The secret life of the reef: the roles of benthos and zooplankton.
Chapter One
The marine reef aquarium is one of the most fascinating and complex ecosystems to recreate and maintain. To be successful, it is essential to understand in depth the ecological and biological dynamics that regulate this delicate environment.
The challenge is to recreate the optimal biotic and abiotic conditions for marine life, including metabolic balances, biodiversity, water chemistry and light . Any sudden changes can cause irreparable damage to the organisms that inhabit it.
This is why it is essential to understand the ecological role of benthic fauna and zooplankton , and how they contribute to the balance of the aquarium .
Benthos and Zooplankton: Pillars of the Ecosystem Microfauna , zooplankton and benthos play vital roles in marine aquariums.
They contribute to nutrient cycling through decomposition of detritus, bioturbation, and at the same time serve as a food source for a multitude of different organisms, including fish and corals.
Their presence and their activity as detritivores/decomposers are fundamental for the balance and stability of the ecosystem.
Through their feeding activity and degradation of organic debris , they indirectly help to maintain low levels of nutrients such as nitrate and phosphate, preventing the proliferation of unwanted algae .
Benthic and zooplankton biodiversity is crucial to a stable ecosystem. Each species plays a unique role, contributing to the decomposition of detritus, the fight against invasive algae and the maintenance of the overall balance.
A good variety of species present ensures that the vital functions of the ecosystem are maintained and that harmful imbalances are avoided.
But what specifically are we talking about when we use the terms microfauna , zooplankton or benthos ?
In marine biology, the terms benthos, zooplankton and microfauna describe categories of aquatic organisms, each with specific dimensions, characteristics and ecological roles. This type of classification has however created a slight confusion in our field, with the use of synonyms or ambiguous definitions, before proceeding I would like to summarize and simplify: The suffix -benthos indicates that we are talking about organisms (microfauna, meiofauna or benthic macrofauna) strictly linked to the seabed and the substrates .
We will therefore talk about macrobenthos , meiobenthos and microbenthos .
The suffix -plankton instead indicates that we are talking about organisms that live in suspension in the water column , either permanently or just for a phase of their life.
Similarly we can divide them into macroplankton , meioplankton and microplankton .
Let's talk about Benthos
The benthos is made up of the set of organisms that live in close relationship with the bottom of aquatic environments , both marine and freshwater. The number of ascribed animal species largely exceeds one million.
These organisms can be fixed or mobile, and their distribution is influenced by various environmental factors such as depth, nature of the substrate, temperature, salinity and oxygen availability.
They can be classified according to their size into:
Macrobenthos: Probably the most interesting in our field, visible to the naked eye, by definition larger than 1.0 mm.
This class includes various species such as molluscs, starfish, crustaceans, corals, echinoderms and polychaetes. They are the true pillars of the stability of our systems.
Meiobenthos: Organisms ranging in size from 0.063 mm to 1.0 mm. They mainly include small crustaceans such as ostracods and copepods, nematodes and foraminifera
Microbenthos: Organisms smaller than 63 microns, mainly composed of protozoa and microorganisms.
A further classification can be made by segmenting them according to the trophic level and the ecological niche occupied. According to their feeding habits they can therefore be divided into: Detritivores (fragmentators, gatherers, collectors, depending on the size of the particles consumed), filter feeders , grazers/scrapers (“grazers”) and finally predators .
Benthic habitats vary greatly, including sandy, rocky, muddy bottoms and coral environments. Each type of bottom hosts different benthic communities, adapted to specific environmental conditions thanks to particular morpho-functional adaptations.
Benthic organisms play fundamental ecological roles and are important both in the marine food chain , serving as food for many fish and other larger organisms, and in the process of decomposition , contributing to nutrient cycling and sediment disposal.
The benthos also strongly influences the chemistry and physical structure of the seafloor.
And zooplankton?
Zooplankton is a large and heterogeneous group of animal organisms of different sizes that live in suspension in the water column .
This category includes a wide range of species, each with distinct ecological characteristics and roles.
Unlike benthic organisms that live in close contact with substrates, zooplankton spend their existence (or part of it) in the water column.
Its mobility is influenced by ocean currents, and its distribution varies based on factors such as temperature, water salinity and the presence of food or predators.
Zooplankton can also be divided into different categories, both based on size and life stages or feeding habits.
Although there are particular categories such as megaplankton or femtoplankton, those of greatest interest in our sector are again:
Macrozooplankton: includes larger organisms, such as some crustaceans, ranging in size from 2 to 20 cm.
Mesozooplankton: this group includes organisms whose size varies from 200 microns to 2 cm, the majority of zooplankton typical of our hobby are included here.
These include: copepods, mysids, amphipods, larvae of crustaceans, molluscs and echinoderms, etc.
Microzooplankton: these are organisms of small size (20-200 microns) of which the majority are invisible to the naked eye. This category includes various ciliated and flagellated protozoa, some copepods (particularly in the juvenile stages), rotifers, larvae and gametes of numerous phyla of benthic organisms.
Another possible categorization is that linked to the life cycle: it is defined as holoplankton when the organisms spend their entire life in the water column and meroplankton when it is only one phase, generally the larval one .
As regards their feeding habits, we can divide them into phytoplanktonivores, detritivores, filter feeders and finally predators.
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