BERMUDA
Biodiversity of Coral Reefs
PAGE INDEX
Study Sites Trends Coral Species Goal
Study Sites: (L) Whalebone Bay, (M) Causeway, (R) John Smith's Bay
This study focused on three main sites located on the south shore (John Smith), in Castle Harbor (Causeway), and on the north shore (Whalebone). Castle Harbor is shallow and has a high impact from pollution and has very low flow rates, the north shore had relatively low wave action and the south shore had a recent large natural disturbance event, hurricane Fabian. Two other sites are used for measures of richness and evenness, North Rock and Wells Beach. North Rock had a deeper reef with strong waves, and Wells beach was in Castle harbor, but further from the pollution and the transects used were deeper then those at the Causeway, and in position to receive maximum wave movement. The different study sites represent different environmental stresses on the coral communities, which I hoped to result in differing community structure. The differential physical parameters for the sites are organized in a table below.
Physical Parameters Measured By Site
John Smith's Bay
Whalebone Bay
Castle Harbor: Causeway
North Rock
Castle Harbor: Wells Bay
Water Depth
(4)
.75 - 4.5 m
(2)
.8 - 2 m
(1)
.25 - 1 m
(5)
2.4 - 6 m
(3)
2 - 3.5 m
Wave Action
4
3
1
5
2
Pollution
0
0
1
0
1
Natural Disturbance: Hurricane
1
0
0
0
0
Disease
BBD
Above: Numbers are relative values from smallest or least (0) to strongest or most. Water depth was actually measured at the site.
Typical Trends in Coral Diversity
Coral diversity has been seen to exist in a unimodal pattern, with decreased richness at shallow waters, maximum richness at 15 to 30 meters deep, and lower richness again in deeper waters. The decrease in richness for shallow areas is due to increased nutrient loading and turbidity that actually decreases light availability and increased disturbance due to land based-pollution, beach traffic, and coral disease. The deeper waters, on the other hand, have decreased richness due to decreased light availability and plankton densities the food sources for autotrophic and heterotrophic coral (Karlson and Cornell 2000).
Generally short intervals of disturbance reduce the presence of hard corals and increase the presence of soft corals (Wakeford, Done et al. 2008).
Bermuda is an atoll containing high latitude coral reef (HLR). HLR’s are at more risk then equatorial reefs because they are seeded by tropical reefs but have a poor or erratic connection to them. This leads to low larval recolonization and, consequently, decreased genetic diversity at the reefs. (Miller and Ayre 2008) Why? The corals are victim to the founder effect. The founder effect is a biological phenomenon where a small number of founders, in this case larvae, end up being the genetic source for a large population. The low genetic diversity that ensues leaves the populations susceptible to changing environmental conditions, as they only have a small gene pool in their “survival” genetic tool kit.
Figure 1: Mustard Hill Coral (NOAA); Grooved Brain Coral (Don Demaria) and Common Brain Coral (Joe Seger). Images from the Florida Museum of Natural History
Bermuda has four hard corals that are major contributors to reefs, denoted by Ross Jones as the DMP (Diploria, Montastraea, Porites) species assemblage. These species include Diploria strigosa, D. labyrinthiformis, Montastraea franksi and Porites astreoides. When studying the south shore of Bermuda Jones found that differences in species composition and richness did not stem from absence of these four key species of hard coral (Jones 2008). Only one of my sites is on the south shore, John Smith's beach, but perhaps the hard corals will follow this same pattern. In my research I noted presence of Diploria strigosa (brain coral), Diploria labyrintiformis (double grooved brain coral) and Porites astreoides (Mustard Coral). I only identified Montastaea fanki (star coral) at one site, North Rock, where loose percent cover estimates were taken. Because of the lack of quality I omitted this data from the results.
D. strigosa is dominant in Bermudian reefs, but has been decimated in Castle Harbor due to human impacts (introducing the causeway, dredging and reclaiming land, creating the municipal bulk waste dump) (Flood, Pitt et al. 2005). These human activities in Castle Harbor have been proven to have a negative impact on coral growth, diversity, and health via physical manifestations including increased sedimentation, decrease flow, and increase turbidity (Flood, Pitt et al. 2005), increased heavy metal availability in the water column, and increased oxidative stress (Morgan, Edge et al. 2005). BBD has been recorded and documented in Bermuda, and should also affect the distribution and overall density of hard corals (Jones 2008).
Above: (L) Sea fan (M) Sea rod (R) Corky Sea Finger
Source: coralpedia, Florida Fish and Wildlife website
The soft corals that I successfully identified included Gorgonia vantalina (Sea fan), Plexaurella sp. (Sea rod), Pseudopterogorgia sp. (Sea Plume) and Briareum asbestinum, (Corky Sea Finger). Soft corals prefer areas with increased water movement and heterogeneous lithosphere (Sánchez, Díaz et al. 1997).
Because Bermuda is such a fragile habitat for coral I wanted to do a broad general study of reef health, via richness and differential species composition, comparing sites with different environmental stressors. While many studies regarding coral health have been conducted in this area, mainly by permanent BIOS staff, few take a big picture approach looking at multiple locations along both coasts (North and South) and multiple environmental stressors (Flood, Pitt et al. 2005; Morgan, Edge et al. 2005; Jones 2008). This study mainly compares sites with different flow rates but also measures community differences in response to depth, disease, and disturbance (due to human activity and natural disaster). Finally, coral diseases may have an effect on the distribution of individual corals and overall diversity.
