Publications
A collection of research published to peer-reviewed journals by members of CMOL.
Assessing the ecological risk of heavy metal sediment contamination from Port Everglades Florida USA
Dimitrios G. Giarikos, Laura White, Andre M. Daniels, Radleigh G. Santos, Paul E. Baldauf, & Amy C. Hirons
Abstract: Port sediments are often contaminated with metals and organic compounds from anthropogenic sources. Remobilization of sediment during a planned expansion of Port Everglades near Fort Lauderdale, Florida (USA) has the potential to harm adjacent benthic communities, including coral reefs. Twelve sediment cores were collected from four Port Everglades sites and a control site; surface sediment was collected at two nearby coral reef sites. Sediment cores, sampled every 5 cm, were analyzed for 14 heavy metals using inductively coupled plasma-mass spectrometry. Results for all three locations yielded concentration ranges (µg/g): As (0.607–223), Cd (n/d–0.916), Cr (0.155–56.8), Co (0.0238–7.40), Cu (0.004–215), Pb (0.0169–73.8), Mn (1.61–204), Hg (n/d–0.736), Mn (1.61–204), Ni (0.232–29.3), Se (n/d–4.79), Sn (n/d–140), V (0.160–176), and Zn (0.112–603), where n/d = non-detected. The geo-accumulation index shows moderate-to-strong contamination of As and Mo in port sediments, and potential ecological risk indicates moderate-to-significantly high overall metal contamination. All four port sites have sediment core subsamples with As concentrations above both threshold effect level (TEL, 7.24 µg/g) and probable effect level (PEL, 41.6 µg/g), while Mo geometric mean concentrations exceed the background continental crust level (1.5 µg/g) threshold. Control site sediments exceed TEL for As, while the reef sites has low to no overall heavy metal contamination. Results of this study indicate there is a moderate to high overall ecological risk from remobilized sediment due to metal contamination. Due to an imminent dredging at Port Everglades, this could have the potential to harm the threatened adjacent coral communities and surrounding protected habitats.
Site Fidelity of Coastal Bottlenose Dolphins (Tursiops truncatus) off Southeast Florida, USA
Graysen D. Boehning, Barbara J. Brunnick, Stefan Harzen, & Amy C. Hirons
Abstract: The coastal bottlenose dolphin is well studied throughout its natural range, though most research focuses on wide, well-protected habitats such as bays and estuaries rather than on narrow coastal sand banks. This study identifies a residential group of coastal bottlenose dolphins utilizing the northwestern Atlantic waters off the coast of Palm Beach County, Florida. From 2014 to 2020, 313 boat surveys were conducted, and 585 individual dolphins were identified using photo-identification. Using seasonal and annual resighting ratios, 24 dolphins were considered full-time residents, 66 dolphins were considered part-time residents, and 478 dolphins were transient. The presence of individuals with high site fidelity indicates that the region is used as a permanent habitat for some individuals, while the presence of transient animals may indicate a possible bridge between populations living to the north and south of the region.
Sympatric otariids increase trophic segregation in response to warming ocean conditions in Peruvian Humboldt Current System
Susana Cárdenas-Alayza, Michael J. Adkesson, Mickie R. Edwards, Amy C. Hirons, Dimitri Gutiérrez, Yann Tremblay, & Valentina Franco-Trecu
Abstract: Determining trophic habits of predator communities is essential to measure interspecific interactions and response to environmental fluctuations. South American fur seals, Arctocephalus australis (SAFS) and sea lions Otaria byronia (SASL), coexist along the coasts of Peru. Recently, ocean warming events (2014–2017) that can decrease and impoverish prey biomass have occurred in the Peruvian Humboldt Current System. In this context, our aim was to assess the effect of warming events on long-term inter- and intra-specific niche segregation. We collected whisker from SAFS (55 females and 21 males) and SASL (14 females and 22 males) in Punta San Juan, Peru. We used δ13C and δ15N values serially archived in otariid whiskers to construct a monthly time series for 2005–2019. From the same period we used sea level anomaly records to determine shifts in the predominant oceanographic conditions using a change point analysis. Ellipse areas (SIBER) estimated niche width of species-sex groups and their overlap. We detected a shift in the environmental conditions marking two distinct periods (P1: January 2005—October 2013; P2: November 2013—December 2019). Reduction in δ15N in all groups during P2 suggests impoverished baseline values with bottom-up effects, a shift towards consuming lower trophic level prey, or both. Reduced overlap between all groups in P2 lends support of a more redundant assemblage during the colder P1 to a more trophically segregated assemblage during warmer P2. SASL females show the largest variation in response to the warming scenario (P2), reducing both ellipse area and δ15N mean values. Plasticity to adapt to changing environments and feeding on a more available food source without fishing pressure can be more advantageous for female SASL, albeit temporary trophic bottom-up effects. This helps explain larger population size of SASL in Peru, in contrast to the smaller and declining SAFS population.
Maternal offloading of arsenic and other trace elements in Peruvian fur seals
Catherine Kooyomjian, Dimitrios Giarikos, Michael Adkesson, & Amy C. Hirons
Abstract: The maternal transfer of 15 elements was examined in Peruvian fur seal (Arctocephalus australis) dam and pup paired vibrissae (whiskers), serum, and milk samples collected from 2009 to 2019. Pup vibrissae, grown in utero, represented gestational transfer, while milk represented lactational transfer. Element concentrations, except arsenic, were highest in vibrissae compared to serum and milk for both dams and pups. Mean arsenic concentrations in pup vibrissae (0.44 μg/g) and milk (0.41 μg/g) were twice as high as dam vibrissae concentrations (0.19 μg/g) and nearly ten times higher than dam (0.06 μg/g) and pup serum (0.04 μg/g) concentrations. Mean arsenic concentrations from 2011 to 2019 increased in dam vibrissae (0.026 μg/g to 0.262 μg/g) and milk (0.361 μg/g to 0.484 μg/g). Pup vibrissae had significantly higher concentrations for 11 of the 15 elements analyzed compared to dam vibrissae, suggesting that element transfer is occurring through recent exposure and remobilization of elements from dam body stores. Potentially high concentrations of aluminum, arsenic, copper, and lead in pup tissues may impact their survival and population health. The impact of regional mining activities can contribute to elevated trace elements through runoff and pose a possible threat to local marine environments.
Accumulation of the toxic metal mercury in multiple tissues of marine‑associated birds from South Florida
Caitlyn Nay, James Gelsleichter, Sarah E. Hill, Amy C. Hirons, & David W. Kerstetter
Abstract: One of the best studied global “hot spots” for ecological mercury (Hg) contamination is south Florida (USA), where elevated Hg concentrations in environmental media and regional wildlife were frst described over thirty years ago. While Hg contamination has lessened in this region, it is still critical to monitor Hg uptake and potential risks in south Florida wildlife, especially in marine-associated birds, which are known to accumulate potentially toxic Hg levels. In this study, total Hg (THg) concentrations were measured in liver, kidney, muscle, and feathers of 101 individuals from seven species of south Florida birds: brown pelican Pelecanus occidentalis, double-crested cormorant Phalacrocorax auratus, herring gull Larus argentatus, laughing gull Leucophaeus atricilla, northern gannet Morus bassanus, royal tern Thalasseus maximus, and osprey Pandion halietus. A sizeable proportion of individuals (>40%) were found to contain THg concentrations in internal tissues that exceeded estimated toxicity thresholds for Hg-related efects. Certain species, especially osprey, were found to exhibit a higher rate of threshold exceedances than others and should continue to be monitored for Hg-related efects in future studies. Feather THg concentrations exhibited a lower rate of toxicity threshold exceedances (12%) and were not signifcantly correlated with those in internal tissues in most cases, suggesting that they may not be well suited for monitoring Hg exposure in these species unless sources of data variation can be better understood. The results of the present study contribute signifcantly to our understanding of trends in Hg accumulation and Hg-related health risks in south Florida marine-associated birds.
Sea otters, mercury, and monitoring climate change
Lawrence K. Duffy, Amy C. Hirons, Jeanne M. Shcaaf, C. Peter McRoy, Maribeth S. Murray, & Mary Van Muelken
Abstract: An increase in mobility of heavy metals, like mercury (Hg), has the potential to be one of the climate change related impacts on Arctic and sub-Arctic ecosystems. Sea level rise and flooding events in high latitude coastal ecosystems could increase the bioavailability of contaminants such as mercury. Mercury concentrations have been used as an indicator of past exposure to heavy metals in ancient Pacific cod and here we report on concentrations in archeologically recovered sea otter bones (Enhydra lutris). Methods utilizing stable isotope ratios can be used to reconstruct ancient food webs and help identify prey which may have bioaccumulated high concentrations of mercury. Modern sea otters have δ13C, δ15N, and mercury values corresponding largely to a benthic diet. Conversely, if higher δ15N and mercury levels were found in ancient sea otter bones located in a coastal ecosystem, these increases may be associated with rising sea level following the last glacial maximum. These data place present day and projected climate change related perturbations, like sea level rise, in a historical context.
Evaluation of trace element concentrations in the
serum and vibrissae of Peruvian pinnipeds
(Arctocephalus australis and Otaria byronia)
Catherine Kooyomjian, Dimitrios Giarikos, Michael Adkesson, & Amy C. Hirons
Abstract: Concentrations of 15 trace elements (aluminum, arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, selenium, tin, vanadium, and zinc) were determined in vibrissae (whiskers) and serum of two sympatric pinniped species, the Peruvian fur seal population (PFS; Arctocephalus australis Peruvian subpopulation) and South American sea lion (SASL; Otaria byronia) at Punta San Juan, Peru during 2011–19 sampling events. Element concentrations were 2–20 times higher in vibrissae than in serum. Vibrissae and serum concentrations of several elements, including aluminum, arsenic, and lead, suggest that environmental contaminants may affect the health of pinnipeds at Punta San Juan. Although toxicity thresholds are unknown in pinnipeds, high concentrations of some elements (especially aluminum, arsenic, and lead) may have adverse impacts on their health such as immunosuppression and impaired reproduction. Arsenic was the only element that increased in mean vibrissae concentration throughout the study period. Female SASL vibrissae contained a mean arsenic concentration three times higher than the male SASL vibrissae mean arsenic concentration, and twice as high as the arsenic mean for all PFS vibrissae. The mean male SASL vibrissae cadmium concentration was five times higher than the vibrissae cadmium mean for both PFS males and females and nearly three times higher than the vibrissae cadmium mean for SASL females. Serum concentrations of aluminum, arsenic, copper, and manganese were significantly higher during moderate to extreme El Niño years compared to La Niña years. With stronger and more frequent El Niño-Southern Oscillation events predicted in the future, it is vital to understand how these trace elements may affect pinniped population health.
Stable isotopes and community surveys reveal differential use of artificial and natural reefs by South Florida fishes
Christopher A. Blanar, Joseph R. Hornbeck, David W. Kerstetter, & Amy C. Hirons
Abstract: Artificial reefs may enhance the biological production of reef-associated flora and fauna, but their trophic structure relative to that of natural reefs remains understudied. We assessed trophic relationships by 1) comparing reef fish communities and 2) comparing δ13C and δ15N in 43 fish species from both artificial reef sites and adjacent natural reef tracts in Broward County, Florida. We tested the effect of sampling location (artificial, first, and second reef), general feeding strategy (herbivore, omnivore, invertivore, and carnivore), phylogeny, and standard length on δ13C and δ15N. The reef fish communities of the artificial and natural reef tracts were significantly different; the artificial sites also exhibited more variability. For all samples, δ13C and δ15N ranged from -19.5 to -13.1‰ and 6.7-13.3‰, respectively. Significant effects were detected for both general feeding strategy and phylogeny. Significant differences were also seen in δ13C and δ15N profiles between artificial and natural reefs; however, these changes were primarily driven by differences in fish community structure, rather than by changes in the feeding strategy or trophic relationships of individual fish taxa. The trophic guild invertivore was the only group of fish to demonstrate significant isotopic differences between both reef tracts (inner and outer) and reef types (artificial and natural). The artificial reef may act more as a foraging corridor between the natural first and second reef tracts for omnivores and carnivores. If the function of artificial reefs is to provide additional foraging habitat for fishes, then perhaps more time is needed for the trophically important, infaunal invertebrate community to develop similarly to the natural reef environment.
Stable isotopes and parasites indicate feeding ecology in Florida, USA, wading birds
Sarah E. Gumbleton, David W. Kerstetter, Christopher A. Blanar, & Amy C. Hirons
Abstract: We assessed δ13C and δ15N profiles and endoparasite community composition in Great Egrets (Ardea alba), Great Blue Herons (A. herodias), and White Ibis (Eudocimus albus) from four wildlife rescue centers (two mainland, two on islands in the Florida Keys) in south Florida, USA to elucidate feeding ecology. We detected among-species differences for δ15N but not δ13C and noted decreased δ13C enrichment in Great Egrets and Great Blue Herons (but not White Ibis) from these centers. Parasite component community and infracommunity species richness were higher in Great Egrets and Great Blue Herons relative to White Ibis, and higher in birds of the same species from mainland centers. Multivariate analysis of parasite infracommunity structure detected cooccurring clusters of parasite taxa characteristic of Great Egrets and Great Blue Herons on the one part, and of White Ibis on the other; mainland Great Egrets and Great Blue Herons had similar parasite communities and clustered separately from conspecifics from the islands. We detected a significant (negative) correlation of infracommunity species richness with δ13C but not δ15N. Lastly, parasite infracommunity Bray-Curtis similarity correlated significantly with stable isotope Euclidean distances. We conclude that the two approaches converge towards similar outcomes, providing complementary and consilient information on host feeding ecology.
Swordfish Xiphias gladius diet in the Florida Straits
Amy M. Heemsoth, Amy C. Hirons, Caroline M. Collatos, & David W. Kerstetter
Abstract: Swordfish Xiphias gladius inhabit the Florida Straits year-round and provide a significant role in the food web as top-level predators. However, little is known about the diet composition and thus ecological role of swordfish in Florida. This study investigated swordfish diet by analyzing stomach contents of 131 swordfish in the Florida Straits from April 2007 to December 2008. Identifiable species included 13 teleost species, 3 cephalopod species, and 1 crustacean species. Cephalopods dominated the swordfish diet by weight (72.4%) and number (69.9%), and ranked highest in importance in the diet by the index of relative importance (IRI; 81.5%). Teleosts occurred the most (99.1%) but represented the second highest importance in diet by weight (25.2%), number (26.3%), and IRI (17.6%). Illex sp. was the prey with the greatest dietary importance, followed by unidentifiable ommastrephid squids. Stomach fullness index values ranged from 0 (empty) to 8.98 (mean = 0.37). A positive significant correlation between swordfish length and prey length was found (r2 = 0.104, P = 0.037), and no significant correlations were found between swordfish weight and prey weight (r2 = −0.075, P = 0.065). This is the first study to report a comprehensive diet of swordfish inhabiting waters in the Florida Straits region and suggests swordfish may be opportunistic feeders, altering their diet when abundance or presence of prey changes.
Heavy metal accumulation in seagrasses in Southeastern Florida
Erin M. Smith, Dimitrios Giarikos, Andre Daniels, & Amy C. Hirons
Abstract: Seagrass beds are among the most ecologically important systems in the marine environment and comprise a large component of the diets of many marine organisms, which provides a pathway for contaminants in the seagrasses to enter the marine food web. In this study, three species of seagrasses, Thalassia testudinum, Halodule wrightii, and Syringodium filiforme, were collected monthly, for one year, in three regional locations in South Florida - Port of Miami, Card Sound region of Biscayne Bay Aquatic Preserve, and Florida Bay. These were analyzed for ten heavy metals using Atomic Absorption Spectroscopy. The metal concentrations varied significantly between the three locations, though each location had similar dominant metals (Cu, Fe, Mn, Zn). Significantly higher concentrations of heavy metals were found during the wet season, with the exception of Zn. Metals such as Fe, Mn, and Zn were found to be significantly higher in leaves with epiphytes.
New host records and range extensions for helminth parasites from wading birds in Southeastern Florida
Sarah E. Gumbleton, David W. Kerstetter, Amy C. Hirons, & Christopher A. Blanar
Abstract: Six species of wading birds collected from wildlife centers throughout South Florida were dissected for parasites. Twenty-six species of parasites represent new host records and five parasite species represent new geographic range extensions. Wading birds feed on a variety of food including other birds (particularly chicks), small mammals, and a wide range of aquatic food items that include fish, amphibians, and invertebrates. The majority of wading bird species are associated with aquatic or semi-aquatic habitats that range from freshwater marshes and meadows to the shores of marine environments (Brooke and Birkhead 1991; Schreiber and Burger 2001; Lovette and Fitzpatrick 2016). In southeastern Florida, wading birds are ubiquitous and can be found using a wide range of habitats ranging from the Everglades to the islands of the Florida Keys. Consequently, these bird species can provide valuable information on foraging ecology across a wide geographic scope.The intent of this study was to assess the endoparasite diversity of common wading birds in southeastern Florida. We examined Great Egrets (Ardea alba), Great Blue Herons (Ardea herodias), Green Herons (Butorides virescens), Yellow-crowned Night-Herons (Nyctanassa violacea), Black-crowned Night-Herons (Nycticorax nycticorax), and White Ibis (Eudocimus albus).
Climate change, one health and mercury
Lawrence K. Duffy, Theresa Vertigan, Bonita Dainowski, Kriya Dunlap, & Amy C. Hirons
Abstract: Climate change is occurring on both regional and global scales. The use and global distribution of toxic metals is increasing and affecting environmental, animal and human health as a result of air, water and food contamination. Mercury (Hg) in major forms Hg°, Hg2+ and methyl mercury (CH3Hg+) are increasingly available around the globe. Both metal and organic contaminants are impacting the health of all species on the planet. Mercury is an example of a metal that can cause or aggravate a disease state, for example, diabetes. Habitat stewardship is needed to maintain a healthy system, and selecting a keystone species as a bio indicator to monitor changes in contaminant levels over time and space is essential. Mercury can be used to monitor the flow of toxics through the food system. The structural organization of food webs and their sensitivity to disturbances are relevant to predicting the fate of Hg bioavailability related to climate change. Hg needs to be monitored across many ecosystems because it impacts not only human health but also the health of the plants and animals. Monitoring studies are needed to identify changes related to climate change. Increased precipitation and sea level rise will result in greater mercury mobility into the coastal and terrestrial food webs.
Combined gut-content and stable isotope trophic analysis of the pelagic stingray Pteroplaytrygon violacea (Bonaparte, 1832) diet from the western North Atlantic Ocean
Abstract: The understanding of trophic relationships is vital for correctly modeling ecosystems and ecosystem effects of fisheries removals. The pelagic stingray is found in epipelagic sub-tropical and tropical waters worldwide and is a common bycatch in pelagic longline fisheries. Between August 2008 and November 2011, 156 specimens (81 males; 75 females) were collected during pelagic longline fishing operations in the US South Atlantic Bight and Gulf of Mexico. Stomach content analyses found that the major prey items were cephalopod molluscs (59.18%), followed by actinopterygiian fishes (37.75%), and decapod crustaceans (35.71%). These concentrations of prey items found in the stomachs coincide with previous studies done in the Pacific Ocean. In contrast to previous studies that found high percentages of empty stomachs (63%), the current percentage of empty stomachs was much lower (25.6%), likely due to shorter times between collection and inspection. Stable isotope analysis (δ13C and δ15N) was performed on white muscle in order to correlate the trophic position with gut-content analysis. The δ13C values ranged from -18.81‰ to -16.70‰, while the δ15N ranged from 6.11‰ to 11.88‰. Modeling of stable isotope data suggest that while squid are occasionally an important part of the pelagic stingray diet, prey usually consist of shrimp and other pelagic crustaceans. Pelagic stingrays fed within two trophic levels, but their prey appeared to feed on different carbon sources than those found in other pelagic elasmobranchs. A deeper understanding of the pelagic stingray diet sources can help fisheries management as it begins to transition into ecosystem based management.
Southward flow on the western flank of the Florida current
Alexander V. Soloviev, Amy C. Hirons, Christopher Maingot, Cayla W. Dean, Richard E. Dodge, Alexander E. Yankovsky, Jon Wood, Robert H. Weisberg, Mark E. Luther, & Julian P. McCreary
Abstract: A suite of long-term in situ measurements in the Straits of Florida, including the ADCP bottom moorings at an 11-m isobath and 244-m isobath (Miami Terrace) and several ADCP ship transects, have revealed a remarkable feature of the ocean circulation - southward flow on the western, coastal flank of the Florida Current. We have observed three forms of the southward flow - a seasonally varying coastal countercurrent, an undercurrent jet attached to the Florida shelf, and an intermittent undercurrent on the Miami Terrace. According to a 13-year monthly climatology obtained from the near-shore mooring, the coastal countercurrent is a persistent feature from October through January. The southward flow in the form of an undercurrent jet attached to the continental slope was observed during five ship transects from April through September but was not observed during three transects in February, March, and November. This undercurrent jet is well mixed due to strong shear at its top associated with the northward direction of the surface flow (Florida Current) and friction at the bottom. At the same time, no statistically significant seasonal cycle has been observed in the undercurrent flow on the Miami Terrace. Theoretical considerations suggest that several processes could drive the southward current, including interaction between the Florida Current and the shelf, as well as forcing that is independent of the Florida Current. The exact nature of the southward flow on the western flank of the Florida Current is, however, unknown.
Trophic linkages of intracoastal waterway seagrass beds in Broward County, Florida
Christina Gabriel, David W. Kerstetter, & Amy C. Hirons
Abstract: Seagrass habitats support marine food webs and provide essential habitat for a variety of species. Seagrasses and associated algae at three locations along the Intracoastal Waterway in Broward County, FL were assessed for their trophic contribution to the marine organisms in the area. Two seagrass species, along with associated algae, invertebrates, and vertebrates, were analyzed for stable carbon and nitrogen isotope ratios to determine trophic relationships. Significant differences were found in d13C and d15N between both seagrass species and among the three sites. The d13C of Johnson’s seagrass Halophila johnsonii ranged from 216.28 to 211.27% while shoal grass Halodule wrightii ranged from 215.78 to 213.36%. The d15N for shoal grass ranged from 4.69 to 7.08% versus 0.80 to 7.86% for Johnson’s seagrass. Neither seagrass species was a dominant food source and epiphytes appeared to be the greater trophic contributor. However, the d13C (216.28 to 211.27%) and d15N (0.80 to 7.86%) of both seagrass species did fall in the fractionation range of potential consumers suggesting that seagrass material could be ingested incidentally while grazing on epiphytes and other primary producers. Our results indicate that seagrass in Broward County are valuable both as a direct food source and as substrate for epiphytes.
Combined stomach content and δ13C/δ15N analyses of oilfish, escolar, snake mackerel and lancetfish in the western North Atlantic
Heidi R. Keller, Amy C. Hirons, & David W. Kerstetter
Abstract: Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length-at-maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal–Wallis test showed the four species to be isotopically segregated in both d13C and d15N. Escolar were the most depleted in d13C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in d13C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in d13C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (d15N = 10.20), followed by snake mackerel (d15N = 9.66), adult oilfish (d15N = 9.32), lancetfish (d15N = 9.05) and juvenile oilfish (d15N = 7.83). A marked change in oilfish d13C and C/N at 30–35 cm fork length coincided with a presumed length-at-maturity.
An international assessment of mangrove management: Incorporation in integrated coastal zone management
Haille N. Carter, Steffen W. Schmidt, & Amy C. Hirons
Abstract: Due to increasing recognition of the benefits provided by mangrove ecosystems, protection policies have emerged under both wetland and forestry programs. However, little consistency remains among these programs and inadequate coordination exists among sectors of government. With approximately 123 countries containing mangroves, the need for global management of these ecosystems is crucial to sustain the industries (i.e., fisheries, timber, and tourism) and coastal communities that mangroves support and protect. To determine the most effective form of mangrove management, this review examines management guidelines, particularly those associated with Integrated Coastal Zone Management (ICZM). Five case studies were reviewed to further explore the fundamentals of mangrove management. The management methodologies of two developed nations as well as three developing nations were assessed to encompass comprehensive influences on mangrove management, such as socioeconomics, politics, and land-use regulations. Based on this review, successful mangrove management will require a blend of forestry, wetland, and ICZM programs in addition to the cooperation of all levels of government. Legally binding policies, particularly at the international level, will be essential to successful mangrove management, which must include the preservation of existing mangrove habitat and restoration of damaged mangroves.
Biogeochemical analysis of ancient Pacific cod bone suggests Hg bioaccumulation was linked to pale sea level rise and climate change.
Maribeth S. Murray, C. Peter McRoy, Lawrence K. Duffy, Amy C. Hirons, Jeanne M. Schaaf, Robert P. Trocine, & John Trefry
Abstract: Deglaciation at the end of the Pleistocene initiated major changes in ocean circulation and distribution. Within a brief geological time, large areas of land were inundated by sea-level rise and today global sea level is 120 m above its minimum stand during the last glacial maximum. This was the era of modern sea shelf formation; climate change caused coastal plain flooding and created broad continental shelves with innumerable consequences to marine and terrestrial ecosystems and human populations. In Alaska, the Bering Sea nearly doubled in size and stretches of coastline to the south were flooded, with regional variability in the timing and extent of submergence. Here we suggest how past climate change and coastal flooding are linked to mercury bioaccumulation that could have had profound impacts on past human populations and that, under conditions of continued climate warming, may have future impacts. Biogeochemical analysis of total mercury (tHg) and δ13C/δ15N ratios in the bone collagen of archeologically recovered Pacific Cod (Gadus macrocephalus) bone shows high levels of tHg during early/mid-Holocene. This pattern cannot be linked to anthropogenic activity or to food web trophic changes, but may result from natural phenomena such as increases in productivity, carbon supply and coastal flooding driven by glacial melting and sea-level rise. The coastal flooding could have led to increased methylation of Hg in newly submerged terrestrial land and vegetation. Methylmercury is bioaccumulated through aquatic food webs with attendant consequences for the health of fish and their consumers, including people. This is the first study of tHg levels in a marine species from the Gulf of Alaska to provide a time series spanning nearly the entire Holocene and we propose that past coastal flooding resulting from climate change had the potential to input significant quantities of Hg into marine food webs and subsequently to human consumers.
Biomixing due to diel vertical migrations of zooplankton: Comparison of computational fluid dynamics model with observations
Cayla Deana, Alexander Soloviev, Amy C. Hirons, Tamara Frank, & Jon Wood
Abstract: Recent studies (Dewar et al., 2006; Wilhelmus and Dabiri, 2014) suggest that diel vertical migrations (DVM) of zooplankton (or other migrating organisms) may have an impact on ocean mixing, though details are not completely clear. Zooplankton that undergo DVM can have an impact on oil transport through the water column, and oil and dispersants can have a negative or even lethal effect on the organisms. Kunze et al. (2006) reported an increase of dissipation rate of turbulent kinetic energy, ε, by four to five orders of magnitude during DVM of zooplankton over background turbulence in Saanich Inlet, British Columbia, Canada. However, the effect was not observed in the same area by Rousseau et al. (2010) and was later reassessed by Kunze (2011). In our work, an 11-month data set obtained in the Straits of Florida with a bottom-mounted acoustic Doppler current profiler revealed strong sound scattering layers undergoing DVM. We used a 3-D non-hydrostatic computational fluid dynamics model with Lagrangian particle injections (a proxy for migrating organisms) via a discrete phase model to simulate the effect of turbulence generation by DVM. We tested a range of organism concentrations from 1000 to 10,000 organisms/m3 based on measurements by Greenlaw (1979) and Mackie and Mills (1983) in Saanich Inlet. At a concentration close to the upper limit, the simulation showed an increase in ε by two to three orders of magnitude during DVM over background turbulence, 10−9 W kg−1. At a concentration of 1000 organisms/m3, almost no turbulence above the background level was produced in the model. These results suggest that the Kunze et al. (2006) observations could have been performed at a larger concentration of migrating zooplankton than those reported by Rousseau et al. (2010). No exact zooplankton concentrations data were provided in either work. The difference between observations and the model can, in part, be explained by the fact that Kunze et al. (2006) measured instantaneous profiles of ε, while the model results on ε were averaged horizontally over the 50 m by 50 m domain. In the Straits of Florida, we observed a small decrease in northward current velocity profiles during migration times after averaging over 11 months of observations. The computational fluid dynamics model reproduced this decrease of current velocity due to turbulence generated by DVM in the Straits of Florida model case. The deviations in the velocity profiles can be explained by the increase in turbulent mixing during vertical migration periods. Comparison of observational data to the model results was complicated by physical factors such as tides, Florida Current meandering, etc., which may have a stronger effect on current velocity profiles than DVM.
Stable isotopes confirm a coastal diet for critically endangered Mediterranean monk seals
Alexandros A. Karamanlidis, P. Jeff Curtis, Amy C. Hirons, Marianna Psaradellis, Panagiotis Dendrinos, & John B. Hopkins III
Abstract: Understanding the ecology and behaviour of endangered species is essential for developing effective management and conservation strategies. We used stable isotope analysis to investigate the foraging behaviour of critically endangered Mediterranean monk seals (Monachus monachus) in Greece. We measured carbon and nitrogen isotope ratios (expressed as δ13C and δ15N values, respectively) derived from the hair of deceased adult and juvenile seals and the muscle of their known prey to quantify their diets. We tested the hypothesis that monk seals primarily foraged for prey that occupy coastal habitats in Greece. We compared isotope values from seal hair to their coastal and pelagic prey (after correcting all prey for isotopic discrimination) and used these isotopic data and a stable isotope mixing model to estimate the proportion of coastal and pelagic resources consumed by seals. As predicted, we found that seals had similar δ13C values as many coastal prey species and higher δ13C values than pelagic species; these results, in conjunction with mean dietary estimates (coastal = 61 % vs. pelagic = 39 %), suggest that seals have a diverse diet comprising prey from multiple trophic levels that primarily occupy the coast. Marine resource managers should consider using the results from this study to inform the future management of coastal habitats in Greece to protect Mediterranean monk seals.
Spectral sensitivity, luminous sensitivity, and temporal resolution of the visual systems in three sympatric temperate coastal shark species
Mieka Kalinoski, Amy Hirons, Andrij Horodysky, & Richard Brill
Abstract: We used electroretinography (ERG) to determine spectral and luminous sensitivities, and the temporal resolution (flicker fusion frequency, FFF) in three sympatric (but phylogenetically distant) coastal shark species: Carcharhinus plumbeus (sandbar shark), Mustelus canis (smooth dogfish), and Squalus acanthias (spiny dogfish). Spectral sensitivities were similar (range ~400–600 nm, peak sensitivity ~470 nm), with a high likelihood of rod/cone dichromacy enhancing contrast discrimination. Spiny dogfish were significantly less light sensitive than the other species, whereas their FFF was ~19 Hz at maximum intensities; a value equal to that of sandbar shark and significantly above that of smooth dogfish (~9–12 Hz). This occurred even though experiments on spiny dogfish were conducted at 12 versus 25 °C and 20 °C for experiments on sandbar shark and smooth dogfish, respectively. Although spiny dogfish have a rod-dominated retina (rod:cone ratio 50:1), their visual system appears to have evolved for a relatively high temporal resolution (i.e., high FFF) through a short integration time, with the requisite concomitant reduction in luminous sensitivity. Our results suggest adaptive plasticity in the temporal resolution of elasmobranch visual systems which reflects the importance of the ability to track moving objects such as mates, predators, or prey.
Trophic levels of North Pacific humpback whales (Megaptera novaeangliae) through analysis of stable isotopes: Implications on prey and resource quality
Briana H. Witteveen, Graham A. J. Worthy, Kate M. Wynne, Amy C. Hirons, Alexander G. Andrews III, & Russell W. Markel
Abstract: Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North Pacific feeding groups were calculated using δ15N of humpback whales and regional primary consumers. The overall mean trophic level for North Pacific humpback whales was 3.6 ± 0.02, indicating a diet of both fish and zooplankton, and, thus, supporting assumptions of humpback whales as generalist predators. The highest mean trophic level was calculated for the north Gulf of Alaska group (4.0 ± 0.03), while the lowest was found for the Russian and the western Aleutian Islands group (3.3 ± 0.08). Differences in mean trophic levels suggest that feeding groups differ in the proportion of fish and zooplankton in their diets.
Using movements, genetics and trophic ecology to differentiate inshore from offshore aggregations of humpback whales in the Gulf of Alaska
Briana H. Witteveen, Jan M. Straley, Ellen Chenoweth, C. Scott Baker, Jay Barlow, Craig Matkin, Christine M. Gabriele, Janet Neilson, Debbie Steel, Olga von Ziegesar, Alexander G. Andrews, & Amy C. Hirons
Abstract: Humpback whales Megaptera novaeangliae have been studied in the coastal waters of the Gulf of Alaska (GOA) since the late 1960s, but information about whales foraging offshore is limited. A large-scale collaborative project (SPLASH) provided opportunities to study humpback whales in both inshore and offshore habitats. Using identification photographs and biopsy samples, we explored individual movements, the distribution of mitochondrial (mtDNA) haplotypes, and trophic levels for humpback whales within 3 regions (Kodiak, KOD; Prince William Sound, PWS; and southeastern Alaska, SEAK) of the GOA to determine whether inshore and offshore aggregations of humpback whales are distinct. Each region was divided into inshore and offshore habitats, creating 6 subregions for comparison. Results documenting 2136 individual whales showed that movement within the study area was most frequent between inshore and offshore subregions within a region. In general, movement between regions was minimal. Tissue samples of 483 humpback whales included 15 mtDNA haplotypes. Pairwise chi-squared tests showed haplotype differences between subregions, but inshore PWS was the only subregion with a haplotype composition significantly different than all other subregions. Trophic levels, as inferred from stable nitrogen isotope ratios, were significantly different among subregions, ranging from 3.4 to 4.5. Pairwise comparisons showed that inshore PWS was again the only subregion that significantly differed from all others. Results suggest that the combined inshore and offshore habitats for KOD and the inshore and offshore habitats for SEAK should each be considered as single regional feeding aggregations, while inshore PWS may represent a separate aggregation from PWS offshore.
Occurrence of an ocean sunfish (Mola mola) larva in the Florida current
David L. Trimm, Jonathan Shenker, Amy C. Hirons, & S. Mochrie
Abstract: Mola mola, the most commonly encountered ocean sunfish, is widely distributed in temperate and tropical waters. It occurs globally in the Indian, Pacific and Atlantic oceans, and is common in the Gulf of Mexico. Several studies have addressed adult distributions, reproductive biology and/or maturation (Nakatsubo, 2008; Fulling et al., 2007; Cartamil and Lowe, 2004). Five areas, including the central gyres of the North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Oceans, have been suggested for sunfish spawning (UNH, 2008). Sunfish are considered one of the most prolific oceanic spawners, with females producing as many as 300 million eggs at one time (Tortonese, 1986). Despite this fact, information on larval stage duration and development is rare and historical data are limited primarily to lone occurrences during ichthyoplankton surveys. Historic larval occurrences in the Gulf of Mexico and northwest Atlantic have been noted since 1869 (Table 1), with 16 individuals documented prior to this study.
Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean
Michael F. Sigler, Lee B. Hulbert, Chris R. Lunsford, Norman H. Thompson, Kathleen Burek, Gregory O’Corry-Crowe, & Amy C. Hirons
Abstract: Pacific sleeper sharks Somniosus pacificus were captured near Steller sea lion Eumetopias jubatus rookeries during the period when Steller sea lion pups are most vulnerable to Pacific sleeper shark predation (first water entrance and weaning). Analysis of stomach contents revealed that teleosts were the dominant prey in August and cephalopods were the dominant prey in May (n = 198). Marine mammals were found in 15% of stomachs regardless of season, but no Steller sea lion tissues were detected. Molecular genetic analysis identified grey whale Eschrichtius robustus and harbour seal Phoca vitulina remains in some Pacific sleeper shark stomachs. Most mammals were cetacean and at least 70% of the cetaceans were probably scavenged. Although Pacific sleeper shark and Steller sea lion ranges overlapped, so predation could potentially occur, the diet study suggested that predation on Steller sea lions is unlikely, at least when pups first enter the water or during weaning. Harbour seals were infrequent prey and may have been consumed alive. Pacific sleeper sharks consume fast-swimming prey like Pacific salmon Oncorhynchus sp., most likely live animals rather than scavenged animals. Pacific sleeper sharks appeared to be opportunistic consumers of the available prey and carrion, feeding both on the bottom and in the water column, and their diet shifted to teleosts and cetacean carrion as the fish grew larger.
Temporal records of δ13C and δ15N in North Pacific pinnipeds: inferences regarding environmental change and diet
Amy C. Hirons, Donald M. Schell, & Bruce P. Finney
Abstract: Sea lion and seal populations in Alaskan waters underwent various degrees of decline during the latter half of the twentieth century and the cause(s) for the declines remain uncertain. The stable carbon (13C/12C) and nitrogen (15N/14N) isotope ratios in bone collagen from wild Steller sea lions (Eumetopias jubatus), northern fur seals (Callorhinus ursinus) and harbor seals (Phoca vitulina) from the Bering Sea and Gulf of Alaska were measured for the period 1951–1997 to test the hypothesis that a change in trophic level may have occurred during this interval and contributed to the population declines. A significant change in δ15N in pinniped tissues over time would imply a marked change in trophic level. No significant change in bone collagen δ15N was found for any of the three species during the past 47 years in either the Bering Sea or the Gulf of Alaska. However, the 15N in the Steller sea lion collagen was significantly higher than both northern fur seals and harbor seals. A significant decline in δ13C (almost 2 ‰ over the 47 years) was evident in Steller sea lions, while a declining trend, though not significant, was evident in harbor seals and northern fur seals. Changes in foraging location, in combination with a trophic shift, may offer one possible explanation. Nevertheless, a decrease in δ13C over time with no accompanying change in δ15N suggests an environmental change affecting the base of the foodweb rather than a trophic level change due to prey switching. A decline in the seasonal primary production in the region, possibly resulting from decreased phytoplankton growth rates, would exhibit itself as a decline in δ13C. Declining production could be an indication of a reduced carrying capacity in the North Pacific Ocean. Sufficient quantities of optimal prey species may have fallen below threshold sustaining densities for these pinnipeds, particularly for yearlings and subadults who have not yet developed adequate foraging skills.
Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus)
Amy C. Hirons, Donald M. Schell, and David J. St. Aubin
Abstract: Growth rates of vibrissae (whiskers), which act as a temporal record of feeding in harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), were estimated using 13C- and 15N-labeled glycine followed by stable-isotope analysis. The labeled glycine was incorporated into keratin and served as a temporal marker for growthrate calculation. One captive harbor seal received two doses 147 days apart, while a second seal received one dose; vibrissae were analyzed after 86 and 154 days. The peak positions indicated that growth began in the fall, continued into spring, but ceased in June, with active growth rates of 0.33 mm/day. Two adult captive Steller sea lions each received two labeled doses during a 308-day period. After 427 days vibrissae in both sea lions showed two peaks corresponding to the markers; growth rates were calculated as 0.05–0.07 mm/day. Growth rates in captive juvenile and wild adult Steller sea lions, 0.10–0.17 mm/day, supported the assumption that major isotopic oscillations in vibrissae of wild sea lions were annual. The multiyear records imply that Steller sea lions retain their vibrissae; harbor seal vibrissae, in contrast, have periods of rapid growth and appear to be shed, at least in part, annually.