Earlier this year my co-authors and I published a paper in Diversity and Distributions that examined a cost-effective way of predicting reef biodiversity for conservation purposes. Here is some background on the issues surrounding the design of Marine Protected Areas (MPAs) and a brief summary of our research findings.
As most of us are aware, our oceans are not as healthy as they once were. On a global scale we are continuing to see a loss of marine biodiversity in our oceans. To address this issue, there has been a push for the global development of MPAs. Although justified by a huge number of studies revealing positive effects, MPA location and configuration is not often based on ecology, but rather driven by social, political or economic concerns. Therefore, MPAs may just be ‘leftover’ areas that do not effectively protect biodiversity and potentially give the public a false sense of security (see here).
The problem with creating MPAs on an ecological foundation stems from the difficulties and costs in surveying marine biodiversity over the geographic areas required. Imagine surveying 100’s of square kilometres of ocean, counting all the fish, algae, snails, amongst other taxa, to determine where to place a no-take zone. It would cost a lot of money and take a lot of time! Plus, using SCUBA you’re limited by depth, restricting your surveys to relatively shallow areas.
An alternative approach is to use biodiversity ‘surrogates’ to predict areas of interest (i.e. where a certain species or community exists). A surrogate in an ecological sense is an ‘indicator’, which is easy to measure and correlates with what we want to conserve (i.e. biodiversity). A simple example of a surrogate could be using a plant community that is easy to survey from aerial photos. If this plant community supports a species of interest, say a rare bird, by mapping the distribution of the plant community, you could determine areas where the bird is likely to live in a cost effective way.
In the marine environment, scientists use habitat maps as surrogates for biodiversity and developing MPAs. As different habitat classes (rocky reef, sand, seagrass, etc.) contain different species living within them, by representing a greater number of habitat classes in a MPA, we can assume we are protecting a high proportion of the biodiversity in that particular area.
However, a number of habitat classes such as temperate rocky reefs display considerable fine-scale variation. Reefs may be structurally complex or flat, they may be sheltered or exposed to swell, or they may be close to or far from sand, naming just a few examples. Previous studies have indicated that such characteristics are important in determining where animals live on temperate reefs. Therefore, incorporating this fine-scale reef variation in MPA design would increase the likelihood of representing and conserving reef biodiversity.
The exciting news is that remote sensing technologies (sonar, aerial photography, satellites, etc.) have improved so much that marine scientists can map the fine-scale structure of temperate reefs. Therefore we can now examine the potential of fine-scale reef variation as a surrogate for reef biodiversity. So in this study, we used high resolution (5 metre pixel size) bathymetric side-scan sonar imagery to:
- Examine the fine-scale, physical variation of temperate reefs and test whether measures of reef variation provided surrogate measures for the abundance, diversity and community composition of sessile invertebrates (sponges and ascidians) and reef fishes.
We surveyed sessile invertebrates using a specialized towed underwater video system and reef fish using baited underwater video stations (BRUVs) – see pics below.
From the side-scan sonar imagery, we found massive differences in the structural complexity of temperate reefs. Some reefs were almost completely flat while others were complex. For example one reef dropped from a depth of 18 metres to a depth of 35 metres over a relatively short distance!
We found that reef structural complexity was a strong predictor of sessile invertebrates, with a greater abundance and diversity on reefs with high structural complexity. However a number of unique species were found only at sites with low structural complexity, indicating that flat reefs have conservation value too.
Generally, physical variables such as structural complexity were relatively poor predictors of the total abundance and diversity of fishes. However, we did find a higher abundance and diversity of fishes at sites further from the reef/sand boundary. In contrast, physical variables were good predictors of the abundance of Leatherjackets, with higher numbers observed further from the reef/sand boundary and at greater depths. This finding indicates that surrogacy relationships for fish may need to be explored at the family or specie level.
So in summary we found that:
- Temperate reefs display considerable physical variation (i.e. structural complexity) which can be measured in a cost-effective and time efficient way using side-scan sonar.
- Certain measures of reef variation are strong predictors of sessile invertebrates and Leatherjackets. Therefore these measures are potential surrogates for sessile invertebrates and Leatherjackets.
- MPAs should represent the fine-scale variation of temperate reefs to better represent and protect temperate reef biodiversity.
For more information follow the link below!
Rees MJ, Jordan A, Price OF, Coleman MA, Davis AR (2014) Abiotic surrogates for temperate rocky reef biodiversity: implications for marine protected areas. Diversity and Distributions 20, 284-296.
This research was supported by the University of Wollongong and NSW Department of Primary Industries.