such as density-vague recruitment (neither density dependent nor density independent) and survival allow prompt recovery, often to preexisting patterns. The one exception was the southern site, which was marked by sea urchin grazing and poor kelp recruitment through the latter half of the 1980s, but a recent wa urchin disease event has led to kelp recruitment in fall 1991. A seeming paradox to the observed Macrocystis dominance is that in almost all areas, some understory patches of old plants have persisted through the 1980s.

1989
Seymour, RJ, Tegner MJ, Dayton PK, Parnell PE.  1989.  Storm wave induced mortality of giant kelp, Macrocystis pyrifera, in Southern California. Estuarine Coastal and Shelf Science. 28:277-292.   10.1016/0272-7714(89)90018-8   AbstractWebsite

The storm-related mortality rates of adult Macrocystis pyrifera in a Southern California giant kelp forest were determined over several winter storm seasons and compared with the hydrodynamic attributes of the most energetic storms. The data include stormy and relatively benign years and an exceptional storm which resulted in almost total destruction of a major Macrocystis forest. High orbital velocities (associated with large, high frequency waves), the presence of breaking waves, and entanglement by drifters were found to increase mortality through stipe breakage or holdfast failure. Longshore variability in wave intensity was found to affect kelp mortality rates. The data suggest that wave breaking may be an important factor in determining the inner boundary of the kelp bed.

Dayton, PK, Seymour RJ, Parnell PE, Tegner MJ.  1989.  Unusual marine erosion in San Diego County from a single storm. Estuarine Coastal and Shelf Science. 29:151-160.   10.1016/0272-7714(89)90004-8   AbstractWebsite

Observations of wave-induced geological damage were made along the San Diego coastline to a depth of 25 m, following the storm of 17–18 January, 1988. Massive damage to limestone reefs occurred, including the shearing of individual sections with in-water weights of over 20 tonnes at the remarkable depth of at least 22 m. Large sections of the walls of a submarine canyon were broken off at a depth exceeding 20 m. The drag and inertial forces from the waves in this storm are shown to be about twice those in the largest previous storms of the century, and it appears to be a 200 year event. In addition to the kelp mortality reported inSeymour et al., 1989, there was extensive mortality among encrusting algal and animal communities. The apparent age of the mature successional communities in the deeper sites supports the engineering estimates of the rarity of this event. The movement of cobbles and boulders at depths almost twice as great as the previously assumed limits on effective sediment transport may require coastal engineers to revise cross-shore transport models.