Global warming and increased atmospheric co2 are causing the oceans to warm, decrease in pH and become hypercapnic. These stressors have deleterious impacts on marine inver - tebrates. Increasing temperature has a pervasive stimulatory effect on metabolism until lethal levels are reached, whereas hypercapnia has a narcotic effect. ocean acidification is a major threat to cal - cifying larvae because it decreases availability of the carbonate ions required for skeletogenesis and also exerts a direct pH effect on physiology. Marine invertebrate propagules live in a multistressor world and climate change stressors are adding to the mix. ocean pH, pco2 and caco3 covary and will change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. To address questions of future vulnerabilities, data on the thermo- and pH/ pco2 tolerance of fertilization and development in marine invertebrates are reviewed in the context of the change in the oceans that are forecast to occur over the next 100-200 years. Gametes and fertilization in many invertebrates exhibit a broad tolerance to warming and acidification beyond stressor values projected for 2100. Available data show that all development stages are highly sensitive to warming. larvae may be particularly sensitive to acidification/hypercapnia. Embryos that develop through the bottleneck of mortality due to warming may succumb as larvae to acidification. Early juveniles may be vulnerable to skeletal dissolution, although warming may diminish the negative impact of acidifi - cation on calcification. The effects of climate change stressors and their interaction differ among life history stages and species. Multistressor experiments show that if thermal thresholds are breached, embryos may not reach the calcifying stage. If the bottleneck for species persistence is embryonic thermotolerance, then the question of compromised calicification due to acidification may not be relevant. our limited knowledge of the interactive effects of climate change stressors is a major knowledge gap. Although climate change is deleterious for development in a broad range of marine invertebrates, some species and regional faunas will be more resilient than others. This has implica- tions for persistence, faunal shifts, species invasions and community function in a changing ocean.

Impact of ocean warming and ocean acidication on marine invertebrate life history stages: Vulnerabilities and potential for persistence in a changing ocean

Ever since Darwin’s early descriptions of coral reefs, scientists have debated how one of the world’s most productive and diverse ecosystems can thrive in the marine equivalent of a desert. It is an enigma how the flux of dissolved organic matter (DOM), the largest resource produced on reefs, is transferred to higher trophic levels. Here we show that sponges make DOM available to fauna by rapidly expelling filter cells as detritus that is subsequently consumed by reef fauna. This “sponge loop” was confirmed in aquarium and in situ food web experiments, using 13C- and 15N-enriched DOM. The DOM-sponge-fauna pathway explains why biological hot spots such as coral reefs persist in oligotrophic seas—the reef’s paradox—and has implications for reef ecosystem functioning and conservation strategies.

https://science.sciencemag.org/content/sci/342/6154/108.full.pdf

Surviving in a Marine Desert: The Sponge Loop Retains Resources Within Coral Reefs

Palaeoecology and evolution of marine hard substrate communities

Zooxanthellae, endosymbiotic algae of reef-building corals, substantially contribute to the high gross primary production of coral reefs1, but corals exude up to half of the carbon assimilated by their zooxanthellae as mucus2,3 Here we show that released coral mucus efficiently traps organic matter from the water column and rapidly carries energy and nutrients to the reef lagoon sediment, which acts as a biocatalytic mineralizing filter In the Great Barrier Reef, the dominant genus of hard corals, Acropora, exudes up to 48 litres of mucus per square metre of reef area per day Between 56% and 80% of this mucus dissolves in the reef water, which is filtered through the lagoon sands Here, coral mucus is degraded at a turnover rate of at least 7% per hour Detached undissolved mucus traps suspended particles, increasing its initial organic carbon and nitrogen content by three orders of magnitude within 2 h Tidal currents concentrate these mucus aggregates into the lagoon, where they rapidly settle Coral mucus provides light energy harvested by the zooxanthellae and trapped particles to the heterotrophic reef community, thereby establishing a recycling loop that supports benthic life, while reducing loss of energy and nutrients from the reef ecosystem

Coral mucus functions as an energy carrier and particle trap in the reef ecosystem

Despite the wide range of functional roles performed by marine sponges they are still poorly represented in many research, monitoring and conservation programmes. The aim of this review is to examine recent developments in our understanding of sponge functional roles in tropical, temperate and polar ecosystems. Functions have been categorised into three areas: (a) impacts on substrate (including bioerosion, reef creation, and substrate stabilisation, consolidation and regeneration); (b) bentho-pelagic coupling (including carbon cycling, silicon cycling, oxygen depletion and nitrogen cycling); and (c) associations with other organisms (facilitating primary production, secondary production, provision of microhabitat, enhanced predation protection, survival success, range expansions and camouflage though association with sponges, sponges as a settlement substrate, disrupting near-boundary and reef level flow regimes, sponges as agents of biological disturbance, sponges as releasers of chemicals and sponges as tools for other organisms). The importance of sponges on substrate, sponge bentho-pelagic coupling, and sponge interactions and associations is described. Although the scientific evidence strongly supports the significance and widespread nature of these functional roles sponges still remain underappreciated in marine systems.

The functional roles of marine sponges

Framework cavities are the largest but least explored coral reef habitat1. Previous dive studies of caverns, spaces below plate corals, rubble and artificial cavities1,2,3 suggest that cavity-dwelling (coelobite) filter-feeders are important in the trophodynamics of reefs2,4,5. Quantitative community data are lacking, however, as the bulk of the narrow crevices interlacing the reef framework are inaccessible to conventional analysis methods6. Here we have developed endoscopic techniques to explore Red Sea framework crevices up to 4 m into the carbonate rock, revealing a large internal surface (2.5–7.4 m2 per projected m2 reef) dominated by encrusting filter-feeders. Sponges alone provided up to 60% of coelobite cover, outweighing epi-reefal filter-feeder biomass by two orders of magnitude. Coelobite community filtration removed more than 60% of the phytoplankton in the course of its less than 5-minute passage through the crevices, corresponding to an uptake of roughly 0.9 g carbon m-2 d-1. Mineralization of the largely allochthonous organic material is a principal source of nutrients supporting coral and algal growth. The supply of new material by coelobites may provide a key to understanding the ‘coral reef paradox’—a rich ecosystem thriving in nutrient-poor water.

Endoscopic exploration of Red Sea coral reefs reveals dense populations of cavity-dwelling sponges

Inorganic nutrients and chlorophyll a concentrations were measured bi-weekly in a transect across a coral reef in the Gulf of Aqaba over a period of 1 yr. The nutrient and chlorophyll concentrations were compared to those in adjacent offshore waters (400 m depth). In reef and off- shore waters, nutrient (ammonium, nitrite, nitrate, phosphate and silicate) and chlorophyll a data showed seasonal changes, with high concentrations in winter and low concentrations in summer. However, throughout the summer, nutrient concentrations in the coral reef waters significantly exceeded those in the offshore waters, while this difference was less pronounced in winter. This dif- ference was caused by nutrient release from regenerative spaces in the reef framework and coral sand. In the reef framework water (i.e. cavity water), nutrient concentrations were 1.2- to 2.3-fold higher than those in the surrounding waters, corresponding to fluxes of 14.5 mmol m -2 d -1 for ammo- nium, 7.7 mmol m -2 d -1 for nitrate, 0.9 mmol m -2 d -1 for nitrite, and 1.3 mmol m -2 d -1 for phosphate. In the less permeable reef sediments, nutrient concentrations exceeded those of the free-stream waters by factors of 15 to 80. Here, the calculated diffusive fluxes were 0.06 mmol m -2 d -1 for ammonium, 0.03 mmol m -2 d -1 for nitrate, 0.01 mmol m -2 d -1 for nitrite, 0.01 mmol m -2 d -1 for phosphate, and 0.07 mmol m -2 d -1 for silicate. Our results highlight the importance of the reef framework and coral sand for the trapping and mineralization of particulate organic matter and the regeneration of nutrients in oligotrophic coral reef waters.

/pdf/effect-of-reef-framework-and-bottom-sediment-on-nutrient-366nds0p7z.pdf

Effect of reef framework and bottom sediment on nutrient enrichment in a coral reef of the Gulf of Aqaba, Red Sea

Seawater samples were collected weekly over fourteen months at 25 m intervals between the surface and 200 m from the offshore waters of the Gulf of Aqaba, Red Sea. Water temperature and dissolved oxygen concentration and percent saturation were measured in situ. Within two hours of sampling, samples were analysed for chlorophyll a , ammonia, nitrate, nitrite, phosphate and silicate. The temperature field depicted a well defined seasonal pattern of winter mixing from December to April and summer stratification from May to November. All other analysed parameters were intimately related to this pattern. Dissolved oxygen showed a maximum and homogeneous distribution in winter and a minimum in summer. Chlorophyll a showed a seasonal pattern close to that of dissolved oxygen, but with a distinct summer peak between 50 and 75 m. Ammonia was absent from the entire water column during summer and relatively abundant and homogeneously distributed in winter. Nitrite had a seasonal pattern similar to that of chlorophy...

Dissolved Oxygen, Chlorophyll a and Nutrients: Seasonal Cycles in Waters of the Gulf of Aquaba, Red Sea

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.agro-article-ce4d2e56-73ec-452a-8f78-b6fbc3c8be15/c/461fenne.pdf

Circulation and winter deep-water formation in the northern Red Sea*

In order to investigate the influence of sediment physical and chemical characteristics on the degradation of deposited organic matter, decomposition in three sediments from the Gulf of Aqaba (Red Sea) that differ in permeability and mineral composition were compared. Freeze-dried Spirulina was added to coarse carbonate and silicate sands from a shallow nearshore region and silt-clay sediment from the deeper center region of the Gulf incubated in laboratory chambers. The stirring in the chambers caused higher solute exchange in the coarse permeable sands relative to the fine less permeable silt due to the generation of advective fluid exchange between the sediment and overlying water. This enhanced exchange increased the decomposition rates of organic matter in the incubated sands. The decomposition rates of total organic carbon in the permeable carbonate (3.0 mg C m −2  d −1 ) and silicate sands (2.0 mg C m −2  d −1 ) exceeded that in the fine-grained sediment (1.4 mg C m −2  d −1 ). Oxygen consumption in the coarse sands was 3-fold higher than in the silt-clay sediment, with highest rates in the carbonate sand. In carbonate and silicate sands of the same grain size, the carbonate sediment was more permeable than the silicate, resulting in 1.4-fold higher fluid exchange rates and 1.4-fold larger sedimentary organic matter mineralization rates. An in situ experiment comparing trapping efficiencies in carbonate and silicate sands showed that the higher fluid exchange rate in the carbonate sand results in larger filtration rates and a faster accumulation of particulate organic matter from the boundary layer. These experiments demonstrate that with respect to sedimentary mineralization rates, higher transport rates in permeable coarse sediments can outweigh the effect of a higher specific surface area in fine-grained silt sediments. In permeable sands, however, the higher specific surface area and fluid exchange in biogenic carbonate sands result in higher mineralization rates than in silicate sands of the same grain size.

Mohammad I. Badran

Papers

Endoscopic exploration of Red Sea coral reefs reveals dense populations of cavity-dwelling sponges

Effect of reef framework and bottom sediment on nutrient enrichment in a coral reef of the Gulf of Aqaba, Red Sea

Dissolved Oxygen, Chlorophyll a and Nutrients: Seasonal Cycles in Waters of the Gulf of Aquaba, Red Sea

Circulation and winter deep-water formation in the northern Red Sea*

Influence of sediment permeability and mineral composition on organic matter degradation in three sediments from the Gulf of Aqaba, Red Sea