Rocky Shores

Rocky shores are areas of transition between the marine environment and the terrestrial environment. The littoral zone between the mean high water mark and the mean low water mark is a challenging habitat for both the terrestrial and the marine species. In many coastal areas, rocky shores are formed in areas where the eroding wave is removing material away from the cliff edge (Cremona, 1986). Depending on the composition and the aspect of the rockface, crevices and gullies are formed on the shore. This provides microhabitats such as rock pools, where marine invertebrates from most phyla can live.


The tide results in different parts of the shore being immersed, depending on which point of the tidal curve is being observed. The daily flooding and ebbing of the tide results in a complex and dynamic gradient of environmental conditions, with increase of the vertical height. Zonation is present, where communities are found in bands or zones across the rocky shore. Different organisms are distributed along this gradient depending on their ability to cope with the present abiotic stresses. A major abiotic factor is the period of immersion as this leads to variable temperature, salinity and osmotic conditions- especially challenging for marine organisms! For example, some sub-littoral species of kelp are well adapted to the submerged marine environment and are unable to cope with the desiccation stress in the intertidal zone. Hence, the vertical range of some kelp species does not extend above the sub-littoral.

The species present on the rocky shore are also dependent on the amount of wave action received. In Britain, there is a fixed pattern of zones found at a rocky shore of a particular exposure. The Ballantine Exposure scale grades a particular shore according to the size and location of the species zones present. (See also the “Research” section to read Bill Ballantine’s book on Marine Reserves.) (Figure from Ballantine, 1961)

I spent an amazing summer at Dale Fort field centre (run by the pioneering environmental education charity; the Field Studies Council) where there are rock shores of many different exposures. Black rock is a very sheltered rocky shore in Dale, Pembrokeshire. It has been graded as 6/7 on the Ballantine Exposure scale and found adjacent to the Gann flats (mud flats where there is extensive soft sediment deposition). The area was once renowned for its rocky shores but its diversity has now is affected by regular bait digging. Stay tuned for Part 2 for a survey of Black rock as a sheltered rocky shore and with exciting info about the creatures we find. Meanwhile here are some more maps and photographs of the Dale peninsula and its inhabitants.


Image credits

1) Ballantine, 1961, A biologically-defined exposure scale for the comparative description of rocky shore, Field Studies Journal, FSC Council Publications Vol 1(3) 17.

2) Dale Fort Field Centre

3) Ordnance Survey

4) Ballantine, 1961, A biologically-defined exposure scale for the comparative description of rocky shore, Field Studies Journal, FSC Council Publications Vol 1(3) 17.

5) Ballantine, 1961, A biologically-defined exposure scale for the comparative description of rocky shore, Field Studies Journal, FSC Council Publications Vol 1(3) 17.

6) Dale Fort Field Centre, algaebase.org and Marlin website

References

Ballantine W., 1961, A biologically-defined exposure scale for the comparative description of rocky shore, Field Studies Journal, FSC Council Publications Vol 1(3) 17.

Cremona, 1988, A Field Atlas of the Seashore

Footage from Earth’s deepest place

James Cameron Breaks Solo Dive Record – In a state-of-the-art submersible, National Geographic explorer-in-residence and filmmaker James Cameron reached the deepest point of the Mariana Trench, breaking a world record for the deepest solo dive. James Cameron mentions it as more a desert like place with very fine sediments and small, white, alien-like animals.

Footage from Earth’s deepest place is available on this link on the BBC website and also on the post entitled “James Cameron’s Deep Sea Challenge: a scientific milestone or rich guy’s junket?”on Deep Sea News blog which discusses the significance of the dive.

James Cameron Completes Record-Breaking Mariana Trench Dive

At noon, local time (10 p.m. ET), James Cameron’s “vertical torpedo” sub broke the surface of the western Pacific, carrying the National Geographic explorer and filmmaker back from the Mariana Trench’s Challenger Deep—Earth’s deepest, and perhaps most alien, realm.

The first human to reach the 6.8-mile-deep (11-kilometer-deep) undersea valley solo, Cameron arrived at the bottom with the tech to collect scientific data, specimens, and visions unthinkable in 1960, when the only other manned Challenger Deep dive took place, according to members of the National Geographic expedition.

After a faster-than-expected, roughly 70-minute ascent, Cameron’s sub, bobbing in the open ocean, was spotted by helicopter and would soon be plucked from the Pacific by a research ship’s crane. Earlier, the descent to Challenger Deep had taken 2 hours and 36 minutes.

via National Geographic

A big congratulations to James Cameron and his team.

James Cameron: “It’s a heck of a ride, you’re just screaming down and screaming back up” 

Seamounts of the Azores

Seamounts are common topographic features in the EEZ of the Azores. The archipelago of the Azores is composed of 9 volcanic islands distributed in 3 groups in the north-eastern Atlantic. The size of the Azores EEZ is about 1 000 000 km2, with an average depth of about 3,000 meters. The large occurrence of seamounts is imputable to the volcanic and tectonically active seafloor, typical of this region.

A total of 63 large (height exceeding 1000 meters) and 398 small (height comprised between 200 and 1000 meters) seamounts have been described in the Azorean EEZ, with a density of 3.3 peaks per 1000 km2 and a mean abundance of 0.42 and 0.07 small and large seamounts, respectively, per 1000 km2. Most of the seamounts have deep summits, between 800 to 1500m.

The Azorean seamounts ecosystems are of considerable biological interest and are extremely important also at the economic and, indirectly, social level.

They are hotspots of marine life: shallow seamounts act as aggregating sites for some marine predators.

The fish skipjack (Katsuwonus pelamis), bigeye tuna (Thunnus obesus), the common dolphin (Delphinus delphis) and the Cory’s shearwater (Calonectris diomedea borealis) have been recorded to be more abundant close to some shallow water seamount summits (shallower than 400 m depth).

via Seamounts in the Azores.