Manage or restrict harvesting of species on subtidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 3
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Background information and definitions

Definition: ‘Managing or restricting harvesting of species’ includes actions taken to avoid or reduce the disturbance, damage or removal of native organisms from structures, with the aim of enhancing their biodiversity.

Subtidal rocky habitats experience intermittent disturbance from storms, sedimentation, pollution and other human activities, which lead to fluctuations in biodiversity (e.g. Balata et al. 2007). These pressures are often more pronounced and frequent on artificial structures, especially those built in urban areas with high human activity and poor water quality, and/or in areas of high wave energy (Airoldi & Bulleri 2011; Moschella et al. 2005). Artificial structures can also be subject to disturbance from recreational or commercial harvesting of species for food, bait, recreation or souvenirs. Such activities can further disturb, damage or remove biodiversity from structure surfaces (Bulleri & Airoldi 2005; Airoldi et al. 2005) and can leave bare space available to opportunistic non-native or other nuisance species (Viola et al. 2017).

In some circumstances, it may be desirable for structures to support multifunctional recreational or commercial activities, potentially diverting pressure away from natural habitats (Evans et al. 2017). If this is not the case, there may be opportunities to manage or restrict harvesting activities that disturb, damage or remove native organisms from subtidal artificial structures, to maintain or enhance their biodiversity. This could include introducing voluntary or enforced spatial or temporal restrictions, promoting sustainable alternatives, educating harvesters on the impacts of their activities, or a variety of other actions that may alter harvesting behaviour with the aim of enhancing the biodiversity of structures. Some artificial structures already have restricted access with existing surveillance. These may offer a means of creating cost-effective “artificial micro-reserves” where historical cultural rights preclude restricting activities in natural habitats (García-Gómez et al. 2010).

Studies of the effects of real or simulated harvesting to illustrate its impact compared with no or managed harvesting, where it is not clear that restricting/managing harvesting would be a feasible conservation action, are not included but are informative (e.g. Airoldi et al. 2005; Bulleri & Airoldi 2005).

^{Airoldi L., Bacchiocchi F., Cagliola C., Bulleri F. & Abbiati M. (2005) Impact of recreational harvesting on assemblages in artificial rocky habitats. Marine Ecology Progress Series, 299, 55–66.}

^{Airoldi L. & Bulleri F. (2011) Anthropogenic disturbance can determine the magnitude of opportunistic species responses on marine urban infrastructures. PLoS ONE, 6, e22985.}

^{Balata D., Piazzi L. & Benedetti-Cecchi L. (2007) Sediment disturbance and loss of beta diversity on subtidal rocky reefs. Ecology, 88, 2455–2461.}

^{Bulleri F. & Airoldi L. (2005) Artificial marine structures facilitate the spread of a non-indigenous green alga, Codium fragile ssp. tomentosoides, in the north Adriatic Sea. Journal of Applied Ecology, 42, 1063–1072.}

^{Evans A.J., Garrod B., Firth L.B., Hawkins S.J., Morris-Webb E.S., Goudge H. & Moore P.J. (2017) Stakeholder priorities for multi-functional coastal defence developments and steps to effective implementation. Marine Policy, 75, 143–155.}

^{García-Gómez J.C., López-Fé C.M., Espinosa F., Guerra-García J.M. & Rivera-Ingraham G.A. (2010) Marine artificial micro-reserves: a possibility for the conservation of endangered species living on artificial substrata. Marine Ecology, 32, 6–14.}

^{Moschella P.S., Abbiati M., Åberg P., Airoldi L., Anderson J.M., Bacchiocchi F., Bulleri F., Dinesen G.E., Frost M., Gacia E., Granhag L., Jonsson P.R., Satta M.P., Sundelöf A., Thompson R.C. & Hawkins S.J. (2005) Low-crested coastal defence structures as artificial habitats for marine life: using ecological criteria in design. Coastal Engineering, 52, 1053–1071.}

^{Viola S.M., Page H.M., Zaleski S.F., Miller R.J., Doheny B., Dugan J.E., Schroeder D.M. & Schroeter S.C. (2017) Anthropogenic disturbance facilitates a non-native species on offshore oil platforms. Journal of Applied Ecology, 55, 1583–1593.}

Study locations

Key messages

Three studies examined the effects of managing or restricting harvesting of species on subtidal artificial structures on the biodiversity of those structures or on human behaviour likely to influence the biodiversity of those structures. The studies were on open coastlines in Italy.

COMMUNITY RESPONSE (1 STUDY)

Fish community composition (1 study): One site comparison study in Italy found different fish community composition around subtidal artificial structures with and without harvesting restrictions. The structure with harvesting restrictions supported species that were absent from unrestricted structures.
Fish richness/diversity (1 study): One site comparison study in Italy found higher fish species richness around a subtidal artificial structure with harvesting restrictions compared with unrestricted structures.

POPULATION RESPONSE (2 STUDIES)

Invertebrate abundance (1 study): One site comparison study in Italy found similar sea urchin abundances around subtidal artificial structures with and without harvesting restrictions.
Fish abundance (2 studies): One of two site comparison studies in Italy found similar total fish abundance around subtidal artificial structures with and without harvesting restrictions, but that abundances varied depending on the species and the survey date. One study found higher seabream abundances around the structure with harvesting restrictions.

BEHAVIOUR (1 STUDY)

Human behaviour change (1 study): One replicated, randomized study in Italy reported that legally restricting human access on subidal artificial structures did not prevent people from harvesting invertebrates and fishes on and around structures.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, randomized study in 2001–2002 on subtidal breakwaters and groynes in five sites on open coastline in the Adriatic Sea, Italy (Airoldi et al. 2005) reported that making access to the breakwaters illegal did not prevent people from harvesting invertebrates and fishes on and around them. At four sites, an average of 0–2 harvesters/2-hour survey were recorded on breakwaters, despite access being illegal. At one site where breakwaters (access illegal) and groynes (access legal) were studied simultaneously, an average of 0–5 harvesters/2-hour survey were recorded. At this site >70% of observations were on groynes, but harvesting also occurred on breakwaters (details not reported). Harvesting species on breakwaters was restricted by making access illegal, but with no apparent enforcement (timing and other details not reported). The number of people harvesting invertebrates and fishes on breakwaters at each of five sites was counted during 2-hour surveys on 152 randomly-selected days between November 2001 and November 2002. Observations at one of the sites included harvesting on groynes, to which access was legal.
Study and other actions tested
Referenced paper
Airoldi L., Bacchiocchi F., Cagliola C., Bulleri F. & Abbiati M. (2005) Impact of recreational harvesting on assemblages in artificial rocky habitats. Marine Ecology Progress Series, 299, 55-66.
A site comparison study in 2002–2003 on three subtidal breakwaters on open coastline in the Adriatic Sea, Italy (Guidetti, Bussotti & Boero 2005; same experimental set-up as Guidetti et al. 2005) found higher abundances of white seabream Diplodus sargus, two-banded seabream Diplodus vulgaris and gilt-head seabream Sparus aurata, but similar abundance of sea urchins Paracentrotus lividus around a breakwater with restricted harvesting, compared with two unrestricted breakwaters. Sixteen years after harvesting restrictions were introduced, abundance was higher around the breakwater with restrictions than those without for white seabream in two of four surveys (restricted: 5–8 individuals/125m²; unrestricted: 0–2/125m²) and for two-banded seabream in three surveys (restricted: 2–46/125m²; unrestricted: 0–14/125m²). In the remaining surveys, abundances were similar around restricted (white: 3–10/125m²; two-banded: 4/125m²) and unrestricted breakwaters (white: 0–8/125m²; two-banded: 1–3/125m²). Gilt-head seabream were present only at the restricted breakwater in three of the surveys (1–2/125m²) and was more abundant in the fourth (restricted: 2/125m²; unrestricted: <1/125m²). Urchin abundance was similar around restricted and unrestricted breakwaters (both 2–11/20m²). Harvesting species on and around a boulder breakwater was restricted by creating a marine protected area in 1986, making fishing illegal with successful enforcement. Fishes and sea urchins were counted during four surveys at 4–7 m depth in 2002–2003 around the breakwater with restricted harvesting and around two nearby breakwaters with no restrictions.
Study and other actions tested
Referenced paper
Guidetti P., Bussotti S. & Boero F. (2005) Evaluating the effects of protection on fish predators and sea urchins in shallow artificial rocky habitats: a case study in the northern Adriatic Sea. Marine Environmental Research, 59, 333-348.
A site comparison study in 2002–2003 on three subtidal breakwaters on open coastline in the Adriatic Sea, Italy (Guidetti et al. 2005; same experimental set-up as Guidetti, Bussotti & Boero 2005) found higher fish species richness and different fish community composition around a breakwater with restricted harvesting, compared with two unrestricted breakwaters, while fish abundances varied depending on the species and survey date. Sixteen years after harvesting restrictions were introduced, the fish species richness was higher around the breakwater with restrictions (24–27 species/breakwater) than those without (13–22/breakwater) and the fish community composition differed in seven of eight comparisons (data reported as statistical model results). Total fish abundance was higher around the restricted breakwater in only one of four surveys (152 vs 63–66 individuals/survey) but was similar in three (319–554 vs 192–841/survey). However, the individual abundances of eight of 12 fish species were higher around the restricted breakwater during two or more surveys (see paper for full results). Three fish species recorded around the restricted breakwater were absent from unrestricted breakwaters. Harvesting species on and around a boulder breakwater was restricted by creating a marine protected area in 1986, making fishing illegal with successful enforcement. Fishes were counted during four surveys at 4–7 m depth in 2002–2003 around the breakwater with restricted harvesting and around two nearby breakwaters with no restrictions.
Study and other actions tested
Referenced paper
Guidetti P., Verginella L., Viva C., Odorico R. & Boero F. (2005) Protection effects on fish assemblages, and comparison of two visual-census techniques in shallow artificial rocky habitats in the northern Adriatic Sea. Journal of the Marine Biological Association of the United Kingdom, 85, 247-255.

Please cite as:

Evans, A.J., Moore, P.J., Firth, L.B., Smith, R.K., and Sutherland, W.J. (2021) Enhancing the Biodiversity of Marine Artificial Structures: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures

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Cease or alter maintenance activities on subtidal artificial structures Action Link	Awaiting assessment	2	Synopsis Link
Create large ridges or ledges (>50 mm) on subtidal artificial structures Action Link	No evidence found (no assessment)	0	Synopsis Link