Beetle burrows on driftwood at Osmington Bay

Patterns in nature: Patterns made by beetle larvae on driftwood at Osmington Bay, Dorset, UK (1)

I saw these curious patterns on a large piece of driftwood washed onto the beach at Osmington Bay. It was partly charred but most noticeable on it were these stripey markings. I thought they had a certain abstract and graphic quality – artistic even.

A closer examination revealed that they were the remains of tunnels created by beetle larvae eating their way along under the bark of the dead tree. Where some bark survived, there were neat bore-holes showing the place that the newly adult insects had emerged.

I am not sure what sort of beetle was responsible for these particular burrows but I’ve read that certain terrestrial Staphylinid Rove Beetles of the Bledus genus rely on sea-soaked timber on the seashore for laying their eggs.

Patterns of beetle larvae tunnels beneath the bark of some driftwood, and emergence holes in the bark, at Osmington Bay, Dorset, UK, part of the Jurassic Coast (2) 

Patterns of beetle larvae tunnels beneath the bark of driftwood at Osmington Bay, Dorset, UK (3)

Pattern of beetle larvae tunnels beneath the bark of driftwood at Osmington Bay, Dorset, UK, part of the Jurassic Coast (4)
 
Pattern of beetle larvae tunnels beneath the bark of driftwood at Osmington Bay, Dorset, UK, part of the Jurassic Coast (5)
 
Driftwood with beetle burrows on the beach at Osmington Bay, Dorset, UK, part of the Jurassic Coast (6) 

Revision of a post first published 19 June 2009

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

Pebbles with holes made by sea creatures

Pebbles with holes: An assortment of pebbles with holes made by sea creatures from the Jurassic Coast World Heritage Site in Dorset, UK (1) 

Pebbles with holes in them are a common occurrence on the beaches along the Jurassic Coast in Dorset – and lots of other U.K. locations as well. Many of these tunnels, burrows or borings have been made by small marine invertebrate animals such as certain species of  bivalved molluscs, polychaete worms, and even sponges. The arrangement of pebbles shown in the photograph above illustrates a selection of the different kinds of holes created by these animals in soft rocks.

In this post I am just going to talk briefly about the larger tunnels which tend to be about a centimeter or more in diameter. These have been excavated by rock-boring bivalve molluscs. There are several types whose habits result in these borings and it is not easy to say which species has made which tunnel from the shape and size of the holes alone. Fortunately, the shells of these creatures often remain in the burrows. The appearance of the shells is diagnostic for each species. Unfortunately, the shells of some of these bivalves are both surprisingly fragile and wedged securely in the burrow so that they are difficult to extract.

The most commonly occurring rock-boring molluscs are the Piddocks and some other related species. From the Pholadidae family, for example, these include the Common Piddock Pholas dactylus Linnaeus and the White Piddock Barnea candida (Linnaeus). From the Hiatellidae family, these include the Wrinkled Rock-borer Hiatella arctica (Linnaeus). And from the Gastrochaenidae, the Flask Shell Gastrochaena dubia (Pennant).

Pebble with holes: Cobble-size stone with large bore holes made by bivalved molluscs called piddocks on the beach at Charmouth, Dorset, UK - part of the Jurassic Coast (2) 

The softer rocks into which these bivalves bore are generally low on the shore and under water most of the time. When pieces of this rock break away, the stone becomes more rounded and worn and ends up as a pebble on the beach – like the one above which was seen at Charmouth in Dorset.

Pebble with holes close-up: Detail of large piddock bore holes and smaller worm burrows in large stone on the seashore at Charmouth, Dorset, UK - part of the Jurassic Coast (3) 

The photograph below shows a flat platform of soft Blue Lias shale extending seawards at Charmouth. If you look closely at the near-vertical edge of the rock where it is lapped by the water, you may be able to see that the shale has many perforations caused by these rock-boring molluscs.

Rock with holes made by bivalve molluscs: A seaweed covered platform of Blue Lias shale with piddock borings visible along the water's edge at Charmouth, Dorset, UK - part of the Jurassic Coast (4) 

Below is a closer view of the seaweed free edge of the rock platform with the piddock holes.

Rock with animal burrows: The vertical edge of a shale platform showing piddock burrows at Charmouth, Dorset, UK - part of the Jurassic Coast (5) 

The next picture shows empty shells still in situ in the burrows. In future posts I will illustrate the actual shells of these rock-boring molluscs and will describe something of their life in such a unique habitat. I will also discuss at a later date the other smaller types of rock-borings made by worms and sponges; and show how they also colonise and leave physical evidence of their presence on mollusc shells. When this evidence is found in shells recovered from archaeological excavations, it provides clues to the environment that was being exploited for its marine resources by people in the past.

Rock with holes containing seashells: Piddock burrows in Blue Lias shale, some showing the two empty white shells of the bivalved mollusc that made the hole, at Charmouth, Dorset, UK - part of the Jurassic Coast (6) 

Pebble with holes bored by bivalved molluscs - from the Jurassic Coast (7)

Revision of a post first published 4 October 2009

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

Driftwood with holes made by Gribbles & Shipworms

Driftwood with infestation damage: Small piece of water-logged driftwood with holes made by Gribbles and Shipworms from the strandine at Rhossili Bay, Gower, South Wales (1) 

The photographs in this post show a small piece of water-logged driftwood about 30 cm long and riddled with holes and tunnels caused by two different types of wood-boring sea creatures. The larger borings are about 1 cm in diameter and many are lined with a smooth calcareous material that has become stained through burial in the beach sediments. These larger borings may be familiar to beachcombers as being made by Shipworms, Teredo navalis Linnaeus. I have talked about these worms – which are not really worms but bivalved molluscs – elsewhere in the blog.

Less familiar, are the much smaller holes and burrows in this piece of soft wood. These have been made by Gribbles, Limnoria lignorum (Rathke). Gribbles are very small marine isopod crustaceans. Crustacea is the major grouping  that includes the crabs, prawns, and sandhopper types of animal. Isopods are a bit like the terrestrial woodlice that you see in gardens – they have an ‘armoured’ body with lots of limbs and joints; and their body is flattened from top to bottom – compared with amphipods such as sandhoppers in which the body is flattened from side to side. Gribbles are very small and their length rarely exceeds 3.5mm.

Shipworms can burrow into hard wood but Gribbles prefer wet, cool and soft wood, like the bases of exposed pilings on piers and jetties. The pictures here show the infestation damage caused by both Gribbles and Shipworms that leads to the destruction and disintegration of the timber.

Gribble holes in driftwood: Detail of small holes and burrows made by marine isopod crustaceans called Gribbles, Limnoria lignorum (Rathke), in a piece of driftwood from the strandline at Rhossili Bay, Gower, South Wales (2) 

Driftwood with infestation damage: Close-up of hole and burrow infestation damage made by marine isopod crustaceans called Gribbles, Limnoria lignorum (Rathke), in a piece of driftwood from the strandline at Rhossili Bay, Gower, South Wales (3) 

Damage by Limnoria lignorum (Rathke): Damage caused by marine isopod crustaceans called Gribbles, Limnoria lignorum (Rathke), and Shipworm molluscs Teredo navalis Linnaeus, in a piece of driftwood from the strandline on Gower, South Wales (4) 

Comparison of Shipworm and Gribble damage: Detail of infestation damage in driftwood - comparing the generally distributed small burrows, caused by Gribbles, with much larger tunnels bored by Shipworm, from Rhossili, Gower, South Wales (5) 

Driftwood on the beach: Small piece of driftwood with holes made by Gribbles and Shipworms in situ as found on the sandy strandline at Rhossili, Gower, South Wales (6)

Driftwood damaged by sea creatures: Detail of infestation damage from wood-boring sea creatures: small tunnels by Gribbles and large tunnels and perforations by Shipworms. Driftwood from Rhossili, Gower, South Wales (7) 

 Revision of a post first published 29 May 2010

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

Benjamin & the pebble full of holes

Benjamin is a young fossil hunter. I met him with his grandparents on Monmouth Beach at Lyme Regis yesterday. He had already found several small ammonite fossils. He had found a bigger ammonite made of fool’s gold but it got broken. It’s really tricky trying to remove fossils from their stoney bed. When Benjamin discovered a rounded pebble riddled with holes of different sizes and shapes, he wondered if it was a fossil too.

I explained that these holes are made by various kinds of seashore creatures like sponges, marine worms that live in mud tubes, and certain seashells. As far as I could tell, the burrows and borings were recent and not fossil. I have written about these creatures and the homes they make for themselves in stones in earlier postings on the blog. So, if you want to find out more and look at lots more photographs of stones and shells with holes, Benjamin, you can click on the following links:

Pebbles with holes made by tube worms 

Pebbles with holes made by sea creatures

Pebbles with holes made by boring sponges

Shells with holes made by boring bivalves

Sponge borings in Flat Oyster Shells 

COPYRIGHT JESSICA WINDER 2012

All Rights reserved

Flat Oyster shells with Polydora ciliata burrows

P1160683aBlog1 Detail of burrows made by the marine polychaete worm Polydora ciliata in a Flat Oyster shell from Whiteford Sands, Gower, South Wales (1) 

Much of the damage sustained by Flat Oyster shells (Ostrea edulis Linnaeus) in life or after, in recent or archaeological specimens, is the result of infestation by worms. Mudtube-dwelling marine polychaete worms such as Polydora ciliata (Johnston) are adept at utilising the nooks and crannies in shells, as well as in rocks and encrusting calcareous algae, for shelter.

The Polydora worms belong to the Family Spionidae which is part of the Class Polychaeta – the Bristleworms. All the species in this group make a u-shaped tube from small particles – usually of mud. The worm insinuates itself and its tube into small crevices in such a way that the two open ends of the u-shape tube open outwards to the seawater. In life, the worm sticks out two long palps which it agitates enthusiastically.

Acidic metabolic by-products from the worm gradually dissolve the shell or stone in which the worm is sheltering. In time this process etches a u-shaped burrow in the hard substrate. These small burrows can be found anywhere over the external surface of the living oyster shell. The presence of the worms and their tunnels does not usually affect the health of the oyster but they can disfigure the shell. In trade terms this means that the oyster cannot be served in its shell in restaurants.

There is a lot more to say on the subject of worm tubes and oysters but I’ll leave that to another day.

P1160682aBlog2 Close-up left valve external surface of a Flat Oyster shell showing damage by the marine worm Polydora ciliata, from the beach at Whiteford Sands, Gower, South Wales (2) 

P1160753aBlog3 View of the entire left valve external surface of a burial-stained Flat Oyster shell with Polydora ciliata borings - from the shore at Whiteford Sands, Gower, South Wales (3)

P1140002aBlog4 Large, thick, old, and stained Flat Oyster shell with moderate marine worm damage - as first seen on Whiteford Sands, Gower, South Wales (4)

P1130999Blog5 Flat Oyster shell (Ostrea edulis L.) in context with a scatter of cockle and mussel shells on the sand at Whiteford, Gower, South Wales (5)

COPYRIGHT JESSICA WINDER 2011

All rights reserved