Corals have long attracted the attention of sciπ≠≥entists. It's an interesting ♣←organism with an equally interesting ecology. Cor§≠★al reefs represent some of the most diverse, co♣mplex and fragile ecosystems in the∑$ world. Ecological and clim♥→atic variables, such as nutrient avai∏←¥lability and water temperature, have a large i>mpact on coral growth.
Much of coral research has focu€ ♦sed on understanding how coαΩrals grow, how corals interact with oth♥↔er organisms, and the impa↔₽↓Ωct of human activity on reef healt÷h. Another important but less well-know§₽πn study is exploring the way corals act as &φ✔€quot;recorders" during growth. Th± ₩e calcium carbonate skeleton ∞£left behind by the organism c←λ¥ontains data on these environmental variables t÷₩ εhat influence coral growth. Thus,"↔ information about ancient climate and ecoloφ ★gy can be learned from ancient corals.
Bones leave a record of grow>€th
Corals are actually ≥ ↔very small soft-bodied organisms that secrete t λhe hard skeletons we see. As c✘™orals grow, they leave ↔∞•behind their old skeletons and grow a new sk≤∏×eleton on top of them. These ancie↓©nt skeletons are preserved under l♠δiving coral, leaving ×< a record of growth. Shallow-water coraε•★ls often form huge reefs as they g≠εrow, aided by symbiotic algae¶₹↑© and tropical sunlight. Deep-sea corals produ✘♣±ce fewer skeletons and survive in cold, dark wat¶<ers by feeding on excess nutrients.
Small coral colonies like these are oftΩ→en found in the hard ♠↔bottom areas of the Blake Platea♦₩u, which are located in the rapids of "∑♣the Gulf Stream. The chemical composition✘♠®≤ of these small, tough corals, along with sur≠ε <rounding coral rubble ₩δ¥and fossil corals, can reve•✔βal the history of temp≠♣→®erature changes at the Blake Plat₽★✔♥eau.
Corals that grow in shallow trop✘≥ical waters are relatively easy to β∏observe and study, but deep-sea co↑¥₩∏rals are harder to observe. Even simple ↑ measurements like growth rates♦↓ are harder to make.
Growth rate is a key variable in ✘γour understanding of coral ecolo¥€¶gy. By measuring growth♥→ rates, we can unlock what corals★•§™ have taught us in past climates. (AddΩ←itionally, deep-sea corals σ→ are now increasingly affecte✔£εd by human activity, s₹↑o it is increasingly importa™£nt that we understand how our acti™→ons affect these org≤γ ♣anisms.) Since we cannot observe deep-sea cor♠←als in their natural habitats for lo ←♣ng periods of time, we m↕ ust take Other methods to determine growth rat≥>e. One way to do this is to m✘Ωark the size of the corδ££al (without destroying λπ↔≥it), let it sit for a while≤γ§σ, and come back to see how much it has grown"↕"♣.
Fortunately, corals leave their mark as they ₩ grow, just like trees do. To take ÷€® advantage of these growth points, or &quo• t;increments," we must determinσ¶e how long they actually represent₽$₹. Determining the growth rate is f ≤airly straightforward once we know it. Howev"≥er, this method is not practical ¥✔≈for deep-sea corals.
Unlock a chemical im'♠σage
One method we use to dete∏→₽δrmine growth rates is to analyze the chemical≠ε₹αs locked into the coral skeleton. Some aspect©∑↕¶s of coral chemistry are controlle↔<β↕d by variables such as water temperature. In π≤§&some deep-sea environments, such ≈→as the Charleston Bulge, temperat✘✘'ures vary over time throughou>↕t the year. Therefore, th<∏ e chemical composition of the ske☆×✔©leton may be recorded fo★εr a year, and we can measure the growth ra¥δ÷€te of these corals.
Scientists cut small coral→↑ fragments across, looking for visible growth li₽↑≈nes. We can correlate these lines with changes in≤ chemical composition and determine whe$αther changes in growth rat<→≤es are related to waterβ™ temperature.
We observed many differe₽∑£nt coral growth patterns on the B♣∑≠&lake Plateau. Hard surfaces are often c ←overed, to some extent, w₹∏ith small "twigs&<>πquot; of coral, each just a few centimeters hiβ≈±gh. Some areas have many c™↕orals tightly clustere↕γd together, some areas have only a few widesprγ ead corals, some large bus♦₹☆♠h-like corals cover t≥'₽he bottom, and some areas have no corals at all$∞£.
None of these pattern§¥s can be random, and just knowing h∞≤λ≈ow fast these corals gr ÷σow, we can determine ★ π∞the most important factors cont™>φδrolling the development of these differen™✘t growth habits.
uncertain future
An unfortunate variable affecting the growt♣Ω¥h habits of deep-sea coral₽§≥ s in other parts of the world is the use ♣↓∑ of fishing methods, where some equipme↔★nt is dragged to the bottom and destroys l ≠☆arge areas of coral. How long can corals recα£ ♣over from these disturbances? W↕Ω ∏hen do coral ecosystems return to these ₩₽Ωareas after being disrupted? Simple age¶✘® measurements are critic≈± ∞al to answering these questions and understand∑↓✔ing these processes.±¶♥
Some of the places we've looked at on ♣αother expeditions incε$lude the skeletons of some corals that appear✘βλ to have died long ago. By stα↓udying the chemical records of these ancient cπεφλorals, we hope to unlock clues about the eco∞αsystems and climates of the timeλ♦↕s in which these corals lived. These lon↔←§×g-dead corals may shed light on how local a↓✘αnd global climates have changedφΩ∞ over time. Much of the infor∞•♥mation on past climates comes from shal§₩≈low records of tropical corals♥"≈. Deep-sea corals may have®↑ recorded similar changes.
---Fred Andrews Department of Geolog©₽y University of Alabama