Rocky shore monitoring
What are vermetid reefs?
The Israeli Mediterranean coast hosts a unique rocky intertidal habitat: the biogenically-built rocky reefs known as "vermetid reefs". These reefs are horizontal, eolianite (calcareous cemented Pleistocene dune) or limestone platforms with a characteristic biogenic rim at their seaward edge that is formed by gregarious, sedentary vermetid gastropods, Dendropoma petraeum, cemented together by calcareous red algae, and a by a crust on the flat made of shells of another vermetid, Vermetus triqueter. The soft rocks themselves are easily abraded by waves and weather at the back of the reef, and the vermetid shells are thought to reduce the erosion at the level where they live, i.e., mostly at mean sea level, and thus protect the rocky platforms from further abrasion (hence their other name – “abrasion platforms”). This leads to the formation of broad horizontal flats at about mid sea level, and the vermetids are therefore the controlling factor in the development of these platforms; These vermetid reefs are typical only to warm temperate or subtropical seas such as the Levant basin and Bermuda.
Biodiversity and community dynamics:
As part of IOLR's National Monitoring Program, since 2009 we have been monitoring the interannual dynamics of community structure on vermetid reefs at 11 sites along the Israeli shore. In four core sites we also monitor the seasonal dynamics. We do that along transects that run parallel to the shoreline at several zones from the edge of the reef to the back of the reef. Along each transect we assess the percent cover or number of organisms inside quadrats. We use multivariate analysis to look for biogeographic, site and season effects on the structure of the community.
This monitoring program has been supported by the Ministry of Environmental Protection since 2013.
So far, we have discovered evidence for biogeographic patterns, as well as strong seasonality, with winter and spring being the most diverse. Sites vary greatly from each other as well.
One of the most the most troubling findings is the almost complete absence of the reef building (ecosystem engineer) vermetid – Dendropoma petraeum, of which only very few individuals and small patches have been found in the hundreds of transect conducted in the past 6 years. The reasons for its rarity are unknown at this stage. This is not the only species that has disappeared, a large predatory whelk that was once abundant on the Israeli rocky shores – Stramonita haemastoma – has also completely vanished from our shores.
As part of the monitoring project, we also sample monthly several biophysical parameters in our four core sites including: chlorophyll, nutrients, alkalinity, DIC, salinity and temperature. We also deployed small temperature loggers on the rocks underwater (0.5 m depth), on the platform surface (intertidal) and above the high shore (air), that log temperature hourly as well as a pressure sensor to measure water level above the rocky platform in one site.