Williams, S.M.

Reef flattening effects on total richness and species responses in the Caribbean

1. There has been ongoing flattening of Caribbean coral reefs with the loss of habitat having severe implications for these systems. Complexity and its structural components are important to fish species richness and community composition, but little is known about its role for other taxa or species-specific responses. 2. This study reveals the importance of reef habitat complexity and structural components to different taxa of macrofauna, total species richness, and individual coral and fish species in the Caribbean. 3. Species presence and richness of different taxa were visually quantified in one hundred 25-m2 plots in three marine reserves in the Caribbean. Sampling was evenly distributed across five levels of visually estimated reef complexity, with five structural components also recorded: the number of corals, number of large corals, slope angle, maximum sponge and maximum octocoral height. Taking advantage of natural heterogeneity in structural complexity within a particular coral reef habitat (Orbicella reefs) and discrete environmental envelope, thus minimizing other sources of variability, the relative importance of reef complexity and structural components was quantified for different taxa and individual fish and coral species on Caribbean coral reefs using boosted regression trees (BRTs). 4. Boosted regression tree models performed very well when explaining variability in total (823%), coral (806%) and fish species richness (773%), for which the greatest declines in richness occurred below intermediate reef complexity levels. Complexity accounted for very little of the variability in octocorals, sponges, arthropods, annelids or anemones. BRTs revealed species-specific variability and importance for reef complexity and structural components. Coral and fish species occupancy generally declined at low complexity levels, with the exception of two coral species (Pseudodiploria strigosa and Porites divaricata) and four fish species (Halichoeres bivittatus, H. maculipinna, Malacoctenus triangulatus and Stegastes partitus) more common at lower reef complexity levels. A significant interaction between country and reef complexity revealed a non-additive decline in species richness in areas of low complexity and the reserve in Puerto Rico. 5. Flattening of Caribbean coral reefs will result in substantial species losses, with few winners. Individual structural components have considerable value to different species, and their loss may have profound impacts on population responses of coral and fish due to identity effects of key species, which underpin population richness and resilience and may affect essential ecosystem processes and services.

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire
Image
Highly complex reef at Bonaire

Importance of differentiating Orbicella reefs from gorgonian plains for ecological assessments of Caribbean reefs

ABSTRACT: Region-wide assessments of coral cover typically rely on meta-analyses of small- scale ecological studies which have combined different coral reef habitats. This is particularly problematic on forereefs where at least 2 habitats can be found; coral-based bioherms and colo- nized hardgrounds (hereafter Orbicella reefs and gorgonian plains), each with very different structure and scleractinian coral cover. Here, we quantify the degree to which the failure to differ- entiate forereef zones dominated by framework building corals, mainly Orbicella spp. (hereafter Orbicella reefs) from gorgonian plains can lead to biased assessments of coral cover. We also pro- vide a baseline of an extensive sample of Caribbean coral reefs in 2010−2012 for the 2 habitats within the forereef. Mean scleractinian coral cover (±SE) at Orbicella reefs was 24 ± 1.3%, more than double the coral cover found on the gorgonian plains (10 ± 1.6%). The difference in coral cover between habitats within the same geomorphological zone is consistent with those calculated from an independent dataset for the basin (Atlantic and Gulf Rapid Reef Assessment). Further- more, the average coral cover calculated for Caribbean Orbicella reefs was more than double the values previously reported for entire reefs in the region a decade ago (10%), which integrated data from different habitats, depths, time periods and surveyors. Differentiating between forereef habitats has provided a meaningful baseline of coral state, which allows for realistic targets for management in the Caribbean basin. 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire
Curacao

Hierarchical spatial patterns in Caribbean reef benthic assemblages

Aim

Coral assemblages on Caribbean reefs have largely been considered to be biogeographically homogeneous at a regional scale. We reassess this in three taxa (corals, sponges and octocorals) using three community attributes with increasing levels of information (species richness, composition and relative abundance) across hierarchical spatial scales, and identify the key environmental drivers associated with this variation.

Location

Caribbean Basin.

Methods

We assessed reefs along 546 transects positioned within the same forereef habitat (Orbicella reef) in 11 countries, using a consistent methodology and surveyors. Spatial variability in richness, composition and relative abundance was assessed at four hierarchical spatial scales – transects (metres), sites (kilometres), areas (tens of kilometres) and regions (hundreds of kilometres) – using permutational multivariate analysis of variance (PERMANOVA). The relevance of contemporary environmental factors in explaining the observed spatial patterns was also assessed using PERMANOVA.

Results

Consistent with previous studies, species richness of coral assemblages, commonly the focus of biogeographical studies, showed little variance at large spatial scales. In contrast, species composition and relative abundance showed significant variability at regional scales. Coral, sponge and octocoral assemblages each varied independently across spatial scales. Rugosity and wave exposure were key drivers of the composition and relative abundance of coral and octocoral assemblages.

Main conclusions

Caribbean reef assemblages exhibit considerable biogeographical variability at broad spatial scales (hundreds of kilometres) when more responsive community attributes were used. However, the high degree of variability within sites (kilometres) highlights the relevance of local ecological drivers such as rugosity and wave exposure in structuring assemblages. The high levels of within-site variability that is not explained by environmental variables may suggest a previously unrealized contribution of anthropogenic disturbance operating at local scales throughout the region.

 

Date
2015
Data type
Scientific article
Theme
Research and monitoring
Geographic location
Bonaire
Curacao