Anthropogenic Effects on Kelp Forests

Network-level containment of single-species bioengineering

10.1101/2021.07.05.451200 ◽

2021 ◽

Author(s):

Victor Maull ◽

Ricard Sole

Keyword(s):

Single Species ◽

Ecological Systems ◽

Dynamic Responses ◽

Interaction Matrix ◽

Anthropogenic Effects ◽

Kelp Forests ◽

Tipping Points ◽

Resident Species ◽

Catastrophic Shifts ◽

High Diversity

Ecological systems are facing major diversity losses in this century due to Anthropogenic effects. Habitat loss, overexploitation of resources, invasion and pollution are rapidly jeopardising the survival of whole communities, as revealed by pronounced population losses. Moreover, the potential of future tipping points further complicate their survival and change our perspective of risk. It has been recently suggested that a potential approach to flatten the curve of species extinction and prevent catastrophic shifts would involve the engineering of one selected species within one of these communities, aiming at helping the maintenance of key conditions compatible with high diversity. Such possibility has started to become part of potential intervention scenarios to preserve coral reefs, kelp forests or soil microbiomes in drylands. Despite its potential, very little is known about the actual dynamic responses of complex ecological networks to the introduction of a synthetic strains derived from a resident species. In this paper we address this problem by modelling the response of a competitive community to the addition of a synthetic strain derived from a member of a stable ecosystem. We show that the community interaction matrix largely limits the spread of the engineered strain, thus suggesting that species diversity acts as an ecological firewall. Implications for future restoration and terraformation strategies are discussed.

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Habitat fragmentation causes collapse of kelp recruitment

Marine Ecology Progress Series ◽

10.3354/meps13422 ◽

2020 ◽

Vol 648 ◽

pp. 111-123

Author(s):

C Layton ◽

MJ Cameron ◽

M Tatsumi ◽

V Shelamoff ◽

JT Wright ◽

...

Keyword(s):

Habitat Fragmentation ◽

Patch Size ◽

Life Stage ◽

Extended Period ◽

Anthropogenic Disturbances ◽

Anthropogenic Sources ◽

Kelp Forests ◽

Natural Disturbances ◽

Short Term ◽

Turf Algae

Kelp forests in many regions are experiencing disturbance from anthropogenic sources such as ocean warming, pollution, and overgrazing. Unlike natural disturbances such as storms, anthropogenic disturbances often manifest as press perturbations that cause persistent alterations to the environment. One consequence is that some kelp forests are becoming increasingly sparse and fragmented. We manipulated patch size of the kelp Ecklonia radiata over 24 mo to simulate persistent habitat fragmentation and assessed how this influenced the demography of macro- and microscopic juvenile kelp within the patches. At the beginning of the experiment, patch formation resulted in short-term increases in E. radiata recruitment in patches <1 m2. However, recruitment collapsed in those same patches over the extended period, with no recruits observed after 15 mo. Experimental transplants of microscopic and macroscopic juvenile sporophytes into the patches failed to identify the life stage impacted by the reductions in patch size, indicating that the effects may be subtle and require extended periods to manifest, and/or that another life stage is responsible. Abiotic measurements within the patches indicated that kelp were less able to engineer the sub-canopy environment in smaller patches. In particular, reduced shading of the sub-canopy in smaller patches was associated with proliferation of sediments and turf algae, which potentially contributed to the collapse of recruitment. We demonstrate the consequences of short- and longer-term degradation of E. radiata habitats and conclude that habitat fragmentation can lead to severe disruptions to kelp demography.

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Effects of marine reserves on predator-prey interactions in central California kelp forests

Marine Ecology Progress Series ◽

10.3354/meps13526 ◽

2020 ◽

Vol 655 ◽

pp. 139-155

Author(s):

DC Yates ◽

SI Lonhart ◽

SL Hamilton

Keyword(s):

Species Interactions ◽

Size Structure ◽

Marine Reserves ◽

Mortality Rates ◽

Kelp Forests ◽

Negative Effects ◽

Central California ◽

Invertebrate Predators ◽

Predatory Fishes ◽

Density And Biomass

Marine reserves are often designed to increase density, biomass, size structure, and biodiversity by prohibiting extractive activities. However, the recovery of predators following the establishment of marine reserves and the consequent cessation of fishing may have indirect negative effects on prey populations by increasing prey mortality. We coupled field surveys with empirical predation assays (i.e. tethering experiments) inside and outside of 3 no-take marine reserves in kelp forests along the central California coast to quantify the strength of interactions between predatory fishes and their crustacean prey. Results indicated elevated densities and biomass of invertebrate predators inside marine reserves compared to nearby fished sites, but no significant differences in prey densities. The increased abundance of predators inside marine reserves translated to a significant increase in mortality of 2 species of decapod crustaceans, the dock shrimp Pandalus danae and the cryptic kelp crab Pugettia richii, in tethering experiments. Shrimp mortality rates were 4.6 times greater, while crab mortality rates were 7 times greater inside reserves. For both prey species, the time to 50% mortality was negatively associated with the density and biomass of invertebrate predators (i.e. higher mortality rates where predators were more abundant). Video analyses indicated that macro-invertivore fishes arrived 2 times faster to tethering arrays at sites inside marine reserves and began attacking tethered prey more rapidly. The results indicate that marine reserves can have direct and indirect effects on predators and their prey, respectively, and highlight the importance of considering species interactions in making management decisions.

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Mechanisms leading to recruitment inhibition of giant kelp Macrocystis pyrifera by an understory alga

Marine Ecology Progress Series ◽

10.3354/meps13550 ◽

2021 ◽

Vol 657 ◽

pp. 59-71

Author(s):

BA Beckley ◽

MS Edwards

Keyword(s):

Field Experiments ◽

Local Community ◽

Kelp Forest ◽

Macrocystis Pyrifera ◽

Forest Recovery ◽

Kelp Forests ◽

Giant Kelp ◽

Combined Effects ◽

Life Stages ◽

Survival And Growth

The forest-forming giant kelp Macrocystis pyrifera and the communities it supports have been decreasing across their native ranges in many parts of the world. The sudden removal of giant kelp canopies by storms increases space and light for the colonization by understory macroalgae, such as Desmarestia herbacea, which can inhibit M. pyrifera recovery and alter local community composition. Understanding the mechanisms by which algae such as D. herbacea interact with M. pyrifera can provide insight into patterns of kelp forest recovery following these disturbances and can aid in predicting future community structure. This study experimentally tested the independent and combined effects of two likely competitive mechanisms by which D. herbacea might inhibit recovery of M. pyrifera in the Point Loma kelp forest in San Diego, California (USA). Specifically, we conducted field experiments to study the individual and combined effects of shade and scour by D. herbacea on the survival of M. pyrifera microscopic life stages, and the recruitment, survival, and growth of its young sporophytes. Our results show that scour had the strongest negative effect on the survival of M. pyrifera microscopic life stages and recruitment, but shade and scour both adversely affected survival and growth of these sporophytes as they grew larger. Canopy-removing storms are increasing in frequency and intensity, and this change could facilitate the rise of understory species, like D. herbacea, which might alter community succession and recovery of kelp forests.

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