Greg Foster

Demography and population dynamics of massive coral communities in adjacent high latitude regions (United Arab Emirates).

Individual massive coral colonies, primarily faviids and poritids, from three distinct assemblages within the southeastern Arabian Gulf and northwestern Gulf of Oman (United Arab Emirates) were studied from 2006–2009. Annual photographic censuses of approximately 2000 colonies were used to describe the demographics (size class frequencies, abundance, area cover) and population dynamics under “normal” environmental conditions. Size class transitions included growth, which occurred in 10–20% of the colonies, followed in decending order by partial mortality (3–16%), colony fission (<5%) and ramet fusion (<3%). Recruitment and whole colony mortality rates were low (<0.7 colonies/m2) with minimal interannual variation. Transition matrices indicated that the Arabian Gulf assemblages have declining growth rates (λ<1) whereas the massive coral population is stable (λ = 1) in the Gulf of Oman. Projection models indicated that (i) the Arabian Gulf population and area cover declines would be exacerbated under 10-year and 16-year disturbance scenarios as the vital rates do not allow for recovery to pre-disturbance levels during these timeframes, and (ii) the Gulf of Oman assemblage could return to its pre-disturbance area cover but its overall population size would not fully recover under the same scenarios.

Detecting end-member structural and biological elements of a coral reef using a single-beam acoustic ground discrimination system

A thematic map of benthic habitat was produced for a coral reef in the Republic of Palau, utilizing hydroacoustic data acquired with a BioSonics DT-X echosounder and a single-beam 418 kHz digital transducer. This article describes and assesses a supervised classification scheme that used a series of three discriminant analyses (DAs) to refine training samples into end-member structural and biological elements utilizing E1′ (leading edge of first echo), E1 (trailing edge of first echo), E2 (complete second echo), fractal dimension (first echo shape) and depth as predictor variables. Hydroacoustic training samples were assigned to one of six predefined groups based on the plurality of benthic elements (sand, sparse submerged aquatic vegetation (SAV)) rubble, pavement, rugose hardbottom, branching coral) that were visually estimated from spatially co-located ground-truthing videos. Records that classified incorrectly or failed to exceed a minimum probability of group membership were removed from the training data set until only ‘pure’ end-member records remained. This refinement of ‘mixed’ training samples circumvented the dilemma typically imposed by the benthic heterogeneity of coral reefs, that is either train the acoustic ground discrimination system (AGDS) on homogeneous benthos and leave the heterogeneous benthos unclassified, or attempt to capture the many ‘mixed’ classes and overwhelm the discriminatory capability of the AGDS. It was made possible by a conjunction of narrow beam width (6.4°) and shallow depth (1.2 to 17.5 m), which produced a sonar footprint small enough to resolve the microscale features used to define benthic groups. Survey data classified from the third-pass training DA were found to: (i) conform to visually apparent contours of satellite imagery, (ii) agree with the structural and biological delineations of a benthic habitat map (BHM) created from visual interpretation of IKONOS imagery and (iii) yield values of benthic cover that agreed closely with independent, contemporaneous video transects. The methodology was proven on a coral reef environment for which high-quality satellite imagery existed, as an example of the potential for single-beam systems to thematically map coral reefs in deep or turbid settings where optical methods are not applicable.

Delineating optimal settlement areas of juvenile reef fish in Ngederrak Reef, Koror state, Republic of Palau

Establishing the effectiveness of habitat features to act as surrogate measures of diversity and abundance of juvenile reef fish provides information that is critical to coral reef management. When accurately set on a broader spatial context, microhabitat information becomes more meaningful and its management application becomes more explicit. The goal of the study is to identify coral reef areas potentially important to juvenile fishes in Ngederrak Reef, Republic of Palau, across different spatial scales. To achieve this, the study requires the accomplishment of the following tasks: (1) structurally differentiate the general microhabitat types using acoustics; (2) quantify microhabitat association with juvenile reef fish community structure; and (3) conduct spatial analysis of the reef-wide data and locate areas optimal for juvenile reef fish settlement. The results strongly suggest the importance of branching structures in determining species count and abundance of juvenile reef fish at the outer reef slope of Ngederrak Reef. In the acoustic map, the accurate delineation of these features allowed us to identify reef areas with the highest potential to harbor a rich aggregation of juvenile reef fish. Using a developed spatial analysis tool that ranks pixel groups based on user-defined parameters, the reef area near the Western channel of Ngederrak is predicted to have the most robust aggregation of juvenile reef fish. The results have important implications not only in management, but also in modeling the impacts of habitat loss on reef fish community. At least for Ngederrak Reef, the results advanced the utility of acoustic systems in predicting spatial distribution of juvenile fish.

Demographics and Population Dynamics Project the Future of Hard Coral Assemblages in Little Cayman

Individual hard coral colonies from four representative reef sites around Little Cayman were surveyed yearly between 2010 and 2015, a period of non-disturbance between two elevated seawater temperature anomalies. Photographic censuses produced 7069 annual transitions that were used to describe the demographics (size class frequencies, abundance, area cover) and population dynamics under non-disturbance environmental conditions. Agariciids, Porites asteroides, and Siderastrea radians have replaced acroporids as the predominant massive corals. Recruitment rates were generally low (2), except for a fourfold recruitment pulse of S. radians that occurred in 2011. On average, 42% of coral recruits survived their first year but only 10% lived longer than four years. Temporal comparisons allowed correction factors to be calculated for in-situ methods that overestimate recruitment of colonies ≤2 cm in diameter and overlook larger colonies. Size class transitions included growth (~33%), stasis (~33%), partial mortality (10% - 33%), and whole colony mortality, which decreased with increasing colony size (typically 30 cm2). Transition matrices indicated that Little Cayman assemblages have declining hard coral populations (λ 150 cm2 surface areas, live area cover may remain relatively stable. Projection models indicated that downward population trends would be exacerbated even by mild disturbance (5% - 10% mortality) scenarios. The fate of hard corals on Little Cayman’s reefs was determined to be heavily dependent on the health and transitions of agariciid colonies. Conservation strategies that currently focus on restoration of Caribbean acroporids should be expanded to include agariciids, which were previously considered “weeds”.

Acoustic Detection and Mapping of Muck Deposits in the Indian River Lagoon, Florida

ABSTRACT Foster, G.; Riegl, B.M.; Foster, K.A., and Morris, L.J., 2018. Acoustic detection and mapping of muck deposits in the Indian River Lagoon, Florida. Locating significant deposits of muck (semifluid, fine-grained, organic-rich sediment) is an important aspect of estuarine conservation and management. The 38-kHz signal of a dual-frequency, single-beam acoustic survey of drift macroalgae was repurposed post hoc to locate and measure the horizontal and vertical extent of muck deposits within Indian River Lagoon, Florida. Raw echo returns were segmented into 5-cm strata of echo intensity, and a series of postprocessing algorithms were written to identify the characteristic pattern of backscatter associated with muck. Twenty-three deposits thicker than 0.5 m were identified within the 283-km2 survey area, nearly all of which were found within depressions of the Indian River (IR). The quantity of muck was estimated at 1.87 × 106 m3, roughly four times the quantity slated for removal from the Eau Gallie River and Elbow Creek (Florida) in 2016. The quantity of muck within the 110-km traverse of the IR Intracoastal Waterway (ICW) was estimated at 5.31 × 106 m3. Muck deposits within the 31-km traverse of the Banana River (BR) ICW were deeper (μ = 1.22 vs. 0.51 m), but muck volume was difficult to estimate because of the uncertain boundaries (i.e. channel width) of the BR ICW. The decision of whether to remove the significant volumes of muck within the 23 deposits and the ICW must consider ecological impact relative to concentrations of muck at the discharge of tributaries. Nonetheless, this extra layer of information was achieved with only a modest increase of surveying and postprocessing effort. Synergies such as this will be important in an era of monitoring and management cost constraints.