FCs are pretty widespread phenomena but they have attracted interest only in the last 15-20 years. Then, my research begin where the few information about them stop.

In order to have a broad understanding of the role of HC in ecology, I am currently working in different marine environments (soft-bottom estuarines and rocky shores), with different 1st habitat formers (seaweeds, seageasses, invertebrates) and different 2nd habitat formers and clients (epiphytes, invertebrates).

a and b reppresent two typical situations in soft-bottom estuarines. Due to lack of hard substrates, seaweeds can only rely in molluscs to settle (a) or seagrasses to be entagled (b) becoming 2nd habitat former. In rocky shores, a similar situation can be explained through epiphytes (c) but lack of substrate is not a problem anymore unless considering the competition.

What among seaweeds?

Even if Facilitation Cascade seems to be simple concept to understand it is in real much more complicate than the expected… and even if it looks very complex, it is in real much easier than the expected…

After a quick explanation about my research, especially when I talk about hundreds or thousands of invertebrates among seaweeds, people usually look at me with that typical face like wondering “What is he talking about? Where does he see all these organisms?“.

Unfortunately, our mind (scientific and not) has always been pretty restricted to allow us to give importance to what is invisible, small… (I remind the “conquest of the invisible” by Pasteur) neglecting a huge amount of species, interactions, functions, biological processes, etc… in a single word… “information“.

It seems to be hard accepting the idea that a little piece of seaweed can host a huge amount of species. That is why in this short clip I try to visually demonstrate what happen when we wash a little piece of seaweed collected from a rocky shore.
The seaweed is a Cystophora scalaris, one of the species I am working most with, and it is a very common canopy-forming seaweed in the rocky shores of New Zealand (Agardh used to relate it to Cystopseira sp. and Sargassum sp. from Mediterranean Sea because of their common role as facilitators in coastal habitats).

The majority of little dots at the bottom of the box are gastropods… but there are still hundreds of invertebrates pretty invisible to the naked eye in a box like this, like amphipods and copepods. The pictures show a clearer view of the epifauna more accurately sieved.


In the following clip I show what happen when we compare the amount of invertebrates in two pieces of the same seaweed species. The first one is a piece of C. scalaris while the second one is a piece of C. scalaris with attached, during a recolonization experiment, a little piece of a natural epiphyte of Cystophora, Jania micrarthrodia.

The difference in the amount of invertebrates is pretty clear. Even if I manually attached the epiphyte, Jania is a natural epiphyte of Cystophora, so what is experimentally happening here is just the emulation of a natural condition. But there is something more…
After deattaching Jania from Cystophora, I can rinse the epiphyte more accurately…

Obviously this quick clip does not want to have any scientific relevance and it is mean to give a very rough idea of what happen when an epiphyte increases the complexity of a seaweed structure and architecture with full advantage for the associated epifaunal assemblage.
Several are the factors here not included: the different size of the seaweed, the rest of smaller and “invisible” invertebrates for naked eye, the accuracy of the washing, etc.
Anyway, a more true view of the invertebrates can be offered by the next pictures, after an accurate sieving.

The epifauna I am considering has usually a size range between 250 μm and 2 mm and the majority of these are amphipods, copepods and gastropods.
In my PhD I am focus on the whole community of invertebrates. Nonetheless my primary focus are gastropods since they can be considered very reppresentative of the epifauna community for my purposes:
– they are slow-moving invertebrates compared with amphipods, copepods or crabs, so they can be collected easly without any virtual lack of information;
– they are relatively easy to identify, at least with a categorization based on morpho-species;
– they reppresent a very high proportion of the community, statistically strong, and a very diverse category of invertebrates: in my studies, gastropods reppresent more and less the 60-70% of the whole biodiversity.


Artificial reefs

In the last 15-20 years Artificial Reefs (hereafter ARs) have attracted a lot of interest in research as well as in recreational fishing and diving. Unfortunately in this case, science and sports meet when the negative effects of human activities (recreational or commercial) affect benthic communities.

Defining univocally an AR can be pretty hard since different countries have different definitions, depending also on the different use they make of them. The London Convention and Protocol/UNEP for the “Guidelines for the Placement of Artificial Reefs“, in 2009, defined an AR as:

…a submerged structure deliberately constructed or placed on the seabed to emulate some functions of a natural reef such as protecting, regenerating, concentrating, and/or enhancing populations of living marine resources.
Objectives of an artificial reef may also include protection, restoration and regeneration of aquatic habitats, and the promotion of research, recreational opportunities, and educational use of the area.
The term does not include submerged structures deliberately placed to perform functions not related to those of a natural reef – such as breakwaters, mooring, cables, pipelines, marine research devices or platforms – even if they incidentally imitate some functions of a natural reef”.

This clear definition is also inherent to the multiple uses of ARs for scientific and recreational purposes.

Several structures, specifically created or rejections, have been used as ARs:

– oil platforms;
– submarines;
– planes;
– shipwrecks;
– and also concrete blocks, tires, etc.

AR colonizationNow… since ARs are structures susceptible to fouling followed by real assemblages (the gif on the right shows a colonization process of an AR), probably the main term coming to mind at this stage is probably “rehabilitation”: it can be seen as a condition for which a specific habitat can be replaced by a better one.
A valid alternative term can be “enhancement”… of biomass, biodiversity, physical parameters, etc. It looks like the majority of ARs has been placed for this specific purpose but the problem is that it does not consider any previous disturbance due to its placement (voluntary or not). In addition, the “enhancement” condition has mainly been used to increase fish assemblages for commercial and recreational fishing, so it is supposed to be adopted mostly in fisheries biology.
Both terms can anyway give a good idea of the ecological relevance of ARs.

Artificial reefs (2)At this stage, people reading this post could wonder why I am using the term assemblage instead than community. This bring up another important point of view we should see ARs from. In most cases, they tend to promote a different biota than natural substrata with the result of a co-existence of benthic organisms. But community and assemblages are not synonymous: while a community is an extremely high level of ecological organization originated by species interactions, an assemblage is a simple co-existence of species living together only for a common benefit.

This common benefit is the main reason for which ARs are ecologically important. They provide and enhance:
– availability of food and feeding efficiency;
– shelter from predation;
– settlement of larvae;
– buffering of physical stress;
– substratum availability, complexity and heterogeneity;
– for scientific community, they also reppresent excellent models for colonization and successional studies.

The substratum availability is one of the most important advantage of placing an AR. In hard-bottom environments, ARs can simply increase the space available for settlement but in soft-bottoms they can create a completely new habitat providing an hard substrate. And that is why sometimes their role can be emphasized to “habitat creation”.

This is the case of Zenobia shipwreck.