Experimental evidence of pollination in marine flowers by invertebrate fauna

Pollen transport by water-flow (hydrophily) is a typical, and almost exclusive, adaptation of plants to life in the marine environment. It is thought that, unlike terrestrial environments, animals are not involved in pollination in the sea. The male flowers of the tropical marine angiosperm Thalassia testudinum open-up and release pollen in mucilage at night when invertebrate fauna is active. Here we present experimental evidence that, in the absence of water-flow, these invertebrates visit the flowers, carry and transfer mucilage mass with embedded pollen from the male flowers to the stigmas of the female flowers. Pollen tubes are formed on the stigmas, indicating that pollination is successful. Thus, T. testudinum has mixed abiotic–biotic pollination. We propose a zoobenthophilous pollination syndrome (pollen transfer in the benthic zone by invertebrate animals) which shares many characteristics with hydrophily, but flowers are expected to open-up during the night

Caribbean-Wide, Long-Term Study of Seagrass Beds Reveals Local Variations, Shifts in Community Structure and Occasional Collapse

The CARICOMP monitoring network gathered standardized data from 52 seagrass sampling stations at 22 sites (mostly Thalassia testudinum-dominated beds in reef systems) across the Wider Caribbean twice a year over the period 1993 to 2007 (and in some cases up to 2012). Wide variations in community total biomass (285 to >2000 g dry m−2) and annual foliar productivity of the dominant seagrass T. testudinum (2000 g dry m−2) were found among sites. Solar-cycle related intra-annual variations in T. testudinum leaf productivity were detected at latitudes > 16°N. Hurricanes had little to no long-term effects on these well-developed seagrass communities, except for 1 station, where the vegetation was lost by burial below ∼1 m sand. At two sites (5 stations), the seagrass beds collapsed due to excessive grazing by turtles or sea-urchins (the latter in combination with human impact and storms). The low-cost methods of this regional-scale monitoring program were sufficient to detect long-term shifts in the communities, and fifteen (43%) out of 35 long-term monitoring stations (at 17 sites) showed trends in seagrass communities consistent with expected changes under environmental deterioration.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Effect of Inorganic and Organic Carbon Enrichments (DIC and DOC) on the Photosynthesis and Calcification Rates of Two Calcifying Green Algae from a Caribbean Reef Lagoon

Coral reefs worldwide are affected by increasing dissolved inorganic carbon (DIC) and organic carbon (DOC) concentrations due to ocean acidification (OA) and coastal eutrophication. These two stressors can occur simultaneously, particularly in near-shore reef environments with increasing anthropogenic pressure. However, experimental studies on how elevated DIC and DOC interact are scarce and fundamental to understanding potential synergistic effects and foreseeing future changes in coral reef function. Using an open mesocosm experiment, the present study investigated the impact of elevated DIC (pHNBS: 8.2 and 7.8; pCO2: 377 and 1076 ?atm) and DOC (added as 833 ?mol L-1 of glucose) on calcification and photosynthesis rates of two common calcifying green algae, Halimeda incrassata and Udotea flabellum, in a shallow reef environment. Our results revealed that under elevated DIC, algal photosynthesis decreased similarly for both species, but calcification was more affected in H. incrassata, which also showed carbonate dissolution rates. Elevated DOC reduced photosynthesis and calcification rates in H. incrassata, while in U. flabellum photosynthesis was unaffected and thalus calcification was severely impaired. The combined treatment showed an antagonistic effect of elevated DIC and DOC on the photosynthesis and calcification rates of H. incrassata, and an additive effect in U. flabellum. We conclude that the dominant sand dweller H. incrassata is more negatively affected by both DIC and DOC enrichments, but that their impact could be mitigated when they occur simultaneously. In contrast, U. flabellum can be less affected in coastal eutrophic waters by elevated DIC, but its contribution to reef carbonate sediment production could be further reduced. Accordingly, while the capacity of environmental eutrophication to exacerbate the impact of OA on algal-derived carbonate sand production seems to be species-specific, significant reductions can be expected under future OA scenarios, with important consequences for beach erosion and coastal sediment dynamics

Filamentous algae dominate a tropical reef community in the Mexican Caribbean: an unexpected organisation of reef vegetation

The algal community of a small marine lagoon in the tropical Mexican Caribbean Sea was studied for 3 years (1994-1997). Filamentous algae dominated the vegetation and calcareous crusts were the principal understory algae, The filamentous algae formed dense mats, their cover showing seasonal variation, ranging between 30% in late winter and early spring, and 80% in summer and autumn. Hurricane Roxane (October 1995) caused increased sedimentation, accompanied by a considerable reduction in cover of the filamentous algae. Cover reached pre-hurricane levels within approximate to 11 months. Herbivorous fishes (mainly scarids) maintained specific feeding areas, which they cleared of filamentous algae, however, they did not control the filamentous algae throughout the lagoon. Water movement was almost completely absent in the lagoon of Chankanaab Park, which together with the low herbivore pressure, were most likely responsible for the unique environment, where a vegetation dominated by thick filamentous mats formed the climax community

Dormancy and foliar density regulation in Thalassia testudinum

The hypothesis that the tropical seagrass, Thalassia testudinum from the Puerto Morelos reef lagoon (Mexican Caribbean) has a dormant apical meristem bank (as opposed to a dormant axillary meristem bank) was investigated by morphological and anatomical analyses of vertical shoot apices. Shoots were grouped as follows: (1) dead shoots (no foliar structures or active meristems), (2) developed shoots (bearing juvenile or mature foliar structures with active meristems), and (3) undeveloped shoots (bearing rudimentary foliar structures but with active meristems). In two beds, regressions of shoot density vs. proportional number of shoots in each of the above-mentioned categories, had negative slopes for developed shoots and positive slopes for undeveloped shoots, whereas no relationship was found between density and proportion of dead shoots, These data suggested that foliar shoot density was regulated by inhibition of foliar development, through suppression of meristem activity. Foliar shoot density increased significantly after experimental nutrient addition ana density of the developed shoots was 544.3 shoots per meter square for control plots and 1044.1 shoots per meter square for fertilised plots. Density of undeveloped decreased after fertilisation and densities were 623.9 and 194.2 shoots per meter square for control and fertilised plots, respectively, indicating that nutrient addition resulted in meristem re-activation in the "undeveloped" group. These results confirm the previous proposed existence of a dormant apical meristem banks for T. testudinum. (C) 2000 Elsevier Science B.V. All rights reserved

Synchronized anthesis and predation on pollen in the marine angiosperm Thalassia testudinum (Hydrocharitaceae)

Synchrony in the anthesis of male and female flowers of the hydrophilous dioecious marine angiosperm Thalassia testudinum was studied by following flower buds of 64 staminate and 34 carpellate flowers in situ during night and day to observe the timing of flower opening. Anthesis of female flowers occurred throughout the day, with a slight peak between 15:00 and 17:00 h. The time lapse between initiation of anthesis and full opening of the flowers was similar to 2 to 3 h. Anthesis in male flowers was highly synchronized, and all ripe primordia initiated anthesis within 1 h at dusk at similar to 18:00 h, and pollen was released within 1 to 2 h. Male flowers in anthesis, or briefly after anthesis, were a targeted food source for herbivorous fish and >30% of the staminate flowers were consumed during our observations. The highly synchronized nocturnal pollen release is unusual for an abiotic pollinator, and we hypothesize that this may be a mechanism to ensure fertilization or, alternatively, may be a reponse to avoid pollen predation by fish

Pollen limitation in a dioecious seagrass: evidence from a field experiment

Pollen limitation is relatively common in plants pollinated by animals, but whether pollen availability may limit the reproduction of water-pollinated plants is much less known. We investigated pollen production and possible limitation of pollen availability in the hydrophilous dioecious seagrass Thalassia testudinum in an area where flowering was abundant (20 to 33% of the shoots produced flowers annually). Fruit production decreased from 86 to 60% after experimental removal of half of the male flowers (estimated pollen: ovule ratio of 6.7 x 10(4):1) during April 2008. In late April to May 2009, when male flowers were less abundant than in the previous year (at a pollen: ovule ratio of 3.7 x 10(4):1), artificial pollination resulted in an increase in fruit production from 65% in control flowers to 91% in the treated flowers in the same plot. This study is the first experimental evidence of pollen limitation in a dioecious plant with hydrophilous pollination