Figuerola Hernández, Miguel

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    Coral reef community structure in La Parguera Natural Reserve ten years after the 2005-06 mass mortalities
    (2020-05-26) Figuerola Hernández, Miguel; Weil, Ernesto F.; College of Arts and Sciences - Sciences; Schizas, Nikolaos V.; Sherman, Clark E.; Cruz Motta, Juan J.; Department of Marine Sciences; Bellido, Carmen
    La Parguera Natural Reserve has one of the best-developed coral reef ecosystems in Puerto Rico, sustaining an important socio-ecological system. In 2005, an unprecedented high thermal anomaly produced intensive and extensive coral bleaching and disease epizootics in the northeastern Caribbean. The consequence was a community phase-shift marked by a dramatic decline in live coral cover (~53%) between 2004-2007 and a significant increase of algae cover. Ten years after this event, changes in the benthic community structure were assessed in terms of general benthic groups and specific scleractinian assemblages. Data was collected using six permanent quadrats along 20 m long transects located at 3 depths intervals in six different reefs across a nearshore-offshore gradient. The main factors in this design were: years (2003, 2007, 2016), reef zones (inner, mid, and outer shelf), depths (2-6, 7-12, and 13-22 m), and reef sites (n= 6). Data from 2003 and 2007 were collected in the field using six randomly placed and temporarily fixed, 1 m2 quadrats divided into a grid of 100, 10 x 10 cm squares for estimation of percentage cover in each of 80 permanent transects (between 8 and 16 per reef). In 2016, the same quadrats were sampled using four photos (0.25 m2) per quadrat (N = 492 photo-quadrats). Coral Point Count area/length analysis was used to measure planar areas and obtain the cover percentage of scleractinian species and benthic groups. Spatio-temporal patterns of variation were assessed with a suite of multivariate routines, which showed that temporal changes in benthic groups and scleractinian assemblages depended on the depth interval considered. For the deeper habitats (13-22 m), temporal changes were different for each reef zone, whereas for shallow (2-6 m) and intermediate (7-12 m) depths, temporal changes were different among sites. Independently of these differences related to depth; overall, cover of the different benthic groups seemed to change more drastically between 2007-2016, when open space was available, whereas scleractinian assemblages remained stable after the drastic changes between 2003-2007. Orbicella spp. consistently dominated scleractinian assemblages across years and zones, but an increase in the relative abundance of weedy and stress-resistant corals (Porites astreoides, Undaria agaricites, and Sideastrea siderea) was observed. Macroalgae and crustose coralline algae (CCA) were top contributors to explain changes in the structure of benthic groups assemblages at the outer-shelf between 2007-2016, whereas turf algae have remained as the dominant benthic group at all inner and middle-shelf habitats. These results indicate that complex spatiotemporal changes in benthic community structure are occurring across the insular shelf off La Parguera, suggesting that the benthic community shifts produced by the 2005-06 thermal anomaly are still present after a decade of massive cnidarian mortalities.