Classification of remote Pacific coral reefs by physical oceanographic environment

Abstract

[1] The oceanographic environment is a key element in structuring coral reef ecosystems by setting the range of physical and chemical conditions in which coral reef-builders live. A cluster analysis of physical and chemical oceanographic data is used to classify coral habitats in the remote tropical and subtropical Pacific Ocean based on average temperature, temperature seasonal cycle, nutrient levels, salinity, aragonite saturation state, storm frequency, intense hurricane hits, and dissolved oxygen as well as temperature anomalies in degree heating weeks. The resulting seven geographic habitats are stable to perturbations in types of data used in the cluster analysis. Based on recent coral reef survey data in the area, the coral cover was related to the identified geographic regions. The habitats tend to be geographically clustered, and each is characterized by a unique combination of oceanographic conditions. Previous studies suggest coral reef habitats are associated with a uniform array of oceanographic conditions, while our results demonstrate that finer-scale variations in physical variables may control coral reef environments. The results better define the physical environment of remote coral reefs, forming a foundation for future work addressing physical habitat perturbation and anthropogenic impacts on reefs.

Rapidly obtained ecosystem indicators from coral reef soundscapes

“…PCA outputs (Fig. 6) and Pearson's correlations (Table 1) reveal associations between acoustic variables and observations from TLP, SPC and photoquadrat data that were consistent across the entire Hawaiian archipelago, and within the 2 oceanographic habitats considered (Freeman et al 2012).…”

“…Grey lines and filled circles indicate mean acoustic pressure spectral density levels during the periods and within the bands indicated (k: kHz). Dark blue and cyan triangles indicate the position of field sites within the 'cool tropics' and 'high latitudes' oceanographic regimes, respectively (Freeman et al 2012). A general trend from 07:00 to 14:00 h is evident in the sites ranging from more algae-dominated to more coral-dominated, which is also reflected in the acoustic metrics with low-frequency sounds characterizing reefs with positive ecological indicators, and high-frequency sounds characterizing reefs with negative ecological indicators (Radford et al 2010) from ecosystem-wide trends.…”

“…1 & 6) (i.e. only the cool tropics reefs or only the high latitude reefs from Freeman et al 2012). Measurements, particularly of algae-related metrics, from the high-latitude reefs may be confounded by differing oceanographic conditions in those areas (cooler temperatures, higher frequency of winter storms, etc.)…”

“…Time-lapse photographic (TLP) data were collected using Canon D10 (or similar) underwater cameras programmed using the Canon Hack Development Kit open-source software package in a manner similar to that described in Freeman et al (2012). Cameras were programmed to collect one image every 5 min, using flash photography if light levels decreased below a software-determined threshold.…”

Quantifying Climatological Ranges and Anomalies for Pacific Coral Reef Ecosystems

“…Such studies have been important for establishing environmental limits to coral reef development [3], identifying broad geographic patterns in environmental habitats in which coral reefs reside [13], [15], and assessing the susceptibility of coral reefs to anomalies in environmental forcings on a global scale [11], [12], [16]. In many previous studies, [3], [13], [14] environmental data were synthesized at 1 × 1° (12,100 km 2 ); a coarse resolution when compared to the size of many of the islands and atolls in the Pacific. Research has shown environmental conditions such as productivity [17], [18] and temperature [19], [20] proximate to islands can be distinct from regional conditions.…”