The ranges of many tropical marine species overlap in a centre of maximum marine biodiversity, which is located in the Indo-Malayan region. Because this centre includes Malaysia, the Philippines, Indonesia, and Papua New Guinea, it has been named the East Indies Triangle. Due to its dependence on the presence of coral reefs, it has recently been referred to as the Coral Triangle. Because these reefs are severely threatened by human activities, large-scale nature conservation efforts involve the establishment of a network of Marine Protected Areas (MPAs), for which it is important to know the position of this diversity hotspot. Although it is recognized where this centre is located approximately, it is unclear where its exact boundaries are. Only in a limited number of biogeographical studies, ranges and diversity centres of Indo-West Pacific (IWP) taxa have been presented. In this regard, tropical corals, marine fishes, and molluscs have received most attention. However, just for reef corals alone several different diversity centres have been proposed. The boundaries of the centre are important for reconstructing the processes that were responsible for its present shape. They may relate to the area’s climatic and geological past or to the dispersal of larvae by currents in combination with ecological constraints that may prevent their settlement. Especially, in brooding organisms, without larvae or other propagules performing long-distance dispersal, isolation mechanisms may have been important for speciation and species diversity. Information on sea-level fluctuation and the past position of coastlines and data on molecular variation between and within species may help to support models that explain the present position of the centre of marine biodiversity. A detailed biogeographical study of the Fungiidae, a family of corals that disperse through larvae, is used to present a model for a diversity centre and the processes that may have caused its present position. For each species, presence–absence data were obtained from many areas in order to plot their distribution patterns. Since several species do not occur on Sunda shelf reefs, the western part of this diversity centre may have been moulded along the Sunda shelf margin since the end of the LGM (17.000–18.000 BP). Species diversity appears to be distributed unevenly among areas within this centre, which depends on habitat heterogeneity, such as cross-shelf gradients in salinity and turbidity. Eventually, the distributions of several model taxa need to be compared in a sufficiently high number of areas in order to find a more common delineation of the Coral Triangle. Many corals are widespread and have a long fossil record. Moreover, coral reefs have not always been located in their present positions. This makes it complex to find which processes have caused a present diversity maximum. Since most species are concentrated in the eastern part of the Indo-Malayan archipelago and part of the West Pacific, this may be the area where most of the youngest species have originated, but sea-level fluctuations probably have been responsible for excluding large continental shelf seas from the Coral Triangle.

Delineation of the Indo-Malayan Centre of Maximum Marine Biodiversity: The Coral Triangle

Coral reefs across the world have been seriously degraded and have a bleak future in response to predicted global warming and ocean acidification (OA). However, this is not the first time that biocalcifying organisms, including corals, have faced the threat of extinction. The end-Triassic mass extinction (200 million years ago) was the most severe biotic crisis experienced by modern marine invertebrates, which selected against biocalcifiers; this was followed by the proliferation of another invertebrate group, sponges. The duration of this sponge-dominated period far surpasses that of alternative stable-ecosystem or phase-shift states reported on modern day coral reefs and, as such, a shift to sponge-dominated reefs warrants serious consideration as one future trajectory of coral reefs. We hypothesise that some coral reefs of today may become sponge reefs in the future, as sponges and corals respond differently to changing ocean chemistry and environmental conditions. To support this hypothesis, we discuss: (i) the presence of sponge reefs in the geological record; (ii) reported shifts from coral- to sponge-dominated systems; and (iii) direct and indirect responses of the sponge holobiont and its constituent parts (host and symbionts) to changes in temperature and pH. Based on this evidence, we propose that sponges may be one group to benefit from projected climate change and ocean acidification scenarios, and that increased sponge abundance represents a possible future trajectory for some coral reefs, which would have important implications for overall reef functioning.

Could some coral reefs become sponge reefs as our climate changes

Marine sponges are able to process a variety of carbon (C), nitrogen (N), phosphorous (P), and silicon (Si) dissolved compounds, in addition to the particulate C, N, and P obtained through regular feeding. While Si fluxes through sponges are exclusively related to the elaboration of their skeleton of biogenic silica, C, N, and P fluxes derive from a complex combination of metabolic processes that include feeding, respiration, egestion, excretion, as well as hosting of large microbial populations within the sponge body. Because of the remarkable abundance of sponges in many benthic marine communities, they have the potential to impact the availability of the compounds they take up and release, affecting the benthic-pelagic coupling and cycling rates of chemical elements that are crucial to determine growth of bacterioplankton and primary producers at the ecosystem level. Unfortunately, our knowledge and understanding of the magnitude of the sponge-meditated nutrient fluxes and their ecological implications depends much on the compound type (i.e. C, N, P, or Si). Herein, we review the available knowledge on the subject with emphasis on recent developments.

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Nutrient fluxes through sponges: biology, budgets, and ecological implications.

Benthic–pelagic coupling on coral reefs: Feeding and growth of Caribbean sponges

This study has benefitted from funding by the
Spanish Ministry of Economy and Competitiveness (CTM2012-37787) to MM; from the Caribbean
Coral Reef Ecosystems Program and the National Museum of Natural History, Washington to KR,
CD, and MM (Contribution Number 986); from Stiftung Drittes Millennium, Fundacion
Biodiversidad, and the Ministerio de Agricultura, Alimentacion y Medio Ambiente to Oceana and RA; from NIWA, New Zealand Foundation for Research, Science and Technology, and
CSIRO’s Division of Marine and Atmospheric Research to MK; the Natural Sciences and Engineering
Council of Canada for Discovery and Ship Time grants to SPL; from the Norwegian
Research Council to RJB and HTR; from The Norwegian Oil and Gas and the Norwegian
Biodiversity Information Centre to HTR; and from the Natural Sciences and Engineering Council
of Canada for Discovery and Ship Time grants to SPL.

/pdf/sponge-grounds-as-key-marine-habitats-a-synthetic-review-of-oed9yad2d5.pdf

Sponge Grounds as Key Marine Habitats: A Synthetic Review of Types, Structure, Functional Roles, and Conservation Concerns

Sponge populations were compared along transects from land-influenced, inner-shelf reefs to ocean-influenced reefs of the 2 largest barrier reefs in the Pacific and Atlantic Oceans. Sponge biomass on Belize reefs in the Caribbean is greater than on comparable reefs of the central Great Barrier Reef (GBR), whereas individual abundance and species richness are simllar in the 2 regions. Inner-shelf sponge populations are comparable in trophic structure with approximately twice as much biomass and rate of carbon consumption on Belize reefs. Sponge populations on clean water reefs of the 2 regions, however, are fundamentally different. With approximately 6 t ~ m e s the blomass, Belize sponges are large and almost totally heterotrophic and consume on average 15 tlmes more organic carbon per unit area than GBR sponge populations, of which ca 50 ''h of the biomass consists of small phototrophic species. The fundamental differences in species colnposition and mode of nutrition of the sponge populations are a result of long temporal and spatial separations of the 2 reglons. The difference In abundance of phototrophic sponges follows a pattern of a greater evolution of symb~oses In the more oligotrophic Pacific Ocean. The greater sponge hiomass and rates of carbon consumption on these Caribbean reefs are suggestive of higher oceanic productivity compared with that of the Pac~fic. lncreascs in the biomass of heterotrophic sponges are proposed as an early warning slgnal for organlc pollution on coral reefs.

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AC Cheshire

Papers

Comparisons of sponge populations across the Barrier Reefs of Australia and Belize: evidence for higher productivity in the Caribbean