Digging for lug

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Digging for lug

Post by allthegearnoidea on Thu May 08, 2008 12:59 am

Two Species of Lugworm
know your quarry



The Lugworm, Arenicola marina, is extremely common around the British coastline, with most books on seashore life describing these animals in great detail. Sea anglers however, have known for many years that Lugworms do not all behave in the same way, they look different, have different habitats and casts and certainly appears to be more than a single species. This was proved correct, when, in 1993, two researchers from Swansea University reclassified Arenicola to include a new species known as Arenicola defodiens.



In addition to a number of genetic differences, their arguments to support this additional species were morphological, environmental and physiological. Amongst anglers, these species are better known as Black Lug A. defodiens and Blow Lug A. marina. Both species are common along areas of the Sussex coastline.

The Lugworm
Differences
So, what are the differences between these two species? Using information from the findings the following should provide an insight into the differing features and ecology of these two species.
The cast, which is the coil of defecated material lying on the sand surface, and frequently seen at low tide, can usually identify the species. Black Lug usually have a neat, round coiled cast, often like a Catherine wheel, while the Blow Lug cast is generally an untidy pile! Many Blow Lug casts may also have an adjacent saucer shaped feeding depression, created from their feeding method while resident in their ‘U’ shaped burrow.


    Blow Lug cast



    Black Lug cast
Burrows
The burrow of Black Lug appears to be vertical and will often descend to depths of up to a metre although most usually the worm can be found at depths between 40-70cm, which must make it the deepest of intertidal burrowers. I have rarely found Blow Lug deeper than 40 cm. Their different burrow depths and alignment could imply different feeding methods, as the method employed by Blow Lug of loosening soil at its head, thus transporting bacterial growth and organic matter from the surface area, would not appear to be copied by Black Lug.


    Blow Lug in burrow
Aquaria
My experiments in aquaria have been unable to keep Black Lug alive in sand for more than 13 days and in that time they produced no casts (regardless of organic matter being placed in the water or on the sand surface). However, Blow Lug would start laying casts within 8 hours and continued for periods of up to 2 months before being released back to their capture area, with no fatalities whatsoever.
Habitats
When both species are found together on the same stretch of shoreline, there is often a suggestion of zonation. Black Lug are usually found lower down the intertidal area, sometimes only visible on the larger spring low tides, while Blow Lug are found in greater numbers higher up the beach, and can often be observed on the smallest neap tides at low water.
Identification
Black Lug is the larger species. I have collected a number in the past between 30 and 40 cm in length, although the average size is between 20 and 30 cm. Blow Lug average between 15 and 20 cm except in the nursery areas and rarely exceed 25 cm. Interestingly, immature Black Lug have not knowingly been found.



    Morphological pattern showing additional segment in Blow Lug
Nursery beds containing immature Blow Lug, identified by the tiniest of casts usually grouped together, are common in the latter part of the summer after larval settlement. Even on a worm no longer than 10 mm, species identification can be determined with the aid of a microscope by the presence of an additional ‘segment’ (see drawing), between the second and third notopodium. This difference is obvious in larger worms and can be seen with the naked eye. Another morphological difference is the structure of the gills, which does need the use of a microscope and requires a bit of practice!

It may be that immature Black Lug can be found below the low tide mark, as it is known that adults extend well into the sub-littoral. Clearly there is further research to be done. A further difference between these two species can be observed during handling. Black Lug usually eviscerates but Blow Lug does not. Again, the reasons for this are unknown, but may be a reaction to stress or a defensive action similar to that exhibited by some sea cucumbers.
From my own studies and building on research from the original study by Cadman and Nelson-Smith, there is a suggestion that Black Lug could be regarded as a substrate specialist. Ranges of salinities and average sand grain size appear to be narrower for Black Lug and observations additionally suggest that they are more likely to be found on the more exposed beaches, and consequently those with less detrital deposits.

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Re: Digging for lug

Post by allthegearnoidea on Thu May 08, 2008 1:02 am


Ragworm
Nereis diversicolor

Ragworms are abundant in estuaries and muddy shorelines, where they live in burrows in the substrate.
Life span
They can live for 1-3 years depending on how fast they reach maturity and spawn.
Statistics
Adults may reach 6-12cm (2-4in) in length and consist of between 90-120 segments.
Physical Description
Ragworms have long, flattened bodies, consisting of many segments each with a pair of parapods, or swimming legs. These parapods are covered with bristles called chaete and are used for crawling and swimming. At the head end, they have a toothed proboscis, four eyes, and two pairs of antennae.
They are variable in colour, typically appearing reddish brown but turning quite green during the spawning season.
Distribution
They are common throughout north-west Europe, along Atlantic coasts to the Mediterranean.
Habitat
Abundant in estuaries and sandy or muddy beaches. They inhabit U- or J-shaped burrows in the sand that may stretch for around 20cm (8 inches) depth.
Diet
The ragworm is both an omnivorous scavenger and efficient predator. When scavenging, it feeds on mud, detritus, phytoplankton and plankton. It is also a active predator, rapidly shooting out its powerful jaws to catch other soft-bodied invertebrates. This species also feeds on phytoplankton by spinning a net at the top of the burrow. By undulating it's body within its burrow it causes a water current which carries phytoplankton into the sticky net. After a while it consumes the net and the particles, then spins another.
Behaviour
The feeding behaviour of the ragworm depends on phytoplankton densities. When densities are high, it uses its net to catch prey. When densities are low, it scavenges or actively hunts prey.
Ragworms are tuned to the lunar phase, reproducing in synchrony at distinct times in the moon phase (e.g. new or full moon, depending on the locality).
Reproduction
Spawning is triggered by a rise in temperature during spring. Females brood eggs within their bodies. As the eggs develop, the female's body becomes brittle and ultimately ruptures, releasing the eggs into the burrow. Males are drawn to the burrow by pheromones and discharge their sperm around the burrow entrance. The female draws this sperm down into the burrow using water currents where they fertilise the eggs. After spawning, both males and female ragworms die.
Conservation status
Rag worms are very abundant. They are important prey for wading birds and are the main prey of at least 15 different bird species. They are also used by anglers as bait for fishing. They are not considered to be threatened.







Last edited by Administrator on Fri Jul 03, 2009 4:40 am; edited 1 time in total

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Re: Digging for lug

Post by fishypaul on Thu May 08, 2008 11:51 am

wonderful info there boss
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Re: Digging for lug

Post by brockster on Sat Aug 16, 2008 12:40 am

a great read !

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Re: Digging for lug

Post by paddy on Fri Jan 02, 2009 12:28 pm

,,nice one,,
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