A Review of the Intertidal Rocky Shore Community at Mar Del Plata

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●●●●●THE NAGISA WORLD CONGRESS. 8: 115-123, 2007
A Review of the Intertidal Rocky Shore Community at Mar Del Plata (Argentina)
Characterized by the Mussel
Brachidontes rodriguezii (d' Orbigny, 1846)
PABLO E. PENCHASZADEH, MARCELO A. SCELZO, GABRIELA PALOMO,
MARTÍN CUEVAS and MAXIMILIANO CLEDÓN
Museo Argentino de Ciencias Naturales- CONICET-UBA, Av. A. Gallardo 470, 1405 Buenos Aires.
Departamento de Ciencias del Mar, Universidad de Mar del Plata, and CONICET Argentina
Corresponding author: [email protected]
Abstract In the rocky shores of Mar del Plata (38˚W 04’S), intertidal mussels monopolize the
macrofauna communities developing beds dominated by the small mytilid Brachidontes
rodriguezii. This species covers 45% to 65% of the mid and upper mid intertidal substrate forming
stratified beds. Vertical protected substrates of the midlittoral show the highest densities of B.
rodriguezii up to 175,000 indiv. m-2 representing a dry biomass of 1,670 g. m-2; upper horizontal
substrates at the same level show lower densities (80,000 indiv. m-2; 592 g. m-2). The horizontal bed
matrix accumulates more sand than vertical beds (19.1 Kg. m-2 and 5.1 Kg. m-2, respectively).
Twenty-six taxa and 14 animal species were recorded within the B. rodriguezii intertidal matrix
while a total of 9 algae species were found living on the mussel bed. The pulmonate limpet
Siphonaria lessoni is the main intertidal herbivore. The invasive barnacle species, Balanus
glandula, was first detected in Mar del Plata in 1974 and today creates an upper midlittoral fringe
at densities up to 5,000 indiv.m -2. This review of the Mar del Plata rocky shore community
summarizes the existing information as we prepare to sample this area with the NAGISA
protocols. The uniqueness of the rocky intertidal of Mar del Plata is the absolute dominance of a
single mussel species Brachidontes rodriguezii in the midlittoral, the presence of a sole species of
Gastropoda, the grazer pulmonate Siphonaria lessoni and the absence, until the mid sixties, of a
barnacle belt.
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Introduction
The first description of the intertidal rocky shore of Mar del Plata was by Olivier et al. (1966).
They described the zonation pattern of the natural rocky littoral zone between Playa Grande and Playa
Chica using Pérés and Piccard’s (1958) terminology. However the study of human impact on these
rocky shores has been limited to two papers on the invasive barnacle species, Balanus glandula, first
detected on artificial panels of the port of Mar del Plata in 1974 (Bastida et al., 1980). Today the
species develops an upper midlittoral fringe on the natural exposed rocky shore of Mar del Plata
(Vallarino and Elias, 1997).
The uniqueness of the rocky intertidal of Mar del Plata is the absolute dominance of a single
mussel species Brachidontes rodriguezii in the midlittoral, the presence of a sole species of
Gastropoda, the grazer pulmonate Siphonaria lessoni and the absence, until the mid sixties, of a
barnacle belt. When compared to with other equivalent temperate rocky intertidal communities the
most striking feature of the Mar del Plata site is the extremely poor number of dominating species and
the lack of predatory snails.
The aim of this paper is to summarize the information of the intertidal rocky shore community of
Mar del Plata (tide pools, rocky tide channels and the Port are not discussed) in an attempt to organize
the current knowledge in a useable form to be accessed by researchers, as the area becomes a NaGISA
site.
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Materal and Methods
Sampling methods
All samples were taken at the intertidal rocky shore of Mar del Plata. Transects were made
along the intertidal area using a frame of 25x25cm to describe the zonation patterns (Olivier et al.,
1966). The vertical distribution of Siphonaria lessoni was quantified by stratified censuses (25x25cm
quadrats) in the upper midlittoral and in the lower supralittoral area. The aggregation patterns and the
dispersion type of Siphonaria lessoni was studied at the lower supralittoral using the Clark & Evans
method (scale photographs) and using colored epoxy to mark the shells (Olivier and Penchaszadeh,
1968). Three denuded areas (625 m2) were studied monthly between December 1965 and March 1968
with a 25x25cm quadrate to detect the percent coverage and settlement time of Brachidontes
rodriguezzi (Penchaszadeh, 1973). Density of the quitons Plaxiphora aurata and Chaetopleura
isabellei were quantified by random censuses on the midlittoral using a 50x50cm quadrat (Brandani et
al., 1974). To detect the percent coverage and settlement time of Balanus glandula, four 100cm2 areas
were randomly selected, denuded and surveyed monthly, from January to December 1991, in the lower
supralittoral and in the upper midlittoral areas (Vallarino and Elias, 1997). To study an artificial
substrate an area of 78 cm2 of Brachidontes rodriguezii patches was sampled monthly at each intertidal
level along the vertical concrete walls (Scelzo et al., 1996).
Study Area
The coastal area of Mar del Plata is an urban open coast exposed to a longshore littoral current
(South to North) and autumn-winter storms. Extensive sandy beaches alternate with quartzitic outcrops
and abrasion platforms (Elias et al, 2003).
The intertidal rocky shore of Mar del Plata consists of natural irregular quartz boulders where
tidal amplitude determines intertidal zonation extending several meters depending on wave splash and
substrate inclination (Plate 1; Olivier et al., 1966). The supralittoral area of Mar del Plata is very well
developed vertically as the rocks form a cliff, which recives heavy wave action. Siphonaria lessoni can
be distributed up to 5m above high tide level. The midlittoral is a band of 0.90 - 2.1m, depending
mainly on the tide level, wind action and exposure.
Semidiurnal tides vary between 0.61 and 0.91m (Isla & Ferrante, 1997). High-energy waves
(mean height of 0.91m) reach a maximum of 2.3m during storms (Lanfredi et al., 1992). It is also
characterized by the presence of Continental Shelf Waters, with seawater temperature ranging from 8
℃ (winter) to 21℃ (summer), and salinity from 33.5 to 33.8 psu (Guerrero & Piola, 1997).
Description and Discussion
Natural rocky shore Supralittoral:
Olivier et al. (1966) described three levels: upper level, influenced only by humidity; middle
level, where the splash water reaches the only during storms; lower level, where the splash water
regularly reaches. They also described three different communities inhabiting the supralittoral levels.
The upper and middle assemblages were characterized by lichen species covering the rock surface of
the upper (orange species) and middle (black species of the genus Verrucaria) supralittoral levels
(Olivier et al., 1966). The limpet Siphonaria lessoni, occupies crevices of the middle and lower levels
(Olivier et al., 1966). In the lower supralittoral this limpet species has a mean total length of 8mm
(min.= 3.1 mm, max. = 16.5mm) and lives directly on the substrate with a mean density of 853
indiv.m-2 (Olivier and Penchaszadeh, 1968). In the lower supralittoral Siphonaria lessoni’s aggregation
and dispersion has been related to wind, wave spray, and humidity and it has been reported to show no
homing behavior (Plate 1 and 2; Olivier and Penchaszadeh, 1968). In the middle and lower levels
supralittoral communities are dominated by Cianophytes species (Calothrix sp., Schizothrix sp.,
Lynbya sp. and Plectonema sp.), form a fine green-brown layer over the substrate of small spray pools
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(Olivier et al., 1966).
Natural rocky shore Midlittoral
The first description of the Mar del Plata natural intertidal rocky shore shows that the upper,
middle and lower levels of the midlittoral were exclusively occupied by a Brachidontes rodriguezii Mytilus edulis platensis mussel community (Olivier et al., 1966). These mitylids represented 95 % of
the total fauna of the intertidal community of the exposed rocky shores (Table 1; Olivier et al., 1966).
The upper limit of the midlittoral being delimited by a belt formed by the red encrusting alga
Hildenbrandtia sp., Nemalion sp. and Siphonaria lessoni (Plate 1 and 2; Olivier et al, 1966). Beneath
the carpet of Hildenbrandtia live some Cianophytes species: Calothrix sp., Brachytrichia sp.,
Phormidium sp., Schizothrix sp., Microcoleus sp., Kyrtuthrix sp.and Lynbya sp. (Penchaszadeh, 1973).
Barnacles (Balanus amphitrite) are mentioned for the first time in the port of Mar del Plata in the
1970s (Bastida, 1971). The invasive barnacle, Balanus glandula, was detected in the Mar del Plata
area in 1974, on artificial panels in the port (Bastida et al., 1980). Today the upper midlittoral fringe of
the exposed natural rocky shores is occupied by this species (Table 1; Vallarino and Elias, 1997).
Barnacle recruitment begins in winter with the heaviest recruitment occurring in August and October.
Balanus glandula densities are greater in the upper mid intertidal (5,050 indiv.m-2) than in the high
intertidal (1,100 indiv. m-2) rocky shore, while mortality is higher in the high intertidal than the upper
mid intertidal. The winter settlement in the Mar del Plata area suggests a breeding season of June July, with settlement apparently requiring at least two winter months. Vallarino and Elías (1997) found
that an initial film must develop on the substratum before is attractive to barnacles based on the scarce
or null colonization of denuded areas during their experiment in June and July. They concluded that
predator absence, wave disturbance and winter settlement may allow Balanus glandula to successfully
colonize the upper mid littoral of the natural Mar del Plata rocky shore (Vallarino and Elias, 1997). As
result of the Balanus glandula invasion the earlier almost completely monopolized belt of
Hildenbrandtia sp. is now a mixed band of the algae and the barnacle.
The dominant species of the mid midlittoral natural rocky shore of Mar del Plata is still the
bivalve Brachidontes rodriguezii, representing the 93% of the total community fauna. The species
covers 45% to 65% of the mid and upper mid intertidal substrate forming stratified beds (Plate 2). The
vertical substrates of the upper mid intertidal carry more individuals (175,140 indiv. m -2) and have
more dry biomass (1,670 g. m-2) of B. rodriguezii than the horizontal substrates of the same level
(81,262 indiv. m-2; 592 g. m-2) which may be related to the greater accumulation of sand on the
horizontal beds (horizontal beds 19.1 Kg. m-2, vertical beds 5.1 Kg. m-2). Twenty-six taxa and 14
animal species were recorded within the B. rodriguezii intertidal matrix while a total of 9 algae species
were found living on the mussel bed. Member species of the community are: small Mytilus edulis
individuals, juveniles of the limpet Siphonaria lessoni living temporary on the mussel bed
Penchaszadeh (1973). Epibionts of the mussels include seaweed species, the most important being:
Ulva sp., Porphyra sp., Chaetomorpha sp., Enteromorpha sp. and Bostrichia sp. These seaweeds
provide habitat for the amphipods Hyale grandicornis and Allorchestes sp. Between the matrix
sediment lives some vagil individuals: Nemerteans and the polychaete Syllis prolixa (Penchaszadeh,
1973). The mussel bed matrix it is also an important recruitment habitat for many intertidal species
that do not live within the matrix as adults: chitons, Plaxiphora aurata and Chaetopleura isabellei;
crabs, Pachycheles haigae and Halicarcinus planatus and the gastropod Siphonaria lessoni.
The upper midlittoral population of Brachidontes rodriguezii has smaller individuals (max. length
= 30 mm) than the lower midlittoral population (max. length = 55 mm) and the presence of little
individuals (1-5mm total length) is common throughout the year (Penchaszadeh, 1973). In the upper
mid intertidal the pulmonate gastropod Siphonaria lessoni, lives on the B. rodriguezii bed, due mainly
to the almost complete mussel coverage of the substrate (Olivier and Penchazadeh, 1968). High
densities in the upper midlittoral (Mean = 3,676 ind./m2) were recorded. Mean shell size of the
individuals (3.9mm) increases as the density of population decreases towards the supralittoral levels.
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Table 1. Main intertidal fauna of the exposed rocky shore of Mar del Plata.
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In the upper midlittoral the Siphonaria lessoni distributes at random without an aggregation pattern
(which is characteristic of supralittoral limpets) and its movements are not specific due to the
homogenous distribution of food and humidity (Olivier and Penchaszadeh, 1968). The reproduction
period of the species is from June to March.
The quitons Plaxiphora aurata and Chaetopleura isabellei are inhabitants of the exposed natural
rocky shore of Mar del Plata. The former lives on both sheltered and exposed surfaces along the
intertidal area, with a bigger mean body length corresponding to the exposed areas (Brandani et al.,
1974). The specific mean density of Plaxiphora is 5 ind./m2 in very exposed rocks, with it's maximum
occurring in the mid-midlittotal level. Chaetopleura lives from the mid-midlittoral to the infralittoral
zone and does not inhabit surfaces exposed to the sun. The specific mean density is 8 ind./m2 with the
maximum number found in crevices of the lower Midlittoral (Brandani et al., 1974). The activity
period of Plaxiphora aurata is restricted to the tide regime, moving just below seawater during high
tide to search for food (Brandani et al., 1974).
In the rocky exposed intertidal areas of Mar del Plata, the winter - early spring settlement of
Balanus glandula allows the species to occupy the high intertidal zone in a season when the
Brachidontes rodriguezii community shows patchiness due to strong winter wave disturbance
(Vallarino and Elías, 1997). Wave disturbance[u2] frequently detaches patches of mussels and Nugent
(1986) found up to 30% bare rock on these surfaces, which increases subtidally. Penchaszadeh (1973)
found an average of 5.1 kg. m-2 of retained sediment between the carpet of mussels and the rock
substrate in vertical walls and 19.1 kg. m-2 in horizontals surfaces which may directly correspond to the
higher density of Brachidontes rodriguezii (175,000 ind. m-2) on the vertical walls.
It seems like the regulation and stability of the intertidal community of the Mar del Plata rocky
shore is influenced by the degree and frequency of disturbance, as well as by the population dynamics
of both mussels and barnacles (Vallarino and Elias, 1997). Space competition has also being pointed
out as the major biological structuring force in the 2 - 4 years period, while later successional stages
were characterized by space monopolization (Nugent, 1986).
The red encrusting alga Hildenbrandtia sp. seem to have neutral or beneficial effects on Balanus
glandula in the intertidal rocky shore of Mar del Plata, where both predators and canopy algae are
absent (Vallarino and Elias, 1997). Nugent (1986) suggests that B. glandula settlement may facilitate
the recovery of the Brachidontes rodriguezii population, allowing the mussels to colonize the upper
midlittoral. However, field experiments must still be done to identify the main ecological interactions
that structure this intertidal temperate community.
Penchaszadeh (1973) described the successional pattern of the rocky upper midlittoral zone in
Mar del Plata, observed by experimentally denuding an area. Recolonization begins with the
establishment of an initial thin microfilm of Diatoms and Bacteria. Followed by a second stage
characterized by the presence of the vagil gastropod Siphonaria lessoni and the decrease of the initial
film. In the third stage the algae Chaetomorpha, Porphyra and Ulva colonize the substrate (a seasonal
process). The red encrusting algae Hildenbrandtia sp. and associated Cianophytes become established
and cover the entire area. After 2 years the mytilid Brachidontes rodriguezii colonizes the substrate
and polychaetes and nemerteans colonize the sand and thin shells accumulated between the mussels
and the rocky substrate; the red algae Hildenbrandtia decreases until it disappears completely. The
sequence ends when the area is indistinguishable from the adjacent mussel bed patches.
Artificial rocky shore (concrete/man made surfaces):
A study was carried out on the vertical wall of two concrete defenses situated perpendicularly to
the Mar del Plata coastline. In 1996 Scelzo et al sampled the upper and middle intertidal and upper
subtidal zones. The mitylid Brachidontes rodriguezii was shown to represent between 70 to 90% of the
total artificial rocky shore community (Table 1), the relative abundance of the species peaking in
winter (July) and reaching a minimum in summer (January). The relative number of B. rodriguezzii
individuals increases from the upper intertidal to the upper subtidal while the proportion of Mytilus
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edulis platensis is very low at all levels. As in natural substrates the Brachidontes rodriguezii
community in artificial substrates was shown to act as a refuge for a great variety of species, due
mainly to the features of its stratified matrix.
Specific organisms were seen to represent each intertidal level. The upper midlittoral hosts the
isopod Sphaeroma serratum, amphipod Hyale grandicornis, gastropod Siphonaria lessoni, nematodes,
Chironomidae larvae and barnacles Balanus spp. The middle midlittoral and upper subtidal hosts
Syllidae polychaetes, Jassa sp. amphipods, Joeropsis sp. Isopods and the crab Pachycheles haigae.
The faunal community was represented by a total of 70 taxa and the authors identified: 43 species, 8
genera, 8 families and 11 superior taxons while finding that fauna increases from fall (May) to summer
(January). The comparatively large number of taxa found during this study is partially due to the
inclusion of upper subtidal samples, which increases the total fauna by incorporating subtidal taxons in
the intertidal zone.
The study of temporal and spatial variation of percentage cover, diversity and biomass of the
intertidal rocky shore community is one of the important ecological gaps yet to be filled. Studying the
successional processes and the existence of alternative dominance states is vital to the detection of
biological interactions that affect intertidal community structure. The future NaGISA censusing and
field experiments in Mar del Plata will be conducted in an attempt to understand the biological
interactions occurring in the intertidal community, specifically in the urban temperate intertidal rocky
shore of the South Atlantic Ocean.
References
Bastida, R. Las incrustaciones biológicas en el puerto de Mar del Plata. Periodo 1966/67. Rev. Mus. Arg. Cien.
Nat. “Bernardino Rivadavia”. Hidrobiologia, 3(2): 203 - 285.
Brandani, A; Faedo, J and Penchaszadeh, P. 1974. Aspectos de la ecologia de los quitones del litoral de Mar del
Plata (Mollusca, Poliplacophora) con especial referencia a sus epibiosis.
Elias, R.; Rivero, M; Vallarino, E. 2003. Sewage impact on the composition and distribution of polychaeta
associated to intertidal mussel beds of the mar del plata rocky shore, argentina. Iheringia. 93(3):309-318.
Guerrero, R. A. & Piola, A. R. 1997. Masas de agua en la plataforma continental. In: Boschi, E. E.ed. El mar
Argentino y sus recursos pesqueros 1. Mar del Plata, Instituto Nacional de Investigacion y Desarrollo
Pesquero. p.107-118.
Isla, F. I. & Ferrante, A. 1997. Corrientes. In: Ilsa, F. I. ed. Estudio del sector de plataforma receptor de la descarga
cloacal de Camet, Mar del Plata. Mar del Plata, Facultad de Ciencias 318 ELIAS, RIVERO & VALLARINO
Exactas y Naturales. p.63-116.
Lanfredi, N. W.; Pousa, J. L. 1992. Wave-power potential along the coast of the Province of Buenos Aires,
Argentina. Energy, Washington, 17:997-1006.
Nugent, P. 1986. Ecologia y biologia de los mejillinares de Brachidontes rodriguezi (D' Orb., 1846) en el litoral
bonaerense. Tesis doctoral. Universidad Nacional de la Plata, 86 pp.
Olivier, S; Escofet, A; Orensanz, J; Pezzani, S; Turro, A and Turro M. 1966. Contribución al conocimiento de las
comunidades benticas de Mar del Plata. I: El litoral rocoso entre Playa Grande y Playa Chica. An. Com.
Invest. Cient. Prov. Buenos Aires. 7: 185 - 206.
Olivier, S. y Penchazadeh, P. Observaciones sobre la ecologia y biología de Siphonaria (Pachysiphonaria) lessoni
(Blainville, 1824) (Gastropoda, Siphonariidae) en el litoral rocoso de Mar del Plata (Buenos Aires). 1968.
Inst. de Biol. Mar. Tomo IX, pp. 469 - 491.
Penchaszadeh, P. 1973 Ecología de la comunidad del mejillín (Brachidontes rodriguezii, D’Orb.) en el
mediolitoral rocoso de Mar del Plata (Argentina): el proceso de recolonización. Physis 32(84):51-64.
Scelzo, M; Elias, R; Vallarino, E; Charrier, M; Lucero, N and Alvarez, F. 1996. Variación estacional de la
estructura comunitaria del bivalvo intermareal Brachidontes rodriguezii (D'Orbigny, 1846) en sustratos
artificiales. Neritica, Vol. 10, p. 87 - 102.
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Atlantic Rocky Shores. The consequences on the intertidal community. Marine Ecology, 18 (4): 319 - 335.
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Legends:
Plate 1) Upper left: general view of the Mar del Plata rocky shore, Upper right: Supralittoral lichens. Down:
Intertidal zonation at a vertical protected wall. Level 1, supralittoral crevices. Level 2, Hildenbrandtia sp.
+ Balanus glandula belt. Level 3, Mussel community, Brachidontes rodriguezii.
Plate 2) Upper left: Siphonaria lessoni in a supralittoral crevice. Upper right: Red incrusting algae Hildenbrandtia
sp. + Balanus glandula. Down: Brachidontes rodriguezii bed during low tide.
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Plate 1
Plate 2
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A Review of the Intertidal Rocky Shore Community at Mar Del Plata

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