Rhodolith bed diversity in the Gulf of California: the importance of rhodolith structure and consequences of disturbance

Abstract

ABSTRACT1. Rhodolith beds, unattached coralline reefs, support a high diversity and abundance of marine species from both hard and soft benthos. We used surveys in multiple shallow (3-20 m) beds in the Gulf of California to (1) examine seasonal patterns in associated floral and faunal diversity and abundance, (2) compare differences in faunal associations between rhodolith beds and adjacent sedimentary habitats, (3) examine the importance of complexity of rhodolith structure to community structure, and (4) estimate the impact of anthropogenic disturbance on rhodoliths and associated species.2. Macroalgal richness was seasonal, and beds supported higher richness in winter (to 36 species) than summer (6-7 species), primarily due to foliose red algae. Strong seasonal variation in the abundance of dominant cover organisms was due to a shift from macroalgae and mat-forming colonial invertebrate species to microalgae.3. The community in a rhodolith bed of high-density thalli (El Coyote average $11000 thalli/ m À2 ) had higher richness (52 versus 30 species) and abundance of epibenthic and crypto-and infaunal species compared with an adjacent sand community. Species diversity and abundance was particularly high for unique cryptofaunal organisms associated with rhodolith interstices. Cryptofauna reached average densities of 14.4 organisms/ cm À3 rhodolith, the majority of which were crustaceans, polychaetes and cnidarians along with rhodolith-specific chitons.4. Results from sampling across a range of rhodolith morphs in the El Requeson bed (with lower average cryptofaunal densities of 2.3 organisms/ cm À3 ) revealed that the total organisms supported by a rhodolith significantly increased with both complexity (branching density) and space available (thallus volume). These data suggest that reducing the population size structure, structural complexity and cover of living rhodoliths could decrease species richness and abundance.5. While disturbance is a natural feature of these free-living beds, increased anthropogenic disturbance from trawling, anchoring and changes in water quality can directly impact the bed community through substrate alteration. Commercial fishing threatens rhodolith beds in the Gulf of California by decreasing rhodolith size and increasing sedimentation and burial rates. In addition to

Seasonal patterns in the maërl community of shallow European Atlantic beds and their use as a baseline for monitoring studies

“…Rhodophyta are dominant in European Atlantic mae¨rl beds (Cabioc'h, 1969;Hily et al, 1992;Birkett et al, 1998;Pen˜a and Ba´rbara, 2008a) and in the Mediterranean (Ballesteros, 1988;Soto, 1990;Mannino et al, 2002), as well as in other geographical areas, such as the Gulf of California (Steller et al, 2003) and Brazil (Amado-Filho et al, 2007;Riul et al, 2009). According to Ballesteros (1988), the abundance of red algal species in Mediterranean mae¨rl beds is related to the great depth where they occur.…”

“…However, in deep Mediterrranean coralligenous assemblages, Garrabou et al (2002) found the lowest seasonality of all subtidal communities, whereas Piazzi et al (2004) recorded a decrease in species richness and algal cover during the cold months. At other latitudes, the mae¨rl-associated flora is seasonally variable (Amado-Filho et al, 2007) and can be richer in winter (up to 30 species, Steller et al, 2003), due to unfavourable conditions during summer.…”

Conservation and management of northeast Atlantic and Mediterranean maerl beds

“…a anchez-Mata et al, 1998;Hall-Spencer et al, 2003;Steller et al, 2003). Many northeast Atlantic maerl beds are productive fishing grounds for scallops and infaunal bivalves and Mediterranean maerl beds are often targeted for demersal fish and cephalopods (Massut!…”

Structure of rhodolith beds from 4 to 55 meters deep along the southern coast of Espírito Santo State, Brazil

“…Los rodolitos son capaces de transformar fondos homogéneos de sedimento suave en sustratos heterogéneos duros, creando un hábitat para numerosas algas e invertebrados que incluyen especies epibénticas, crípticas e infaunales (Steller et al 2003); por ello, los rodolitos son considerados especies fundamentales (Foster et al 2007). En un estudio reciente que evaluó la biota marina en la zona económica exclusiva de Brasil (área marina que se extiende 320 km mar adentro), se mostró que el aumento en la diversidad de organismos epibénticos puede asociarse con la presencia de mantos de rodolitos.…”

“…Hasta este estudio, los muestreos en la zona submareal del estado de Espírito Santo a profundidades mayores dque 5 m habían consistido en actividades de dragado "no amigables con el ambiente" y todas las muestras obtenidas de L. abyssalis aparecían adheridas a los rodolitos mediante su órgano de fijación, lo que indica su asociación con los mantos de rodolitos 22º S, considered the largest area supporting rhodolith beds in the world (Foster 2001). Rhodoliths are capable of transforming homogeneous soft sediment bottoms into heterogeneous hard substrata, providing habitat for a number of other algae and invertebrates, including epibenthic, crypto and infaunal species (Steller et al 2003). For the reasons given, rhodoliths are foundation species (Foster et al 2007).…”