Shifting Baselines in Coral Bleaching Resilience

Tropical corals live at or near their upper thermal limits and are sensitive to periods of elevated sea surface temperatures. As our global climate rapidly warms, the frequency, magnitude, and duration of coral bleaching events is increasing, resulting in widespread losses in coral cover and increased mortality. Yet, corals native to variable thermal reef environments often resist bleaching temperatures, and these habitats have also promoted increased thermal tolerance. On Ofu Island, American Samoa, branching coral species from a highly variable (HV) pool have higher bleaching resistance than corals from a nearby moderately variable (MV) pool. In addition, MV corals were able to increase heat tolerance when moved into the HV pool, providing promising evidence for the persistence of some reefs under projected climate change. In this study, we investigated the breadth of thermal tolerance in massive coral species in the backreef of Ofu Island. We transplanted populations of two massive corals, Porites lobata and Goniastrea retiformis, from three contrasting backreefs separated by months, transplanted and native coral samples were weighed and then exposed to a controlled acute thermal stress assay. Physiological bleaching responses – chlorophyll and photosynthetic efficiency – were quantified to elucidate heat stress resistance. For both species, coral transplants in the HV pool had reduced growth, decreased photosynthetic efficiency, and greater chlorophyll loss following acute heat stress. Variation in growth and thermal tolerance was instead driven by native backreef, not acclimatization or genomic differences. More importantly, the thermal regime of the HV pool surpassed regional records and the magnitude of variability increased, potentially exceeding local stress thresholds of massive coral species. This study strongly contrasts previous research, and could be the first demonstration of a shifting baseline from increased to decreased resilience for corals residing in high-frequency variable environments.https://digitalcommons.odu.edu/sciences_achievement/1012/thumbnail.jp

The Transfer Treadmill: Forging An Institutional Identity in a Multicampus System

An examination of Wright College, a community college in Chicago, reveals that it has no particular magic formula for transfer success. Wright \u27s strong transfer programs should be recognized as an outgrowth of the college\u27s unique development within a 7-college district. Faculty and administrative commitment to the centrality of the transfer function, combined with student needs and preferences, allows for a continual reinforcement of the primacy of transfer in Wright \u27s institutional identity. Wright \u27s historically-driven image of itself as a "junior college, " and it reputation as such in the surrounding communities, have persisted over time and guided the college\u27s priorities and decisionmaking

Adaptive Divergence, Neutral Panmixia, and Algal Symbiont Population Structure in the Temperate Coral \u3ci\u3eAstrangia poculata\u3c/i\u3e Along the Mid-Atlantic United States

Astrangia poculata is a temperate scleractinian coral that exists in facultative symbiosis with the dinoflagellate alga Breviolum psygmophilum across a range spanning the Gulf of Mexico to Cape Cod, Massachusetts. Our previous work on metabolic thermal performance of Virginia (VA) and Rhode Island (RI) populations of A. poculata revealed physiological signatures of cold (RI) and warm (VA) adaptation of these populations to their respective local thermal environments. Here, we used whole-transcriptome sequencing (mRNA-Seq) to evaluate genetic differences and identify potential loci involved in the adaptive signature of VA and RI populations. Sequencing data from 40 A. poculata individuals, including 10 colonies from each population and symbiotic state (VA-white, VA-brown, RI-white, and RI-brown), yielded a total of 1,808 host-associated and 59 algal symbiont-associated single nucleotide polymorphisms (SNPs) post filtration. Fst outlier analysis identified 66 putative high outlier SNPs in the coral host and 4 in the algal symbiont. Differentiation of VA and RI populations in the coral host was driven by putatively adaptive loci, not neutral divergence (Fst = 0.16, p = 0.001 and Fst = 0.002, p = 0.269 for outlier and neutral SNPs respectively). In contrast, we found evidence of neutral population differentiation in B. psygmophilum (Fst = 0.093, p = 0.001). Several putatively adaptive host loci occur on genes previously associated with the coral stress response. In the symbiont, three of four putatively adaptive loci are associated with photosystem proteins. The opposing pattern of neutral differentiation in B. psygmophilum, but not the A. poculata host, reflects the contrasting dynamics of coral host and algal symbiont population connectivity, dispersal, and gene by environment interactions

High salinity tolerance of the Red Sea coral Fungia granulosa under desalination concentrate discharge conditions: an in situ photophysiology experiment.

Seawater reverse osmosis desalination concentrate may have chronic and/or acute impacts on the marine ecosystems in the near-field area of the discharge. Environmental impact of the desalination plant discharge is supposedly site- and volumetric- specific, and also depends on the salinity tolerance of the organisms inhabiting the water column in and around a discharge environment. Scientific studies that aim to understand possible impacts of elevated salinity levels are important to assess detrimental effects to organisms, especially for species with no mechanism of osmoregulation, e.g., presumably corals. Previous studies on corals indicate sensitivity toward hypo- and hyper-saline environments with small changes in salinity already affecting coral physiology. In order to evaluate sensitivity of Red Sea corals to increased salinity levels, we conducted a long-term (29 days) in situ salinity tolerance transect study at an offshore seawater reverse osmosis (SWRO) discharge on the coral Fungia granulosa. While we measured a pronounced increase in salinity and temperature at the direct outlet of the discharge structure, effects were indistinguishable from the surrounding environment at a distance of 5 m. Interestingly, corals were not affected by varying salinity levels as indicated by measurements of the photosynthetic efficiency. Similarly, cultured coral symbionts of the genus Symbiodinium displayed remarkable tolerance levels in regard to hypo- and hypersaline treatments. Our data suggest that increased salinity and temperature levels from discharge outlets wear off quickly in the surrounding environment. Furthermore, F. granulosa seem to tolerate levels of salinity that are distinctively higher than reported for other corals previously. It remains to be determined whether Red Sea corals in general display increased salinity tolerance, and whether this is related to prevailing levels of high(er) salinity in the Red Sea in comparison to other oceans.Research in this study was supported by King Abdullah University of Science and Technology (KAUST)

Adaptive Signatures in Thermal Performance of the Temperate Coral Astrangia poculata

Variation in environmental characteristics and divergent selection pressures can drive adaptive differentiation across a species\u27 range. Astrangia poculata is a temperate scleractinian coral that provides unique opportunities to understand the roles of phenotypic plasticity and evolutionary adaptation in coral physiological tolerance limits. A. poculata inhabits hard bottom ecosystems from the northwestern Atlantic to the Gulf of Mexico and withstands an annual temperature range up to 20° C. Additionally, A. poculata is facultatively symbiotic and co-occurs in both symbiotic ( brown ) and aposymbiotic ( white ) states. Here, brown and white A. poculata were collected from Virginia (VA) and Rhode Island (RI), USA and exposed to heat (18-32° C) and cold (18-6° C) temperatures during which respiration (R) of the coral host along with photosynthesis (P) and photochemical efficiency (Fv /Fm) of Breviolum psygmophilum photosymbionts were measured. Thermal performance curves (TPCs) of respiration revealed a pattern of countergradient variation with RI corals exhibiting higher respiration rates overall, and specifically at 6, 15, 18, 22, and 26°C. Additionally, thermal optimum (Topt) analyses show a 3.8° C (brown) and 6.9° C (white) higher Topt in the VA population, corresponding to the warmer in situ thermal environment in VA. In contrast to respiration, no origin effect was detected in photosynthesis rates or Fv/Fm, suggesting a possible host-only signature of adaptation. This study is the first to consider A. poculata\u27s response to both heat and cold stress across symbiotic states and geography and provides insight into the potential evolutionary mechanisms behind the success of this species along the East Coast of the US

Complex Dynamics of Coral Gene Expression Responses to Low pH Across Species

Coral capacity to tolerate low pH affects coral community composition and, ultimately, reef ecosystem function. Low pH submarine discharges (‘Ojo’; Yucatán, México) represent a natural laboratory to study plasticity and acclimatization to low pH in relation to ocean acidification. A previous \u3e2‐year coral transplant experiment to ambient and low pH common garden sites revealed differential survivorship across species and sites, providing a framework to compare mechanistic responses to differential pH exposures. Here, we examined gene expression responses of transplants of three species of reef‐building corals (Porites astreoides, Porites porites and Siderastrea siderea) and their algal endosymbiont communities (Symbiodiniaceae) originating from low pH (Ojo) and ambient pH native origins (Lagoon or Reef). Transplant pH environment had the greatest effect on gene expression of Porites astreoides hosts and symbionts and P. porites hosts. Host P. astreoides Ojo natives transplanted to ambient pH showed a similar gene expression profile to Lagoon natives remaining in ambient pH, providing evidence of plasticity in response to ambient pH conditions. Although origin had a larger effect on host S. siderea gene expression due to differences in symbiont genera within Reef and Lagoon/Ojo natives, subtle effects of low pH on all origins demonstrated acclimatization potential. All corals responded to low pH by differentially expressing genes related to pH regulation, ion transport, calcification, cell adhesion and stress/immune response. This study demonstrates that the magnitude of coral gene expression responses to pH varies considerably among populations, species and holobionts, which could differentially affect acclimatization to and impacts of ocean acidification

Lineage-Specific Transcriptional Profiles of Symbiodinium spp. Unaltered by Heat Stress in a Coral Host

Dinoflagellates of the genus Symbiodinium form an endosymbiosis with reef building corals, in which photosynthetically derived nutrients comprise the majority of the coral energy budget. An extraordinary amount of functional and genetic diversity is contained within the coral-associated Symbiodinium, with some phylotypes (i.e., genotypic groupings), conferring enhanced stress tolerance to host corals. Recent advances in DNA sequencing technologies have enabled transcriptome-wide profiling of the stress response of the cnidarian coral host; however, a comprehensive understanding of the molecular response to stress of coral-associated Symbiodinium, as well as differences among physiologically susceptible and tolerant types, remains largely unexplored. Here, we examine the transcriptome-wide response to heat stress via RNA-Seq of two types of Symbiodinium, the putatively thermotolerant type D2 and the more susceptible type C3K, resident within the same coral host species, Acropora hyacinthus. Contrary to previous findings with coral hosts, we find no detectable change in gene expression across the dinoflagellate transcriptome after 3 days of elevated thermal exposure, despite physical evidence of symbiosis breakdown. However, hundreds of genes identified as orthologs between the C and D types exhibited significant expression differences within treatments (i.e., attributable solely to type, not heat exposure). These include many genes related to known thermotolerance mechanisms including heat shock proteins and chloroplast membrane components. Additionally, both the between-treatment similarities and between-type differences remained pervasive after 12-18 months of common garden acclimation and in mixed Symbiodinium assemblages within the same coral host colony

High-Frequency Temperature Variability Mirrors Fixed Differences in Thermal Limits of the Massive Coral \u3ci\u3ePorites lobata\u3c/i\u3e

Spatial heterogeneity in environmental characteristics can drive adaptive differentiation when contrasting environments exert divergent selection pressures. This environmental and genetic heterogeneity can substantially influence population and community resilience to disturbance events. Here, we investigated corals from the highly variable back-reef habitats of Ofu Island in American Samoa that thrive in thermal conditions known to elicit widespread bleaching and mortality elsewhere. To investigate the relative importance of acclimation versus site of origin in shaping previously observed differences in coral tolerance limits at Ofu Island, specimens of the common Indo-Pacific coral Porites lobata from locations with differing levels of thermal variability were acclimated to low and high thermal variation in controlled common garden aquaria. Overall, there were minimal effects of the acclimation exposure. Corals native to the site with the highest level of daily variability grew fastest, regardless of acclimation treatment. When exposed to lethal thermal stress, corals native to both variable sites contained elevated levels of heat shock proteins and maintained photosynthetic performance for 1–2 days longer than corals from the stable environment. Despite being separated by \u3c5 \u3ekm, there was significant genetic differentiation among coral colonies (FST=0.206, PCladocopium sp. (ITS type C15). Our study demonstrates consistent signatures of adaptation in growth and stress resistance in corals from naturally thermally variable habitats, suggesting that differences in the amount of thermal variability may be an important contributor to adaptive differentiation in reef-building corals