Héctor Nava

Chemical and mechanical bioerosion of boring sponges from Mexican Pacific coral reefs

SUMMARY Species richness (S) and frequency of invasion (IF) by boring sponges on living colonies of Pocillopora spp. from National Park Isla Isabel (México, East Pacific Ocean) are presented. Twelve species belonging to the genera Aka, Cliona, Pione, Thoosa and Spheciospongia were found, and 56% of coral colonies were invaded by boring sponges, with Cliona vermifera Hancock 1867 being the most abundant species (30%). Carbonate dissolution rate and sediment production were quantified for C. vermifera and Cliona flavifodina Rützler 1974. Both species exhibited similar rates of calcium carbonate (CaCO3) dissolution (1.2±0.4 and 0.5±0.2 kg CaCO3 m–2 year–1, respectively, mean ± s.e.m.), and sediment production (3.3±0.6 and 4.6±0.5 kg CaCO3 m–2 year–1), resulting in mean bioerosion rates of 4.5±0.9 and 5.1±0.5 kg CaCO3 m–2 year–1, respectively. These bioerosion rates are close to previous records of coral calcification per unit of area, suggesting that sponge bioerosion alone can promote disequilibrium in the reef accretion/destruction ratio in localities that are heavily invaded by boring sponges. The proportion of dissolved material by C. vermifera and C. flavifodina (27 and 10.2%, respectively) confirms that chemical bioerosion plays an important role in sponge bioerosion and in the CaCO3 cycle in coral reefs.

Boring sponges, an increasing threat for coral reefs affected by bleaching events

Coral bleaching is a stress response of corals induced by a variety of factors, but these events have become more frequent and intense in response to recent climate-change-related temperature anomalies. We tested the hypothesis that coral reefs affected by bleaching events are currently heavily infested by boring sponges, which are playing a significant role in the destruction of their physical structure. Seventeen reefs that cover the entire distributional range of corals along the Mexican Pacific coast were studied between 2005/2006, and later between 2009/2010. Most of these coral reefs were previously impacted by bleaching events, which resulted in coral mortalities. Sponge abundance and species richness was used as an indicator of bioerosion, and coral cover was used to describe the present condition of coral reefs. Coral reefs are currently highly invaded (46% of the samples examined) by a very high diversity of boring sponges (20 species); being the coral reef framework the substrate most invaded (56%) followed by the rubbles (45%), and the living colonies (36%). The results also indicated that boring sponges are promoting the dislodgment of live colonies and large fragments from the framework. In summary, the eastern coral reefs affected by bleaching phenomena, mainly provoked by El Niño, present a high diversity and abundance of boring sponges, which are weakening the union of the colony with the reef framework and promoting their dislodgment. These phenomena will probably become even more intense and severe, as temperatures are projected to continue to rise under the scenarios for future climate change, which could place many eastern coral reefs beyond their survival threshold.

New species of excavating sponges (Porifera: Demospongiae) on coral reefs from the Mexican Pacific Ocean

Three new species of coral reef boring sponges were found in remote coral reefs from Revillagigedo Island, an archipelago that is 386 km from the continent. Cliona medinae sp. nov. is a sponge with orange-yellow papillae characterized by short almost straight spirasters. Cliona tropicalis sp. nov., is a yellow papillate sponge with a spicule complement similar to the species included in the Cliona viridis complex. However, the new species differs from the rest of the species mainly in its external morphology and by differences in the size and shape of spicules. Thoosa purpurea sp. nov. is characterized by its purple colour, and the spicular complement formed by tylostyles, two amphiaster categories, bi- tri- and tetra-radiate oxyasters and smooth or microspined centrotylote oxeas. In addition, Cliothosa tylostrongylata sp. nov. is also described from coral reefs from the southern Mexican Pacific Ocean. This is a light red species, with tylostyles and tylostrongyles as megascleres and ramose and nodulose amphiasters as microscleres. The four species were found exclusively excavating skeletons of live or dead corals of the genus Pocillopora. This study increases the number of boring sponges known from the Mexican Pacific Ocean to 22 species and it is the first study on marine sponge fauna from the Revillagigedo archipelago.

A comparison of sponge assemblage patterns in two adjacent rocky habitats (tropical Pacific Ocean, Mexico)

ABSTRACT Sponge assemblages were examined simultaneously in 2 shallow habitats (consolidated rocks and boulder tops) in May and November 2002 in Mazatlán Bay. Important differences were found between the assemblages in the 2 habitats, despite them being only 40–50 m apart. Total (35) and exclusive (25) species richness were higher on boulders than on consolidated rocks (22 and 12, respectively), and only 10 species occurred in both habitats simultaneously. Non-metric multidimensional scaling (nMDS) in combination with analysis cluster revealed a disjunct pattern in the distribution of sponges between habitats. These analyses also showed that the structure of these assemblages varied less over time in consolidated rocks (60% similarity between times) than in the boulders (40% similarity). In fact, the number of species was less variable on consolidated rocks (from 15 to 16 species from May to November) than on boulders (from 12 to 32). The patterns presented here show that the sponge assemblages were not homogeneous in rocky habitats but varied over small spatial scales. The assemblages were more stable on consolidated rocks (the most stable habitat), but diversity was higher in the unstable habitat than on consolidated rocks. However, although the habitat type played an important role in explaining these differences, variables covarying with depth, such as water movement and habitat stability, constituted major environmental factors responsible for the differences observed in sponge assemblage structure between habitats. Nomenclature: Hooper & van Soest, 2002.

Coral boring Aka-species (Porifera: Phloeodictyidae) from Mexico with description of Aka cryptica sp. nov.

This paper focuses on Aka species boring coral of the East Pacific Ocean and the Caribbean Sea (Mexico). The new species Aka cryptica sp. nov. is described from Mexican Pacific coral reefs, which constitutes the first time that a species of the genus Aka is reported from the East Pacific Ocean. The new species lives cryptically boring coral species of the genus Pocillopora . It is characterized by the small size of their papillae (from 1 to 4.5 mm high and from 0.8 to 1.8 mm in diameter), and oxeas (from 67 to 120 μm), and their exposed parts blend in well with background colours which tend to be overlooked during benthic marine surveys. In addition, Aka coralliphaga and Aka brevitubulata from Mexican Caribbean coral reefs are redescribed. The latter species is reported for the first time in Mexico.