Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Patch size drives settlement success and spatial distribution of coral larvae under space limitation

Space availability is a key factor linked to the settlement success of marine invertebrates. Settlement space on coral reefs is predicted to become increasingly fragmented and occupied by competitors under future disturbance regimes, yet how this impacts coral settlement remains largely unknown. We test the effects of space limitation on larval settlement in three common Indo-Pacific corals (Acropora valida, Acropora digitifera and Anacropora spinosa) by manipulating substrate area while maintaining a constant larval supply. Settlement success was highly variable among coral species, with reduced space leading to an up to four-fold increase in settlement of A. valida larvae, a two-fold decrease in settlement of\ua0An. spinosa larvae and no significant effect for A. digitifera. All species displayed similar spatial settlement patterns, whereby larvae settled gregariously irrespective of how much space was available. At the same time, settlers were found to increasingly occur in aggregates (in direct contact with each other) as space decreased. We propose that increased settler aggregations, coupled with settlement intensification for some species, facilitates the formation of chimeras as space becomes limiting. In colonial organisms, the formation of aggregates and particularly chimeric individuals may offset the negative effects of increased competition for space by allowing settlers to rapidly exceed size-escape thresholds, thereby increasing the likelihood of survival

Freshwater input, upwelling, and the evolution of Caribbean coastal ecosystems during formation of the Isthmus of Panama

Caribbean biota underwent major ecological and evolutionary transformation in the Plio-Pleistocene but a lack of detailed paleoenvironmental reconstruction prevents thorough resolution of cause and effect. We quantify levels of upwelling and freshwater input into Caribbean coastal shelf ecosystems over the last ~6 Ma with >3300 stable isotope measurements from 74 fossil serially-sampled gastropods by normalizing δ18O values to open-ocean δ18O from planktonic foraminifera. We find that the influence of Pacific-like upwelling in the southwestern Caribbean (SWC) was low after 4.25 Ma but coastal ecosystems were heavily influenced by seasonal freshening until ~2.5 Ma, after which time low freshwater conditions were established. The origination of modern oligotrophic coastal conditions was therefore a result of oceanographic change causing declining upwelling, and declining nutrients from terrestrial sources. We speculate that a southward shift of the intertropical convergence zone, associated with Northern Hemisphere glaciation, reduced rainfall and terrestrial nutrient input and contributed to biotic turnover in the SWC, including the proliferation of modern reef communities

Molecular evidence of cryptic speciation in the "cosmopolitan" excavating sponge Cliona celata (Porifera, Clionaidae)

Over the past several decades molecular tools have shown an enormous potential to aid in the clarification of species boundaries in the marine realm, particularly in morphologically simple groups. In this paper we report a case of cryptic speciation in an allegedly cosmopolitan and ecologically important species—the excavating sponge Cliona celata (Clionaidae, Hadromerida). In the Northeast Atlantic and Mediterranean C. celata displays a discontinuous distribution of its putative growth stages (boring, encrusting, and massive) leading us to investigate its specific status. Phylogenetic reconstructions of mitochondrial (COI, Atp8) and nuclear (28S) gene fragments revealed levels of genetic diversity and divergence compatible with interspecific relationships. We therefore demonstrate C. celata as constituting a species complex comprised of at least four morphologically indistinct species, each showing a far more restricted distribution: two species on the Atlantic European coasts and two on the Mediterranean and adjacent Atlantic coasts (Macaronesian islands). Our results provide further confirmation that the different morphotypes do indeed constitute either growth stages or ecologically adapted phenotypes as boring and massive forms were found in two of the four uncovered species. We additionally provide an overview of the cases of cryptic speciation which have been reported to date within the Porifera, and highlight how taxonomic crypsis may confound scientific interpretation and hamper biotechnological advancement. Our work together with previous studies suggests that overconservative systematic traditions but also morphological stasis have led to genetic complexity going undetected and that a DNA-assisted taxonomy may play a key role in uncovering the hidden diversity in this taxonomic group