Marine worms = worms living in a marine environment
They belong to many different groups, including: Annelida (segmented worms with both tube worms and bristle worms), Platyhelminthes(flatworms), Nematoda(roundworms), Nemertea(ribbon worms), Sipunculid worms (peanut worms), Echiura (Spoon Worms and Innkeeper Worms), Chaetognatha(arrow worms), Hemichordata(acorn worms), and Phoronida(horseshoe worms).
All those marine worms are very different. The only things that they have in common might be: their global shape and the fact that they are called “worms”.
Here, I am gonna focus on my favourite group which is Annelids, segmented worms, and more specifically on Polychaetes.
Polychaetes = worms with lots of bristles
QU'EST-CE QU'UN POLYCHAÈTE?
QU'EST-CE QU'UN POLYCHAÈTE?
Vers marins de l’ordre Polychaeta, qui comprend les formes errantes (en mouvement) et tubicoles (principalement sédentaires).Ils ont sur la plupart des segments une paire d’appendices charnus et semblables à des pattes portant de nombreux poils (chaetae).
Polychètes = ont de nombreux (poly) poils (chaetae)
Biodiversity and habitats
Lots of species
The group of polychaete worms shows the greatest diversity of annelid worms. Majority of the 10,000 species of polychaetes are marine and exhibit a variety of habitats for which they show physical adaptations.
At first, one could think that they all look the same. It is exactly what I thought before taking a closer look at them. Now, I can tell you that they all are VERY different depending on their family! The shape of their head can vary a lot and give information on the way they feed.
Can you see differences between worms on the pictures below?
Those worms are coming from Alabama (USA).
Diversity in living habitats
Polychaetes are widespread: they can be found in all oceans around the world, at all temperatures and depths.
Marine worms tend to live either under boulders of rocky ocean floors, among algaes, in the mud, in sandy mud, or in sand.
Some polychaetes build tubes in which to live. Some species tolerate the extremely high temperatures near hydrothermal vents and some others live in the coldest ocean temperatures of the abyssal plain. They can be found from the seashore to the deepest depths of the ocean!
For instance, the polychaete above has been discovered in 2008 in a mud volcano, at a depth of 2,200 m. Note its striking resemblance to Bob Marley! That explains why Portuguese researchers who discovered it called it: Bobmarleya gadensis.
Important roles in ecosystems
Play a role in sediments
Polychaetes live in or on the sediment. They influence the marine nutrient cycling by coupling biological and physicochemical cycles of both water and sediment.
By the way they are moving in the sediment (through foraging and burrowing activities), they enhance oxygen penetration in the sediment, promote remineralization of organic matter and influence other biogeochemical processes.
Provide food for fish
In addition to forming a link between the water column and the sediments, marine worms also form an important link in the marine food web.
Many of them filter particles from the water or graze on and in the sediment, while others are predators and scavengers.
Furthermore, many marine predators such as fish feed on those worms.
Polychaetes can act as ecosystem engineers with bioconstructions. This is the case of polychaetes living in a tube (Lanice conchilega) or reef polychaetes (Sabellaria alveolata, Phragmatopoma caudata).
An ecosystem engineer is any organism that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on ecosystems by impacting other species and increasing the habitat complexity. As a result, ecosystem engineers are important for maintaining the health and stability of the environment they are living in.
Since all organisms impact the environment they live in one way or another, it has been proposed that the term “ecosystem engineers” be used only for keystone species whose behavior very strongly affects other organisms.
Sabellaria alveolata reefs
The tubes formed by Sabellaria alveolata form large reef-like hummocks, which serve to further stabilize the boulders.
Seashore Lanice conchilega reef
Lanice conchilega have the capacity to affect the stability and sedimentation within the habitat.
Phragmatopoma caudata reef
The worms remain in their tubes and are almost never seen. At low tide, when above the water, they close the entrance to their tubes and when submerged, they extend their tentacles out of the tube to catch food particles.
Polychaetes are interesting
A bioindicator is any species or group of species whose function, population, or status can reveal the qualitative status of the environment. Bioindicators can tell us about the cumulative effects of different pollutants in the ecosystem and about how long a problem may have been present.
... thanks to their diversity and abundance
Those marine worms represent the most abundant group in communities living in marine sediments.
In terms of species number but also of abundance of individuals.
... thanks to their short life cycle
Life expectancy of many polychaete species is counted in days or weeks and they have high reproduction rates.
This means that sensitive species can disappear quite fast after an environmental change (e.g. pollution). This lead to a rapid response to any change in the population.
... thanks to their lifestyle
They have a sedentary lifestyle.
Their relative immobility implies chronic exposure to any toxic substance. This means that they would not be able to avoid environmental disturbances.
Thus, any long-term change should be reflected at the level of the communities of Polychetes.
... thanks to the way they feed
Exposure to substances present in the water column is maximum in organisms filtering water.Other marine worms are feeding on top of the sediment so they have close contact with the sediment.
Both feeding types are exposed to pollutants present either in the sediment or in the water.
... thanks to their small body size
Their small size makes biomonitoring easier to implement. Biomonitoring correspond to monitoring based on the use of bioindicators, which provides information on the state of the environment as well as on the influence of the accumulation of pollutanton organisms and ecosystems. This small size also allows laboratory experiments to assess responses to environmental changes under controlled conditions.
Marine worms are interesting organisms to focus on for the analysis of the health of marine communities living at the bottom of the water column. Polychaetes huge biodiversity allows to estimate the quality of the environment.
Polychaetes represent a biological indicator of biodiversity, organic enrichment, heavy metal pollution, and organic contaminants.
Marine worms are amazing because:
They have a huge biodiversity
They can be found in all oceans around the world
They have an important role in sediments through bioturbation
They provide food for fish
They can be keystone species and ecosystem engineers
They are interesting bioindicators to estimate the quality of the environment