Coralline Algae & Ocean Acidification CONTAINING A CONTEXT FOR TEACHING, AND BACKGROUND INFORMATION RELATING TO ACHIEVEMENT STANDARD DEMONSTRATE UNDERSTANDING OF PROCESSES IN THE OCEAN SYSTEM CARBON CYCLE - CARBONATE CHEMISTRY

Coralline Algae Contain calcium carbonate in their cell walls Come in two distinct forms – geniculate and non-geniculate - Geniculate corallines have upright branches that consist of alternating calcified and non-calcified segments, forming turfs on substrates. - Non-geniculate corallines are completely calcified and form pink crusts over substrate surfaces, commonly known as ‘crustose’ coralline algae. Non-geniculate coralline algae – Auckland Islands. PHOTO CREDIT: Rebecca McLeod.

Coralline Algae Habitat Broad range of habitats - Tropics to pole - Intertidal zone to euphotic zone - Rocky shores, tropical reefs, seagrass meadows - Unattached to substrate, in a growth form known as a rhodolith or maerl (non-geniculate forms only) Rhodoliths - Lithothamnion crispatum (below), and Sporolithon durum, (above). PHOTO CREDIT: MPI – Rhodolith beds in Northern New Zealand.

Coralline Algae – Auckland Island Sampling The Auckland Islands (part of New Zealand’s Sub-Antarctic group) lie approximately 375km south of Stewart Island on the Campbell Plateau. Little is known about the diversity and taxonomy of coralline species around New Zealand’s Sub-Antarctic islands. In 2016 the Sir Peter Blake Trust Young Blake Expedition collected coralline algae samples at a range of representative habitats in the intertidal zone around the east coast inlets of the Auckland Islands. Island-Map-2 n.net/codes/Introductio n/into2.html

Coralline Algae – Genetic Analysis Auckland Island Samples The samples will be analysed at NIWA in Wellington. Genetic and anatomical techniques will be used to determine the taxonomy of the samples. In terms of genetic analysis, DNA will be extracted from the samples and then the segment of DNA that is needed for examination will be copied millions of times using PCR (polymerase chain reaction). One specific gene will be sequenced initially, as this is a good way of sorting the samples and checking them against the existing dataset of DNA sequences, to determine differences. Depending on the nucleotide differences between already recorded sequences and those of the Auckland Island samples, an indication will be given as to whether new species have been discovered. Brenton Twist pipetting coralline material for genetic analysis at NIWA in Wellington. PHOTO CREDIT: Wendy Nelson.

Coralline Algae – Why study it? It is important to have an understanding of what is present in the marine ecosystem of the Auckland Islands, because if the impacts of climate change on ecological communities is going to be seen, the Sub- Antarctic will be one of the first places to experience change. With baseline data collected, overtime, the rate and scale of change, and the effect that it is having can be determined. Coralline algae play an especially important role as an indicator of global climate change, as the calcium carbonate in their cell walls put them at risk of dissolution due to ocean acidification. Seaweed collection, Smith Harbour, Auckland Island. PHOTO CREDIT: Brendon O’Hagan.

Ocean Acidification – What is it? After remaining constant for millions of years, the pH of surface seawater has fallen from 8.2 to 8.1 in a few hundred years - a 30% increase in acidity/decrease in alkalinity. Reactions that occur in ocean acidification are equilibrium reactions - they will remain at equilibrium until a change occurs that throws out the balance. In the case of ocean acidification, the change that has occurred is the increase in atmospheric carbon dioxide which has subsequently increased the amount of carbon dioxide that is dissolved in the oceans. As carbon dioxide is more soluble in colder waters than warmer, this could result in greater impacts in the Southern Ocean which surround the Auckland Islands. Estimated change in sea water pH caused by human created CO2 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project (GLODAP) and the World Ocean Atlas.

Ocean Acidification – Carbonate Chemistry As carbon dioxide reacts with the seawater, carbonic acid is formed (H 2 CO 3 ). This disassociates into hydrogen ions (H + ) and bicarbonate ions (HCO 3 - ). The hydrogen ions produced from this reaction increase the acidity and lower the pH of the oceans. This is intensified by the fact that the bicarbonate ions also disassociate into more hydrogen ions (H + ) and carbonate ions (CO 3 2- ). Carbonate Chemistry – Ocean Acidification:

Ocean Acidification – Carbonate Chemistry Under normal circumstances carbonate ions help to resist changes in ocean acidity through what is known as the carbonate buffer system. If an acid is added to seawater, carbonate ions (CO 3 2- ) work to reduce the acidity by tying up excess hydrogen ions (H + ), producing bicarbonate ions. Carbonate buffer system -

Ocean Acidification – Carbonate Chemistry As ocean acidity is increasing, the concentration of available carbonate ions for organisms, such as coralline algae, to use for the secretion of calcium carbonate shells and skeletons is decreasing. This is because the carbonate ions are becoming tied up, and biologically unavailable as bicarbonate ions, leading to oceans being under-saturated in carbonate ions and organisms requiring greater energy expenditure for calcification to occur. Carbonate chemistry – biologically unavailable carbonate ions:

Ocean Acidification – Carbonate Chemistry Further to this, calcium carbonate (CaCO 3 ) which is insoluble in seawater, reacts with carbonic acid (H 2 CO 3 ) and dissolves. This results in the dissolution of calcium carbonate skeletons and shells of marine organisms. Pteropod shell when placed in sea water with pH and carbonate levels projected for the year

Ocean Acidification – Calcium Carbonate There are three different mineral forms of calcium carbonate (aragonite, calcite and the rare mineral vaterite) each of which have a different solubility. The structure of calcite means that calcium ions (Ca 2+ ) can be substituted for magnesium ions (Mg 2+ ), forming magnesium calcites, with varying magnesium ion concentrations. Calcium carbonate polymorphs calcite, aragonite and vaterite and the additives for their formation. Images by Andrea Niedermayr, TU Graz -

Ocean Acidification – Calcium Carbonate & Coralline Algae The three coralline algae orders have differing concentrations of magnesium in their cell walls. Those species with a high magnesium content (high Mg-calcite) are more soluble in seawater than aragonite and calcite. Coralline algae, particularly non-geniculate species, can also contain aragonite in their skeletons, predominantly in their attachment area. This form of calcium carbonate is less soluble than high-Mg calcite, but more soluble than pure calcite. Therefore coralline algae are more susceptible to changes in ocean acidity than organisms that have other forms of calcium carbonate in their shells and skeletons. Non-geniculate coralline algae in the intertidal zone, Auckland Island. PHOTO CREDIT: Rebecca McLeod.

Ocean Acidification – Possible Impacts As the consequences of global climate change begin to be seen in the oceans, the impacts of lowered calcification rates and higher dissolution rates in coralline algae will have possible impacts on their wider ecological community. Coralline algae have been shown to have an importance in the life history of other marine species. They are considered settlement inducers for marine invertebrates such as paua, corals and kina. Therefore a change in a coralline algal population due to ocean acidification may also invoke a change in populations of species which use the algae in their lifecycle. Five paua larvae after settlement on Phymatolithon repandum – coralline algae species. PHOTO CREDIT: Kate Neill /coralline-algae-and-paua-settlement

Ocean Acidification – Possible Impacts As carbon dioxide concentrations increase, and the energy needed for calcification increases, non-calcified fleshy algae will gain a competitive advantage over coralline algae, changing the composition of benthic communities. As all species are part of a dynamic ecological system, it is hard to predict the full range of consequences on coralline algae due to ocean acidification, but as sea water acidity increases it is highly likely that there will be an impact on calcifying species, which will in turn impact their ecological community. Non-geniculate coralline algae that developed on surfaces bathed in unaltered seawater from a reef (left) and those that developed in seawater with pH lowered to the level predicted for the year 2100 (right). This particular study saw “a 92-percent decrease in the area covered by crustose coralline algae in the tanks with lower pH compared with tanks at the pH level of today's ocean. Non-calcifying fleshy algae increased by 52 percent”

Ocean Acidification – Discussion/Research Questions 1.Why are the oceans absorbing more carbon dioxide currently than they did prior to the industrial revolution? 2.Why are the Sub-Antarctic Auckland Islands a good place to investigate the rate and scale of change in coralline algae species due to ocean acidification? 3.Why is the ocean considered a carbon sink? 4.What is meant by the terms ‘physical pump’ and ‘biological pump’? 5.Are coralline algae part of the physical pump or the biological pump? 6.How might altered calcification rates impact the biological pump? 7.Could ocean acidification benefit some species? If so, how? 8.What other marine organisms have calcium carbonate components and therefore face the possible impacts of ocean acidification? Geniculate and non-geniculate coralline algae species, Auckland Islands. PHOTO CREDIT: Rebecca McLeod

Ocean Acidification – Quiz Take a quiz with your class with questions based on this presentation - Geniculate and non-geniculate coralline algae species, Auckland Islands. PHOTO CREDIT: Rebecca McLeod