Last month, MPA News examined the scientific understanding of climate change in the marine environment, and what global ocean warming could entail for the planning and management of MPAs. Following publication, we spoke with three more scientists, who lent further insight to the issues involved.
Pristine reefs and the impact of warming
Susie Westmacott of the University of Newcastle upon Tyne (UK) has studied the impact of the great bleaching event of 1998 on Indian Ocean coral reefs. (The event corresponded with higher sea temperatures, which caused many corals to lose their colorful symbiotic algae and, in some cases, die.) In a paper she co-wrote for the report Coral Bleaching: Causes, Consequences,and Response (see box at end of article), Westmacott stated that the reefs least at risk from human activity -- and potentially in pristine condition -- seemed to suffer the greatest bleaching and loss of coral cover.
On its surface, her finding might seem to contradict the belief of many coral reef researchers that undamaged reefs are generally more resilient to climate-related stressors. However, Westmacott has an explanation.
"The more vulnerable species of coral still exist in [pristine] locations," said Westmacott, "and the coral cover is generally far higher than in those areas which have already been impacted [by other stressors] -- where only the more resilient species remain."
The good news, she says, is that these more vulnerable species are often the fast-growing species, and thus might regenerate most quickly. "The important point to note is that these areas -- either protected or simply remote from human activity -- have the greatest chance of recovery," she said. "Whereas, those areas impacted and with a high level of pressure are less likely to recover. It is important, therefore, to protect the [pristine] areas even though at first glance -- and initially in the short term -- it may seem that they are impacted the most."
Response to bleaching on Great Barrier Reef
Areas of the Great Barrier Reef -- particularly inshore reefs -- suffered severe damage from the 1998 bleaching event. Now, the Great Barrier Reef Marine Park Authority (GBRMPA) is collaborating with the Australian Institute of Marine Sciences (AIMS) and the US National Oceanic and Atmospheric Administration to assess the causes and consequences of coral bleaching and develop a climate-change risk assessment. The results could have long-term implications for management of the Great Barrier Reef.
For the reef areas at greatest risk from climate change (i.e., inshore reefs), GBRMPA may consider decreasing other pressures on those reefs, says Alison Green, director of GBRMPA's Information Support Group. Such pressures primarily include fishing and poor water quality due to land-based pollution, she says. GBRMPA has already taken a step in this direction, instituting a program aimed at reducing the runoff of land-based pollutants into Great Barrier Reef waters.
"GBRMPA and AIMS also support a network of automatic weather stations which provide an early warning system for coral bleaching conditions on the Great Barrier Reef," said Green. "This monitoring program provides real time alerts for water temperatures and other environmental conditions that may lead to coral bleaching." When an alert is triggered, GBRMPA can respond with aerial and sea-level surveys, documenting the patterns of bleaching and recovery.
In outreach work for GBRMPA, Green provides coral research advice to MPA managers in Pacific island nations. Although it is still rare for local managers to incorporate climate change or coral bleaching into their planning processes, she says, they welcome advice on how to do so. She suggests they conduct research and monitoring surveys of the same type as GBRMPA, but on a smaller scale. "I recommend that they do a simple survey to determine the extent and severity of the bleaching event, and whether the affected colonies recover or not," she said.
Tropical vs. temperate response to warming
In the tropics, a change in sea surface temperature of 1-2 degrees Celsius can spell the difference between a bleached and unbleached reef, severely altering the ecosystem if the corals die. In temperate waters, however, a change of 1-2 degrees Celsius -- in and of itself -- can yield little direct effect on species survival.
"In tropical marine systems, species have a narrower range of temperatures that they're adapted to, and a lot of species are living at the upper edge of their temperature range," said Sue Sogard, a biologist with the US National Marine Fisheries Service. "In temperate regions, though, there is more flexibility in terms of the range of temperatures that species can tolerate."
Sogard has studied the response to temperature change of two commercially fished species: sablefish and walleye pollock. She found they were able to grow effectively at temperatures much higher than they would normally experience. The limiting factor was food availability. Higher water temperatures led to higher metabolic rates and greater consumption in the fish; if food levels didn't rise in parallel, fish growth potential was limited. When food levels were low, the fish moved to colder water.
Rising ocean temperatures could have a critical effect on food availability. Most notably, if global warming were to shift or slow ocean thermohaline circulation or modify local current patterns -- as theorized by some scientists (MPA News 3:1) -- primary production would be fundamentally altered. Any existing efforts to protect species or ecosystems, such as with fishery closures, would be affected by shifts in species distribution and habitats. "There's not enough physical information yet to know what's going to happen," said Sogard.
For more information
Susie Westmacott, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, United Kingdom. E-mail: s.westmacott [at] ncl.ac.uk.
Alison Green, Great Barrier Reef Marine Park Authority, PO Box 1379, Townsville Qld 4810, Australia. Tel: +61 7 4750 0700; E-mail: alison [at] gbrmpa.gov.au.
Sue Sogard, National Marine Fisheries Service, Hatfield Marine Science Center, 2030 Marine Science Dr., Newport, OR 97365, USA. Tel: +1 541 867 0222; E-mail: susan.sogard [at] hmsc.orst.edu.
Box: Coral bleaching report available
The report Coral Bleaching: Causes, Consequences and Response, published by the University of Rhode Island Coastal Resources Center, is available online: http://www.crc.uri.edu/comm/htmlpubs/coral.html