Lophelia pertusa and Ocean Acidification

Part I What do you know about ocean acidification? 1.What is ocean acidification and what is causing it? 2.How might ocean acidification affect marine animals like the deep-sea coral, Lophelia?

Before exploring the effects of acidification on Lophelia, let’s see what adding CO 2 to water does to its pH.

What might acidification do down deep? To understand how ocean acidification may affect deep-sea corals, we first need to review Lophelia’s basic biological requirements.

What does Lophelia need to survive? 1.HARD SUBSTRATE for larvae to settle 2.FOOD to fuel growth & reproduction 3.COLD TEMPERATURE 4.MINERALS to build a hard skeleton

HARD SUBSTRATE for larvae to settle Dead corals Oil rigsShipwrecks Carbonate rock Although much of the seafloor is covered in deep, soft sediment, there are different types of hard substrate in the deep-sea that Lophelia can settle on…

FOOD to fuel growth & reproduction Think … currents! Unlike shallow-water corals with zooxanthellae (i.e., photosynthetic algae) that manufacture food, Lophelia live in the deep sea without light, AND without zooxanthellae. So what does this deep-sea coral eat? Lophelia feed on small animals and particles of food captured in its stinging tentacles (i.e., nematocysts). These food particles are carried by currents flowing past the coral. More on this later.

COLD TEMPERATURES found in deep water As depth increases, water temperature decreases Lophelia, a cold-water coral, is adapted to live in temperatures between 4-12°C ( °F) Depending on the local thermocline, Lophelia is found in deep water, as 2500 meters.

GULF OF MEXICO Where do we find Lophelia? Lophelia is most common throughout the Atlantic at meters (about feet) deep In the Gulf of Mexico, Lophelia is typically found between meters

MINERALS to build a hard skeleton Hard skeletons provide… The ability to build a hard skeleton is critical to the survival of Lophelia, as well as to many other organisms that depend on Lophelia. A HOME for the soft coral polyps

MINERALS to build a hard skeleton PROTECTION of the coral’s soft tissues Hard skeletons provide…

MINERALS to build a hard skeleton SUBSTRATE for corals & other sessile (non-mobile) organisms to settle Hard skeletons provide…

MINERALS to build a hard skeleton HABITAT for a diverse community of animals Hard skeletons provide…

MINERALS to build a hard skeleton What makes Lophelia’s skeleton so hard? CALCIUM CARBONATE (CaCO 3 ) Shells of many marine organisms Egg shells Chalk Antacid tablets (Tums) This common mineral is also the main component in:

Lophelia and Ocean Acidification Do you think ocean acidification will affect Lophelia’s ability to build a hard skeleton? If so, how?

Part II Let’s do an experiment, exploring how acidification may (or may not?) affect coral skeletons.

Testing the effect of pH on coral skeleton loss pH = ~7.5pH = ~5pH = ~6 What do you predict will happen to the coral piece after 1 week? Coral skeleton piece Freshwater Freshwater + 10ml vinegar Freshwater + 5ml vinegar #1#3#2

Part III Background on how Lophelia makes its skeleton and how the ocean is getting more acidic

How do these soft polyps make such a hard skeleton?

Polyp Anatomy

Coral polyps have two main layers of tissue: Oral Tissue This layer separates the coral polyp from the ocean environment; all exchanges between the coral and the surrounding seawater occur across this layer, except in the gastrovascular cavity Aboral Tissue This layer separates the coral’s soft polyp tissue from its hard skeleton

Polyp Anatomy Let’s zoom in and take a closer look at how these tissue layers help Lophelia build its hard skeleton.

CALICOBLASTIC EPITHELIUM Oral tissue The site of hard skeleton production Aboral tissue Coelenteron Skeleton Seawater The calicoblastic epithelium, the bottom layer of the aboral tissue, is responsible for producing the coral’s hard skeleton.

CALICOBLASTIC EPITHELIUM Oral tissue Aboral tissue Coelenteron Skeleton Seawater The process is called “calcification” Calcification takes place in the “calcifying fluid” within the calicoblastic epithelium layer.

skeleton seawater calicoblastic epithelium oral tissue aboral tissue coelenteron HCO 3 - Anion Calcification… First, an anion from the coral polyp is exchanged for a bicarbonate anion (HCO 3 - ) from the surrounding seawater.

HCO 3 - CO H + Anion skeleton seawater calicoblastic epithelium oral tissue aboral tissue coelenteron Calcification… Next, because of the high pH maintained by the polyp in its calcifying fluid, the bicarbonate (HCO 3 - ) dissociates into a carbonate anion (CO 3 2- ) and a proton (H + ).

Anion skeleton seawater calicoblastic epithelium oral tissue aboral tissue coelenteron HCO 3 - CO (2)H + Ca 2+ Calcification… The polyp then pumps 2 protons (H + ) from the calcifying fluid in exchange for a calcium cation (Ca 2+ ) from the surrounding seawater.

skeleton seawater calicoblastic epithelium oral tissue aboral tissue coelenteron Calcification! 2H + CaCO 3 HCO 3 - Anion CO Ca 2+ Finally, calcium (Ca 2+ ) combines with carbonate (CO 3 2- ) to form calcium carbonate (CaCO 3 ), which precipitates to form the coral skeleton.

For example, by maintaining a high pH (i.e., basic pH) in the calcifying fluid, Lophelia enables bicarbonate (HCO 3 - ) to dissociate into carbonate (CO 3 2- ) and protons (H + ), maintaining the necessary saturation state within the calcifying fluid. Calcification: A controlled process Lophelia controls the calcification process by regulating its internal chemistry in the calcifying fluid

Calcification: A controlled process However… Regulating your internal environment requires energy Conditions in the surrounding (external) environment can make this internal regulation much easier OR much more difficult How are we affecting Lophelia’s external ocean environment?

Ocean Acidification: Changing Lophelia’s external environment 1. The ocean acts as a “sink” for a lot of the carbon dioxide from the atmosphere, including both the carbon dioxide found naturally in the atmosphere and that added from pollution.

Ocean Acidification: Changing Lophelia’s external environment 2. When carbon dioxide mixes with water, it forms carbonic acid.

Ocean Acidification: Changing Lophelia’s external environment 3. This carbonic acid splits into hydrogen ions and bicarbonate.

Ocean Acidification: Changing Lophelia’s external environment 4. Some of the bicarbonate ions split into hydrogen ions and carbonate ions.

Notice, the concentration of protons (H + ) in seawater increases Ocean Acidification – Lophelia’s external environment

This increase in H + causes the whole carbonate equilibrium to shift back to the left, so there is less carbonate in the seawater. Ocean Acidification – Lophelia’s external environment

Buffers regulate the pH of a solution The ocean’s high buffering capacity slows the decrease in pH caused by ocean acidification Countering the impacts of acidification Fortunately, seawater has buffering capacity! Various anions present in seawater bind to the positive hydrogen ions, removing these protons from solution and countering the effect of ocean acidification How it works…

Even though seawater is a great buffer to resist these changes, it’s not enough Carbon dioxide pollution is causing the ocean to become more acidic Countering the impacts of acidification Still, the oceans are becoming more acidic.

What did we find in our experiment? How is the experiment similar/different from the real world? What do you predict will be the impact(s) on Lophelia?

Part IV Now let’s examine what does happen with ocean acidification and its impact on live corals.

Ocean Acidification and its effects on Lophelia What happens when the concentration of protons in seawater increases? pH decreases and the water becomes more acidic IMPACT ON LOPHELIA: CONSEQUENCE #1: acidic solutions can dissolve coral skeletons and the shells of other marine animals

Ocean Acidification and its effects on Lophelia What happens to the animal when the pH in seawater decreases? The difference between Lophelia’s internal environment(i.e., calcifying fluid) and its external environment (i.e., seawater) is even greater. IMPACT ON LOPHELIA: CONSEQUENCE #2: To maintain homeostasis with its external environment, Lophelia now must work harder to maintain a suitable internal pH to favor CaCO 3 production. skeleton seawater calicoblastic epithelium oral tissue aboral tissue coelenteron 2H + CaCO 3 HCO 3 - Anion CO Ca 2+

Ocean Acidification and Lophelia Ocean acidification makes it more difficult for Lophelia and other organisms with hard shells to form their skeleton As its surrounding environment changes, Lophelia must expend more and more energy to regulate its internal conditions and ensure calcification can occur

Other implications of ocean acidification If ocean acidification requires Lophelia to expend more energy to maintain a suitable internal environment for creating its hard skeleton… 1.How will Lophelia generate the energy necessary to regulate its internal environment? 2.What if ocean acidification affects the availability of Lophelia’s food sources?

Part V Deep-Sea Research Exploring the “C’s”: Climate Change and Cold-water Coral matechange/climatechange.html matechange/climatechange.html