Filling a gap:dynamics of space occupancy on a mussel-dominated subtropical rocky shore

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Two sessile filter-feeders of similar body sizes, the goose barnacle Capitulum mitella and mussel Septifer virgatus, occur in patches on a moderately wave-exposed rocky shore of south Japan in the western Pacific. Their pattern of coexistence was investigated through field observations and experimental manipulation, focusing in particular on seasonally variable modes of facilitation under harsh environmental conditions found in the upper intertidal. Field observations and reciprocalremoval experiments showed a high survivorship of C. mitella in both mixed patches (containing C. mitella and S. virgatus) and Capitulum-only patches. In contrast, S. virgatus exhibited a substantially higher survivorship in the mixed than in single situations, indicating that S. virgatus was positively affected by the presence of C. mitella, while the latter was not influenced by the presence of the former in the upper intertidal. An artificial patch transplant experiment demonstrated that C. mitella enhanced S. virgatus survivorship and growth both in summer when thermal stress was severe and in winter when physical disturbance caused by wave action was strong. In contrast, the artificial shade treatment enhanced S. virgatus survivorship only in summer. In summer, thermal conditions (temperature and interstitial humidity within patches) were harsher in the unshaded (S. virgatus-only) than in the mixed (C. mitella + S. virgatus) and shaded treatments (S. virgatus with artificial shade). In contrast, the effect of severe physical condition as evidenced by the extent of shell wear in mussels was more pronounced in the shaded and unshaded treatments than in the mixed treatment in winter. These results suggest that C. mitella had 2 different habitat-modifying functions: (1) amelioration of thermal stress and (2) amelioration of physical stress; the artificial shade performed only the first of these.

Section: Coexistence In Similar-sized Sessile Organismsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Variable modes of facilitation in the upper intertidal: goose barnacles and mussels

Kawai¹,

Tokeshi²

2004

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“…Increased abundances and/or diversities within mussel beds have been reported for a variety of mussel species, including Mytilus californianus (Kanter 1980) (Stephenson & Stephenson 1972, Peake & Quinn 1993. It has also been fo.und that species outcompeted for primary space by mussels can live epizoically on the mussel shells (Lohse 1993, Tokeshi & Romero 1995. Even beds created by zebra mussels Dreissena polymorpha benefit populations of a wide variety of small invertebrates (Dermott 1992, Stewart & Haynes 1994.…”

Section: Discussionmentioning

confidence: 99%

Habitat alteration and community-level effects of an exotic mussel, Musculista senhousia

Crooks¹

1998

189

159

The mussel Musculista senhousia is capable of marked habitat alteration through the construction of byssal mats on the surface of soft sed~ments Here 1 demonstrate the importance of this alteration on sedimentary properties and res~dent macrofaunal assemblages of a tidal flat in Mission Bay, San Diego, California, USA, where the mussel is exotic. In well-developed mats, percent fine sediments, percent combust~ble organic matter, and sediment shear strengths were increased relative to adjacent areas without mats. Comparisons of naturally occurring areas with and without mats of M. senhousia, as well as compansons of the same tidal flat when mussels were seasonally present and absent, revealed that assemblages w~thin mussel mats differ from those in sediments without mats. The primary effect of the mussel and its mats was facilitation of other organisms. Total densities of all macrofaunal ~ndiv~duals as well as specles richness were typically higher inside than outside mussel mats. Two species that exhibited large enhancements of densities within mussel mats were the tanaid Leptochelia dubia and the gastropod Barleeia subtenuis. Oligochaetes, a numerically important component of the tidal flat, appear least facilitated by the presence of mats. A shortterm, manipulative experiment that examined the effects of mussel mat mimics on the colonization of macrofauna suggested that the presence of physical structure alone can produce several of the patterns observed in naturally occurring mussel mats. These results highlight that alteration of habitats is an important effect of exotic species, and that these habitat alterations can have subsequent effects on resident biotic communities.

“…On marine rocky shores, primary rock surfaces are frequently occupied by dense popul a t i o n~ of mytilid bivalves (cf. Seed 1976, Suchanek 1985, Seed & Suchanek 1992 which form an intricate matrix of 3-dimensional habitat structures that can be inhabited by polychaetes and other organisms (Suchanek 1979, 1985, Tsuchiya & Nishihira 1985, 1986, Tsuchiya & Bellan-Santini 1989, Tokeshi & Romero 1995a. These organisms constitute a unique assemblage, as the majority of taxa cannot exist without the protection provided by mussel beds on a n exposed shore (Tokeshi & Romero 1995a).…”

Section: Introductionmentioning

confidence: 99%

“…Seed 1976, Suchanek 1985, Seed & Suchanek 1992 which form an intricate matrix of 3-dimensional habitat structures that can be inhabited by polychaetes and other organisms (Suchanek 1979, 1985, Tsuchiya & Nishihira 1985, 1986, Tsuchiya & Bellan-Santini 1989, Tokeshi & Romero 1995a. These organisms constitute a unique assemblage, as the majority of taxa cannot exist without the protection provided by mussel beds on a n exposed shore (Tokeshi & Romero 1995a). Although a considerable body of information exists on the dynamics of mussel beds in both intertidal (Dayton 1971, Paine 1971, 1974, Paine & Levin 1981 and subtidal (Dean & Hurd 1980, Schoener & Schoener 1981, Chalmer 1982, Greene & Schoener 1982, Okamura 1986) systems, few studies have investigated the spatial patterns and interspecific relationships of species coexisting in these mussel-matrix habitats (Tsuchiya & Nishihira 1985, 1986, Tokeshi et al 1989b).…”

Section: Introductionmentioning

confidence: 99%

Polychaete abundance and dispersion patterns in mussel beds:a non-trivial 'infaunal' assemblage on a Pacific South American rocky shore

Tokeshi¹

1995

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Patterns of abundance and spatial dispersion were analysed in an assemblage of polychaetes associated with mussel beds in a wave-exposed rocky intertidal habitat on the Pacific coast of subtropical South America. Mussel beds were made up of 2 zones in the intertidal, the lower, more extensive zone formed by Semimytilus algosus and the upper by Perumytilus purpuratus. Total polychaete density in the Semimytilus habitat was in the range of 18800 to 36300 lnd. m-2, comparable to some high values recorded for polychaete communities In soft sediments. Thls Indicates that musselbed environments on hard substrata are not a marginal but major habitat for polychaetes (free-rang~ng forms in particular) on the predominantly rocky coast of western South America. Populations of 6 taxa (Pseudonereis. Halosydna, Lumbrineris, Scoloplos, Mediomastus and Tj~posyllis) demonstrated moderate seasonal fluctuations, with numbers generally low in austral winter and reaching maxima in spring/summer. Numerically, Typosyllis was the most abundant taxon, accounting for 52 to 71 % of all individuals. All the taxa showed a contagious (aggregated) dispersion, with the deposit feeder Mediomastus demonstrating the strongest aggregation and lergest fluctuations over a year. Another deposit feeder with limited mobll~ty, Scoloplos, also demonstrated relatively strong aggregation. Iwao's h -m regression analysis revealed that mean crowding measure was linearly related to mean density in Pseudonereis, Halosydna, Lumbrineris and Scoloplos, with the highest value of slope P (2.06) for Scoloplos, while no relation was evident in Mediomastus and Typosyllis. Density was generally lower in the upper Perumytilus habitat, in particular for the 2 free-ranging taxa Halosydna and Typosylljs, while the free ranger Syllis had a higher density in the Perumytilus than in the Semimytilus bed. All taxa were more strongly aggregated in the Perumytilus than in the Semimytilus habitat, probably reflecting the variability and more patchy occurrence of favourable microhabitats and available resources in the former. Among the 5 taxa that occurred in abundance In both Semimytilus and Perumytllus habitats, the less moblle deposit feeder Scoloplos had the highest degree of contagion indicating ~t s patchy, aggregated distribution patterns, whlle the predaceous, completely free-ranging Halosydna demonstrated a relatively weak aggregation. Overall, the lack of regular dispersion patterns and the consistent occurrence of contagious distributions suggested that polychaetes associated with mussel beds did not demonstrate territorially based interactions as seen in some sessile, tubedwelling species. Complex, coarse-grained habitat structures of mussel beds support high abundances and species richness of polychaetes, allowing the expression of taxa-specific patterns of dispersion as a result of interactions beween behaviours and environmental conditions.