A Review of the Intertidal Rocky Shore Community at ...

A Review of the Intertidal Rocky Shore Community at Mar Del Plata (Argentina) Characterized by the Mussel Brachidontes rodriguezii (d' Orbigny, 1846)

PABLO E. PENCHASZADEH1, MARCELO A. SCELZO2, GABRIELA PALOMO1, MARTÍN CUEVAS1 and MAXIMILIANO CLEEDÓN2

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Museo Argentino de Ciencias Naturales- CONICET-UBA, Av. A. Gallardo 470, 1405 Buenos Aires. 2 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 representing a dry biomass of 1,670 g. m ; upper horizontal substrates at the same level show lower densities (80,000 indiv. m ; 592 g. m ). The horizontal bed matrix accumulates more sand than vertical beds (19.1 Kg. m and 5.1 Kg. m , 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 . 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. -2

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Key words: low diversity, mussels, superabundance, SW Atlantic

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. 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 nearest neighbour Clark & Evans method (scale photographs) and using colored epoxy to mark the shells (Olivier and Penchaszadeh, 1968). Three denuded areas (625 m ) were studied monthly between December 1965 and March 1968 with a 25x25cm quadrate to detect the percent coverage and settlement time of Brachidontes rodriguezii (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 100cm 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 cm of Brachidontes rodriguezii patches was sampled monthly at each intertidal level along the vertical concrete walls (Scelzo et al., 1996). 2

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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). 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 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 (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., Lyngbya sp. and Plectonema sp.), form a fine green-brown layer over the substrate of small spray pools (Olivier et al., 1966). -2

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 Lyngbya 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 ) than in the high intertidal (1,100 indiv. m ) 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 ) and have more dry biomass (1,670 g. m ) of B. rodriguezii than the horizontal substrates of the same level (81,262 indiv. m ; 592 g. m ) which may be related to the greater accumulation of sand on the horizontal beds (horizontal beds 19.1 Kg. m , vertical beds 5.1 Kg. m ). 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 platensis 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: Nemertean Lineus bonaerensis and the polychaetes Syllis prolixa, Protoariciella uncinata, Paleanotus intermedius, Halosydnella australis, Neanthes succinea and Lummbrineris tetraura (Penchaszadeh, 1973, Elías and Bremec,2004). 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 (15mm 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 Penchaszadeh, 1968). High limpet densities in the upper midlittoral (Mean = 3,676 ind./m ) were recorded. Mean shell size of the individuals (3.9mm) increases as the density of population decreases towards the supralittoral levels. -2

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PABLO E. PENCHASZADEH, MARCELO A. SCELZO, GABRIELA PALOMO, MARTÍN CUEVAS and MAXIMILIANO CLEDÓN

Table 1. Main intertidal fauna of the exposed rocky shore of Mar del Plata.


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./m 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./m 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 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 of retained sediment between the carpet of mussels and the rock substrate in vertical walls and 19.1 kg. m in horizontals surfaces which may directly correspond to the higher density of Brachidontes rodriguezii (175,000 ind. m ) 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. 2

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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 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

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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, amphipods, 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, thus increasing the total fauna . 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. 1971. 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, Polyplacophora) con especial referencia a sus epibiosis. Elias, R.; Bremec, C. 2004. Lombrices de mar. In: Boschi, E. E. ed. Entre mareas. Cap.14: 123-130. 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: Isla, F. I. ed. Estudio del sector de plataforma receptor de la descarga cloacal de Camet, Mar del Plata. Mar del Plata, Facultad de Ciencias. 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. Ecología y biología 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 bénticas 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 Penchaszadeh, 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. Cah. 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. Vallarino, E. y Elias R. 1997. The dynamics of an introduced Balanus glandula population in the Southwestern 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

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Plate 2

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