MARINE AND FISHERY SCIENCES 37 (1): 41-52 (2024)

https://doi.org/10.47193/mafis.3712024010106

ABSTRACT. Light pollution poses a significant global threat to biodiversity, driven by the

increasing coastal urbanization and the resulting growth of artificial light at night (ALAN). Howev-

er, to date, the scientific community has focused mainly on studying its ecological effects within the

terrestrial environment. It is only recently that attention has turned to coastal marine systems which

are crucial due to their essential contribution at the ecosystem level. These environments, character-

ized by their high productivity, also play a crucial role in protecting coasts against erosion. The aim

of this case study was to investigate the possible effects of ALAN on the sea urchin species Para-

centrotus lividus in four areas of an Italian rocky coast, selected according to a gradient of light

intensity (0, 0.4, 3 and 25 lux), from April 2022 to February 2023. Effects of ALAN were examined

by measuring the density and size of sea urchins and also their reactivity to a stress condition

through an innovative technique of overturning sea urchins to study their physiological response in

the presence or absence of artificial light. In addition, the permanence of sea urchins in the four

areas was evaluated through an efficient tagging test. Results show how these organisms, typically

nocturnal, suffer negative effects of ALAN in terms of minor density and mobility, expressed as the

speed of response to an adverse event, compared to a dark area.

Key words: Italy, light pollution, mobility, sea urchin, tagging.

Efectos de la luz artificial nocturna sobre la movilidad del erizo de mar Paracentrotus lividus

RESUMEN. La contaminación lumínica plantea una importante amenaza global para la biodiver-

sidad, impulsada por la creciente urbanización costera y el consiguiente crecimiento de la luz artifi-

cial nocturna (ALAN). Sin embargo, hasta la fecha, la comunidad científica se ha centrado principal-

mente en estudiar sus efectos ecológicos dentro del medio terrestre. Solo recientemente se ha presta-

do atención a los sistemas marinos costeros, que son cruciales debido a su contribución esencial a

nivel de ecosistema. Estos ambientes, caracterizados por su alta productividad, también juegan un

papel crucial en la protección de las costas contra la erosión. El objetivo de este estudio de caso fue

investigar los posibles efectos de ALAN en el erizo de mar Paracentrotus lividus en cuatro áreas de

una costa rocosa italiana, seleccionadas según un gradiente de intensidad de luz (0, 0,4, 3 y 25 lux),

desde abril 2022 a febrero 2023. Se examinaron los efectos de ALAN midiendo la densidad y el tama-

ño de los erizos de mar y también su reactividad a una condición de estrés mediante una técnica inno-

vadora de volcar los erizos de mar para estudiar su respuesta fisiológica en presencia o ausencia de

luz artificial. Además, se evaluó la permanencia de los erizos de mar en las cuatro áreas mediante una

prueba eficiente de marcaje. Los resultados muestran cómo estos organismos, típicamente nocturnos,

sufren efectos negativos de la ALAN en términos de menor densidad y movilidad, expresada como

velocidad de respuesta ante un evento adverso, en comparación con un área oscura.

Palabras clave: Italia, contaminación lumínica, movilidad, erizo de mar, marcado.

*Correspondence:

davide.dibari@szn.it

Received: 12 May 2023

Accepted: 15 August 2023

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

ORIGINAL RESEARCH

Effects of artificial light at night on the mobility of the sea urchin

Paracentrotus lividus

DAVIDE DIBARI*

Stazione Zoologica Anton Dohrn, Via Francesco Caracciolo, 80122 - Naples, Italy.

ORCID Davide Di Bari https://orcid.org/0009-0003-6537-6092

INTRODUCTION

Numerous marine ecosystems are subjected to

the influence of natural light regimes that modu-

late both the behavior of the species inhabiting

them as well as their interactions across trophic

levels (Davies et al. 2016). These light regimes

determine critical aspects, such as the timing and

success of predatory activity, consequently

impacting the prey’s ability to escape (Garratt et

al. 2019). However, the use of artificial light

sources by humans to carry out their activities is

altering natural conditions even in the marine

environment. These sources of artificial light at

night (ALAN) range from temporary lights used

for navigation and fishing, through intermittent

ones produced by lighthouses, to permanent ones,

such as those emitted by oil rings and cities on the

coast (Davies et al. 2014), due to the constant

illumination of residences, walks, piers and mari-

nas (Garratt et al. 2019). This growing anthropic

pressure is increasingly threatening key ecologi-

cal processes shaping these ecosystems (Lui-

jendijk 2018) and, in particular, intertidal and

shallow subtidal habitats. They provide various

ecosystem goods and services, such as tourism

and recreation, raw material production, coastal

protection and erosion control, nutrient cycliza-

tion, water purification and carbon sequestration

(Barbier et al. 2011).

In particular, herbivorous sea urchins play a

fundamental role in shallow subtidal marine envi-

ronments, both as grazers by limiting algal bio-

mass, and as prey of organisms belonging to dif-

ferent species, such as fish, crustaceans, starfish,

otters and humans (Pearse 2006). Changes in

their density can lead to sudden, persistent and

large variations in the structure and functioning

of the ecosystem in which they live (regime

shifts), as in the case of the transformation of

macroalgal forests into barrens or habitats domi-

nated by algal felts (Benedetti-Cecchi et al.

1998). These habitats represent alternative states

of the same system: the macroalgal forest is

extremely productive because it accumulates a lot

of biomass and maintains a high specific diversity

within it; on the contrary, felts and barrens repre-

sent less diversified systems and accumulate less

biomass (Stewart and Konar 2012; Filbee-Dexter

and Scheibling 2014). Specifically, the sea urchin

Paracentrotus lividus represents a model organ-

ism used for a long time in different fields of

study of biology, such as immunology (Pinsino

and Alijagic 2019), ecotoxicology (Macedo et al.

2017), development (Romancino et al. 2017),

biochemistry (Karakostis et al. 2016) and ecology

(Boarda et al. 2017). Thanks to these studies,

many aspects of this species are known at differ-

ent levels of biological organization and therefore,

theoretically, it should be easier for researchers to

develop hypotheses to test and carry out studies

supported by previous knowledge acquired. In

addition, P. lividus represents a species of com-

mercial interest and potentially at risk due to over-

fishing by humans (Ceccherelli et al. 2011). In

Italy its capture is regulated by the Ministerial

Decree of 1995 which establishes the size, period

and quantities permitted (MRAAF 1995).

Factors influencing the activity of sea urchins

are varied, including hydrodynamics, food avail-

ability and the presence of predators (Benedetti-

Cecchi et al. 1998), but also harvest by humans

for food purposes (Farina et al. 2020). Herbivo-

rous sea urchins carry out most of their activities

at night (Dee et al. 2012) and it makes them the-

oretically more influenced by ALAN than other

strictly diurnal organisms. In fact, during the day

sea urchins remain safe from possible predators

in shelters in the crevices among the rocks, while

at night they come out to feed (Hereu 2005).

Depending on the species of sea urchin, reactions

to different daylight intensities include color

change, ambulacral pedicel reactions, and hiding

in shelters (Millott 1976). In addition, photoperi-

od variations have been shown to affect the repro-

duction of sea urchins, such as P. lividus (Shpigel

42 MARINE AND FISHERY SCIENCES 37 (1): 41-52 (2024)

et al. 2004) and Arbacia lixula (Wangesteen et al.

2013). In particular, it has been observed that in

P. lividus prolonged periods of illumination

reduce the rate of gametogenesis, while reduced

periods of illumination increase it (Shpigel et al.

2004). However, there is no conclusive evidence

of the presence of a particular structure capable of

receiving light signals and it is assumed that these

organisms rely solely on a photosensitive superfi-

cial epidermal nerve network (Millott 1976; Ull-

rich-Lüter et al. 2011).

Hypotheses tested were: 1) the density of the

sea urchin P. lividus is greater at night than at day,

outside their shelters among the rocks, in order to

confirm the hypothesis that they are nocturnal

organisms; 2) at night the density and size of P.

lividus are greater in areas not subjected to ALAN

and similar between areas subjected to ALAN and

diurnal ones, such as possible stress conditions,

variations in circadian rhythms and increased risk

of predation; and 3) the time of the overturning

test increases with a higher light intensity as a

consequence of greater stress conditions.

MATERIALS AND METHODS

Study site

The study was carried out on a rocky coast

along the promenade of Punta Righini (43° 40'

08"N, 10° 40'73"E) in Castiglioncello in the

province of Livorno (Tuscany, Italy) from April

2022 to February 2023 (Figure 1). The area is

characterized by the presence of dark zones alter-

nating with others with different types and inten-

sity of night lighting, due to the presence of street

lamps along the promenade and LED spotlights at

the restaurant ‘La Baracchina’.

The habitat has an algal benthic population

consisting mainly of algal turf and thin tubular

sheet-like (TTS), to a lesser extent Halimeda

tuna, Laurencia obsuta, Ellisolandia elongata,

Padina pavonica and Valonia macrophysa. The

most commonly present animal organisms are

crabs, shrimps, hermit crabs, gastropods, actinias,

mullets, sea stars, sea cucumbers and the two

most common species of sea urchin along the

Italian coasts in superficial subtidal habitat: P.

lividus and A. lixula. The latter species is present

in a minimum percentage (2%) and therefore it

was considered appropriate to test hypotheses

only on the sea urchin P. lividus, also to avoid

including biological differences existing between

the two species in the results.

In April 2022 four areas of equal extension and

characterized by different ALAN levels were

identified through light intensity measurements

carried out using a lux meter (Digital Lux Meter

LX1330B, range 0,1-200.000 lux) in the presence

of a new moon (Figure 1). Proceeding from west

to east, in the first area the light of street lamps of

the walk does not reach the study habitat since it

is located a few tens of meters from it remaining

completely dark (Dark 1 area – 0 lux). The second

area was illuminated by the headlights of the

restaurant ‘La Baracchina’, which produced a rel-

atively strong light (Restaurant area – 25 lux).

Continuing south, we found the first street lamp

of the promenade of Punta Righini, which howev-

er was not active and the area was almost com-

pletely dark (Dark 2 area – 0.4 lux). The fourth

area was below one of the working street lamps

of the promenade. This LED lighting was very

dim compared to that emitted by the restaurant’s

spotlights, which allowed for an intermediate

experimental condition between the two extremes

of high illumination and total darkness (Prome-

nade area – 3 lux). Those four selected areas were

similar in terms of rocky substrate and presence

and abundance of main algae species.

Measurement and tagging methods

All measurements were replicated every two

months for a total of 6 different sampling periods

(April, June, August, October and December

DIBARI: EFFECTS OF ALAN ON MOBILITY OF SEA URCHINS

2022, and February 2023) to obtain results not

attributable to the seasonal period but to an annual

average. All measurements were carried out in

subareas of similar extension for each of the four

study areas. In each sampling period the subarea

was changed but the same experimental condition

of the area was maintained. Sea urchins were then

relocated to an area not examined in this study and

far from the sampling location to avoid possible

pseudoreplication errors (Waller et al. 2013).

To determine whether sea urchins present in

the four chosen sites were representative of them,

it was considered appropriate to carry out a pre-

liminary test by tagging them in each area and

checking their presence a week later to determine

if they were sedentary. To choose the most appro-

priate tagging method among those observed in

the scientific literature (Duggan and Miller 2001;

Boarda et al. 2015), a first test was carried out

between the two most commonly used methods.

44 MARINE AND FISHERY SCIENCES 37 (1): 41-52 (2024)

Figure 1. Study site indicating the four selected areas with different lighting levels. 1) Dark 1 area –0 lux. 2) Restaurant

area –25 lux. 3) Dark 2 area –0.4 lux. 4) Promenade area –3 lux.

The first consisted of perforating the sea urchin

with a hypodermic needle and passing a 0.25 mm

monofilament fishing line through the hole creat-

ed, into which a colored vinyl tube was inserted.

This technique requires that gonads or other vital

organs of the sea urchin not be pierced so that

there are not high mortality rates (Ebert 1965).

The second was the plastic beads method, which

is based on the use of small 2 mm microplastics

rings inserted and glued into the aboral part of sea

urchins in a number equal to 5 per organism (Bur-

nell 2015).

The test was performed in an area near the

study site. Fifteen sea urchins of similar size (3-

5 cm) were tagged for each of the two selected

systems (Figure 2). After 7 days, sea urchins were

recovered and viewed. The evaluation criteria

included the number of sea urchins found, mortal-

ity, stress status and, for the second method test-

ed, the number of beads left.

Once the most valid approach was established,

10 sea urchins were marked in each study area.

After a week, characterized by calm seas, the

areas were visited again to assess the number of

urchins found and to give a qualitative estimate of

the distance from the point of release.

Density and size

In order to evaluate possible differences in the

average density of sea urchins in areas character-

ized by different night lighting, a non-destructive

sampling was carried out in the four study areas

by counting organisms outside their shelters

among rocks. Since daytime sampling is general-

ly carried out in the literature, it was considered

interesting to compare densities in natural light

conditions with those made at night in dark and

artificially lit areas. In the same days, size meas-

urements of sea urchins were also carried out

within each zone using a caliper.

Overturning tests

Finally, an innovative overturning test was per-

formed on sea urchins. It consisted of placing sea

urchins in inverted position on a flat surface and

measuring the time to return to the usual position

with the oral surface facing the substrate and the

aboral surface towards the water column (Figure

3). In fact, oral surface is less defended by spikes

and potentially more vulnerable to attacks of pos-

sible predators. Therefore, sea urchins in good

DIBARI: EFFECTS OF ALAN ON MOBILITY OF SEA URCHINS

Figure 2. Hypodermic needle (A) and beads (B) tagging methods used to test the mobility of sea urchins.

health overturned very quickly, whereas if they

were stressed, they took longer to return to the

position that guarantees maximum defense (Bose

et al. 2019). The hypothesis was that ALAN could

generate stress conditions such as to compromise

this anti-predatory behavior.

The test was conducted approximately one

hour after dusk, placing organisms (n =10 for

each of 4 areas) of similar size (3-4 cm) in the

center of a basin filled with water. After 30 sec in

a natural position, so that they acclimatized to the

new substrate, they were overturned. A red light

was used to see during all measurements in the

dark and not to distort the test. In fact, the light

produced by this color was less dazzling than, for

example, a white light (Figueiro et al. 2019).

Data analysis

The experimental design foresaw the compari-

son between annual averages of day and night

densities of sea urchins in each of 4 zones; the

comparison between annual averages of densities

and nocturnal sizes of sea urchins in illuminated

and unlit areas; and the comparison between

annual averages of night overturning times of sea

urchins in illuminated and dark areas. Independ-

ent samples were analyzed using the t-test to esti-

mate the effect of ALAN on sea urchins. For the

realization of analyses, the statistical software R

was used considering p<0.05.

RESULTS

Tagging methods

Hypodermic needle method

Fifteen sea urchins were randomly taken (11 P.

lividus and 4 A. lixula) to which this first method

was applied. After a week, sea urchins were all

found, but it was noted that they had lost a large

number of spikes, a symptom of a state of strong

stress probably due to the treatment applied.

Moreover, once placed in a poorly sheltered area

and overturned, they were not very reactive in

movements and 3 organisms were even dead

(Figure 4).

Beads method

Fifteen sea urchins were randomly taken (11 P.

lividus and 4 A. lixula) to which this second

method was applied. After a week, sea urchins

46 MARINE AND FISHERY SCIENCES 37 (1): 41-52 (2024)

Figure 3. Three positions, overturned (A), intermediate (B) and natural (C), of a sea urchin during an overturning test.

ABC

were all found. They did not lose spikes and the

average of beads found per organism was 4.25

(Figure 5). Moreover, once placed in a poorly

sheltered area and overturned, they were very

reactive in their movements, and in a few min-

utes they moved to shelters between the rocks

where they had been taken. Consequently, the

bead method was considered appropriate to mark

10 sea urchins in each of 4 areas to assess their

level of permanence. After a week, all the sea

urchins had remained in the same area where

they had been tagged, even within 2 m of the

point of release following the application of the

tagging.

Density and size

Analyses showed significant differences

between day and night densities in the two areas

not illuminated at night: Dark 1 t0.05(1),10 =7.92

and Dark 2 t0.05(1),10 =8.29. In the Dark 1 sam-

pling area, the average number of sea urchins at

night was statistically higher than during the day.

Very similar results were also observed for the

Dark 2 area. On the other side, there were no sig-

nificant differences for the two illuminated areas.

Particularly, nighttime values were almost the

same as daytime values in the Restaurant area

with greater illumination. In addition, results also

showed significant differences between nocturnal

densities in the two dark sites with the most illu-

minated density of the Restaurant area, e.g. Dark

1 t0.05(1),10 =6.51 and Dark 2 t0.05(1),10 =5.48,

respectively. Night densities of sea urchins in

dark areas were higher than in lit areas. Addition-

ally, there was a drastic decrease in the number of

sea urchins found outside their shelters in the

most illuminated area (Figure 6). Instead, analy-

ses showed no significant differences in the size

of sea urchins under different experimental con-

ditions of presence and absence of artificial light-

ing (Figure 7).

DIBARI: EFFECTS OF ALAN ON MOBILITY OF SEA URCHINS

Figure 4. Effects of the hypodermic needle method: spikes lost by sea urchins (A) and dead sea urchins (B).

Figure 5. Some of the sea urchins found after using the beads

method.

Overturning tests

Significant differences were observed between

annual averages of Dark 1 and Dark 2 areas and

that of the Restaurant area, t0.05(1),118 =13.47 and

t0.05(1),118 =13.41, respectively; while there were

no differences between the Promenade area with

dim light and the others (Figure 8). Results also

showed a high variability in times of the Restau-

rant area that was the most illuminated by light

sources.

DISCUSSION

Results of this study confirm that sea urchins

are nocturnal organisms that come out of their

shelters mainly at night to carry out their needs.

This study also supports the hypothesis that arti-

ficial light pollution at night has negative effects

on the mobility of the sea urchin P. lividus. In

fact, these nocturnal organisms have photorecep-

tors potentially alterable by ALAN (Ullrich-Lüter

et al. 2011). In particular, this study showed that

nocturnal densities of sea urchins were very sen-

sitive to ALAN, especially higher in dark areas

than in the restaurant, where there were LED

spotlights at an intensity of 25 lux, while there

appear to be no significant effects due to the light

of streetlights of the promenade with a luminous

intensity equal to 3 lux.

Regarding the size of sea urchins, no signifi-

cant differences that support the hypothesis that

sea urchins are larger in dark areas than in illumi-

nated ones were observed. Rather, it seems to be

an opposite trend, although not statistically

proven, to what has been hypothesized. Satthong

et al. (2019) postulated that night lighting may

have a positive effect on the growth of algae sea

urchins feed on that leading to increased growth

of sea urchin and to counteracting visible effects

of ALAN on them. However, results remain diffi-

cult to interpret due to some existing factors such

48 MARINE AND FISHERY SCIENCES 37 (1): 41-52 (2024)

Figure 6. Box plots of the day and night densities of sea urchins in each of the four study areas. Mean (±standard error): Dark

1 (day) =35.17 ±2.61 sea urchins; Dark 1 (night) =59.67 ±2.17 sea urchins; Dark 2 (day) =35.51 ±1.88 sea urchins;

Dark 2 (night) =56.67 ±2.08 sea urchins; Promenade (day) =39.17 ±0.87 sea urchins; Promenade (night) =46.67 ±

2.56 sea urchins; Restaurant (day) =37.52 ±2.11 sea urchins; Restaurant (night) =40.67 ±2.35 sea urchins.

Dark 1 Dark 2 Promenade Restaurant

Number of sea urchins

Day Night

Area

Day Night Day Night Day Night

as different hydrodynamism and predation, which

act on the size in different ways and intensities in

the four areas.

Finally, regarding the reactivity of sea urchins

evaluated with the overturning test, it was found

as suggested, that exposure to high ALAN inten-

sities determinates a decrease in their motility fol-

lowing an unfavorable event such as their acci-

dental overturning. Probably, the anti-predatory

behavior of rapid repositioning in the normal

position was altered as a consequence of the

increased stress condition of sea urchins due to an

excessive alteration of their normal circadian

rhythms. In fact, sea urchins are organisms highly

susceptible to stress factors and even a simple

handling of a few seconds can alter, at least in the

short term, self-righting and predator escape

speed (Bose et al. 2019). In addition, a high vari-

ability was observed in the times of the high illu-

mination area compared to others, particularly

dark ones, perhaps due to different effects of

ALAN on individual organisms. These results

support the hypothesis that ALAN affects the life

of sea urchin with consequences on their activi-

ties, the extent of which is yet to be assessed.

Further studies could extend the research to

other areas for a deeper understanding of the

behavior of P. lividus and address the potential

effects of ALAN on other nocturnal behaviors of

sea urchin, partly already studied during the day,

such as reproduction (Shpigel et al. 2004), preda-

tion (Sala and Zabala 1996) and different types of

foraging (Bulleri et al. 1999). Moreover, it would

be interesting to test the effects of an ALAN inten-

sity gradient on sea urchin photoreceptors from a

biochemical point of view to establish luminous

intensity limits that determines its alteration.

In conclusion, it is unthinkable to be able to

completely eliminate ALAN from our lives

because it is now an integral part of modern soci-

ety. Nevertheless, there are several practical and

effective methods to try at least to limit this form

of pollution such as keeping a proper distance

between two adjacent light sources, reducing the

DIBARI: EFFECTS OF ALAN ON MOBILITY OF SEA URCHINS

Figure 7. Box plots of the sizes of sea urchins at night in each

of the four study areas. Mean (±standard error):

Dark 1 =42.46 ±3.05 mm; Dark 2 =41.85 ±2.36

mm; Promenade =53.92 ±1.72 mm; Restaurant =

54.54 ±2.51 mm.

Figure 8. Box plots of the times to return to the natural posi-

tion during the overturning tests on the sea urchins in

each of the four study areas. Mean (±standard error):

Dark 1 =54.77 ±2.09 s; Dark 2 =55.47 ±2.55 s;

Promenade =133.72 ±8.72 s; Restaurant =287.65 ±

21.03 s.

Size (mm)

Dark 1 Dark 2 Promenade Restaurant

Area

Dark 1 Dark 2 Promenade Restaurant

Area

600

500

400

300

200

100

Time (s)

intensity of the light source to that strictly neces-
sary to carry out the activity for which it was
appointed, turning off lights when not needed,
replacing obsolete lighting types for others with
good performance, as well as those with high
consumption and cost for others with less envi-
ronmental impact, and placing light sources with
a correct direction of the light beam (Di Bari et al.
2023). Unfortunately, at European level, while
widely recognizing ALAN as a serious threat to
biodiversity, there are still no precise laws estab-
lishing common rules regarding this environmen-
tal problem. Thus, these decisions are left locally
to politicians for whom in many cases it is diffi-
cult to introduce voluntary mitigation measures
when they would conflict with economic gains
and security concerns (Davis et al. 2014). In par-
ticular, due to increasing urban development,
coastal marine environments are among the most
affected areas of light pollution (Bird et al. 2004),
often causing negative effects on organisms that
inhabit them, as in the case of the mobility of P.
lividus. However, the current knowledge of these
impacts in marine ecosystems is not yet sufficient
to determine the magnitude of the problem and its
possible interactions with other anthropogenic
pressures, so as to implement effective and realis-
tic management strategies (Davies et al. 2014)
that allow to find the best compromise between
human requirements and the needs of other
organisms (Gaston et al. 2012).
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