Manage or restrict harvesting of species on intertidal artificial structures
Overall effectiveness category Awaiting assessment
Number of studies: 2
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.
Intertidal rocky habitats experience intermittent disturbance from storms, sedimentation, pollution and other human activities, which lead to fluctuations in biodiversity (e.g. Vaselli et al. 2008). 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 (Bulleri & Airoldi 2005).
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 intertidal 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.
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.
Vaselli S., Bertocci I., Maggi E. & Benedetti-Cecchi L. (2008) Effects of mean intensity and temporal variance of sediment scouring events on assemblages of rocky shores. Marine Ecology Progress Series, 364, 57–66.
Supporting evidence from individual studies
A replicated, randomized study in 2001–2002 on intertidal 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
A replicated, site comparison study in 2006 on six intertidal breakwaters in ports and on open coastline in the Gibraltar Strait, Gibraltar and the Alboran Sea, Spain (Espinosa et al. 2009) found that breakwaters with restricted human access supported similar densities of ribbed Mediterranean limpets Patella ferruginea but with larger average size and more balanced sex ratios, compared with unrestricted breakwaters. Limpet density was similar on breakwaters with restricted access (0–7 limpets/m) and those without (3–7/m) (data not statistically tested). On average, limpets were larger on breakwaters with restricted access (4–7 cm) than without (3–4 cm) in seven of nine comparisons, but were similar in two comparisons (both 4 cm). Limpet sex ratio on restricted breakwaters ranged from 2: 1 (males: females) to 18: 1, while the ratio on unrestricted breakwaters ranged from 41: 1 to 117: 1 (data not statistically tested). Harvesting species on breakwaters was restricted by restricting site access. Three breakwaters were in private or military areas with restricted access and surveillance (timing and other details not reported) while three had no access restrictions. Limpet harvesting was technically forbidden at all sites due to its protected species status. Limpets on breakwaters were counted, measured and sexed during low tide during June–August 2006.Study and other actions tested