Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

Preliminary study of the population and reproductive dynamics

of Echinaster sepositus (Spinulosida: Echinasteridae) in Cala del Racó

Daniel López Casares*1,2; https://orcid.org/0000-0001-9014-0776

José Carlos Hernández Pérez2; https://orcid.org/0000-0002-1539-1783

José Tena Medialdea1; https://orcid.org/0000-0002-2391-699X

José Rafael García March1; https://orcid.org/0000-0003-1646-5331

1. Instituto de Investigación en Medio Ambiente y Ciencia Marina (IMEDMAR-UCV) Universidad Católica de Valencia.

Av del Port 15, 03710 Calpe, Alicante, España; danilcasares97@gmail.com (*Correspondence), josetena@ucv.es,

jr.garcia@ucv.es

2. Universidad de La Laguna. Av, Astrofísico Francisco Sánchez, S/N, 38206 La Laguna, Santa Cruz de Tenerife, España;

jocarher@ull.edu.es

Received 14-VI-2023. Corrected 06-XII-2023. Accepted 20-XII-2023.

ABSTRACT

Introduction: The red starfish (Echinaster sepositus) is one of the most common asteroid species in the

Mediterranean Sea. However, information about their biology or their role in benthic communities is scarce.

Objective: This study aims to provide new information on the ecology of this species through the temporal

characterization of the population of E. sepositus in Cala del Racó (Alicante, Spain) and the in situ monitoring

of its reproductive cycle.

Methods: For this purpose, three study areas were established at different depths. For each of the recorded

starfish, data about the size, the substrate on which it was found, the area, the depth and the sex in the case of

observing the reproduction were collected.

Results: A total of 19 samplings have been carried out throughout a year of study. In this way, it has been pos-

sible to observe that the density of individuals increases in the shallower zone during autumn and winter, when

the temperature drops to 14.13 ºC, while it decreases in spring and summer when the temperature rises to 27.17

ºC. Those results are reversed in the deepest part of the study. The highest density of individuals (0.51 ind/m2)

occurred in October. Arborescent photophilic algae and crustose coralline algae were the substrates with the

highest number of E. sepositus recorded. Medium to large specimens are located preferably on crustose coralline

algae or arborescent photophilic algae, while smaller individuals were mostly located on Posidonia oceanica. No

specimens of E. sepositus were observed spawning.

Conclusions: Data leads to assume that there is a migration of starfishes towards more superficial areas when the

water is at colder temperature and towards deeper areas when the temperature increases. It is valued the possibil-

ity that there is a change in the nutritional needs of E. sepositus throughout its development. According to our

observations, the future reproduction studies should be concentrated between late-summer and early-autumn.

Key words: starfish; population density; population characterization; temporal monitoring; in situ reproduction.

https://doi.org/10.15517/rev.biol.trop..v72iS1.58967

SUPPLEMENT

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

INTRODUCTION

The genus Echinaster comprises a total of

30 species, although this figure is still under

debate since some new morphotypes are being

described (Lópes et al., 2016; Seixas et al.,

2019). These are medium-sized starfish whose

color varies between yellow and red, with five

cylindrical-conical arms and a small central

area. Their skin is thick and covered with

glands that offer them a good chemical defense,

which probably explains the absence of pedicel-

lariae in the Echinaster species (Turner, 2013).

In the present work we focus on the study

of one of the most emblematic species of the

genus Echinaster: the one commonly known as

red Mediterranean starfish, Echinaster sepositus

(Retzius, 1783). This species belongs to the class

Asteroidea, superorder Spinulosacea, order Spi-

nulosida, family Echinasteridae, genus Echinas-

ter and subgenus Echinaster. It was described

by Aristotle in ancient Greece more than 2 300

years ago in the Historia Animalium, being

the first starfish to be mentioned in science

(Turner, 2013). In recent years it has been used

as a model species for studies of systematics

and morphology of asteroids (Lafay et al., 1995;

Mah & Blake, 2012). Its distribution covers the

entire Mediterranean basin and the temperate

waters of the eastern Atlantic, from the south-

eastern limit of the English Channel to Cape

Verde. It is a species that inhabits from shallow

waters (less than 2 m) to depths of 250 m (Wirtz

& Debelius, 2003) and can live in a wide variety

of environments, such as soft sediment bot-

toms, rocky substrates, phanerogams seagrass

or communities of coralline algae (Entrambasa-

guas et al., 2008). The spatial distribution of E.

sepositus varies depending on the algal cover,

the sand cover and the depth (Entrambasaguas

et al., 2008). However, the exact causes of these

variations remain unknown. Furthermore, the

RESUMEN

Estudio preliminar de la población y dinámica reproductiva de Echinaster sepositus

(Spinulosida: Echinasteridae) en Cala del Racó

Introducción: La estrella de mar roja (Echinaster sepositus) es una de las especies de asteroideos más comunes

del mar Mediterráneo. Sin embargo, la información sobre su biología o su papel en las comunidades bentónicas

es escasa.

Objetivo: Este estudio pretende aportar nueva información sobre la ecología de esta especie mediante la carac-

terización temporal de la población de E. sepositus en la Cala del Racó (Alicante, España) y el monitoreo in situ

de su ciclo reproductivo.

Métodos: Con este fin se establecieron tres zonas de estudio a distintas profundidades. Para cada una de las

estrellas registradas se tomaron datos de tamaño, el sustrato sobre el que se encuentra, la zona, la profundidad y

el sexo en caso de observar la reproducción.

Resultados: A lo largo de un año de estudio se han realizado un total de 19 muestreos. De esta forma se ha podido

observar que la densidad de individuos aumenta en la zona menos profunda durante otoño e invierno, cuando la

temperatura del agua baja hasta los 14.13 ºC, mientras que se reduce en primavera y verano, cuando la tempera-

tura se eleva hasta los 27.17 ºC. Este resultado se invierte en la zona más profunda del estudio. La mayor densidad

de individuos ha sido observada en octubre (0.51 ind/m2). Las algas fotófilas arborescentes y las algas coralinales

costrosas han sido los sustratos con un mayor número de E. sepositus registrados. Los ejemplares de tamaños

medianos a grandes se localizan preferentemente sobre algas coralinales costrosas o algas fotófilas arborescentes,

mientras que los individuos de menor tamaño se sitúan mayormente sobre Posidonia oceanica. No se observaron

ejemplares de E. sepositus reproduciéndose.

Conclusiones: Los datos permiten presuponer que existe una migración entre las zonas más superficiales, cuando

la temperatura del agua es menor, y zonas más profundas cuando la temperatura aumenta. Se valora la posibilidad

de la existencia de un cambio en los requerimientos nutricionales de E. sepositus a lo largo de su desarrollo. De

acuerdo con nuestras observaciones, los estudios futuros sobre la reproducción de esta especie deben concentrarse

entre finales de verano y principios de otoño.

Palabras clave: estrella de mar; densidad poblacional; caracterización poblacional; monitoreo temporal; repro-

ducción in situ.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

density of individuals varies among apparently

similar locations, which suggests that it could

be affected by factors, biotic or abiotic, that act

on scales of hundreds of meters or even less

(Chapman & Underwood, 2008; Underwood

& Chapman 1996). E. sepositus feeds on detri-

tus and small organisms that are found on the

substratum by the evagination of their stomach

towards the outside of the buccal opening (Vas-

serot, 1961). There are indications that they

also feed on sponges, although the defensive

systems of many species can repel the starfish

(Waddell & Pawlik, 2000). Villamor & Becerro

(2010) also observed a certain affinity of E.

sepositus by areas where encrusting algae pre-

dominate, characterized by having associated

small invertebrates and being a place of recruit-

ment for many species of benthic invertebrates.

E. sepositus is a dioecious species, although

some authors have described an “accidental

hermaphroditism” in up to 4 % in the individu-

als studied (Cognetti & Delavault, 1962; Scheib-

ling & Lawrence, 1982). The Mediterranean

red starfish reproduces only sexually, through

external fertilization, giving rise to a lecithotro-

phic larva whose period prior to settlement

does not usually exceed a week (Turner, 2013).

The gonads are found in pairs on each limb and

communicate with the exterior by means of the

gonopores, located on the side of the arms, near

the central disc (Turner, 2013).

Lecithotrophic larvae have an energy

reserve in the form of a yolk that is consumed at

the time of settlement. This means, with respect

to the planktotrophic larvae, a higher prob-

ability of successful recruitment and a higher

survival of settlers (Byrne et al., 1999; Villinski

et al., 2002), but a lower number of larvae emit-

ted. The inability of the lecithotrophic larvae to

feed also implies limited dispersal capacity in

relation to planktotrophic larvae and can have

large consequences on the genetic structure of

their populations, although the high probability

of settling near the areas inhabited by adults of

the same species favors the location of an area

good enough for their vital development (Cis-

neros, 2016). Species that have a lecithotrophic

larvae have a buffer system through which they

limit the large population fluctuations suffered

by other echinoderms, both in decrease as well

as population growth (Uthicke et al., 2009). It

has been seen that in the northwestern Medi-

terranean Sea the spawning of gametes occurs

during the months of summer, especially dur-

ing June and July, when the starfishes have a

greater gonadal weight (Villamor & Becerro,

2010). However, in September 2015, the spawn-

ing of E. sepositus was observed a few days apart

at different points along the coast of Catalonia

(Cisneros, 2016). On October 18, 2018, the

emission of gametes of E. sepositus was record-

ed during a night dive in Cala del Racó (Calpe,

Alicante) and the same group of researchers

observed this phenomenon again the following

week at the same time (Diana López, personal

communication, 2018).

Gametogenesis in asteroids may be regu-

lated by endogenous factors such as age, nutri-

tional status or size, or by exogenous factors

such as photoperiod, temperature or food avail-

ability (Mercier & Hamel, 2009). Among all

these factors, the photoperiod is probably the

most important factor in controlling the repro-

duction in asteroids, and not only the annual

photoperiod, but also the daily one (Basch &

Pearse, 2022; Byrne et al., 1999; Georgiades et

al., 2006; Gibson et al., 2011; Pastor-de-Ward

et al., 2007; Stewart & Mladenov, 1997). This

influence has been corroborated by multiple

manipulative experiments in different species

of starfish (Pearse & Beauchamp, 1986; Pearse

& Bosch, 2002; Pearse & Eernisse, 1982; Pearse

& Walker, 1986). On the other hand, previous

studies have described that the influence of

nutritional status or food availability sometimes

follows an inverse relationship with the gonadal

index, so that the direct influence of feeding on

the reproduction of asteroids remains unclear

(Barker & Xu, 1991; Chen & Chen, 1992;

Farmanfarmaian et al., 1958; Grange et al.,

2007; Rubilar et al., 2005).

While predation on offspring can be avoid-

ed with parental care, species that do not pro-

tect the clutch develop alternative strategies to

avoid high mortality thereof (Balshine, 2012).

To avoid predation by diurnal animals, some

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

groups synchronize the spawning of gametes

during twilight or nocturnal hours, when mor-

tality is considerably lower (Čech et al., 2005;

Metcalfe et al., 1999). Despite the lack of previ-

ous scientific observations on the relationship

between light and the laying of gametes in E.

sepositus, the last observations of spawning

in Cala del Racó were made during the night,

which has led us to hypothesize that daily

photoperiod would be influencing the spawn-

ing of this species, possibly to ensure greater

offspring survival.

Despite being one of the most common

starfish in the Mediterranean Sea, informa-

tion about the biology of E. sepositus or its

role in benthic communities is scarce and

sometimes contradictory (Villamor & Becerro,

2010). Besides, some populations of E. sepositus

in the northwestern Mediterranean have been

reduced in the last decade. Among the main

causes is the direct extraction of individuals for

ornamental aquariums or souvenirs (Villamor

& Becerro, 2010), practice that is widespread

and that lacks an appropriate system of regu-

lation (Olivotto et al., 2011). For this reason,

the main objective of this work is to improve

the knowledge of the ecology of this species

through annual night monitoring via fixed

sampling stations. The specific objectives are,

in the first place, to perform a characterization

with temporal monitoring of the population of

E. sepositus in Cala del Racó (Calpe), where the

spawning was recorded in 2018 and, in the sec-

ond place, to try to record in situ, once again,

the spawning of this species.

MATERIALS AND METHODS

Study area: The study took place in Cala

del Racó (38º38’09’’ N & 0º04’16’’ E), in the

town of Calpe (Alicante, Spain). The waters of

Cala del Racó bathe the west of the “Peñón de

Ifach”. This calcareous outcrop was declared a

Nature Reserve by the Generalitat Valenciana

(Decree 1/1987), on 1987, January 19. How-

ever, it was not until 1993 when a plan of park

administration was approved. The marine area

that surrounds the rock has been declared a

Zone of Special Conservation Area for Birds

(ZEPA) under (Directive 79/409/CEE, 1992)

and includes a Site of Community Importance

(SCI Espacio Marino de Ifach: ESZZ16006) for

hosting funds of Posidonia oceanica in a good

state of conservation.

Cala del Racó is protected from the wind

and waves due to the geographical protection

of the adjacent mountains (Oltá, Bernia and

Mascarat). However, on the south face it is

more exposed to waves. The substrate of the

study area is composed of rocks or boulders

with a high presence of photophilic algae that,

with the gradient of depth, gives way to dif-

ferent biocenoses of fine sand and Posidonia

oceanica meadows. On this side, the P. oceanica

meadows extend from 6 to 22 m deep (Abbiati

et al., 2017) (Fig. 1).

Experimental design: All the dives were

carried out with the logistical support of the

marine station of the Instituto de Investig-

ación en Medio Ambiente y Ciencia Marina

(IMEDMAR-UCV). Sampling began in May

2021 and finished in May 2022. They were

distributed based on the results of the gonadal

maturation of Villamor & Becerro (2010) and

the information obtained during the registra-

tion of the spawning of E. sepositus gametes

that occurred in 2018 in Cala del Racó. Since

the aforementioned gamete spawning lasted for

at least two weeks and was recorded overnight,

the dives in this study were conducted during

the night with variable frequencies depending

on the period of the year: weekly during the

period with the highest probability of spawning

(October 2021), biweekly during the periods

of moderate probability of spawning (between

May and October 2021 and between Novem-

ber and December 2021), and monthly in

periods of lesser spawning probability (from

January to May 2022). The samplings were

made to coincide with the full moon and the

new moon whenever the weather conditions

allowed it, to know if gametogenesis in E.

sepositus followed a lunar pattern, as has been

detected in captivity in other starfish such as

Protoreaster nodosus (Scheibling & Metaxas,

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

2008). However, spawning records have not

been analyzed because this phenomenon has

not been detected during this study.

For data collection and characterization of

the E. sepositus population, all samplings were

carried out with the help of autonomous diving

equipment. Three fixed areas were established

for the entire studio. Zone 1 was found at an

average depth of 3.5 m and is made up of a

mainly rocky environment, with a large cover

of arborescent photophilic algae and crusty

coralline algae, although small patches of P. o c e -

anica and sand were also found. Zone 2 had an

average depth of 5 m and included the interface

between the rocky surface and the beginning

of the meadow of P. oceanica, for which reason

substrates both common to Zone 1 and Zone

3 occurred. Zoe 3 was located at an average

depth of 7 m and was made up mostly of P.

oceanica meadow and sandy bottoms, although

some scattered rocky surfaces were also found.

The zones were separated by a limited depth

gradient of 3 to 7 m. However, the environ-

ment observed at each depth changed rapidly.

In each of the 3 zones mentioned above, a line

transect of 50 x 2 m was established and the

presence of the starfish E. sepositus was noted.

Therefore, a 100 m2 surface was sampled in

each transect. For each starfish observed, the

depth, the corresponding area (1, 2 or 3), the

distance of the transect at which it was located

and the substrate (naked rock, arborescent

photophilic algae (AF), crusted coralline algae

(CCA), sand, sponges, P. oceanica leaves or P.

oceanica rhizomes) were recorded. In case of

observing a starfish on more than one of these

substrates at the same time, we would consider

the substrate as “mixed substrate. The length

of the arm opposite to the madreporite (LB)

was also recorded, that is, the distance from the

end of the arm to the beginning of the central

area. The reason for measuring LB is that Bodí

Broseta (2019) showed with R2 = 0.78 that this

is the best variable to estimate the total length

(i.e. the distance between the end of the arm

and the end of the opposite arm) (TL) of E.

sepositus individuals.

A database was built with Microsoft Excel

(2016) with all the data collected from each

observed individual. A data matrix was devel-

oped and the E. sepositus density (individuals/

m2) was determined for each of the surveys and

zones. In this way, descriptive graphs showing

the changes in the density of starfishes for the

Fig. 1. A) Map of the study area located in Cala del Racó (Calpe), west of the Natural Park of Peñón de Ifach. Coordinates:

38º 38’ 03’’ N & 0º 04’ 16’’ E. B) Exact location of the transects of monitoring carried out it the different sampling areas. Zone

1: 3.5 m deep, rocky surface. Zone 2: 5 m deep, interface between rocky and Posidonia oceanica meadow surfaces. Zone 3:

7 m deep, P. oceanica meadow surface (GVA Viewer, 2022).

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

entire year, in each of the zones, were gener-

ated. Besides, a one-way analysis of variance

(ANOVA) was used to determine if there were

significant differences between the densities

of E. sepositus recorded in each of the zones.

Water temperature was also recorded twice a

month in vertical profiles of up to 15 m depth,

using the oceanographic probe AAQ-RINKO

177 (LFE Advantech CO., Ltd.) to relate the

seasonal temperature changes with the popula-

tion changes of E. sepositus. Subsequently, the

Ocean Data View (ODV) program was used to

graphically represent the temperature profiles

taken throughout the study year.

The size distribution of the starfishes was

also analyzed by zone (measured in LB). Since

LB measures were continuous quantitative data,

LB measurements were classified into the fol-

lowing 6 categories: “< 3 cm”, “3-4 cm”, “4-5 cm”,

“5-6 cm”, “6-7 cm” and “>7 cm”. The program

IBM SPSS Statistics was used to perform a

Pearson Chi-square analysis to see if there was

a statistically significant dependency between

the zone and the size of the starfishes. For this

work, the sizes were grouped into 3 categories:

SMALL if its LB is less than 4 cm, MEDIUM if

its LB is between 4 and 6 cm, and BIG if its LB is

greater than 6 cm. On the other hand, another

Pearson Chi-square analysis was performed

to see if there was a statistically significant

dependency between the LB and the substrate

in which the individuals were found. For this

analysis, the same 3 categories as in the previ-

ous Chi-square were used: SMALL, MEDIUM,

BIG. Subsequently, the program R-Project 4.1.3

(R Core Team, 2022) and the “readxl” package

were used to graphically represent the size dis-

tribution (SMALL, MEDIUM, BIG) in each of

the substrates using a barplot.

RESULTS

After 19 days of sampling, a total of 488

individuals of E. sepositus were recorded, with

an average number of 25.7 starfish per sample

with a standard deviation of 11.2.

Echinaster sepositus density in each of the

sampled zones: ANOVA showed significant

differences in density in each of the zones (F

= 4.01, P = 0.002). In Zone 1, 120 individu-

als were found (24.6 % of the total) with an

average density of 0.06 individuals/m2. Such

density increased irregularly from spring (time

with a lower density in Zone 1) to winter, when

the density reached twice the maximum value

recorded in this area (0.14 ind/m2). There was

also another peak density in summer (0.1–0.11

ind/m2), although not as marked as the one

that appeared from December to March. The

lowest densities were recorded between spring

and summer, with zero individuals recorded on

one occasion.

In Zone 2, 218 individuals were found

(44.7 % of the total encounters) and an aver-

age density of 0.11 ind/m2. In this case, the

maximum density was observed in spring (0.24

ind/m2). This density was reduced in sum-

mer and increased again between October and

November, where the second highest density

peak occurred (0.17–0.19 ind/m2). The lowest

recorded starfish density (0.02 ind/m2) was

observed in May.

In Zone 3, 150 individuals were found

(30.7 % of the total encounters), with an aver-

age density of 0.08 ind/m2. The individual

density remained between 0.01 and 0.06 from

May to August. From September, the density

increased progressively until October, when it

reached its maximum (0.24 ind/m2). After this

peak, the density remained lower between 0.11

and 0.15 ind/m2 and then it reached a second

peak in January (0.21 ind/m2). In the following

months, the density declined until it equaled

the low densities found in spring.

The sampling day with the highest num-

ber of starfish found was the 21st of October

of 2021, in autumn. Up to 51 individuals were

recorded in one transect (0.51 ind/m2). On the

contrary, on May 10th, 2022, in spring, the low-

est E. sepositus density in a sample was recorded

(0.09 ind/m2) (Fig. 2).

The water temperature showed the typical

seasonal variations of the Western Mediter-

ranean Sea, with a minimum temperature of

14.13 ºC in March 2022 and a maximum of

27.17 ºC in August 2021. As usual in these

waters, the summer period presented a seasonal

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Fig. 2. Echinaster sepositus density (ind/m2) in the different sampling zones during the study. Zone 1: 3.5 m deep, rocky

surface. Zone 2: 5 m deep, interface between rocky and Posidonia oceanica meadow surfaces. Zone 3: 7 m deep, P. oceanica

meadow surface.

thermocline, while the winter months present-

ed homogeneity of temperature in the water

column. Between mid-November 2021 and Jan-

uary 2022 and in July 2022, there was missing

data due to malfunction of the oceanographic

probe (Fig. 3).

Percentage of appearance of Echinaster

sepositus in the different types of substrates:

Of the 120 individuals studied in Zone 1, 68

individuals (59.6 %) were found on AF. Subse-

quently, 29 specimens (24.17 %) were found on

CCA, 11 starfish (9.17 %) on mixed substrate,

6 (5 %) on rhizomes of Posidonia plants and 4

individuals (3.3 %) on bare rock. Finally, the

substrates in which a smaller number of starfish

were found were Posidonia leaves and sponges,

with only one specimen on each (< 1 %). No

individual was found on the bare sand. Of the

218 sightings of E. sepositus in Zone 2, 120

(55 %) occurred on AF, 39 encounters (17.9 %)

were observed on the rhizome of P. oceanica,

21 (9.6 %) on CCA, 16 (7.3 %) on mixed sub-

strate, 10 (4.6 %) on bare rock and 8 (3.67 %)

on the leaves of P. oceanica. Finally, there were

3 records of starfish (1.38 %) on sandy bottom

and a specimen was sighted on a sponge (0.46

%). In Zone 3, 150 individuals of E. sepositus

were recorded. Of the total of sightings, 110

(73.3 %) occurred on the rhizomes of P. o c e -

anica, 23 records (15.3 %) occurred on Posido-

nia leaves, 7 starfish (4.67 %) were observed

on the sandy bottom and 5 individuals (3.3

%) appeared on a substratum occupied by

AF. Finally, in the CCA and mixed substrates,

3 and 2 sightings were recorded respectively,

which represents 2 and 1 % of the sightings.

No specimen of E. sepositus has been recorded

on sponges or on bare rocks. The percentage of

appearance of E. sepositus in the different types

of substrates is shown in Table 1.

Size distribution of Echinaster sepositus

in the sampling areas: The starfish studied in

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

Zone 1 had an average LB of 5.8 cm, a maxi-

mum LB of 8.8 cm and a minimum LB of 2.9

cm, with a peak of individuals between 5 and

6 cm. In Zone 2, an average size of 5.3 cm, a

maximum size of 9.4 cm and a minimum of 3.4

cm were recorded, with a predominant size dis-

tribution between 4 and 6 cm in this zone. Indi-

viduals which were in Zone 3 have an average

LB of 4.34 cm, a maximum LB of 6.2 cm and a

minimum LB of 2.6 cm and a very noticeable

peak of specimens between 4 and 5 cm (Fig. 4).

The Pearson Chi-square analysis showed

that there was a statistically significant rela-

tionship between the different zones and the

different sizes grouped into categories: SMALL,

MEDIUM, BIG, with 95 % confidence. So the

distribution of the different sizes of starfish in

each zone was not uniform and they had size

segregation per zone (P < 0.001) (Table 2).

While the small starfish were located mostly in

Zone 3, most of the largest animals were found

in Zones 1 and 2. Similarly, another Chi-square

analysis established, with 95% confidence, that

there was a statistically significant relationship

between the different substrates and the starfish

sizes (again grouped into SMALL, MEDIUM,

BIG) (P < 0.001) (Table 3). The individuals of

medium to large sizes were located preferen-

tially on substrates covered by AF and CCA.

On the other hand, medium to small starfish

were found preferentially in the rhizomes or the

leaves of P. oceanica (Fig. 5).

Reproduction in Echinaster sepositus:

After 19 samplings carried out during one year

of research, there was no record of spawning of

E. sepositus.

Table 1

Percentage of appearance of E. sepositus in the different types of substrates in each of the zones.

AF CCA Rock P. l e a v e s P. rhizomes Sand Sponge Mix

Zone 1 56.67 24.17 3.33 0.83 5.00 0.00 0.83 9.17

Zone 2 55.05 9.63 4.59 3.67 17.89 1.38 0.46 7.34

Zone 3 3.33 2.00 0.00 15.33 73.33 4.67 0.00 1.33

AF: arborescent photophilic algae; CCA: crusted coralline algae; P. leaves: leaves of Posidonia oceanica; P. rhizomes: rhizomes

of P. oceanica. Zone 1: 3.5 m deep, rocky surface. Zone 2: 5 m deep, interface between rocky and P.oceanica meadow surfaces.

Zone 3: 7 m deep, P.oceanica meadow surface.

Fig. 3. Oceanographic profile of the station at a depth of 15 m of temperature values during the sampling period in Calpe.

Between mid-November 2021 and January 2022 and in July 2022, there was missing data due to malfunction of the

oceanographic probe.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

DISCUSSION

Populations of the Mediterranean red star-

fish follow an aggregated distribution, so that

they can be absent or be very abundant in loca-

tions close to each other. However, the factors

determining this distribution remain unknown

(Villamor & Becerro, 2010). A greater variability

of habitats favors a greater settlement of species

that can occupy the different niches, regulat-

ing different ecological parameters such as

abundance and distribution of species (Hewitt

et al., 2005; Zajac et al., 2003). The high density

of individuals observed in Cala del Racó could

be due to the diversity of habitats occurring in

a relatively small area, including rocks, sandy

bottoms and meadows of P. oceanica (Abbiati

et al., 2017). Another characteristic of the study

area that could help to explain the high density

of individuals in Cala del Racó, is the protec-

tion to the North and East winds offered by the

Peñón de Ifach and the West winds from the

Fig. 4. Distribution of the sizes (cm) of the number of individuals of Echinaster sepositus registered in each of the sampling

zones. Zone 1: 3.5 m deep, rocky surface. Zone 2: 5 m deep, interface between rocky and Posidonia oceanica meadow surfaces.

Zone 3: 7 m deep, P.oceanica meadow surface.

Table 2

Result of Pearson’s Chi-Square analysis between the different substrates and the sizes of Echinaster sepositus grouped into

categories.

Crosstab between Zone*LB (category)

BIG MEDIUM SMALL Total

Study areas Zone 1 52 64 4 120

Zone 2 58 150 10 218

Zone 3 3 111 36 150

Total 113 325 50 488

Pearson’s Chi-Square Test

Value gl Asymptotic significance (bilateral)

Pearson’s Chi-Square Test 95.881 4 <.001

Likelihood ratio 105.572 4 <.001

N of valid cases 488

Zone 1: 3.5 m deep, rocky surface. Zone 2: 5 m deep, interface between rocky and P.oceanica meadow surfaces. Zone 3: 7 m

deep, P.oceanica meadow surface. gl: degrees of freedom. LB: length of the arm.

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

Morro the Toix outcrop. An earlier study by

Villamor & Becerro (2010) indicated a change

in the communities at a depth of 5 m produced

by the hydrodynamics, which makes the pres-

ence of E. sepositus accidental. However, in our

study area, there have been 120 records of star-

fish in Zone 1, whose average depth was 3.5 m.

In Zone 1, located at a shallower depth,

there was an increase in the density of starfishes

from December to March, when the tempera-

ture of the water drops to 14 ºC, and there was

a decrease in density in spring and summer,

when the water temperature reaches 27 ºC. In

Zone 3, on the contrary, the density of indi-

viduals begins to increase from the month of

August to October-November and decreases

again during winter and early spring, except

for records taken in the sampling carried out

Fig. 5. Size distribution of Echinaster sepositus grouped into categories in each of the substrates considered in the study.

(Small: LB lower than 4 cm. Medium: LB between 4 and 6 cm. Big: LB bigger than 6 cm).

Table 3

Result of Pearson’s Chi-Square analysis between the different study areas and the sizes of Echinaster sepositus grouped into

categories.

Croostab between Substrate*LB (category)

BIG MEDIUM SMALL Total

Substrate AF 64 121 4 189

Sand 0 8 2 10

CCA 22 26 4 52

Sponge 1 1 0 2

Mix 9 21 1 31

P. le a ve s 1 27 5 33

P. rhizome 8 112 34 154

Rock 8 9 0 17

Total 113 325 50 488

Pearson’s Chi-Square Test

Value gl Asymptotic significance (bilateral)

Pearson’s Chi-Square Test 96.312 14 <.001

Likelihood ratio 111.036 14 <.001

N of valid cases 488

gl: degrees of freedom. LB: length of the arm.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

in January. These data suggest that the popu-

lation of E. sepositus would be moving, from

deeper and colder areas in summer, to shal-

lower and warmer areas in winter. Changes

in the behavior of starfish due to temperature

have already been studied. A study carried out

with Astropecten irregularis (Pennant, 1777)

concluded that this species exhibited a seasonal

pattern of abundance, with maximum densities

in summer and minimum densities during the

winter (Freeman et al., 2001). Similar results

already described in A. irregularis by Chris-

tensen (1970), recorded a decrease in popula-

tion density in the coldest months. This author

contemplated the idea that these starfish could

even “hibernate” during certain months of the

year. The starfish Asterias rubens Linnaeus,

1758 also shows a greater density in the warm

months and less in the cold months. However,

in A. rubens, its variation is due to the seasonal-

ity of its main food, mussels (Gallagher et al.,

2008). In the same way, it is possible that the

movement observed in E. sepositus at different

depths is due, not only to the temperature itself,

but also to the seasonal availability of food.

In Zone 1, most of the starfishes were

located on AF (56.7 %) and on CCA (24.17 %).

In Zone 2, the substrates with the highest num-

ber of E. sepositus specimens were AF (55.1 %)

and the rhizomes of P. oceanica with 17.9 % of

the records. In Zone 3, 73.3% of the starfishes

were located between the rhizomes of P. o c e -

anica and 15.3 % on the leaves. The appearance

of starfishes in sand, bare rock or sponges was

much lower. This study coincides with previous

ones that mention the presence of E. sepositus

in seagrass, sand, rock, pebbles and crusted

coralline algae (Bacallado et al., 2020; Caballero

et al., 2000; Clark & Downey, 1992; Entram-

basaguas et al., 2008; Villamor & Becerro,

2010). A study conducted on the Catalan coast

concluded that the abundance of E. sepositus

was only correlated with the percentage cover

of crusted coralline algae (Villamor & Becerro,

2010). However, in Cala del Racó only 10.6 % of

the sightings occurred over coralline algae, well

behind sightings over AF and rhizomes of P.

oceanica, 38.7 % and 31.5 %, respectively. As for

the presence of red starfish on rocky bottoms,

our data showed a greater similarity with the

observations of E. sepositus made on the coast

of Corsica by Raisch (2018), where E. sepositus

appeared in greater abundance in the tussock

and shrub algae.

If we focus on the relationship between the

size of the starfishes and the area in which they

were found, we observed a clear predisposition

of medium and large individuals in Zone 1 and

Zone 2, which were at an average depth of 3.5

to 5 m respectively. Nevertheless, the smallest

specimens were located preferably in Zone 3,

which was at an average depth of 7 m. A clear

preference of medium and large individuals was

also observed by substrates covered by arbores-

cent photophilic algae and by crusted coralline

algae. Instead, the smallest starfishes tend to

be in the Posidonia meadow, both in the leaves

and in the rhizome. One of the reasons why

this phenomenon happens could be a change

in nutritional requirements of E. sepositus at

different stages of growth. At the same time, it

could be due to a hydrodynamic reason. Hydro-

dynamic plays a central role in the ecology of

environment shorelines influencing survival,

morphology, movement, feeding and repro-

duction (Denny, 2006). Adverse hydrodynamic

conditions can produce changes in the behavior

of some echinoderms (McEuen, 1988). The

Zone 1, where AF and CCA substrates abound,

was the shallower and more exposed environ-

ment to currents. Smaller starfishes might have

a harder time withstanding these currents while

feeding on the algae that grow on the rocks.

The Posidonia meadow, together with a

greater depth, would offer a calmer environ-

ment for smaller starfish. Species of the genus

Echinaster feed on microscopic organisms and

detrital materials by internal digestion or may

consume tissues partially digested from larger

organisms by external digestion (Turner, 2013).

The observation of a starfish with its stomach

everted indicates that it is feeding at the time

(Lawrence, 2013). Observations made in aquar-

iums indicate that E. sepositus feeds on different

groups of invertebrates, microbial films and

carrion (Brooks & Gwaltney, 1993; Ferguson,

12 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

1984; Jangoux & Lawrence, 1982; Scheibling

& Lawrence, 1982; Sloan, 1980). They have

also been found with the stomach evaginated

on multiple invertebrates, algae and sediments

(Ferguson, 1969). However, no study has shown

what E. sepositus eats in the wild (Turner, 2013).

Some authors considered sponges as a key food

for E. sepositus (Sarà & Vacelet, 1973; Vasserot,

1961). However, subsequent studies have not

found a consistent trophic relationship between

the Mediterranean red starfish and the sponges

(Maldonado & Uriz, 1998). The presence of E.

sepositus on sponges has been anecdotal during

the sampling year in Cala del Racó, unlike 33 %

of appearance on sponges of E. gramicola in an

investigation by Ferguson (1969). This could

support the results obtained by Maldonado &

Uriz (1998). It is necessary to carry out special-

ized studies on the feeding of E. sepositus since

there are many knowledge gaps to be resolved

(Turner, 2013). Despite the feeding of E. seposi-

tus was not the main objective of the present

work, the results obtained in the location of the

starfishes in the different substrates, and the

differentiation of size in each one of the sub-

strates, provide useful information to improve

the development of future research.

Regarding the reproductive cycle, there is

a great variety of strategies in asteroids regard-

ing reproduction, which can be seasonal or

continuous (Mariante et al., 2010). Seasonal

reproduction has been demonstrated in some

species of the genus Echinaster in the Atlantic

Ocean and the Gulf of Mexico (Chen & Chen,

1992; Ferguson, 1975; Guzmán & Guevara,

2002; Scheibling & Lawrence, 1982; Turner,

2013). The main advantage of this kind of

reproduction is the synchronization of game-

togenesis in males and females, which makes

fertilization more likely (Bos et al., 2008; Car-

valho & Ventura, 2002; Raymond et al., 2007).

After 19 samplings carried out during a year in

Cala del Racó, no specimen of E. sepositus has

been observed reproducing. For the spawning

to occur in the time intervals between the sam-

plings, it should have happened in a short time

window of a few days in summer and autumn,

but no indications of it were recorded. It is more

probable to suppose that the laying of gametes

in E. sepositus did not happen that year because

it does not occur annually. The reproduction in

the subgenus Echinaster (Echinaster) could be

dependent on environmental conditions such

as temperature, hydrodynamics or the amount

of available food, which would determine the

starfish of spawning; as it happens with the

subgenus of Echinaster (Otilia) (Mariante et

al., 2010; Scheibling & Lawrence, 1982). The

importance of temperature in gametogenesis

has also been mentioned for Marthasterias

glacialis, a species of starfish that inhabits from

the sublittoral to depths of 180 m and that lays

gametes in surface waters, where tempera-

ture increase is maximum in spring-summer

(Benítez-Villalobos et al., 2006; Mercier &

Hamel, 2009; Minchin, 1987).

Despite reproduction not being observed,

the highest density of individuals (0.51 ind/m2)

occurred in October, far exceeding the densities

recorded in the samplings directly before and

after. This date coincides with the time of the

year in which the reproduction of E. sepositus

was recorded in this same area in 2018. This

timing also seems to adjust to the maximum

gonadal development registered for the months

of June and July by Villamor & Becerro (2010).

During breeding events, asteroids congregate

to facilitate external fertilization after spawning

(Hancock, 1958). To have occurred in the same

time intervals between sampling, spawning

would have had to take place within a short

window of a few days in summer and autumn.

However, no evidence of this was recorded.

Another possibility is that gamete spawning in

E. sepositus did not occur that year, possibly due

to some water conditions such as temperature,

hydrodynamics or the amount of available food

(Mariante et al., 2010). The conditions of the

water could also be the ones that explained the

time difference between the different records

of reproduction in E. sepositus. For future

research, we recommend repeating the sam-

pling intensity, and concentrating the effort in

the months of September and October, when

data indicate that the probability of observing

spawning is higher.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 72(S1): e58967, marzo 2024 (Publicado Mar. 01, 2024)

Ethical statement: the authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

ACKNOWLEDGEMENTS

This study would not have been possible

without the Instituto de Investigación en Medio

Ambiente y Ciencia Marina (IMEDMAR-UCV)

of the Universidad Católica de Valencia, for the

contribution of its facilities, its resources and its

time. Special agreements to: Clara Téllez, Diana

López, Ana Bodí, Teresa Uribe, Marina Muñoz

and María José Valera for their help in the dives.

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