Benjamin J. Greenstein

Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective

Abstract In recent years, marine scientists have become increasingly alarmed over the decline of live coral cover throughout the Caribbean and tropical western Atlantic region. The Holocene and Pleistocene fossil record of coral reefs from this region potentially provides a wealth of long-term ecologic information with which to assess the historical record of changes in shallow water coral reef communities. Before fossil data can be applied to the modern reef system, critical problems involving fossil preservation must be addressed. Moreover, it must be demonstrated that the classic reef coral zonation patterns described in the early days of coral reef ecology, and upon which “healthy” versus “unhealthy” reefs are determined, are themselves representative of reefs that existed prior to any human influence. To address these issues, we have conducted systematic censuses of life and death assemblages on modern “healthy” patch reefs in the Florida reef tract that conform to the classic Caribbean model of reef coral zonation, and a patch reef in the Bahamas that is currently undergoing a transition in coral dominance that is part of a greater Caribbean-wide phenomenon. Results were compared to censuses of ancient reef assemblages preserved in Pleistocene limestones in close proximity to each modern reef. We have determined that the Pleistocene fossil record of coral reefs may be used to calibrate an ecological baseline with which to compare modern reef assemblages, and suggest that the current and rapid decline of Acropora cervicornis observed on a Bahamian patch reef may be a unique event that contrasts with the long-term persistence of this taxon during Pleistocene and Holocene time.

An integrated study of echinoid taphonomy : predictions for the fossil record of four echinoid families

Field observations of four common tropical Western Atlantic regular echinoids, Diadema antillarum, Eucidaris tribuloides, Echinometra lucunter and Tripneustes ventricosus, reveal that they are reduced to essentially bleached skeletons, devoid of organic material, within six days of death. This suggests that, in the absence of organic connective tissues, the degree to which stereom interlocks across plate sutures may become an important factor in determining the amount of breakage suffered by the corona in response to biostratinomic processes

Taphonomic alteration of reef corals; effects of reef environment and coral growth form; I, The Great Barrier Reef

Taphonomic alteration in coral death assemblages showed high variability with respect to reef environment and growth form at Orpheus Island on the Great Barrier Reef Australia. A greater degree of physical and biological alteration occurred in the lower-energy leeward Pioneer Bay site relative to the higher-energy windward Iris Point site. Greater degrees of taphonomic alteration also occurred at 6-7 m than 2-3 m water depth within each site. Clear gradients in the degree of taphonomic alteration of reef corals with reef environment indicate the utility of corals as taphonomic indicators in ancient reef settings. Because greater taphonomic differences between depths occurred at the high wave-energy site relative to the lour wave-energy site, differentiation of fossil reef taphofacies might be greatest in high energy reef settings. Interpretation of ancient reef sedimentary environments may be aided by analysis of taphonomic alteration. of reef corals.

Taphonomic Alteration of Reef Corals: Effects of Reef Environment and Coral Growth Form II: The Florida Keys

Abstract In a companion study to earlier work in the Indo-Pacific, taphonomic alteration in reef-coral death assemblages was assessed in four distinct reef habitats ranging from 2–30 m water depth in the Florida Keys reef tract. Physical and biological taphonomic attributes measured from coral specimens showed great variability with respect to reef environment. Physico-chemical degradation (abrasion and dissolution) was greatest in reef-crest and patch-reef environments. With the exception of encrusting foraminifera, coverage by epi- and endobionts was higher in deep-reef environments (20 m and 30 m). Variability in dissolution and abrasion is likely the result of the different energy regimes present in the reef habitats examined. Variability in biological attributes results from a combination of increased residence time of coral skeletons on substrates in deep-reef environments, higher overall coral skeletal densities of corals inhabiting deep reef environments, and increased nutrient availability in the deep reefs sampled. Clear gradients in the degree of taphonomic alteration of reef corals with reef habitat indicate the utility of corals as taphofacies indicators in ancient reef settings. In contrast to shallow-water reefs on the Great Barrier Reef, taphonomic alteration of corals in the Florida Keys was equitable across growth forms.

Is the fossil record of regular echinoids really so poor? A comparison of living and subfossil assemblages

Live (biocoenoses) and dead (taphocoenoses) populations of regular and irregular echinoids inhabiting shallow water environments of San Salvador and Leestocking Island, Bahamas (and elsewhere in the Caribbean) have been censused over the last five years to test Kiers (1977) hypothesis that the relatively poor fossil record of the regular echinoid is the result of taphonomic bias. In general, results reveal that distributions of living regular echinoids are not reflected by accumulations of their carcasses, while the reverse is true for irregular taxa: subfossil material is more often associated with living populations suggesting that irregulars may have relatively greater likelihood of preservation

Preservation of in situ reef framework in regions of low hurricane frequency: Pleistocene of Curaçao and Bonaire, southern Caribbean

Luxuriant fringing reefs along the southwestern shores of the Caribbean islands of Curacao and Bonaire (12°N), located outside the most frequent hurricane tracks, are rarely affected by major storms. Consequently, reef growth and long-term preservation are potentially optimal and distinct from reefs experiencing greater hurricane frequency. Hurricane Lenny (November 1999) took an unusual west-to-east track, bisecting the Caribbean Basin north of these islands, but generated heavy waves (3-6 m) that severely damaged reefs along the normally leeward shores. Massive coral colonies >100 years old were toppled, but even at the most severely damaged sites, 82–85% of colonies remained in growth position. Late Pleistocene (125 ka) elevated reefs in the Lower Terrace of Curacao record even higher proportions of corals in growth position (93%), possibly reflecting a low hurricane frequency during the Pleistocene highstand. In comparison, coeval Pleistocene reefs in regions that today experience a high hurricane frequency (Great Inagua Island and San Salvador, Bahamas) have lower proportions of corals preserved in growth position (79% and 38%, respectively). These results are consistent with the hypothesis that reefs in regions experiencing very low hurricane frequency, like the southern Caribbean, are more likely to be preserved with corals in primary growth position in comparison to regions with higher hurricane frequency.

Taphonomic bias and the evolutionary history of the family Cidaridae (Echinoderamata; Echinoidea)

-The class Echinoidea apparently originated during the Ordovician Period and diversified slowly through the Paleozoic Era. The clade then mushroomed in diversity beginning in Late Triassic time and continued expanding into the present. Although this evolutionary history is generally accepted, the taphonomic overprint affecting it has not been explored. To gain a more accurate perception of the evolutionary history of the group, I have compared the diversity history of the family Cidaridae (Echinodermata: Echinoidea) with the preservational style of fossil type species using literature-derived data. The Cidaridae apparently originated in Middle Triassic time and diversified slowly through the Neocomian (Early Cretaceous). Diversity was maintained through the remainder of the Cretaceous and Tertiary Periods, reflecting the diversity history of the subclass. Characterization of the preservational style of type fossil material for the family revealed the following breakdown of preservational states: 60% of species were described on the basis of disarticulated skeletal material, primarily spines; 20% based on intact coronas denuded of spines, apical system, Aristotles lantern and peristomial plates; 10% based on large coronal fragments; and 10% based on other skeletal elements. This distribution may represent the effect of a disarticulation threshold on the condition of echinoid carcasses before final burial and suggests that preservation of intact specimens may be very unlikely. For cidaroids, previous work has suggested that this threshold is likely to be reached after 7 days of decay. Comparison of the diversity history of the Cidaridae with the preservation data reveals that characteristic patterns of taphonomic overprint have affected the group since its origination in Middle Triassic time, and the nature of that overprint has changed over time: the early diversity history of the group is characterized by occurrences of fragmented fossil material, with spines predominant; further radiation of the group in mid-Jurassic time coincided with an increase in modes of preservation, ranging between exceptionally well-preserved material and disarticulated skeletal elements. Finally, type material is more rarely described from younger stratigraphic intervals (Miocene-Pleistocene) and consists predominantly of disarticulated skeletal elements and coronal fragments larger than an interambulacrum in size. Intact, denuded coronas are noticeably lacking. The number of type species of Cidaridae described in each stratigraphic interval has not been consistent during post-Paleozoic time. Middle Triassic, Malm (Upper Jurassic), Senonian (Upper Cretaceous) and Eocene series yielded significantly (a = .05) higher numbers of type specimens per million years, while the Lias (Lower Jurassic), Dogger (Mid-Jurassic), Lower Cretaceous and Paleocene yielded significantly (a = .05) lower numbers of type specimens per million years. This may be the result of a combination of taxonomic, sampling, and geographical biases. Benjamin J. Greenstein. Department of Geology, Smith College, Northampton, Massachusetts 01063 Accepted: June 6, 1991

Effect of Hurricane Hugo on molluscan skeletal distributions,Salt River Bay, St. Croix, U.S. Virgin Islands

Just prior to the passage of Hurricane Hugo over St. Croix, U.S. Virgin Islands, 35 molluscan skeletal samples were collected at 30 m intervals along a sampling transect in Salt River Bay, on the north-central coast. Three months after the hurricane, the transect was resampled to permit direct assessment of storm effects on skeletal distributions. Results indicate that spatial zonation of molluscan accumulations, associated with environmental transitions along the transect, was maintained in the wake of the hurricane. However, limited transport was diagnosed by comparing the compositions of prestorm and poststorm samples from the deepest, mud-rich subenvironment on the transect. In aggregate, the species richness of samples from the southern half of this zone increased from 16 to 40, and the abundance of species that were not among the characteristic molluscs of this subenvironment increased from 11% to 26%. These storm effects could probably not have been recognized, and attributed directly to Hugo, had there been no prestorm samples with which to compare directly the poststorm samples.

Comparison of recent coral life and death assemblages to pleistocene reef communities: Implications for rapid faunal replacement on recent reefs

Marine ecologists and paleoecologists are increasingly recognizing that the Pleistocene and Holocene fossil record of coral reefs is the exclusive database from which an assessment of the long-term responses of reef communities to environmental perturbations may be obtained. The apparent persistence of coral communities in the face of intense fluctuations in sea level and sea surface temperature during glacial and interglacial stages of Pleistocene time is in marked contrast to dramatic fluctuations in reef community structure documented by short-term monitoring studies. We compared the taxonomic structure of live and dead coral communities on a modern patch reef currently undergoing a community transition to late Pleistocene facies exposed in the Cockburn Town fossil coral reef. Multidimensional scaling revealed that specific taxa and colony growth forms characterize life, death, and fossil assemblages. The recent decline of thickets ofAcropora cervicornis is represented by their abundance in the death assemblage, whilePorites porites dominates the coral life assemblage. Although additional study of Pleistocene reefal facies is required, the greater similarity of the death assemblage to the fossil assemblage suggests that the present Caribbean- wide decline ofA. cervicornis is without a historical precedent.

Taphonomy of Crown-of-Thorns Starfish - Implications for Recognizing Ancient Population Outbreaks

A field experiment was conducted to determine whether in situ mass mortality of Acanthaster planci subsequent to a simulated outbreak would leave a recognizable signature in surficial reef sediments. Constituent particle analyses comparing sediments that received starfish carcasses to those that did not revealed that, after a four year interval, the mass mortality was reflected by elevated abundances of starfish ossicles in 1–2 mm and 2–4 mm size classes, but not in >4 mm and 0.5–1 mm size classes. Additional field study of starfish taphonomy revealed that the abundance of starfish ossicles in surficial sediments decreases through two orders of magnitude between two weeks and four years post-mortem, while tumbling experiments suggest that the size distribution of starfish ossicles is modified by physical processes: the <0.5 mm size classes increases at the expense of the >4 mm class. Taphonomic biasing increased the abundance of crown-of-thorms starfish (COTS) skeletal elements in the 0.5–1 mm size fraction, while the 1–2 mm size and 2–4 mm fractions produced the most reliable signature of starfish mass mortality based on element abundance. Our results demonstrate the importance of taphonomic processes in altering the original size frequency distribution of the COTS skeleton and their potential for biasing predictions of past population levels derived from constituent particle analyses of surficial reef sediments.