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Sibert, EC, Cramer KL, Hastings PA, Norris RD.  2017.  Methods for isolation and quantification of microfossil fish teeth and elasmobranch dermal denticles (ichthyoliths) from marine sediments. Palaeontologia Electronica. 20:1-14. Abstract

Ichthyoliths — microfossil fish teeth and shark dermal scales (denticles) — are found in nearly all marine sediments. Their small size and relative rarity compared to other microfossil groups means that they have been largely ignored by the paleontology and paleoceanography communities, except as carriers of certain isotopic systems. Yet, when properly concentrated, ichthyoliths are sufficiently abundant to reveal patterns of fish abundance and diversity at unprecedented temporal and spatial resolution, in contrast to the typical millions of years-long gaps in the vertebrate body fossil record. In addition, ichthyoliths are highly resistant to dissolution, making it possible to reconstruct whole fish communities over highly precise and virtually continuous timescales. Here we present methods to isolate and utilize ichthyoliths preserved in the sedimentary record to track fish community structure and ecosystem productivity through geological and historical time periods. These include techniques for isolation and concentration of these microfossils from a wide range of sediments, including deep-sea and coral reef carbonates, clays, shales, and silicate-rich sediments. We also present a novel protocol for ichthyolith staining using Alizarin Red S to easily visualize and distinguish small teeth from debris in the sample. Finally, we discuss several metrics for quantification of ichthyolith community structure and abundance, and their applications to reconstruction of ancient marine food webs and environments.

Cramer, KL, O'Dea A, Carpenter C, Norris RD.  2017.  A 3,000 year record of Caribbean reef urchin communities reveals causes and consequences of long-term decline in Diadema antillarum. Ecography. : Blackwell Publishing Ltd   10.1111/ecog.02513   Abstract

Urchins are the last abundant grazers of macroalgae on most Caribbean reefs following the historical overexploitation of herbivorous fishes. The long-spined urchin Diadema antillarum was particularly effective at controlling macroalgae and facilitating coral dominance on Caribbean reefs until its ecological extinction from a catastrophic disease epidemic in the early 1980s. Despite their important role in the structure and functioning of Caribbean reef ecosystems, the natural dynamics of Caribbean reef urchin communities are poorly known due to the paucity of ecological survey data prior to large-scale human disturbances and the Diadema dieoff. To help resolve the baseline abundances and ecological roles of common urchin taxa, we track changes in urchin abundance and composition over the past 3,000 years from analysis of subfossil urchin spines preserved in reef matrix cores collected in Caribbean Panama. Echinometra consistently dominated the subfossil spine assemblage, while Diadema was consistently rare in the subfossil record in this region. Rather than increasing during a period of heightened human exploitation of their fish competitors and predators, Diadema began declining over a millennium ago. Convergent cross mapping (CCM) causality analyses reveal that Diadema abundance is causally related to coral community composition. Diadema is negatively affected by Acropora cervicornis dominance, likely due to the tight association between this coral and the threespot damselfish, an effective Diadema competitor. Conversely, Diadema positively affects the abundance of the coral Madracis mirabilis, possibly via its control of macroalgae. Causal relationships were not detected among abundances of individual urchin taxa, indicating that inter-specific echinoid competition is not a factor limiting Diadema recovery. Our detailed record of prehistorical and historical urchin community dynamics suggests that the failure of Diadema to recover over 30 years after its mass mortality event may be due in part to the prey release of damselfish following the long-term overfishing of piscivorous fishes. This article is protected by copyright. All rights reserved.

Cramer, KL, O’Dea A, Clark TR, Zhao J-xin, Norris RD.  2017.  Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish. Nature Communications. 8:14160.: The Author(s)   10.1038/ncomms14160   Abstract

Caribbean coral reefs have transformed into algal-dominated habitats over recent decades, but the mechanisms of change are unresolved due to a lack of quantitative ecological data before large-scale human impacts. To understand the role of reduced herbivory in recent coral declines, we produce a high-resolution 3,000 year record of reef accretion rate and herbivore (parrotfish and urchin) abundance from the analysis of sediments and fish, coral and urchin subfossils within cores from Caribbean Panama. At each site, declines in accretion rates and parrotfish abundance were initiated in the prehistorical or historical period. Statistical tests of direct cause and effect relationships using convergent cross mapping reveal that accretion rates are driven by parrotfish abundance (but not vice versa) but are not affected by total urchin abundance. These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence.

Cramer, KL, Leonard-Pingel JS, Rodriguez F, Jackson JBC.  2015.  Molluscan subfossil assemblages reveal the long-term deterioration of coral reef environments in Caribbean Panama. Marine Pollution Bulletin. 96:176-187.   10.1016/j.marpolbul.2015.05.031  
Cramer, KL.  2014.  Historia del impacto humano sobre los ecosistemas costeros del Caribe panameño. Historia Natural del Istmo de Panamá. , Panamá: Albacrome S.A.
Jackson, JBC, Donovan MK, Cramer KL, Lam V.  2014.  Status and Trends of Caribbean Coral Reefs: 1970-2012. , Gland, Switzerland: Global Coral Reef Monitoring Network, International Union for Conservation of Nature
Cramer, KL.  2013.  History of human occupation and environmental change in western and central Caribbean Panama. Bulletin of Marine Science. 89:955-982.   10.5343/bms.2012.1028   AbstractWebsite

Humans have altered terrestrial and marine coastal environments in Central America through land clearing and fishing for over 10,000 yrs. The intensity of human disturbance has been strongly influenced by local physiographic and climatic conditions that affect the productivity of the land and sea. The importance of these factors is readily apparent along the Caribbean coast of Panama. Environmental conditions have played an important role in the differing histories of population and environmental disturbance in Bocas del Toro along the western coast and Costa Arriba de Colon (Costa Arriba) along the central coast. Both regions suffered catastrophic mortality of indigenous peoples soon after European contact and did not return to pre-contact levels until at least the 19th century. During the Spanish colonial era, Bocas del Toro remained relatively sparsely populated until the early 20th century due to its isolation from the Pacific by high mountains, excessive rainfall, and relatively smaller area of alluvial flood plains for human habitation and agriculture. In contrast, the low-lying topography of Costa Arriba was conducive to early colonial occupation in the 16th century and rapid population growth and environmental disturbance since the mid-19th century. This earlier onset of intense human disturbance is likely responsible for the more degraded state of coral reefs in Costa Arriba compared to Bocas del Toro. The timeline of human interaction with the coastal environment of Caribbean Panama thus provides a deeper-time perspective from which to more accurately assess the causes of the recently observed collapse of Caribbean coral reefs.

Cramer, KL, Jackson JBC, Angioletti CV, Leonard-Pingel J, Guilderson TP.  2012.  Anthropogenic mortality on coral reefs in Caribbean Panama predates coral disease and bleaching. Ecology Letters. 15:561-567.   10.1111/j.1461-0248.2012.01768.x   AbstractWebsite

Ecology Letters (2012) Abstract Caribbean reef corals have declined precipitously since the 1980s due to regional episodes of bleaching, disease and algal overgrowth, but the extent of earlier degradation due to localised historical disturbances such as land clearing and overfishing remains unresolved. We analysed coral and molluscan fossil assemblages from reefs near Bocas del Toro, Panama to construct a timeline of ecological change from the 19th centurypresent. We report large changes before 1960 in coastal lagoons coincident with extensive deforestation, and after 1960 on offshore reefs. Striking changes include the demise of previously dominant staghorn coral Acropora cervicornis and oyster Dendrostrea frons that lives attached to gorgonians and staghorn corals. Reductions in bivalve size and simplification of gastropod trophic structure further implicate increasing environmental stress on reefs. Our paleoecological data strongly support the hypothesis, from extensive qualitative data, that Caribbean reef degradation predates coral bleaching and disease outbreaks linked to anthropogenic climate change.

Jackson, JBC, Cramer KL, Friedlander A, Hooten A, Lam V.  2012.  Tropical Americas coral reef resilience workshop report, April 29-May 5, 2012. :33pp..: Global Coral Reef Monitoring Network
Robertson, DR, Cramer KL.  2009.  Shore fishes and biogeographic subdivisions of the Tropical Eastern Pacific. Marine Ecology-Progress Series. 380:1-17.   10.3354/meps07925   AbstractWebsite

We examined the geographic distributions of 1135 species of resident shore fishes to assess biogeographic subdivision of the Tropical Eastern Pacific (TEP), which stretches from the Gulf of California to northern Peru. Using hierarchical clustering refined by Analysis of Similarity (ANOSIM), we determined geographic groupings in the distributions of the entire fauna, of regional endemics and of 3 functional (habitat) groups of species. We also examined the distributions of local endemics throughout the TEP and how differences in faunal size versus faunal composition among sites contribute to the subdivision pattern. Our results indicate that: (1) the continental coast contains 2 provinces, the Cortez (Gulf of California and lower Pacific Baja) and the Panamic (southward), each of which has a peak in abundance of local endemics and of overall species richness; (2) the northern and southern boundaries of the TEP are located near Magdalena Bay on Baja California (similar to 25 degrees N) and the southern shore of the Gulf of Guayaquil (similar to 4 degrees S), respectively; and (3) the 5 oceanic islands/archipelagos collectively represent a third, Ocean Island Province. Relative to mainland areas, the fauna of the ocean islands is smaller, has a different functional-group composition, and includes more transpacific species and more highly localized endemics. The 3-province pattern probably developed in response to the formation of the Gulf of California, the rise of the Isthmus of Panama, immigration from the north, south and west to the TEP, and differing environmental conditions between and within provinces. In contrast, barriers to dispersal within this geographically simple region are weak and likely had much less influence.

Cramer, KL, Perryman WL, Gerrodette T.  2008.  Declines in reproductive output in two dolphin populations depleted by the yellowfin tuna purse-seine fishery. Marine Ecology Progress Series. 369:273-285.   10.3354/meps07606   AbstractWebsite

Reproductive data for 2 pelagic dolphin subspecies in the eastern tropical Pacific, the eastern spinner (ES) dolphin Stenella longirostris orientalis and northeastern pantropical spotted (NEPS) dolphin S. attenuata attenuata, were obtained from aerial photographs taken between 1987 and 2003. Two measures of reproductive output were estimated: proportion of adult dolphins with calves ('proportion with calves') and length at which calves disassociated from their mothers ('length at disassociation'). Trends in length at disassociation were investigated to determine if the proportion with calves was affected by possible changes in calving interval, but no changes were found. Proportion with calves for ES dolphins was stable from 1987 to 1993, then declined from 1993 to 2003; proportion with calves for NEPS dolphins decreased steadily from 1987 to 2003. For both species, proportion with calves was related to number of dolphins in the school of the focal species and/or proportion of the school made up of the focal species. For NEPS dolphins, annual number of purse-seine sets on dolphins was a predictor of both proportion with calves and length at disassociation. Because NEPS dolphins are the main species targeted by the fishery, the link between fishing activity and both measures of reproductive output indicates that the fishery has population-level effects beyond reported direct kill. Decline in reproductive output is the proximate cause or one of the proximate causes of the failure of dolphin populations to recover at rates expected after reduction of high bycatch levels.

Cramer, KL.  1998.  Trace element characterization of San Diego Bay invertebrates. Journal of Undergraduate Research, University of California, San Diego.