Bleaching in foraminifera with algal symbionts: implications for reef monitoring and risk assessment

Abstrac

Bleaching in foraminifera with algal symbionts: implications for reef monitoring and risk asessment

Reef-dwelling larger foraminifers share key characteristics with reefbuilding corals: they are prolific producers of calcium carbonate, they are physiologically dependent upon algal endosymbionts, and representatives of both groups have suffered bleaching episodes in recent decades. Since 1991, bleaching has been observed in populations of Amphistegina in all subtropical oceans, with peak bleaching in 1992 and secondary peaks in 1998 and 2005. Amphistegina populations exhibiting chronic, intermediate-intensity bleaching characteristically show anomalously high incidences of shell breakage, shell deformities, evidence of predation, and microbial infestation. Asexual reproduction is profoundly affected; broods from partly bleached parents typically have fewer individuals, many of which are anomalous in shape and size. Key differences between bleaching in corals and Amphistegina are that corals typically bleach by expelling their symbionts, while Amphistegina bleach when damaged symbionts are digested, and that mass coral bleaching requires high light but correlates most consistently with elevated temperatures, while bleaching in Amphistegina is induced by light. Amphistegina are particularly sensitive to the shorter (300-490 nm) wavelengths of solar radiation, which have increased in intensity relative to longer visible wavelengths (>;490-700 nm) in clear reef waters over the past 30 years as a consequence of stratospheric ozone depletion. Abundances and visual assessments of Amphistegina populations can be used as a low-cost risk-assessment tool. These protists are sensitive to environmental conditions over days to weeks, and provide a method to quickly distinguish between water quality (local) and photo-oxidative (global) stresses. Risk assessments based on the combined use of in situ measurements and low-cost indicators can provide resource managers with essential information to decide when more costly chemical or molecular procedures are needed to determine local sources of stress

Why Do Bio-Carbonates Exist?

Calcium carbonate precipitation associated with biotic activity is first recorded in Archaean rocks. The oldest putative fossils related to hydrothermal vents have been dated at ~3.77 Ga (possibly 4.29 Ga). Stromatolites, the oldest dated at 3.70 Ga, have since occurred through Earth history, despite dramatic changes in physical and chemical conditions in aquatic environments. A key question is: what advantages do photosynthesizing aquatic prokaryotes and algae gain by precipitating carbonates? We propose the Phosphate Extraction Mechanism (PEM) to explain the benefits of biomineralization in warm, oligotrophic, alkaline, euphotic environments. Carbonate precipitation enhances access to otherwise limited carbon dioxide and phosphate in such environments. This mechanism also provides an explanation for prolific production of carbonates during times of elevated atmospheric carbon dioxide at intervals in the Phanerozoic.JIB acknowledges funding from the Basque Government to the Research Group IT1602-22. L.P., P.H. and G.M.-V. participation did not involved external funding aside from their academic institutions

Reefs at Risk: A Map-Based Indicator of Threats to the Worlds Coral Reefs

This report presents the first-ever detailed, map-based assessment of potential threats to coral reef ecosystems around the world. "Reefs at Risk" draws on 14 data sets (including maps of land cover, ports, settle-ments, and shipping lanes), information on 800 sites known to be degraded by people, and scientific expertise to model areas where reef degradation is predicted to occur, given existing human pressures on these areas. Results are an indicator of potential threat (risk), not a measure of actual condition. In some places, particularly where good management is practiced, reefs may be at risk but remain relatively healthy. In others, this indicator underestimates the degree to which reefs are threatened and degraded.Our results indicate that:Fifty-eight percent of the world's reefs are poten-tially threatened by human activity -- ranging from coastal development and destructive fishing practices to overexploitation of resources, marine pollution, and runoff from inland deforestation and farming.Coral reefs of Asia (Southeastern); the most species-rich on earth, are the most threatened of any region. More than 80 percent are at risk (undermedium and high potential threat), and over half are at high risk, primarily from coastal development and fishing-related pressures.Overexploitation and coastal development pose the greatest potential threat of the four risk categories considered in this study. Each, individually, affects a third of all reefs.The Pacific, which houses more reef area than any other region, is also the least threatened. About 60 percent of reefs here are at low risk.Outside of the Pacific, 70 percent of all reefs are at risk.At least 11 percent of the world's coral reefs contain high levels of reef fish biodiversity and are under high threat from human activities. These "hot spot" areas include almost all Philippine reefs, and coral communities off the coasts of Asia, the Comoros, and the Lesser Antilles in the Caribbean.Almost half a billion people -- 8 percent of the total global population -- live within 100 kilometers of a coral reef.Globally, more than 400 marine parks, sanctuaries, and reserves (marine protected areas) contain coral reefs. Most of these sites are very small -- more than 150 are under one square kilometer in size. At least 40 countries lack any marine protected areas for conserving their coral reef systems

Symbiont-Bearing Foraminifera: Harbingers of Global Change?

Rapidly increasing human populations are altering the Earth\u27s environments at unprecedented rates. Major categories of anthropogenic change include increasing input of anthropogenic nutrients to aquatic systems, increasing concentrations of greenhouse gases, and ozone depletion. Foraminifera have recorded countless global change events in the geologic record, ranging from the subtle to mass extinction events. Taxa suspected to have harbored algal endosymbionts, particularly the larger benthic foraminifera and planktonic foraminifera characteristic of warm, shallow surface waters of the pelagic realm, have typically responded dramatically to environmental changes. The purpose of this paper is to explore why these foraminifera should be particularly susceptible to ongoing anthropogenically-induced global change, to examine some of the evidence that they are responding, and to make some predictions as to how their assemblages may respond in the 21st century and beyond. Benthic foraminiferal assemblages are known to be sensitive to coastal nutrification; large, symbiont-bearing foraminifera lose dominance to small, fast-growing herbivorous and detritivorous species when nutrient supply increases in tropical reef-associated environments. Symbiont-bearing benthic foraminifera also appear to be sensitive to increasing intensities of biologically-damaging ultraviolet radiation, exhibiting damage to symbionts, calcification and reproduction, as well as increased susceptibility to infestation and predation. On the other hand, the larger rotaliid and globigerinid taxa, which secrete low-Mg calcite shells, may fare well as atmospheric CO2 concentrations increase, at least relative to the high-Mg calcite miliolid foraminifera and aragonitic corals, as falling pH of surface waters increases energetic expenditures for calcification

Evolution and Function of Coral Reef Ecosystems

For biologists, a coral reef is a marine community characterized by abundant corals. For geologists, a coral reef is a rigid skeletal structure in which stony corals are major framework constituents, with coralline and calcareous algae, mollusks, foraminifers, and other calcifying organisms contributing to the total reef volume. Zooxanthellate corals are highly specialized symbioses between coral hosts and dinoflagellate algae called zooxanthellae. As a result of this symbiosis, coral reefs thrive in clear, nutrientpoor, shallow waters of tropical oceanic islands and continental shelves. Rapidly increasing human populations are threatening coral reefs on multiple fronts. Nutrification, sedimentation, chemical pollution, and overfishing are significant and often interrelated local threats of global extent. Increasing concentrations of atmospheric CO2 threaten to destabilize climate, induce global warming, and alter ocean chemistry. Corals under temperature stress become more sensitive to sunlight, thus, the combination of ozone depletion and global warming is particularly damaging. The fossil record of biogenic reefs and carbonate-producing communities has much to contribute to our understanding of living species and to predictions of how communities may respond to anthropogenically induced environmental change. Reef communities are geologically both productive and fragile, producing thick limestone buildups under favorable conditions, but suffering the most from widespread extinctions under regional or global environmental perturbations

Diving in Graduate Education: The Past and the Future

Thirty years ago, to pursue a dissertation that required SCUBA diving required only basic SCUBA training, gear, and possibly a boat. Even buddies were often considered optional. Today, to do exactly the same type of field work requires a team of at least three divers who are trained not only in SCUBA but also in medic first aid, emergency oxygen administration, and tank handling. Scientists 30 years ago logged their samples and maybe their dives. Today, the dive team must file a dive plan, log each dive in detail, and submit post-dive, monthly, and annual diving-activity reports. The obvious advantages today are that scientific divers are better trained to cope with emergencies and they are accountable for their diving activity. Less obvious benefits are training in planning, accountability, teamwork, and often proposal-writing. The obvious disadvantages are monetary costs and time. The intangible cost to science is the virtual elimination of small, low-cost individual projects, particularly in relatively remote locations