Action: Remove and relocate habitat-forming (biogenic) species before onset of impactful activities
Key messagesRead our guidance on Key messages before continuing
- One study examined the effects of removing and relocating habitat-forming species before onset of impactful activities on subtidal benthic invertebrates. The study was in the Fal Estuary (UK).
COMMUNITY RESPONSE (1 STUDY)
- Overall community composition (1 study): One replicated, paired, controlled study in the Fal Estuary found that invertebrate community composition was different in plots where maërl bed habitat had been removed and relayed compared to undisturbed maërl after five weeks, but similar after 44 weeks.
- Overall species richness/diversity (1 study): One replicated, paired, controlled study in the Fal Estuary found that invertebrate species richness was lower in plots where maërl bed habitat had been removed and relayed compared to undisturbed maërl after five weeks, but similar after 44 weeks.
POPULATION RESPONSE (1 STUDY)
- Overall abundance (1 study): One replicated, paired, controlled study in the Fal Estuary found that invertebrate abundance was different in plots where maërl bed habitat had been removed and relayed compared to undisturbed maërl after five weeks, but similar after 44 weeks.
Marine biogenic habitats are habitats created by the occurrence of specific marine species, such as coral reefs, oyster reefs, mussel beds, or kelp forests (Jones et al. 1994). They form a new complex environment for other species to live in and can locally promote subtidal benthic invertebrate biodiversity. Many populations of marine biogenic species have declined or been depleted due to the multiple threats they are under, including habitat damage or loss and direct physical damages from anthropogenic activities (Airoldi et al. 2009). As a pre-emptive conservation measure, biogenic species can potentially be temporarily removed to allow for an impactful activity to occur, then relocated back into their original location, or at a different location. Such measures have been trialled to preserve maërl habitat and its associated faunal community during the dredging of new shipping channels (Sheehan et al. 2015).
When this intervention is undertaken for species which do not form habitats, evidence has been summarised under “Species management – Remove and relocate invertebrate species before onset of impactful activities”.
Airoldi L., Connell S.D. & Beck M.W. (2009) The loss of natural habitats and the addition of artificial substrata. Pages 269–280 in: Wahl M. (eds) Marine Hard Bottom Communities. Springer, Berlin, Heidelberg.
Jones C.G., Lawton J.H. & Shachak M. (1994) Organisms as ecosystem engineers. Pages 130–147 in: Ecosystem Management. Springer, New York, NY.
Sheehan E.V., Bridger D., Cousens S.L. & Attrill M.J. (2015) Testing the resilience of dead maerl infaunal assemblages to the experimental removal and re-lay of habitat. Marine Ecology Progress Series, 535, 117–128.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2012–2013 of 24 plots in six sites of maërl bed in the Fal Estuary, southwest England, UK (Sheehan et al. 2015) found that plots where maërl bed habitat had been temporarily removed then relayed had fewer invertebrate species, reduced abundance, and a different community composition, compared to plots of undisturbed maërl, after five weeks but not after 44 weeks. After five weeks, the removed-relayed plots had fewer species (54 species/core) and lower abundance (155 individuals/core) compared to undisturbed maërl plots (species: 94; abundance: 282), and a different community composition (community data presented at statistical model results and graphical analyses). After 44 weeks, species richness and abundance were similar in the removed-relayed plots (species: 93; abundance: 263) and the undisturbed maërl plots (species: 91; abundance: 178), and community compositions were similar. Dredging of shipping lanes was planned in Falmouth Harbour. This trial study aimed to assess the feasibility of removing and relaying maërl as a mitigation action prior to dredging. Four 5 m2 plots were selected at each of six sites. One of two treatments was attributed to each plot: maërl removed then relayed, undisturbed maërl (representing natural maërl where no dredging for shipping lane occurred). In September 2012, the top 0.3 m of maërl was dredged from the removed-relayed plots and relayed to its original position 12 h later (to mimic the duration of shipping lane dredging). Five maërl samples were collected using a hand corer (25 cm length, 10 cm diameter) from one plot/treatment/site after five and 44 weeks. Invertebrates associated with maërl habitat (>0.5 mm) were counted.