Cliff Ross

Climate change and ocean acidification effects on seagrasses and marine macroalgae

Although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO2 ], and lower carbonate [CO3 (2-) ] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO2 ]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (≥ 85%) with most species capable of utilizing HCO3 (-) ; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO2 -only users, lead us to conclude that photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated [CO2 ] similar to terrestrial C3 species. In the tropics, many species live close to their thermal limits and will have to up-regulate stress-response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO2 ] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO2 ] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO2 ] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H(+) and DIC. These fluxes control micro-environments that promote calcification over dissolution and may be more important than CaCO3 mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO2 ocean; therefore, it is critical to elucidate the research gaps identified in this review.

Chemical Defenses: From Compounds to Communities

Marine natural products play critical roles in the chemical defense of many marine organisms and in some cases can influence the community structure of entire ecosystems. Although many marine natural products have been studied for biomedical activity, yielding important information about their biochemical effects and mechanisms of action, much less is known about ecological functions. The way in which marine consumers perceive chemical defenses can influence their health and survival and determine whether some natural products persist through a food chain. This article focuses on selected marine natural products, including okadaic acid, brevetoxins, lyngbyatoxin A, caulerpenyne, bryostatins, and isocyano terpenes, and examines their biosynthesis (sometimes by symbiotic microorganisms), mechanisms of action, and biological and ecological activity. We selected these compounds because their impacts on marine organisms and communities are some of the best-studied among marine natural products. We discuss the effects of these compounds on consumer behavior and physiology, with an emphasis on neuroecology. In addition to mediating a variety of trophic interactions, these compounds may be responsible for community-scale ecological impacts of chemically defended organisms, such as shifts in benthic and pelagic community composition. Our examples include harmful algal blooms; the invasion of the Mediterranean by Caulerpa taxifolia; overgrowth of coral reefs by chemically rich macroalgae and cyanobacteria; and invertebrate chemical defenses, including the role of microbial symbionts in compound production.

Phylogenetic and Chemical Diversity of Three Chemotypes of Bloom-Forming Lyngbya Species (Cyanobacteria: Oscillatoriales) from Reefs of Southeastern Florida

ABSTRACT The cyanobacterial genus Lyngbya includes free-living, benthic, filamentous cyanobacteria that form periodic nuisance blooms in lagoons, reefs, and estuaries. Lyngbya spp. are prolific producers of biologically active compounds that deter grazers and help blooms persist in the marine environment. Here, our investigations reveal the presence of three distinct Lyngbya species on nearshore reefs in Broward County, FL, sampled in 2006 and 2007. With a combination of morphological measurements, molecular biology techniques, and natural products chemistry, we associated these three Lyngbya species with three distinct Lyngbya chemotypes. One species, identified as Lyngbya cf. confervoides via morphological measurements and 16S rRNA gene sequencing, produces a diverse array of bioactive peptides and depsipeptides. Our results indicate that the other two Lyngbya species produce either microcolins A and B or curacin D and dragonamides C and D. Results from screening for the biosynthetic capacity for curacin production among the three Lyngbya chemotypes in this study correlated that capacity with the presence of curacin D. Our work on these bloom-forming Lyngbya species emphasizes the significant phylogenetic and chemical diversity of the marine cyanobacteria on southern Florida reefs and identifies some of the genetic components of those differences.

Dragonamides C and D, linear lipopeptides from the marine cyanobacterium brown Lyngbya polychroa.

Two new linear lipopeptides, 1 and 2, and a known compound, curacin D, have been isolated from a marine cyanobacterium, brown Lyngbya polychroa, collected from Hollywood Beach, Fort Lauderdale, Florida. Their planar structures were elucidated by 1D and 2D NMR techniques, and absolute configurations were assigned using chiral HPLC. The new compounds were assigned the trivial names dragonamide C (1) and dragonamide D (2), as their peptide moiety is related to previously reported dragonamides A and B.

Macroalgal extracts induce bacterial assemblage shifts and sublethal tissue stress in Caribbean corals.

Benthic macroalgae can be abundant on present-day coral reefs, especially where rates of herbivory are low and/or dissolved nutrients are high. This study investigated the impact of macroalgal extracts on both coral-associated bacterial assemblages and sublethal stress response of corals. Crude extracts and live algal thalli from common Caribbean macroalgae were applied onto the surface of Montastraea faveolata and Porites astreoides corals on reefs in both Florida and Belize. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene amplicons was used to examine changes in the surface mucus layer (SML) bacteria in both coral species. Some of the extracts and live algae induced detectable shifts in coral-associated bacterial assemblages. However, one aqueous extract caused the bacterial assemblages to shift to an entirely new state (Lobophora variegata), whereas other organic extracts had little to no impact (e.g. Dictyota sp.). Macroalgal extracts more frequently induced sublethal stress responses in M. faveolata than in P. astreoides corals, suggesting that cellular integrity can be negatively impacted in selected corals when comparing co-occurring species. As modern reefs experience phase-shifts to a higher abundance of macroalgae with potent chemical defenses, these macroalgae are likely impacting the composition of microbial assemblages associated with corals and affecting overall reef health in unpredicted and unprecedented ways.

Effects of short-term hypersalinity exposure on the susceptibility to wasting disease in the subtropical seagrass Thalassia testudinum

Seagrass meadows are a vital component of coastal ecosystems and have experienced declines in abundance due to a series of environmental stressors including elevated salinity and incidence of disease. This study evaluated the impacts of short-term hypersalinity stress on the early stages of infection in Thalassia testudinum Banks ex König by assessing changes in cellular physiology and metabolism. Seagrass short shoots were exposed to ambient (30 psu) and elevated (45 psu) salinities for 7 days and subsequently infected for one week by the causative pathogen of wasting disease, Labyrinthula sp. The occurrence of wasting disease was significantly lower in the hypersalinity treatments. Additionally, while exposure to elevated salinity caused a reduction in chlorophyll a and b content, T. testudinums health, in terms of photochemical efficiency, was not significantly compromised by hypersalinity or infection. In contrast, plant respiratory demand was significantly enhanced as a function of infection. Elevated salinity caused T. testudinum to significantly increase its in vivo H(2)O(2) concentrations to levels that exceeded those which inhibited Labyrinthula growth in a liquid in vitro assay. The results suggest that while short-term exposure to hypersalinity alters selected cellular processes this does not necessarily lead to an immediate increase in wasting disease susceptibility.

Bioassay-guided isolation and identification of desacetylmicrocolin B from Lyngbya cf. polychroa.

Bioassay-guided fractionation of a non-polar extract of Lyngbya cf. polychroa resulted in the isolation of the cytotoxic desacetylmicrocolin B (1) as well as the known compounds microcolins A (2) and B (3). Compound 1 was found to inhibit the growth of HT-29 colorectal adenocarcinoma and IMR-32 neuroblastoma cells with half maximal inhibitory concentration (IC(50)) values of 14 nM for both cancer cell types. Microcolins A and B were found to have little activity against two strains of the marine fungus Dendryphiella salina with LD(50) values above 200 microg/mL. Compounds 1, 2, and 3 were obtained by reverse-phase chromatography and their structures were determined by NMR and MS. In this paper we report the isolation, identification, and biological activity of 1.

Nitric oxide and heat shock protein 90 co-regulate temperature-induced bleaching in the soft coral Eunicea fusca

Coral bleaching represents a complex physiological process that is affected not only by environmental conditions but by the dynamic internal cellular biology of symbiotic dinoflagellates (Symbiodinium spp.) and their cnidarian hosts. Recently, nitric oxide (NO) has emerged as a key molecule involved with the expulsion of Symbiodinium from host cnidarian cells. However, the site of production remains under debate, and the corresponding signaling pathways within and between host and endosymbiont remain elusive. In this study, using freshly isolated Symbiodinium from the soft coral Eunicea fusca, I demonstrate that thermally induced stress causes an upregulation in Symbiodinium heat shock protein 90 (Hsp90). In turn, Hsp90 shows a concomitant ability to enhance the activity of a constitutively expressed isoform of NO synthase. The resulting production of NO constitutes a signaling molecule capable of inducing Symbiodinium expulsion. Using nitric oxide synthase (NOS) and Hsp90 polyclonal antibodies, thermal stress-induced Hsp90 was shown to co-immunoprecipitate with a constitutive isoform of NOS. The specific blocking of Hsp90 activity, with the Hsp90 inhibitor geldanamycin, was capable of inhibiting NO production implicating the involvement of a coordinated regulatory system. These results have strong evolutionary implications for Hsp90–NOS chaperone complexes among biological kingdoms and provide evidence for a new functional role in symbiotic associations.

Isolation of Parvalbumin Isotypes by Preparative HPLC Techniques

Parvalbumins are highly stable Ca2+ binding proteins, present in large quantities in the sarcoplasmic reticulum in the white muscle of most lower vertebrates and fish. The properties of these proteins make them promising antigens for the use as a specific biomarker for fish species identification. Parvalbumin isotypes were isolated, on a preparative scale level, by use of size exclusion chromatography (SEC) and anion exchange HPLC. The utility of this technique, with regard to maximizing purified isotypes, is discussed.

Elevated Temperature and Allelopathy Impact Coral Recruitment

As climate change continues to alter seawater temperature and chemistry on a global scale, coral reefs show multiple signs of degradation. One natural process that could facilitate the recovery of reef ecosystems is coral recruitment, which can be influenced by the benthic organisms in a local habitat. We experimentally tested both a global stressor (increased seawater temperature) and a local stressor (exposure to microcolin A, a natural product from a common marine benthic cyanobacterium) to determine how these stressors impacted coral larval sublethal stress, survival and settlement. Larvae of Porites astreoides had the same survival and settlement as the controls after exposure to increased temperature alone, but elevated temperature did cause oxidative stress. When exposed to natural concentrations of microcolin A, larval survival and settlement were significantly reduced. When larvae were exposed to these two stressors sequentially there was no interactive effect; but when exposed to both stressors simultaneously, there was a synergistic reduction in larval survival and an increase in oxidative stress more than in either stressor treatment alone. Increased seawater temperatures made larvae more susceptible to a concurrent local stressor disrupting a key process of coral reef recovery and resilience. These results highlight the importance of understanding how interactive stressors of varying spatial scales can impact coral demographics.