Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. ...Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012-2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maximum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium.
Mollusc shells of several species were deployed on racks and on the seafloor for up to two years on eutrophic and mesotrophic reefs in the Java Sea, a modern epeiric sea. Taphonomic indicators of ...shell preservation decreased during the study, but some ligament, periostracum, and shell color persisted throughout. Shell fragmentation was negligible except for species with easily chipped margins; weight loss was less than 5% for sturdy shells and up to 15% for shells with chipped margins. Shells deployed in mesh bags on the sediment surface had low encrustation and bioerosion, probably because of partial or complete burial. Areal encrustation on shells in bags was greater at the mesotrophic site than the eutrophic site, but animal encrustation and biovolume of encrusters was greater at the eutrophic site. Shells elevated on racks were encrusted rapidly at all sites; animal encrustation rates were correlated positively with productivity, and biovolume of encrusters was greater on nearshore eutrophic reefs than on offshore mesotrophic reefs. Bioerosion rates were variable but also tended to be higher at the more productive site. Natural shells also exhibited a positive, though less strong correlation with productivity suggesting that encrustation intensity and shell bioerosion may serve as relative indicators of productivity in the fossil record.
Shell-encrusting assemblages have uniquely high ecological fidelity among paleocommunities because adjacent epibionts coexisted in ecological time, and the abundances and spatial relationships of the ...various members are accurately preserved. This study presents a quantitative reconstruction of communities on brachiopod shells (Composita and alate spirifers) from the Carboniferous of North America. Thirty-one epibiont communities, comprised of a total of 1180 encrusted brachiopods, are analyzed in terms of epibiont abundance (e.g., percent areal cover), ecological diversity (e.g., Shannon-Wiener Index), and the role of larval recruitment and spatial competition in structuring the communities. Mississippian epibiont communities contain from seven to 14 encrusting taxa that occupy up to 25 percent of host shell surfaces. These communities are spatially dominated by trepostome bryozoans, but also include common lower Paleozoic epibionts, such as encrusting ctenostome bryozoans, hederellids, cornulitids, and edrioasteroids. Pennsylvanian epibiont communities contain between eight and 16 epizoan taxa that occupy up to 34 percent of shell surfaces. They are dominated by fistuliporoid or trepostome bryozoans and increasing proportions of erect bryozoans (e.g., fenestellids), encrusting foraminiferans, and articulate brachiopods. Carboniferous epibionts, like their modern counterparts, exist in loosely organized ecological communities that vary widely in abundance and composition in space and geological time. There is little evidence for tight controls on community structure. Much of the variation is attributed to vagaries in the magnitude and selective nature of larval recruitment. Evidence of competition between community members is rare, except where a high percentage of the shell surface is covered. In these cases, sheetlike bryozoans are usually most abundant. Solitary epibionts are surprisingly successful competitors in one-on-one encounters, but apparently lose areal cover to longer-lived colonial encrusters during ecological succession.
Island outlook Hubbard, Dennis; Gischler, Eberhard; Davies, Peter ...
Science (American Association for the Advancement of Science),
09/2014, Letnik:
345, Številka:
6203
Journal Article
The corals
Acropora palmata
and
A. cervicornis
are important Caribbean reef-builders that have faced significant mortality in recent decades. While many studies have focused on the recent demise of ...these species, data from areas where
Acropora
spp. have continued to thrive are limited. Understanding the genetic diversity, recruitment, and temporal continuity of healthy populations of these threatened
Acropora
spp. and the hybrid they form (“
Acropora prolifera
”) may provide insights into the demographic processes governing them. We studied three reef sites with abundant
A. cervicornis
,
A. palmata
, and hybrid
Acropora
populations offshore of Ambergris Caye, Belize at Coral Gardens, Manatee Channel, and Rocky Point. Samples were collected from all three
Acropora
taxa. We used microsatellite markers to determine: (1) genotypic diversity; (2) dominant reproductive mode supporting local recruitment; (3) minimum and maximum genet age estimates for all three acroporids; and (4) the history of hybrid colonization at these sites. We found that
Acropora
populations were highly clonal with local recruitment primarily occurring through asexual fragmentation. We also estimated the ages of 10
Acropora
genets using recent methodology based on somatic mutation rates from genetic data. Results indicate minimum ages of 62–409 yr for
A. cervicornis,
187–561 yr for
A. palmata
, and 156–281 yr for the
Acropora
hybrids at these sites. Our data indicate that existing
A. cervicornis, A. palmata,
and
Acropora
hybrid genets persisted during the 1980s Caribbean-wide
Acropora
spp. collapse, suggesting that these sites have been a refuge for Caribbean
Acropora
corals. Additionally, our data suggest that formation of extant hybrid
Acropora
genets pre-dates the widespread collapse of the parent taxa.
Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. ...Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012–2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maximum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium.
The taphonomic loss of soft-bodied organisms and ubiquitous time averaging make reconstruction of ecological interactions in fossil communities difficult. This study employs an actualistic analysis ...of epibiont communities on scallops to infer preservation potential and life-span overlap in ancient epibiont associations. Spirorbid, serpulid, and sabellid annelids, sponges, barnacles, and cheilostome and cyclostome bryozoans form dense covers on the scallops Chlamys hastata and C. rubida in moderately deep waters around San Juan Island, Washington. Serpulids, spirorbids, cyclostomes, and cheilostomes dominate on lower surfaces of living scallops and on the interiors of dead shells. In some instances, up to 100% of the areal epibiont cover on these surfaces would likely be preserved in the fossil record. In contrast, live specimens of Chlamys were covered on their upper surfaces (left valves) by encrusting sponge, barnacles and the agglutinated tubes of sabellid polychaetes. Assemblages from these surfaces had correspondingly low preservation potential. Sponge disappeared rapidly after death of the host and valves previously encrusted by sponge were particularly clean and unfouled. On most Chlamys shell surfaces, one third to one half of the epibiont cover on a shell at a given time is composed of skeletons of dead organisms. Observed overgrowths resulted primarily from organisms encrusting dead organisms and organisms growing over mineralized portions of other live epibionts. This study, unlike some paleoecological studies, found few unambiguous examples of competitive interactions.
Concavo-convex brachiopods are generally assumed to have lived with their convex valves against the sediment. This orientation is based primarily on the a priori assumption that the upturned ...commissure would prevent fouling of the brachiopods' mantle cavity. Here, I present epibiontic and taphonomic evidence from orthids and nonproductid strophomenids that concavo-convex brachiopods lived in the reverse life orientation, with the convex valve on top. Ten testable epibiontic and taphonomic criteria are proposed to establish the uppermost valve during encrustation and whether epibionts encrusted primarily live or dead hosts. The criteria are evaluated for 11 collections of Ordovician and Devonian nonproductid concavo-convex brachiopods that contain a total of over 500 brachiopods and 4000 epibionts. In all cases, the results support a convex-up orientation and the encrustation of live hosts. Five criteria concern epibiont growth patterns and show that (1) epibionts predominate on convex valves, (2) epibionts are not restricted to shell margins, (3) distinct exposed and cryptic faunas, as predicted theoretically and described in previous studies, exist on convex and concave valves respectively, (4) epibiont colonies were often truncated by the commissures and hinges of live hosts, and (5) growth patterns of some epibionts indicate live hosts. Five taphonomic criteria show that (1) concavo-convex shells have greater epibiont cover than other morphologies, (2) internal surfaces of disarticulated specimens are rarely encrusted, (3) interiors of articulated specimens are rarely mud-filled, (4) standard taphofacies indicators suggest little postmortem exposure, and (5) sedimentological reconstructions suggest rapid burial. Convex-up brachiopods suggest that the Paleozoic mud bottoms they lived on were probably firmer than usually assumed and that a more complex functional interpretation of concavo-convexity is required. Hydrodynamic stability was important to many concavo-convex, plano-convex, and unequally bi-convex brachiopods. Brachiopods with these morphologies probably lived in the more stable orientation on their concave or flat valve. Productid brachiopods, although also concavo-convex, lived convex valve down and are ecologically distinct from earlier concavo-convex taxa. Productids were anchored, semi-infaunally, by spines and were more similar to Mesozoic oysters in orientation and shell function.
A new enigmatic Lower Cambrian fossil, Spygoria zappania, is described From the Nevadella zone (Botoman) of Lander County, central Nevada. In gross morphology, Spygoria fossils consist of stacks of ...small (5–10 mm in diameter) irregular calcified cups that are preserved in vertical, concave-up life orientation. Stacks are linked laterally into large monospecific bioherms which flourished in a shallow turbulent marine environment. The Spygoria organism is interpreted as a metazoan which presumably inhabited the uppermost cup in each stack and periodically secreted new cups as it grew upward. Absence of holdfast structures suggest that the organism was held in place by sticky mud until opportunistically cementing to adjacent individuals. The affinity of Spygoria remains problematical, though we suggest that its stacked structure somewhat resembles the cone-in-cone structure of Cloudina, which formed similar dense thickets in shallow turbulent carbonate environments during the terminal Proterozoic.
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