Coral size-frequency distributions as indicators of reef health: Monitoring and modeling approaches  (Year 1 of 1) Project Number: SEGM-2003-03-03 Principle Investigators: Lirman, D. Region(s):  The reef communities of the Florida reef tract conform the only living tropical coral reef system in the continental United States. However, several interacting factors have contributed to the consideration of this ecologically, economically, and aesthetically unique system as an “ecosystem at risk”. Increasing pollution, altered biotic relationships, and extreme environmental conditions have all been proposed as factors influencing the documented decline in reef condition in the region. Direct hydrological connections between the coastal lagoons and the Florida reef tract have been established with well-documented net flows across all major tidal channels. Florida Bay and Biscayne Bay are shallow environments that experience high frequency and variability of physical and biological variables such as temperature, salinity, nutrients, and phytoplankton blooms that can have significant negative impacts if they reach the reef communities. Based on patterns of water exchange with the shelf margin, explicit spatial relationships between reef development, coral condition, and proximity to areas with wide connections to the coastal lagoons have been proposed. Considering the influence of natural (e.g., water flow) and human (e.g., urban development) gradients, a distinct spatial disturbance gradient has been hypothesized where coral reef communities closer to shore and areas with wide connections to coastal bays would experience increased stress and reduce health. Reefs of the Florida reef tract can be divided into two types, outer bank reefs located along the seaward edge of the shelf and patch reefs located within the inner lagoon between the Florida Keys and the outer bank reefs. The location of patch reefs in close proximity to the urban centers of the Florida Keys and directly exposed to water flows across tidal channels makes these ideal habitats to test the hypothesis that both natural and human-based sources of stressors create an inshore-offshore disturbance gradient that should be reflected in coral condition. This hypothesis was tested using a combination of random population surveys and coral growth and survivorship studies.   Between 2001 and 2003, 66 patch-reef sites (10 in BNP, 40 in the Upper Keys, 10 in the Middle Keys, six in the Lower Keys) were surveyed to document the distribution and abundance of corals, and size-structure of coral populations using a nested sampling design. The Florida reef tract was divided into four regions: 1) Biscayne National Park (BNP), 2) Key Largo, 3) Middle Keys, and 3) Lower Keys. Within each region, two areas inshore (< 4 km from shore) and offshore (> 4 km from shore), were further delineated based on an initial analysis of patch-reef distribution. The location of survey sites within each stratum (4 regions x 2 areas) was determined at random from the digital GIS coverage of benthic habitats. At each location, divers surveyed haphazardly located 10-m2 transects where maximum length and width as well as maximum colony height of coral colonies were measured. In 2001, nine permanent sites were established in the Upper Keys (four offshore, five inshore) where colony-based growth and mortality would be documented through repeated sampling at annual intervals. Two of these inshore sites are within SPAs (Hen and Chickens and Cheeca Rocks). Within each site, colonies of Siderastrea siderea, S. radians, and Porites astreoides within different size classes were measured, photographed, and marked with metal tags. In 2003, the permanent sites within the Key Largo region were relocated once again and all tagged colonies encountered were measured and photographed. In 2003, the permanent sites within the Key Largo region were relocated and all tagged colonies encountered were measured and photographed. A total of 14,982 colonies were measured in our surveys of 66 patch reefs. Mean and maximum colony size showed significant patterns with respect to reef location. For P. astreoides, S. siderea, S. radians, and M. cavernosa, mean and maximum colony size decreased significantly with increasing distance to shore (linear regression, p < 0.05). Mean colony size was significantly larger on inshore patch reefs compared to offshore sites for all coral species (t-tests, p < 0.05), except D. clivosa and D. stokesii for which no significant differences in mean size were found with respect to distance to shore. While percent coral cover was significantly higher on inshore patch reefs compared to offshore sites, no significant patterns in coral cover were detected based on region (two-factor ANOVA with region and distance to shore as factors). Coral population structure showed clear inshore-offshore gradients within patch-reef habitats. These patterns were consistent among species and regions which indicates a high level of environmental influence on this endpoint. When corals are grouped into 2-cm size classes (roughly the maximum growth rates documented), patterns of population size structure show differences based on species, life history characteristics, and distance to shore. In general, broadcast spawners such as Diploria spp. and M. faveolata have well-spread populations with a limited proportion of colonies within the smallest size categories and a large portion of the population biomass on medium to large-size colonies. In contrast, brooding corals like P. astreoides and S. radians have narrower populations with a large percentage of colonies within the smaller size classes. When data were grouped according to distance to shore, growth rates of S. siderea, S. radians, and P. astreoides differed significantly between inshore and offshore reefs (ANCOVA, test for unequal slopes, p < 0.05). S. siderea, S. radians, and P. astreoides grew significantly faster on inshore reefs compared to offshore reefs. Percent partial mortality was higher on offshore reefs than on inshore reefs for all three coral species, while S. radians was the species that experienced the highest percent partial mortality. Publications Data collected during this project were incorporated into a manuscript accepted for publication in Restoration Ecology (Lirman and Miller, 2003). In this paper, we use the newly developed coral population models to predict the rates of convergence between restored and undamaged reef habitats at two ship-grounding sites within the FKNMS. A second publication that will include the structural data (i.e., coral abundance, distribution, size-structure, growth, survivorship, recruitment) collected in this project will be sent out for review at Ecology in 2-3 months. Future Research The initial observations of coral population structure along inshore-offshore gradients suggest that the documented differences in size-structure may be explained by the differences in recruitment, growth, and partial mortality patterns measured at the permanent sites. Offshore sites had higher recruitment but also higher rates of partial mortality and lower growth rates compared to inshore sites. These patterns, if persistent, may provide an explanation for the observed structural differences. However, additional sites need to be established to determine whether these documented patterns are consistent among regions. Similarly, it is important to determine whether the recruitment, growth, and mortality patterns documented between 2001 and 2003 are consistent through time. Future efforts will concentrate on continuing monitoring of established permanent sites as well to establish additional permanent sites within regions not included in the prior research. Leg 1    Begin Date: 4/1/2003   End Date: 10/30/2003   Support Vessel/Platform: R/V Research Diver System Ops Days Dives Dive Time (hrs) Depth (m) SCUBA 9 37 52.36 39

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Updated: May 28, 2004