Jellyfish blooms influence plankton dynamics in coastal waters worldwide and can negatively impact tourism in the coastal eastern U.S.A., yet factors that affect bloom development and distribution are not well understood. We are using the stinging “sea nettle”, Chrysaora quinquecirrha, as a model system to examine physical factors that control jellyfish populations in Chesapeake Bay. Chrysaora has the potential to control the flow of energy and nutrients through the food web due to its seasonally high abundance and its extremely high consumption rates. The impact of sea nettles on the Chesapeake ecosystem and economy might be better understood if their presence could be predicted.
We developed a preliminary model that describes the preferred habitat of the medusan form of Chrysaora. This empirically-derived model predicts the probability of Chrysaora encounter as a function of sea-surface temperature and salinity. Our habitat model can be applied to near-real time estimates of temperature and salinity derived from hydrodynamic models. This method allows nowcasts to be generated for the distribution and likelihood of Chrysaora occurrence in Chesapeake Bay by identifying locations where ambient conditions coincide with Chrysaora’s preferred habitat.
We have recently received funding from NOAA’s Coastal Ocean Program to further develop the habitat model in order to more accurately forecast the distribution of Chrysaora in Chesapeake Bay and to expand the use of nowcasting capability.
Current predictions of our preliminary habitat model can be viewed here.
This research is in collaboration with: Drs. Christopher Brown (NOAA/NESDIS/ORA), Raleigh Hood (UMCES Horn Point Laboratory), Thomas Gross (Chesapeake Research Consortium) and Jennifer Purcell (Western Washington University, Shannon Point Marine Center).
This listing is a selection of more recent publications. For a list of publications, please visit the Vita page.
The occurrence of low dissolved oxygen (DO), caused by vertical stratification and excess nutrient inputs, is an important and widely occurring physical feature in aquatic systems. Because some gelatinous species, such as the lobate ctenophore, Mnemiopsis leidyi, are more tolerant of low DO concentrations than their prey and competitors, hypoxia may have profound effects on trophic interactions. Predation, clearance and digestion rates of ctenophores feeding on zooplankton (primarily Acartia tonsa) were measured at 1.0, 2.0, 3.0 mg l-1 and air-saturated (approximately 7 mg l-1) DO. Clearance of zooplankton by large ctenophores (mean 22.5 ml, range 7-46 ml) was greater at low DO concentrations than under normoxic conditions. By contrast, consumption of zooplankton by small (mean 2.9 ml, range 1-10 ml) M. leidyi did not differ among DO levels. Similarly, ctenophore digestion rates were unchanged at oxygen concentrations as low as 1 mg l-1. Jumping frequency of A. tonsa copepods decreased significantly with decreasing DO concentration (1.0, 2.0, 3.0 mg l-1 and air saturated). Such changes in prey behavior in low DO could affect both encounter and capture rates potentially making less-tolerant prey more vulnerable to predation in hypoxic waters. Gelatinous species, which are more tolerant of hypoxia than fish, may be able to inhabit regions of low oxygen that are avoided by zooplanktivorous fish with high oxygen requirements. This could lead to dominance of gelatinous predators in areas affected by severe hypoxia and may alter energy pathways in these systems.
The mesohaline region of Chesapeake Bay had high densities of the scyphomedusan, Chrysaora quinquecirrha, and low densities of the ctenophore, Mnemiopsis leidyi, in 1987-1990 and 1995. By contrast, 1996-2000 had much lower medusa and higher ctenophore densities. Predation on copepods (Acartia tonsa) was intense in 1996-2000 and copepod densities were low when ctenophores were abundant. At equivalent sizes, the feeding potentials of ctenophores were greater than those of medusae, with clearance rates about 1.2 times greater by volume and about 3 times greater by carbon biomass. M. leidyi ctenophores more negatively influence copepod populations than C. quinquecirrha medusae because they are more effective predators of copepods, and have broader spatial and temporal occurrence, wider salinity and temperature ranges, greater densities, and a more flexible life history. Because they consume ctenophores, C. quinquecirrha medusae actually positively affect copepod abundance. C. quinquecirrha and M. leidyi could be considered keystone predators because of their far-reaching effects on the plankton food web. The balance between medusae and ctenophores in Chesapeake Bay was greatly affected by climatic factors. Medusa abundances were high when dry years prevailed prior to and during 1987-1990 and 1995. By contrast, medusa abundances were low when dry and wet years alternated before and during 1996-2000. Significant variables that favored medusae in 1987-1990 and 1995 were high salinity, warm temperature, and high solar irradiance. The North Atlantic Oscillation Index was significantly inversely correlated with medusa numbers from 1960-1995. Ocean climate clearly affects gelatinous predator abundances, with consequences that cascade throughout the plankton food web.
Stressors resulting from, or exacerbated by, human activities increasingly
alter ecological systems. Behavioral responses that enhance survival of
stressed individuals may be critical for local populations to persist. Although
the types and intensities of stressors can vary over the geographic range
of a species, little is known regarding geographical variation in adaptive
behavioral responses to stressors, especially in marine and estuarine species
subject to human impact. To explore varied behavior in response to low dissolved
oxygen (a human perturbation), we examined two geographically distinct populations
of the copepod, Acartia tonsa. Chesapeake Bay copepods, historically
exposed to oxygen gradients, avoided hypoxic bottom waters. In contrast,
Florida copepods not typically exposed to hypoxia did not avoid lethal oxygen
concentrations. Our results suggest that local behavioral adaptations may
result from consequences of anthropogenic perturbations and may limit the
ability to apply biological data across regions. Geographical differences
in behavioral responses of important prey species may also result in geographic
variation in the severity of disruption of aquatic food webs.
Increased loadings of nutrients resulting from human activities in the watershed and airshed have resulted in low dissolved oxygen concentrations in bottom waters of the Patuxent River, a tributary of Chesapeake Bay. In this paper, we synthesize existing and newly collected field and laboratory data to examine spatial and temporal variation in bottom dissolved oxygen, the prevalence of hypoxia-induced mortality of fishes, the tolerance of gelatinous zooplankton and other Patuxent River biota to low dissolved oxygen, and the influence of bottom dissolved oxygen on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous predators and zooplankton prey. We then use the synthesized information to configure a spatially-explicit individual-based model and to predict the effects of current, improved, and worsened dissolved oxygen concentrations on the survival of larval fish and fish eggs in the mesohaline region of the Patuxent River.
Bottom waters in much of the mesohaline Patuxent River are below 50% dissolved oxygen saturation during summer. The system is characterized by a high degree of spatial and temporal variation in dissolved oxygen concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions and trophic interactions in the river. Within the Patuxent River food web, gelatinous zooplankton are among the most tolerant of severe hypoxia, while several of the ecologically and economically important finfish are among the most sensitive. The effect of low dissolved oxygen on vertical distributions of Patuxent River biota varies among species, depending on mobility and physiological tolerance. Model results indicate that improving or decreasing dissolved oxygen concentrations from current conditions may have opposite effects on fish eggs and larvae. Because planktonic bay anchovy eggs suffer considerable mortality due to direct exposure to low oxygen, improving dissolved oxygen should increase their hatching success. In much of the mesohaline Patuxent River, however, increasing dissolved oxygen concentrations may increase predation mortality of fish larvae consumed by gelatinous predators. The net result of the changes in biotic interactions resulting from low dissolved oxygen is unknown. Nevertheless, a precautionary approach towards fisheries and ecosystem management would recommend reducing nutrients to levels at which low oxygen effects on estuarine habitat are reduced, and where possible, eliminated. The presence of abundant gelatinous species that tolerate low oxygen concentrations and fish that are sensitive to low oxygen may make the Patuxent River, and similar estuaries, particularly susceptible to hypoxia-induced alterations in food web dynamics.
Outbreaks of noxious biota, which occur in both aquatic and terrestrial systems, can have considerable negative economic impacts. For example, an increasing frequency of harmful algal blooms worldwide has negatively affected the tourism industry in many regions. Such impacts could be mitigated if the conditions that give rise to these outbreaks were known and could be monitored. Recent advances in technology and communications allow us to continuously measure and model many environmental factors that are responsible for outbreaks of certain noxious organisms. A new prototype ecological forecasting system predicts the likelihood of occurrence of the sea nettle (Chrysaora quinquecirrha), a stinging jellyfish, in Chesapeake Bay.
Sea nettles are ideal organisms for evaluating this approach because their occurrence is closely related to salinity and sea-surface temperature (SST), and these two environmental variables can be estimated in near-real time with existing techniques and models. Nowcasts of the likelihood of encountering sea nettles in the bay, as well as information on sea nettle life history and the components involved in creating the maps, are provided on a Web site (http://coastwatch.noaa.gov/seanettles). This project is an initial but exciting step toward developing a general approach that combines real-time data derived from disparate sources, such as numerical circulation models, operational satellites, and moored sensor systems, to generate nowcasts and forecasts of the development and distribution pattern of noxious marine biota.
Hypoxic conditions are common in many coastal environments such as Chesapeake Bay. While medusae appear to be quite tolerant of low dissolved oxygen (DO) concentrations, the effects of hypoxia on the benthic polyp stages are unknown. Chrysaora quinquecirrha (DeSor) polyps, and were subjected to 5 DO treatments (air-saturated [control], 3.5, 2.5, 1.5 and 0.5 mg l-1) in the laboratory. Polyp survival and development were documented over 24 d. Virtually no mortality occurred in any treatment during the first 5 d. Total polyp mortality after 24 d was 59.3% at the lowest DO concentration, whereas < 3% mortality was observed in the air-saturated treatment. Formation of stolons and strobilae occurred in all treatments, however, the proportions of polyps undergoing stolonation and strobilation were significantly greater in all DO concentrations above 0.5 mg l-1. Polyp encystment was not observed in any treatment over the course of the 24 d experiment. These results indicate that polyps can survive and asexually propagate even during prolonged exposure to hypoxic conditions.
The native habitats of the ctenophore, Mnemiopsis, are temperate
to subtropical estuaries along the Atlantic coast of North and South America,
where it is found in an extremely wide range of environmental conditions (winter
low and summer high temperatures of 2 and 32 °C,
respectively, and salinities of <238).
In the early 1980s, it was accidentally introduced to the Black Sea, where
it flourished and expanded into the Azov, Marmara, Mediterranean and Caspian
Seas. We compile data showing that Mnemiopsis has high potentials
of growth, reproduction and feeding that enable this species to be a predominant
zooplanktivore in a wide variety of habitats; review the population distributions
and dynamics of Mnemiopsis in U.S. waters and in the Black Sea region;
and examine the effects of temperature and salinity, zooplankton availability
and predator abundance on Mnemiopsis population size in both regions,
and the effects of Mnemiopsis on zooplankton, ichthyoplankton and
fish populations, focusing on Chesapeake Bay and the Black Sea. In both
regions, Mnemiopsis populations are restricted by low winter temperatures
(<2 °C). In native habitats, predators
of Mnemiopsis often limit their populations, and zooplanktivorous
fish are abundant and may compete with the ctenophores for food. By
contrast, in the Black Sea region, no obvious predators of Mnemiopsis
were present during the decade following introduction when the ctenophore
populations flourished. Additionally, zooplanktivorous fish populations
had been severely reduced by over fishing prior to the ctenophore outbreak.
Thus, small populations of potential predators and competitors for food enabled
Mnemiopsis populations to swell in the new habitats. In Chesapeake
Bay, Mnemiopsis consumes substantial proportions of zooplankton daily,
but may only noticeably reduce zooplankton populations when predators of Mnemiopsis
are uncommon. Mnemiopsis also is an important predator of fish
eggs in both locations. In the Black Sea, reductions in zooplankton,
ichthyoplankton and zooplanktivorous fish populations have been attributed
to Mnemiopsis. We conclude that the enormous impact of Mnemiopsis
on the Black Sea ecosystem occurred because of the shortage of predators and
competitors in the late 1980s and early 1990s. The appearance of the
ctenophore, Beroe ovata, may promote the recovery of the Black Sea
ecosystem from the effects of the Mnemiopsis invasion.
Low dissolved oxygen concentrations [DO] occur at depth in many marine and estuarine environments. Human effects on the ecosystems, especially nutrient enrichment and depletion of commercial species, may cause increased jellyfish populations. Herein, we review existing information on the vertical distribution of pelagic cnidarians and ctenophores (referred to subsequently as “jellyfish”) relative to [DO] in environments that experience seasonal hypoxia (Chesapeake Bay, the Gulf of Mexico), and in environments having a permanent oxycline (the Black Sea, marine lakes and fjords, and the oxygen minimum zone). Most species of jellyfish do not live in hypoxic waters, however, some species occur in high densities at very low [DO]. Some accumulate at the pycnocline/oxycline just above severely hypoxic waters. Most data to date are on the scyphomedusan Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi in Chesapeake Bay. Experiments have shown prolonged survival of these species in [DO] < 2 mg l-1. Hypoxic conditions alter trophic interactions in complex ways. For example, low [DO] reduced the escape abilities of fish larvae and copepods thereby increasing their vulnerability to predation. Some jellyfish appear to be more tolerant of low [DO] than fishes, which may give jellyfish an adaptive advantage over fishes in eutrophic coastal environments.
In the vicinity of the Pribilof Islands in the Bering Sea, abundance of food
available to surface-foraging seabirds was greater during the chick-rearing
period in 1988 than in 1987, whereas abundance of food available to pursuit-diving
seabirds was greater in 1987. Here we examine how breeding success and resource
allocation of surface-foraging black-legged kittiwakes Rissa tridactyla (BLKI) and pursuit-diving thick-billed murres Uria
lomvia (TBMU) varied with the fluctuations
in their food supply. We also examine a difference in resource allocation
among parents raising chicks at the large colony on St. George Island and
those at the nearby small colony on St. Paul Island. We studied breeding success
(BS), field metabolic rates (FMR, assessed by using doubly labeled water),
foraging distribution, and nest attendance of parents and growth rate (GR)
of chicks. The BS of BLKIs was lower in 1987 (a season of less abundant food
for kittiwakes) than in 1988 (a season of more abundant food), and parents
had higher FMRs in 1987 than in 1988. At-sea distributions and nest attendance
suggested that in 1987 BLKIs foraged farther from the colonies, which could
have resulted in the higher FMR of the parents. GR of BLKI chicks did not
vary between 1987 and 1988. The BS of TBMUs was not significantly different
between 1987 (a season of more abundant food for TBMUs) and 1988 (a season
of less abundant food). Parent TBMUs had similar FMRs between the seasons.
Densities of foraging TBMUs were higher within 20 km around colonies in 1987
than in 1988. Although the total time parent TBMUs spent foraging did not
vary inter-seasonally, they performed more foraging trips of a shorter duration
in 1987 than in 1988, and the GR of TBMU chicks was higher in 1987 than in
1988. Inter-colony comparisons do not suggest that parents reproducing at
the large colony work harder to raise their young compared to parents breeding
at the small colony. In 1987 parent BLKIs failed in raising young at the large
colony, whereas one-third of BLKIs fledged their chicks at the small colony.
In 1988, however, RS and FMRs of parent BLKIs were not significantly different
between the colonies. Also, TBMUs at the large colony had higher BS than those
at the small colony in both 1987 and 1988. Furthermore, in both years parent
TBMUs feeding young at the small colony foraged farther from the colony and
had significantly higher FMRs than at the large colony. These results suggest
that fluctuations in food supply affect resource allocation in seabirds. However,
a decrease in food abundance is likely to cause an increase in energy expenditures
of parent BLKIs, whereas growth rates of their chicks are less affected. For
the TBMUs, food shortages are likely to cause a decrease in growth of the
chicks, but not an increase in energy expenditures of the parents.
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1. The foraging ecology of Brunnich's guillemots Uria lomvia was studied during the breeding season in south-eastern Svalbard. In the region of Storfjorden there are two large breeding colonies comprising a total of about 540 000 individuals. These birds forage in the western part of Storfjorden and further to the south. Their main prey are polar cod Boreogadus saida, pelagic amphipods Parathemisto spp. and euphausiids Thysanoessa inermis. 2. A ship-based transect survey was used to record bird abundance and the acoustically determined biomass of presumed prey. The five transects were divided into 33 segments, each 8-11 km in length. The resolution of the survey was 150 m, and analyses of correlations between predators and prey were performed at length scales from 150 m to 9 km. We differentiated acoustic signals into aggregated and dispersed categories according to the estimated horizontal distribution of presumed prey. 3. Foraging guillemots were consistently more strongly correlated with the aggregated prey than with dispersed prey over scales ranging from 150 m to 9 km. Correlations were weak at small scales (150 m - 1 km) and increased and stabilized at scales of 2-3 km. The spatial scale at which we obtained a shift from weak to strong correlations between guillemots and their prey was similar to the scale at which the spatial variances in both guillemot and prey abundance were high. 4. Guillemots showed low correlations with prey at low prey densities. Similarly, correlations between guillemots and prey were low at low bird densities. The data support the hypothesis that the birds associate with prey patches with densities above a certain threshold, and that `regional' prey abundances affect local use of patches. 5. The numerical aggregative response curves between guillemot and prey density were classified as being neither hyperbolic (type II) or sigmoidal (type III) within the range of prey densities observed in this study. The aggregative response curves were sensitive to spatial scales, which suggest that studies of response curves should be conducted at a range of spatial scales.
Marine bird and mammal surveys were conducted in the Eastern Barents Sea and Kara Sea during the period 3 August to 10 September 1995. We made observations along a total distance of 9336 km. Seabird and marine mammal abundances were greater in the Barents Sea, while aquatic birds and shore birds were more abundant in the coastal regions of the Kara Sea and in the Ob and Jenisej Bays. We observed a total of 13,418 birds of 35 species and 457 mammals of nine species throughout the survey. Distribution and abundance maps are presented for 24 of the most numerous species.
The at-sea distribution of thick-billed murres (Uria lomvia) in southeastern Svalbard waters was studied during the summers of 1992, 1993, and 1996. The Storfjordrenna region south of Svalbard was confirmed as an important foraging area for thick-billed murres; murre aggregations were located at distances of 85 to 126 km from the closest breeding colonies. Fish, mainly polar cod (Boreogadus saida), but also capelin (Mallotus villosus), were the main prey found in 16 murres and 3 black-legged kittiwakes (Rissa tridactyla) collected from these aggregations. Murres were seen flying with fish in their beaks at four locations 78 to 102 km away from the colonies. Murre aggregations were associated with frontal zones between cold Arctic waters and warmer Atlantic water, and in areas with strong stratification in salinity at 15-30 m. A positive association was found between the abundance of murres and the occurrence of cetaceans. Murres and other marine birds were often seen near surfacing cetaceans. The most common cetaceans were minke whales (Balaenoptera acutorostrata) and white-beaked dolphins (Lagenorhynchus albirostris).
During the late summer of 1997, for the first time ever recorded, most of the continental shelf of the eastern Bering Sea was covered by aquamarine waters, resulting from a massive bloom of coccolithophores. Light reflecting off the calcium carbonate plates of the flagellated coccolithophores gave the water its anomalous color, which was first observed in July. The bloom was also clearly visibly from space, as shown by some of the first images from the multispectral sea-viewing wide-field-of-view sensor (SeaWiFS) scanner in September.
Light penetration into the water column, essential for primary production by diatoms and other phytoplankton, was markedly reduced. This shift potentially altered the trophic dynamics throughout the food web of one of the world’s most productive ecosystems.
We investigated the foraging distribution of 2 species of murres (Uria lomvia and U. aalge) in relation to Acoustically Determined Biomass (ADB) and hydrographic structure surrounding the Pribilof Islands, Bering Sea, Alaska, USA. The distribution and abundance of both murre species were similar; therefore, we combined data for thick-billed and common murres in the analysis. We found that murre densities were higher in frontal regions than in non-frontal regions. Maximum ADB was also found to be elevated in the frontal zone. Within frontal regions, high densities of murres were associated with regions containing relatively high levels of ADB. In contrast, we did not find significant correlations between murre density and ADB in the study area as a whole. We postulate that murres restrict their foraging to the frontal region because prey can be located more predictably within this zone than in other areas in the vicinity of the Pribilof Islands.