Kelp forests are mysterious underwater regions with a high kelp density, which covers many of the world’s long coastlines. They are known as one of the most dynamic and productive ecosystems on Earth. Smaller regions of anchored kelp are kelp beds. Kelp forests are present worldwide throughout polar and temperate coastal oceans.
For those who don’t know, the term ‘kelp’ refers to marine algae.
The kelp forest ecosystem’s architecture is based on its inert physical structure, which determines the affiliated species that define its community structure. Structurally, the ecosystem comprises three guilds of kelp and two guilds held by other algae.
- The well-known canopy kelps include the most prominent species and often frame floating canopies that extend to the sea surface (e.g., Alaria and Macrocystis).
- Stipitate kelps usually extend a few meters above the seafloor and grow in thick aggregations (e.g., Ecklonia and Eisenia).
- Prostrate kelps rest near and along the seafloor (example, Laminaria).
- The benthic assembly is constituted of other algal species example, foliose and filamentous functional groups, articulated corallines) and sessile animals along the ocean bed.
- Encrusting coralline algae often extensively and directly cover geologic substrate.
Model studies in the kelp forest environment have principally focused on trophic interactions (the bonds between food webs and the organisms), especially the knowledge and top-down trophic processes. Bottom-up processes are normally driven by the abiotic conditions needed for primary producers to grow, such as nutrients and availability of light, and the following transfer of energy to consumers at other trophic levels. For instance, kelp’s occurrence is usually correlated with the oceanographic upwelling region, which provides surprisingly high concentrations of nutrients to the regional environment.
This allows kelp to support herbivores and grow, which in turn support the feeders at higher trophic levels. By contrast, predators limit the biomass of species at lower trophic levels through consumption in top-down processes. In the lack of predation, these lower-level species thrive because resources that promote their energetic requirements are not restricted.
In an example from Alaskan kelp forests, sea otters check populations of herbivorous sea urchins through heavy predation. When sea otters are eliminated from the ecosystem (for instance, by human exploitation), urchin populations are vividly released from predatory control and develop dramatically. This leads to enhanced herbivore pressure on regional kelp stands. The decay of the kelp itself results in the physical ecosystem structure loss and, subsequently, the decline of other species associated with this habitat.
In an Alaskan kelp forest environment, sea otters are the keystone species that mediate this trophic watercourse. In California, kelp forests endure without sea otters, and the control of herbivorous urchins is mediated by a suite of predators, including large fishes and lobsters.
The effect of eliminating one predatory species in this system differs from Alaska because excess exists in the trophic levels, and other predatory species can continue to monitor urchins. However, removing different predators can dramatically release urchins from predator pressure and let the system follow trajectories towards kelp forest degradation.
Similar examples exist in Australia, Nova Scotia, Chile, and South Africa.
The relative significance of top-down versus bottom-up control in kelp forest ecosystems and trophic interactions’ strengths continue to be the subject of substantial scientific investigation.