Patrones de diversidad de poliquetos en hábitats intermareales tropicales selectos

Few studies have quantitatively compared benthic macrofaunal assemblages between different tropical intertidal habitats over differing spatial scales. The present study uses spatially nested material from vegetated (seagrass) and non-vegetated (mudflat) habitats in SW Thailand to address this issue. Polychaetes were the numerically dominant component of benthic assemblages throughout the region, comprising over 74% of the total macrofauna. Despite great within-site and sample variation, based on species diversity, polychaete assemblages were mostly site-specific. Not so visibly obvious were the evident differences in polychaete assemblages between habitats. The spatial pattern of polychaete diversity is explored.Pocos estudios han comparado cuantitativamente el macrozoobentos entre diferentes hábitats intermareales tropicales a diferentes escalas espaciales. Para remediar esta situación, esta investigación utiliza y compara material colectado en praderas marinas y zonas sin vegetación en la costa suroeste de Tailandia a diferentes escalas espaciales. Los poliquetos formaron la mayor parte del zoobentos, constituyendo el 74% del total. Pese al alto nivel de variación entre muestras, basado en la diversidad de especies, los conjuntos de poliquetos mostraron mayor afinidad a su lugar de colecta. Diferencias entre cada hábitat, aunque difíciles de apreciar a simple vista, son corroboradas estadísticamente. Se exploran cambios en la diversidad asociados con cambios en la escala espacial. &nbsp

Scales of biodiversity in abyssal benthic polychaetes (abstract presented at the Sixth International Polychaete Conference)

As part of an European Union Marine Science and Technology (MAST) initiative, polychaete assemblages were studied from the Madeiran Abyssal Plain (MAP). Three other sites from the northeast Atlantic were used for comparative purposes. The sites lie under a gradient of surface productivity from a seasonal high productivity site on the Porcupine Abyssal Plain (PAP) to an oligotrophic non-seasonal site on the Cap Verde Abyssal Plain (EUMELI). Two sites of intermediate productivity were on the Tagus Abyssal Plain (TAP) and MAP. Data was analyzed to determine abundance, distribution within sediment, diversity and faunal similarity of MAP with the other three sites. MAP was show to have reduced abundance (approx. 250 ind m-2)and diversity compared to the other three sites. It is not apparent why MAP should show low polychaete abundance as it lies under a higher surface productivity regime than EUMELI. One possible explanation comes from a biogeochemical analysis which suggests that a turbidity current has passed through in the last 1000 yrs, re-working the sediment. Within sediment distribution of polychaetes at MAP revealed penetration of the 0–5 cm layer, similar to PAP and unlike the superficial distribution recorded form the oligotrophic EUMELI site. Analysis of beta diversity at MAP does not lend support to the idea of a latitudinal diversity gradient, being lower than both northerly and southerly sites. Surface and sub-surface deposit-feeding cirratulids, spionids and paraonids dominate the fauna. A dominant predator, Sigambra sp., was abundant in three of the sites. At the species level, faunal similarity was low, in the region of 15–20% between-site and 30–50% within-site. It appears that although similar in terms of functional groups, the sites are quite separate in terms of species composition, supporting the hypothesis that the abyss is not populated by one uniform species pool. Detailed taxonomic work on the more abundant “cosmopolitan” species is required to verify biogeographical distributions

Polychaete species diversity in the central Pacific abyss: Local and regional patterns and relationships with productivity

We investigated the relationship between productivity and local species diversity, and the degree of species turnover, at 8 sites on the central equatorial Pacific abyssal plain. The 8 sites span a 4-fold difference in seafloor particulate organic carbon (POC) flux and, hence, community productivity. The sites are similar in water depth (4300 to 5100 m), degree of isolation from terrigenous influences, and hydrodynamic regime. Three sites lie under the influence of equatorial upwelling, and are subject to enhanced deep POC flux derived from high overlying primary production. The remaining sites lie beneath the oligotrophic north Pacific gyre. The number of polychaete species collected at a single site ranged from 14 to 113, with at least 90% apparently being new to science. We found no evidence for the purported unimodal relationship between productivity and diversity seen in other ecosystems, including deep-sea slopes, and found only weak evidence of a monotonic increase in diversity with productivity. Rates of species turnover were low over scales of ~200 to 3000 km for the dominant polychaete species in the communities, and all sites were dominated by a core group of biogeographically widespread, locally abundant species. In contrast, there was little between-site similarity in the long list of rare species found at each site, implying either a high turnover of rare species at 200 to 3000 km scales, or incomplete sampling of the rare species list at each site. More intensive sampling studies using both morphological and molecular methods are needed to resolve the distribution patterns of rare species in the Pacific abyss. Local polychaete species diversity beneath equatorial Pacific upwelling (measured by rarefaction) appears to be unusually high for the deep sea, exceeding by at least 10 to 20% that measured in abyssal sites in the Atlantic and Pacific, and on the continental slopes of the North Atlantic, North Pacific, and Indian Oceans

Evidence for episodic recruitment in a small opheliid polychaete species from the abyssal NE Atlantic

The abundance and size spectra of an infaunal opheliid polychaete species was followed over a two year period (September 1996-October 1998) in meiofaunal-(32 µm-1 mm) and macrofaunal -(> 250 µm) samples collected at an abyssal site (4850 m depth) in the NE Atlantic. The site, situated on the Porcupine Abyssal Plain (PAP), is characterised by the episodic deposition of aggregated phytodetritus. The response of the fauna to this seasonal food supply was addressed by time-series sampling within the MAST-III BENGAL programme. In autumn 1996, small opheliid juveniles (mean length: 281 µm in September and 254 µm in October) were sampled only in the meiofauna samples. In March 1997, juvenile specimens of the opheliid, which were on average nearly twice as large (mean length: 480 µm) as those collected in 1996 were sampled in both both meio- and macrofaunal samples. The occurrence of only small juvenile individuals in 1996 suggests that a synchronous recruitment event had taken place earlier during that year. Small juveniles (mean length: 252 µm) were also abundant in a sample collected at the PAP site in May 1991, immediately following the deposition of a pulse of phytodetritus. The opheliid population structure in 1997 and 1998 indicates the slow progression of the settled cohort, possibly supplemented by a further, but relatively minor recruitment event in March 1998. Size spectra analysis implies that either growth was slow or that immigration of larger juveniles had augmented the population. The PAP opheliid may be an opportunist, which waits for optimal conditions before converting its slowly accumulated energy into reproduction. In addition, this species can apparently maintain a stable pool of developing juveniles if the organic pulse fails to materialise. The present study also shows that a more holistic approach is necessary to investigate the life cycles of some organisms, which lie close to the boundary between the meiofauna and macrofauna

Post-Tsunami Recovery of Shallow Water Biota and Habitats on Thailand’s Andaman Coast

There have been very few quantitative studies of the intertidal and shallow water biota of the Andaman Coast of Thailand and thus it was very difficult to provide precise estimates of the impact of the tsunami on coastal resources. Some quantitative data from Laem Son National Park existed, having been collected by the present authors, and these indicated that the most severe impacts were on the intertidal sand beach fauna, on rocky shore assemblages and on the seaward edge of mangrove forests. Inside the forests there was heavy deposition of coarse sediment on the forest floor and this led to changes in the species composition of the infauna. Most, but not all, sea grass beds escaped serious damage. By 2008 intertidal sediment assemblages contained a similar number of individuals to that recorded before the tsunami. Pre-tsunami data indicate that open coast, estuarine and seagrasses assemblages are naturally highly variable and thus were well adapted to recovering from the tsunami disturbance. Offshore sediments lack pre-tsunami information, but they too appear to be normal. Size frequency analysis of a population of the heart urchin Brissopsis luzonicus indicate that some individuals survived the tsunami but that there is heavy domination by the first post-tsunami cohort suggesting heavy colonization of disturbed seafloor. The trees in the seaward fringe of the most exposed mangrove forests still have to recover from tsunami damage, although the benthic fauna within the forest has returned.<br/

Temporal change in deep-sea benthic ecosystems: a review of the evidence from recent time-series studies

Societal concerns over the potential impacts of recent global change have prompted renewed interest in the long-term ecological monitoring of large ecosystems. The deep sea is the largest ecosystem on the planet, the least accessible, and perhaps the least understood. Nevertheless, deep-sea data collected over the last few decades are now being synthesised with a view to both measuring global change and predicting the future impacts of further rises in atmospheric carbon dioxide concentrations. For many years, it was assumed by many that the deep sea is a stable habitat, buffered from short-term changes in the atmosphere or upper ocean. However, recent studies suggest that deep-seafloor ecosystems may respond relatively quickly to seasonal, inter-annual and decadal-scale shifts in upper-ocean variables. In this review, we assess the evidence for these long-term (i.e. inter-annual to decadal-scale) changes both in biologically driven, sedimented, deep-sea ecosystems (e.g. abyssal plains) and in chemosynthetic ecosystems that are partially geologically driven, such as hydrothermal vents and cold seeps. We have identified 11 deep-sea sedimented ecosystems for which published analyses of long-term biological data exist. At three of these, we have found evidence for a progressive trend that could be potentially linked to recent climate change, although the evidence is not conclusive. At the other sites, we have concluded that the changes were either not significant, or were stochastically variable without being clearly linked to climate change or climate variability indices. For chemosynthetic ecosystems, we have identified 14 sites for which there are some published long-term data. Data for temporal changes at chemosynthetic ecosystems are scarce, with few sites being subjected to repeated visits. However, the limited evidence from hydrothermal vents suggests that at fast-spreading centres such as the East Pacific Rise, vent communities are impacted on decadal scales by stochastic events such as volcanic eruptions, with associated fauna showing complex patterns of community succession. For the slow-spreading centres such as the Mid-Atlantic Ridge, vent sites appear to be stable over the time periods measured, with no discernable long-term trend. At cold seeps, inferences based on spatial studies in the Gulf of Mexico, and data on organism longevity, suggest that these sites are stable over many hundreds of years. However, at the Haakon Mosby mud volcano, a large, well-studied seep in the Barents Sea, periodic mud slides associated with gas and fluid venting may disrupt benthic communities, leading to successional sequences over time. For chemosynthetic ecosystems of biogenic origin (e.g. whale-falls), it is likely that the longevity of the habitat depends mainly on the size of the carcass and the ecological setting, with large remains persisting as a distinct seafloor habitat for up to 100 years. Studies of shallow-water analogs of deep-sea ecosystems such as marine caves may also yield insights into temporal processes. Although it is obvious from the geological record that past climate change has impacted deep-sea faunas, the evidence that recent climate change or climate variability has altered deep-sea benthic communities is extremely limited. This mainly reflects the lack of remote sensing of this vast seafloor habitat. Current and future advances in deep-ocean benthic science involve new remote observing technologies that combine a high temporal resolution (e.g. cabled observatories) with spatial capabilities (e.g. autonomous vehicles undertaking image surveys of the seabed)