BIOT Science Expedition 2014 - Dr Elizabeth Widman Initial Report

Scleractinian Coral Functional Diversity Surveys

Dr Elizabeth Widman, Warwick University

Background

Investigations into how species diversity relates to system-level properties, such as ecosystem functioning, have been largely unsuccessful and have failed to produce general principles (Lawton 1999; Simberloff 2004; McGill et al. 2006). To address the shortcoming of species-only approaches a renaissance of sorts is taking place in community ecology (McGill et al. 2006): species-level data is being supplemented with trait-level data in some systems. It has been discovered that functional trait diversity plays an important role in: ecosystem processes (Hooper et al. 2005), the resilience of ecosystems to environmental stressors (Folke et al. 2004), and the provision of ecosystem services (Díaz et al. 2007). While trait-based approaches have shown great promise in other branches of ecology, such as plant ecology (Shipley et al., 2006) it remains largely unexplored in marine and especially coral reef ecology.

One major advantage in quantifying the abundance and diversity of traits rather than species alone is that it allows one to link empirical measurements on the species level directly to macro-scale functioning (Cadotte et al. 2009). Another key reason for embracing trait-based approaches in coral reef ecology is that focusing on trait diversity bypasses taxonomic uncertainties brought about by genetic and genomic tools (Fukami et al. 2008) while retaining ecological identities.

Gaining an understanding of what makes reefs in Chagos far more resilient to climate related stressors, compared to other regions of the Indian Ocean, is central to its appropriate management. In turn gaining such insights require that we understand and quantifying organismal fitness relative to the changing environmental variables associated with climate change (i.e. increased water temperatures, acidity, storm frequency and intensity). The traits which species possess, their environmental plasticity, and their combinations are the ultimate determinants of whether a species will survive, thus, any monitoring and research program operating under the vision of conserving resilience must logically account for, on some level, the species traits presents on the reefs of the Chagos Archipelago.

Constructing a coral trait-database for Chagos (see output section) and conducting a functional diversity survey on the Chagos archipelago are the first step towards understanding the coral species traits and trait-combinations that are present on the reefs. Explorations into what different trait diversities and combinations mean in terms of resilience and/or resistance to future stress events can then be explored.

Methods

Analytical approaches used in assessing a broad range of functional diversity metrics require a minimum of two datasets: a species x site matrix (i.e. species site composition) and a species x trait matrix. Species composition was determined for 27 sites using an established phototransect methodology (Widman 2012). Phototransect sites were surveyed across five atolls (Salamon, Peros Banhos, the Great Chagos Bank, Egmont, and Diego Garcia) and at 6 depths (25m, 20m, 15m, 8m, 5m, and 2m) where possible. For reference each image is geotagged (by syncing the camera timer with a GPS on a buoy which is dragged throughout the dive) and also depth tagged (by including a dive computer in every image; see Figure 1 for details). The species composition for each site will be determined by analysing the images using CPCe software (Kohler & Gill).

Figure 14: Overview of the underwater sampling method (far left diagram). Images of the reef surface were taken along a transect from a known distance, measured by a PVC pole attached to a camera rig (centre image). A GPS unit fixed to a floatation device (far right image) was towed throughout the dive in order to record the position of each image taken.

Output

A trait database will be constructed for the coral species in Chagos using the species list compiled by Doug Fenner on the 2014 expedition and a number of existing coral trait databases (i.e. Widman 2012 2014). Using this trait database, along with the species composition that will be derived from analysing the photos, a battery of trait-based analyses will be undertaken to understand the functional composition of reefs on the Chagos archipelago.

The relationship between coral trait diversity and other relevant datasets collected on the same reef sites during the 2014 expedition will be explored. These datasets include fish diversity (Dr Samoilys and Dr Koldewey), coral disease (Dr Couch), and temperature history (Prof Charles Sheppard and Anne Sheppard). Future collaborations have already been discussed to maximise the depth and breadth of this functional analysis.

When the analysis is complete the result will be an archipelago-wide survey of reef functional composition. This will improve not only our basic understanding of how the reef functions but also give insight on macro-ecological properties such as functional redundancy and resilience to specific stressors. Ultimately, understanding macro-ecological reef properties such as ‘functioning’, resilience and resistance to stressors helps inform managers and decision makers.